Muscle and Nerve Anatomy

Question 1

Transmembrane potential of skeletal muscle:

Answer 1

-90mV

Question 2

Nernst equation:

Answer 2

chemical work = electrical work

Question 3

Equilirium potentials
K+:
NA+:
CL+:

Answer 3

K+ -97mV
Na +66mV
Cl -90mV

Thus; chloride is the only ion in equillibrium if only the transmembrane concentration and the potential differences are taken into consideration.

Question 4

The Na/K pump is a ____:_____ pump.

Answer 4

3:2

two forces pulling K from outside to inside the cell

1. transmembrane potential (-90mV)
2. active K+ transport(-7mV)

Na remains in equilibrium because of its impermeability due to mechanical barrier imposed by cell membrane. Small amount of Na that does not enter the cell is actively pumped out.

Question 5

Membrane potential reaches critical level at _____ in human muscle cells

Answer 5

-65 to -75

close to resting state of Na (+66mV)

Question 6

Resting Membrane:
K channels are ____
Na channels are ____

Answer 6

open
closed

Question 7

depolarization causes ____ fold increase in Na permeability. Increases permeability to K also after about a 1msec delay

Answer 7

500

Question 8

Membrane recovery occurs after inactivation of ______ and increased _____ permeability responsible for the rapid recovery towards resting membrane potential

Answer 8

Na+ channels
K+

Question 9

hyperpolarization occurs secondary to _____ conductance

Answer 9

K+

Question 10

______ is the connective tissue around individual axons within each fascicle

Answer 10

endoneurium

Question 11

____ is the collagenous tissue binding each fascicle (of axons)

Answer 11

perineurium

Question 12

_____ binds individual fascicles together. Outermost layer of support for the peripheral nerve, continuous with the duramater of the spinal roots. VASA NERVORUM is located here

Answer 12

epineurium

vasa nervorum is located here which supplies blood to that particular nerve

Vitally important when you start discussing blood supply to particular nerve such as with Wegeners.

Question 13

Unmyelinated fibers share a single ______

Answer 13

schwann cell

also known as c-fibers (pain fibers)

Question 14

Junctions between schwann cells are called _____

Answer 14

nodes of ranvier

Question 15

Resting transmembrane potential in peripheral nerves are _____ at the somma and _____ at the axon

Answer 15

-70mV, -90mV

Question 16

After about _____ of depolarization, the membrane reaches the critical level and an action potential develops with the same maximal response regardless of the kind or magnitude of the stimulus

Answer 16

10-30mV

Question 17

____ is minimal current intensity below which no response can be elicited even if the current is applied for an indefinite period (at least 300ms)

Answer 17

rheobase

Question 18

____ is the minimal duration of a current required to excite the cell at twice the rheobase strength

Answer 18

chronaxie

Question 19

what are the two forces pulling K from outside to inside the cell?

Answer 19

1. transmembrane potential (-90mV)
2. Active K transport (-7mV)

Question 20

Nerve conduction studies evaluate which nerves?

Answer 20

Large 1-A myelinated alpha fibers

Question 21

Large 1-A alpha fibers:
diameter:
velocity:

Answer 21

diameter: 10-20nanometers
velocity: 50-120m/s

Question 22

NCS cannot localize _____

Answer 22

pain. pain is carried by unmyelinated C fibers which can’t be picked up on NCS.

Loss of sensation to touch/pin-prick yes. Pain, no.

Question 23

What is saltatory conduction?

Answer 23

action potential depolarizes from node of ranvier to node of ranvier in myelinated fibers as Na travels along the axon

Question 24

The rate of propagation is proportional to ____

Answer 24

diameter of the nerve. So the larger the diameter, the faster the conduction velocity.

This is clinically important bc when you do things distally, the nerve is smaller in diameter, therefore studies done distally will have a different velocity than proximal studies.

Question 25

In an unmyelinated fiver, the conduction velocity varies proportional to ____

Answer 25

the square root of the diameter.