Nervous Tissue

Question 1

What is a neuron? What do they constitute? What are they located?

Answer 1

structural and functional unit of nervous system
constitute: most sensory receptors, conducting pathways, and integration centers

in CNS

Question 2

What is nervous tissue consisted of?

Answer 2

neurons and supporting cells (non-conducting)

Question 3

What do supporting cells provide? What are there categories?

Answer 3

physical support and protection, electrical insulation, metabolic exchange

neuroglia in CNS, Schwann cells in PNS, and satellite cells in ganglia

Question 4

What is a defining characteristic of neurons?

Answer 4

terminally differentiated, do not divide, although regeneration of axon is possible

Question 5

What is a soma?

Answer 5

cell body - contains nucleus, surrounded by cytoplasm = perikaryon

Question 6

What are Nissl substance, neurilemma, and melanin, lipofuscin?

Answer 6

nissl = rER
neurilemma = plasma membrane surrounding cell
melanin and lipofuscin = age pigment within cell body

Question 7

What are some characteristics of neurons?

Answer 7

1 or more dendrites - highly branched neuron processes
receive stimuli from other neurons or environment (Afferent)
single axon - transmits stimuli to other neurons or effector cells (Efferent)

axons arise from axon hillock, terminates in distal swelling called terminal bouton

Question 8

What is axonal transport? What are the types?

Answer 8

movement of products down axon
slow axonal transport carries cytoskeletal elements; fast carries membrane-bound organelles

anterograde transport = from cell body down axon = uses kinesin

retrograde transport = from axon to cell body = uses dynein

Question 9

What are the basic neuron types?

Answer 9

multi-polar neuron: most common, several dendrites (motor neuron)
bipolar: single dendrite opposite axon
unipolar: no dendrites on soma, axon only (sensory neuron)
pseudo unipolar: single dendrite and axon fuse; soma off to one side (dorsal root ganglia)

Question 10

What is the physiology of the nervous conduction?

Answer 10

sodium and chloride higher outside cell
potassium higher inside cell
due to Na-K pumps in neuron cell membrane, Na pumped out and K pumped in. net = -80 resting membrane potential inside cell

Question 11

What does an action potential do in the cell body?

Answer 11

“all or none” response
arises in cell body as a result of efferent stimulus
causes region of plasma membrane to depolarize
voltage gated Na channels open and sodium rushes into cell
voltage gated K leak channels open and K rapidly leaks out of cell
causes reversal of resting potential (goes to zero)
membrane loses polarity = becomes depolarized
Na channels close and refractory period begins, then K channels close and membrane repolarizes
action potential then conducted to effector cell at synapse via neurotransmitter

Question 12

What are neuromuscular junctions?

Answer 12

specialized junctions between neurons or between neuron and effector cell

each synapse unidirectional and response to stimulis may be either excitatory or inhibitory

Question 13

What is entrainment?

Answer 13

more a pathway is used = easier it is to access

Question 14

What is the terminal bouton separated from effector cells by?

Answer 14

synaptic cleft

Question 15

What does the terminal bouton contain?

Answer 15

mitochondria and membrane bound synaptic vesicles containing neurotransmitters

Question 16

Signaling molecules release from:
diffuse across synaptic cleft and do what?

Answer 16

pre-synaptic membrane
bind to receptor molecules on post-synaptic membrane

Question 17

What neurotransmitters are used in the CNS? PNS?

Answer 17

CNS = GABA, dopamine, serotonin
PNS = acetylcholine and norepinephrine

Question 18

What is the ANS divided into? What do those divisions use?

Answer 18

sympathetic = norepinephrine as excitatory neurotransmitter (adrenergic)
parasympathetic = promotes relaxation using acetylcholine as excitatory neurotransmitter (cholinergic)

Question 19

What does the peripheral nervous tissue contain? Where are the cell bodies located?

Answer 19

contains afferent and efferent fibers of either somatic or auntonomic nerves
cell bodies of peripheral nerves located in CNS or in ganglia

Question 20

What is a peripheral nerve?

Answer 20

bundle of axons or fascicle

Question 21

What are Schwann cells derived from? What do they do?

Answer 21

neural crest associated with axons
provide metabolic support and electrical insulation

nuclei along length of axon belong to Schwann cells

Question 22

In non-myelinated nerves where do axons lie?

Answer 22

in channels with Schwann cell, surrounded by single layer of neurilemma from Schwann cell
(PNS)

Question 23

What are myelinated nerves?

Answer 23

insulated by many concentric layers of plasma membrane from many Schwann cells

Question 24

What is the sheath of Schwann?

Answer 24

consists mostly of cell membrane forms myelin sheath = axon
many axons bound together in fascicle form nerve

Question 25

What are the nodes of Ranvier? What are they responsible for? What occurs only at nodes?

Answer 25

gaps in myelin sheath between adjacent Schwann cells
responsible for rapid, saltatory conduction
membrane depolarization occurs only at nodes, not beneath Schwann cell.

Question 26

What are the myelinated nerves in the CNS? What is the rate of conduction dependent upon?

Answer 26

oligodendrocytes
diameter of axon (bigger = faster)
myelin also increases conduction rate

Question 27

What is peripheral nervous tissue? What is unique about it? What does it exhibit?

Answer 27

larger nerves containing several fascicles surround by additional layer of connective tissue (epineurium)
cells of perineurium are unique because not just fibroblasts
blood vessels tend to follow epi- and perineruium

Question 28

What are preganglionic and postganglionic neurons?

Answer 28

pre = neurons have cell bodies in gray matter of brain and cord of CNS
post = with cell bodies located in ganglia

Question 29

What are ganglia? What are they derived from?

Answer 29

discrete aggregations of postsynaptic neuron cell bodies located outside the CNS
embryologically derived from neural crest, like all peripheral nerves

Question 30

What is the purpose of ganglia? Where are they located?

Answer 30

each cell body (soma) is surrounded by satellite cells, derived from neural crest - provide structural and metabolic support

location
symp = parallel vertebral column
para = lie in or near effector organ

Question 31

What kind of sympthetic and parasympathetic ganglia are there?

Answer 31

sympathetic = prevertebral (located anterior to spine) and paravertebral (located in sympathetic trunk)

parasympathetic = located in or near effector organ