Spinal Cord I: Overview Flashcards
Division of spinal segments
31
- 8 cervical
- 12 thoracic
- 5 lumbar
- 5 sacral
- 1 coccygeal
Division of Vertebrae
33
- 7 cervical
- 12 thoracic
- 5 lumbar
- 5 sacral
- 4 coccygeal
Foramen Magnum
the space that the spinal cord passes through to connect to the brainstem
Passing order of vertebrae & spinal segments
- first 7 cervical pass above respective vertebrae, 8th pass above first thoracic vertebra (below 7th)
- remaining nerves pass below vertebrae
- 4 coccygeal vertebrae fused; passes below first coccygeal vertebra
- sacral segments also fused
Dermatomes
areas of skin whose sensory info project via certain spinal nerves
Dermatomes and Segmental Organization
- spinal cord segments send and receive info on certain parts of the body
- cervical segments > arms and head
- thoracic segments > trunks
- lumbar, sacral, coccygeal segments > legs
vertebral body
most ventral aspect of vertebrae
spinous process
most dorsal aspect of the vertebrae
vertebral foramen
space through which the spinal cord projects
superior and inferior articular process
help connect vertebrae to one another via facet joint
intervertebral foramen
space that spinal nerves pass through the vertebrae
intervertebral disk and facet joint
cartilaginous joints that (1) allow for minor movements of the spine and vertebrae, (2) act as ligaments to hold the vertebrae together, (3) act as shock absorbers
Longitudinal arterties
- anterior spinal artery provides blood supply to the anterior aspect of the spinal cord
- 2 posterior spinal arteries provide blood supply to the posterior aspect of the spinal cord
segmental arteries
derived from vertebral arteries + others that can then branch off into radicular arteries that run along the dorsal and ventral nerve roots
Meninges (3)
- dura mater > outermost and thickest layer
- arachnoid mater > middlemost layer; important for cerebrospinal fluid circulation and blood vessel supply
- pia mater > innermost layer
Denticulate ligaments
extensions of the pia mater that anchor the spinal cord to the dura mater (meninge)
- located between spinal nerves
Lumbar Cistern (definition)
region from conus medullaris to end of dural sac
conus medullaris
tapering end of the spinal cord, located around the first lumbar vertebra
filum terminale
extension of the pia mater that helps anchor the spinal cord to the vertebral canal
- filum terminale internum is pia mater, externum fuses with dura mater
Lumbar cistern (important info)
- spinal cord is shorter than the vertebral column
- after spinal cord ends, dura, arachnoid, and pia mater continues
- subarachnoid space is filled with cerebrospinal fluid (ideal for performing lumbar punctures)
- spinal nerves extend down the canal before passing through their respective intervertebral foramen (creates cauda equina)
dorsal roots
comprised of sensory axons that enter the spinal cord
dorsal root ganglia
contains the cell bodies of sensory neurons
- lie approximately in the intervertebral foramen
ventral root
comprised of motor axons that leave the spinal cord
spinal nerve
contains both motor and sensory axons leaving and entering the spinal cord
ventral ramus
contain motor and sensory axons innervating the ventral portion of the body (spinal segment)
dorsal ramus
contain motor and sensory axons innervating dorsal portion of the body (spinal segment)
sympathetic ganglia
located near the intervertebral foramen at each spinal segment
- contain afferent and efferent nerve cell bodies responsible for the sympathetic nervous system (spinal segment)
white mater
exterior portion of the spinal cord that contains mostly axons
gray mater
interior portion of the spinal cord that contains mostly cell bodies
dorsal horn
contains mainly interneuron cell bodies for sensory integration and pathways
ventral horn
contains the cell bodies of motor neurons which drive muscle activity and interneurons
Lissauer’s tract
ascending and descending small fibers that generally terminate in the SG
- fibers convey pain, temperature, and light tough
substantia gelatinosa
collection of cells that receive direct input from the dorsal roots
nucleus proprius
similar function to the SG but more ventral and medial in position
Reasons for Spinal cord enlargements
- quantity of white mater decreases from rostral to caudal segments (axons projecting bw the brain and lower spinal segments must pass thru upper spinal segments first > tapering of white mater from cervical to coccygeal segments)
- gray mater is largest in the cervical and lumbar segments ( neurons are needed for the motor and sensory control of limbs)
cervical enlargement
responsible for upper limbs
lumbar enlargement
responsible for lower limbs
stretch reflex
- spinal reflex
- activation of stretch receptors in a muscle activates motor neurons of the same muscle
- monosynaptic reflex (sensory fiber synapses directly onto motor neuron it controls)
- helps increase muscle tension to protect it from being torn
reciprocal inhibition
- while some muscles are activated, their antagonists are inhibited
- reciprocal pathway of stretch reflex is disynaptic (sensory axon synapses onto single interneuron which inhibits antagonistic motor neurons)
- ensures antagonist muscles don’t interfere with the driving muscles of reflex
flexor reflex
- spinal reflex
- activation of pain receptors activates motor neurons of flexor muscles
- polysynaptic reflex (sensory fiber synapses onto many interneurons, which then synapse onto many motor neurons)
- important for pain avoidance
crossed reflex
- during flexor reflex, pain signals from one leg cross to the other leg to activate extensor muscles and anchor the leg
- mediated by crossed interneurons
- specific crossed reflex ensures that we maintain balance while flexor reflex occurs
Autonomic nervous system
- sympathetic neurons located in sympathetic ganglia of the thoracic and lumbar spinal cord (responsible for flight or flight responses)
- parasympathetic neurons located inside the brainstem and sacral spinal cord (responsible for rest and digest responses)
locomotion
- central pattern generator > collection of interneurons in the spinal cord that are responsible for driving rhythm of locomotion and pattern of motor neuron activity
- interneurons modulated by (1) visual system for object recognition and avoidance, (2) vestibular system for balance, (3) proprioceptive and sensory systems for limb positioning and placement
** brain & brainstem initiate locomotion, spinal cord maintains, different systems modulate
