3- Spinal Cord

what does the spinal cord do?

receives sensory information

integrates motor commands from higher centers with sensory input

output to skeletal muscles

output to visceral organs

communicates between motor and sensory neurons

projection to higher centers

reception from higher centers

where does the spinal cord terminate?

L2, conus medullaris

what spinal nerves form the brachial plexus and lumbosacral plexus?

brachial plexus: C5-T1

lumbosacral plexus: L1-S4

what lies in the ventral median fissure?

sulcal branch of the anterior spinal artery

ventral lateral sulci

exit of motor neurons

dorsal lateral sulci

entrance of sensory axons

where is the dorsal intermediate sulci located? what does it do?

above T6

separates the fasciculus gracilis and fasciculus cuneatus

what nerves are the dorsal root?

sensory nerves - GSA and GVA

what is in the lateral division of the dorsal root? what is in the medial division?

lateral: nociceptive and thermal receptors (GSA) and GVA receptors. They are smaller and not myelinated

medial: mechanical (discriminative) touch, vibration, and proprioceptive receptors (GSA). They are large and heavily myelinated

what are the NT and neuromodulators in the dorsal root?

glutamate, substance P, calcitonin gene related protein (CGRP)

what nerves are in the ventral root? what is the primary NT for these neurons?

motoneurons (GSE), axons from autonomic preganglionic autonomic neurons (GVE)

acetylcholine

what are spinal nerves?

mixed nerves, contain both motor and sensory

where do spinal nerves exit the vertebrae?

C1-C7 - above named vertebra

C8: below C7 vertebra

T1 below - below named vertebra

what is gray matter?

neuronal cell bodies, dendrites, and initial parts of axons

what is white matter?

myelinated and unmyelinated axons

what is Rexed lamina?

arrangement in cell columns or layers in gray matter by similar function. Goes from I-X

what are interneurons?

have sensory functions and receive input from GSA and GVA

Receive input from higher centers to process sensory input

can transmit sensory info via ascending tracts

also part of reflex arcs

what is the significance of Lissauer’s tract (posterolateral tract)?

gives redundancy in sensory system

branches ascend or descend a little in this tract prior to terminating in posterior horn

what lamina compose the dorsal horn of gray matter? what are in these lamina?

LI-VI

LI: posteromarginal nucleus

LII: substantia gelatinosa

LIII, IV: nucleus proprius

what info do small DRG fibers carry? where do they terminate? where do they synapse?

predominantly thermal and noxious

terminate largely in LI, II, V

synapse at the spinal cord

what info do large diameter DRG fibers carry? where are they located? where do they synapse?

mechanical info (touch, vibration, some proprioception)

collateral/parallel to posterior horn

synapse at medulla

main function of dorsal horn?

receive and process sensory input

site of origin for some ascending tracts like the anterolateral system (pain and temperature)

also contain some descending tracts

contain circuits - processing and modulation of sensory info like pain modulation

main function of ventral horn?

primarily motor related functions

contain motoneurons (lamina IX) and interneurons (lamina VIII and IX)

these interneurons integrate descending info and sensory info prior to activation of MN’s and are part of reflex arcs

what is the somatotropic arrangement of motor cell columns in the ventral horn lamina IX?

medial - proximal

lateral - distal

anterior - extensors

posterior - flexors

what is lamina VIII primarily involved in?

intersegmental processing

has some projections to reticular formation of the brainstem

what is in the intermediate zone lamina VII?

mostly proprioception (GSA) pathways

Posterior Thoracic Nucleus (Clarke’s Column) - origin of posterior spinocerebellar tract

Central Cervical Nucleus - origin for anterior spinocerebellar tract

Intermediolateral Nucleus - contains preganglionic autonomic neurons from T1-L2/3 level responsible for preganglionic sympathetic

Sacral Visceromotor nucleus - in S2-4 level that is responsible for preganglionic parasympathetic system

what info does posterolateral tract of Lissauer carry? where does it lie?

primarily sensory fibers, pain temp, some touch

tract branches as axons enter the spinal cord

branches ascend/descend in the posterolateral tract before terminating in posterior horn

what is the anterior white commissure? what axons pass through it?

it is the region of axons crossing midline

it is mostly axons of posterior horn cells - pain, thermal, non-discriminative touch

what tracts are in the Anterolateral System? where is it located?

Spinothalamic, Spinoreticular, Spinomesencephalic, Spinohypothalamic

anterior and lateral funiculi

what is the spinothalamic tract? what info does it carry? what is its origin and termination? where does it decussate?

part of the Anterolateral System

info: pain, temp, light touch (non-discriminative)

origin: contralateral in the posterior horn esp from lamina I and V

terminate: thalamus

decussate: AWC near level of origin

what info does the Posterior Column carry? what are its 2 parts? what is its origin and termination? where does it decussate?

info: touch - pressure, highly discriminative, vibration, some proprioception

Fasciculus Cuneatus contains UE info from T6 and above. lateral to FG

Fasciculus Gracilis contains LE info throughout the spinal cord. medial to FC

origin: mostly DRG and some posterior horn

terminate: medulla in Nucleus Cuneatus and Gracilis

decussate: medulla

what info does the spinocerebellar tract carry? what are its parts?

info: unconscious proprioception

posterior and anterior spinocerebellar tracts

posterior spinocerebellar tract info, origin and termination, decussation

info: unconscious proprioception info from ipsilateral LE

origin: posterior thoracic nucleus (Clarke’s) in C8-L2

termination: ipsilateral cerebellum

decussate: does not decussate

anterior spinocerebellar tract info, origin, termination, decussation

info: unconscious proprioception info from contralateral LE

origin: lamina V-VII of lumbar regions

termination: ipsilateral cerebellum

decussate: AWC then again in the cerebellum before terminating in the cerebellum

function of the Lateral Corticospinal Tract? where is it located? origin, termination, decussation?

voluntary motor pathway and modulation of sensory info

posterior medial portion of the lateral funiculus

origin: contralateral cerebral cortex

termination: motor - primarily in anterior horn, sensory - primarily in posterior horn

decussate: caudal medulla (pyramidal decussation)

function of the Anterior Corticospinal Tract? location? origin, termination, decussation?

primarily control trunk muscles

located in the anterior funiculus

origin: same as corticospinal tract (contralateral cerebral cortex)

termination: anterior horn then out to muscle

decussate: AWC near level of termination

what tracts do you usually observe in SC injury?

Lateral Corticospinal Tract, Spinothalamic tract, Posterior columns/Medial Lemniscus pathways

what is the pathway of reflex?

afferent fiber —> interneuron/motor nueron —> target tissue

what is a monosynaptic vs polysynaptic reflex? examples?

monosynaptic: have 1 synapse - 1 sensory and 1 motor neuron, patellar stretch reflex, quick muscle stretch

polysynaptic: have multiple synapse, sensory, motor and interneurons involved, can be slower but more complex

what is a segmental vs intersegmental reflex?

segmental: occurs only in 1 level of spinal cord

intersegmental: occurs in multiple levels of spinal cord

can reflexes be modulated?

yes