0-1 Chapter 13 the Spinal Cord Flashcards
paraplegia
paralysis of lower limbs
quadriplegia
paralysis of all four limbs
hemiplegia
paralysis of one side of the body only
Functions of the Spinal Cord
conduction
locomotion
reflexes
central pattern generators
are pools of neurons providing control of flexors and extensors that cause alternating movements of the lower limbs
spinal cord
cylinder of nervous tissue that arises from the brainstem at the foramen magnum of the skull
Number of Spinal Nerves
31 pair of spinal nerves
•first pair passes between the skull and C1
•rest pass through intervertebral foramina
spinal cord ends at
inferior margin ends at L1 or a little beyond
occupies the upper two-thirds of the vertebral canal
segment
part of the spinal cord supplied by each pair of spinal nerves
spinal cord divided into the
cervical, thoracic ,lumbar, and sacral regions
two areas of the cord are thicker than elsewhere
- cervical enlargement –nerves to upper limb
* lumbar enlargement –nerves to pelvic region and lower limbs
medullary cone (conus medullaris)
cord tapers to a point inferior to lumbar enlargement
cauda equina
bundle of nerve roots that occupy the vertebral canal from L2 to S5
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
Meninges of the Spinal Cord
from superficial to deep
dura mater, arachnoid mater, and pia mater
dura mater
–forms loose-fitting sleeve around spinal cord –dural sheath
–tough, collagenous membrane surrounded by
arachnoid mater
arachnoid membrane
subarachnoid space
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
subarachnoid space
gap between arachnoid membrane and the pia mater
•filled with cerebrospinal fluid (CSF)
lumbar cistern
subarachnoid space inferior to medullary cone that contains cauda equina and CSF
pia mater
–delicate, translucent membrane that follows the contours of the spinal cord
terminal filum
fibrous strand of pia mater that extends beyond the medullary cone within the lumbar cistern
coccygeal ligament
formed from fusion of terminal filum and dura mater
•anchors the cord and meninges to vertebra Co1
denticulate ligaments
extend through the arachnoid to the dura
•anchors spinal cord to limit side to side movement
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
folic acid
(a B vitamin) as part of a healthy diet for all women of childbearing age reduces risk
gray matter
neuron cell bodies with little myelin
–site of information processing –synaptic integration
white matter –
abundantly myelinated axons
–carry signals from one part of the CNS to another
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
posterior (dorsal) root of spinal nerve carries only
sensory fibers
anterior (ventral) root of spinal nerve carries only
motor fibers
gray commissure
connects right and left sides
•punctured by a central canal lined with ependymal cells and filled with CSF
lateral horn
visible from T2 through L1
•contains neurons of sympathetic nervous system
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
columns or funiculi
three pair of these white matter bundles
–posterior(dorsal), lateral, and anterior(ventral) columns on each side
tracts or fasciculi
subdivisions of each column
ascending tracts
carry sensory information up the spinal cord
descending tracts
carry motor information down the spinal cord
–all nerve fibers in a given tract have a similar origin, destination, and function
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
contralateral
when the origin and destination of a tract are on opposite sides of the body
ipsilateral
when the origin and destination of a tract are on the same side of the body
–does not decussate
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
sensory signals travel across three neurons
first order neurons
second order neurons
third order neurons
first order neurons
detect stimulus and transmit signal to spinal cord or brainstem
second order neurons
continues to the thalamus at the upper end of the brainstem
Ascending tracts decussates at
Second order neuron
third order neurons
carries the signal the rest of the way to the sensory region of the cerebral cortex
Major Ascending Tracts
- gracile fasciculus
- cuneate fasciculus
- spinothalamic tract
- spinoreticular tract
- posterior (dorsal) and anterior (ventral) spinocerebellar tracts
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
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
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
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
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