Neurology S4 Flashcards
Motor system pathway
Originate in cerebral cortex
- 30% motor cortex, 30% premotor cortex (associated), 40% somatosensory cortex
- Descend through internal capsule to brainstem; form medullary pyramids
- Lower medulla – 85% decussate - descend as lateral corticospinal (LCS) tract. 15% descend as anterior corticospinal (ACS) tract
- LCS tract terminates in ventral horn – especially motor pools of distal limb muscles – control of skilled movements
- ~15% synapse directly with lower motor neurons; remainder with interneurons
- ACS tract – some fibers decussate in spinal cord – especially motor pools of axial muscles
Corticobulbar tract
Originate in cerebral cortex
- 30% motor cortex, 30% premotor cortex (secondary), 40% somatosensory cortex
- Descends through internal capsule to brainstem
- Terminate on cranial nerve motor nuclei in midbrain, pons & medulla
- Mainly bilateral innervation of motor nuclei
- Controls voluntary muscles of the head and neck, e.g.
muscles of facial expression, extraocular, etc.
Vestibulospinal Tract
Originates from nuclei in pons remain ipsilateral.
vestibular and M.O.,
- Innervate anti-gravity muscles - balance reflexes.
- Involved in movements of the body required for maintaining equilibrium, aiding in maintaining body posture.
Tectospinal Tract
Main inputs from superior and inferior colliculi; decussate (contralateral).
• Innervate Muscles of neck coordinate eyehead movements, responses to visual & auditory stimuli
Reticulospinal Tract
Widespread inputs, including from motor cortex; remain ipsilateral.
• Medullary (lateral tract)
- Flexor reflex facilitation
- Extensor reflex inhibition
- Pontine (medial tract) - Extensor reflex facilitation
- Role in regulation of posture and rhythmic movements
Rubrospinal
Rubrobulbar Tract
Originate from red nucleus, inputs include motor cortex; decussates.
• Control flexor tone of distal limb muscles, and also tone of facial muscles.
Tabes Dorsalis
Tabes Dorsalis is a late complication of a syphilis infection (part of tertiary syphilis) where the central processes of the dorsal root ganglion degenerate, thus affects the dorsal columns (fasciculus gracilis and cuneatus) specifically. As a result, patients develop a loss to fine touch and conscious proprioception (resulting in loss to two-point discrimination and ataxia).
What is clonus
muscular spasm involving repeated, often rhythmic, contractions) as signals are no longer inhibited and pass round and round the other interneurones.
What is reflex
A spinal reflex is an involuntary, unlearned, automatic reaction to a specific stimulus that does not require the brain, with the pathway described as a “reflex arc”
There are 5 components to the reflex arc:
receptor (e.g. muscle spindle)
- An afferent fibre (e.g. muscle spindle
An integration centre (e.g. lamina IX of spinal cord)
- An integration centre (e.g. lamina IX of spinal cord)
- An efferent fibre (e.g. α-motoneurone)
- An effector (e.g. muscle)
LMN Their cell body are located in 2 sites:
in the gray matter of the spinal cord lamina IX (spinal motor nucleus)
• in motor nuclei of the brain stem
What is co-activation ?
Activation of both alpha & gamma motor neurons which required for normal M contraction if only alpha MN activated abnormal contractions occurs & eventualy will be inhibited
muscle tone
The firing pattern of the motor unit is called:
Spontaneous firing of neurons at rest
At any time, a fraction of muscle are always contracted
spontaneous activity (at rest) interference pattern (at voluntary activity)
Key spinal neural levels
Diaphram
Biceps
Nipple
Umbilicus
Hip flexion
Quadriceps
Diaphram C3-5
- Biceps C5-6
- Nipple T4
- Umbilicus T10
- Hip flexion L1-2
Quadriceps L3-4
Key spinal neural levels
Knee flexion
Great toe
Foot plantar flexion
Bladder
Anal sphincter
Knee flexion S1
- Great toe L5
- Foot planter flexion S1-2
- Bladder S2-4
- Anal sphincter S2-4
