Basis Of Neural Control Flashcards Preview

Neurology > Basis Of Neural Control > Flashcards

Flashcards in Basis Of Neural Control Deck (29):
1

Communication

Occurs via electrical signals, through neurons

Dendrites to cell body to axon

2

Electrical signals

Action potentials

Receptor potentials and postsynaptic potentials

3

Action potentials

Or none

Initiated by summation of inputs

When depolarization is above threshold

4

Graded potentials

Sum of currents flowing

Sum to reach action potential threshold

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

5

Chronaxie

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

6

AP threshold

Rate of depolarization increases rapidly

Opening and closing of voltage sensitive channels in the cell membrane

Voltage sensitive Na channels

7

Action potential

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

8

Ion movement during the action potential

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

9

Properties of an action potential

Na dependent depolarization

Blocked by specific Na channel blocker- TTX

AP overshoot

10

Inactivation/repolarization phase

Membrane permeability to Na is short lived

k permeability increases temporarily

11

AP

Na and K channel kinetics

12

Undershoot phase

After hyperpolarization

Increased K conductance which activates Na/K pump

Blocked by TEA

If no K conductance cannot hyperpolarization

13

Absolute refractory periods

Na channels that were active are inactivated after AP

14

Relative refractory periods

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

15

Accommodation or depolarizing block

Higher threshold for activation

Reduced AP amplitude and fewer generated

Na channel inactivation and K conductance are longer lasting

16

Ca sensitivity

Increase in external Ca decreases excitability via threshold potential

Decrease in external Ca increases excitability

17

AP origination

At axon hillock

Nerve cells sum up signal from dendrites

Is depolarizing is greater than hyperpolarization than action potential

18

Propagation

Usually unidirectional precedes refractory zone


Flows passively, velocity, amplitude and duration are unchanged

19

Orthodromic

From cell body to the axon

AP artificially induced by electrical stimulation of axon

20

Antidromic AP

Propagates back to cell body, not refractory

21

AP conduction velocity

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

22

Capacitance

Proportional to fiber diameter

Increases as axon diameter increases because membrane surface area increases

Increasing axon diameter decreases CR and velocity will increase

23

Problems with axon diameter

Metabolically expensive and nerves take up too much space

24

Myelin

Decreases C, conductance

Increases distance between charges

25

Saltatory conduction with myelin

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

26

Myelinated vs. unmyelinated

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

27

Demyelination

Hinders signaling in NS and may lead to nerve death

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

28

Primary demyelination

Mylin itself attacked and damaged or destroyed

29

Secondary demyelination

Violent inflammation phase which destroys axon itself

Nerve signal thus blocked and myelin degenerated