CH 7, Part 5

Question 1

Absolute Refractory Period

Answer 1

period during and immediately following an action potential during which a second action potential CANNOT be generated in response to a second stimulus, regardless of the strength of that stimulus
- ends when voltage-gated sodium channels reset

Question 2

Relative Refractory Period

Answer 2

period immediately following the absolute refractory period during which it is possible to generate a second action potential, but ONLY with a stimulus stronger than that needed to reach threshold under resting conditions
- begins when voltage-gated sodium channels reset (-55 mV –> -70 mV)
- would have to get enough excess sodium from dendritic region into the hillock region to overcome repolarization of the hillock region
Two Phases:
(1) comes to an end when voltage-gated potassium channels close (-75 mV)
(2) occurs when voltage-gated potassium channels shut and the resting membrane potential (-75 mV)

Question 3

Graded Potential

Answer 3

small changes in membrane potential that occur when ion channels open or close in response to a stimulus, such as the binding of neurotransmitters to receptors; the magnitude of the potential change varies with the strength of the stimulus
- electrical impulses that decrement
- depolarizations (electrical impulses) that fall apart the farther away they move from their point of origin

Question 4

Temporal Summation

Answer 4

the addition of graded potentials generated at a particular site that occurs when it is stimulated at a high frequency
- presynaptic neuron increases its firing frequency to get the postsynaptic neuron to reach threshold by itself
- allows for increased sodium in postsynaptic neuron, polarizing it into threshold so postsynaptic neuron can generate an action potential

Question 5

Spatial Summation

Answer 5

the addition of graded potentials generated at different locations that occurs when they are stimulated more or less simultaneously
- when multiple presynaptic neurons work together to get a postsynaptic neuron to reach threshold

Question 6

GABA

Answer 6

gamma-aminobutyric acid
- an amino acid neurotransmitter
- inhibitory neuron
- GABA receptors are chlorine channels
- hyperpolarizes neurons
- when chloride receptors open, charge inside cell will become more negative because chloride has the chemical driving force to enter
- how the firing frequency change determine whether an action potential is inhibited or reaches threshold

Question 7

Excitatory Graded Potential

Answer 7

a graded depolarization caused by neurotransmitter binding to receptors on the postsynaptic neuron

Question 8

Inhibitory Graded Potential

Answer 8

a graded hyperpolarization caused by neurotransmitter binding to receptors on the postsynaptic neuron

Question 9

Benzodiazepines

Answer 9

• any benzodiazepine drug mimics the neurotransmitter GABA
• anxiety has historically been considered when neurons are generating an excessive amount action potentials at one time
• when benzos are taken, amount of GABA in brain increases
  (1) GABA begins binding to neuroreceptors in brain
  (2) voltage-gated chloride channels open
• this will make it more difficult for neurons to reach threshold
  
  • they will stop firing, and thus, reduced anxiety
• however, everything that occurs in the brain is slowed down because benzos bind randomly to any neurons

Question 10

Non-myelinated Neuron Structure

Answer 10

• have voltage-gated sodium channels lining the entire length of the axon
• must be able to drive up to +30 mV so need sodium to be able to come through entire length or else action potential will falter
• rate in which action potential propagated down axon is slow

Question 11

Myelinated Neuron Structure

Answer 11

• Myelin Sheath: type of insulation wrapped around the axon which prevents the leakage of ions
  (1) under myelin sheath, area is depolarized to +30 mV
  
  • rate in which potassium leaves has increased, rate in which sodium enters has decreased
    (2) sheath prevents potassium ions from leaking out so that repolarization does not happen
    (3) impulse traveling under sheath stays very very charged and does NOT decrement to any significant degree
    - do not need voltage-gated sodium channels under sheath, but are plentiful in gaps
• myelin sheath allows neurons to propagate its action potential down its axon much faster by maintaining the charge in the insulated region
  
  • recharging only needs to occur in the Nodes of Ranvier, allowing it to move faster