Question

Provide an example of a simple/basal nervous system and a complex/derived nervous system. Explain how their functions differ.

Answer 1

Simple/Basal Nervous System

The nervous system is the part of an animals body that co-ordinates it's behavior and transmits signal between different body areas.

At the most basic level,the function of the nervous system is to control movement of the organism and to affect the environment.

This is achieved by sending signals from one cell to others,or from one part of the body to others.

Example: Worms are the simplest bilaterian animals,and reveal the bsic structure of the bilaterian nervous system is the most staright forward.

Structure

Brain of most annelids eg:worms, including the leeches and terrestrail earthworms is relatively simple in a structure.Earthworm brain is bilobed mass lying above the pharynx in three body segment.Two cerebral ganglia(bundles of nerve cells)form a primitive bilobed brain from which sensory and motor fibres lead to other areas of the body.They have a pair of ventral nerve cords.A ganglionic swelling of the cord is found in each body segment.Gaint axpns, usually few in number,travel the length of the cord.They may belong to one cell or be composed of many neurons.These axons are capable of very rapid conduction of impulses to the segmental muscles.

Function

Axonal function is to mainly permit the worm to contract very rapidly as a defence against predators.

Slow crawling movements of worms are mediated by a series of reflex arcs.

Function of nervous system of annelids include certain behavioral capabilities including perception,motor co-ordinates and learning.

Functions in leech

Two rhythmic movements generated like heartbeat and swimming which is produced by heart excitor motor neurons.

Complex/Derived Nervous System

The nervous system is a complex collection of nerves and specialized cells known as neurons that transmits signal between different parts of the body.It is essentially the body's electrical wiring.

Eg:Humans Nervous System

Structurally,the nervous system has two components:the central nervous system and the peripheral nervous system.

Central nervous system is made up of the brain,spinal cord and nerves.

Peripheral nervous system consists of sensory neurons,ganglia and nerves that connect to one another and to the central nervous system.

Functionally,the nervous system has two main subdivisions:the somatic,or volountary,and the autonomic,or involuntary.

The autonomic nervous system regultes certain body processes,such as blood pressure and the rate of breathing that work without conscious effort.

The somatic system consists of nervous that connect the brain and spinal cord with muscles and sensory reception in the skin.