Nerves

Question 1

Nervous tissue composed of:

Answer 1

mostly cells

neurons

glia (supporting cells - glue)

Question 2

Nucleus

Answer 2

group of neuron cell bodies inside the CNS

found in GRAY MATTER of CNS

Question 3

Ganglion

Answer 3

group of neuron cell bodies outside the PNS

Two kinds:

• sensory
• autonomic

Question 4

Tract

Answer 4

group of CNS axons projecting from one place to another

form WHITE MATTER of CNS

Question 5

Nerve

Answer 5

group of fibers in the PNS

Question 6

Afferent

Answer 6

towards a source

sensory

Question 7

Efferent

Answer 7

away from a source

motor

Question 8

Two areas of the spinal cord:

Answer 8

1) Gray Matter - cell bodies - butterfly

2) white

Question 9

Nissl Stain

Answer 9

stains the RER of neurons

axons dont stain (no protein production)

usually more staining at the ventral horn

Question 10

Typical neuron structure (in CNS)

Answer 10

• multipolar
• cell body with array of organelles
• multiple tapered dendrites
• single axon of uniform diameter that has collaterals that branch at right angles to form synapses at the presynaptic terminals

Question 11

Axon hillock

Answer 11

where axon begins

Question 12

Initial segment of axon

Answer 12

site where action potentials are generated

voltage gated ion channels here

Question 13

Nissl substance (RER)

Answer 13

synthesizes NT or its precursors

Question 14

Neuron cell body

Answer 14

• nissl substance
• lots of golgi
• microtubules, microfilaments, neurofilaments

Question 15

Spines

Answer 15

• increase surface area on dendrites
• flexible and active
• contain actin in the neck, no microtubules
• lose spines as we age
• neurotransmitter vesicles can fuse with them

Question 16

Axons

Answer 16

• no RER (Nissl)
• use mainly chemical NT
• Na/K pumps located along entire length

Question 17

Anterograde axonal transport:

Answer 17

• transport NT from cell body to terminal(400 mm/day)

- Kinesin ATPase

Question 18

Retrograde axonal transport:

Answer 18

• recycle substances
• destroy garbage
• 200 mm/day
• Axon terminals can take up toxins/viruses and transport them to the cell body

Question 19

Glial cells in CNS

Answer 19

• in white matter
• oligodendrocytes: make myelin
• microglia: macrophage (smallest)
• fibrous astrocytes: CT, sometimes act like neurons

NOTE: see the same glial cells in gray matter but protoplasmic astrocytes instead

Question 20

Glial cells in PNS

Answer 20

• satellite cells: microenvironment, insulate, allow metabolic exchange
• Schwann: make myelin

Question 21

Oligodendrocytes versus Schwann

Answer 21

O: myelinate up to 50 segments of 50 different axons

S: myelinate only a single segment of ONE axon

Question 22

Demyelination diseases:

Answer 22

1) multiple sclerosis: CNS myelin

2) Guillain-Barre: PNS myelin

Question 23

What is myelin

Answer 23

membranes of the myelin glial cells wrape around and squeeze out cytoplasm

Question 24

How do axons increase conduction velocity?

Answer 24

-increase axon diameter: more current flows through larger tube because decreased resistance

• insulation so passive current flows further down the axon
  
  • thicker sheath = faster conduction

Question 25

Nodes of Ranvier

Answer 25

- voltage gated ion channels of myelinated axons only here - Na/K pumps only here (myelinated uses less energy) - Action potentials jump from node to node

Question 26

Saltatory conduction

Answer 26

-Action potentials jump from node to node

Question 27

Regeneration

Answer 27

- axon degenerates distal to the cut (anterograde/Wallerian degeneration) - cell body undergoes retrograde chromatolysis - PNS can regenerate - CNS cannot because no macrophages (microglia are ineffective), instead astrocytes form glial scar and oligodendrocytes undergo apoptosis

Question 28

PNS regeneration:

Answer 28

- myelin and axonal debris cleared quickly by macrophages - schwann cells provide a tube for axon sprout growth - slow (1-4 mm/day)

Question 29

Inhibitory molecules on myelin suppress CNS axon regeneration:

Answer 29

- nogo - myelin associated glycoprotein (MAG) - oligodendrocyte-myelin glycoprotein (OMgp)

Question 30

Largest neurons in the spinal cord gray matter

Answer 30

ventral horn, motor neurons

Question 31

Retrograde transport diseases

Answer 31

- polio | - tetanus

Question 32

Both retrograde and anterograde transport diseases

Answer 32

- herpes | - rabies

Question 33

Intermediate Zone:

Answer 33

-site of termination of the dorsal axons in the spinal cord

Question 34

Why myelin conducts faster

Answer 34

- insulation - decreased capacitance (charges dont try to meet outside charges) - larger diameter - saltatory conduction

Question 35

Unmyelinated action potentials:

Answer 35

graded, slower

Question 36

Na/K pump in action potential:

Answer 36

-makes the concentration gradient that powers the action potential