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Anatomy > Spinal Cord 1 > Flashcards

Spinal Cord 1 Flashcards

1
Q

Formation of the vertebral canal and its contents

A

Formation - vertebral foramina form a bony tubular cavity, while other accessory structures add to the boundaries of this vertebral canal
Contents - the canal contain neural tissue and other structures associated with the protection and metabolic support of the neural tissue

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2
Q

anterior boundary of vertebral canal

A

vertebral bodies, intervertebral discs, posterior longitundinal ligament

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3
Q

posterior boundary of vertebral canal

A

vertebral laminae and the ligamentum flavum

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4
Q

lateral boundaries of the vertebral canal

A

vertebral pedicles and the intervertebral foramina

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5
Q

Contents of the vertebral canal

A
  1. spinal cord proper
  2. spinal nerve rootlets/roots
  3. spinal meninges
  4. epidural fat
  5. cerebral spinal fluid (CSF)
  6. bv
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6
Q

spinal cord proper

A

includes gray and white matter

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7
Q

spinal nerve rootlets/roots

A

L and R dorsal and ventral

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8
Q

spinal meninges

A

pia mater, arachnoid mater, dura mater

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9
Q

Spinal cord - external structure/dimensions

A
  1. superior end at foramen magnum, continuous superiorly with brainstem
  2. Inferior end (conus medullaris) at L1/L2 vertebral disc level (L3/4 in newborns)
  3. Shape - an irregular cylinder
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10
Q

Conus medullaris

A
  1. differential growth rates for vertebral column and spinal cord
  2. knowledge importance for spinal taps - level of spinal cord and ligamentum flavum last to puncture to enter epidural space
  3. spinal cord is ~18 in long
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11
Q

cervical enlargement

A

supplies upper limbs, spinal cord segments (C5-T1)

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12
Q

lumbosacral enlargement

A

supplies lower limbs; spinal cord segements L1 - S3

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13
Q

Longitudinal grooves help to

A

delineate L R and column sections

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14
Q

different longitudinal grooves

A
  1. ventral (anterior) median fissure
  2. dorsal (posterior) median sulcus
  3. ventral lateral sulci and dorsal lateral sulci
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15
Q

ventral (anterior) median fissure

A

wide groove on the anterior midline (a good landmark)

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16
Q

dorsal (posterior) median sulcus

A

narrow groove on the posterior midline

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17
Q

ventral lateral sulci and dorsal lateral sulci

A

lateral grooves at site of respective rootlet attachments (dorsal is much more prominent)

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18
Q

internal structure of spinal cord

A

Spinal cord - rootlet - root - spinal nerve - rami

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19
Q

3 primary features of spinal cord

A

white gray matter and central canal

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20
Q

describe the white and gray matter in spinal cord

A

white is superficial, while the gray matter is found deeper, forming an H like shape

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21
Q

describe the central canal

A

the most central within the middle of the gray matter and contains csf

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22
Q

how is white matter formed

A

by neural fiber processes (axons) with minimal cell bodies. The axons are bundled to form tracts. Various tracts are organized within columns. The dorsal, lateral, and ventral columns are delineated by the external longitudinal grooves mentioned previously. The ascending tracts rely info to the brain, while descending tracts relay info to he periphery.

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23
Q

what are dorsal columns formed by

A

primary ascending sensory fibers

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24
Q

primary sensory neurons

A

start at the receptor in the skin and synapse with secondary sensory neurons

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25
Q

secondary sensory neurons

A

in spinal cord or medulla. They cross the midline leading to the 3

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26
Q

3 sensory neurons

A

end in the cerebral cortex

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27
Q

dorsal columns function to

A

transmit fine touch and proprioception on the same side of the spinal cord as souce (ipsilateral)

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28
Q

dorsal column connections

A

synapse with secondary fibers within nuclei of medulla, which then cross the midline and ascend to synapse with the tertiary neurons in the thalamus and eventually terminate in the contralateral brain.

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29
Q

what are secondary fibers typically

A

decussators (cross midline)

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30
Q

location of spinothalamic tract

A

found in both the lateral and ventral columns of white matter

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31
Q

formation of spinothalamic tract

A

bundles formed by secondary ascending gibers

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32
Q

function of spinothalamic tract

A

transmit pain and temperature on the opposite side of the spinal cord as source (contralateral)

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33
Q

what do unilateral lesions on spinothalamic tract cause

A

contralateral anesthesia (1-2 segments below lesion). Tested using pin pricks and knowledge of dermatomes

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34
Q

what does the spinothalamic tract pass through

A

the medulla without crossing, then secondary fibers terminate (synapse with the tertiary) in the thalamus before continuing to cortex

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35
Q

lateral corticospinal (pyramidal) tract found in

A

the lateral column of white matter

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36
Q

lateral corticospinal (pyramidal) tract formed by

A

descending upper motor neurons (UMN), which originate in the motor cortices of the cerebrum (brain0

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37
Q

lateral corticospinal (pyramidal) tract UMN fibers

A

cross the midline in the medulla at the pyramids, thus run contralaterally in the spinal cord (contra to brain) HOWEVER, this can be though of as “this tract is ipsilateral (same side of spinal cord) realtive to the muscles it innervates)

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38
Q

lateral corticospinal (pyramidal) tract synapse with

A

lower motor neurons in the ventral gray horn for eventual distribution to skeletal muscle for voluntary motor control

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39
Q

lesion of lateral corticospinal (pyramidal) tract

A

leads to paralysis below the level of damage

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40
Q

gray matter is primarily formed by

A

neural cell bodies, axon terminal branches, dendrites, and interneurons.

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41
Q

how is gray matter divided into

A

portions (horns) which vary in size/shape throughout spinal cord levels

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42
Q

ventral (anterior) horns

A

found at all levels of spinal cords and contains somatic motor neuron cell bodies (GSE, aka lower motor neurons (LMN) that innervate skeletal muscle)

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43
Q

GSE

A

general somatic efferents

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44
Q

somatic refers to

A

voluntary skeletal muscle and skin of limbs and torso wall

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45
Q

efferent refers to

A

going away from, thus mtor from CNS to muscle, viscera

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46
Q

Dorsal (posterior) horns

A

found at all levels of the spinal cord. It contains central processes of sensory neuron axons (GSA) and interneurons (Ia - interneurons) which integrate various sensory and motor neurons

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47
Q

GSA

A

general somatic afferents

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48
Q

lateral horns (or intermediolateral cell columns)

A

found only at spinal cord segments T1 to L2. It contains preganglionic sympathetic neuron cell bodies (GVE) this autonomic fibers of the sympathetic system

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49
Q

GVE

A

general visceral efferent

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50
Q

visceral refers to

A

involuntary, smooth muscle, organs

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51
Q

gray commissure

A

found at all levels of spinal cord. It is the deepest/central region of spinal cord, contains central canal. Connects the left and right gray columns (area of decussation)

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52
Q

Central canal

A

continuous with the 4th ventricle of the brain, found through entire length of spinal cord. It is the most central feature found within the gray commissure. It contains the csf, but may be occluded in the aged or diseased spinal cord.

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53
Q

Ventral nerve roots

A

a series of ventral (motor) roots respective to each spinal cord segment, individually are a collection of motor axons going to the periphery

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54
Q

how is a single ventral root formed

A

by a series of ventral rootlets from a single spinal cord segment level; is symmetrical bilaterally (L and R ventral roots)

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55
Q

a ventral rootlet is formed

A

along the ventral lateral sulcus and is a collection of axons from motor neurons in the lateral (GVE) and ventral gray horns (GSE). They contain motor fibers only

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56
Q

Dorsal nerve roots

A

a series of dorsal (sensory) roots respective to each spinal cord segment, individually are a collection of sensory axons going to the spinal cord

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57
Q

a single dorsal nerve root is

A

a collection of central axonal processes from pseudounipolar neuron cell bodies located in the dorsal root (spinal) ganglion,

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58
Q

the spinal ganglion is found

A

near the intervertebral foramina (it is important to note that all spinal nerve sensory neuron cell bodies are found within these ganglia)

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59
Q

a single dorsal root splits into

A

a series of dorsal rootlets which enter the spinal cord at the dorsal lateral sulcus; symmetrical bilaterally (L and R dorsal roots)

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60
Q

dorsal nerve roots contain

A

sensory fibers only

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61
Q

Typical spinal nerve description

A

formed near the intervertebral foramen and distal to the spinal ganglion. It is formed by the joining of a dorsal nerve root and a ventral nerve root, each relative to the same spinal cord segment level. It contains both motor (efferent) and sensory (afferent) fibers

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62
Q

how many spinal nerves

A 
31L 
8 cervical (C1-C8)
12 Thoracic (T1-T12)
5 Lumbar (L1-L5)
5 Sacral (S1-S5)
1 coccygeal (Co)
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63
Q

how do the spinal nerves exit the vertebral canal (cervical)

A

by passing superior to the vertebra of the corresponding number.

a. C1-C7 spinal nerves exit ABOVE C1-C7 vert, respectively
b. C8 spinal nerve exits BELOW the C8 vertebra, thus above the T1 vertebra.
c. relatively short spinal nerves with a more horizontal trajectory to exit.

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64
Q

how do the spinal nerves exit the vertebral canal (thoracic and lumbar)

A

exit the vertebral canal inferior to the pedicles of the vertebra with the same number.

a. ex: the right T6 spinal nerve exists below the right pedicle of the 6th thoracic vertebra
b. spinal nerves are successfully longer the further inferior, thus having an oblique to vertical trajectory to exit; due to the spinal cord being shorter than the vertebral column with relatively the same number of segments.

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65
Q

how do the spinal nerves exit the vertebral canal (sacral)

A

the sacral spinal nerves S1-S4 are found within the sacral canal and do not exit as a spinal nerve. Each must branch into their dorsal and ventral rami to exit through dorsal and ventral sacral foramina, respectively

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66
Q

where do S5 and Co1 spinal nerves exit

A

through sacral hiatus

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67
Q

spinal cords ends at

A

L1/L2 vertebral level, thus the dorsal and ventral roots of levels L2 to Co continue within the vertebral canal to their respective exit points. This collection of rootlets/roots is terms the cauda equina.

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68
Q

where is the cauda equina located

A

in the area of the thecal/dural sac called the lumbar cistern, a significant space filled with csf

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69
Q

size of spinal nerve

A

relatively short ~2cm

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70
Q

spinal nerve divisions

A

divides into a dorsal ramus and a ventral ramus

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71
Q

what do rami contain

A

both afferent (sensory) and efferent (motor) fibers

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72
Q

dorsal rami does what

A

innervate the skin, muscles, and joints of the vertebral column and nearby structures

73
Q

ventral rami does what

A

innervate all the structures lateral and anterior to the vertebral column and including the limb structures/embryological derivatives. Thus, the ventral rami are much Larger than the dorsal rami.

74
Q

how is a spinal cord segment defined

A

by the spinal nerve it produces

75
Q

31 spinal nerve pairs means

A

31 spinal cord segments

76
Q

with a shorter spinal cord,

A

the segments of the spinal cord do not directly correspond anatomically with the same named vertebra, particularly in the lower spinal cord

77
Q

all 5 lumbar segments location

A

found inside the T11 T12 vertebrae

78
Q

all sacral/coccygeal segments are found

A

inside the L1 vertebra

79
Q

Dermatome

A

the area of skin innervated by a single spinal cord segment

80
Q

sensory bodies for each dermatome are located

A

in the dorsal root ganglia of the paired spinal nerves

81
Q

dermatome pattern of the torso

A

consistently banded with some overlap.

82
Q

segmentation of intercostal nerves (thoracic spinal nerves)

A

they are segmental, in that they provide sensory ad motor function for that one segment of the torso

83
Q

T4 innervates

A

nipples

84
Q

T10 innervates

A

umbilicus

85
Q

C6 innervates

A

pad of thumb

86
Q

C8 innervates

A

pinky

87
Q

S5 innervates

A

anus

88
Q

why is the dermatome pattern of the limbs much more complex

A

because the ventral rami of the cervical and lumbosacral regions form plexuses, which feed to the upper and lower limbs

  1. allowing nerve fibers form various spinal cord segments to form the peripheral nerves
  2. thus, the dermatome pattern of the limb does not match the cutaneous nerve distribution
  3. with no plexus in the torso region, the dermatomes and the cutaneous nerve distributions are very similar, if not identical
89
Q

what happens to the limbs during development

A

they rotate

90
Q

general rule for segmental muscle innervations, particularly of the limbs,

A

that most muscles are innervated via 2 or more spinal nerves and that 1 spinal nerve helps to supply many muscles

91
Q

spinal meninges

A

3 layers of connective tissue covering the spinal cord

92
Q

describe the spinal dura mater

A
  1. is the most exterior and densest meninx
  2. forms a sac which closes inferiorly at sacral vertebral level 2 (S2)
  3. is open superiorly, continuous with the cranial dura mater at the foramen magnum, enclosing the entire CNS (dural sac or thecal sac, sheath)
  4. continues laterally at sleeve like projections (dural sheaths) around the dorsal and ventral roots of the spinal nerves, and is continuous with the coverings of the spinal nerves (epineurium)
  5. bony anchors - attaches to the bony framework of the foramen magnum and the intervertebral foramen
  6. continues beyond the sac at S2 as the external filum terminale (coccygeal ligament), which anchors the sac to the coccyx
93
Q

meningitis

A

a viral, bacterial, or other microorganism based infection causing inflammation of the meninges. This is considered life threatening. A lumbar puncture to extract CSF is used to diagnose.

94
Q

Spinal arachnoid mater

A
  1. is the intermediate layer, more delicate than dura mater, lines the dura mater
  2. lines the entire dural sac down to its termination at S2, as well as extending into the sleeves surrounding the dorsal and ventral roots (follows dura mater everywhere)
  3. along with the deeper lying pia mater, forms fine strands of tissue (trabeculae) between these 2 layers resulting in a web like (arachnoid) appearance
95
Q

Spinal pia mater

A
  1. is the most internal and most delicate layer of the meninges
  2. envelops the spinal cord like a glove (its skin), its associated bv, the rootlets, and dorsal/ventral roots, finally merging with the epineurium of the spinal nerves
  3. forms the denticulate ligament, reinforced with denser connective tissue. This is an expanse of tissue found between the dorsal and ventral rootlets, bilaterally. These tooth like projections pierce the arachnoid into the dura at about 21 locations on each side. This attachment helps to stabilize the cord within the center of the dural sac
  4. ends inferiorly at the conus medullaris except for its prolongation, the internal filum terminale, which extends from the tip of the conus medullaris.
96
Q

epidural (extradural) space is located

A

external to the dural sac.

97
Q

contents of the epidural sac

A

a cushioning layer of adipose tissue (fat) and an extensive plexus of veins (the internal vertebral venous plexus)

98
Q

subdural space

A

a potential space located between the spinal dura mater and arachnoid mater. Normally these 2 meningeal layers are separated only by a very thin layer of lubricant and this subdural space does not really exist (potential space). however, this potential space can become a space when, for instance, blood invades this area (subdural hematoma)

99
Q

subarachnoid space is located

A

between the arachnoid and pia mater layers. It is filled with CSF

100
Q

CSF is primarily produced by

A

the choroid plexuses of the ventricles in the brain.

101
Q

how do the cranial and spinal subarachnoid spaces communicate

A

freely, as does the flow of the CSF

102
Q

what is below the conus medullaris

A

an expanded area of the subarachnoid space termed the lumbar cistern which contains CSF surrounding the cauda equina. The higher volume of CSF combined with the absence of the spinal cord results in an excellent location to extract CSF or inject anesthetics (lumbar puncture)

103
Q

epidural v spinal anaesthesia

A
  1. epidural needs larger dose 2. epidural has a longer onset of analgesia 3. epidural can be performed at any level, spinals only in lumbar region 4. epidurals can be used segmentally whereas spinals are more generalized
104
Q

Blood supply of spinal cord and innervation of surrounding structures

A

Arterial supply of the spinal cord, venous drainage, innervation of vertebral column contents

105
Q

3 main arteries of spinal cord

A

they are branches of the vertebral arteries within the cranium

a. Single anterior spinal artery
b. paired posterior spinal arteries

106
Q

single anterior spinal artery

A

located in the anterior median fissure, supplies twice as much as the smaller posterior spinal arteries

107
Q

paired posterior spinal arteries

A

passing longitudinally near posterolateral sulci

108
Q

secondary suppliers of the spinal cord

A

they enter laterally - the segmental spinal arteries branch from various vessels ( deep cervical, ascending cervical, and vertebral arteries in the neck; posterior intercostal arteries in the thorax; and lumbar arteries in the abdomen) and enter through each intervertebral foramin and give rise to

  1. anterior and posterior radicular arteries
  2. anterior and posterior segmental medullary arteries
109
Q

anterior and posterior radicular arteries

A

course along the anterior and posterior spinal root/rootlets to help supply these structures

110
Q

radicular refers to

A

roots

111
Q

anterior and posterior segmental medullary arteries

A

periodically reinforce the main spinal arties (8-10 in number). usually, one is significantly larger than the others, the great anterior segmental medullary artery.

112
Q

where does the great anterior segmental medullary artery typically arise

A

on the left side from 1 of the lower intercostal arteries. This is our first looks into arterial anastomosis

113
Q

arterial anastomosis

A

where arteries communicate from 2 different sources for purposes of re routing blood to regulate or maintain blood flow.

114
Q

Venous drainage

A
  1. dorsal and central spinal veins, which directly drain the spinal cord, generally distribute similar to that of the spinal arteries
  2. internal vertebral plexus
115
Q

dorsal and ventral spinal veins

A
  1. vary in number but generally 3-5 anterior and 3-5 posterior, one at each primary sulcus/fissure
  2. found on surface of spinal cord, enveloped within the spinal pia mater
  3. drain into the internal vertebral plexus which lies in the epidural space
116
Q

internal vertebral plexus

A

a valveless system of venous channels in the epidural space, which connects with the dural sinuses in the cranium, the external vertebral plexus surrounding the vertebral column and with major veins of the thorax, abdomen, and pelvis

117
Q

internal vertebral plexus clinically

A

the valveless system and its high degree of interconnection allows for the spread of infection and neoplastic cells (precursors of tumors, cancer, etc)

118
Q

innervation of vertebral column contents

A
  1. each spinal nerve provides 2-4 small recurrent meningeal branches (aka sinuvertebral nerves, recurrent nerves of Luschka, meningeal branch of spinal nerves)
  2. They return to the vertebral canal via the intervertebral foramina to supply fibers
119
Q

recurrent meningeal branches return to the vertebral canal via the intervertebral foramina to supply….

A
  1. sensory fibers for the periosteum of the vertebrae, the posterior longitudinal ligament, the outer portion of the annulus fibrosus, and the meninges
  2. autonomic fibers to the vessels to aid in regulation of blood flow, sensory and sympathetic fibers to meninges, ligaments, and IV discs
120
Q

clinical observation of innervation of vert. column contents

A

intervertebral disc rupture and meningitis MAY irritate these recurrent branches, leading to increased reflexive tone and referred pain.

121
Q

what is a spinal reflex

A

a fast, automatic, hard wired muscular reaction to a stimulus. Initially, the neural activity reaches only as high as the spinal cord, thus does not directly incorporate voluntary, brain activity. These reflexes are important for protecting the body

122
Q

reflex arc

A

the neural pathway from the stimulus to the effector. 5 components

123
Q

5 components in a typical spinal reflex

A
  1. receptors (muscle spindle)
  2. sensory neurons (Ia)
  3. synapsing (integration, communication, processing)
  4. motor neurons (alpha)
  5. effectors (muscles, glands)
124
Q

receptors

A

range from a simple dendrite to a complex sense organ, specialized to sense or receive a specific change or status in the environment, termed a stimulus.

125
Q

2 kind of receptor

A

exteroceptive and proprioceptive

126
Q

exteroceptive receptors

A

are aroused by changes inn the external environment and involve such organs as 1. the skin for touch, vibration, pain or temp 2. the eyes for vision
3. the vestibular apparatus for acceleration of the head, pull of gravity

127
Q

proprioceptive receptors

A

excited by changes in skeletal position, thus important for movement control.

128
Q

proprioception

A

provides knowledge of body position (static) and body movement (dynamic). Arguably the most dominant proprioceptive receptor is the muscle spindle. Golgi tendon organs also provide important information about the strain/tension of the muscle and its associated tendon

129
Q

Afferent (sensory) neuron

A
  1. A pseudounipolar (t shaped) whos cell body is located in the dorsal root ganglia
  2. the axon is divided into a portion peripheral to the cell body (peripheral process) and a portion central to the cell body (central process)
  3. the receptor stimulates the peripheral process, the signal propagates along the axon, continuing through the dorsal root and rootlet on the central process to enter the spinal cord
130
Q

synapsing/integration - simple

A

synapsing may be simple, a sensory neuron synapsed directly with a motor neurons, called a monosynaptic reflex

131
Q

synapsing/integration - complex

A

incorporation of interneurons increases the number of synaptic points in a reflex arc to 2 (disynaptic) or more (polysynaptic). The interneuron is usually a multipolar neuron whos cell body and dendrites are located in the dorsal gray horn and the very short axon terminates on the efferent neuron, also within the gray matter.

These more complex circuits result in various muscle activation patters.

132
Q

Interneurons will most typically have

A

inhibitory influence on its target, but may be excitatory

133
Q

efferent (motor) neuron

A

multipolar neurons, whos cell bodies and dendrites are located in the gray matter and their axons pass out the ventral rootlets to the ventral root to spinal nerves, to rami and finally to an effector (muscles, glands)

134
Q

2 general types of motor neurons

A

somatic and visceral

135
Q

describe somatic motor neurons

A
  1. cell bodies of GSE neurons in ventral gray horn
  2. GSE neurons are LMN, which are stimulated by UMN from the motor cortices of the brain for voluntary contractions and or stimulated by GSA and interneurons (IN) for reflexes
136
Q

what are alpha motor neurons

A

GSE/LMN neurons which stimulate skeletal muscle (extrafusal fibers)

137
Q

motor unit

A

an alpha motor nueron and all the muscle fibers it innervates

138
Q

size of motor unit

A

can vary in size from ~5 muscle fibers (slow or fast twitch) to ~2000 muscle fibers (ex: gastrocnemius). The degree of fine tune control v power needed from that muscle dictates this variation

139
Q

details of the motor unit

A

contains only 1 type of muscle fiber (slow or fast twitch), however, the entire muscle has a unique mixture of various fiber types, thus various types/sizes of motor units that the CNS can influence to control strength and endurance outputs

140
Q

gamma motor neurons

A

GSE/LM neurons which stimulate muscle spindle fibers (intrafusal)

141
Q

describe visceral motor neurons

A
  1. cell bodies of GVE neurons in lateral gray horn found at levels T1-L2
  2. GVE neurons originating inside the spinal cord are preganglionic neurons, these fibers course through ventral root, spinal nerve, white ramus communicans to the sympathetic trunk
  3. eventually it stimulates a postganglionic neuron that acts as the effector (motor) neuron to stimulate an effector (smooth muscle, gland)
142
Q

effector

A

the structure acted on by the efferent nueron

143
Q

for a GSE neuron, what are the effectors

A

the target organ is skeletal muscle OR intrafusal muscle spindle fibers

144
Q

for a GVE neuron, what are the effectors

A

smooth muscle, cardiac muscle, arrector pili muscle, or glands

145
Q

Myotatic or stretch reflex

A

the most fundamental spinal reflect. It is a monosynaptic reflex that is elicited by tapping a tendon

146
Q

what is the result of the tendon tap (stretching of the tendon)

A

subsequent stretch of the skeletal muscle and its associated muscle spindle

147
Q

what happens to quickly stretch muscle spindles

A

stimulate their Ia afferent neurons

148
Q

what do Ia afferent neurons do during a muscle stretch

A

propagate their action potentials through the dorsal spinal nerve system to directly terminate on the efferent neurons (GSE alpha motor neurons) within the ventral gray horn of the spinal cord

149
Q

efferent neurons after a muscle stretch

A

(alpha mn) travel through the ventral spinal nerve system to terminate at the neuromuscular (myoneural) junction

150
Q

what happens to the extrafusal muscle fibers after a tendon tap

A

they are stimulated leading to muscle contraction. This is called autogenic excitation because the muscle spindle stimulated its own skeletal muscle.

151
Q

path of tendon tap

A

tendon tap -> muscle spindle -> Ia -> alpha mn -> skeletal muscle contracts

OR

tendon tap -> muscle spindle -> Ia -> Ia-IN -> inhibits alpha mn of antagonist m

152
Q

what else does the monosynaptic stretch reflect have

A

a disynaptic reflex response. Thi is called reciprocal inhibition. The same Ia afferent stimulates a Ia-interneuron (Ia-IN), which in turn inhibits the alpha mn of the antagonistic muscle. this activity may/should result in relaxation of the antagonist muscle (reduced tone or a reduction in the likelihood of contraction)

153
Q

1a neuron

from, to, characteristics, and yields

A

from: muscle spindle
to: spinal cord
characteristics: sensitive to length change and velocity of length change of the muscle
yields: proprioception; T reflex; reciprocal inhibition

154
Q

II from, to, characteristics, and yields

A

from: muscle spindle
to: spinal cord
characteristics: sensitive to length changes only
yields: proprioception

155
Q

1b from, to, characteristics, and yields

A

from: GTO
to: spinal cord
characteristics: stimulated by stress/strain on the GTO at muscle/tendon junction
yields: Proprioception, autogenic inhibition

156
Q

alpha mn from, to, characteristics, and yields

A

from: spinal cord
to: muscle
characteristics: is a LMN, affected by sensory fibers, interneurons, and UMN
yields: contraction of the muscle

157
Q

gamma nm from, to, characteristics, and yields

A

from: spinal cord
to: muscle spindle
characteristics: is a LMN, affected by interneurons and UPM
yields: resets the spindle; regulates muscle tone

158
Q

what are muscle spindles

A

capsules scattered throughout skeletal muscles, aligned parallel to these muscle fibers

159
Q

describe muscle spindles

A

sensitive to muscle length and the velocity of changes in muscle length. They provide a tonic signal via the Ia and II sensory fibers. They contain their own intrafusal muscle fibers within the capsule.

160
Q

what stimulates the intrafusal muscle fibers of muscle spindles

A

the gamma motor neurons, yielding 2 functions: sensor reset and muscle tone

161
Q

what happens with increased output of the muscle spindles

A

generally causes autogenic excitation and reciprocal inhibition

162
Q

tonic means

A

being constantly active, never going to zero

163
Q

Golgi Tendon Organs (GTO)

A

a proprioceptor that is sensitive to strain/tension on a muscle/tendon. It is embedded within the muscle/tendon junction in series with muscle fibers. It provides a phasic signal via Ib sensory fibers. It leads to inhibition of the stimulation of the sameP muscle it is found in (autogenic inhibition)

164
Q

Phasic means

A

being active in bursts, particularly when stimulated, returning to 0 at some point

165
Q

purposes of the gamma loop

A
  1. reset (shorten) muscle spindle following skeletal muscle contraction/shortening
  2. regulate muscle tone
166
Q

how are gamma motor neurons stimulated

A

by higher brain centers and interneurons

167
Q

what do gamma mn do

A

innervate muscle spindles, causing the intrafusal muscle fibers to contract, leading to 2 outcomes

168
Q

2 outcomes from gamma nm causing muscle fibers to contract

A
  1. the muscle spindle will shorten to match the shortened skeletal muscle, “resetting” the muscle spindle so it can pick up a new stretch within the skeletal muscle (maintain continuous monitoring of the muscle length changes)
  2. the sensory components of the spindle will be stimulated, increasing the Hz of the signal on the Ia sensory neuron, leading to stimulation of the alpha motor neurons back to the associated skeletal muscle -> regulating muscle tone.
  3. Thus, muscle length and tone can be regulated through a circuit (loop) within the lower centers
  4. it adjusts the gain of the stretch reflex, which adjusts the activity level of the alpha mn, thus regulating muscle length and tone
169
Q

muscle tone is the balance of

A

many excitatory and inhibitory influences acting on the alpha motor neurons of a given muscle.

170
Q

Much inhibitory influence on muscle comes from

A

higher brain centers.

171
Q

what does a major loss of inhibitory signal from the brain (like a spinal cord lesion) result in

A

hypertonicity (rigidity) or spasticity

172
Q

damage to UMN usually results in

A

spastic paralysis (because reflexes still work)

173
Q

damage to LMN usually results in

A

flaccid paralysis (no signal - voluntary or reflexive - can get to the muscle because the alphas are out

174
Q

what can UMN do

A

excite Gamma mn, alpha mn (yielding more muscle activity), or have an inhibitory effect on the motor neuronal pool (yielding less muscle tone)

175
Q

If UMN are damaged details

A

no voluntary control nor inhibitory signals can get to a particular level of the spinal cord, thus paralysis. however, the reflexes still work thus spastic paralysis is found.

176
Q

example causes of spastic paralysis

A

stroke, MS, CP, ALS

177
Q

symptoms of spastic paralysis

A

person involuntarily jerks, tremors, twitching, hypertonia, stiff muscles, etc

178
Q

if LMN are damaged details

A

No voluntary nor reflexes can get tot he muscles. No activity on the alpha motor neuron, thus cannot contract the muscle at all. the voluntary pathway and the reflexive arc are broken, thus absolutely no muscle activity = flaccid paralysis

179
Q

example causes of flaccid paralysis

A

myasthenia gravis, ALS

Anatomy (4 decks)

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