Nervous system

The nervous system is responsible for coordinating all of the body's activities. It controls not only the maintenance of normal functions but also the body's ability to cope with emergency situations.

Activity

Explore the female and male nervous systems.

Brain

The brain is a mass of soft nerve tissue, which is encapsulated within the skull. It is made up of grey matter, mainly nerve cell bodies, and white matter which are the cell processes. The grey matter is found at the periphery of the brain and in the centre of the spinal cord. White matter is found deep within the brain, at the periphery of the spinal cord and at the peripheral nerves.

The brain is divided into:

• Cerebrum - the largest part of the brain. It is the centre for thought and intelligence. It is divided into right and left hemispheres. The right hemisphere controls movement and activities on the left side of the body. The left hemisphere controls the right side of the body. Within the cerebrum are areas for speech, hearing, smell, sight, memory, learning and motor and sensory areas.
• Cerebral cortex - the outside of the cerebrum. Its function is learning, reasoning, language and memory.
• Cerebellum - lies below the cerebrum at the back of the skull. Its functions are to control voluntary muscles, balance and muscle tone.
• Medulla - controls heart rate, breathing, swallowing, coughing and vomiting. Together with the pons and the midbrain, the medulla forms the brainstem that connects the cerebrum to the spinal cord.

Lobes of the brain

It is important to have an understanding of how the brain functions and which parts control our functioning and behaviour. For example, when a person suffers from a stroke, parts of the brain may become dysfunctional. If it is the frontal lobe, speech, thought and movement may be affected.

Activities - Lobes of the brain

The peripheral nervous system connects the central nervous system to the rest of the body. The main divisions of the this system are:

• The autonomic nervous system — which controls the automatic functions of the body: the heart, smooth muscle (organs) and glands. It is divided into the “fight-or-flight” system and the “resting and digesting" system.
• The somatic nervous system — which allows us to consciously or voluntarily control our skeletal muscles. The somatic system contains 12 cranial nerves and 31 spinal nerves.
• Nerves — which are made up of special cells called neurons. Neurons are comprised of a dendrite, a cell body and an axon. Impulses travel to the dendrite into the cell body and then onto the axon. A special sheath called myelin, which increases the conductivity of the neuron, covers some nerves.

As messages travel from one neuron to the next they move across a synapse. At each synapse there is a chemical called a neurotransmitter. At various parts of the body specific neurotransmitters facilitate communication, for example dopamine (motor function), serotonin (mood) and endorphins (painkillers). Sensory neurons carry messages from a receptor to the brain. The brain then interprets the message. Motor neurons then send the message to an affector in muscles and glands.

The receptor neuron (sensory organ) sends a signal to the sensory neuron which passes to the brain/spinal cord. From here, this signal is sent to the motor neuron and then on to the affector (muscle/gland).

The neurone

The basic unit of the nervous system, is a specialised cell called the neurone. These nerve cells make up a massive network of specialised cells that transmit messages, very rapidly, from one part of the body to another. Information is transmitted via electrical impulses.

The neurone is comprised of a nerve cell and its adjoining processes called an axon and dendrites. Every nerve cell has one or more processes attached to it. Electrical impulses enter the neurone via the dendrites and leave via the axon. The space between the axon of one cell and the dendrites of another is called a synapse. Specialised chemicals called neurotransmitters help conduct impulses through the synapse onto the next cell.