0-1 Chapter 13 the Spinal Cord Flashcards
(134 cards)
1
Q
paraplegia
A
paralysis of lower limbs
2
Q
quadriplegia
A
paralysis of all four limbs
3
Q
hemiplegia
A
paralysis of one side of the body only
4
Q
Functions of the Spinal Cord
A
conduction
locomotion
reflexes
5
Q
central pattern generators
A
are pools of neurons providing control of flexors and extensors that cause alternating movements of the lower limbs
6
Q
spinal cord
A
cylinder of nervous tissue that arises from the brainstem at the foramen magnum of the skull
7
Q
Number of Spinal Nerves
A
31 pair of spinal nerves
•first pair passes between the skull and C1
•rest pass through intervertebral foramina
8
Q
spinal cord ends at
A
inferior margin ends at L1 or a little beyond
occupies the upper two-thirds of the vertebral canal
9
Q
segment
A
part of the spinal cord supplied by each pair of spinal nerves
10
Q
spinal cord divided into the
A
cervical, thoracic ,lumbar, and sacral regions
11
Q
two areas of the cord are thicker than elsewhere
A
- cervical enlargement –nerves to upper limb
* lumbar enlargement –nerves to pelvic region and lower limbs
12
Q
medullary cone (conus medullaris)
A
cord tapers to a point inferior to lumbar enlargement
13
Q
cauda equina
A
bundle of nerve roots that occupy the vertebral canal from L2 to S5
14
Q
meninges
A
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
Q
Meninges of the Spinal Cord
from superficial to deep
A
dura mater, arachnoid mater, and pia mater
16
Q
dura mater
A
–forms loose-fitting sleeve around spinal cord –dural sheath
–tough, collagenous membrane surrounded by
17
Q
arachnoid mater
A
arachnoid membrane
subarachnoid space
18
Q
arachnoid membrane
A
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
Q
subarachnoid space
A
gap between arachnoid membrane and the pia mater
•filled with cerebrospinal fluid (CSF)
20
Q
lumbar cistern
A
subarachnoid space inferior to medullary cone that contains cauda equina and CSF
21
Q
pia mater
A
–delicate, translucent membrane that follows the contours of the spinal cord
22
Q
terminal filum
A
fibrous strand of pia mater that extends beyond the medullary cone within the lumbar cistern
23
Q
coccygeal ligament
A
formed from fusion of terminal filum and dura mater
•anchors the cord and meninges to vertebra Co1
24
Q
denticulate ligaments
A
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
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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
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anterior (ventral) root of spinal nerve carries only
motor fibers
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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
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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
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columns or funiculi
three pair of these white matter bundles
| –posterior(dorsal), lateral, and anterior(ventral) columns on each side
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tracts or fasciculi
subdivisions of each column
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ascending tracts
carry sensory information up the spinal cord
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descending tracts
carry motor information down the spinal cord
| –all nerve fibers in a given tract have a similar origin, destination, and function
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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
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contralateral
when the origin and destination of a tract are on opposite sides of the body
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ipsilateral
when the origin and destination of a tract are on the same side of the body
–does not decussate
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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
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sensory signals travel across three neurons
first order neurons
second order neurons
third order neurons
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first order neurons
detect stimulus and transmit signal to spinal cord or brainstem
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second order neurons
continues to the thalamus at the upper end of the brainstem
46
Ascending tracts decussates at
Second order neuron
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third order neurons
carries the signal the rest of the way to the sensory region of the cerebral cortex
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Major Ascending Tracts
* gracile fasciculus
* cuneate fasciculus
* spinothalamic tract
* spinoreticular tract
* posterior (dorsal) and anterior (ventral) spinocerebellar tracts
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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
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proprioception
nonvisual sense of the position and movements of the body
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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
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descending tracts
carry motor signals down the brainstem and spinal cord
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descending tracts
involves two neurons
upper motor neuron
| lower motor neuron
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two neuron pathway
–upper motor neuron in cerebral cortex
| –lower motor neuron in spinal cord
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upper motor neuron
originate in cerebral cortex or brainstem and terminates on a lower motor neuron
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lower motor neuron
in brainstem or spinal cord
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Lower motor neuron
Alpha motor neuron
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axon of lower motor neuron
leads the rest of the way to the muscle or other target organ
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Corticospinal tracts
Carry motor information for precise movements
| Anterior and lateral
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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
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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
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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
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spinal cord communicates with the rest of the body by way of
spinal nerves
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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
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nerves of peripheral nervous system are ensheathed in
Schwann cells
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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
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fascicles
nerve fibers gathered in bundles
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perineurium
wraps fascicles
| •composed of up to 20 layers of overlapping, squamous , epithelium-like cells
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epineurium
bundles numerous fascicles that constitutes whole nerve
•composed of dense irregular connective tissue
•protects nerve from stretching and injury
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Classification of Nerve Fibers
sensory (afferent) nerves
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sensory (afferent) nerves
–carry signals from sensory receptors to the CNS
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motor (efferent) nerves
–carry signals from CNS to muscles and glands
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mixed nerves
–consists of both afferent and efferent fibers
| –conduct signals in two directions
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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:
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Nerve Plexuses
5
```
cervical plexus
brachial plexus
lumbar plexus
sacral plexus
coccygeal plexus
```
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cervical plexus
in the neck, C1 to C4
| •supplies neck and phrenic nerve to the diaphragm
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brachial plexus
```
near the shoulder, C5 to T1
Musculocutaneous
Radial
Axillary
Median
Ulnar
```
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lumbar plexus
in the lower back, L1 to L4
Femoral
Obturator
98
somatosensory function
carry sensory signals from bones, joints, muscles, and the skin
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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
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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
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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
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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
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four important properties of a reflex
require stimulation
quick
involuntary
stereotyped
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reflexes include
glandular secretion and contraction of all three types of muscle
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conditioned reflexes
include some learned responses
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somatic reflexes
since they involve the somatic nervous system
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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
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proprioceptors
specialized sense organs to monitor the position and movement of the body parts
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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
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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
