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360 Cards in this Set

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  • Back
Homeostasis is in a state of _______?
dynamic constancy
What is the state of dynamic constancy?
In this state, a given variable (like glucose) may vary in the short term, but its fairly constant when averaged over long term.
When homeostasis is maintained, its referred to as ___________; when its not maintained, its referred to as _________.
physiology ; pathophysiology
What are homeostatic control systems?
They are what mediate the activities of cells, tissues, and organs to be regulated and integrated with each other so that any change in the extracellular fluid initiates a reaction to correct the change.
what is a steady state of the homeostasis control system?
a system in which a certain variable (i.e. temperature) doesn't change
what is equilibrium in the homeostatic control system?
when a certain variable is not changing
what is the difference between steady state and equilibrium systems of homeostasis?
They both have a certain variable not changing but with a steady state, some input on energy is required to maintain the constancy.
what is the set point of the homeostatic control system?
The operating point

(in car driving example, this is the speed limit)
what is the negative feedback system?
in which an increase or decrease in the variable being regulated brings about responses that tend to move variable in opposite direction of the original change
what is the positive feedback system?
it accelerates the process

(ex. oxycotin being released by brain when baby is being born)
which feedback is the most common?
negative feedback
what is feedforward feedback?
this anticipates changes in regulated variables such as internal body temperature or energy availability, so it improves the speed of homeostatic responses and minimizes fluctuations in the level of the variable being regulated (it reduces the amount of deviation from the set point)
what are solutes?
substances that dissolve in liquid
what is a solvent?
the liquid that the solute is dissolved in
what is a solution
this is whats formed when a solute is dissolved in a solvent
what is the most abundant solvent in the body?
Water

- it accounts for about 60% of total body weight
what is an ionic bond?
The attraction between two oppositely charged ions.

Ex. Na+ with Cl- = NaCl (sodium chloride)
what are hydrophilic molecules?
"water-loving" - molecules that have a number of polar bonds and/or ionized groups will dissolve in water
what are hydrophobic molecules?
"water-fearing" - molecules composed mostly of carbon and hydrogen are insoluble in water because their electrically neutral covalent bonds are not attracted to water molecules
what are amphipathic molecules?
Molecules that have a polar or ionized region at one end and a nonpolar region at the opposite end
what do amphipathic molecules do in water?
They aggregate into spherical clusters.

Their polar regions form hydrogen bonds with water molecules at the surface of the cluster, while the nonpolar regions cluster together away from the water
what does the ability of water to dissolve NaCl crystals depend on?
Depends on the electrical attraction between the polar water molecules and the charged sodium and chloride ions
what is solute concentration?
The amount of the solute present in a unit volume of solution.
What is osmosis?
The movement of WATER across a selectively permeable membrane from area of LOW solute concentration to an area of HIGH solute concentration
What is diffusion?
The movement of SOLUTES from areas of HIGH concentration to areas of LOW concentration
why is negative feedback the most common?
because it promotes stability
why is positive feedback less common?
because it promotes change
What are characteristics of Ionic compounds?
- held together by ionic bond
- electrostatic interaction between ions
- result from loss and gain of electrons between atoms
- dissociate when dissolved in water
what are characteristics of polar compounds?
- held together by covalent bonds (but electrons shared unequally)
- results in a molecule with charged ends

Ex. H2O - in which oxygen has slight negative charge and hydrogen has slight positive charge
what are characteristics of non-polar compounds?
- held together by covalent bonds (equal sharing of electrons)
- no charged ends
what are characteristics of lipids?
- Non-polar, so won't dissolve in water
- Will only dissolve in non-polar solvents
- will dissolve in other lipids
How does water work as the universal solvent?
- Water is a polar covalent molecule
Substances with charged ends, or those that dissociate into ions will dissolve in water

- The charged ends and ions will remain in solution because they are attracted to the charged ends of the water molecules
What are the two transport mechanisms?
Passive and active mechanisms
What are passive mechanisms?
- require no cellular enery
- can only transport substances down a concentration gradient (from an area of high concentration to an area of low concentration
_______ compounds dissociate when dissolved in water
Ionic
Which energy powers the passive mechanism transport?
Random kinetic energy thats in the molecules themselves
what are active mechanisms?
- require expenditure of cellular energy in the form of ATP

- can be used to transport large substances and others which can't pass through the membrane by passive means
what factors determine whether a substance can diffuse through a membrane?
- solubility

(lipid soluble vs. water soluble)
how can lipid soluble substances freely diffuse through cell membranes?
By dissolving in the phospholipid bilayer
Can water soluble substances diffuse through cell membranes?
Maybe be able to depending on size and molecular charge
How does molecular size matter when it comes it diffusion through the cell membrane?
If small enough, a water soluble substance may be able to diffuse through the pores or channels in the transmembranal proteins

If too large, can't pass by simple diffusion
How does molecular charge matter when it comes to diffusion through cell membranes?
The pores behave as if they're lined with positive charges so positively charged substance will pass with difficultly

Negatively charged ones also diffuse with difficulty while neutral ones should be able to freely pass through
what is osmotic pressure?
pressure exerted against a membrane due to diffusion of water occurring across it
what is osmolarity?
- measurement of number of solute particles within a solution
- this then determines osmotic pressure
- as a standard, its compared against the number of solute particles found within red blood cells
What is the osmolarity of red blood cells?
0.30 x 6.0221415 × 10^23
What is isoosmolar?
when a solution has the same osmolarity as a RBC (300 osmoles)
What is hyperosmolar?
if a solution has a higher osmolarity than a RBC
what is hypoosmolar?
if a solution has a lower osmolarity than a RBC
How do we determine the osmolarity of solutions? EXAMPLE
- With .25M NaCl - take # of ions:

- So that would be Na+ and Cl-, which equates to 2 ions

- then you multiple the .25M with the number of ions (2):

2 x .25 = .5M

- Because each NaCl dissociates into 2 particles, it has an osmolarity of 2 osmoles
What is tonicity?
The effect a solution has on the volume of a RBC
What is hypertonic?
- A solution that causes a RBC to crenate (shrink)

- they have more dissolved solutes than the cytoplasm of a cell so water moves by osmosis out of the cell (from high to low concentration)
What is hypotonic?
- A solution that causes a RBC to lyse (swell and burst)

- has fewer solutes than a cell so water diffuses into the cell
What is isotonic?
- A solution that causes no change in volume in a cell

- there is an equal number of solute particles on both sides of the cell membrane so theres no net movement of water
What is simple diffusion?
- Net movement of substances from area of high concentration to low.
What are examples of lipid soluble substances?
fatty acids

steroid hormones

oxygen

carbon dioxide
how do lipid soluble substances diffuse?
- can freely diffuse across cell membranes down a concentration gradient
how do water soluble molecules diffuse?
- must be transported by other mechanisms

- they may pass through pores if they are small enough
Whats the polarity of water soluble solutes?
They are polar

- so they can not dissolve in the lipid bilayer

- they may diffuse through pores if small enough
What is the polarity of lipid soluble solutes?
They are nonpolar

- so they may dissolve in the lipid bilayer and freely diffuse across membranes
How does the charge on a substance affect diffusion?
- Negative and positive ions pass with difficultly

- small neutral particles diffuse more easily
what are some examples of water soluble molecules?
Glucose

amino acids
what is facilitated diffusion?
- diffusion assisted by membrane proteins which act as carriers

- transport occurs from an area of high to low concentration

- molecules bind to specific carriers and are then able to diffuse through to the opposite side
What is saturation in facilitated diffusion?
when there are more molecules to be transported than carriers available, so the rate of transport becomes limited to how fast carriers are freed up
What are the characteristics of active mechanisms?
- require the expenditure of cellular energy

- can transport large amounts of materials

- can transport against a concentration gradient
Which mechanisms are active?
- active transport

- endocytosis

- exocytosis
How does endocytosis membrane transport happen?
The membrane invaginates to enclose the substance within a vesicle
what is endocytosis?
- an active mechanism used to bring large volumes of materials into a cell
what is pinocytosis?
specifically refers to endocytosis of liquids
what is phagocytosis?
specifically refers to the endocytosis of solids
what is exocytosis?
- an active mechanism by which larger amounts of substances can be removed from the cell
how does exocytosis membrane transport happen?
-A vesicle containing a substance (for example, could be a protein product made by the cell) is moved up to the membrane

- then the vesicle fuses with the cell membrane and ruptures, releasing the substance to the outside
what does the nervous system do for the body?
- allows body to interact and respond to external stimuli through both conscious and reflex activities
What does the central nervous system consist of?
brain and spinal cord
what does the peripheral nervous system consist of?
cranial and spinal nerves
the peripheral nervous system is divided into which two nervous sytems?
somatic nervous system

autonomic nervous system
what is the somatic nervous system composed of?
- all sensory nerves

- those motor nerves to the skeletal muscles
the autonomic nervous system is purely a ______ system.
motor
the autonomic nervous system is subdivided into?
parasympathetic

sympathetic
what do the parasympathetic and sympathetic nervous systems do?
Innervate:

- smooth muscle
- cardiac muscle
- glands
during what time does the parasympathetic nervous system dominate?
at rest
during what time does the sympathetic nervous system dominate?
during "fight or flight" responses
Which cells are "excitable" cells?
- cells that have resting potentials

- neuron and muscle cells
why are neuron and muscle cells considered excitable cells?
because there is a measurable electrical potential difference between the inside of the cell membrane and the outside
what is the resting membrane potential?
This is the electrical potential difference between the inside and outdie of the cell membrane in some cells
what is the normal value of the resting membrane potential?
70 millivolts
what is critical for the functioning of both neurons and muscle cells?
the resting potential
which part of the cell is electronegative?
the inside with respect to the outside
what are the only neurons that are capable of regneration?
peripheral neurons
what are the chances of regeneration taking place?
The farther away from the some that the damage occurs, the more likely regeneration can take place
What do nissl bodies produce?
proteins which function as regeneration or growth factors to stimulate new axonal growth (called sprouting)
what is sprouting?
new axonal growth
what does the Schwann cell sheath serve as a guide for?
directing the direction of axonal growth
what is an action potential?
- small, electrical current thats propagated along the length of a neuron

- action potentials are electrical events
ow are action potentials generated?
by changes in electrical potentials across neuronal membranes
what is the significance of action potentials?
allows transmission of signals from one point to another
In order for cells to be able to generate action potentials, what has to be there?
there has to be an electrical potential difference between the inside of the cell membrane and the outside at rest
What is the resting potential due to?
- the unequal distribution of ions across the neuron cell membrane

- Na+ is in higher concentration outside the cell than inside

- K+ is in higher concentration inside cell than outside

- Concentration of cations in the extracellular fluid is much more greater than concentration of cations in the cytoplasm so the net effect is that the inside is electronegative (or less positive) than the outside
Which ion is the resting membrane more permeable to?
75 times more permeable to potassium than sodium
How is electronegativity created inside a cell?
There is more K+ inside the cell than Na+ - the anions cannot diffuse across the membrane -

Therefore, the net effect is that the inside is losing positive charges faster than the outside, which is what creates electronegativity inside
what is the sodium-potassium pump?
This is an active transport mechanism that restores balance since Na+ tends to diffuse into the cell and K+ tends to diffuse out through the concentration gradient
when is the sodium-potassium pump considered a co-transport mechanism?
- because the same membrane protien transports both Na+ and K+

- first transports 3 Na+ out of cell and then 2 K+ into cell

- This maintains the unequal distribution of ions and thus maintains the resting potential
what does the neuron membrane have that contains channels which open and close?
Neuron membranes have transmembranal proteins which contain channels that open or close
What is the reason for transmembranal proteins having opening/closing channels?
These channels allow rapid diffusion of specific ions such as Na+ and K+
what are chemically-gated ion channels?
channels that are opened by the binding of specific neurotransmitters
what are voltage-gated ion channels?
channels that are opened by changes in membrane voltage
how do neurons and muscle cells use canges in their membrane potential?
as signals for receiving, integrating, and sending information
what can cause a change in membrane potential?
- changes in ion concentration on the two sides of the membrane

- changes in the permeability of the membrane of any of the ions
What are the two type of signals that can be produced by changes in membrane potential?
- graded potentials (carried for short distance)

- action potentials (carried for long distance)
what is a graded potential?
- localized change in membrane potential which occurs in response to a stimulus

- can be either depolarization or hyperpolarization
how does a graded potential result?
from the opening of gated channels in the membrane which allow ions to flow through
The number of gated channels which open is proportional to what?
- The intensity of the stimulus

- therefore, the greater the stimulus, the greater the change in membrane potential
what are the 3 terms used to describe changes in membrane potential relative to resting potential?
- depolarization

- repolarization

- hyperpolarization
what is depolarization?
used to describe a change in potential in the positive direction

Ex. if membrane potential changed from - 70 mV up to - 50 mV
what is repolarization?
used to describe the return of the membrane potential back to resting potential

Ex. returning of membrane potential from - 50 mV to - 70 mV
what is hyperpolarization?
used to describe a change in membrane potential in the negative direction

Ex. if membrane potential changed from - 70 mV to - 90
what is a synapse?
- the junction between 2 neurons
basically the point of communication between 2 neurons that operate sequentially

- there is no physical contact between their cell membranes
what is a synaptic cleft?
the gap between a synapse
what is a presynaptic neuron?
the neuron that an action potential is being transferred from
what is a postsynaptic neuron?
the neuron that an action potential is being transferred to
what must happen in order for an action potential to be transmitted from the presynaptic neuron to the postsynaptic?
a neurotransmitter must be released from the presynaptic neuron and bind to the receptors on the postsynaptic neuron
neurotransmitters function as ______ signals when going from pre to post synaptic neurons?
chemcial
Neurotransmitters cause what to happen to the postsynaptic membrane?
either depolarization or hyperpolarization of the postsynaptic membrane takes place depending on the specific neurotransmitter
what is an excitatory neurotransmitter?
a neurotransmitter that cuases depolarization of the postsynaptic membrane
what is an inhibitory neurotransmitter?
a neurotransmitter that causes hyperpolarization to happen
Acetylcholine is a _______ neurotransmitter.
excitatory
what is an excitatory postsynaptic potential (EPSP)?
- This is the action potential produced by excitatory neurotransmitters in the postsynaptic membrane

- This is a graded depolarization that moves the membrane potential closer to the threshold for firing an action potential (excitement)
what are cholinergic neurons?
these are neurons that release acetylcholine
where is acetylcholine found?
- the neuromuscular junctions

- all ganglia of the autonomic nervous system

- postsynaptic neurons of the parasympathetic nervous system
what type of neurotransmitters are epinephrine and norepinephrine?
excitatory neurotransmitters
which nervous system are epinephrine and norepinephrine associated with?
- sympathetic nervous system and the "fight and flight response"
what are adrenergic neurons?
neurons which release norepinephrine
what type of neurotransmitter is glutamate?
excitatory neurotransmitter
In which nervous system does glutamate function in?
central nervous system
where in the nervous system does glumate function and what does it do?
functions in the hippocampus and plays a role in memory
What is substance P?
an excitatory neurotransmitter in the pathway that transmits the sensation of pain
which type of polarization do inhibitory neurotransmitters result in?
hyperpolarization
what is an inhibitory postsynaptic potential (IPSP)?
- This is the action potential produced by inhibitory neurotransmitters in the postsynaptic membrane

- Its a graded hyperpolarization that moves the membrane potential further from the threshold for firing an action potential (inhibition)
what are the two ways that an inhibitory postsynaptic potential (IPSP) can occur?
(Depends on the specific neurotransmitter)

- Chloride channels can open and Cl- will flow in, making the inside even more electronegative

- K+ channels can open and K+ can diffuse out, making the inside more electronegative
what are the 3 common inhibitory neurotransmitters in the central nervous system?
- Glycine

- GABA

- Endorphins
What happens to the response of a neuron when an IPSP is generated in a postsynaptic neuron?
That neuron can't respond if stimulated at that time by an excitatory neurotransmitter from a diferent presynaptic neuron
What are 2 types of adrenergic receptors?
- alpha receptors

- beta receptors
what do alpha receptors bind?
norepinephrine
where are alpha receptors found?
- in the smooth muscles of arterioles

- in the radial muscles of the iris
what do alpha receptors do?
their stimulation causes vasoconstriction, which increases blood pressure and pupillary dilation (mydriasis)
what do beta receptors bind?
epinephrine and norepinephrine
where are beta receptors found?
- in heart muscle

- bronchioles

- skeletal mucles
what do beta receptors do?
their stimulation causes:

- increased heart rate and contractility

- bronchodilation,

- increased force of skeletal muscle contraction
what are two types of cholinergic receptors?
- nicotinic receptors

- muscarinic receptors
where are nicotinic receptors located?
in the motor end plate of skeletal muscles
what do nicotinic receptors do?
their stimulation causes skeletal muscle contraction
where are muscarinic receptors located?
in targe organs of the parasympathetic nervous system, such as:

- heart

- digestive tract

- iris
what do muscarinic receptors do?
their stimulation causes:

- decreased heart rate

- increased contractions of the digestive smooth muscle

- pupillary constriction (miosis)
what are histamine receptors?
they are not truly a neurotransmitter, but have some neurotransmitter-like functions
what are the two types of histamine receptors?
- H1 receptors

- H2 receptors
where are H1 receptors located?
- capillaries

- arteriolar smooth muscle

- smooth muscles of the bronchioles
stimulation of H1 receptors cause what?
- increased capillary permeability

- vasodilation

- bronchoconstriction
where are H2 receptors located?
within the gastric glands
stimulation of H2 receptors cause what?
increased production of hydrochloric acid
what are possible drug effects on synaptic effectiveness?
- release and degradation of neurotransmitter inside the axon terminal

- increased neurotransmitter release into synapse

- prevention of neurotransmitter release into synapse

- inhibition of synthesis of neurotransmitter

- reduced reuptake of neurotransmitter from synapse

- reduced degradation of neurotransmitter in synapse

- agonist (evoke same response as neurotransmitter) or antagonists (block response) can occupy receptors

- reduced biochemical response inside dendrite
how is a receptor potential generated?
by mechanoreceptors in skin transmitting mechanical tension to ion channels
which parts of the body have a greater number of receptors?
- Those parts of the body that have greater contact with the environment

- like fingertips, lips, and genitalia
where is the sense of touch integrated?
in the somesthetic cortex of the parietal lobe
what is refraction?
bending of light
how do light rays travel?
in a straight line, unless they encounter a medium with a different optical density
when does light travel more quickly?
in less dense media (like air)
when does light travel slower?
in more dense media (like water)
what happens when a light ray crosses from air into a denser medium?
The ray changes direction at an angle that depends on the density of the medium and the angle at which it strikes the surface
what do the refractive structures of the eye allow?
for us to focus an accurate image of an object onto the retina
what is a convex surface?
curved surface
how does light bend when travelling through a convex surface?
inwards
how does convergence and divergence work for light entering the eye?
- light waves diverge in all directions from every point of an visible object

- eventually, the light rays converge (meet) so that the image is focused on the retina
whats the cornea of the eye?
- the anterior clear portion of the outermost part of eye

- allows light to enter
what is the aqueous humor of the eye?
clear, watery fluid within the anterior chamber of eye
what is the iris of the eye?
muscular colored portion of eye, which surrounds the pupil and regulates its size
what is the pupil of the eye?
opening in the iris which admits light into the posterior chamber
what is the ciliary body of the eye?
produced aqueous humor and anchors the suspensory ligaments (also called zonules)
what are the lens of the eyes?
brings light rays to a point of focus on the retina
what is the vitreous body of the eye?
- thick, gelatinous fluid in the posterior segment of the eye

- maintains shape of the eyeball
what is the retina of the eye?
- innermost tunic of the posterior segment
which part of the eye contains photoreceptors?
retina
what is the fovea centralis of the eye?
region of retina which contains the cones
what are the cones of the eye?
photoreceptors for bright light, color vision
what are the rods of the eye?
photoreceptors for dim light, black and white vision
what is the optic disk of the eye?
the blind spot; its the point at which all optic nuerons leave the retina to become the optic nerve
what is the trabeculae of the eye?
small canals located at the junction of the iris and cornea
which part of the eye is responsible for draining the aqueous humor from the anterior chamber?
trabeculae
what is the canal of schlemm of the eye?
receives aqueous humor from the trabeculae and returns it to the venous circulation
what produces aqueous humor?
specialized capillary beds in the ciliary bodies
how does the aqueous humor travel?
- circulates into the posterior chambers, through the pupil and into the anterior chamber

- absorbed by the trabeculae and returned to the bloodstream by the Canal of Schlemm
how does gluacoma happen?
- if the production of aqueous humor doesn't doesn't equal absorption
where are the cones of the eyes concentrated?
in the fovea centralis
In the retina, the blood vessels run on the ______ and they do not pass through the ________
surface ; vitreous humor
how will parallel right rays bend when striking a convex surface?
will bend to converge to a point focus
what is the focal length?
distance between the convex surface (or lens) and the point focus
how does the focal length change?
- changes with the degree of curvature of the convex lens

- the greater the curvature, the shorter the focal length
what is the accomodation reflex?
the process by which the lens changes its degree of convexity
what is the function of the accomodation reflex?
allows the eye to adjust to viewing objects which are near and those which are far away
Light rays entering the eye from a nearby object will be ______ as they strike the eye
diverging
Light rays entering the eye from a far away object will be ______ when they strike the eye
parallel
how does accommodation for far vision work?
- when looking at distant object, sympathetic nerves to iris are stimulated, which causes mydriasis, which allows more light rays to enter
what are the ciliary muscles doing during accommodation for far vision?
they relax, which puts tension on the zonules and lens flattens out (becomes less convex)

- this is because less refraction is needed since the lines are parallel
how does accommodation for near vision work?
- parasympathetic neurons in oculomotor nerves are stimulated, causing miosis, which decreases number of light rays entering the eye
what are the ciliary muscles doing during accommodatiion for near vision?
they contract, which releases tension on the zonules and the lens rounds up (becomes more convex)

- this is because greater refraction is needed to focus the diverging light rays onto the retina
what is prebyopia?
age-related loss of near vision
what happens to the lens as we age?
lens becomes stiffer, making accommodation more difficult

- lens must be elastic to regain its spherical shape during accommodation for near vision

- because of this, adults around age 45 may have to wear reading glasses or bifocals for close work
what causes astigmatism?
due to unequal curvatures in different parts of the lens and/or cornea

- can cause blurry vision
what type of lens causes light rays to converge?
convex lens
what type of lens causes light rays to diverge?
concave lens
what causes myopia?
an elongated eyeball in which the lens can't focus light rays onto the retina
what is myopia?
-near sightedness

- point focus falls in front of the retina
how is myopia corrected?
by a concave lens which pushes the focal point back farther into the retina
what is hyperopia?
- far sightedness

- light rays are brought to a point focus behind the retina
what causes hyperopia?
when the eyeball is too short
how is hyperopia corrected?
by a convex lens, which shortens the focal length and moves the point focus onto the retina
what happens if glaucoma is left untreated?
pressure can reflect back through the eyeball and cut off the retinal blood supply causing blindness
how is an open-angle glaucoma caused?
by increased production of aqueous humor by the ciliary bodies

- the trabeculae are open and function

- drainage is normal, but production is increased
how is a closed-angle glaucoma caused?
by blockage of the trabeculae

- production is normal but it can't drain
what determines the amount of light which is allowed to enter the posterior segment of the eye?
pupil size
what control are the muscles of the iris under?
autonomic control
what is miosis?
pupillary constriction
what type of stimulation to the iris causes miosis?
parasympathetic stimulation
what is mydriasis?
dilation
what type of stimulation to the iris causes mydriasis?
sympathetic stimulation
what type of drugs cause mydriasis?
adrenergic drugs (like ephedrine)
what type of drugs cause miosis?
cholinergic drugs
what controls pupil size?
pupillary light reflex
_____ light causes stimulation of the ______ nerve, which causes miosis
bright ; oculomotor
____ light causes stimulation of the ______ nerve to the iris, which causes mydriasis
dim ; sympathetic
which cranial nerves mediate the pupillary reflex?
CN II and CN III
CN II carries _____ information about light from the ____ to the _____.
sensory; eye ; brain
CN III carries ____ information from the _____ to the _____.
motor ; brain ; pupils
The pupillary light reflex should be consensual - what does that mean?
means a light shown in one eye should cause constriction in both
which part of the eye is extremely complex, having 10 layers?
retina
where is the fovea centralis in the eye located?
in the center of an area called the macula lutea
whats the peripheral retina?
the rest of the area of the retina where the rods are distributed throughout
the cones of the eye function in what type of light?
high, acuity, bright-light color vision
the rods of the eye function in what type of light?
dim-light, black and white vision
how does light strike the cone?
since the cone is attached to an individual optic neuron, light must strike that cone in order for an action potential to be generated in the neuron
how does light strike the rods?
since there are many rods which synapse with a single optic neuron, the light ray can strike any of the individual rods attached to a neuron and generate an action potential in that neuron
what makes the photoreceptor cells unique?
they are depolarized at rest and hyperpolarized upon activation
how do the photoreceptors depolarize and hyperpolarize?
- absence of light depolarizes the cells and they secrete an inhibitory neurotransmitter

- inhibition turns off the bipolar cells and prevents the ganglion cells from initiating an action potential

- a light stimulus hyperpolarizes the photoreceptors, thus reducing secretion of the inhibitory neurotransmitter and allowing the bipolar cells to depolarize

- the bipolar cells release an excitatory neurotransmitter that stimulates the ganglion cells to initiate an action potential
what forms the optic nerve?
the axons of the ganglion cells
what forms the optic chiasm?
its formed at the base of the brain where the two optic nerves meet
what travels through the optic tracts?
the action potential
what do the optic tracts travel through?
the lateral geniculate nuclei in the thalamus
the ______ sends the action potential to the _____ of the occipital lobe.
lateral geniculate nuclei ; visual cortex
whats the medial half of the retina called?
nasal hemiretina
whats the lateral half of the retina called?
temporal hemiretina
where do all neurons orginating in the nasal hemiretinas cross over at and where do they travel to?
cross over at the optic chiasma to travel in the optic tract of the opposite side
what do all the neurons originating in the temporal side do?
they stay on the same side as their origination
optic nerves are each composed of neurons from ____ eye, but the optic tracts each contain neurons originating from ___ eyes.
one ; both
lesions in the left optic nerve will cause?
total blindness in the left eye
lesions in the left optic tract will cause?
loss of the right half of the visual field (because you lose the nasal hemiretinal neurons from the right eye and the temporal hemiretinal neurons from the left eye)
lesion in the longitudinal region of the optic chiasma will cause?
loss of stereoscopic vision as each occipital cortex now receives input from just one eye; loss of peripheral vision
what is binocular (stereoscopic) vision?
when each eye sees a slightly different view because of the location of the eys in the head
how does binocular (steroscopic) vision result?
result of having overlap in the visual fields of both eyes
what allows us to have depth perception?
steroscopic vision (binocular vision)
what does depth perception allow the the brain to do?
allows them to compare the slightly different images coming in from each eye and then accurately locating the object in space
how is sound energy transmitted?
by the vibration of molecules in solids, liquids, or gases
what are the zones of sound waves?
- compression

- rarefaction
what is the compression zone of sound waves?
where the molecules are closer together and pressure is higher
what is the rarefaction zone of sound waves?
where molecules are farther apart and pressure is lower
what cuases the zones to ripple outward and transmit sound over a distance?
air molecules bumping into each other
what is frequency or pitch?
the number of zones of compression or rarefaction in a given time
how is frequency or pitch measured?
in cycles per second or Hertz (Hz)
what type of pitches do faster vibrations produce?
higher
what is the range of human hearing?
30 - 20,000 Hz in adults

- children may be able to hear lower frequencies around 20 Hz
which pitch do humans have a harder time hearing as they get older?
higher pitch
how is amplitude or loudness defined?
by the difference between the pressure of molecules in the zones of compression and rarefaction
the greater the amplitude, the _____ the sound.
louder
how is loudness measured?
on a logarithmic scale, with decibel as the unit
whats the normal range (loudness of hearing)?
0-85 decibels

- sounds louder than 85 can cause damage
sound waves begin as what type of waves in the atmosphere?
as pressure waves
how do sound waves enter the ear?
- channeled in by pinna

- enter the external acoustic meatus

- where they are channeled to the tympanic membrane

- transferred to middle ear into auditory ossicles

- these then transmit to oval window, the entrance to inner ear
what part of the ear converts the sound waves to mechanical vibrations?
tympanic membrane
what are the auditory ossicles?
Maleus, incus, stapes
because oval window is much smaller than tympanic membrane, what happens?
total force per unit amplified 15-20 times
what is the attentuation reflex?
response to extremely loud sound, the muscles of the ossicles will "lock up" and prevent transmission to the inner ear

- this protects inner ear against potentially damaging sound
whats the function of the eustachian tube of the ear?
equalizes pressure on either side of the tympanic membrane
what happens when the pressure is higher inside the middle ear than in the auditory canal (like when going up in airplane)
the tympanic membrane bulges outward and sound is distorted
what is the cochlea
- snail shell shaped part of ear

- portion of inner ear involved with the sense of hearing
what is the vestibular apparatus?
- involved with sense of equilibrium
where are receptors of static equilibrium found?
within the utricle and saccule
where are the receptors for dynamic equilibrium found?
within the semicircular canals
where are vibrations of the stapes transmitted?
tot he oval window, which then begins to vibrate
what does the organ of corti contain?
receptors for the sense of hearing
as ____ bend, this generates an action potential in the _____ neurons attached to each hair cell
hair cells ; cochlear
where are the action potentials in the ear transmitted?
transmitted by cochlear in the vestibulocochlear nerve (CN VIII) to the temporal lobes of the brain where they are integrated as sound
what is perilymph?
fluid that fills the scala vestibuli and the scala tympani
what is endolymph?
fluid that fills the cochlear duct (also called the scala media)
what does the organ of corti sit on top of?
the basilar membrane
what is the tectorial membrane of the ear?
its an immovable structure which anchors the tips of the hair cells that "rock" when the basilar fiber vibrates
where does depolarization in the ear occur?
in the cochlear neurons
what are the steps of sound transmission through the inner ear?
- Sounds coming through external auditory canal move the tympanic membrane

- membrane moves bones of ossicles

- ossicles move the oval window

- movement of fluids move basilar membrane

- vibrations are disspated by the round window
what are stereocilia?
they are hairlike structures protruding from hair cells of the Organ of Corti

They are in contact with the tectorial membrane
what happens when the stereocilia bend?
when they bend in one direction, the cell depolarizes and causes neurotransmitter release

when bent in opposite direction, the cell repolarizes and it stops neurotransmitter release
what is unique about the polarization of stereocilia?
they are unusual in that K+ influx causes depolarization
basilar fibers are shortest near the ______ and get progressively longer at the _____.
oval window ; apex (heliotrema)
what type of sound do the shorter and longer basilar fibers respond to?
shorter fibers respond to higher sound frequencies

longer fibers respond to lower sound frequencies
how does the brain integrate pitch?
by monitoring which fibers are vibrating along the basilar membrane

(specific fibers vibrate in response to sounds of specific pitch)
the human ear is most sensitive to sounds at approx. _____ Hz
3000
what type of frequency is more likely to damage the hair cells of the Organ of Corti?
high frequency
what are the 3 mechanisms that determine the level of loudness?
- rate of action potentials generated by specific hair cells is increased as loudness increases

- loud sounds tend to stimulate more hair cells than softer sounds of the same pitch

- there are specific hair cells that respond only to loud sounds
when does conduction deafness occur?
when there is any damage to the conduction pathway, which interferes with transmission of sound from the atmosphere to the inner ear
whats the most common cause of conduction deafness?
ear infections in early childhood - if tympanic membrane becomes scarred
how can a person with conduction deafness still hear sound?
if a tuning fork is placed against the temporal bone

- and because neurological pathways are still functional, they can benefit from hearing aids
how do neural or nerve deficit occur in the ear?
from damage to the stereocilia or cochlear nerve
what are environmental causes for neural/nerve deficit of the ear?
long-term exposure to loud sound or high frequencies can damage hair cells and result in nerve deficit
genetic causes of neural/nerve deficit has been known to affect what in the ear?
- number of turns in the cochlea

- action in the sterocilia, affecting the degree of the stiffness of the hair cells

- ion transport channels associated with the generation of receptor potentials
what are cochlear implants?
electronic devices that by-pass the cochlear structures by directly stimulating the cochlear nerve
what tests cause be used to distinguish between conduction and nerve deficits?
bone conduction tests like the Weber and Rinne tuning fork tests
how do bone conduction tests work?
use vibrating tuning forks placed in contact with the head

this action bypasses external auditory canal and middle ear to compare "air conduction" through the external auditory canal with "bone conduction" through the bones of the skull
how does the weber test for hearing loss work?
performed using a 255 or 512 Hz fork

Stem of vibrating tuning fork placed over midline of frontal bone
how do we know if its conduction or nerve deficit through the weber test?
conduction deficit: if tone perceived in the affected ear

nerve deficit: if tone not heard in affected ear
in the rinne test, what happens in normal hearing?
tones are louder by air conduction than by bone conduction because structures in inner ear amplify sound
what does the rinne test for hearing compare?
air and bone conduction
how do you have static equilibrium?
when you are maintaining head position while the body is standing still
what are receptors for static equilibrium called?
macula
where are macula's located?
in both the utricle and saccule
what does each macula consist of?
hair cells, with tips of the hairs anchored in gelatinous "block"

the gelatinous structure contains crystals called otoliths (meaning "ear stones")
whats the vestibular function of the stereocilia and otoliths?
- each hear attached to vestibular nerve

- when head level, hairs project straight up

- when head tilts, gelatinous membrane containing otoliths will slide in the downward direction

- otolithes provide weight to gelatinous membrane, thus making it easier to slide in response to gravity
what are cristae ampullaris?
receptors for dynamic equilibrium
where are cristae ampullaris located?
in the semicircular canals
where are the semicircular canals hair cells anchored?
in a moveable membrane called the cupula, which acts as a sail
what are the semicircular canals filled with?
endolymph
whats inside the endolymph of the semicircular canals?
the "sail" of each crista
what happens when you begin to spin?
- first endolymph in semicircular canal in that plane (there are 3 planes) lags behind due to inertia

This causes the cupula to lag and therefore the hairs are bent, generating an action potential in vestibular neurons
what happens when you continue to spin?
gradually, the endolymph will catch up and cupula will stand straight up again

at this point, unless your eyes are open, you will lose the sensation of spinning
what happens when you suddenly stop spinning?
the endolymph will continue to move for several seconds again, due to inertia

the hairs will now be bend in opposite direction even if you are still standing
what is nystagmus?
its a reflex that can be noticed in a persons eyes when they stop spinning - mimics the movements noted when person is spinning
how is nystagmus caused?
by the brain getting "erroneous" info as the hairs of the crista are bent while the endolymph is still spinning even when person has stopped
where are kinesthetic receptors located?
in muscles, tendons, and joints
what is the function of kinesthetic receptors?
to relay info as to muscle length and limb position
how do kinesthetic receptors play a role in equilibrium?
they allow us to orient our limbs 3-dimensionally in space to support our weight
how are visual cues important in equilibrium?
- we rely on visual input to assure us that our heads are level and that movement is or isn't taking place
why is standing on one foot more difficult with your eyes closed?
because you're removing the visual input which helps you maintain your balance
how is vestibular information transmitted?
through the thalamus to the system of vestibular centers in the parietal lobe
where is vestibular information integrated?
with information from the proprioreceptors
what are the four types of taste buds?
- sweet: located on anterior tip of the tongue

- salty: on anterior lateral portions of the tongue

- sour: on posterior lateral portion of the tongue

- bitter: at the base of the tongue
what are the receptors for the sense of taste called?
taste bud
sesnes of taste and smell are considered to be _____ senses
chemical
what does a taste bud do when it comes in contact with specific chemicals?
it will depolarize and an action potential will be initiated in neurons, which then join with the facial nerve (anterior tongue) or the glossopharyngeal nerve (posterior tongue)
which taste are we most sensitive to?
bitter
what is a reason that we could be sensitive to bitter taste?
many toxic chemicals stimulate the bitter taste buds and therefore initiate a gag response
where are the receptors for olfaction located?
in the nasal mucosa, high up in the nasal cavity
what is the purpose of the holes in the cribiforme plate?
for the passage of olfactory neurons to form the olfactory nerve (CN 1)
which of the senses is least understood?
olfaction - because its so subjective in nature
what must a chemical be in order to produce a smell?
must be volatile, so that can be "sniffed" up into nasal cavity to reach olfactory receptors
Olfaction is the only sensation that terminates within the ______ system of the brain
limbic
what is the limbic system of the brain?
primitive area of cerebrum which also integrates basic emotions such as aggression, fear, sexual responses, and pleasure
what is pain a response to?
tissue damage - damaged tissues release chemicals which stimulate neurons in the pain pathways
what are examples of pain-associated chemicals?
- bradykinens

- prostaglandin E (PGE)

- histamine

- cytokines
what are nociceptors?
they are "bare" nerve endings for pain to be sensed by since unlike other senses, sensory neurons (which detect pain) don't have highly specialized receptors
where do chemical pain mediators bind?
onto ion channels on the nociceptor membrane
what are the 2 pain pathways which convey action potentials to the brain?
- lateral spinothalamic pathway

- spinoreticular pathway
what does the lateral spinothalamic pathway (aka anterolateral pathway) do?
carries pain sensation which is higly localized and very rapid

ex. when you step on a pin, you know exactly where the pain stimulus is coming from
what does the spinoreticular pathway do?
carries pain sensation which is slower and less localized

ex. when you have abd pain, you can't tell exactly what structure is causing the pain
where does the lateral spinothalamic tract carry pain information?
to the thalamus
where does the spinoreticular tract carries pain information?
to the reticular activating system
what is the reticular activating system?
diffuse system of neurons which radiates to the cerebral cortex and plays a role in level of consciousness, alertness, and awakefulness