Neuro Lecture B3

Question 1

Graded Potential

Answer 1

A local change of membrane potential, the amplitude of which increases with the amplitude of the stimulus

Question 2

Length Constant

Answer 2

the distant over which a localized graded potential declines to 1/e (or 37%) of its original size in an axon or skeletal muscle fiber.

Question 3

Threshold

Answer 3

A level of the membrane potential that will trigger an action potential

Question 4

Impulse

Answer 4

Action Potential ( or spike)

Question 5

Receptive ending of neurons respond electrically to what specific stimuli

Answer 5

Primary afferent (touch, sound, light) or other neurons (chemical messengers released by other cells)

Question 6

Sensory receptors express????

Answer 6

receptor potentials

Question 7

Other neurons express???

Answer 7

Postsynaptic potentials

Question 8

stimulation of the sensory ending of an afferent neuron produces what kind of response?

Answer 8

A local depolarization (due to the receptors) producing a local response to that sensory ending. adjacent regions are decremental depolarized by the spreading of positive charges

Question 9

Larger-diameter axons tend to have greater or shorter length constants?

Answer 9

greater

Question 10

The length constant of a cellular cable increases or decreases with electrical resistance of the membrane?

Answer 10

Increases

Question 11

The length constant of a cellular cable increases or decreases with electrical resistance of the cytoplasm?

Answer 11

decreases

Question 12

Length constant?

Answer 12

distance over which a graded electrical potential decays in a cable like conductor (dendrite or axon) to 37% of its max amplitude

Question 13

Are action potential considered graded or decremental?

Answer 13

no, action potentials are often described as all or none.

Question 14

Where is the trigger zone (dense population of depolarization-sensitive sodium channels) in multipolar neurons?

Answer 14

The axon Hillock

Question 15

Where is the impulse initiation zone in pseudo unipolar and bipolar afferent neurons?

Answer 15

sensory endings (hence why they are AFFERENT neurons)

Question 16

What is the definition of threshold?

Answer 16

voltage required to open masses of channels

Question 17

The rising phase of an action potential thus reflects what?

Answer 17

the membrane depolarizing towards Ena

Question 18

The falling phase of the impulse represents what?

Answer 18

efflux of K ions down their electrochemical gradient eventually repolarizes the membrane

Question 19

Voltage-gated Na, K and Ca channels form a superfamily of structurally similar channels. Each channel has four identical subunits clustered around a central pore. What does each subunit contain?

Answer 19

Six membrane spanning segments
A charged voltage sensor compartment
A pore loop that confers ion selectivity

Question 20

Describe the ball and chain model of inactivation

Answer 20

Voltage sensitive part of the Na channel mediates its later inactivation during depolarization. So the positively charged ball moves into the pore during depolarization closing the Na channel

Question 21

What is the absolute refractory period?

Answer 21

reflects the inactivation of virtually all Na channels

Question 22

what is the relative refractory period?

Answer 22

a new impulse can be evoked by a larger stimulus, reflects the incomplete return of inactivated Na channels to a normal closed state plus residual K currents.

Question 23

Where are Na channels found?

Answer 23

Axon initial segment (initiation zone), at nodes of Ranvier and presynaptic terminals.

Question 24

K channels found?

Answer 24

paranodal and juxtaparanodal portions of both peripheral and central myelinated axons, in presynaptic terminals, as well as at axon initial segment.

Question 25

Does myelinated or unmyelinated axons produce rapid conduction?

Answer 25

myelinated

Question 26

In both unmyelinated and myelinated axons, action potentials propagate with or without decrement (reduction)?

Answer 26

without

Question 27

In unmyelinated axons, the impulse in one region causes positive charge to flow passively within the cell, depolarizing the adjacent Na channel-rich region beyond threshold. The process recurs down the length of the axon to yield???

Answer 27

Continous conduction

Question 28

In myelinated axons, positive charge entering each node of Ranvier during an impulse moves internally down the electrical gradient towards the next node. The impulse that jumps from one node to the next ensure rapid, ??

Answer 28

saltatory conduction

Question 29

Myelinated or Unmyelinated axons conduct relatively slow?

Answer 29

Unmyelinated axons

Question 30

What factors limit conduction velocity?

Answer 30

small diameters (limits intracellular current spread) and lack of sequential driving of all axonal segments.

Question 31

Myelinated axons support impulses only at what?

Answer 31

Nodes with minimal time lost driving currents between successive nodes

Question 32

what increases conduction velocity

Answer 32

larger length constant, large diameter axons (due to less resistance), increased intermodal distances

Question 33

Uncharged lidocaine and procaine readily cross the membrane, subsequently gaining a charge and blocking what?

Answer 33

the voltage-gated Na channel, therefore a suppression of action potentials is seen