Nerves Part 2

Question 1

What is the difference between a glial cell and a Oligodendrocyte?

Answer 1

A single oligodendrocyte wraps around and ensheathes many different axons.

Question 2

What is Dysmyelination/Hypomyelination?

Answer 2

Inherited myelin disease in which there is failure t myelinate axons during fetal life or early infancy.

Question 3

What is demyelination?

Answer 3

The breakdown of pre-existing myelin; Slows down the conduction velocity and can make it impossible for the AP to proceed.

Question 4

Describe Gullain-Barre syndrome.

Answer 4

Autoimmune damage to myelin and nodes of ranvier of peripheral neurons; Weakness or paralysis

Question 5

Describe Multiple Sclerosis.

Answer 5

Autoimmune disease attacks oligodendrocytes; Resulting in demyelination of CNS neurons.

Question 6

Describe Schwann cell function in the PNS.

Answer 6

Regulate environment of the axons but do NOT insulate axons electrically.

Question 7

Where are unmyelinated axons in the CNS?

Answer 7

Within grooves made by folding of oligodendrocyte cytoplasm.

Question 8

Describe the variability of synapses.

Answer 8

1. Axon-dendrite
2. Axon-Soma
3. Axon-Axon
4. Dendrite-Dendrite

Question 9

What is the fate of a neurotransmitter?

Answer 9

Either degraded in the cleft or taken back up (active transport) into the presynaptic ending; Could also go into glial cells.

Question 10

Discuss the Motor end plate.

Answer 10

The skeletal muscle cell membrane at the motor end plate has junctional folds that contain receptors for Ach (Nicotinic cholinergic receptors); These receptors keep the Ach confined to the region.

Question 11

What is the fate of Ach?

Answer 11

It is degraded by acetylcholinesterase and transported to the basal lamina in the synaptic cleft; Made by the skeletal muscle cell.

Question 12

Describe in general how ligand-gated ion channels work.

Answer 12

1. First messenger binds to outward facing, ligand binding domain of receptor.
2. Ligand binding cases a conformational change in receptor and opens the channel.
3. Ions flow through via passive transport.
4. Target cell depolarizes.
5. Depolarization initiates an event in the cell.

Question 13

What do gap junctions allow to happen?

Answer 13

They allow the flow of ions between cytoplasms of adjacent cells.

Question 14

How do molecules and organelles get transported along the axon?

Answer 14

Microtubules; Microtubule associated proteins (MAPs) use ATP to genereate changes in shape which produces movement along the microtubule.

Question 15

What are the two directions of axon transport?

Answer 15

Anterograde: From the soma, towards the axon terminal

Retrograde (Dyenin): From the axon terminal to the soma.

Question 16

Discuss Anterograde transport.

Answer 16

Uses the Kinesin family of MAPs.

1. Fast: Used to transport components of membranous organelles.
2. Slow: Transports some proteins of the cytoskeleton and various enzymes.

Question 17

Describe mixed nerves.

Answer 17

Mixed nerves have more than one type on nerve; Some are afferent axons, some are efferent. Some axons are myelinated, some are not.

Question 18

What is the perineurium?

Answer 18

A protective barrier that surrounds and defines a bundle of axons (fasicle); Forms the blood-nerve barrier.

Question 19

What is the Epineurium?

Answer 19

Dense Ct surrounding several fascicles to form a nerve trunk; Made by fibroblasts.

Question 20

What is the Endoneurium?

Answer 20

Loose CT surrounding each myelinated axon or collection of unmyelinated axons; External to myelin and Schwann cell basal lamina.

Question 21

What is a ganglion?

Answer 21

A cluster of neuronal cell bodies and glial cells outside the CNS; All derived from the neural crest.

Question 22

Discuss the myelination of pre-ganglionic and post-ganglionic neurons.

Answer 22

Pre-ganglionic neurons are myelinated; Post-ganglionic neurons are unmyelinated.

Question 23

Describe post-ganglionic neurons.

Answer 23

Numberous dendrites with a single unmyelinated axon.

Question 24

What are satellite cells?

Answer 24

Glial cells that surround, support and sustain the post-ganglionic cell bodies

Question 25

Whats the difference between a Schwann cell and an oligodendrocyte?

Answer 25

A single Oligodendrocyte provides myelin to more than one internode segment and to more than on neuron.