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Anatomy > Peripheral Nerves > Flashcards

Peripheral Nerves Flashcards

1
Q

Peripheral nervous system composed of:

A
  • cranial nerves

- spinal nerves

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2
Q

Motor components of PNS

A
  • Somatic motor system

- Visceral motor system

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3
Q

Somatic motor system:

A
  • motor nerves

- effect skeletal muscle

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4
Q

Visceral motor system:

A
  • Autonomic ganglia and nerves

- effect smooth, cardia muscles and glands

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5
Q

Sensory components of the PNS

A
  • sensory ganglia and nerves

- sensory receptors

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6
Q

Number of cranial nerves in PNS

A
  • above spinal cord
  • 12 pairs
  • usually all “special”
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7
Q

Number of spinal nerves in PNS:

A
  • 31 pairs

- cord down segmentally

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8
Q

Subdivision of spinal nerves:

A
  • 8 cervical
  • 12 thoracic
  • 5 lumbar
  • 5 sacral
  • 1 coccygeal
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9
Q

Spinal cord segment contains:

A
  • pair of dorsal root

- pair of ventral root

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10
Q

Gray matter in the spinal cord:

A
  • butterfly region

- contains the neuron cell bodies of the ventral root

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11
Q

White matter in the spinal cord:

A
  • bundles of axons organized into tracts (or fasciculi)

- white because of myelin

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12
Q

Dorsal root

A
  • afferent (sensory)
  • posterior
  • cell bodies contained in the dorsal root ganglion
  • contains axons from dorsal root ganglion cells will synapse in the dorsal horn
  • derived from NCC
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13
Q

Dorsal root gangion:

A
  • contain cell bodies of the dorsal root
  • because their embryonic origin is NCC they lie outside the spinal cord
  • no synapses in the ganglia (just collection of cell bodies)
  • pseudounipolar
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14
Q

Spinal nerve

A

-point at which the ventral and dorsal root meet (IE: contains 2 nerve fibers)

  • divides into two branches (ramus)
    1) ventral ramus
    2) dorsal ramus
  • Both contain motor AND sensory fibers
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15
Q

Ventral root

A
  • efferent (motor)
  • anterior
  • only contains axons (cell bodies in the gray matter of the spinal cord)
  • the axons of ventral horn motor neurons synapse at neuromuscular junctions or at autonomic ganglia (think of sympathetic/parasympathetic)
  • derived from neural tube
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16
Q

proprioception

A

muscle position sensing

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17
Q

Innervation of skin

A

-most peripheral fibers end in the dermis (some lower part of epidermis)

EXAMPLES

  • pacinian corpuscle
  • meissner corpuscle
  • merkel’s disks
  • free nerve endings
  • ruffini’s corpuscle
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18
Q

Dermatome

A
  • slice of skin that is innervated by cutaneous branches of the spinal nerves
  • 30 (b/c no C1 dermatome)
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19
Q

Myotome

A
  • a segment of skeletal muscle supplied by branches of a spinal nerve
  • two parts: epimere and hypomere
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20
Q

Epimere

A

deep muscles of the back

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21
Q

Hypomere

A

intercostal muscles

abdominal muscles

limb muscles

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22
Q

Dorsal ramus:

A
  • supply epimere/skin covering it and joints between vertebrate
  • smaller
  • not many specific names
  • innervates skin of back, joints between vertebrate
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23
Q

Ventral ramus:

A
  • supply hypomere and skin
  • many specific names
  • widespread distribution
  • more motor/sensory fibers than dorsal
  • innervates skin, muscles, and joints of body wall and limbs
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24
Q

Cutaneous nerve:

A
  • supplies specific dermatome

- has BOTH fiber types

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25
Q

Muscular nerve:

A
  • supply specific myotome

- has BOTH fiber types

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26
Q

Trunk innervation:

A

individual dorsal and ventral rami innervate overlapping dermatomes

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27
Q

Limb innervation:

A

adjacent ventral rami may join in a plexus to form nerves that supply overlapping dermatomes and myotomes

28
Q

Dorsal Horn:

A

mostly axons of sensory neurons

29
Q

Ventral horn:

A

mostly cell bodies of motor neurons

30
Q

SNS and ANS comparison:

A
  • SNS is voluntary
  • SNS innervates the body wall, ANS the viscera
  • SNS innervates skeletal muscle, ANS cardiac/smooth
  • SNS is one nerve system, ANS is two nerve system
  • different NT/receptors
  • ANS divided into two components
31
Q

Autonomic Nervous System

A

(synonymous to visceral motor system)

concerned with the motor innervation of smooth, cardiac muscle and glands

TWO DIVISIONS:

  • sympathetic (works with the body)
  • parasympathetic (doesn’t respond to daily life)

*in both 2 neurons form the autonomic pathway

32
Q

Two neuron types in ANS

A
  • preganglionic

- postganglionic

33
Q

preganglionic neurons

A
  • neuronal bodies in the CNS (gray matter of spinal cord)

- axons exit in cranial and spinal nerves

34
Q

postganglionic

A
  • cell bodies in autonomic ganglia in PNS
  • course on arteries to the viscera

Formed by NCC

35
Q

Location of the sympathetic neurons

A
  • preganglionic neurons in the spinal cord from T1-L2 (there are 14)
  • Postganglionic go EVERYWHERE

(IE) prevertebral, vertebral, adrenals

“Fight or Flight”

36
Q

How do preganglionic cells go to body wall

A

1) paravertebral ganlia

2) prevertebral ganglia: supply the abdominopelvic viscera (below diaphragm)

37
Q

White ramus

A

preganglionic sympathetic axons that enter and synapse in a paravertebral ganglion

-can synapse at that level, go up, down, or through the sympathetic trunk

38
Q

Gray ramus

A

postganglionic sympathetic axons that leave the paravertebral ganglia and rejoin spinal nerve to go to body wall

  • innervate sweat glands and smooth vascular muscle
  • NON-MYELINATED NERVES
39
Q

How do autonomic neurons get to viscera?

A

spinal nerves carry either pre/post ganglionic axons to the viscera

40
Q

Example pathway through abdominopelvic visceral innervation

A

Gray matter -> preganglionic -> pass tyhrough paravertebral -> ventral root of spinal nerve -> white rams -> paravertebral -> becomes splanchnic nerve -> synapses in prevertebral ganglion -> postganglionic axons innervate viscera

41
Q

Where are prevertebral ganglia located?

A

in front of the vertebrate

NOT in the thorax (only paravertebral ganglia)

42
Q

Splanchnic nerves contain

A
  • autonomic axons
  • sensory fibers (visceral pain information)
  • they are preganglionic axons that do not synapse at the paravertebral ganglia
43
Q

Location of greater splanchnic nerve

A

T5-T9

44
Q

Location of lesser splanchnic nerve

A

T10-T11

45
Q

Location of least splanchnic nerve

A

T12

46
Q

Lumbar splanchnic nerves

A

-from L1-3

arises below the diaphragm

47
Q

Sympathetic nerves

A

-mixed nerves (carry visceral pain fibers from thoracic and abdominal viscera)

48
Q

Referred pain

A
  • pain from viscera is carried back to the CNS by sympathetic nerves and is referred to dermatomes of the body wall that match the sympathetic innervation
  • visceral afferent fibers course with sympathetic and parasympathetic nerves
  • visceral pain fiber is activated and goes back to the spinal cord, neurons in the cord are confused and pain is referred to dermatomes corresponding to the same spinal cord level that the affect nerve enters the CNS
  • referred pain is dull and poorly localized
49
Q

Parasympathetic division

A
  • preganglionic cell bodies in brainstem
  • they exit with cranial nerve III, VII, IX, X (4 cranial nerves carry parasympathetic 3, 7, 9, 10)

OR

  • cell bodies in sacral (spinal) cord levels in ventral roots of S2, 3, 4
  • only go through visceral structures NOT through the body wall
  • Rest or digest
  • parasympathetic nerves carry visceral sensations other than visceral pain
50
Q

Where do parasympathetic nerves synapse?

A

ganglia in head or neck

or

in terminal ganglia

*post ganglionic axons go only to visceral structures

51
Q

Vagus Nerve

A

carries parasympathetics to thoracic and 2/3 of abdominal viscera

  • peristalsis and gland secretion
  • cranial nerve 10
52
Q

Sacral outflow of parasympathetic nerves

A
  • they are always presynaptic
  • they leave through ventral rami of the S2-4 but then branch off and become pelvic splanchnic
  • synapse at terminal ganglia of the organ

pelvic splanchnic nerves innervate distal 1/3 of gut
-peristalsis and gland secretion of transverse colon, descending, sigmoid, and rectum

make bladder contract, dilate erectile tissues

53
Q

Paravertebral ganglia

A

preganglionic cells synapse at 31 paravertebral ganglia that supply the body wall and viscera

-paravertebral ganglia emerge as splanchnic nerves that go on to synapse in prevertebral ganglia

54
Q

Prevertebral ganglia

A

supply the abdominopelvic viscera (below diaphragm)

-named based on artery to visceral structure

55
Q

Cholinergic transmission

A

acetylcholine is the principal transmitter released by:

1) all preganglionic autonomic neurons (both sympathetic and parasympathetic)
2) all parasympathetic postganglionic neurons
3) some sympathetic postganglionic neurons innervating sweat glands and the smooth muscle of some blood vessels that supply skeletal muscle

56
Q

Adrenergic transmission

A
  • most sympathetic postganglionc neurons release norepinephrine
  • the adrenal medulla releases 80% epinephrine, 20% n-epi
57
Q

Sequence of events in chemical transmission in the ANS

A

action potential -→ calcium influx -→ exocytosis

58
Q

Neuroeffector junction in ANS

A
  • Unlike skeletal muscle no specialized end-plate structures on autonomic target cell
  • nerve terminals of the postganglionic fibers end in close proximity to the cells innervated and consist of a series of bead-like varicosities
59
Q

varicosities

A
  • contain the synaptic vesicles and are the site of their release
  • Target cells have receptors for the transmitters of their controlling nerves distributed over their surfaces
60
Q

Transmitter removal in ANS

A
  • ACh hydrolyzed by acetylcholinesterase

- n-epi is mainly removed by direct sodium-driven reuptake into the nerve terminals

61
Q

ACh receptors

A
  • two major types:
    1) nicotinic (N)
    2) muscarinic (M)
62
Q

Nicotinic receptors

A
  • two major sub-types
    1) N1 on the skeletal muscle end-plate where somatic motoneurons innervate the skeletal muscle fibers

2) N2 mediate transmission at all ganglionic synapses (BOTH sympathetic or parasympathetic)

**All nicotinic receptors are ligand-gated channels that depolarize the postsynaptic membrane (always excitatory)

63
Q

Muscarinic

A

located on all ANS target cells that are sensitive to ACh

NOT ligand-gated channels

-G-protein coupled receptors (excitatory or inhibitory)

64
Q

Excitatory M receptors

A
  • increase IP3/DAG
  • stimulate the opening of calcium channels
  • decrease cAMP
65
Q

Inhibitory M receptors

A
  • decrease cAMP

- stimulate the opening of potassium channels.

66
Q

N-epi and epi receptors

A

*GPCR

alpha 1: increase IP3/Ca, open K+ channels

  • not in the heart
  • Excitatory

alpha 2: located on presynaptic nerve terminals of adrenergic and postganglionic cholinergic nerve fibers

  • decrease cAMP, inhibit the opening of calcium channels, and inhibit NT release
  • sympathetic outflow in the gut
  • inhibitory

beta 1: found only in the heart

  • They increase cAMP
  • excitatory

beta 2: increase cAMP

  • responsible for all inhibitory adrenergic actions on the target cells (ie) dilate bronchiole smooth muscle
  • inhibitory
  • only one where epi/n-epi not equally potent (epi much more potent)
67
Q

Prevertebral ganglia

A
  • found below the diaphragm
  • presympathetic neurons go to paravertebral ganglia come out as root of splanchnic and then synapse at prevertebral to come out as postsympathetic neurons
  • celiac, superior mesenteric, inferior mesenteric ganglion

Anatomy (9 decks)

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