Exam 2 - Lecture 22 (Membrane Potential 3)

Question 1

You turn a dog’s hind paw’s dorsal surface down into the ground while the dog is in a standing position. The dog is able to correct the movement by returning the plantar surface of its paw back to the ground. This test examines the sense of _____.
What sensory receptors are involved?

Answer 1

Proprioception; Golgi-tendon organ and muscle spindle

Question 2

Where are Meissner’s corpuscles located and what are their function?

Answer 2

Located in the skin at the tip of the dermal papillae; sense touch and vibrations < 100 Hz

Question 3

What are the 3 steps in CNS recognition of sensory stimulus?

Answer 3

1. Sensory stimulus generates receptor potential
2. Receptor potential goes over threshold
3. AP

Question 4

What is the length of the axon that is myelinated?

Answer 4

> 1 micrometer

Question 5

What are 2 structures that are unique to myelinated axons (besides the myelin sheath)?

Answer 5

1. Internodes

2. Nodes of Ranvier

Question 6

What do oligodendrocytes make and where?

Answer 6

Myelin in the CNS

Question 7

What do Schwann cells form and where?

Answer 7

Myelin in the PNS

Question 8

What two things affect the speed of a signal along an axon?

Answer 8

size and whether it is myelinated or not

Question 9

What can be used as an example to explain the flow of electrical current down an axon?

Answer 9

wire cable

Question 10

What is STE and what does it equal?

Answer 10

signal transmission efficiency; = membrane resistance divided by longitudinal resistance (Rm/Rin)

Question 11

When membrane resistance increases, _____ current is lost across the cable.

Answer 11

Less (Rm)

Question 12

How can a current travel without significant decrement?

Answer 12

Low longitudinal resistance (Rin); faster speed and longer distance

Question 13

What is the flow of electrical current down nonmyelinated axons?

Answer 13

Local current spreads along axon, activating adjacent VG Na+ and K+ channels, generating AP

Question 14

Where are VG Na+ and K+ channels located in a nonmyelinated axon?

Answer 14

All along the axon

Question 15

Propagation of an AP is _____ (decremental/nondecremental).

Answer 15

Nondecremental

Question 16

How does a myelin sheath around an axon affect STE?

Answer 16

Increases STE

Question 17

Local current reaches a _____ (longer/shorter) distance in a myelinated axon.

Answer 17

longer

Question 18

Where are VG Na+ and K+ channels located in a myelinated axon?

Answer 18

Nodes of Ranvier/between two internodes

Question 19

What is myelin?

Answer 19

Plasma membrane of oligodendrocytes or Schwann cells

Question 20

What is saltatory conduction?

Answer 20

AP jumps from node of Ranvier to node of Ranvier

Question 21

How do larger axon diameters affect Rin (inside resistance)?

Answer 21

Decrease Rin

Question 22

How does myelination affect Rm (membrane resistance)?

Answer 22

Increases

Question 23

Larger myelinated axon = _____ internode and _____ conduction speed

Answer 23

longer; faster

Question 24

What are 2 ways that diameter of axons are classified?

Answer 24

1. Letter system

2. Numerical system (sensory fibers)

Question 25

What are 2 examples of demyelination disease?

Answer 25

1. Multiple sclerosis (human)

2. Degenerative myelopathy

Question 26

What is multiple sclerosis?

Answer 26

Demyelination disease where Ab’s attach own myelin sheaths

Question 27

What is degenerative myelopathy and what does it result in?

Answer 27

Myelin sheaths are attached in the spinal cord; results in progressive muscle weakness and incoordination, complete paralysis, muscle atrophy

Question 28

What is degenerative myelopathy similar to in humans?

Answer 28

ALS

Question 29

Loss of myelin _____ STE and APs cannot reach the NoR.

Answer 29

decrease

Question 30

What happens to VG Na+ and K+ channels that reappear along demyelinated areas of axons?

Answer 30

Return of VG channels diminishes with repeated demyelination episodes