Histology of the Nervous System

Question 1

classifications of neurons based on morphology

Answer 1

unipolar

pseudounipolar

bipolar

multipolar

Question 2

motor neurons

Answer 2

efferent neurons, multipolar with many dendrites and one long axon

somatomotor neurons and sympathetic neurons have this morphology

Question 3

sensory neurons

Answer 3

afferent neurons

pseudounipolar with cell body in the dorsal root ganglia with a short, single process that divides into a long afferent process brining impulses from sensors in the body wall or viscera and a shorter, efferent process that enters the dorsal horn of the spinal cord via the dorsal root

Question 4

interneurons

Answer 4

short, multipolar neurons in the spinal cord that are involved in reflexes by receiving a sensory impulse in the dorsal horn and relaying it to somatomotor neurons in the ventral horn

Question 5

neurogli or glial cells

Answer 5

non-conducting cells that provide structural, metabolic, and functional support for neurons

Question 6

supporting cells in the CNS

Answer 6

neuroglia and ependymal cells that form the epithelium lining the CSF-producing ventricles and central canal of the spinal cord

include oligodendrocytes, astrocytes, and microglia

Question 7

supporting cells in the PNS

Answer 7

Schwann cells and satellite cells

Question 8

Schwann cells

Answer 8

surround axons in both unmyelinated and myelinated nerves

produce the myelin sheaths in myelinated nerves - lipid rich, happens in nerves to muscle or sensory form body wall

does not myelinate neurons going to or from the visceral compartment

Question 9

satellite cells

Answer 9

functions similarly to Schwann cells, but surround the nerve cell bodies instead of the axons

Question 10

oligodendrocytes

Answer 10

the CNS equivalent of PNS Schwann cells

they produce myelin and myelinates many axons with extensions of cell processes, forms many internodal segments

Question 11

astrocytes

Answer 11

a scaffolding in brain tissue and have cell processes that surround neuron processes and that also extend to blood vessels

Question 12

microglia

Answer 12

phagocytic cells

Question 13

What do astrocytes and oligos develop from?

Answer 13

neural crest

Question 14

What does microglia develop from?

Answer 14

monocyte precursors in the bone marrow

Question 15

blood-brain barrier

Answer 15

established by artery endothelium tight junctions

astrocyte end feet help this structure

Question 16

perkaryon

Answer 16

the cytoplasm of neurons

Question 17

Nissl bodies

Answer 17

compact stacks of rER that extend into the dendrites

Question 18

axon hillock

Answer 18

the tapering of the cell body at the origin of the axon

lack of Nissl bodies is an easy way to distinguish dendrites from axons

Question 19

dendritic spines

Answer 19

structures that increase the surface area for synapses

Question 20

dendrites

Answer 20

relatively short and branch to varying degrees

axons synapse on dendrites

distally, dendrites contain microtubules and nuerofilaments for transport of materials in both directions

they also have free ribosomes that distinguish them form axons

Question 21

autoimmune target in multiple sclerosis

Answer 21

myelin basic protein, helps form myelin sheaths

part of the intracellular compartment of layers calle dmajor dense lines

Question 22

myelin sheaths

Answer 22

made by Schwann cell wrapping around the axon

cytoplasm and organelles of the Schwann cells are squeezed to the periphery to form the neurilemma or Sheath of Schwann, consists of stacked layers of Schwann cell membrane

proteins/glycoproteins with positive charges help compact the layers by connecting cell membranes

Question 23

axons

Answer 23

carry impulse from cell body to toher neurons or effector cells like muscle, and can be many feet long

initial segment is the thinnest part betweent he axon hillock and the myelin sheath, it is the site where the axon potential is generated

most of the length of an axon contains microtubules and neurofilaments and mitochondria like dendrites, but typically lack ribosomes, required for transport of materials since most everything is manufacutred in the nucleus

Question 24

slow transport

Answer 24

0.2-4 mm/day

only anterograde (cell body to terminal)

conveys structureal elements like tubulin, actin, neurofilament proteins and other matrix proteins and enzymes

Question 25

fast transport

Answer 25

20-4000 mm/day

both directions

anterograde fast transport is for membrane-limited organelles, synaptic vesicles, mitochondria, and low molecular weight molecules such as amino acids, neurotransmitters, sugars, and calcium

retrograde fast transport to the cell body is for similar components plus molecules endocytosed at the terminal

Question 26

nerve impulse

Answer 26

membrane depolariztion due to sodium ion influx, creating an action potential

Question 27

synapse

Answer 27

specialized site of transmission of an impolse from one neuron to another or from a neuron to a muscle cell or gland cell

Question 28

directions of synapses

Answer 28

axodendritic - axon to dendrite

axosomatic - axon to cell body

axoaxonal - axon to axon

axospinous - on dendritic spines

Question 29

features of a synaptic bouton

Answer 29

synaptic vesicles with neurotransmitters

mitochondria and smooth ER

presynaptic density with conical dense, inward projections of the membrane

synaptic cleft, which is the EC space

postsynaptic density on the cytoplasmic side of the postsynaptic membrane

Question 30

steps of impulse transmission

Answer 30

action potential

opens voltage-gated ion channels

calcium enters terminal

triggers neuroransmitter release through exocytosis

neurotransmitter attaches to postsynaptic receptors

conformation change opens ion channels

propagation of impulse

Question 31

two consequences of impulse transmission

Answer 31

excitatory postsynaptic potential

inhibitory postsynaptic potential

Question 32

Schmidt-Lanterman clefts

Answer 32

narrow bands of continuity of cytoplasm from the axon to the exterior of the sheath

Question 33

Node of Ranvier

Answer 33

the exposed axon segment between sequential Schwann cells

action potentials exhibit saltatory conduction as they jump form one node to another, which is faster than continuous conduction

Question 34

intraperiod lines

Answer 34

the extracellular layers of myelin sheath

Question 35

protein O

Answer 35

a transmembrane glycoprotein that connects adjacent layers in both the intracellular and extracellular domains

a major structural component of myelin

Question 36

internodal segments or internodes

Answer 36

the Schwann cells with their myelin sheaths

Question 37

unmyelinated neurons

Answer 37

usually go to and from internal viscera such as the intestines

one Schwann cell surrounds many axons of unmyelinated nerves

Question 38

epineurium

Answer 38

the connective tissue sheath enveloping the entire nerve

Question 39

endoneurium

Answer 39

the delicate connective tissue around each individual neuron and its Schwann cell neurilemma

Question 40

perineurium

Answer 40

surrounds groups of neurons, but is not the equivalent of connective tissue perimycium in skeletal muscle

dense fibrous layer that helps form a nerve/blood barrier in the PNS an dhas properties of connective tissue, epithelium, an dmuscle

perineurial cells produce collagen-like fibroblasts, have tight junctions wtih each other as well as contractile filaments as in muscle cells, what makes nerves contract when severed

Question 41

nerve injury

Answer 41

only the distal segment dies

if the cut segments are realigned, the axons can regenerate and reattach to the detached segment

regenerating axons grow about 1 mm per day