Page 70 - Handbook of Electronic Assistive Technology

Chapter 3 • Functional Posture 57

Cerebrum

Brain Stem

Cerebellum

Spinal Cord

FIGURE 3-3 Diagram of the central nervous system�

• The cerebellum is important for correcting posture and smoothing out movements.
The medial zone in particular is involved in controlling posture and equilibrium,
influencing the axial and girdle parts of the body, as well as the organisation of motor
synergies (coordinated multijoint movements) (Latash and Hadders-Algra, 2008).

Each system combines to provide a base of axial stability for more distal mobility and
skilled or refined coordinated limb movements. Damage to the brain and neural system
often interrupts the flow of messages along various nerve pathways. This disruption of sig-
nals can cause changes in muscle tone, movement patterns and the retention or reemer-
gence of primitive reflexes (Bobath, 1990; Carr and Shepherd, 2014).
What Is Muscle Tone?

All muscles maintain a level of residual tension or resistance to stretch, even when relaxed
and at rest; this enables them to respond and move quickly and easily when required.
Without this tension, we would not be able to maintain and control an upright posture and
resist the force of gravity; conversely, too much tension can lead to movement difficulties
and other problems.
This tension is known as muscle tone and is ultimately controlled by impulses from the
brain and nervous system and occurs through a mechanism known as the stretch reflex.
When a muscle is stretched, an impulse is generated in the muscle spindle and is transmit-
ted via the sensory neuron to the grey matter of the spinal cord. Here the sensory neuron
synapses (connects) with the motor neuron, and the transmitted impulse results in mus-
cle contraction. While agonist muscles (prime movers) contract in response to stretch-
ing, antagonist (opposing) muscles must relax. Their relaxation is brought about via an