Physiology-Nervous Tissue & Cellular Function

Question 1

What type of neuron is mostly found in the CNS?

Answer 1

Multipolar

Question 2

What type of neurons transmit most sensory impulses from the PNS to the CNS?

Answer 2

Bipolar and pseudounipolar

Question 3

What cells form the myelin sheath around CNS axons? PNS axons?

Answer 3

Oligodendrocytes in CNS. Schwann cells in PNS.

Question 4

What cells allow for neuronal migration in the CNS to occur during growth?

Answer 4

Astrocytes

Question 5

What cells maintain an appropriate ion concentration in the CNS?

Answer 5

Astrocytes

Question 6

What cells form the blood-brain barrier in the CNS?

Answer 6

Astrocytes

Question 7

What cells are the macrophages of the CNS?

Answer 7

Microglia

Question 8

What cells secrete and circulate CSF in the CNS?

Answer 8

Ependymal cells, they have cilia to beat around the CSF they secrete.

Question 9

What cells surround and support nerve cell bodies in the PNS?

Answer 9

Satellite cells

Question 10

How do the synaptic inputs in the CNS differ from those in the neuromuscular junction?

Answer 10

There are excitatory AND inhibitory inputs in the CNS.

Question 11

Is synaptic transmission more or less efficient in the CNS compared to the neuromuscular junction?

Answer 11

Less efficient. It takes many EPSPs firing in unison to trigger and action potential in the target neuron.

Question 12

What two factors determine the size of the graded synaptic potential (EPSP or IPSP)?

Answer 12

How many neurotransmitters are released and the density of receptors for that neurotransmitter on the cell body.

Question 13

Why is an EPSP generated closer to the axon hillock more likely to cause an action potential in the target neuron?

Answer 13

The axon hillock is the primary integrating center and has the most VG Na+ channels to cause an action potential. Additionally, EPSPs decay as they move through the cell body, so the closer they are to the integrating center, the higher the grade will be that is integrated at the axon hillock.

Question 14

What are two ways EPSPs are integrated in the target neuron?

Answer 14

Temporal (consecutive EPSPs add together) and Spatial (simultaneous EPSPs from different synapses add together) Summation.

Question 15

What two ways can local synaptic connections be arranged in the nervous system?

Answer 15

Divergence of convergence.

Question 16

What are the different types of axoaxonic synapses?

Answer 16

Type I: Neuron A synapses on the axon hillock of neuron B and alters the likelihood of generating an AP in neuron B. Type II: Neuron A synapses on axon terminal of neuron B and alters the amount of neurotransmitter released by neuron B onto neuron C by altering the amount of Ca2+ present in neuron B.

Question 17

What is presynaptic facilitation?

Answer 17

A type II axoaxonic synapse where Ca2+ entry into axon B is increased by axon A. This increases the amount of neurotransmitter released onto neuron C by neuron B.

Question 18

What is presynaptic inhibition?

Answer 18

A type II axoaxonic synapse where Ca2+ entry into axon B is decreased by axon A. This decreases the amount of neurotransmitter released onto neuron C by neuron B.

Question 19

What are the three types of neuronal circuits?

Answer 19

Feedforward excitation (A excites B which excites C), feedforward inhibition (A excites B which inhibits C) and disinhibition (4 neurons where 1 & 4 are excitatory and 2 & 3 are inhibitory. A excites B which inhibits C which allows increased firing of D).

Question 20

What are the main inhibitory and excitatory neurotransmitters in the CNS?

Answer 20

Inhibitory: GABA. Excitatory: Glutamate

Question 21

What is the function of neuropeptides?

Answer 21

To modulate the action of classical neurotransmitters

Question 22

You have a patient that comes back to you after having hip surgery. He complains that he cannot feel anything down the front of his thigh. Assuming that a nerve was transected during his operation, what microscopic changes would you observe proximally and distal to the transected portion of the nerve?

Answer 22

Proximally you would see a retrograde reaction (cell body swelling, eccentrically located nucleus, dispersion of Nissl substance and RER replaced by polyribosomes). Distally you would see an anterograde reaction (degeneration and clearance of axon, myelin sheath and axon terminals by Schwann cells & macrophages in PNS and microglia, astrocytes and macrophages in CNS)

Question 23

You have a patient that comes back to you after having hip surgery. He complains that he cannot feel anything down the front of his thigh. Assuming that a nerve was transected during his operation, how will this nerve attempt to regenerate?

Answer 23

1) Stumps swell 2) Axons sprout from nearest Node of Ranvier on proximal segment 3) Sprouts contact Schwann cell guidance tunnels 4) Secondary Schwann cell proliferation forms guidance tunnels along former axon course 5) Sprouts grow 2-5 mm/day, myelinate and innervate target tissue

Question 24

What happens if regenerating axonal sprouts cannot cross the injury site to the Schwann guidance tunnels?

Answer 24

They form a neuroma and the muscle fibers are permanently dennervated.

Question 25

What type of nerve injury has the best prognosis?

Answer 25

Crush injuries closer to the site of innervation. The endoneurial sheaths remain in tact.

Question 26

What factors limit regrowth of axons when nerves are injured in the CNS?

Answer 26

1) Absence of laminin & fibronectin in CNS, they promote growth 2) Inhibitory glycoproteins on oligodendrocytes 3) Oligodendrocytes do not form guidance tunnels 4) Glial cell cytokine release 5) Glial scar at injury site produces inhibitor proteoglycans.