Nervous System

This chapter describes the structure of neurons, the cells of the nervous system and how they connect with each other. It then describes the brain, spinal cord and the nerves that transmit nerve impulses through the body.

Objectives

After completing this section, you should know:

• the role of the nervous system in coordinating an animal’s response to the environment
• that the nervous system gathers, sorts and stores information and initiates movement
• the basic structure and function of a neuron
• the structure and function of a synapse and neurotransmitter chemicals
• the nervous pathway known as a reflex with examples
• that training can develop conditioned reflexes in animals
• that the nervous system can be divided into the central and peripheral nervous systems
• that the brain is surrounded by membranes called meninges
• the basic parts of the brain and the function of the cerebral hemispheres, hypothalamus, pituitary, cerebellum and medulla oblongata
• the structure and function of the spinal cord
• that the peripheral nervous system consists of cranial and spinal nerves and the autonomic nervous system
• that the autonomic nervous system consists of sympathetic and parasympathetic parts with different functions

Summary

• The neuron is the basic unit of the nervous system. It consists of a cell body with a nucleus, filaments known as dendrites and a long fibre known as the axon often surrounded by a myelin sheath.
• A nerve is a bundle of axons.
• Grey matter in the brain and spinal cord consists mainly of brain ells while white matter consists of masses of axons.
• Nerve Impulses travel along axons.
• Adjacent neurons connect with each other at synapses.
• Reflexes are automatic responses to stimuli. The path taken by nerve impulses involved in reflexes is a reflex arc. Most reflex arcs involve 3 neurons - a sensory neuron, a relay neuron and a motor neuron. A stimulus, a pin in the paw for example, initiates an impulse in the sensory neuron that passes via a synapse to the relay neuron situated in the spinal cord and then via another synapse to the motor neurone. This transmits the impulse to the muscle causing it to contract and remove the paw from the pin.
• The nervous system is divided into 2 parts: the central nervous system, consisting of the brain and spinal cord and the peripheral nervous system consisting of nerves connected to the brain and spinal cord. The autonomic nervous system is considered to be part of the peripheral nervous system.
• The brain consists of three major regions: 1. the fore brain which includes the cerebral hemispheres (or cerebrum), hypothalamus and pituitary gland; 2. the hindbrain or brain stem containing the medulla oblongata and 3. the cerebellum.
• Protective membranes known as the meninges surround the brain and spinal cord.
• There are 12 pairs of cranial nerves that include the optic, olfactory, accoustic and vagus nerves.
• The spinal cord is a cable of nerve tissue surrounded by meninges passing from the brain to the end of the tail. Spinal nerves emerge by a ventral and dorsal root between each vertebra and connect the spinal cord with organs and muscles.
• The autonomic nervous system controls internal body functions not under conscious control. It is divided into 2 parts with 2 different functions: the sympathetic nervous system that is involved in the flight and fight response including increased heart rate, bronchial dilation, dilation of the pupil and decreased gut activity. The parasympathetic nervous system is associated with decreased heart rate, pupil constriction and increased gut activity.

Learning Activities

Library of Resources

Presentations and Blackboard quizzes can be accessed by students of Otago Polytechnic.