Spinal Cord Flashcards
Mammal spinal cord
Have Brain and Spinal Cord
Central
Spine and spinal cord are segmented and specialized
Reflex Pathways, Conduit, Central Pattern Generators
Properties of cord segments
Each major region has characteristic cross-sectional anatomy: the anatomy reflects the # of neurons (both cell bodies and axons) found throughout the cord
The efferent regions get smaller going down
Always less white matter in the sacral cord than in the cervical cord.
Thus it makes sense that the cervical cord is the largest; more things going out AND coming in. Very large dorsal horns.
Where the cord ends is called
the conus medullaris
Properties of the cervical cord
oval
gray matter: enlarged ventral horn
white matter: large W:G ratio, post. intermediate sulcus
properties of thoracic cord
round
lateral horn, narrow dorsal and ventral horns
large W:G ratio, post. intermediate sulcus
properties of lumbar cord
round
large dorsal and ventral horns
W:G = 1:1
properties of sacral horn
round
almost continuous dorsal– ventral horns
Small W:G ratio
Major landmarks of the spinal cord, clockwise from noon
Posterior median sulcus Lissauer's tract Central canal Anterior median fissure Anterior white commissure Posterolateral sulcus Posterior intermediate sulcus
Things for pain and temp
Lissauer’s tract
Substantia gelatinosa
Anterior white commissure
vertebral arteries in the cervical region
Each vertebral artery gives rise to an anterior spinal artery which fuses into a single vessel and travels along the anterior median fissure
Each posterior inferior cerebellar artery gives rise to a posterolateral (posterior) spinal artery which travels along each posterolateral sulcus
Vertebral arteries below the cervical region
The spinal cord is largely supplied by radicular arteries
Throughout the cord, venous drainage occurs through a series of veins that feed into radicular veins which drain into the epidural venous plexus. The anterior and posterior spinal veins travel along their respective fissures/sulci.
Neuropathy
dysfunction from a particular nerve or set of nerves (PNS)
Both sensory and motor, localized
Radiculopathy
impingement of a given spinal root
Sensory OR motor, follows dermatome or myotome
Myelopathy
a spinal cord disorder resulting in loss of nerve function
sensory OR motor loss. Lots of different presentations. May involve more than one limb or more than one side.
Afferent Tract Neurons
The major ascending pathways. Both soma (for pain + temp and for proprioception) in the gray matter and myelinated axons (for all somatosensory modalities) in the white matter.
Different diameters of neurons dictate different pathways
Interneurons
Have short processes in the cord, often glycinergic, part of many central pattern generators and reflexes
Motor neurons
The axons of upper motor neurons (UMN) are found in the white matter. The cell bodies of lower motor neurons (LMN) are found in the gray matter, in specialized LMN pools
Propriospinal neurons
Neurons that provide communication between cord segments. All different lengths
act like interneurons
Lissaue fusciulus- what kind of neurons
pain and temp
thin diameter fibers
Renshaw cells
provide negative feedback on LMNs at level of spinal cord
Constant inhibition is needed
Lots of “microcircuits” in the spinal cord, must coordinate flexor/extensor activation and inactivation at each segment
Glycinergic (like GABA in the brain)
– Large amounts in jaw and facial musculature
Blocked by strychnine
– Convulsions
Motorneurons
Neurons are upper or lower motor neurons
LMN = a neuron directly innervating muscle *UMN = a neuron in a series of neurons in the brain that will innervate a LMN
Where we find propriospinal neurons and what they’re like
Ascending Descending Travel in Propriospinal tract (“Fasciculus Proprius”) Bilateral or unilateral Can be short, medium or long axons
Lamina I
Marginal Zone (Pain and Temp Primary Afferent terminals, 2nd order cell bodies)
marginal zone of waldeyer:nociceptive, thermoreceptive, itch
at all levels
Lamina II
Substantia Gelatinosa (Interneurons that receive input from Pain and Temp Fibers)
Lamina II S.G. of Rolando (pain fibers)
at all levels
Lamina III-IV
Nucleus Proprius (Interneurons that receive input from non-nociceptive fibers)
mechanoreceptive (nucleus proprius)
at all levels. Sensory processing
Lamina V
Terminals of GVAs, 2nd order cell bodies
pain (referred pain here)
Lamina VI
Terminals of proprioceptive afferents, 2nd order cell bodies
proprioceptive
Lamina VII
Contains both:
IML/Lateral horn (T1-L2, S2-S4)
Cell bodies of preganglionic autonomic cell bodies
Nucleus Dorsalis of Clarke (C8-L3)
Terminals of proprioceptive afferents, 2nd order cell bodies
from the notes:
proprioception (lateral horn included). Nucleus dorsalis of clarke C8-L3)…also sacral autonomic nucleus
Lamina VIII
Interneurons and propriospinal neurons that receive input from UMN’s
Lamina IX
LMN’s that receive input from UMN’s
Lamina X
Mostly interneurons
The LMN pools in RL IX show anatomic and functional segregation
α-MNs and γ-MNs are scattered in different LMN pools
Flexors and extensors are segregated (relatively) dorsal to ventral
Humuncular organization from axial muscles to extremeties, medial to lateral
crossed extension reflex
A flexor reflex involves several segments of the spinal cord, activating multiple LMNs. Interneurons and propriospinal neurons modulate these effects.
In a crossed-extension reflex, the flexor reflex is activated, and contralaterally, the antagonist muscles are activated
Complex, coordinated movements can be completely controlled by the spinal cord
myotactic reflex
reflex works within spinal circuits: Clinical Clues
In the patellar tendon reflex, stretching the muscle spindle leads to a direct activation of LMN through the stretching of the quadriceps
Central Pattern Generators in the Spinal Cord of Humans?
Lobectomized kids are not paraplegic
Paraplegic humans cannot regain function as cats
Central Pattern Generator without sensory input hasn’t yet been established
