The Nervous System
The nervous system (NS) can be divided anatomically into central and peripheral nervous systems.
The central nervous system (CNS) includes the brain, which consists of the cerebrum, cerebellum, subcortical structures and brainstem as well as the spinal cord. The brain is surrounded by cerebrospinal fluid (CF), which supports and nourishes the brain and absorbs shock during rapid head movements.
The peripheral nervous system (PNS) consists of 12 pairs of cranial nerves and 31 pairs of spinal nerves as well as sensory receptors, which connect the CNS to sensory organs, such as the eyes and ears, organs of the body, muscles and glands.
Major differences between the CNS and PNS are the following:
- CNS tracts (groups of fibers) transmit impulses to other neurons, whereas PNS nerves transmit impulses from nerves to end organs such as muscles in the arms and legs.
- all of the CNS components are housed within bone (skull or vertebral column), whereas most of the PNS components are outside of the bone.
There are three main structures of the brain that play a vital part in our ability to function, which include the cerebrum, the brainstem as well as the cerebellum.
The Cerebral Cortex or cerebrum: it makes up the vast majority of the human brain and is the most highly evolved and organized structure of the human body. The cerebrum is the seat of consciousness and is responsible for voluntary functions.
It is divided into a left and a right hemisphere, which are connected by the corpus callosum and each side controls the opposite side of the body.
The two hemispheres differ in terms of:
- the way they process information: the left cerebral hemisphere processes material in an analytic and logical manner whereas the right cerebral hemisphere processes information as a whole (holistic) and intuitive way.
- their functions: the left hemisphere primarily controls verbal functions such as speech and language and the right hemisphere is primarily responsible for visual spatial (non-verbal) functions, processing of music as well as interpretation of a person's rhythm and stress pattern when speaking (intonation).
The Cerebellum:
This brain structure is located just above the brainstem, toward the back of the brain.
- functions: the major responsibility involves coordination and smoothness in time and space of voluntary motor movements, balance, muscle tone, movement range, strength and maintenance of body equilibrium.
- possible impairments: intention tremors; incoordination of motor movement; the inability to judge distance and when to stop (dysmetria); limb ataxia; staggering, wide based walking (ataxic gate), slurred speech (ataxic dysarthria), weak muscles (hypotonia); abnormal eye movement (nystagmus).
The Brain Stem:
It is a brain structure that is continuous with the spinal cord and comprised of the midbrain, pons, and medulla. All of the information to and from our body passes through the brain stem on the way to or from the brain.
- functions: important for controlling respiration, heart rate, blood pressure, digestion, temperature, swallowing and sweating; reflexes to seeing and hearing; affects levels of alertness, ability to sleep and sense of balance.
- possible impairments: coma or minimally conscious state, may affect lung capacity for breathing (affects speech); difficulty with the organization and perception of the environment; slurred speech; difficulty with swallowing food and water.