Spinal Cord Flashcards
Which segment of the vertebrae does not have a dermatome? What does it innervate instead?
C1- dura in posterior cranial fossa
What part of the spinal cord receives sensory information?
dorsal root
What is sensory information sent up to the brain through?
ascending tracts
Through what does the spinal cord receive signals from brain?
descending tracts (motor)
What transmits signals to somatic and visceral targets?
motor ventral roots
Where are the enlargements of the spinal cord?
cervical (C4-T1) and lumbosacral (L1-S2)
What is at the caudal end of the spinal cord?
conus medullaris
What is not part of the spinal cord but is formed from lumbosarcal nerve roots?
cauda equina
What contains the ascending and descending bundles of the spinal cord?
white matter
How many funiculi are in each half of the spinal cord?
3
bundles of 1+ fasciculi=?
funiculus (column)
What does the gray matter of the spinal cord contain?
neuronal cell bodies, dendrites and myelinated and unmyelinated axons
Divisions of gray matter in spinal cord and their functions
dorsal horn- sensory
intermediate zone- integrative functions
ventral horn- motor
lateral horn- T1-L2 housing preganglionic sym neuronal bodies
What part of the spinal cord contains the central canal?
gray commissure
What does the zone/tract of Lissauer/posterolateral fasciculus (tract) consist of?
(un)&myelinated dorsal root fibers that enter medial portion of the zone, propriospinal fibers that interconnect levels of substantia gelatinosa
What part of the spine contains the intermediolateral cell column with preganglionic sympathetic neuronal bodies?
T1-L2 lateral horn of thoracic segment
What segment of the spine contains intermediolateral cell column with preganglionic parasympathetic neuronal bodies ?
intermediate gray zone of S2-S4
How do you label the laminae zone?
I-IX dorsal to ventral and X is at central canal `
What laminae are in the dorsal horn?
1-VI
What laminae are in the intermediate gray zone?
VII
What laminae are in the ventral horn?
8 and 9
Laminae I and II
I- has dorsal root fibers that mediate pain, temperature, touch
II- contains substantia gelatinosa neurons that modulate pain and temp afferent fibers
Laminae 3 and 4
both have proper sensory nucleus that recieves from substantia gelatinosa and contribute to spinothalamic tracts mediating pain, temp and crude touch
Laminae V and VI
V- neck of dorsal horn, receives descending fibers from corticospinal and rubrospinal tracts and gives rise to axons contributing to spinothalamic tracts
VI- only in cervical and lumbar segments; lateral- gets desc. corticospinal and rubrospinal fibers, medial segments gets afferents from mm. spindles and joint afferents
What laminae is only in cervical and lumbar regions?
VI
Laminae VII (intermediate zone)
has nucleus of Clarke
C8-L2
gets muscle and tendon afferents, is the origin of spinocerebellar tract,
intermediolateral cell column (IML), parasympathetic neurons, and renshaw cells
What level is the IML in?
T1-L2
Where are the parasym neurons of the spinal cord? What is this referred to as?
S2-S4 in the sacral autonomic nucleus; craniosacral outflow
Where are Renshaw cells found?
laminae VII
What is intermediolateral cell column at T1-L2 referred to as?
sympathetic outflow
What is the function of renshaw cells?
inhibitory (glycinergic) synapses (could synapse multiple) alpha motor neurons; REGULATE ALPHA MOTOR NEURONS LEAVING THE VENTRAL HORN
What is recurrent inhibition controlled by?
renshaw cells
Steps of recurrent inhibition.
- alpha motor neuron excited
- activates renshaw cells via excit. cholinergic axon collaterals
- renshaw cell inhibts via glycinergic or GABA synapses
Laminae VIII and IX
get input from descending motor tracts and the neurons somatotopically arranged
laminae X
surrounds central canal and is the site of convergence for somatic and visceral afferents
Somatotopic organization of motor neurons in the ventral horn: Neurons located POSTERIOR innervate…?
flexors
Somatotopic organization of motor neurons in the ventral horn: Neurons located ANTERIOR innervate…?
EXTENSORS
Somatotopic organization of motor neurons in the ventral horn: Neurons located MEDIALLY innervate…?
AXIAL AND LIMB GIRDLE musculature
Somatotopic organization of motor neurons in the ventral horn: Neurons located LATERALLY innervate…?
distal parts of extremities
inhibitor neurochemicals of spinal cord gray matter
glycine, GABA and opioid peptides
excitatory neurochemicals in spinal cord gray matter
acetylcholine and glutamate
What neurochemicals does the dorsal horn contain?
glutamate, neuropeptides or GABA to modulate excitatory input
Example of opiod peptide and what they are co-released with
enkephalin; GABA
intermediate gray neurons may contain what neurochemicals?
glycinergic interneurons, GABA, glutamate
Acetylcholine
preganglionic autonomic neurons in ventral horn
ventral horn has what in their interneurons?
GABA and glutamate
How does the central process enter the spinal cord?
dorsal root
What is exteroceptive sensory information in the representative level of the spinal cord?
fibers that respond to external stimuli like pain, non discrimative and discriminative touch and vibratory sense
What is proprioceptive sensory information in the representative level of the spinal cord?
fibers carrying info from muscle, joint and tendons
What is interoceptive sensory information in the representative level of the spinal cord?
mainly carries nociceptive info from viscera
What neurons are in the dorsal root ganglia?
pseudounipolar (primary sensory neurons)
what is the dominant neurotransmitter of the DRG? but what others are invovled?
glutamate; CGRP (calcitonin gene related peptide) and substance P
What is the entry point into the DRG for small caliber fibers?
lassauers tract (dorsolateral tract)
What is the neurotransmitter for motor components?
acetylcholine
Spinal cord tracts occupy what in spinal white matter?
stable and specific localization
Spinal reflex- discharges ____ motor neuron in response to _____ stimulation?
efferent, afferent
What are the primary receptors involved in initiation of the stretch reflex?
muscle spindles
What do m. spindles sense?
length and velocity of muscle
muscle spindles composition
8-10 fibers surrounded by a intrafusal fiber CT capsule- intrafusal fibers are at center in nuclear bag or single file in chains, embedded in muscle parallel to extrafusal muscle fibers, group 1a sensory fibers are coilded around central part of spindle
what on the m spindles are activated when the mm. stretches?
group 1a sensory fibers
stretch/myotatic/deep tendon reflex
common
monosynaptic (2 neuronal arcs)
- m. stretched by tap
- intrafusal fibers stimulated 1a afferents
- 1a synapses with alpha motor neurons to cause contraction of stretched m.
- 1a fibers also synapse w. inhibitory interneurons which synapses with alpha motor neuron innervating an antagonist mm. (reciprocal inhibition)
inverse myotatic (stretch) reflex
polysynaptic and reduces the period of mm contraction to prevent overstretching; GOLGI TENDON is the sensory receptor in the mm. tendon that senses TENSION when stretched
- golgi tendon activated to send info to 1b sensory afferents in interneurons in spinal cord
- interneuron inhibits alpha motor neuron that innervates same muscle
- muscle stops contracting/stretching
What is the sensory receptor in inverse myotatic (stretch) reflex?
golgi tendons
What is the sensory afferent that info is sent to in inverse myotatic (stretch) reflex?
1b
Flexion (withdrawl) reflex
mediated by nociceptors in free nerve endings (not muscles); polysynaptic reflex
steps of flexion/withdrawl reflex
- pain stimulus
- free nerve endings stimulated to convey info to spinal cord
- synapse with 3-4 excitatory interneurons to stimulate alpha motor neurons
- activates contraction of ipsilateral flexors while relaxes ipsilateral extensors
net effect=withdraw limb in reponse to pain/noxious stimuli and often occurs with crossed extension reflex
cross extension reflex
nociceptors trigger flexion reflex on ipsilateral side and crossed extension on contralateral side
- same afferents that signal spinal cord to trigger F reflex stimulate interneurons to send axon collaterals through ant. commissure
- multisynaptic connections made w/ alpha motor neurons to innervate contralateral flexors and extensors
- alpha motor neurons cause contralateral flexor m. to relax and contralateral extensor muscles to contract
What does the flexion and crossed extension reflexes permit?
extension of limb contralateral to site of noxious stimulation (pain) and withdrawl (flexion) of limb ipsilateral to noxious stimuli