13 - Spinal Cord: Motor Systems Flashcards
Describe how skeletal muscle contraction is controlled
motor neurons originating in the primary motor cortex synapse with another motor neuron in the brainstem or the spinal cord
what is the corticospinal tract
connects primary motor cortex to the spine
- controls upper limb, trunk, lower limb via spinal nerves
cortex –> spine –> spinal nerve –> control structures in the body (upper limb, trunk and lower limb)
Motor neuron crosses over in the medulla (decussate) to corticospinal tract
Hand: would go to cervical ventral root
Foot: would go to lumbar ventral root
all axons are bundled together
What is the corticobulbar tract
connects primary motor cortex to the brainstem
- controls head and neck via cranial nerves
primary motor cortex –> brainstem –> out through cranial nerve –> controls muscles of the head and neck (face)
What would happen if there were a lesion in the cortex above the brainstem crossing (ex. stroke)
contralateral sign (signs on the opposite side to the side of the brain that is affected) - from underneath the brainstem crossing
- touch and pressure
- proprioception
- pain and temperature
- motor
What would happen if there were a lesion in the spinal cord
ipsilateral signs (deficits in the same side as lesion) - b/c sensory information can’t get past the break and motor information can’t come go down and past it
- touch and pressure
- proprioception
- motor
All information already crossed over = ipsilateral signs
contralateral signs - b/c information immediately crosses over at the top of the spinal cord
- pain and temperature
What is the direct motor pathway
primary motor cortex –> internal capsule (deep cortex) –> pyramidal tracts (brainstem) –> corticospinal tracts (spinal cord)
What is the lateral corticospinal tract
contains axons of upper motor neurons that control skeletal muscle in the distal part of limbs (upper and lower)
90% of axons already crossed
Anterior corticospinal tract
contains axons of upper motor neurons that control skeletal muscle in the proximal limb and trunk (midline, proximal to limb – hip, shoulders)
10% of axons uncrossed
only cross over at level they need to leave at
How are lower motor neurons of the ventral grey horn organized
kinda homonculus
lateral in grey matter –> more distal part of appendages
medial parts of body = more medial in grey matter
Describe white matter tracts
larger at the top of the spinal cord and become smaller as they descend
really big in cervical –> very small in sacral
(because they spread out as you go down)
Describe grey matter tracts
larger in the areas innervating the limbs (lumbar and sacral and cervical)
contains:
dorsal horn (sensory)
lateral horn (neuronal cell bodies of the sympathetic nervous system)
ventral horn (motor)
What does the thoracic segment include
includes a lateral grey horn (preganglionic sympathetic neuron)
What is the facial nerve
right facial nerve innervates muscles on the right side of your face
facial expression, blinking eye
Contains sensory and motor
Somatic: close mouth, occulair, obicullus
Sensory: taste sensations,
Parasympathetic: make tears to wash cornea (lacramal)
Upper motor neuron lesions
damage to soma in cortex or axon in coricospical tract
lower limb injury
results in spastic paralysis (muscle that you lost control over has muscle tone = very stiff)
- hypertonia = increase muscle tone
- hyperreflexia = better reflexes
- positive babinski = abnormal response to touch sensations (flexing foot when you should curl towards stimulus)
- clonus = repetetive muscle reflex (keeps repeating)
Lower motor neuron lesions
damage to spinal cord grey matter or peripheral nervous system (cranial or spinal nerve)
upper limb injury
results in flaccid paralysis: can’t control muscle, no muscle tone (need brace)
- hypotonia = reduction muscle tone
- hyporeflexia = muscle not activated, lower reflex
- fasciculations = bundle of muscle fibres contract on their own
- atrophy = wasting away (b/c can’t use the muscle)
