Neurological Basis of Movement Flashcards
Do efferent (motor neurones) leave the spinal cord dorsally or ventrally?
Ventrally
Do afferent (sensory) neurones enter the spinal cord doorsally or ventrally?
Dorsally
What aspect of a muscle detects stretch at the beginning of a reflex arc?
Muscle spindle
What does stretch of the muscle spindle produce?
An action potential
What are the steps that follow stretch detection after a tendon is struck with a hammer?
1) stretch of spindle
2) 1a afferent neurone activated
3) enters the spinal cord
4) excitatory synapse with alpha motor neurone occurs in cord (homonymous muscle contracts)
= 4) simultaneously, excitatory synapse with inhibitory interneurone - inhibits alpha motor neurone that projects to heteronymous muscle (antagonist relaxes)
What is the role of the Golgi tendon organ in reflexes?
It produces an inverse myotatic reflex. Unlike the muscle spindle it is activated by prolonged muscle contraction and via a 1b afferent pathway inhibits contraction as a protective measure (e.g. Makes you drop heavy things)
Activation of alpha motor neurones causes what?
Muscle contraction
What is the role of the gamma motor fibre (neurone)?
It keeps the muscle spindle under tension (taut) so that it can always detect stretch even when muscle contracted (allowing alpha motor neurones to continue firing and continue contraction)
Without gamma motor neurones what would happen to the muscle spindle during muscle contraction?
It would become flaccid and unable to mediate movement / detect stretch
Where are the cell bodies of both alpha and gamma motor neurones located?
The anterior horn if the spinal cord
What do alpha motor neurones do that gamma motor neurones do not?
Directly adjust the length of the muscle
When does the brain become involved in movement?
During voluntary movement
In which lobe of the brain is the motor cortex located?
The posterior part of the Frontal Lobe
What is the corticospinal tract?
The tract which conveys axial and limb MOTOR CONTROL
It is a DESCENDING tract
Where does the corticospinal tract begin?
In the (pre-central gyrus) primary motor CORTEX of the brain
Where do the fibres that will ultimately innervated the limbs decks sate in the corticospinal tract?
In the medulla (these fibres comprise 75-90% of all fibres in this tract)
What does the terms ‘Pyramids’ refer to the corticospinal tract?
The pyramids are the corticospinal tracts as they go through the medulla
What lobe of the brain is the somatosensory cortex located in?
The parietal
Briefly, what does the somatosensory cortex do?
Receives sensory info via ascending pathways and filters irrelevant sensory signal via descending fibres
(Damage can result in many symptoms including Agraphesthesia - problems processing complex sensory info)
What does the premotor area of the brain do?
Plans intended movements requiring visual guidance
What does the supplementary motor area do?
Co-ordinates voluntary movements
What does the posterior parietal cortex do?
Integrates other sensory info - damage may result in agnosia (failure to know)
What is Apraxia?
An inability to perform certain motor movements despite sensory and motor pathways remaining intact
What is the most important ascending (sensory) tract feeding back to the CNS?
The Spinothalamic
What sensations does the Spinothalamic tract send up to the CNS?
Pain
Temperature
Touch
Pressure
Through what does the Spinothalamic tract project to the cortex?
The thalamus
What is the role of the thalamus in the Spinothalamic tract and dorsal columns?
It processes sensory information before it sends it on to the cortex
What sensory information does the Spinocerebellar tract relay and to where?
It relays proprioceptive information to the cerebellum
What do the dorsal ascending tracts deal with?
Joint position and fine discriminatory touch
What effect does tetanus toxin have and how?
Tetanus toxin inhibits both inhibitory neurotransmitters Glycine and GABA resulting in dangerous over-activity of muscle “tetanic spasm” which can even result in long bone fractures
What does a lower motor neurone innervate?
Skeletal muscle
What neurotransmitter do LMNs release at the neuromuscular junction?
Acetylcholine
What two types of nerve fibre are found in LMNs?
Alpha and gamma
Where do LMNs arise?
Brainstem (muscles of head and neck) Spinal cord (muscles of rest of body)
What do upper motor neurones innervate?
Lower Motor Neurones
Where do UMNs arise?
In the brain
What neurotransmitter do UMNs release?
Glutamate (excitatory)
What principle explains how the left side of the brain controls the motor function of the right and vice versa?
Decussation of the pyramids
Where does decks satin occur in the Spinothalamic tract?
As it ascends, crosses over in the white ventral commissure in the spinal cord
Axial motor control is associated with which division of the corticospinal tract?
The VENTRAL corticospinal tract
Limb motor control is associated with which division of the corticospinal tract?
The LATERAL corticospinal tract
