Spinal Cord, Spinal Nerves, & Associated Structures Flashcards
peripheral nervous system
all parts external to the CNS
. 12 pairs cranial nerves arise from ganglia in the brain
. 31 pairs of spinal nerves arise from/attached to the spinal cord
motor neuron function
relay motor impulses from the CNS to muscle fibers and glands
motor neuron structure
They have a unipolar structure with a proximally located cell body and single
axon
sensory neuron function
relay impulses from receptors in the body to the CNS
sensory neuron structure
pseudounipolar structure with a centrally located cell body and an axon that is divided into a central process and a peripheral process.
PNS subdivisions of body
somatic & autonomic
somatic component on PNS
. structures of the body wall and limbs
. voluntary system.
somatic sensory neurons
. neurons convey information from receptors in skin, joints, & skeletal muscles to CNS
. detect touch, pain, pressure, temp, and proprioception.
somatic motor neurons
neurons relay impulses from the CNS and innervate voluntary muscle fibers
autonomic component of PNS
. visceral structures: organs, vessels, and glands
. involuntary/visceral system.
visceral sensory neurons
. convey info from receptors located in organ wall, vessels & glands to CNS
. detect stretch, pain, temp, chemical irritation, hunger
visceral motor neurons
relay impulses from the CNS and innervate smooth
muscle, cardiac muscle, and glands
where does spinal cord run?
through the vertebral canal from the foramen magnum to the L1 or L2 vertebrae
inferiorly
meninges
encased in protective membranes
spinal cord functions
. motor & sensory innervation of the body inf. to head
. Provides conduction pathway for signals between the body and brain
. Major reflex center
primary tissues in spinal cord
white & gray matter
white matter
. interconnected, myelinated axon tracts connecting parts of the spinal cord to each other or brain
. contains glial cells that support &nourish nervous tissue
gray matter
Forms the central core of the spinal cord.
why is gray matter gray?
axons in it are unmyelinated
Gray matter shape
transverse cross-section, it is “H”-shaped with two ventral horns and two dorsal horns
what do ventral horns contain?
cell bodies of motor neurons (somatic and visceral)
what do dorsal horns contain?
interneurons & prox. axons of sensory neurons (somatic & visceral)
interneurons
in CNS and transmit impulses between other
neurons
spinal nerves are composed of ___
motor and/or sensory neurons
Fila
(sl. filum; axons, rootlets) emerge from the dorsal and ventral surfaces of the spinal
cord and unite to form ventral and dorsal roots
ventral root
. consists of motor axons (fibers) exiting the spinal cord
where are cell bodies of ventral root neurons?
gray matter of the spinal cord.
dorsal root
consists of central processes of sensory neuron axons (fibers) entering the spinal cord.
where are cell bodies of dorsal root neurons?
dorsal root ganglia (DRG) located on the lateral end
of the dorsal root adjacent to, or within, the intervertebral foramina.
spinal nerve proper formation
(aka mixed spinal nerve): Formed by the union of the dorsal and ventral nerve roots of a single spinal cord segment.
Spinal nerve proper characteristics
. Contains both motor and sensory axons/fibers
. Only a few mm. long; located w/in or just external to an intervertebral foramen
spinal nerves split into ___
dorsal & ventral primary rami
dorsal primary ramus
. Supplies motor and sensory innervation to deep back mm.
. Supplies cutaneous sensory innervation to the skin of the back via post. cutaneous n. branches
. smaller than ventral ramus
ventral primary ramus
. Supplies motor and sensory innervation to muscles of lat. & ant. body wall, plus limbs
. Supplies cutaneous sensory innervation to these regions
. Connects to sympathetic chain via rami communicantes
branches of ventral rami to body wall
. Intercostal nerves that further branch into following:
. lat. cutaneous n., large post. & ant. branches
. ant. cutaneous n.
which ventral rami form plexuses?
rami that supply motor &; sensory innervation to limbs & neck merging together
how many segments is the spinal cord divided into and what are they?
31 segments; one segment for each pair of spinal nerves: 8 cervical; 12 thoracic; 5 lumbar; 5 sacral; and,
1 coccygeal
each spinal cord segment innervated a ___
dermatome
cervical enlargement
related to nerves of upper limb
Origination of brachial plexus
lumbosacral enlargement
related to nerves to lower limbs
Origination of lumbo-sacral plexus
conus medullaris
Inferior to the lumbar enlargement is the tapered inferior end of the cord
Dermatome
Specific segment of skin supplied by single spinal nerve
Which spinal nerve DOES NOT inner age a segment of skin?
C1
Why are dermatomes clinically important?
Can indicate potential damage to spinal nerves
T/F cutting a spinal nerve produces complete anesthesia of dermatome it supplies
F, dermatomes overlap so it only causes reduction in sensitivity
How many spinal nerves must be cut to produce zone of total sensory loss?
3
Does the vertebral column or spinal cord grow faster?
Vertebral column
How spinal cord corresponds with vertebral column in fetal stage
At same level
At birth where does spinal cord end
Inferiorly at about same level as L3
In adults how do the cervical spinal cord and vertebrae correspond?
Same level
In adults, how do thoracic and lumbar vertebrae correspond with spinal cord?
Spinal nerve segments are superior to the corresponding vertebra with disparity increasing inferiorly (conus medullaris at L1/L2)
Cauda equina
Long dorsal and ventral roots of lumber and sacral spinal cord segments that droop inferiorly to lumbar and sacral intervertebral foramina
Where do spinal nerves exit the vertebral column?
Intervertebral foramina or sacral foramina
How many cervical nerve pairs are there compared to vertebrae?
8 pairs but 7 vertebra
Where do nerve exit in cervical spine?
C1-C7 nerves exit superiority to corresponding numbered vertebra, C8 is between C7 and T1
Where do nerves exit thoracic, lumbar, and sacral spine?
Inferior to corresponding numbered vertebrae
Where do C1 set of spinal nerves exit spine?
Between skull and C1 post. To Atlanto-occipital synovial joints
Where does C2 set of spinal nerves exit?
Between C1 and C2 post. To lateral Atlanto-axial synovial joints
Where do S1-S4 rami pass through?
Ventral rami pass throughVentral sacral foramina, dorsal rami pass through dorsal sacral foramina
Where do S5 and coccygeal sets of spinal nerves exit?
Sacral hiatus
Meninges of brain
Dura, arachnoid, and pita mater
Dura mater
. Outermost rough fibrous CT layer
. Forms Dural sac from brain to S2 and filum terminale externum
. Creates dural sleeve around spinal roots that is replaced by epineurium
Filum terminale externum
Slender ligament continues inferiorly and anchors dura to coccyx
arachnoid mater
. Delicate, transparent membrane lining dura
. Arachnoid trabeculae: thing strands connecting to pia mater
Pia mater
. Thin layer adhered to spin, cord, and spinal nerve roots
. Denticulate ligaments between dorsal and ventral roots pinning arachnoid mater to dura between spinal nerves
. Filum terminale interum
Denticulate ligaments
Along right and left sides, strong lateral extension of pia that anchor spinal cord laterally to the dura
Filum terminale internum
Strong strand of pia extends inferiorly beyond conus medullaris to terminal end of dural-arachnoid sac
Epidural space
. Between dura and vertebral canal wall
. Filled w/ fat and internal vertebral venous plexus (thin walled veins)
. None in skill
Why is there no fat filled epidural space in skull?
Dura fuses to periosteum of skull
Subdural space
. Potential space between dura and arachnoid
. Contains only film of watery liquid
Subarachnoid space
. Between arachnoid and pia
. Full of CSF
CSF function in subarachnoid space
Pressure of CSF pushes arachnoid membrane against dura so spinal cord and brain are buoyed up by CSF
Lumbar cistern
. Enlarged are of subarachnoid space between inf. Extentsion of cord and inf. Extentsion of dural-arachnoid sac (L2-S2) with pool of CSF
. Contains cauda equina
How are sensory nerves organized within dorsal horn?
Somatic sensory neurons posterior (upper part of horn) to visceral sensory neurons
How are motor neurons organized in ventral horn?
Somatic motor neurons more anterior (upper part of horn) than visceral motor neurons
Difference between roots and rami
Roots only carry sensory or motor neurons, rami carry ALL types of neurons (sensory and motor)
Sympathetic chain
Assists in visceral motor system
. Connected to ventral Ramos via rami communicantes
Do dorsal rami have plexuses?
NO
What is a nerve plexus?
Nerve fibers that blend together and create new nerves
What are the 2 plexuses formed from ventral rami?
Brachial plexus and lumbo-sacral plexus
Sciatica
Herniated disc that impinges on sciatic nerve (L4-S3 spinal nerves)
Which nerve roots are affected from disc herniation?
Spinal roots that are inferior to herniation (L5 spinal roots affected from L4 disc herniation)
What is lumbar cistern used for medically?
Lumber punctures for CSF testing