Nervous System III

Question 1

What are Astrocytes?

Answer 1

• highly branched glial cells in CNS believed to make up half of all cells in brain
• form functional network, can communicate with one another

Question 2

What are functions of Astrocytes?

Answer 2

• take up and release chemicals at synapses (feet at synapse, augment signalling)
• provide neurons with substrates for ATP production
• help maintain homeostasis in the ECF (take up K + and H20)
• surround vessels (part of BBB and influence localized blood flow)

Question 3

What are microglia?

Answer 3

• specialized immune cells that reside in the CNS
• serve to protect and preserve neuronal cells from pathogens and facilitate recovery from metabolic insults (survey area)
• use phagocytosis

Question 4

Why does microglia have to protect brain?

Answer 4

Immune cells cannot readily enter ECF of brain because of BBB

Question 5

What happens if microglia are activated pass the threshold?

Answer 5

• these cells start to display detrimental properties
• Alzheimer’s disease, ALS, neuropathic pain

Question 6

What are ependymal cells?

Answer 6

Line fluid filled cavities in the brain and spinal cord

Question 7

What is functions of ependymal cells?

Answer 7

• help to circulate cerebrospinal fluid that fills these cavities and surrounds the brain and spinal cord
• cerebrospinal fluid helps with protection, chemical stability, clearing wastes

Question 8

What are satellite glial cells?

Answer 8

• exist within ganglia in the PNS
• form a supportive capsule around cell bodies of neurons (sensory and autonomic)

Question 9

What happens in a peripheral neuron injury?

Answer 9

CNS repair less likely to occur naturally, glia tend to seal off and form scar tissue
- cannot repair spinal cord injury and synapses cannot reform

Question 10

How do schwann cells guide the regenerating axon?

Answer 10

Create a tube
- 1 mm/day in small neurons
- 5 mm/day in large neurons

Question 11

Why are neurons and muscle cells excitable?

Answer 11

Due to their ability to propagate electrical signals over long distances in response to a stimulus

Question 12

What is the Goldman-Hodgkin-Katz equation?

Answer 12

• predicts membrane potential that results from contribution of all ions that can cross
• combined contribution of each ion (concentration x permeability)
  -different from Nernst (calculates a single ion)

Question 13

What is resting membrane potential in most neurons?

Answer 13

~ 70 mV, mainly due to K+

Question 14

What alters the membrane potential?

Answer 14

A change in the K+ concentration gradient or change in permeability to ions

Question 15

What does not happen with a significant change in membrane potential (-70 to +30 mV)?

Answer 15

• does not indicate a change in concentration gradients of a given ion
• very few ions need to move to alter membrane potential (to alter by 100 mV, 1 out of 100,000 K+ ions must enter or leave cell)
• concentration gradients for ions remain relatively constant during alterations

Question 16

What is ion permeability altered by?

Answer 16

Opening or closing ion channels

Question 17

What are the 5 major types of ion channels?

Answer 17

Na+ channels, K+ channels, Ca2+ channel, Cl- channel, monovalent cation channels (allow Na+ and K+ to pass)

Question 18

What is conductance?

Answer 18

The ease with which ions flow through a channel
- varies with gating state
-channel protein isoform

Question 19

What is a mechanically gated channel?

Answer 19

Open in response to physical forces (pressure or stretch), found in sensory neurons

Question 20

What is a chemically gated ion?

Answer 20

Neurons respond to ligands binding including Extracellular neurotransmitters and neuromodulators or intracellular signalling molecules

Question 21

What is a voltage-gated channel?

Answer 21

Responds to changes in the cells membrane potential (gate is sensitive to charge)

Question 22

What are properties of gated channels?

Answer 22

Much variation:
- voltage gated channels opening can vary from channel to channel (low or high threshold)
- speed at which channels open or close varies
- many channels open to depolarizations will close during repolarization
- some spontaneously inactivate

Question 23

Each major channels have subtypes and some have many:

Answer 23

• varying properties between subtypes (different conductance’s, gating thresholds)
• multiple isoforms that express different gating
• modified by different pathways and proteins