Posture and movement Flashcards
What has gone wrong in neurological disorders?
Control of movement
How many combinations of muscles are required for co-ordinated action?
more than 750 muscles
Define posture
posture is stable position on which movement is superimposed
what occurred to a patient due to cerebral damage?
Could not maintain posture on one side of their body
What does the physiology of posture involved?
Postural control via static and phasic reflexes
- static reflexes involve sustained contraction of muscles
- dynamic reflexes are short term phasic reflexes
What is postural sway?
type of stretch reflexes involved?
Is the horizontal movement of the centre of gravity even when a person is standing still
Feedback mechanism that enables one to control their posture
moving stretches some muscles which sends an important reflex back to contract
myotatic stretch reflexes constantly adjust
- Stretched reflex in constant use- constant feedback from muscle spindles
- Is a posture dynamic like pendulum oscillations
- Centre of mass circular movements
- A-P 7mms
- Postural sway is a reflex at the level of the spinal cord
Along what tracts is primary control maintained?
Along the extrapyramidal motor tracts, particularly the vestibulospinal (lower brain stem control)
muscles required to initiate a stretch reflex
o When stretched- tendon jerk- pulls on muscle, muscle spindle detects that, sends a message back, synapse on motor neurone which fire the neuromuscular junction to contract the muscle.
• To contract one muscle, must relax the opposite/ antagonist muscle.
o An inhibitory neurone is present to relax the opposite muscle.
This circuitry doesn’t work in PD where co contraction occurs- agonist and antagonist muscles contract at the same time.
How does posture control vary the excitability of alpha and gamma motor neurones?
• It changes sensitivity of spinal reflexes/ muscle spindle in order to override ‘pattern’.
- Alpha- gamma co-activation
- Alpha motor neurone sends a message to the main muscle fibres to contract
- Has a pairing with the gamma neurone where muscle spindles can also contract: gamma motor neurone output to contractile end portions of spindle fibre
- Descending pathways coactivating alpha and gamma neurones
3 higher control reflexes?
- vestibular reflexes
- visual reflexes
- joint reflexes
Vestibular reflex
- Needs information from orientation to vertical vestibular apparatus (sense organ) to prevent a fall
- IMPORTANT: Reflex below consciousness-
- Neural pathway: inner ear —> vestibular nuclei —> spinal motor neurones
- Lean to left- excite sensors on right- recover vertical
Visual relexes
- Powerful input for posture control
- Looking up at the clouds; brain will interpret the movement of clouds as you moving as well causing you to fall
- Direct descending pathway from nuclei in brain stem to spinal cord
- Eye –> lateral geniculate nucleus —> midbrain —> descending reflex pathways —> spinal motor neurones
Pressure receptors
- Important receptors for maintenance posture
- Skin pressure receptors; standing on the soles of your feet, pressure receptors monitor the distribution weight
- Clinically if destroyed eg tabes dorsalis
Cortical control
- Extensive cortical control
- Is a learnt control that is used for correction
- Can be lost through loss of gravity control; don’t know what is vertical
3 primary control centres
brain stem
spinal cord
cerebellum
2 side circuits
cerebellum
basal ganglia
What is involved before movement?
o Tone, posture, balance
o 3 systems: visual, vestibular, proprioception (touch and pressure receptors)
o (Pressure receptors in your glutes tell you how you are sitting)
Start of movement?
o Initiation of voluntary movement
o Where basal ganglia is involved
During movement?
o Monitoring control messages and actual position
o Cerebellum compares the signal from the primary motor cortex (cerebrum) with that from periphery/ muscle spindles and detects mismatches
o Muscle spindles and vestibular apparatus detects the rate of change of length (not just the change of length), so predict where you are going to be in 2 seconds. Will detect if an error will occur.
o Results in smooth movement co-activation from alpha and gamma
o Cerebellum drives gamma motor neurons maintaining the parallel system
During stop?
o Requires brakes on before reaching goal which involves both the basal ganglia and cerebellum
o Cerebellum will predict where you will be and will signal when to put the brakes on and basal ganglia stops the movement
o Both relies on feed back to predict end point or end up overshooting
6 brain areas involved in controlling movement?
- Occipital lobe
- Temporal lobe
- Lateral sulcus
- Frontal lobe
- Central sulcus
- Parietal lobe
Prefrontal cortex
- Ideas and motivation
- People with head injuries will damage this area
- Needs a trigger eg thirst so wants a drink
Premotor cortex
- Premotor cortex and other high-level association areas function
- Function: idea, motivation and conceptualisation
- The goal is to make a plan e.g. how do I get the drink
Supplementary motor cortex
(motor asociation cortex/ secondary motor cortex)
- makes the strategy to carry out the plan
- like which muscles will work
- needs input- how much distance the muscles will move by
- need info from visual cortex which will go to the posterior parietal cortex
Posterior parietal cortex
- Analyses sensory information related to postulated movement particularly visual e.g. touch
- Activates supplementary motor area and premotor cortex
- Function: to plan and write a programme for movement
- Programme needs to know our position, environment, what the task is
Cerebellum
- Balance- must superimpose first from pre-motor cortex
- Co-ordination- alpha gamma
- Motor memory eg learn to juggle, riding a bike
- Monitors and compares and corrects if there’s a mismatch to ensure smooth movement
- 210 mph signals must be fast- signal from the muscle spindles to the cerebellum
Basal ganglia
• Also goes via the thalamus
• Has roles in the programming, sizing and which muscles are involved
• Are groups of nuclei found in the middle
o Functions: amplitude settings- how much the muscles will contract
o Timing sequences- fast or slow
o Programming, sizing and which muscles contract
• Two pathways: direct and indirect
Primary motor cortex
- Found just in front of the central sulcus
- Activates spinal motor neurons via cortico spinal tracts
- Descending pathway from the cortex to the spine
- Most cross over in the brain stem ie the medulla- important for diagnosis
- Homunculus- single fasiculus to large muscle groups
- Motor homunculus
Spinal cord
-• Activates muscles
• Grey matter and wires around it
• Send wire to the muscle
• Signal arrives anterior horn cell —> anterior root –> common peripheral nerve –> muscle synapse –> neuromuscular junction
