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71 Cards in this Set

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The smallest particle of an element that can take part in a chemical reaction.
A minute particle of an atom that is negatively charged. These electrons revolve around the nucleus of an atom.
Positively charged particles within the nucleus of an atom.
A chemical combination of tow or more atoms.
An electrically charged atom or molecule, which means that there are more electrons than protons (negative) or vice versa (positive)
A negatively charged ion. It is an atom or molecule that has more electrons than protons.
A positively charged ion. It is an atom or molecule that has less electrons than protons.
Organic Ions. Ions with carbon in them.
Cell Membrane
A layer of four molecules that surrounds the cell and separates the cell's internal parts from the external enviroment
Structure of a cell membrane.
Phospholipid Bi-Layer and proteins.
A lipid that contains phosphorus. The major form of lipids in the cell membrane. The cell a 50:50 mix by weight of proteins and lipids.
What forms cell membrane channels or pores?
Formed by protein molecules.
What are the characteristics of cell membrane channels?
Filled with protoplasm (70-85% water). Have an electrical charge on their wall that is negative or positive.
What is the purpose of cell membrane channels?
Allows ions that are positively or negatively charged to pass through the membrane.
What can pass through cell membrane channels?
Will only allow one specific substance to pass through it. ie. sodium, potassium
Selective permeability
The cell membrane selectively controls the exchange of materials between the cell and its enviroment. The membrane allows the passage of certain substances while restricting the passage of others.
How does size affect permeability?
Large molecules and ions have a difficult time passing through the cell membrane.
How does solubility of a substance in lipid effect permeability?
Substances that dissolve easily in lipids pass through the membrane more readily than other substances since a major part of the cell membrane consists of lipid molecules.
How does charge affect permeability?
Can determine how easily the ion enters or leaves the cell. Oppositely charged ions attract each other more readily.
How does the presence of carrier molecules affect permeability?
The membrane contains special protein molecules called "carriers" that are capable of attracting and transporting substances across the membrane regardless of size.
How do leak channels affect permeability?
At rest, channels may leak certain ions. Muscle and nerve cells have twice as many K+ leak channels as they have Na+ leak channels.
What is the overall effect of leak channels?
Adds to the tendency of the cell to be (-) inside and (+) outside.
Movement of a substance from an area of high concentration to one of lesser concentration until equilibrium is reached.
Active Transport
Movement of substances, usually ions, against a higher concentration with the aid of a carrier molecule.
What is cytoplasm composed of?
Water (75-90%), proteins, lipids, carbohydrates, and ions.
What are the important Ions that exist in the cytoplasm and extracellular fluid of nerve and muscle cells?
Na+, K+, Cl-, and A-
What is the ratio of K+?
Inside (27/1)
What is the ratio of A-?
only inside
What is the ratio of Na+?
Outside (10/1)
What is the ratio of Cl-?
Outside (14/1)
Resting membrane potential
The combined electrical charge of all components inside a neuron or muscle cell fiber. It is the voltage difference between the inside and outside of a cell membrane when the cell is at rest.
What two factors maintain the resting membrane potential?
Unequal distribution of ions across the cell membrane (^Na+ and Cl- outside and ^K+ and A- inside), and the relative permeability of the cell membrane to Na+ and K+ ions. (at rest the permeability of the cell membrane is 50-100 times greater to K+ than Na+).
Resting Stage
The state of a cell before an action potential occurs.
What are the ion concentrations inside a cell during resting stage?
There is a high concentration of K+ and A-. K+ can leak out through leakage channels, but A- and the small amount of Cl- stay inside. This keeps the charge (-) inside the cell.
What are the ion concentrations outside a cell during resting stage?
There is a high concentration of Na+. Some can leak in but it gets carried out of the cell by active transport. This keeps the charge (+) outside the cell.
What is the electrical charge from inside to outside a cell during resting stage?
What are the only "excitable" cells?
Nerve and muscle cells.
What is the sequence of events that occur when the cell membrane depolarizes?
When stimulus of sufficient strength is applied, permeability to Na+ is greatly increased allown Na+ in through channels. When membrane potential hits -55mV cell reaches Threshold Stimulus. Diffusion of Na+ greatly increases. Electrical potential becomes more positive until it reaches +30mV.
What is the point when depolarization begins?
Once threshold stimulus is reach (-55mV)
What occurs once the events of depolarization begin?
An action potential is initiated in the neuron which will spread along the axolemma over the course of approximate 1 millisecond.
What occurs during the spreading of an action potential?
The depolarization at one point of the axolemma causes Na+ to start flowing through their channels in adjacent areas of the membrane.
Continuous Conduction
Spreading of an action potential from one adjacent area of the membrane to the next until it travels down the entire length of the unmyelinated nerve or muscle cell.
Saltatory conduction.
The spreading of an action potential from on adjacent area of the membrane to the next until it travels down the entire length of the myelinated nerves.
How long does depolarization and reversal of the membrane potential take to complete?
about 0.5 milliseconds.
All-or-None Law
If a stimulus is strong enough to initiate a nerve impulse (threshold stimulus), the action potential will spread over the entire nerve or muscle cell at a constant and maxium strength for the existing conditions or it will not occur at all.
What is the sequence of events that occur when the cell membrane repolarizes?
When the cell membrane potential reach +30mV, the potassium ion channels open and allow K+ to move outward and at the same time the Na+ channels close and prevent the Na+ from continuing to move into the cell. Outter movement of K+ causes the outer surface of the cell membrane to become electrically (+). Heavy loss of (+) ions leaves the inner surface of the cell membrane (-) again. Returns cell to resting potential. Goes as far as -90mV. Active transport of the Na+ and K+ restore the resting balance of ions. Na+ are actively transported outside and K+ are moved back into the cell via the sodium-potassium pump.
Refractory Period
The period of time during which the cell membrane of a nerve or muscle cell recovers from a depolarized state to a resting state and cannot generate another action potential.
Absolute Refractory Period
The period of time during which a second action potential cannot be initiated, even with a very strong (suprathreshold) stimulus.
Relative Refractory Period
The period of time following the absolute refractory period during whicvh a second action potential can be produced, but only if the stimulus strength is great than the normal threshold stimulus (suprathreshold).
When does the Relative Refractory Period occur?
When the membrane potential is close to its resting stage.
How does stimulus strength affect speed of nerve impulse?
Speed of a nerve impulse is independent of stimulus strenth.
How does size affect speed of nerve impulse?
Axons with large diameters transmit impulses faster than those with small diameters.
How does myelinization affect speed of nerve impulse
Assists axons to conduct impulse at higher speeds.
How does temperature affect speed of nerve impulse?
Conduct at higher speeds if the temperature is high, and at slower speeds if the temperature is low.
What are the characteristics of A Fibers?
Motor and Sensory. Myelinated. Have large axon diamters (5-20um). Conduct impulses rapdily (27-280mpr). Subdivided into alpha, beta, gamma, and delta fibers in decreasing order of size.
What is the function of A fibers?
Somatic nervous system. Large sensory nerves that send impulses related to touch, pressure, position of joints, and temperature. All motor nerves that conduct impulses to the skeletal muscles. Related to detecting danger in the outside enviroment.
What are the characteristics of B fibers?
Myelinated. Middle sized diameters (2-3um). Conduct impulses at speeds up to 32mpr.
What are the functions of B fibers?
Autonomic nervous system. Conduct sensory impulses from the viscera to the brain and spinal cord. All autonomic motor nerves that extend from the brain and spinal cord to the autonomic ganglia.
What are the charactersistics of C fibers?
Unmyelinated. Have small axon diameters (0.5-1.5um). Conduct impulses at very slow speeds of 1-4mpr.
What are the functions of C Fibers?
Conduct sensory impulses for pain, touch, pressure, heat, and cold from the skin and pain from the viscera. Autonomic motor neurons that extend from the autonomic ganglia to stimulate the heart, smooth muscle, and glands.
What occurs when an action potential travels down the axon to the pre-synaptic terminal?
the action potential causes the Ca+ channels to open allowing Ca+ to enter the pre-synaptic terminal which triggers the synaptic vesicles to release neurotranmitter into the synaptic cleft.
What occurs when a neurotransmitter is released into the synaptic cleft??
It binds to the cell membrane of the post-synaptic terminal (dendrite, cell body, axon, or muscle fiber).
What occurs when a neurotransmitter has been bound to a post-synaptic terminal of a neuron?
Causes the channels in the membrane to become more permeable to Na+, thus setting in motion the process of depolarization and the initiation of another action potential.
Myasthenia Gravis
Decreased receptors sites resulting in the blocking of transmission of an impulse to the muscle fibre.
Poison that blocks the receptor sites of muscles. Since the muscles of respiration depend upon neuromuscular transmission to initiate their contraction, death will result due to asphyxiation.
Botulism Toxin
Inhibits neurotransmitter release from pre-synaptic vesicles thus inhibiting muscle contraction.
Alzheimer's disease
One belief is that the disease prevents neurotransmitter release in association and commissural neurons within the brain, thus preventing an impulse from being transmitted completely.