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Flashcards in 0-1 Chapter 13 the Spinal Cord Deck (134):
1

paraplegia

paralysis of lower limbs

2

quadriplegia

paralysis of all four limbs

3

hemiplegia

paralysis of one side of the body only

4

Functions of the Spinal Cord

conduction
locomotion
reflexes

5

central pattern generators

are pools of neurons providing control of flexors and extensors that cause alternating movements of the lower limbs

6

spinal cord

cylinder of nervous tissue that arises from the brainstem at the foramen magnum of the skull

7

Number of Spinal Nerves

31 pair of spinal nerves
•first pair passes between the skull and C1
•rest pass through intervertebral foramina

8

spinal cord ends at

inferior margin ends at L1 or a little beyond
occupies the upper two-thirds of the vertebral canal

9

segment

part of the spinal cord supplied by each pair of spinal nerves

10

spinal cord divided into the

cervical, thoracic ,lumbar, and sacral regions

11

two areas of the cord are thicker than elsewhere

•cervical enlargement –nerves to upper limb
•lumbar enlargement –nerves to pelvic region and lower limbs

12

medullary cone (conus medullaris)

cord tapers to a point inferior to lumbar enlargement

13

cauda equina

bundle of nerve roots that occupy the vertebral canal from L2 to S5

14

meninges

three fibrous connective tissue membranes that enclose the brain and spinal cord
–separate soft tissue of central nervous system from bones of cranium and vertebral canal

15

Meninges of the Spinal Cord
from superficial to deep

dura mater, arachnoid mater, and pia mater

16

dura mater

–forms loose-fitting sleeve around spinal cord –dural sheath
–tough, collagenous membrane surrounded by

17

arachnoid mater

arachnoid membrane
subarachnoid space

18

arachnoid membrane

layer of simple squamous epithelium lining dura mater and a loose mesh of collagenous and elastic fibersspanning the gap between the arachnoid membrane and the pia mater

19

subarachnoid space

gap between arachnoid membrane and the pia mater
•filled with cerebrospinal fluid (CSF)

20

lumbar cistern

subarachnoid space inferior to medullary cone that contains cauda equina and CSF

21

pia mater

–delicate, translucent membrane that follows the contours of the spinal cord

22

terminal filum

fibrous strand of pia mater that extends beyond the medullary cone within the lumbar cistern

23

coccygeal ligament

formed from fusion of terminal filum and dura mater
•anchors the cord and meninges to vertebra Co1

24

denticulate ligaments

extend through the arachnoid to the dura
•anchors spinal cord to limit side to side movement

25

spina bifida

congenital defect in which one or more vertebrae fail to form a complete vertebral arch for enclosure of the spinal cord
–in 1 baby out of 1000
–common in lumbosacral region

26

folic acid

(a B vitamin) as part of a healthy diet for all women of childbearing age reduces risk

27

gray matter

neuron cell bodies with little myelin
–site of information processing –synaptic integration

28

white matter –

abundantly myelinated axons
–carry signals from one part of the CNS to another

29

Gray Matter in the Spinal Cord

spinal cord has a central core of gray matter that looks like a butterfly-or H-shaped in cross section

30

posterior (dorsal) root of spinal nerve carries only

sensory fibers

31

anterior (ventral) root of spinal nerve carries only

motor fibers

32

gray commissure

connects right and left sides
•punctured by a central canal lined with ependymal cells and filled with CSF

33

lateral horn

visible from T2 through L1
•contains neurons of sympathetic nervous system

34

White Matter in the Spinal Cord

white matter of the spinal cord surrounds the gray matter
•consists of bundles of axons that course up and down the cord
–provide avenues of communication between different levels of the CNS

35

columns or funiculi

three pair of these white matter bundles
–posterior(dorsal), lateral, and anterior(ventral) columns on each side

36

tracts or fasciculi

subdivisions of each column

37

ascending tracts

carry sensory information up the spinal cord

38

descending tracts

carry motor information down the spinal cord
–all nerve fibers in a given tract have a similar origin, destination, and function

39

decussation

as the fibers pass up or down the brainstem and spinal cord they cross over from the left to the right side and vice versa

40

contralateral

when the origin and destination of a tract are on opposite sides of the body

41

ipsilateral

when the origin and destination of a tract are on the same side of the body
–does not decussate

42

Ascending Tracts

•ascending tracts carry sensory signals up the spinal cord
•sensory signals travel across three neurons from origin in receptors to the destination in the sensory areas of the brain

43

sensory signals travel across three neurons

first order neurons
second order neurons
third order neurons

44

first order neurons

detect stimulus and transmit signal to spinal cord or brainstem

45

second order neurons

continues to the thalamus at the upper end of the brainstem

46

Ascending tracts decussates at

Second order neuron

46

third order neurons

carries the signal the rest of the way to the sensory region of the cerebral cortex

47

Major Ascending Tracts

•gracile fasciculus
•cuneate fasciculus
•spinothalamic tract
•spinoreticular tract
•posterior (dorsal) and anterior (ventral) spinocerebellar tracts

48

Gracile fasciculus

Three neuron pathway
CONTRALATERAL
Carries touch and vibration from lower part of body (below t6)
First order neuron - unipolar - sensor to brainstem - cell body posterior root ganglion
Second order neuron - multipolar - begins with cell body in brainstem - crosses over at brainstem and continues contra laterally to thalamus
Third order neuron - multipolar - cell body in thalamus and axon goes to cortex

49

Cuneate fasciculus

Three neuron pathway
CONTRALATERAL
Carries touch and vibration from upper part of body (above t6)
First order neuron - unipolar - sensor to brainstem - cell body posterior root ganglion
Second order neuron - multipolar - begins with cell body in brainstem - crosses over at brainstem and continues contra laterally to thalamus
Third order neuron - multipolar - cell body in thalamus and axon goes to cortex

50

Spinothalamic tract

Three neuron pathway
Carries pain and temperature
First - unipolar- ends in posterior horn of spinal cord at level it enters -
Second - multipolar - cell body in posterior horn at spinal cord level where first entered - decussates at level of spinal cord and ascends CONTRALATERAL to the thalamus
Third order - multipolar - thalamus to cortex

51

Spinorecticular

Four neuron pathway
Carry pain
First - unipolar- ends in posterior horn of spinal cord at level it enters -
Second - multipolar - cell body in posterior horn at spinal cord level where first entered - decussates at level of spinal cord and ascends CONTRALATERAL to the brainstem (reticular formation)
Third order - multipolar- from brainstem (reticular formation) to the thalamus
Fourth order - multipolar - thalamus to cortex

52

Spinocerebellar tracts

Two neuron
Ipsilateral
Carry proprioceptive signals
First order - unipolar - end in posterior horn of spinal cord
Second order neuron - begins in posterior horn of spinal cord

Anterior tract---posterior horn, decussates at level, ascends to cerebellum and decussates again

Posterior tract--posterior horn, ascends to cerebellum

53

proprioception

nonvisual sense of the position and movements of the body

54

medial lemniscus

formed from the second-order neurons of gracile and cuneate systems that decussate in the medulla
–tracts of these nerve fibers lead the rest of the way to the thalamus

55

descending tracts

carry motor signals down the brainstem and spinal cord

56

descending tracts

involves two neurons

upper motor neuron
lower motor neuron

57

two neuron pathway

–upper motor neuron in cerebral cortex
–lower motor neuron in spinal cord

58

upper motor neuron

originate in cerebral cortex or brainstem and terminates on a lower motor neuron

59

lower motor neuron

in brainstem or spinal cord

60

Lower motor neuron

Alpha motor neuron

61

axon of lower motor neuron

leads the rest of the way to the muscle or other target organ

62

Corticospinal tracts

Carry motor information for precise movements
Anterior and lateral

63

Corticospinal tracts lateral

Two neuron
CONTRALATERAL
Multipolar
Cell body upper motor neuron in cortex - axon decussates in medulla and descends in lateral corticospinal tract and stops in anterior horn of spinal cord at level it needs to exit
Lower motor neuron exits through anterior root, joins spinal nerve and goes to muscle forming neuromuscular junction

64

Anterior corticospinal tract

Two neuron
CONTRALATERAL
Multipolar
Cell body upper motor neuron in cortex - axon descends to exit level and decussates and stops in anterior horn of spinal cord at level it needs to exit
Lower motor neuron exits through anterior root, joins spinal nerve and goes to muscle forming neuromuscular junction

65

pyramids

ridges on anterior surface of the medulla oblongata formed from fibers of this system

66

tectum

midbrain region

67

Poliomyelitis and ALS

both diseases cause destruction of motor neurons and production of skeletal muscle atrophy from lack of innervation

68

poliomyelitis

–caused by the poliovirus
–destroys motor neurons in brainstem and anterior horn of spinal cord
–signs of polio include muscle pain, weakness, and loss of some reflexes
•followed by paralysis, muscular atrophy, and respiratory arrest
–virus spreads by fecal contamination of water

69

amyotrophic lateral sclerosis (ALS)

Lou Gehrig disease
–destruction of motor neurons and muscular atrophy
–also sclerosis(scarring) of lateral regions of the spinal cord
–astrocytes fail to reabsorb the neurotransmitter glutamate from the tissue fluid
•accumulate to toxic levels

70

spinal cord communicates with the rest of the body by way of

spinal nerves

71

nerve

a cordlike organ composed of numerous nerve fibers (axons) bound together by connective tissue

72

mixed nerves

contain both afferent (sensory) and efferent (motor) fibers

73

nerves of peripheral nervous system are ensheathed in

Schwann cells

74

Schwann cells

–forms neurilemma and often a myelin sheath around the axon
–external to neurilemma, each fiber is surrounded by basal lamina and then a thin sleeve of loose connective tissue –endoneurium

75

fascicles

nerve fibers gathered in bundles

76

perineurium

wraps fascicles
•composed of up to 20 layers of overlapping, squamous , epithelium-like cells

77

epineurium

bundles numerous fascicles that constitutes whole nerve
•composed of dense irregular connective tissue
•protects nerve from stretching and injury

78

Classification of Nerve Fibers

sensory (afferent) nerves

79

sensory (afferent) nerves

–carry signals from sensory receptors to the CNS

80

motor (efferent) nerves

–carry signals from CNS to muscles and glands

81

mixed nerves

–consists of both afferent and efferent fibers
–conduct signals in two directions

82

ganglion

cluster of neurosomas outside the CNS
–enveloped in an endoneurium continuous with that of the nerve

83

Number of Spinal nerves

31 pairs of spinal nerves (mixed nerves)

84

spinal nerves by segment

–8 cervical (C1 –C8) C1 between skull and atlas
•others exiting at intervertebral foramen
–12 thoracic (T1 –T12)
–5 lumbar (L1 –L5)
–5 sacral (S1 –S5)
–1 coccygeal (Co)

85

proximal branches

–each spinal nerve has two points of attachment to the spinal cord
–posterior (dorsal) root is sensory input to spinal cord
–anterior (ventral) root is motor output out of spinal cord

86

posterior (dorsal) root

is sensory input to spinal cord
•posterior (dorsal) root ganglion –contains the somas of sensory neurons carrying signals to the spinal cord

87

anterior (ventral) root

is motor output out of spinal cord
•six to eight rootlets that leave spinal cord and converge to form anterior root

88

cauda equina

formed from roots that arise from L2 to Co

89

distal branches of spinal nerves

distal to vertebral foramen, the nerve divides into:
anterior ramus
posterior ramus
meningeal branch

90

anterior ramus

innervates the anterior and lateral skin and muscles of the trunk
•gives rise to nerves of the limbs

91

posterior ramus

innervates the muscles and joints in that region of the spine and the skin of the back

92

meningeal branch

reenters the vertebral canal and innervates the meninges, vertebrae and spinal ligaments

93

Nerve Plexuses

anterior rami branch and anastomose repeatedly to form five nerve plexuses:

94

Nerve Plexuses

5

cervical plexus
brachial plexus
lumbar plexus
sacral plexus
coccygeal plexus

95

cervical plexus

in the neck, C1 to C4
•supplies neck and phrenic nerve to the diaphragm

96

brachial plexus

near the shoulder, C5 to T1
Musculocutaneous
Radial
Axillary
Median
Ulnar

97

lumbar plexus

in the lower back, L1 to L4
Femoral
Obturator

98

somatosensory function

carry sensory signals from bones, joints, muscles, and the skin

99

sacral plexus

in the pelvis, L4, L5 and S1 to S3

Sciatic nerve

Common fibular
Tibular

100

proprioception

brain receives information about body position and movements from nerve endings in muscles, tendons, and joints

101

motor function

primarily to stimulate muscle contraction

102

radial nerve injury

–passes through axilla
–crutch paralysis
–wrist drop

103

sciatic nerve injury

sciatica

sharp pain that travels from gluteal region along the posterior side of the thigh and leg to ankle
–ninety percent of cases result from herniated intervertebral disc or osteoporosis of lower spine

104

chickenpox

common disease of early childhood
–caused by varicella-zoster virus
–produces itchy rash that clears up without complications
•virus remains for life in the posterior root ganglia
–kept in check by the immune system

105

shingles

shingles(herpes zoster) –localized disease caused by the virus traveling down the sensory nerves by fast axonal transport when immune system is compromised
–common after age of 50
–painful trail of skin discoloration and fluid-filled vesicles along path of nerve
–usually in chest and waist on one side of the body

106

dermatome

a specific area of the skin that receives sensory input from a pair of spinal nerves

107

dermatome map

a diagram of the cutaneous regions innervated by each spinal nerve

108

dermatomes overlap their edges as much as

50%
–necessary to sever or anesthetize three successive spinal nerves to produce a total loss of sensation in one dermatome

109

reflexes

quick, involuntary, stereotyped reactions of glands or muscle to stimulation
–automatic responses to sensory input that occur without our intent or often even our awareness

110

four important properties of a reflex

require stimulation
quick
involuntary
stereotyped

111

reflexes include

glandular secretion and contraction of all three types of muscle

112

conditioned reflexes

include some learned responses

113

somatic reflexes

since they involve the somatic nervous system

114

pathway of reflex arc

somatic receptors
afferent nerve fibers
integrating center
efferent nerve fibers
skeletal muscles

115

muscle spindle

stretch receptors embedded in skeletal muscles

116

proprioceptors

specialized sense organs to monitor the position and movement of the body parts

117

stretch (myotatic) reflex

when a muscle is stretched, it ‘fights back’ and contracts which maintains increased tonus, making it stiffer than unstretched muscle

118

tendon reflex

reflexive contraction of a muscle when its tendon is tapped

119

knee-jerk (patellar) reflex

is monosynaptic reflex
•one synapse between the afferent and efferent neurons

120

reciprocal inhibition

reflex phenomenon that prevents muscles from working against each other by inhibiting the antagonist

121

flexor reflex

the quick contraction of flexor muscles resulting in the withdrawal of a limb from an injurious stimulus
•requires contraction of the flexors and relaxation of the extensors in that limb

122

polysynaptic reflex arc

pathway in which signals travel over many synapses on their way back to the muscle

123

crossed extension reflex

the contraction of extensor muscles in the limb opposite of the one that is withdrawn
–maintains balance by extending other leg

124

ipsilateral reflex arc

one in which the sensory input and the motor output are on the same sides of the spinal cord
–flexor reflex

125

contralateral reflex arc

one in which the input and output are on opposite sides
–crossed extension reflex

126

intersegmental reflex

one in which the input and output occur at different levels (segments) of the spinal cord

127

The Tendon Reflex

in response to excessive tension on the tendon
–inhibits muscle from contracting strongly
–moderates muscle contraction before it tears a tendon or pulls it loose from the muscle or bone

128

tendon reflex

organs

proprioceptors in a tendon near its junction with a muscle
–Golgi tendon organ -1mm long, nerve fibers entwined in collagen fibers of the tendon

129

complete transection–

complete severance of cord
–immediate loss of motor control below level of injury
–above C4 poses the threat of respiratory failure
–spinal shock
–paralysis

130

paraplegia

paralysis of both lower limbs

131

quadriplegia

paralysis of all four limbs

132

hemiplegia

paralysis on one side of the body

133

paresis

partial paralysis or weakness of the limbs