Functional Hierarchy of the Motor System Flashcards
How are muscles directly controlled in the spinal cord?
Alpha motorneurons
What do brainstem nuclei control?
Posture and balance
What are the higher brain centres that control brainstem nuclei?
Cerebral cortex
Basal ganglia
Cerebellum
What is the result of lesions involving the lower motor neurons?
Flaccid paralysis
Muscle atrophy
What is the result of lesions involving the upper motor neurons?
Spasticity
Some paralysis, may be transient
What is the result of a corticospinal lesion?
Weakness (paresis)
What is the basis of the spatial map of body musculature in the spinal cord?
Proximal areas mapped by medial motorneurones
Distal areas mapped by lateral motorneurones
From where does the spinal cord receive descending input?
Brainstem
From where does the spinal cord receive direct cortical input?
Corticospinal (Pyramidal) tract
Where does sensory input enter the system?
Enters at all levels
In what form does sensory input enter the spinal cord?
Proprioceptors
Touch
Pain
In what form does sensory input enter the brainstem?
Vestibular system informs about balance
In what form does sensory input enter at the level of the cortex?
Visual Olfactory Auditory Emotional Intellectual cues
What is the result of damage to sensory inputs?
Paralysis (at spinal cord)
Where is the stretch reflex found?
Every muscle
What is an example of a common stretch reflex?
Patellar tendon (knee jerk reflex)
What is the basis of the stretch reflex?
Muscle spindle fibres send impulses to the spinal cord
Synapse in spinal cord
Efferent impulses to alpha motor neurones cause contraction of stretched muscle
Efferent impulses to antagonist muscles are damped
What is the significance of the stretch reflex?
Detects level of spinal cord damage
Impaired reflexes indicate areas of nerve damage
What type of information does the flexor reflex process?
Information from pain (nociceptors) in skin, muscles and joints
How many synapses are involved in the flexor reflex?
Polysynaptic
What does the flexor reflex do?
Withdraws body part away from painful stimulus and in towards the body
How does the flexor reflex work?
Increased sensory action potentials cause increased activity in flexor muscles via excitatory interneurones
At the same time the antagonistic extensors are inhibited
Where are interneurones activated in the flexor reflex?
Several spinal segments
How is the body prevented from falling over during the flexor reflex?
Contralateral limb extends:
Excitatory interneurones crossing the spinal cord excite the contralateral extensors
Inhibition of contralateral flexors
Sensory info enters the brain in the contralateral spinothalamic tract
Why is the flexor reflex slower than the stretch reflex?
Several interneurones so small synaptic delay
Nociceptive fibres have smaller diameter so conduct more slowly
What is the function of the golgi tendon organ at spinal level?
Protective e.g prevents muscle tear due to excess load (can be overridden)
How can you continue to hold something that is important, yet heavy, without dropping it?
Descending voluntary excitation of alpha motor neurones can override the inhibition from the golgi tendon organs and maintain contraction
How ca the stretch reflex be overridden?
Descending inhibition hyperpolarizes the alpha motor neurones and stretch reflex can not be evoked
What is the result of high gamma motor neurones?
Muscles become extremely resistant to stretch (spastic)
What area of the spinal cord will stretch reflex affect?
One or two spinal segments (highly localised)
What area of the spinal cord will flexor reflex affect?
Spreads through several spinal segments
What is the effect of a more powerful pain stimulus?
Greater spinal spread, larger response
What is the function of facilitation?
Increases the effect of sensory input
What is the Babinski sign?
Extension but not flexion of foot, toes fan yp and out (indicates damage/disruption to corticospinal tract)
What are the consequences of spinal shock?
Loss os sensation
Loss of bowel, bladder, sexual regulation
What causes spinal shock?
Loss of supraspinal excitation, reflexes not evoked for 2-6 weeks
What is clonus?
Oscillatory muscle contraction/relaxation caused by stretch
