lecture 7/8- neurophysiology I and II

Question 1

nervous system divisions (general)

Answer 1

1. CNS
2. PNS

Question 2

CNS divisions (2)

Answer 2

brain and spinal cord

Question 3

PNS divisions

Answer 3

1. afferent (sensory)
2. efferent (autonomic and somatic)

Question 4

efferent divisions

Answer 4

1. autonomic –> parasympathetic and sympathetic
2. somatic

Question 5

cells of the nervous system

Answer 5

• neurons
  (excitable)
  -glial cells (not excitable)

Question 6

4 types glial cells found in the CNS

Answer 6

-ependymal cells
-astrocytes
-microglia
-oligodenrocytes

Question 7

2 types of glial cells found in PNS and functions

Answer 7

schwann cells= form myelin sheaths, secrete neurotropic factor

satellite cells= support cell bodies

Question 8

neuron parts

Answer 8

dendrites= receive signals

cell body (soma)= integrates information

axons= carry info to axon terminal

signal is passed on to next neuron or target cell

Question 9

what is a nerve?

Answer 9

neuron= 1 cell

nerve= bundle of axons from multiple neurons

Question 10

what are two diseases caused by demyelination?

Answer 10

MS: multiple sclerosis, degeneration of CNS myelin, progressive

Guillain-Barre syndrome: autoimmune degeneration of PNS myelin, sudden onset, temporary

Question 11

why does demyelination result in impaired functions?

Answer 11

demyelination causes impaired conduction of electrical signals alonf the axon

loss of function depends on the neurons/nerves affected

Question 12

what is the resting membrane potential of a neuron

Answer 12

-70mV

Question 13

what type of channels control the permeability of the neuronal membrane?

Answer 13

gated channels!

-mechanically gated, chemically gated, voltage gates

Question 14

2 types of electrical signals in neurons

Answer 14

graded potentials
- depolarization or hyperpolarization
(EPSP or IPSP)
electrical signals travel as + or - charges
-lose strength as they travel

action potentials
- all or none
- only depolarization
- amplitude is stable (strength is conserved)

Question 15

is depolarization excitatory or inhibitory?

Answer 15

excitatory!

Question 16

Give an overview of neuronal electrical signalling

Answer 16

1. signal input in dendrites
   - change in ion permeability
   - generates graded potential
2. graded potential spreads through soma
   - reaches axon hillock (high density Nav channels)
   -if threshold is reaches, AP initiates
3. AP conducted along axon
4. At axon terminal, AP triggers neurotransmitter release
5. NT binds to receptors on postsynaptic dendrites/membrane

Question 17

graded potentials: what happens
if there is more stimulus?
of channel density increases?

Answer 17

more stimulus= more activation of channels

increased channel density= increased sensitivity to stimuli

Question 18

Ohms law

Answer 18

V= IR
or
I= V/R
current depends on electrochemical gradient of ion and resistance that opposes the flow

Question 19

two sources of resistance to current flow in cells?

Answer 19

1. Rm, membrane resistance
   - membrane is normally a good insulator (high Rm)
   - open channels allow ion flow (decreases Rm)
2. Ri, internal resistance of cytoplasm
   -inversely related to cell diameter
   - larger diameter= lower Ri

Question 20

do subthreshold graded potential trigger an AP?

Answer 20

NO

Question 21

do suprathreshold graded potentials trigger an AP?

Answer 21

YES

Question 22

spatial summation

Answer 22

currents from almost simultaneous graded potentials combine

Question 23

temporal summation

Answer 23

currents from two graded potentials from one postsynaptic neuron occur close together in time

Question 24

how does ion permeability change during an AP?

Answer 24

• Na channels open and close faster than K+ channels
  -rise in permeability of Na (Pna) drives rising phase of an AP
• rise in Pk drives falling phase

Question 25

explain AP in terms of mV

Answer 25

at resting (-70mV), activation gate closes the channel

depolarizing stimulus arrives at channel, activation gates open (-55mV)

When activation gate opens, Na+ enters the cell (0mV)

Inactivation gate closes and Na+ entry stops (+30mV, hyperpolarization)

K+ leaves the cell, the gates reset to original position (-70mV, hyperpolarization)

Question 26

what limits how soon after an AP another can be triggered?

Answer 26

refractory period

(absolute and relative)

Question 27

absolute refractory period

Answer 27

most Nav channels are inactivated

No stimulus (regardless of strength) can trigger another AP

excitability=0

Question 28

relative refractory period

Answer 28

some Nav channels recovered from inactivation

but Kv channels still open (slow to close)

stronger stimulus needed to account for fewer available Nav channels and hyperpolarizing K+ efflux

excitability still recovering

Question 29

biological current convention

Answer 29

biological current is defined as the movement of positive charges

Na+ entry= inward current
K+ exit= outward current

Question 30

AP is regenerated as the current moves

Answer 30

along axon and activates Nav channels

Question 31

current can move backwards but AP…

Answer 31

does not due to refractory period

Question 32

myelinated axons and saltatory conduction

Answer 32

high density of Na+ channels at the nodes of ranvier

Question 33

3 ways that myelin is an insulator and enhances AP propagation

Answer 33

1. it increases membrane resistance (Rm) and enhances current flow along the axon
2. action potential are only generated at Nodes of Ranvier
3. it decreases membrane capacitance

Question 34

Membrane capacitance

Answer 34

a measure of how much charge needs to be separated across the membrane to produce a given voltage