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403 Cards in this Set
- Front
- Back
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What is a stimulus? |
A detectable change in the internal or external environment of an organism |
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What does a stimulus lead an organism to do? |
Respond to it |
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What are the benefits of organisms responding to stimuli? |
Increases their chance of survival if the stimuli is harmful as they can avoid it and move to a beneficial stimuli. Greater chance of passing on alleles to the next gen and producing offspring |
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What type of organism responses do selection pressures favour? |
Ones that have a more approriate response to this stimuli (the selection pressure - environmental change) |
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What are receptors? What do they do? |
Cells, organs and proteins on cell-surface membranes which detect stimuli |
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Are there different kinds of receptors? |
Yes there are specific receptors for each stimuli |
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What are co-ordinators?examples? |
They connect info between the receptor and the effector . The brain , intermediate neurone and the hormonal system are examples |
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What are effectors? What do they do? |
Cells , tissues , organs , systems and glands that bring about a response to a stimuli |
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How do responses vary? |
They can be on a molecular level or efdect the behaviour of a whole organism |
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In what organisms does hormonal communication occur? |
Large multi-cellular organisms |
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In what systems do hormones travel? What process by? |
The blood - circulatory system via diffusion |
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Why is the nervous system a more effective system for transferring info compared to the hormonal system? |
It is much more rapid |
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What is used to transfer info in the nervous system? |
Electrical impulses down neurones |
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Why is the nervous system rapid compared to hormonal system |
Little diffusion occurs ( which is slow) - only occurs at synapse. Electrical impulses are rapid compared to hormones diffusing in blood |
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What does the sensory neurone do? |
Transmits electrical impulses from receptors the central nervous system |
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What is the central nervous system made up of? |
The spinal chord and the brain |
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What does the motor neurone do? |
Transmits electrical impulses from the central nervous system to the effector |
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What does the co-ordinator do in a simple reflex arc? |
Transmits electrical impulses from the sensory neurone to the motor neurone |
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What happens when electrical impulses reach the end of a neurone (synapse)? |
Neurotransmitters take the infromation across the synapse to the next neurone |
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What is a synapse? |
A gap between two neurones |
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What is the peripheral nervous system made up of? |
All the neurones that connect the central nervous system to the rest of the body |
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Is the peripheral nervous system concious or subconcious actions? |
Both |
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What are the the concious and subconcious activities of the peripheral nervous system? |
Concious - moving hands to play a video game for example Subconcious - flight or fight response , resting and digesting (muscles contracting in digestive system) |
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What is a tropism? |
The growth of part of a plant in response to a directional stimulus such as light and gravity |
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What stimuli to plants grow towards/away from? |
Towards positive stimulus and away from negative stimulus |
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Why is this directional growth beneficial for shoots and roots? |
Shoots grown towards light and away from gravity to maximise light absorption to increase the rate of photosynthesis Roots grow away from light and with the force of gravity as this increases the probability of roots growing into the soil where they can absorb water and mineral ions for photosynthesis and growth Increases survival |
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What receptors do climbing plants have? Why? |
Sense of touch so they can find things to climb up to reach the light for photosynthesis |
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What is the actual molecular cause of these tropisms? |
Growth factors |
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What are growth factors? |
Hormones/chemicals that can speed up or slow down plant growth. They control plant growth so can control plants bending towards or away from stimuli |
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What is the light tropism called? What do positive and negative indicate? |
Phototropism. Positive grow towards light , negative grow away from light |
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What is the gravity tropism called? What do positive and negative indicate? |
Gravitropism. Positive the plant grows with the force of gravity downwards and negative the plants grows upwards against the force of gravity |
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What parts of plants are growth factors produced? Why? |
The tip of the shoots and roots as these parts are growing |
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What happens after the growth factors are produced at the tips? |
Move to other tissues in the plant via diffusion and active transport when directional stimuli occurs |
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What are auxins? what do they do? |
A type of grow factor that causes cell elongation in the shoot and inhibits cell elongation in the roots |
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What phrase should you remember to know how the auxins effect the roots and shoots? |
Inhibits in the roots , promotes in the shoots |
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What is hydrotropism? |
Plant growing away or to water positive/negative |
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What is the auxin called that reacts to directional stimuli and causes bending of the roots and shoots? |
Indoleacetic acid (IAA) |
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Explain what happens when a shoot responds to directional light stimuli. |
In the tip of the shoot IAA is produced. IAA evenly diffuses down the shoot. However , light on one side causes IAA to move to the shaded side (active transport) to create a greater conc on the shaded side. IAA promotes cell elongation in the shoots so the shaded cells elongate more than the light cells which causes the shoot to bend towards the light |
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What happens when roots respond the directional light stimuli? |
IAA moves to shaded side where it inhibits cell elongation in the roots. Light cells elongate more causing the root to bend away from the light |
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Explain what happens when a horizontal root responds to gravity stimuli. |
IAA produced in tip of root and it diffuses evenly into the rest of the root. The force of gravity causes it to collect on the lower side of the root resulting in a higher concentration. IAA inhibits in the root so the upper side elongates more and the root bends downwards with the force of gravity |
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What happens when shoots respond to the directional stimulus of gravity? |
IAA collects on lowe side to give greater conc. IAA promotes cell elongation in shoots so cells on lower side elongate more causing shoot to bend upwards against the force of gravity |
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How does gravity effect distribution of IAA carrier proteins? |
More in lower side so more IAA on lower side |
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What does the acid growth hypothesis explain? |
How IAA causes cell elongation in the shoots |
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What is the acid growth hypothesis? |
Hydrogen ions are actively transported from the cytoplasm of cells into spaces in the cell wall of the cells. This causes thedell walls to become more plastic so they can stretch more and elongate |
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Why do the hydrogen ions come from in the acid growth hypothesis? |
IAA is an acid so it will have H+ ions as they make something acidic |
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Why may older parts of shoots and roots not be able to respond to directional stimuli? |
They develop greater rigidity with age so less likely to elongate and bend in response |
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What are the two types of responses to stimuli mobile organisms can occur out to ensure their survival with positive stimuli? |
Taxes and kinesis |
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What are the characteristics of taxes? |
Straight line and directional |
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Explain how taxes works? How does this increase chances of survival? |
Organisms move towards or away from a stimulus in a straight line when the stimulus is directional - like light. Move towards if positive and away if negative. This increases survival as they move to favourable conditions |
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What are the characteristics of kinesis? |
Changes speed and direction many times by turning. It is non-directional |
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Explain how kinesis works? How does this increase chances of survival? |
In favourable conditions the organism moves slow and changes direction less as it wants to stay in that area - increases probability. In non-favourable environments the organism moves faster and turns more to increase the probability of moving into a new area however turning can decrease if they are far distances away to move greater distances and turn sharply. Increases chance of being in favourable conditions for survival |
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What are examples of non-directional stimuli? Why are they? |
Humidity and temp as they dont provide a clear gradient from one extreme to the other , it varies |
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Is the reflex arc a subconcious response? Why? |
Yes as it by passes the brain so doesnt require any decision making |
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What are the three characteristics of the reflex arc? |
Rapid ,short-lived and localised |
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Why is the reflex arc localised? |
Neurotransmitters are secreted directly onto effector muscle |
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Why is the reflex arc short lived? |
Neurotransmitters on effector are removed quickly |
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When a reflex arc occurs what has happend by the time the prain receives the info that pain has occured? |
Reflex action has already occured and you have been moved away from the harmful stimuli |
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What three neurones make up the reflex arc? |
Sensory , co-ordinator and motor |
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What is the sequence of the reflex arc? |
Stimulus , receptor , sensory neurone , co-ordinator , motor neurone , effector , response |
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What is the importance of the reflex arc? |
They protect us from harmful stimuli as they rapidly move us away from it to prevent harm and increase chances of survival |
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What is the reflex arc rapid? |
By passes brain , neurone pathway is short with few synapses so diffusion is limited. Diffusion is the slowest part |
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Apart from protection from harm what are 3 benefits of the reflex arc? |
Info doesnt go to brain so sensory overload doesnt occur We still receive pain info to the brain so we can learn to avoid harmful stimuli in the future Effective from birth so works in babies to protect them and they do not need to learn |
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Why are receptors specific? |
They can only detect one particular type of stimuli |
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What stimuli does the pacinian corpuscle detect? |
Mechanical energy such as pressure and vibrations |
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What stimuli do the photoreceptors (rod and cones ) detect? |
Iight |
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Is the pacinian corpuscle a receptor? |
Yes its a pressure receptor |
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What is sensory reception? |
Detecting a stimuli |
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What is sensory perception? |
Making sense of stimuli. E.g via the brain |
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What form can receptors take? |
Cells , proteins on cell membranes etc |
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Where are pacinian corpuscles found? |
Deep in the skin mostly on hands , feet and external genitals |
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What is the structure of the pacinian corpuscle? |
A single end of a sensory neurone wrapped in layers ofconnective tissue with viscous gel between the layers. They have an outter capsule too |
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What happens to the structure when pressure is applied to the pacinian corpuscle? |
The connective tissues deform and press on the sensory neurone ending |
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What does deformation of connective tissue cause to happen in the end of the sensory neurone? |
Stretch-mediated sodium channels on the cell membrane of the end of the sensory neurone open and allow the passge of sodium ions. Permeability to sodium ions is increased |
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What are the charges like on the inside of the sensory neurone cell compared to the outside at rest? (No stimuli) |
Inside is more negative (less posotitive) and outside is more positive -resting potential |
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What is the cause of this resting potential? |
The sodium potassium pump transports 3 Na + out of cell for every 2 K + in so less positve charges on inside and more positive charges on outside. - also impermeable to sodium but permeable to potassium |
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What are the two different ways of describing this difference in charge at rest? |
Polarised and potential difference |
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How is this resting potential maintained? |
Stretch mediated sodium channels are too narrow at rest to allow the passage of sodium ions so the potential difference cannot be changed |
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Where do the sodium ions move when the channels open due to deformation? |
Move into cell down electrochemical gradient to change the potential difference and balance out charges |
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What is this known as when the ions move to balance out the charge differences? |
Depolarisation |
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What is the correct term for what is produced when a stimuli causes depolarisation? |
Generator potential |
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What do generator potentials cause? |
The trigger of an action potential |
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Why dont all generator potentials trigger an action potential? |
Not large enough so dont exceed threshold which would trigger one (for weak stimuli) |
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What is the size of a generator potential determined by? |
Larger stimuli cause more movement of sodium ions so there is a larger change in potential difference resulting jn a larger generator potential to be formed |
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How is the strength of a stimuli measured via action potentials? Why? |
Frequency of action potentials as we cannot measure the size to determine size of stimuli as all action potentials are of the same size |
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What is a transducer? |
Coverts one form of energy into another |
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How does the pacinian corpuscle act as a transducer? |
It converts mechanical energy (pressure) into an action potential which is a form of electrical energy |
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How does light enter the inside of the eye? |
Through the pupil and is focused by the lens onto the retina at the back of the eye |
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How is the amount of light entering the eye controlled? |
Muscles in the iris change the shape of the pupils which controls how much light enters |
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Where are the photoreceptor cells found? |
The retina |
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What is the fovea? |
Part of the retina |
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What are the two types of photoreceptors called? |
Cone cells and rod cells |
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What photoreceptors are found in the retina? |
Both cones and rods |
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What photoreceptors are found in the fovea? |
Cone cells only |
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How do the photoreceptors act as transducers? |
Turn light energy into an action potential which is electrical energy |
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How does the action potential formed by the photoreceptors reach the brain? |
Travels down the bipolar neurone connected to the photoreceptor and then to a sensory neurone which makes up the optic nerve at the back of the eye and then it goes to the brain |
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What is the blind spot of the eye? |
The part of the eye where the optic nerve leaves there are no photoreceptors so no image can be formed. Our brains fill in the gap |
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What is the function of the light sensitive optical pigments found in the photoreceptors? |
They absob photons of light (stimuli) which bleaches the pigments and causes a chemical change resulting in a change in membrane permeability of sodium ions so depolarisation can occur and a generator potential is produced - if big enough it triggers an action potential |
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Which photoreceptor can form colour images ? Why? |
Cones as they can detect different wavelengths of light. Rods cannot so they form black and white images |
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Which photoreceptor is more sensitive to light? |
Rods |
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Which photoreceptor has the greatest visual acuity? |
Cones |
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What is the shape of rod cells? |
Like a rectangle |
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Which photoreceptor is largest in number? |
The rods |
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Which part of the retina are more rods found in? Why? |
Peripheral retina , lowest intensities of light and they are sensitive to light so can detect this little stimuli |
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Do rod cells form images at night or day? Why? |
Night as they can give images in dim light due to sensitivity to light (little stimuli) |
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What is the name of the light sensitive optical pigment in the rods? How much light is required to break it down? |
Rhodopsin, little light for breakdown |
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What is the connection of rods to bipolar neurones like? |
Multiple rods connected to one bipolar neurone which is connected to one sensory neurone - retinal convergence |
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What is the purpose of retinal convergence of the rod cells? |
Greater probability of the threshold value being exceeded by the generator potential to trigger an action potential as one neurone picks up stimuli from a large area so weak generator potentials from little light stimuli can combine to exceed threshold |
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Why does retinal convergence results in poor visual acuity? |
Location of a photon can be pinpointed as it could be anywhere in the area of the mulitple rods , brain cannot tell difference as one sensory neurone is used for all. Cannot distinguish between points close together , they appear as one blob so there is little detail in the image |
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What is the shape of cone cells? |
Like a triangle/cone |
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What are the number of cones like in the peripheral retina? |
Low as low light intensity and they have poor sensitivity |
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When will cones be used , night or day? Why? |
Day as they have poor sensitivity so only detect high light intensities |
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Are there different types of cones? |
Yes 3 which respond to different wavlengths of light to produce a coloured image |
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What is the nam of the light sensitive optical pigment in the cones? |
Iodopsin |
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Do different types of iodopsin exist? Why? |
Yes for each different type of cone cell |
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What is required to break down iodopsin? |
Large light intensities |
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How are the cone cells connected to bipolar neurones? |
One cone is connected to a single bipolar cell and single sensory neurone |
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If the cones do not have retinal convergence the generator potential must come from... |
One cone cell alone |
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Why do cones have good visual acuity? |
One cone to one bipolar neurone so positions of photons in space can be pinpointed as the stimuli comes from a smaller area. Two photons close together can be distinguished as they will trigger two seperate action potentials giving the image greater detail |
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Why do many cones exist in the fovea? |
It is opposite the pupil so it receives the high intensities of light which the cone cells detect |
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Why do cones have poor sensitivity? |
One cone per generator potential so more photons are required to exceed threshold - more stimuli required |
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How can the body respond to internal stimuli? |
Receptors are found within our body and they detect internal changes (stimuli) and send it to the central nervoud system |
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What part of the nervous system responds to and control our internal environment? |
Autonomic nervous system - part of the peripheral nervous system |
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Is the autonomic nervous system concious or subconcious? |
Subconcious |
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What are the different parts of the autonomic nervous system? |
Sympathetic and parasympathetic |
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Which parts of the autonomic nervous system speed things up and which slow down? |
Sympathetic speeds things up and parasympathetic slows things down |
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How does speeding up/slowing down work? |
Effectors are stimulated to heighten awareness and prepare for activity or effectors are inhibited to slow down activity in resting conditions -conserves energy and replenishes bodys reserves |
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Why is the sympathetic system and the parasympathetic system antagonistic? |
The actions of these seperate parts oppose eachother so they can work to cancel out eachothers effects which regulates systems in the body - balance |
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What is the name of the muscle in the heart which contracts? |
Cardiac muscle |
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The heart is myogenic. What does this mean? |
Contraction of the cardiac muscle is initiated in the muscle itself rather than by outside electrical impulses sent to it |
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Where does the wave of electrical activity to produce a contraction originate from? |
The sinoatrial node (SAN) |
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Where is the sinoatrial node found? |
The wall of the right atrium |
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Why is the sinoatrial node known as the pacemaker? |
Waves of electrical activity originate from it to start contraction so it determines the rhythm of the heartbeat |
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What happens after a wave of electrical activity is given out by the sinoatrial node? |
The electrical activity spreads out across the walls of both atria of the heart and this causes them to contract (atrial systole) |
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What happens to the electrical activity after atrial systole? |
Travels to the atrioventricular node (AVN) found in the bottom right atrium between the two atria |
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Why doesnt it travel straight down to the ventricles after atrial systole? |
Non-conductive tissue found in the atrioventricular septum prevent this |
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Where does the atrioventricular node pass the electrical activity to? |
Down the Bundle of His which is located in the septum to the bottom of the heart - the apex |
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What is the bundle of his made up of? |
Purkyne tissue fibres |
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Why is there a delay before the AVN releases the wave of electrical activity down the bundle of his? |
To allow atrial systole to complete so the atria can be fully emptied into the ventricles - efficiency |
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What happens when the electrical activity reaches the apex? |
It travels up either side of the ventricles as the bundle of his splits into two bits of purkyne tissue that extend into the walls of the ventricles |
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How does ventricle systole occur? |
When the electrical activity reaches the ventricle walls it causes the ventricles to contract simultaneously from the bottom upwards |
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What is the medulla oblongata and where is it found? |
It is found at the bottom of the brain and it controls heart rate by determining how often the sinoatrial node sends electrical activity down the bundle of his to make it contract - this is down subconciously |
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How does the medulla oblongata decide whether to speed up or slow down the heart? |
Receives info about internal stimuli from receptors then sends more impulses down sympathetic/parasympathetic system to stimulate cardiac muscle or inhibit it |
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Which two receptors are involved in controlling heart rate? |
Pressure receptors and chemoreceptors |
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Where are these heart rate control receptors found? |
In the carotid arteries and the aorta |
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Whats another place only chemoreceptors are found? |
The medulla |
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What stimuli do the pressure receptors detect? |
Low blood pressures and high blood pressures |
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What stimuli do the chemoreceptors detect? |
Changes in blood pH (lower and higher than normal) |
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What causes a decrease in blood pH? |
Higher concentration of CO2 from respiration as when dissolved it is acidic |
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When there is higher CO2 there is lower... |
O2 |
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When there is lower CO2 there is higher... |
O2 |
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What happens after these receptors detect the stimuli in the blood? |
Electrical impulses are sent along sensory neurones to the medulla oblongata and the info is processed so the impulses are sent to the sinoatrial node via the autonomic nervous system to either increase electrical activity (sympathetic) or decrease (parasympathetic) - two different centres in the medulla |
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What happens when pressure receptors detect high blood pressures? |
More impulses sent down parasympathetic neurones which decreases electrical waves sent out to lower heart rate and decrease pressure. Neurotransmitters are secreted which bind to the sinoatrial node |
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What happens when pressure receptors detect low blood pressures? |
More impulses sent down sympathetic neurones so waves of electrical activity from sinoatrial node are increased to increase heart rate and pressure. Neurotransmitters are secreted which bind to sinoatrial node |
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What happens when chemoreceptors detect low blood pH? |
More impulses sent down sympathetic neurones to increases heart rate, neurotransmitters are secreted and bind to sinoatrial node |
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Why does heart rate have to increase with low pH levels? |
CO2 in blood which causes low pH is removed from the body at a quicker rate and more O2 is taken in so pH rises |
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What happens when chemoreceptors detect high pH levels? |
Impulses sent down parasympathetic neurones to reduce waves of electrical activity to slow heart rate. Neurotransmitters bind to the SAN |
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Why does heart rate have to decrease with high pH levels? |
CO2 in blood can build up which causes a decrease in pH as it is acidic , not removed as quickly |
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Why does heart rate increase during exercise? |
More aerobic respiration occurs which releases more CO2 into blood and decreases pH levels. Chemoreceptors detect this so heart rate speeds up to remove CO2 at a quicker rate to increase pH and also to provide muscles with O2 at a faster rate to meet the demand for aerobic respiration |
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What is the name of the sympathetic neurotransmitter? |
Noradrenaline |
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What is the name of the parasympathetic neurotransmitter? |
Acetylcholine |
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Contrast the nervous system and the hormonal system. |
Nervous : rapid , localised , short-lived , temporary change , specific and transmits info using nerve impulses in neurones. Hormonal : slow, widespread , can be permanent , long-lasting and transmits info using hormones in yhe blood which can be any target cell in the body |
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What does a motor neurone look like? |
Cell body with many dendrites with a long axon to the rightand an axon terminal with many dendrites |
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What does the cell body contain? |
Nucleus and all cell organelles |
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Why does the cell body have a lot of rough endoplasmic reticulum? |
For the production of neurotransmitters which are secreted at synapses (dendrites at terminal) |
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What is the difference between a dendron and a dendrite? |
Dendron is the larger main part coming off of the cell body and the dendrites is smaller branching of the dendron |
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The dendrites and dendrons carry the nerve impulse... |
To the cell body |
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The axon carries the nerve impulse... |
Away from the cell body and to the terminal |
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What is the myelin sheath? |
Made up of schwann cell membranes which contain the lipid myelin and wraps around the axon |
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What is the function of the myelin sheath? |
It provides insulation to the axon and speeds up conductance due to saltatory conduction occuring. Stops nerve impulse leaking and provides protection |
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What are the nodes of ranvier? |
Constrictions between adjacent schwann cells where no myelin is present - conduction can occur |
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How does the structure of the sensory neurone compare to the motor neurone? |
A very long dendron so the cell body is located in middle of neurone with axon on the right |
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How does the structure of the sensory neurone compare to the intermediate neurone? |
A cell body with many short dendrons and one short axon , appears circular |
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How permeable is the axon membrane to sodium and potassium ions? |
Just the bilayer is not permeable as the ions are charged. Channel proteins allow ions to pass but some are voltage gated so they are closed when the membrane potential takes a certain value - not permeable |
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What is the resting potential of the axon? |
-70 /65 mV |
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How is the resting potential of the axon maintained? |
Via the sodium-potassium pump. ATP is used to actively transport 3 sodium ions out of the membrane for every 2 potassium ions in. Creates conc gradients and also means inside is more negative than outside as less positive ions. This means there is a potential difference and the membrane is polarised. Electrochemical gradients too . Sodium channels are closed so they cannot diffuse down electrochemical gradient but some potassium channels are open and they diffuse down conc gradient which further decreases charge on inside as even more positive ions leave axon. Depolarisation cannot occur as sodium ions cannot move so this potential difference is maintained. |
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How is an action potential initiated? |
When a generator potential is great enough to exceed a threshold value and depolarise the axon membrane. This means the stimuli needs to be great enough. All stimuli cause generator potentials to form by depolarisation but this depolarisation needs to be great enough for it to propagate down the axon (exceed threshold) |
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How does depolarisation occur? |
Energy from stimuli causses closed sodium channels to change shape so sodium ions can diffuse through - axon increases permeability to sodium ions. Diffuse down electrochemical gradient to balance out charges either side so membrane depolarises |
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When depolarisation occurs what happens to the potential difference value? |
Increases to 40 mV |
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What happens when potential difference reaches 40 mVs? |
The sodium channels close again and voltage gated potassium channels open so potassium ions diffuse down their concentration gradient (and charge gradient) this causes inside axon to become more negative again but even more than the resting potential |
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What is it called when potential difference of axon is lower than the resting potential? |
Hyperpolarisation |
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How is resting potential restored after an action potential? |
Voltage gated potassium channels close and the sodium- potassium pump restores resting potential from hyperpolarisation |
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Why is the action potential said to be self-propagating? |
Acts like a wave of depolarisation. Each part of the axon which depolarises acts as a stimulus for the next part of the axon to depolarise so it travels down the neurone by itself like a dominoe effect |
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What is the all-or-nothing principle? |
A stimulus is either great enough to initiate an action potential or it isn't and all action potentials are of the same size regardless of the size of the stimuli. Only a threshold value must be exceeded. |
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How does a threshold value prevent sensory overload? |
Not every stimuli will result in an action potential being sent to the brain |
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How is the size of the stimuli determined if all action potentials are of the same size? |
The frequency of the nerve impulses. Greater frequency = larger stimuli. Also diff neurones have different threshold value (large ones that only large stimuli can exceed) so the brain can see which neurones are sending impulses - more neurones = greater stimuli or particular neurones with large threshold values |
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What is a localised electrical current in an axon? |
Occurs between depolarised and polarised part of the axon |
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Why is nerve impulse conductance much quicker in myelinated neurones compared to non-myelinated neurones? |
In non-myelinated the entire length of the axon must be depolarised for an action potential to propagate but in myelinated neurones depolarisation can only occur at the nodes of ranvier as the myelin sheath is an insulator so the localised currents are between each node and action potentials jump from node to node skipping out parts of the axon so the conductance is much quicker - saltatory conduction |
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What 3 factors effect speed of conductance down a neurone? |
Diameter of axon Temperature Myelinated vs non-myelinated |
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How does the diameter of the axon affect speed of conductance of the nerve impulse? Why? |
Larger diamter = quicker conductance because less ions leak so potentials are easier ti maintain and there is less resistance to the flow of ions which change the potentials |
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How does temperature affect speed of conductance of the nerve impulse? |
High temp increases speed as rate of diffusion increases. Also increases rate of respiration as this is an enzyme controlled process and ATP is used by sodium-potassium pump at resting potential |
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Why may temperatures over 40 degrees slow conductance? |
Denature respiration enzymes so no ATP for sodium potassium pump and protein channels are denatured |
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What is the refractory period? |
The membrane of the axon that has just been depolarised cannot be depolarised again so no new action potentials can be initiated in this part of the axon |
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Why is the refractory period important? (3) |
Ensures action potentials travel in one direction as depolarisation could act as a stimulus in either direction but refractory period stops it from depolarising the part that has just depolarised and is being repolarised. Produced discrete impulses (impulses dont overlap) as ensures there is time between each impulse so each impulse can be detected seperately It limits the number of action potentials formed ina given time as the refractory period lasts a certain amount of time - so limits strength of stimuli that can be detected |
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Generator potentials cause depolarisation but what happens when threshold value is reached? |
More depolarisation as it causes more sodium channels to open (positive feedback) - forms action potential |
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What is the absolute refractory period? |
Axon is not excitable so no depolarisation can occur at all as sodium channels will not open - potassium ions diffuse out for hyperpolarisation |
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What is the relative refractory period? |
Depolarisation can occur but as this is when hyperpolarisation is occuring a much larger stimulus is required to reach threshold as potential difference is a lot lower. Membrance excitiablility slowly increases as resting potential is reached |
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What do localised electrical currents cause? |
Further depolarisation of the axon as they act as a stimulus |
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What is a synapse and what occurs at the synapse? |
A junction/gap between neurones where neurotransmitters diffuse across so nerve impulses can be transmitted from neurone to neurone and information can be transferred |
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What is the name of the gap between two neurones? |
The synaptic cleft |
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What is the end of the pre-synaptic neurone called and what is its function? |
The synaptic knob. It secretes neurotransmitters into the gap |
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Why does the synaptic knob have many mitochondria? |
To actively transport the calcium ions out that diffuse in when an action potential arrives. Use ATP to recombine hydrolysis products of neutransmitter to make more neurotransmitter which is stored in the synaptic vesicles |
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Why does the synaptic knob have lots of endoplasmic reticulum? |
The manufacturing of the neurotransmitter |
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Where are neurotransmitters stored before their secretion into the synaptic cleft? |
Synaptic vesicles |
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How is the neurotransmitter released into the synaptic cleft? |
Synaptic vesicles fuse with the membrane and release the neurotransmitter via exocytosis |
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What do the neurotransmitters do after they have diffused across the synaptic cleft? |
Bind to receptors on sodium channel proteins which are of a complementary shape |
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What does the arrival of an action potential at the pre-synaptic neurone cause? |
Voltage gated calcium channels open as voltage changes. Calcium ions diffuse in and their presence causes synaptic vesicles to fuse with the pre-synaptic membrane and release neurotransmitters into the synaptic cleft(exocytosis) |
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What does the binding of the neurotransmitter to the receptor on the postsynaptic sodium channels cause? |
Sodium channels open so sodium ions diffuse into post-synaptic neurone down the concentration gradient |
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Why does the influx of sodium ions into the post-synaptic neurone cause an action potential to be initiated in the post-synaptic neurone? |
Changes the membrane potential as many more positive ions on inside - depolarisation. Acts as a stimulus for depolarisation of the next part of the axon and this carries on down the axon - action potential |
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How is the neurotransmitter removed from the synaptic cleft? |
Enzymes hydrolyse neurotransmitter and the products of hydrolysis diffuse into pre-synaptic neurone to be combined again to form more neurotransmitter |
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What would happen if the neurotransmitter was not broken down and removed from the synaptic cleft? |
Sodium channels would remain open so neurone could never repolarise to resting potential. More action potentials would be generated as depolarisation would continue |
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How does the breakdown of neurotransmitter mean that action potentials are discrete? |
Makes time where postsynaptic neurone is not depolarised and only depolarises when more neurotransmitter is secreted due to another action potential. Time inbetween action potentials so they do not overlap |
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What neurotransmitter are cholinergic synapses specific to? |
Acetylcholine |
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What is the name of the enzyme which breaks down acetylcholine? |
Acetylcholinesterase |
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What are the hydrolysis products of acetylcholine? |
Choline and ethanoic acid |
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What are inhibitory synapses? |
Prevent the formation of new action potentials in the post synaptic neurone |
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What are excitatory synapses? |
Help to form action potentials in the post synaptic neurone |
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How do inhibitory synapses work? |
Release a neurotransmitter that binds to chloride ion protein channel receptors instead of sodium so chloride ions diffuse into post-synaptic neurone instead of sodium. This causes further polarisation instead of depolarisation. Potassium channels open so potassium ions diffuse out down conc gradient and further polarise the membrane. Membrane is hyperpolarised to -80 mV do it is much harder for depolarisation to occur so harder for action potential to be initiated as more sodium ions are required |
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Why are synapses unidirectional? |
Sodium channels with receptors only present on the post-synaptic membrane so depolarisation can only happen to the post-synaptic neurone |
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Why do small stimuli result in an insufficient concentration of neurotransmitters in the synaptic cleft? |
They are low frequency so less calcium ion channels open as theyre volatage gated. Less calcium ions diffuse in so less exocytosis of neurotransmitter |
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What may a low concentration of neurotransmitter in the synaptic cleft result in? |
Action potential cannot form in next neurone as less sodium channels open so less sodium ions diffuse in - depolarisation isnt great enough to exceed threshold value |
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What are the two ways to overcome the problem of a low conc of neurotransmitter in the synaptic cleft? |
Use spatial or temporal summation |
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What is spatial summation? |
Multiple pre-synaptic neurones are hooked up to one post-synaptic neurone so the small neurotransmitter concs released are put together to form a large enough conc to exceed threshold of depolarisation in postsynaptic neurone and form an action potential |
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What is temporal summation? |
The pre-synaptic neurone releases neurotransmitter many yimes in a short period so neurotransmitter conc builds up as it isnt broken down as short space of time so there is enough to exceed threshold in next neurone |
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How can one stimuli result in multiple responses? |
One neurone hooked up to multiple - one action potential splits into many |
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How can multiple stimuli result in one response? |
Many neurones hooked up to one so many action potentials form one action potential |
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Affect of drugs on synapses? |
If the neurotransmitter is excitatory the drug will create more action potentials as enzymes cannot break down drug so sodium channels never close action potentials keep being formed . Causes more neurotransmitter to be released, inhibits enzyme - makes stimuli seem greater than it is If the neurotransmitter is inhibitory the drug will stop action potentials being formed as it bind to chlride ion receptors membrane remains hyperpolarised and drug not broken down by enzyme. These drugs mimic the affects of the neurotransmitter Stops release of neurotransmitter - stimuli seems to be less
Or will simply block receptors so neurotransmitters cannot work and no action potentials will form as no channels open Depends on type of synapse |
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How can drugs affect enzyme which breaks down neurotransmitter? |
Stop it working so neurotransmitter is not broken down. So constant action potentials form or non at all ( excitatory vs inhibitory) |
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How can drugs affect neurotransmitter concentration? |
Stimulate release to increase it so more action potentials or inhibit release to decrease it so less action potentials |
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What is the neuromuscular junction? |
Where a motor neurone meets a skeletal muscle fibre (effector) |
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What is the post synaptic membrane at a neuromuscular junction? |
Muscle fibre membrane (has sodium channels with receptors) |
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Contrast the synapse and neuromuscular junction. |
Both use neurotransmitters , receptors , sodium-potassium pump for repolarisation and enzymes breakdown neurotransmitter. But neuromuscular junctions cannot be inhibitory , it is only neurone to effector , only motor neurones , muscle fibre membrane not neurone membrane and action potentials end after effector |
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What is homeostasis? |
The maintenance of a constant internal environment which is maintained by phsiological control systems |
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What does the internal environment consist of? |
Tissue fluids |
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How does homeostasis protect cells from external changes? |
Maintains tissue fluid which surrounds cells so cells also do not change which allows them to function properly |
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Why is maintaining a stable core temp and blood pH important? |
Enzyme catalyze many metabolic processes in the body. They are sensitive to these changes and the changes may reduce their functioning or denature them all together. Need to be kept optimum so body can function properly |
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What is optimum body temp and blood pH? |
37 degrees. Around pH 7 |
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Why must the water potential of the blood and tissue fluid be maintained? |
Prevent cells from expanding and shrinking - even bursting (osmosis occurs) in extreme cases as reduces their functioning. |
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What makes blood water potential constant? |
Having a constant blood glucose concentration |
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Apart from water potential why is a constant blood glucose concentration important? |
Cell respirariin as there needs to be a reliable source of a respiratory substrate so the body can be supplied with ATP for its many functions |
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How does cells expanding /shrinking affect enzyme activity? |
Either increases or reduces their conc which affects the rate of the reaction they catalyze |
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Why is homeostasis important for survival? |
Means organisms can survive in a range of environments as body is less affected by external changes |
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How is the nervous system involved in homeostasis feedback mechanisms? |
Receptors detect deviation from optimum level (the stimuli) sends info to coordinator and then effector which responds by returning level to optimum - may go further and then receptor detects again and sets off another effector. The system creates its own stimuli |
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Can deviation from the optimum point be in either direction? |
Yes |
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What is negative feedback? |
When something deviates from its optimum level in either direction the body works by responding and restoring the level to its optimum |
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If a level can deviate in both directions how many negative feedback mechanisms are required? |
2 - one for each type of deviation as different responses are required |
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What is positive feedback? |
When a deviation from an optimum level results in the body responding by causing further deviation from the optimum point |
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Why can homeostasis only provide control within certain limits? |
If the deviation is too extreme then the effectors may not be able to reverse the change |
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Do multiple negative feedback mechanisms working together provide more control? |
Yes |
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What happens when a homeostatic system breaks down? |
The brain stops working so negative feedback cannot occur and positive feedback occurs instead - it happens when the deviation is too large |
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Why isnt positive feedback involved in homeostasis? |
It doesnt keep the internal environment at a constant level - it deviates from it |
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What bodily system is used to regulate blood glucose concentration? |
The hormonal system |
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What is the normal blood glucose concentration? |
5 mmoldm^-3 |
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What causes blood glucose conc to increase? |
Consuming foods that are hydrolysed to glucose and absorbed. Glycogen in storage in the liver is broken down Other sources such as glycerol and amino acids are converted into glucose |
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What causes blood glucose conc to decrease? |
Used in respiration to produce ATP Put into storage as glycogen |
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What system is in place in the body to maintain blood glucose conc at the optimum point? |
A double negative feedback system of hormones which counteract deviations from the optimum point (either above or below) one increases conc and one decreases |
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What is insulins overall effect on blood glucose conc? |
Decreases it |
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What is glucagons overall effect on blood glucose conc? |
Increases it |
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How does adrenaline effect blood glucose conc? |
Increases it |
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What are hormones produced by? |
Glands |
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Where are insulin glucagon and adrenaline produced? |
Insulin and glucagon in the pancreas and adrenaline in the adrenal glands above the kidney |
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How are hormones transported and what do they effect? |
Diffusion via the blood and effect target cells |
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Why do hormones have long lasting effects compared to neurotransmitters at synapses? |
Not broken down as quickly |
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What do the cells of the pancreas produce? |
The digestive enzymes found in pancreatic juice |
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Where the islets of langerhans found? |
Throughout the cells of the pancreas |
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What do the islets of langerhans produce? |
Insulin and glucagon |
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Which specific islet of langerhans cells produce each hormone? |
Alpha cells produce glucagon and beta cells produce insulin |
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What are the target cells of insulin and glucagon? |
Liver cells and muscle cells |
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What 3 processes can these hormones cause to occur in the liver? |
Glycogenesis Glycogenolysis Glucaneogenesis |
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What is glycogenesis? |
Glycogen is produced by the condensation of glucose molecules and it is stored in the liver |
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What is glycogenolysis? |
Glycogen from the liver is hydrolysed into glucose monomers |
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What is glucaneogenesis? |
Other sources such as glycerol and amino acids are converted into glucose when glycogen is not available |
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How does the body know when to secrete a large amount of insulin to decrease blood glucose concentration? |
The receptors on the B cells detect an increase in conc from the optimum point - this is a stimulus for them to respond by secreting insulin into the blood plasma |
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How does insulin work to reduce blood glucose conc? |
It is a globular protein so it has a specific 3D shape. It binds to complementary glycoprotein receptors on muscle and liver cell membranes as they are the target cells. This binding causes the tertiary sturcture if glucose channel proteins to change so they open. Glucose diffuses from the blood into the cells. Glucose channel proteins increase in number as vesicles fuse with membrane to form more. Mostly happens in muscles for respiration. Enzymes which cause glycogenesis are activated in liver Respiration rate is increased to use up glucose so more diffuses into cells Glucose is stored as fat |
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What is the name of the glucose carrier protein? |
GLUT4 |
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What happens to insulin secretion when optimum blood conc is restored? |
It is reduced in response to this stimulus |
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How does glucagon work to increase blood glucose conc? |
Alpha cells detect drop in blood glucose conc below optimum level. This is a stimuli for them to respond by secreting more glucagon into the blood plasma. Glucagon has a complementary shape to specific protein receptors on the live cells membrane. It binds to them which sets of a second messenger process to cause glycogenolysis. Enzymes are activated which cause glucaneogenesis Rate of respiration is decreased |
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Explain the second messenger model. |
Binding of glucagon to transmembrane protein receptor causes protein on the inside of the cell to change its tertiary structure which activates the enzyme adenylate cycalse. Adenyl cyclase converts.ATP to cyclic AMP (cAMP) which acts as a second messenger and binds to the enzyme kinase which is then activated to convert glycogen to glucose |
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What happens to glucagon secretion when optimum blood glucose conc is restored? |
It responds to this stimulus by being reduced |
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Which other hormone uses a second messenger model? |
Adrenaline |
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What stimuli cause the adrenal glands to secrete adrenaline? |
Stress and excitement cause low concs of glucose |
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What else does adrenaline cause apart from increase blood glucose conc? |
Activates glucagon and inhibits insulin |
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Can adrenaline cause glucaneogenesis? |
No , only glycogenolysis |
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What is diabetes? |
A metabolic disorder where the body cannot control its blood glucose conc due to problems to do with the hormone insulin |
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What causes type 1 diabetes and what is it? |
Immune system attacks b cells of islets of langerhans so the body cannot produce insulin so blood glucose conc stays high and only slowly reduces when it is used in exercise |
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What causes type 2 diabetes and what is it? |
Obesity , little exercise and poor diet. Glycoprotein receptors on the target cells lose their responsiveness to insulin so glycogenesis cannot occur and blood glucose conc remains high |
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What is another cause of type 2 diabetes? |
Inadequate supply of insulin so still no control |
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What do people with type 1 diabetes do to control it? |
They inject insulin as they cant produce it themselves. The correct dose much be calculated so optimum level can be reached - prevent overshoot. This is done by monitoring blood glucose conc. They much manage their diet and exercise too |
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Why cant insulin be taken orally? |
Its a protein so it would be digested |
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What do people with type 2 diabetes do to control it? |
Regulate their diet as there receptors unresponsive. Exercise toofl. If they do have an inadequate supply of insulin they can have inejctions too. Drugs can slow glucose absorption in the ileum |
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What are the number of cases of type 2 diabetes like recently? |
Increasing |
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What should health advisors do about type 2 diabetes? |
Educate people on the risks to reduce the cases , tell them about diet and exercise |
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What should the food industry do about type 2 diabetes? |
Provide healthier options and make it easier for people to be healthym however this conflicts with profits as people want unhealthy food |
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What is the response of the muscles to stimuli? |
They contract to bring about a movement - usually |
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How do muscles receive the stimuli information? |
Action potential travels from receptor to neuromuscular junction , depolarisation occurs in muscle due to neurotransmittee action and travels via T tubules to sarcoplasmic reticulum - dominoe effect then occurs which results in the response. |
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What are the 3 types of muscles present in the body? |
Skeletal , cardiac and smooth |
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What do cardiac muscles do? Where are they found? |
Contract to pump blood around the body as they make up the heart. Myogenic - contraction initiates in the muscle from the Sinoatrial node |
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Where is smooth muscle found? What does it do? |
In organs such as intestines and arteries , it forms rings so it can tighten upon contraction |
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What is skeletal muscle? Where is it found? |
Contracts to move the skeleton. Found in limbs and is attached to the skeleton via tendons |
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Why are skeletal muscles found in pairs? What are these pairs said to be? |
Muscles can only pull not push so need a muscle to move the limb in one way and one to move it the other. Therefore they are antagonistic pairs |
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Is the contraction of the different types of muscle concious or subconcious? |
Concious - skeletal Unconcious - smooth and cardiac |
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What is the job of ligaments? |
Attach bones together at the joints |
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Are ligaments or tendons elastic? |
Ligaments |
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What are the two different types of skeletal muscle? |
Fast-twitch and slow-twitch |
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Why do two different types of skeletal muscle exist? |
They allow for different types of physical activity |
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What are the characteristics of slow-twitch muscles? |
Contract slowly , less powerful contraction and work for long periods of time so they are suited for endurance activity such as marathon running |
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What are the characteristics of fast-twitch muscles? |
Contract rapidly , produce powerful contractions so are suited for intense exercise over a short period of time such as weight lighting |
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What is the main type of respiration slow-twitch muscles carry out? Why? |
Aerobic. To prevent lactic acid build up (from anaerobic) so they can work for long periods of time and there is less demand for ATP due to weaker and slower contractions so there is time for respiration pathway to occur and meet the demand |
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What is the main type of respiration fast-twitch muscles carry out? Why? |
Anaerobic as there is a high demand as muscles contract more and faster. Anaerobic is much faster at supplying ATP. Lactic acid build up doesnt matter as muscles only work for short periods |
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How are slow-twitch muscles adapted for aerobic respiration? |
Many mitochondria (site of respiration) , rich supply of blood vessels to bring glucose and oxygen , large store of myoglobin |
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What is myoglobin? |
A molecule which stores oxygen |
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How are fast-twitch muscles adapted for anaerobic respiration? |
Phosphocreatine store , lots of anaerobic resp enzymes ,multiple myosin and large store of glycogen (store of glucose without blood supply) |
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What is phosphocreatine and its function? |
Stored in cells and provides a source of phosphate groups to add to ADP to synthesise ATP for an extra ATP supply in anaerobic conditions , however it runs out quickly all is turned into creatine |
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What is the simplified structure of the muscle? |
Many myofibrils make up a muscle fibre (one cell due to fusion of muscle cells) and many muscle fibres make up the whole muscle -into bundles and then the bundles go together |
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What is the strength of a lone myofibril? Many myofibrils? |
Not much but collectively they are strong. |
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What is a myofibril made up of? |
Many sarcomeres that are made up of myosin filaments and actin filaments with tropomyosin wrapped round actin |
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Why do muscle cells fuse together to form a muscle fibre? |
Junction between adjacent cells would be a point of weakness so this would reduce the overall strength of the muscle One muscle fibre = one cell |
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When the cells fuse together what do they end up sharing? |
Cytoplasm (sarcoplasm) , nuclei ,mitochondria and sarcoplasmic reticulum attached to T tubules which are connected to the sarcolemma |
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If muscle fibres are one cell and myofibrils make them up what are myofibrils? |
Technically organelles |
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Why do muscle fibres run parallel from tendon to tendon? |
So the force from contraction is in one direction |
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Is mysosin thick or thin? |
Thick |
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Is actin thick or thin? |
Thin |
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What is the appearance of myosin? Why? |
Mascara brush due to myosin heads |
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What forms between myosin and actin? How? |
Crossbridges. Myosin heads bind to binding sites on actin during contraction |
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Why cant crossbridges form during relaxation of the muscle? |
Tropomyosin covers the binding sites so myosin heads cannot bind. In contraction tropomyosin moves to expose binding sites |
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What is troponin? |
Protein which calcium ions bind to on tropomyosin and cause it to move to expose the actin binding sites |
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What are striations? |
Muscle is stripped in appearance due to actin and myosin overlap in some parts of the sarcomere but not all |
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What is the Z line? |
End of sarcomere. Z to Z is one sarcomere - actin is attached here middle of actin is Z line (actin in two adjacent sarcomere) |
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What is the H zone? |
Myosin only area in centre of sarcomere |
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What is the I band? |
Actin only area at both edges of sarcomere next to Z lines |
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What is the A band ? |
The whole length of myosin. Stripped due to some filament overlap and the H zone included which is just myosin |
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What colour is H zone? |
Light |
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What colour is I band? |
Iight |
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What colour is A band? |
Some dark due to overlap but some light due to H zone |
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How do you remember regions and colours of the sarcomere? |
lIgHt dArk edgeZ |
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What happens to the bands and regions of the sarcomere upon contraction? |
Length of sarcomere shortens as Z lines move towards eachother due to actin being pulled in by myosin heads. I band therefore decreases as actin overlap increases , H zone decreases and can even disappear as overlap of myosin increases. A band stays the same size as it is determined by myosin length but darkness increases as H decreases in size and overlap increases |
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What is the structure of an actin filament? |
Two actin polymers twisted around eachother Polymer made from actin molecules binded together |
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Where are myosin filaments for either side of the sarcomere joined? |
Tail to tail in the H zone at the M line |
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What will you see if you look at the crossection of a sarcomere at different points? |
Small dots - actin only large dots - myosin only. Small and large - overlap of actin and myosin |
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Why are many neuromuscular junctions present for each muscle? |
Fibres can contract quickly ( no time for action potential to spread) and simultaneously ( not a domino effect) |
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How do motor units of the muscle allow control? |
Little force required - only a few units stimulated Large force required - many units stimulated |
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What is the mechanism for muscle contraction called? |
The sliding filament mechanism |
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What proof is there for the mechanism? |
A band remains same size - proves filaments dont shorten so overlap must occur |
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What types of proteins are myosin and actin? |
Myosin tails fibrous but heads are globular to give specific shape , actin is globular |
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What are the events that take place to cause muscle contraction? |
Action potentials arrive at the neuromuscular junction which causes voltage gated calcium ion channels to open so calcium ions diffuse into the synaptic knob. This causes vesicles containing neurotransmitter acetylcholine to fuse with the presynpatic membreane and release acetylcholine into the synaptic cleft. It diffuses across the gap and binds to complementary receptors on sodium ion channels on the muscle cell membrane which causes the proteins tertiary structure to change so the channel opens and sodium ions diffuse into the muscle and the muscle membrane is depolarised. Depolrisation travels to sarcoplasmic reticulum via T tubules and causes voltage gated calcium ion channels to open so calcium ions diffuse out into the muscle where they bind to troponin on tropomyosin which causes tropomyosin to move (as tertiary structure changed) and expose binding sites on actin so myosin heads can bind and form cross bridges ( ADP must bind to head so they are able to bind). Once attached myosin heads changed angle ( perform powerstroke) which pull actin filament and releases ADP. ATP attached so myosin head detatches and ATP is hydrolysed by ATP hydrolase which is activated by presence of calcium ions. Energy from hydrolysis moves head to its original position. Binds further down actin for more contraction |
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What happens when the action potential in the muscle ceases? |
Calcium ions actively transported back into sarcoplasmic reticulum for restimulation - so tropomyosin covers binding sites again and contraction stops - relaxation and filaments slide back to original position |
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Example of slow twitch and fast twitch muscles. |
Slow is calf Fast is bicep |
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Why must a specific salt concentration and amount of of water be maintained in the blood? |
To ensure the blood water potential remains constant |
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Why is having a specific water potential of the blood necessary? |
It prevents osmosis of cells occuring and this osmosis could result in cells shrinking or expanding which reduces their functioning |
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How does the water potential of the blood remain constant even when our intake and removal varies from day to day - which should in theory effect salt conc and amount of water. |
Osmoregulation occurs - homeostatic control of blood water potential |
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How are salts intaken and lost from the body? |
Taken up from the diet and lost in urine , faeces and sweat |
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How is water intaken and lost from the body? |
Diet and aerobic respiration (product is water) lost via urinating , faeces , sweating , breathing. So more exercise = more water loss |
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What in the body is responsible for osmoregulation? |
Hormones - negative feedback system which keeps blood water potential at an optimum point. |
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How is water potential returned to optimum point when the water potential decreases? |
Hormones cause more water to be absorbed from the urine to increase water potential - this concentrates the urine. |
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How is the water potential returned to the optimum point when water potential is too high? |
Hormones work to reduce the amount of water absorbed from the urine into the blood.so excess water is removed from the blood to decrease water potential. This dilutes the urine and increases its volume |
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What detects the deviation from the optimum blood water potential? |
Osmoreceptors in the hypothalamus of the brain detect this stimulus |
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How exactly do the osmoreceptors detect water potential stimulus? |
Changes in water potential of the blood causes their cells to expand or shrink because osmosis occurs |
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What happens if the osmoreceptors detect a too low water potential? |
They produce ADH which passes to the posterior pituitary gland and is secreted into the blood plasma |
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What happens if the osmoreceptors detect a too high water potential? |
More nerve impulses are sent to the pituitary gland so less ADH is secreted |
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How does ADH change blood water potential? |
Increases the permeability to water of the distal convoluted tubule and the collecting duct so more water can be reabsorbed into the blood |
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Low conc of ADH... |
Less permeable |
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High conc of ADH... |
Very permeable to water |
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What is the mechanism by which ADH works? |
ADH hormone travels from the pituitary gland to the kidneys via diffusion in the blood. It binds to complementary shaped receptors on the cell-surface membranes of the cells that make up the distal convoluted tubule and the collecting duct. This binding activates the enzyme phosphorylase on the inside of the cell which causes vesicles in the cells containing aquaporins to fuse with the cell surface membrane which increases the number of aquaporins in the membrane so permeability is increased - more water diffuses in via osmosis |
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What are aquaporins? |
Water channel proteins |
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What causes the movement of water from the inside of the distal convoluted tubule and the collecting duct into the interstitial space and then the blood? |
Osmosis occurs as the loop of henle ensures the water potential of the interstitial space is always less than inside of the tubules |
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ADH increases permeability to water but it also increases permebility to.... |
Urea so urea diffuses out into the interstitial space which furthers lowers the water potential so more osmosis occurs |
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When the water potential of the blood is too there is an imcrease in ADH secretion but they action potentials are also sent to... |
The thirst centre of the brain to encourage the individual to drink and increase blood water potential |
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What happens to the ADH induced aquaporins if the ADH concentration decreases? |
They reduce in number so permeability decreases |
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Why is osmoregulation using ADH negative feedback? |
Returns to optimum point if level deviates and secretion of ADH results in the reduction of its own secretion |
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Why part of the pituitary gland secretes ADH? |
Posterior |
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What are the many functional units of the kidney called? |
Nephrons |
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What is the function of the nephron? |
Forms urine which removes waste from the blood |
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What are the individual parts of the nephron called? |
Renal/bowmans capsule , proximal convoluted tubule , loop of henle , distal convoluted tubule and the collecting duct |
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What does the renal capsule surround? |
The glomerulus which is a mass of knotted capillaries |
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Which end is the nephron tubule closed at? |
At the renal capsule |
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What process occurs in the renal capsule? |
Ultrafiltration of the blood to form the glomerupar filtrate which goes on to form urine to be stored in the bladder |
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What process occurs at the proximal convoluted tubule? |
Selective reabsorption from the glomerular filtrate - useful substances (glucose and water) absorbed and waste is not |
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What is the function of the loop of henle? |
Controls water potential of the interstitial space via sodium ions - which leads to absorption of water from the distal convoluted tubule and the collecting duct |
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What is the function of the collecting duct? |
Urine from many distal convoluted tubules empty into it and it carries the urine into the renal pelves which goes down the ureter to the bladder to be stored |
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What vessel supplies the kidneys with blood? |
The renal artery - linked to the aorta |
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How does the blood from the renal artery enter the nephron? |
Renal artery brances into the afferent arteriole which enters the renal capsule and forms the glomerulus |
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What is the exiting vessel of the renal capsule called? |
Efferent arteriole |
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How does the afferent arteriole compared to the efferent? What does this cause? |
Efferent has smaller diameter so blood volume decreases so hydrostatic pressure of the blood increases in the glomerulus |
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What does the efferent arteriole form after leaving the renal capsule? |
The capillaries which surround the convoluted tubules and the interstitial space - blood supplu is important for selective reabsorption of the filtrate into the blood |
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How is blood from the kidney returned to the heart? |
Capillaries come together to form the renal vein which carries blood to the vena cava |
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What does the high hydrostatic pressure of the blood in the glomerulus cause? |
Ultrafiltration. Water and small molecules are forced out of the capillary into the bowmans capsule to form the glomerular filtrate |
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What substances cannot leave the capillary in ultrafiltration? Why? |
Proteins and cells as they are too large , cannot fit through holes in the endothelium of the capillary |
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What 3 layers must the filtrate pass across to reach the renal capsule? |
Through the endothelium pores , across the basement membrane ajd through gaps in the podocytes which form the inner layer of the renal capsule. Endothelium and basement membrane = capillary |
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How are podocytes specialised to be the site of ultrafiltration? |
They have spaces and gaps in them to allow the filtrate to pass through , it doesnt have to go through the cell |
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What is a common example of a small molecule rebsorbed in the proximal convoluted tubule? |
All glucose |
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How is the proximal convoluted tubule specialised for its function? |
The epithelial cells of the tubule have microvilli to increase SA for absorption , they have infoldings on the otherside for large SA for absorption into blood. Many mitochondria which provide ATP for the sodium-potassium pump as substances are absorbed via a co-transport mechanism |
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How does the loop of henle work to ensure large amounts of water are reabsorbed from the filtrate? |
Ascending limb actively transports Na+ into the interstitial space to decrease its water potential. Water remains in the tubule as its thick walls means it is impermeable to water. So water potential of ascending limb stays high. However descending limb is permeable to water so water moves out via osmosis and its water potential inside decreases. Also causes water to move out of distal convoluted tubule and the collecting duct. This water is reabsorbed into the blood via the capillaries. Water potential of descending limb decreases as the filtrate moves downwards as more and more water moves out. Reaches lowest water potential at the hairpin of the loop and then Na+ leaves but water stays the same so water potential increases as filtrate goes up ascending limb. It decreases downwards again in the collecting duct as water continues to move out down the whole length due to the countercurreny multiplier Higher Na+ conc as you go down into medulla - gradient Na+ diffuse into descending limb too down conc gradient |
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How does the counter current multiplier work? |
Filtrate in collecting duct and ascending limb flow in opposite directions. So filtrate of collecting duct always meets intersitial space with a lower water potential than itself so water always moves out of the collecting duct via osmosis which leads to max absorption of water as less osmosis would occur if the liquids ran parallel |
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How should the water potential of the urine compare to the blood? |
Must be lower |
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What does a longer loop of henle result in? |
More concentrated urine as osmosis occurs its whole length - longer length = more osmosis |
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What is the other function of the distal convoluted tubule? |
Cells have microvilli and mitochondria for final reabsorption which makes final adjustments to the urine produced (absorb water and ions) |
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What is the permeability of the descending limb to sodium like? |
permeable so Na+ diffuse in down conc gradient |
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Is depolarisation positive feedback? Why? |
Yes Opening of some sodium channels causes many more to open , deviates further from the norm instead of returning |
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In the nephron where is the majority of water absorbed? |
PCT |
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What resists the ultrafiltration of the blood in the kidneys? |
Same reasons tissue fluid is reabsorbed into circularatory system Has to pass through basement membrane of capillary |
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Why doesnt absorbing more water from the filtrate increase the water potential of the blood if it is too low? What does? |
Water came from blood in the first place so reabsorbing only prevents it decreasing further by conserving Only drinking water can increase it - thats why action potentials are sent to thirst centre from osmoreceptors |
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Why does fluctuate around optimum point in neg feedback? |
Has to fall or rise to set point before response occurs as receptors detect this set point |
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What is the structure of myosin? |
Many tails with heads is a molecule and myosin filament is many molecules together |
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What is the difference between taxes and taxis? |
Taxes is plural |
