Motor Systems in the Spinal Cord

Question 1

List the different components of the Pyramidal System.

Answer 1

1. Corticospinal Tract
2. Corticobulbar Tract (from cortex to motor nuclei in the brainstem)

Question 2

Describe the Corticospinal Pathway.

Answer 2

Associated with Fine Motor Movement

Primary Motor Cortex –> Cerebral Peduncles –> Pyramids –> Pyramidal Decussation (85%) - LCST (Distal Limb Muscles)
–> Other 15% continue as ACST (Proximal Limb Muscles)

ACST and LCST will synapse with a LOWER MOTOR NEURON!

Question 3

Differentiate between the clinical presentation for the following lesions:

1. Unilateral lesions of the Corticospinal Tract
2. Unilateral lesions of the Lateral Corticospinal Tract

Answer 3

1. Unilateral lesions of the Corticospinal Tract - result in contralateral spastic hemiplegia or spastic hemiparesis

2. Unilateral lesions of the Lateral Corticospinal Tract - result in ipsilateral paralysis or paresis of the distal limb musculature innervated by those spinal segments below the level of the lesion.

Question 4

Where is the corticospinal tract located?

Answer 4

Medial 3/5 of the Cerebral Peduncles

Question 5

What happens to the corticospinal tract at the level of the Foramen Magnum?

Answer 5

~85% of fibers will decussate (in the pyramidal decussation in the MEDULLA) and form the LATERAL CORTICOSPINAL TRACT (Descends to ALL levels of the Spinal Cord)

Question 6

What happens to the neurons in the Corticospinal Tract that DO NOT decussate in the Pyramidal Decussations?

Where do they decussate?

Answer 6

Stay in the Cervical Spinal Levels

Form the Anterior Corticospinal Tract and will innervate motor neurons that stay in the TRUNK

**** Decussate @ the level where they will EXIT the Ventral Root! (Not in the Medulla!)

Question 7

Where does a positive Babinski’s sign indicate that there is a problem?

Answer 7

Upper Motor Neuron Problem

Question 8

Lesions of a Lower Motor Neuron will result in what clinical presentations?

Answer 8

1. Flaccid paralysis. Muscle is completely “limp” and there is no resistance to passive movement.
2. Areflexia. The loss of the efferent component of the reflex arc to a muscle results in the an absence of the associated muscle reflex
3. Atonia. Destruction of gamma motor neurons or their axons results in the absence of muscle tone
4. Atrophy. Denervated muscle atrophies due to the loss of stimulation from the motor neurons
5. Fasciculations or “twitching” of the denervated muscle, probably due to hypersensitivity of the motor end plate

Question 9

Describe the organization of the Ventral Horn.

Answer 9

Lateral: Limb Musculature

Medial: Trunk Musculature

Question 10

Define Lower Motor Neuron.

Answer 10

LAST motor neuron!

(The neuron that directly innervates the muscle)

Question 11

What type of neurons are Alpha and Gamma neurons?

Answer 11

Lower Motor Neurons

Question 12

Describe the composition of the Anterior White Commissure.

What happens when you have a lesion to this structure?

Answer 12

Composed of SECONDARY axons in the Direct Spinothalamic Pathway (pain and temperature)

Lesion: These fibers may be involved in central cord lesions such as vascular occlusion; syringomyelia or intramedullary tumors may compromise this structure and result in bilateral loss of pain and temperature of the corresponding sensory dermatome (Normally in the Shoulders and Upper Arms)

Question 13

Describe the Lateral Reticulospinal Tract.

Answer 13

Origin: Group of Medullary Reticular Nuclei

**** The Lateral Reticulospinal Tract is considered the principal descending pathway for autonomic responses such as bladder and bowel continence and pupillary dilation

*** Lateral Reticulospinal Tract is the probable link between the reticular formation, and the sympathetic and parasympathetic nuclei of the spinal cord.

Question 14

Describe a Bilateral Lesion of the Lateral Reticulospinal Tract.

Answer 14

Loss of Conscious Control of Bladder and Bowel (Has to have the ENTIRE cord cut! Cannot just be a UNILATERAL lesion)

*** HORNER’S SYNDROME!!!

Question 15

Lesions of Anterior horn will result in what?

Answer 15

IPSILATERAL Lower Motor Paralysis at the level of the lesion

Question 16

Where does Fasciculus Cuneatus originate?

Answer 16

Mid-Thoracic Area

*** Remember it supplies the UPPER EXTREMITIES!

Question 17

Differentiate between an Atonic and Reflexive Bladder.

Answer 17

Patients with ANY reflex is NOT going to be in Spinal Shock!

Atonic Bladder: Lesions of the dorsal roots of S2-4 or Dorsal Funiculi; Results in a FLACCID bladder and Increased Bladder Capacity; Voluntary Voiding is possible but often INCOMPLETE

Reflex Bladder: Transection of the spinal cord ABOVE S2 interrupts the Lateral Reticulospinal Tract and the patient is not able to voluntarily void (loss of sacral autonomics). This can occur after SPINAL SHOCK

Question 18

Describe the Rubrospinal Tract.

Answer 18

Starts in the Red Nucleus in the Midbrain

• Immediately decussates and then continues through the Pons and the Medulla

**** Synapses with the LMN at the respected Vertebral Level

Question 19

Describe the tracts involved in the Anteromedial Descending Group.

What is their Function?

Answer 19

1. Anterior corticospinal
2. Lateral and medial reticulospinal
3. Lateral and medial vestibulospinal
4. Tectospinal tracts

Function: bilateral control of axial and proximal limb musculature during postural movements