Basis Of Neural Control

Question 1

Communication

Answer 1

Occurs via electrical signals, through neurons

Dendrites to cell body to axon

Question 2

Electrical signals

Answer 2

Action potentials

Receptor potentials and postsynaptic potentials

Question 3

Action potentials

Answer 3

Or none

Initiated by summation of inputs

When depolarization is above threshold

Question 4

Graded potentials

Answer 4

Sum of currents flowing

Sum to reach action potential threshold

Amplitude and duration of the stimulating current are important in reaching threshold

Question 5

Chronaxie

Answer 5

Clinical ex of muscle disease

Used to ID appropriate current for chronic electrical stimulation to sustain muscle contraction and depolarization

Electrical stimulation can detect denervation associated changes

Question 6

AP threshold

Answer 6

Rate of depolarization increases rapidly

Opening and closing of voltage sensitive channels in the cell membrane

Voltage sensitive Na channels

Question 7

Action potential

Answer 7

Resting state, Na out and K in

Threshold which is Na coming in, K channels closed

Depolarization, more Na channels open

Repolarization, Na gates inactive and K active

Undershoot is only K gate active

Question 8

Ion movement during the action potential

Answer 8

Na channels open and Na enters the cell once threshold

As reach depolarization K channels open and Na close

k continues to leave until after undershoot then excess K outside diffuses away restoring resting potential

Question 9

Properties of an action potential

Answer 9

Na dependent depolarization

Blocked by specific Na channel blocker- TTX

AP overshoot

Question 10

Inactivation/repolarization phase

Answer 10

Membrane permeability to Na is short lived

k permeability increases temporarily

Question 11

AP

Answer 11

Na and K channel kinetics

Question 12

Undershoot phase

Answer 12

After hyperpolarization

Increased K conductance which activates Na/K pump

Blocked by TEA

If no K conductance cannot hyperpolarization

Question 13

Absolute refractory periods

Answer 13

Na channels that were active are inactivated after AP

Question 14

Relative refractory periods

Answer 14

Early, some Na channels are still inactivated

Need a stronger than normal stimulus for AP to occur

K+ conductance elevated opposing depolarization of the membrane

Question 15

Accommodation or depolarizing block

Answer 15

Higher threshold for activation

Reduced AP amplitude and fewer generated

Na channel inactivation and K conductance are longer lasting

Question 16

Ca sensitivity

Answer 16

Increase in external Ca decreases excitability via threshold potential

Decrease in external Ca increases excitability

Question 17

AP origination

Answer 17

At axon hillock

Nerve cells sum up signal from dendrites

Is depolarizing is greater than hyperpolarization than action potential

Question 18

Propagation

Answer 18

Usually unidirectional precedes refractory zone

Flows passively, velocity, amplitude and duration are unchanged

Question 19

Orthodromic

Answer 19

From cell body to the axon

AP artificially induced by electrical stimulation of axon

Question 20

Antidromic AP

Answer 20

Propagates back to cell body, not refractory

Question 21

AP conduction velocity

Answer 21

Dependent on axon membrane capacitance and internal resistance

Rate is inversely related to capacitance and axonal resistance

Reduced resistance increases velocity, resistance will decrease as axon size increases

Large diameter leads to increased velocity

Question 22

Capacitance

Answer 22

Proportional to fiber diameter

Increases as axon diameter increases because membrane surface area increases

Increasing axon diameter decreases CR and velocity will increase

Question 23

Problems with axon diameter

Answer 23

Metabolically expensive and nerves take up too much space

Question 24

Myelin

Answer 24

Decreases C, conductance

Increases distance between charges

Question 25

Saltatory conduction with myelin

Answer 25

Current from action potential at a node flows through myelinated axon

1 node to next is saltatory conduction

AP can move quickly across internodes to save metabolic energy

Question 26

Myelinated vs. unmyelinated

Answer 26

Greater conductance velocity than unmyelinated axons 100 times greater in diameter

Decreased membrane capacitance which is more efficient

Increases membrane resistance which minimizes current loss across the membrane

Question 27

Demyelination

Answer 27

Hinders signaling in NS and may lead to nerve death

In PNS demyelination diseases there are two modes of attack: primary and secondary

Question 28

Primary demyelination

Answer 28

Mylin itself attacked and damaged or destroyed

Question 29

Secondary demyelination

Answer 29

Violent inflammation phase which destroys axon itself

Nerve signal thus blocked and myelin degenerated