Neuroscience 13c – Control of Posture
Anil Chopra
1. List the different types of physical information used in postural control systems.
2. State which biological sensors produce which kind of information
3. Understand that different senses interact and that weighting may occur in cases of
sensory conflict.
4. Be able to distinguish automatic (reflex) and voluntary movements and posture
5. Understand the influence of cognitive factors on postural behaviour.
Sensory information about the environment comes from a number of different
sources:
 Vision - Position, speed, direction, motion of other objects
 Otoliths - Gravity (tilt), linear acceleration
 Semicircular canals - Rotational velocity and acceleration
 Proprioception - Force, pressure, motion within the body.
If the task is simple, then all the sources are not needed.
If there is sensory loss then control is adaptive and there is some degree of
redundancy, therefore people lacking information from one sense can perform
remarkably well if the motor task is not too difficult.
Causes for sensory loss can include:
 Illness - Menière's disease, cataract, neuropathy
 Injury - Physical injury, poisoning, drug toxicity
 Ageing - Visual, proprioceptive and vestibular performance is worse in older
people
Some of the compensatory mechanisms that people adopt when they have sensory
loss:
 Stance - Wide base of stance front to back and side to side to increase stability
 Stance - Knee hyperextends to provide passive stability by locking the joint
 Gait - Trunk and arms move little to reduce the need for control of moving masses
 Gait - Knee again hyperextends to provide stability
Patients often find it difficult to keep balance when they have their eyes closed.
Conscious Action
Most postural tasks do not require conscious control:
- simple tasks such as maintaining a stance does not requite conscious control
- tasks such as orienting, control of head altitude and movement of support can
be carried out without conscious control.
Autonomic reactions are triggered by particular combinations of sensory stimuli and
are appropriate for particular situations. Voluntary compensation may be required if
the autonomic action is not sufficient
Conscious anticipation produces a postural set – i.e. a tendency to respond in a
particular way to an expected perturbation
Sensory Weighting
Most information sent by the various sources is concurrent i.e. it is interpreted in the
same way. When it is not, the brain can give more weight to certain senses e.g. the
illusion of movement when stationary if an adjacent train is moving.
If this is prolonged or severe, then it can produce motion sickness.
Voluntary Control
Automatic reactions are stimulated when a certain set of information is received,
however if the response is inappropriate, then voluntary compensation can occur.
Conscious anticipation produces a postural set, i.e. a tendency to respond in a specific
way, appropriate to an expected perturbation.