Spinal Cord, Reflexes and Muscle Tone Flashcards
What is at the apex of the motor system control hierarchy?
The cerebral cortex
What are the 4 types of motor movements?
- Reflexive
- Postural
- Voluntary
- Rhythmic
Describe voluntary movement
- Most complex and least autonomic
- Originate from frontal lobe
- Eg. speaking
- Contributed by Primary motor, premotor and prefrontal regions
- Also involves basal ganglia, cerebellum, brain stem + spinal cord
Describe rhythmic movement
- Eg. basic motor patterns for walking and breathing
- Initiated/maintained by subcortical structures - brainstem + cord
- Little contribution from cortex
- Coordinated by CPGs
Describe reflexive movement
- Simplest types of motor response in reflex arc
- 2 nerve cells (motor, sensory) + synapse
- Eg. stretch reflex
- Rapid and automatic responses
- Sometimes involve both sides of body
Describe postural movement
- In response to changes in position
- Involves vestibular apparatus and proprioceptors
- Mediated by descending reticulospinal projections from brain stem to cord
- Automatic stereotyped responses
- Keep centre of gravity in optimum position
Where are central pattern generators located within the central nervous system?
Networks of neurons within spinal grey matter or brain stem
What actions do CPGs control?
Eg. walking, chewing, breathing
The cerebral cortex is able to generate movements directly (eg. via corticospinal tract) but how many it influence movements indirectly?
Via projections to basal ganglia, brain stem, cerebellum and spinal cord.
There are cortical projections to the reticular formation of the brain stem which influence descending pathways to the spinal cord (i.e. the reticulospinal pathways). What do they contribute to the regulation of?
Normal muscle tone
What role does the cerebellum play in motor control?
Does not generate movements itself but ‘advises’ motor areas of frontal lobe, helping to ensure that actions are performed in a smooth, precise and coordinated manner.
It’s like the manager making sure everything is running well.
What are the results of cerebellar damage, and hence what is cerebellar ataxia?
Clumsiness and poor coordination
What is meant by the ‘error signal’ sent by the cerebellum to the frontal lobe?
When intended movements are compared with actual movements to detect any discrepencies. Info is fed back to frontal lobe via efferent projections from cerebellum representing ‘error signal’ used to correct on-going movements and make them more accurate.
Which type of movement is corrected by the cerebellum: ballistic or non-ballistic?
Non-ballistic. Ballistic movements are very rapid so there is no time for the cerebellum to make “on-line” corrections once the movement has started.
What neurotransmitter controls basal ganglia loops?
Dopamine
What are the 3 roles of basal ganglia (loops) in motor control?
- Initiation of voluntary actions
- Selection of a particular action among range of possible actions
- Learning and performance of various repetetive, semi-automatic behaviours
What do the brain and spinal cord derive from in embryologic development?
Neural tube
Of the developing spinal cord, name the following:
- Two divisions
- What divides them
- The plates and what they contain
- Anterior (ventral) region and posterior (dorsal) region
- Divided by a groove called sulcus limitans
- Ventral part -> basal plate (motor)
- Dorsal part -> alar plate (sensory)
Where are the cell bodies of the sensory neurons contained?
In the dorsal root ganglia
What is the shape and structure of the spinal cord grey matter?
‘H’ shape - surrounded by white matter, divided into dorsal horns and ventral horns.
Describe the divisons of the spinal cord white matter (funiculi)
Three longitudinal columns (funiculi): posterior, lateral and anterior
Contain descending pathways from the brain and numerous ascending pathways (eg. spinothalamic tract)
Which level of the spinal cord has the most white matter?
Cervical - all descending and ascending pathways present here.
Which level(s) of the spinal cord has the most grey matter?
Cervical and lumbosacral - due to proportion to the amount of muscle tissue at each level.
Thoracic has least
Which of the laminae of Rexed make up the dorsal horn?
Laminae I - VI
Where are laminae VII, VIII, IX and X located?
- VII and X are in the mid-region of the cord
- VIII and IX correspond to anterior horn
There’s more than one column for IX
What are cells of the anterior horn cell also referred as?
Lower motor neurones
Describe the medial-lateral gradient of the lower motor neurones?
The most medial columns of the grey matter supply proximal muscles, whilst the motor neurones supplying the distal limb muscles are placed laterally.
Describe the dorsal-ventral gradient of the lower motor neurones?
Neurones supplying flexor groups are closer to the back of the spinal cord, extensors towards the front.
Anterior = extensor Posterior = flexor
What does the spinal accessory nucleus (C5,6) supply?
Trapezius and SCM
What does Onuf’s nucleus (S2,3,4) supply?
External urethral and anal sphincters - important for continence.
What mechanism underlies the deep tendon reflex?
The muscle spindle mechanism
What happens to the stretch reflex in a patients with upper motor neuron lesion such as stroke?
Stretch reflex is normally ‘damped down’ by descending influences from brainstem - this is lost in stroke/UMNL. The stretch reflex becomes abnormally strong -> hyperreflexia and hypertonia.
Increased tone is velocity dependent, meaning more resistance is felt when joints and flexed and extended rapidly.
What happens in a lower motor neurone lesion to the muscle?
Loss of motor nerve supply to muscle -> flaccid paralysis, atonia, areflexia, disue atrophy, fasiculations
What are features of UMN lesions?
- Hyperreflexia
- Hypertonia
- Clonus
- Spasticity
- Pyramidal weakness
What are the two spinal reflexes that coordinate automatic limb withdrawal from a noxious stimulus?
The flexor reflex + crossed extensor reflex
Flexor reflex = polysnaptic, extends over several spinal cord segments, cutaneous reflex
May form basic template for CPG for walking
