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Puder; Intro to Spinal Cord Pathways
Terms in this set (27)
What is a pathway?
A chain of neurons
A tract is 1 group of neurons/axons in a pathway
Upper motor neurons v Lower motor neurons re: synapse location
Lower motor neurons always synapse on muscle
What makes up a sensory pathway?
It brings sensory information to conscious levels (cortex)
in the pathway
1) Receptor (pseudounipolar)
2) Relay from lower center to thalamus
3) Relay from thalamus to cortex
(axons of the 3 neurons in the pathway)
1) Axons in the cord form
2) Relay axons to thalamus form
3) Relay axons from thalamus to cortex form
What makes up a motor pathway?
Relays motor info from cortex to muscle
2 neurons in pathway
1) 1 in cortex sending info to spinal cord (upper motor neuron)
2) 1 in spinal cord sending info to muscle (lower motor neuron)
2 tracts in pathway
1) Axons from cortical neurons (cortical spinal neurons)
2) Axons from spinal cord to muscle (peripheral nerve)
Pathway of a spinal reflex
Stimulus --> receptor to receive and send stimulus --> afferent pathway --> integration center --> efferent pathway --> effector organ
A reflex doesn't involve the brain
Function of the spinal cord reflex
Compensate for unexpected perturbations
Coordinate patterns of muscle activation
Protection from painful or damaging stimuli
What does the anterolateral system deal with?
somatic pain (sharp, well organized, easy to describe precisely) and temperature
How is the anterolateral system valuable therapeutically?
It is used to test the integrity of the nervous system and the location of the lesions
Pathway of anterolateral system
First order neurons
(pseudounipolar) have cell bodies located in posterior root ganglion. The neuron projects into the spinal cord through the
(the first order axons are called posterolateral fasciculus). It synapses in the
[red dot] (which contain cell bodies of the second order neuron). Substantia gelatinosa is found in the posterior horn of the gray matter.
2. Second order neuronal axon decussates (crosses midline) through the anterior white commisure and becomes the anterolateral system <-- this group of axons is called the
3. The anterolateral system/spinothalamic tracts project up through brainstem [red oval], synapse in thalamus with the third-order neuron, and then synapse in the cortex
In sensory pathways, when does the neuron "cross"?
At sensory neuron #2
What occurs if there is a lesion in the peripheral nerve of the anterolateral system? (i.e., the 1st order neuron of the anterolateral system)
Loss of pain and temperature at that dermatome level
What occurs if there is a lesion in the spinothalamic tract (the part of the anterolateral system after cross-over) or in the thalamocortical fibers?
Loss of pain and temperature sensation on the contralateral side of the body below the level of the lesion
What does the Posterior Columns/Medial Lemniscus pathway deal with?
Fine or discriminatory touch
Position and vibratory sense
Pathway of Posterior Column/Medial Lemniscus
1. First order neurons (pseudounipolar neurons) have cell bodies located in the posterior root ganglion. It projects into the spinal cord through the posterolateral sulcus. If entering spinal cord sections
T6 or below
, the axons go into the posterior columns of the spinal cord and are called
. If entering spinal cord sections
, the axons go into the posterior columns and are called
. It then ascends in either the fasciculus gracilus or cuneatus until it reaches the medulla.
2. In the medulla you find the cell body of the second order neuron,
. Second order neuronal axons then crosses over. The crossing over tract is called the medial lemniscus
3. Medial lemniscus projects up through brainstem, synapses in the thalamus with the third-order neuron. It then goes up to synapse in the cortex.
What occurs if there is a lesion to the Posterior Column/Medial Lemniscus Pathway?
Key point: The PC/ML pathway does NOT cross in the spinal cord. Therefore any lesion to this pathway in the spinal cord will produce
losses of fine touch, vibratory, position sense, etc...
Difference in the pathway of Anterolateral System and the Posterior Column/Medial Lemniscus
Not much! The only difference is the type of peripheral receptors
; free nerve endings (pain and temperature)
Posterior column/medial lemniscus
; peripheral receptors [Merkels disks, Pacinian, Ruffini, Meisner's corpuscles] (fine touch, 2 pt discrimination, vibratory sense)
ALSO; ALS system decussates immediately in the spinal cord, while the PC/ML system decussates in the medulla
What is Syringomyelia? What are symptoms?
Cavitation of the central canal of the spinal cord
Destroys the anterior white commissural fibers of the spinothalamic tracts (ALS)
Pain sensation lost bilaterally but tactile sensation is intact as there is no damage to posterior columns
***Brown-Sequard Syndrome definition and symptoms
Spinal hemisection (damage to half the spinal cord)
Pressure and temperature are lost contralateral to the lesion, and paralysis and posterior column information are lost ipsilaterally
Here you have lost all three of your major body pathways; good way to determine which is ipsilateral and which is contralateral
SHOWS UP ON BOARDS
Pathway for Reflex Proprioception
This pathway does not go to consciousness - only to cerebellum for feedback from muscles for influencing muscle coordination & muscle tone.
What does Voluntary motor pathway deal with?
Initiates skilled movements carried out by somatic skeletal muscle especially hand and finger movements.
Voluntary Motor Pathway course
1. Cell bodies (upper motor neurons) originate from the
cerebral motor cortex
in the precentral gyrus or paracentral lobule.
2) The axons in the corticospinal tract decussate in the caudal medulla and descend further in the lateral funiculus as the lateral corticospinal tract (this is still neuron #1 = UMN)
3) When at the right spinal cord level, the lateral corticospinal tracts synapse on cell bodies (lower motor neurons) of lower motor neurons in the
4) It then projects out to the periphery to innervate skeletal muscle
: There exists a somatotopic localization pattern in the LCST whereas the LE is represented laterally and the UE is represented medially throughout the brainstem and spinal cord.
What makes up the Voluntary Motor Pathway?
2 neuron pathway
upper motor neuron
lower motor neuron
(cell bodies in anterior horn of spinal cord and axons are peripheral nerves)
Spastic paresis, hyperreflexia, babinski sign
; Upper motor neuron lesion symptoms or Lower motor neuron symptoms?
Upper motor neuron lesion
Flaccid paralysis, hyporeflexia, muscle atrophy/fasciculations
; Upper motor neuron lesion symptoms or Lower motor neuron symptoms?
Lower motor neuron lesion
Recall that lower motor neuronal lesions are ipsilateral
UMN lesion or LMN lesion; ipsilateral
lower motor neuron lesion
What is the significance of the names Corticospinal Tract and Lateral Corticospinal Tract re: Voluntary Motor Pathway
is pre-decussation (above the crossing)
Lateral Corticospinal Tract
is post-decussation (below the crossing)
both deal with the upper motor neuron axon
Cheat for Ipsilateral/Contralateral
If the lesion is underneath the crossing for that pathway, you're ipsilateral
If the lesion is above the crossing for that pathway, you're contralateral
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