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Microanatomy > MA4 - PNS and Muscle > Flashcards

MA4 - PNS and Muscle Flashcards

1
Q

What are the two components of the PNS?

A

somatic nervous system; autonomic nervous system

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2
Q

What are the divisions of the somatic nervous system?

A

afferent (sensation); efferent (locomotion)

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3
Q

What is the function of the autonomic nervous system? (3)

A

[broadly speaking, homeostatic control of internal tissues] control of heart rate; control of peristalsis/blood pressure; control of glandular secretions

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4
Q

What are the divisions of the autonomic nervous system?

A

sympathetic; parasympathetic; enteric

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5
Q

What is the function of the sympathetic nervous system? (2)

A

fight or flight; efferent functions

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6
Q

What is the function of the parasympathetic nervous system? (2)

A

rest and digest; efferent functions

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7
Q

What is the function of the enteric nervous system? (2)

A

digestion; mostly efferent but some afferent functions

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8
Q

What are the three components of neurons?

A

soma; dendrites; axons

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9
Q

Define soma.

A

neuronal cell body

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10
Q

Describe the activity of the soma’s nucleus.

A

highly euchromatic nucleus with a large nucleolus

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11
Q

What is the Nissl substance?

A

granules of ribosomes and rough ER

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12
Q

What is the function of dendrites?

A

receive synaptic inputs from other neurons on small projections called dendritic spines

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13
Q

Neurofilaments are a type of

A

intermediate filament

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14
Q

What is the composition of the axon membrane skeleton?

A

actin-spectrin network

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15
Q

What are the functions of the axon membrane skeleton? (2)

A

supports plasma membrane; anchors ion conductance proteins necessary for saltatory conduction

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16
Q

What is the function of microtubules in axons?

A

provide a highway for vesicular transport within axons

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17
Q

What are the two forms of microtubule-dependent transport?

A

anterograde transport; retrograde transport

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18
Q

Define anterograde transport.

A

movement of vesicles + cargo from soma to axonal periphery via kinesin

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19
Q

Define retrograde transport.

A

movement of vesicles + cargo from axonal periphery to soma via dynein

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20
Q

Where does biosynthesis occur in neurons?

A

synthesized in soma and then transported

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21
Q

Define synapse.

A

cell-to-cell junction that mediates intercellular signaling from neuron to target cell

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22
Q

List and describe the sequence of events in synaptic communication.

A

axonal action potential reaches terminal; voltage gating of Ca2+ channels triggers fusion of synaptic vesicles w/ presynaptic membrane; diffusion of neurotransmitters across synaptic cleft; binding of neurotransmitters to receptors on postsynaptic membrane; activation of response in target cell

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23
Q

What are the three types of neurons?

A

afferent; efferent; interneurons

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24
Q

In what direction do afferent neurons conduct impulses?

A

periphery to CNS

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25
Q

What are the possible myelination states of afferent neurons?

A

can be either myelinated or unmyelinated

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26
Q

What is the morphology of afferent neurons?

A

pseudounipolar morphology

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27
Q

In what direction do efferent neurons conduct impulses?

A

CNS to periphery

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28
Q

What are the possible myelination states of efferent neurons?

A

can be either myelinated or unmyelinated

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29
Q

What is the morphology of efferent neurons?

A

multipolar morphology

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30
Q

In what direction do interneurons conduct impulses?

A

between neurons

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31
Q

What is the distribution of interneurons?

A

abundant in CNS, but restricted to enteric ganglia in PNS

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32
Q

What is the function of glial cells?

A

serve as support cells for neurons

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33
Q

What are the two types of Schwann cells?

A

myelinating Schwann cells; non-myelinating Schwann cells

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34
Q

Myelinating Schwann cells are recruited by

A

axons that are >1 micron in diameter

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35
Q

Non-myelinating Schwann cells are recruited by

A

axons that are <1 micron in diameter

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36
Q

What are satellite cells?

A

cells that associate with soma and proximal dendrites of neurons in ganglia of somatosensory, sympathetic, and parasympathetic divisions

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37
Q

What is the function of satellite cells? (2)

A

provide physical and trophic support to associated neurons; act as barrier that controls access of substances to neuron

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38
Q

What is the distribution of enteric glial cells?

A

only present in ganglia of enteric division

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39
Q

Describe the morphology of enteric glial cells. (2)

A

resemble astrocytes of CNS; bigger than satellite cells

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40
Q

What is the function of enteric glial cells? (2)

A

provide physical and trophic support to associated enteric neurons; act as barrier that controls access of substances to enteric neuron

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41
Q

What are ganglia?

A

clusters of neuronal cell bodies and supporting glial cells in PNS

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42
Q

What makes up a nerve fiber?

A

nerve fiber = axon + myelin sheath

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43
Q

Nerve fibers are bundled into

A

fascicles

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44
Q

Organize the hierarchy of nerves, nerve fibers, and fascicles.

A

nerve fibers → fascicles → nerves

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45
Q

What are the two broad types of nerves?

A

cranial nerves (originate in brainstem); spinal nerve (originate in spinal cord)

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46
Q

What are the three types of connective tissue of nerves?

A

epineurium; perineurium; endoneurium

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47
Q

What is the epineurium?

A

outermost connective tissue layer of nerve

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48
Q

What is the composition of the epineurium?

A

type 1 collagen fibrils parallel to the long axis of nerve

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49
Q

The epineurium contains what kind of cells?

A

connective tissue cells such as fibroblasts and adipocytes

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50
Q

Describe the relationship between the epineurium and vasculature.

A

epineurium contains larger blood vessels that supply the nerve

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51
Q

What is the perineurium?

A

layer of flattened cells that surround each fascicle of nerve

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52
Q

What is the function of the perineurium?

A

contributes to blood-nerve barrier through tight junctions between perineurial cells

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53
Q

Describe the relationship between the perineurium and vasculature.

A

perineurium surrounds blood vessels (arterioles and venules) that enter endoneurium

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54
Q

What is the endoneurium?

A

connective tissue that packs between nerve fibers in nerve fascicle

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55
Q

Describe the composition of the matrix component of the endoneurium.

A

rich in collagen parallel to nerve fibers, together with ground substance

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56
Q

Describe the composition of the cellular component of the endoneurium.

A

Schwann cells with a few fibroblasts, macrophages, and mast cells

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57
Q

What are the two components of the endoneurium?

A

matrix and cellular components

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58
Q

What are Schmidt-Lanterman clefts?

A

periodically-spaced cytosolic inclusions within myelin sheath that provide metabolic support for sheath

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59
Q

How do Schmidt-Lanterman clefts appear in section?

A

appear as V-shaped discontinuities in nerve fibers

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60
Q

How do nodes of Ranvier appear in section?

A

appear in longitudinal section as butterfly-like discontinuities in nerve fibers

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61
Q

What are nodes of Ranvier?

A

specialized region of axonal membrane that are free of myelin (i.e. gap between adjoining Schwann cells)

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62
Q

Nodes of Ranvier have a high density of

A

voltage-gated sodium channels

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63
Q

(T/F) All sensory neurons are unmyelinated.

A

False. They can be either unmyelinated or myelinated.

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64
Q

Where are somata (cell bodies) of the somatic nervous system located?

A

in dorsal root ganglia

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65
Q

What does it mean for sensory neurons to be pseudounipolar?

A

lack dendrites; have a bifurcated axon instead

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66
Q

Describe the features of the bifurcated axon of pseudounipolar nerves.

A

one branch of axon projects into periphery; other branch projects through dorsal roots to form synapses in dorsal horn of spinal cord

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67
Q

Describe the role of axon thickness in signal transmission. Give two examples.

A

thick axons = faster transmission; touch-sensitive neurons are thick and myelinated (fast transmission); pain-sensitive neurons are thin and unmyelinated (slow transmission)

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68
Q

What are the two types of sensory neuron terminals?

A

non-encapsulated endings; encapsulated endings

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69
Q

Describe the defining feature of non-encapsulated nerve endings.

A

nerve ending is exposed in tissue

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70
Q

Non-encapsulated nerve endings are used by what kinds of nerves?

A

neurons that sense pain, temperature, and light touch

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71
Q

Give an example of a non-encapsulated ending.

A

Merkel ending (senses light touch)

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72
Q

Describe the defining feature of encapsulated nerve endings.

A

nerve endings are encapsulated in structure that facilitates sensation

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73
Q

Encapsulated nerve endings are used by what kinds of nerves?

A

neurons that sense pressure, texture, and muscle elongation

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74
Q

What are the three main types of encapsulated endings?

A

Pacinian corpuscle; Meissner’s corpuscle; muscle spindle

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75
Q

Pacinian corpuscles detect

A

pressure + rate of tissue displacement

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76
Q

Meissner’s corpuscles detect

A

texture

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77
Q

Muscle spindles detect

A

rate/extent of muscle elongation

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78
Q

Where are the somata of autonomic nerves located?

A

in the ventral horn of the spinal cord

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79
Q

Describe the myelination state of autonomic nerves.

A

ALL myelinated

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80
Q

What neurotransmitter is used by autonomic nerves?

A

acetylcholine

81
Q

What are the three types of motor neurons?

A

alpha, beta, gamma

82
Q

Describe the features of alpha-motor neurons.

A

have very large axons

83
Q

What is the function of alpha-motor neurons?

A

stimulate contractions of skeletal muscle fibers

84
Q

Describe the features of beta- and gamma-motor neurons.

A

have smaller axons than alpha-motor neurons

85
Q

What is the function of beta- and gamma-motor neurons?

A

stimulate contractions of specialized myofibers of muscle spindles

86
Q

(T/F) Muscle cells cannot undergo cell division.

A

TRUE

87
Q

How are muscle fibers/myofibers formed?

A

formed by fusion of precursor myocytes

88
Q

What are myofibrils?

A

specialized organelles that mediate contraction

89
Q

What is the composition of myofibrils?

A

composed of myofilaments (thin filaments + thick filaments)

90
Q

Most skeletal muscle fibers are activated by

A

alpha-motor neurons

91
Q

Can muscle fibers be innervated by more than one neuron?

A

No. Each muscle fiber is innervated by only one motor neuron.

92
Q

Activation by a motor neuron causes

A

its innervated myofiber to depolarize.

93
Q

How is depolarization of a motor neuron conveyed?

A

depolarization is conveyed to myofibrils via T-tubules, which penetrate from sarcolemma down to myofibrils

94
Q

What are T-tubules?

A

invaginations of plasma membrane that wrap around myofibrils to elicit excitation-contraction coupling

95
Q

What are terminal cisternae?

A

specializations of sarcoplasmic reticulum that sit in close apposition to T-tubules

96
Q

What is the function of terminal cisternae?

A

excitation in T-tubules triggers release of Ca2+ from terminal cisternae, which initiates muscle contraction

97
Q

What is a triad?

A

combination of 1 T-tubule + 2 terminal cisternae

98
Q

What is the function of a triad?

A

site where excitation-contraction coupling occurs

99
Q

Where are triads located?

A

positioned between border of A-band and I-band

100
Q

How does calcium release from the terminal cisternae activate myofilament contraction?

A

through the troponin/tropomyosin mechanism

101
Q

What is the composition of sarcomeres?

A

central thick filaments flanked by thin filaments on each side

102
Q

Thick filaments are polymers of

A

type II myosin

103
Q

What is the function of thick filaments?

A

provides the molecular motor that drives muscle contraction

104
Q

How are thin filaments oriented in sarcomeres?

A

minus/pointed end points toward center of sarcomere

105
Q

Describe how the length of a sarcomere changes during contraction.

A

myosins move from (-) to (+), so when thick filaments move on thin filaments, the sarcomere shortens

106
Q

Describe the activity of the thin filament at the plus/barbed end.

A

plus/barbed ends of thin filaments are cross-linked via alpha-actinin to plus/barbed ends of thin filament of neighboring sarcomere

107
Q

What are the five elements of a sarcomere?

A

Z-line; I-band; A-band; H-band; M-line

108
Q

Describe the Z-line.

A

where thin filaments of neighboring sarcomeres are cross-linked

109
Q

Describe the I-band.

A

area with thin filaments but not thick filaments

110
Q

Describe the A-band.

A

area with thick filaments

111
Q

Describe the H-band.

A

area of the A-band with thick filaments but not thin filaments

112
Q

Describe the M-line.

A

area at center of sarcomere where thick filaments are cross-linked

113
Q

**Label the following diagram of a sarcomere.

A

**image

114
Q

Contraction of a sarcomere results in shortening of which elements?

A

causes shortening in I- and H-bands, but NOT in A-bands

115
Q

What is internal force coupling?

A

intermediate filaments (mostly desmin) transmit force of contraction b/w myofibrils and b/w myofibrils + rest of cell

116
Q

What is lateral force coupling? (3)

A

force is transmitted b/w myofibers through endomysium; force transmitted through perimysium which connects adjacent fascicles; contraction force is then transmitted laterally to adjacent muscle through epimysium

117
Q

What is the endomysium?

A

connective tissue that separates muscle fibers in skeletal muscle

118
Q

What is the perimysium?

A

connective tissue that encapsulates fascicles of skeletal muscle

119
Q

Describe the vasculature and innervation associated with the perimysium.

A

perimysium has arterioles, venules, and small nerves that branch of larger vessels/nerves of the epimysium

120
Q

What is the epimysium?

A

outermost connective tissue of skeletal muscle

121
Q

What are the three types of tissue associated with skeletal muscle?

A

endomysium; perimysium; epimysium

122
Q

What is longitudinal force coupling?

A

force transmitted longitudinally to tendons through junctions called myotendinous junctions

123
Q

Describe the sequence of events associated with the reflex circuit. (3)

A

sensory neuron stimulates motor neuron and interneurons in spinal cord; motor neurons signal to target muscle; interneurons can inhibit opposed motor neurons

124
Q

What are varicosities?

A

bulges within an axon that generate synapses outside of nerve endings

125
Q

Varicosities are primarily used by what kind of nerve?

A

efferent postganglionic nerves

126
Q

(T/F) The sympathetic nervous system mediates both efferent and afferent functions.

A

False. It has only efferent neurons.

127
Q

Describe the sequence of efferent signals in the sympathetic system and the structures they pass through.

A

preganglionic cell body → paravertebral ganglion → postganglionic cell body → innervation of target tissue

128
Q

Preganglionic sympathetic neurons receive input from

A

the CNS

129
Q

Preganglionic sympathetic neurons’ somata are located in

A

the spinal cord

130
Q

Describe the axons of preganglionic sympathetic neurons.

A

short and myelinated

131
Q

Postganglionic sympathetic neurons receive input from

A

receive input from preganglionic neurons

132
Q

Postganglionic sympathetic neurons’ somata are located in

A

the sympathetic ganglia

133
Q

Describe the axons of postganglionic sympathetic neurons.

A

long and unmyelinated

134
Q

What neurotransmitter do postganglionic sympathetic neurons use?

A

norepinephrine

135
Q

(T/F) The parasympathetic nervous system mediates both efferent and afferent signaling.

A

FALSE. It, like the sympathetic system, also only contains efferent neurons and does NOT contain afferent neurons or interneurons.

136
Q

Describe the sequence of efferent signals in the parasympathetic system and the structures they pass through.

A

preganglionic cell body → paravertebral ganglion → visceral ganglion → postganglionic cell body → innervation of target tissue

137
Q

Preganglionic parasympathetic neurons receive input from

A

the CNS

138
Q

Preganglionic parasympathetic neurons’ somata are located in

A

spinal cord

139
Q

Describe the axons of preganglionic parasympathetic neurons.

A

long, myelinated axons that contact postganglionic neurons in parasympathetic ganglia or near target tissue

140
Q

Postganglionic parasympathetic neurons receive input from

A

receive input from preganglionic neurons

141
Q

Postganglionic parasympathetic neurons’ somata are located in

A

the parasympathetic (visceral) ganglia, which are located near the target tissue

142
Q

Describe the axons of postganglionic parasympathetic neurons.

A

short, unmyelinated axons

143
Q

What neurotransmitter do postganglionic parasympathetic neurons use?

A

acetylcholine

144
Q

What are myoepithelial cells?

A

stellate epithelial cells that express smooth muscle actin

145
Q

How are myoepithelial cells induced to contract?

A

induced to contract by autonomic efferent neurons

146
Q

How do myoepithelial cells drive luminal contents into ducts?

A

squeezing by myoepithelial cells in glands helps to drive luminal contents into ducts.

147
Q

Sympathetic linkage to the heart involves what nerves?

A

sympathetic cardiac nerves

148
Q

Parasympathetic linkage to the heart involves what nerve?

A

vagus nerve

149
Q

What are the three layers of the heart?

A

epicardium; myocardium; endocardium

150
Q

What is the function of the epicardium?

A

provides protection/support

151
Q

What is the function of the myocardium?

A

mediates contraction through cardiomyocytes, which are contractile cardiac muscle cells

152
Q

What is the function of the endocardium?

A

provides internal support

153
Q

The endocardium of the heart is contiguous with

A

the endothelium

154
Q

(T/F) Cardiac muscle cells can have more than one nucleus.

A

True. They can have single or double nuclei.

155
Q

Describe the appearance of cardiomyocytes.

A

striated

156
Q

Are cardiomyocytes capable of expansion or division?

A

cardiomyocytes are capable of hypertrophy (cell expansion), but CANNOT undergo hyperplasia (cell division)

157
Q

How are cardiomyocytes linked?

A

linked end-to-end via intercalated discs, which forms cardiac muscle fibers

158
Q

(T/F) Cardiomyocytes are arranged in fascicles.

A

False. Instead, groupings of fibers fuse and split, which contributes to the squeezing action of the heart.

159
Q

How are myofilaments organized in cardiomyocytes?

A

organized into sarcomeres, like in skeletal muscle, but important to remember that cardiomyocyte myofilaments use different genes than those of skeletal muscle

160
Q

Describe excitation-contraction coupling in cardiomyocytes.

A

use diads (1 terminal cisterna + 1 T-tubule) instead of triads

161
Q

The epicardium is what layer of the heart muscle?

A

outermost layer

162
Q

The epicardium is rich in

A

adipocytes

163
Q

Compare the T-tubules found in cardiomyocytes to those found in skeletal muscle.

A

T-tubules in cardiomyocytes are bigger and are positioned near Z bands (not b/w A and I bands in skeletal muscle)

164
Q

What is the function of intercalated disks?

A

transmit force of contraction from one cardiomyocyte to the next

165
Q

What is the function of the fascia adherens in intercalated disks?

A

fascia adherens is the patch in which thin filaments from sarcomeres insert, allowing force of sarcomere contractions to be communicated from one cell to the next

166
Q

Fascia adherens are found on what aspect of intercalated disks?

A

transverse aspect

167
Q

What is the function of desmosomes in intercalated disks?

A

link intermediate filaments (rich in desmin) of adjoining cardiomyocytes together

168
Q

Desmosomes are found on what aspect of intercalated disks?

A

both transverse + longitudinal aspects

169
Q

What are the three components to intercalated disks?

A

fascia adherens; desmosomes; gap junctions

170
Q

What is the function of gap junctions in intercalated disks?

A

allow excitation to pass between cells

171
Q

Gap junctions are found on what aspect of intercalated disks?

A

only longitudinal aspect

172
Q

Intercalated disks stain with

A

eosin (they are highly eosinophilic)

173
Q

Which cells serve as the pacemakers of the heart?

A

specialized cardiomyocytes of the sinoatrial node (intrinsic frequency of ~100 cycles per minute)

174
Q

How is the excitation generated by the sinoatrial node transferred?

A

SA node [→ gap junctions →] atrial cardiomyocytes [→ gap junctions →] AV node [→ bundle of His →] Purkinje fibers [→ gap junctions →] excitation of ventricular cardiomyocytes

175
Q

(T/F) Sympathetic and parasympathetic innervation is critical for the intrinsic depolarization/repolarization cycles of cardiomyocytes.

A

False. Sympathetic and parasympathetic innervation can help regulate the frequency of these cycles, but is not required for these cycles to take place.

176
Q

Where can Purkinje cardiomyocytes be found in section?

A

located at the interface b/w myocardium and endocardium

177
Q

The ganglia of the enteric system are organized into what two plexi?

A

submucosal Meissner’s plexus; myenteric Auerbach’s plexus

178
Q

The enteric plexi are controlled by which nervous system?

A

autonomic nervous system (specifically, postganglionic sympathetic and preganglionic parasympathetic)

179
Q

Describe the common morphological features of the enteric ganglia.

A

smaller than literally all the other ganglia; closely packed somata surrounded by enteric glial cells; little EC matrix

180
Q

Where is the myenteric/Auerbach’s plexus located?

A

enteric ganglia in muscularis propria b/w outer longitudinal and inner circular muscle layers

181
Q

What is the function of the myenteric/Auerbach’s plexus?

A

controls peristaltic contractions of muscularis propria

182
Q

Where is the submucosal/Meissner’s plexus located?

A

enteric ganglia in submucosa

183
Q

Compare the size of the submucosal/Meissner and myenteric/Auerbach plexi.

A

ganglia of myenteric/Auerbach are more numerous but smaller than those of submucosal/Meissner

184
Q

What is the function of the submucosal/Meissner’s plexus?

A

controls actions of mucosa (i.e. glands, contractions of smooth muscle of muscularis mucosae, etc.)

185
Q

What is the major target of efferent enteric neurons?

A

smooth muscle

186
Q

Describe the shape of smooth muscle cells (SMCs).

A

fusiform (long, thin with pointy end) shape w/ central nucleus

187
Q

Are smooth muscle cells capable of expansion or cell division?

A

capable of both cell expansion and cell division

188
Q

How do smooth muscle cells appear in longitudinal section?

A

appear long and thin with highly eosinophilic cytosol

189
Q

How do smooth muscle cells appear in transverse section?

A

appear small, w/ nucleus frequently out of plane

190
Q

Smooth muscle cells are commonly organized into

A

fascicles (but they do NOT form fibers like skeletal or cardiac muscle)

191
Q

What structure within smooth muscle cells mediates contractions?

A

myofilaments

192
Q

What are dense bodies? (2)

A

structures that anchor myofilaments within cytosol and at sarcolemma; myofilaments radiate out of the dense bodies

193
Q

(T/F) Dense bodies are striated.

A

False, they are NOT striated

194
Q

Smooth muscle cells are surrounded by

A

an external lamina

195
Q

What is the function of the external lamina that surrounds smooth muscle cells?

A

fused onto external laminae of neighboring SMCs, which pulls on adjoining SMCs during contraction

196
Q

How are smooth muscle cells usually innervated/excited?

A

can be excited by nerves (synapses), hormones (endocrine receptors), or external force (mechanoreceptors)

197
Q

Give an example of how smooth muscles use mechanoreceptors for contraction.

A

full bladder has relaxed smooth muscle, but as the bladder empties, mechanoreceptors on SMC activate, initiating contraction that drive remaining fluid from bladder

198
Q

Describe excitation-contraction coupling in smooth muscle.

A

mediated through caveolae of sarcolemma (no diads or triads); if activation reaches threshold, Ca2+ released from sarcoplasmic reticulum which drives contraction by activating MLCK/MLCP system and promotes myosin activity

199
Q

What is the function of caveloae in smooth muscle?

A

sites of calcium influx (since SMCs lack a T-tubule system)

Microanatomy (7 decks)

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