Kaplan Ch. 4 - The Nervous System

Question 1

What are glial cells (aka neuroglia)?

Answer 1

Glial cells are cells in the nervous system that support the function of neurons. Some examples to be familiar with are astrocytes, ependymal cells, oligodendrocytes / Schwann cells, and microglia

Question 2

Astrocyte

Answer 2

Nourishes neurons and forms blood-brain barrier (controls transmission of solutes from bloodstream to nervous tissue)

Question 3

Ependymal cell

Answer 3

Line the ventricles of the brain and produce CSF (provides physical support and shock absorption to the brain)

Question 4

Microglia

Answer 4

Phagocytes that ingest and break down waste products and pathogens in the brain

Question 5

Oligodendrocyte

Answer 5

ONLY in the CNS - produce myelin around axons

Question 6

Schwann Cell

Answer 6

ONLY in PNS - produce myelin around axons

Question 7

How are neurotransmitters stored in the presynaptic neuron?

Answer 7

In vesicles

Question 8

How are neurotransmitters releases from vesicles to the synaptic cleft?

Answer 8

Action potential reaches axon terminal, causing voltage gated calcium channels to open and allowing calcium to flow into the presynaptic neuron. This increase in calcium triggers fusion of the membrane bound vesicles with the cellular membrane at the synapse, resulting in exocytosis of the neurotransmitters into the cleft.

Question 9

How does the neurotransmitter receptor type dictate whether a signal is excitatory or inhibitory?

Answer 9

Receptor can be ligand gated ion channel or G protein coupled receptor.

LGIC will result in either depolarization (excitatory) or hyperpolarization (inhibitory).

GPCR will cause changes in either cAMP or influx of calcium to post synaptic neuron.

Question 10

What are the 3 ways in which neurotransmitters are inhibited at the cleft?

Answer 10

1) enzymes in the cleft can break down the neurotransmitters
2) channels in the presynaptic neuron can reuptake the neurotransmitter back into the presynaptic neuron
3) neurotransmitters can diffuse out of the synaptic cleft

Question 11

Explain how an electrical signal is conducted down a neuron.

Answer 11

Excitatory and inhibitory input from other neurons act on the dendrites of the soma. These inputs are summed to determine the overall input. If the overall input is excitatory and reaches the threshold value (-55 to -40 mV) then the membrane will be depolarized. This results in the opening of voltage gated sodium channels that allows for an influx of sodium with its concentration gradient into the cell. This makes the voltage more positive, until it reaches around +35 mV. At the point, voltage gated potassium channels open and sodium channels are rendered inactive. Potassium flows out of the cell with its concentration gradient resulting in a decrease in membrane voltage. The potassium flows out of the cell in excess, causing hyper polarization or a voltage more negative than resting membrane potential. The resting membrane potential is restored by Na+/K+ ATPase, which uses ATP to actively transport 3 Na+ outside the cell for every 2 K+ brought into the cell.

Question 12

What are the 2 kinda of neural signal summation?

Answer 12

1) temporal = multiple signals are integrated during a short time
2) spatial = response depends on location of firing

Question 13

Two types of refractory periods

Answer 13

1) absolute: no amount of stimulation will cause another action potential
2) relative: a greater than normal stimulus will cause an action potential