Flashcards in Functional Hierarchy of the Motor System Deck (37)
How are muscles directly controlled in the spinal cord?
What do brainstem nuclei control?
Posture and balance
What are the higher brain centres that control brainstem nuclei?
What is the result of lesions involving the lower motor neurons?
What is the result of lesions involving the upper motor neurons?
Some paralysis, may be transient
What is the result of a corticospinal lesion?
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?
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?
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?
What is the result of damage to sensory inputs?
Paralysis (at spinal cord)
Where is the stretch reflex found?
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?
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)