12.2 - Nervous System

The human nervous system consists of a giant network of nerve cells or neurons and nerve tissues which convey information between the sensory receptors, organs and effectors. It can be divided into 2 main subsystems:

• Central nervous system (CNS), which consist of the brain and spinal cord
• Peripheral nervous system (PNS), which includes all the nerve tissue outside the CNS

The human brain consists of the cerebrum, cerebellum, medulla oblongata, thalamus and hypothalamus.

Figure 3 - The human brain.

Characteristics and functions of Human Brain

1. Cerebrum

• Largest and most complex part of the brain.
• Can be divided into left and right hemispheres.
• Folded surface increases the surface area to contain more nerves.
• Centre of control for emotions, hearing, sight, personality and controlled actions.
• Receives the sensory input and performs integrative functions.
• Responsible for many mental abilities such as learning, memorizing, language skills and mathematical skills.

2. Hypothalamus

• Involved in homeostatic regulation.
• Coordinating centre for body temperature, water balance and blood pressure.
• Controls the release of several hormones from the pituitary gland.

3. Cerebellum

• Located below the cerebrum.
• Coordinating centre for body movements.

4. Medulla oblongata

• Situated at the anterior of the cerebellum.
• Regulates internal body processes that are unconscious.
• Reflex centre for vomiting, swallowing, coughing, sneezing and hiccupping.

5. Pituitary gland

• Located at the base of the hypothalamus.
• Main gland in the endocrine system that secretes hormones that affect other glands and body functions.

The spinal cord is situated within the vertebral column. It is surrounded by cerebrospinal fluid that acts a shock absorber and provides the spinal cord with nutrients. It consists of white and grey matter. The spinal nerves emerge from the spinal cord through the dorsal and ventral roots. The functions of the spinal cord include:

• Processes certain types of sensory information and sends out responses via the efferent neurons.
• Contains the neural pathway for reflexes.
• Contains neurons that convey signals to and from the brain.

Figure 4 - In cross-section, the grey matter looks like a butterfly or the letter H. It consists mainly of cell bodies of neurons. It is surrounded by the white matter. The white matter contains myelin-coated axons of neurons that extend through the whole spinal cord.

Characteristics and Functions in the Structures of the spinal cord

• Dorsal root ganglion: Contains the cell bodies of the sensory neurons.
• Dorsal root: Contains the axon of the sensory neuron which transmits the nerve impulses from the sensory receptor to the spinal cord.
• Ventral root: Contains the motor neuron that carries the impulses from the spinal cord to the effectors.
• Spinal nerve: Contains the sensory and motor neurons.

Figure 5 - PNS connects sensory receptors and effectors to the CNS.