4. The Peripheral Nervous System Tanzania.pptx

Nervous system

1. The peripheral nervous system

2. The peripheral nervous system (PNS) is a component of the nervous system that connects the central nervous system (CNS) to the rest of the body. The PNS is responsible for both sending information from different areas of the body back to the brain and carrying out commands from the brain to various body parts. All nerves that link the body to the brain and spinal cord make up the peripheral nervous system. The peripheral nervous system can be divided into 1. Voluntary (somatic) and 2. Involuntary (autonomic) nervous system

3. All nerves that link the body to the brain and spinal cord make up the peripheral nervous system. The peripheral nervous system can be divided into 1. Voluntary (somatic) and 2. Involuntary (autonomic) nervous system The voluntary nervous system is composed of sensory and motor neurons. It is concerned with activities under the direct control of the brain, such as kicking a football. The involuntary nervous system is composed of sensory and motor neurones . It is concerned with unconscious activities in the body, such as the heartbeat, peristalsis and sweating.

4. The peripheral nervous system also comprises of cranial and spinal nerves. The cranial nerves arise from the brain and they form receptors and effectors in the head. Generally, the function of these nerves is to transmit impulses from the sensory organ to the brain for interpretation. The spinal nerves arise from the spinal cord through the intervertebral foramen of the vertebrae. The spinal nerves occur in pairs and each with two roots namely dorsal and ventral root. These two roots join together before they pass through the inter-vertebral foramen. The dorsal root is made up of sensory nerve fibres whereas ventral root is made up of motor nerve fibres .

5. The autonomic nervous system controls the involuntary actions of smooth muscles and certain glands. It is divided further into the sympathetic nervous system which has mainly excitatory effect on the body, and the parasympathetic nervous system which has mainly calming influence. The two systems oppose each other in action. For example, if the sympathetic system causes the muscles to contract, the parasympathetic system causes the muscles to relax. Also, if the sympathetic system constricts the arteries, the parasympathetic system dilates the arteries

6. Reflex action A reflex action is a rapid, automatic response to a stimulus. A reflex action is made possible by neural pathways called reflex arcs which carry the impulses to and from the spinal cord. Thus, this pathway does not involve the brain. Examples of reflex action includes; the changes in size of the pupil when subjected to bright or dim light, sudden withdrawal of hand or leg when pricked by a sharp or hot object, coughing or sneezing, knees jerk in response to a blow or someone stamping the leg, and salivation at the sight or smell of food.  

7. simple reflex action AND conditioned reflex action. A simple reflex action is an automatic response that is not learnt. Simple reflex actions are always quick and automatic. An example of reflex action is knee jerk. The knee jerk reflex produces the same response even if it is done many times. Simple reflex action is characterized by the following the same stimulus will always result into the same response. In reflex action response is coordinated by the spinal cord. In the simplest reflex action there is no involvement of relay neurone . The stimulus passes directly from the sensory to motor neurone and only one synapse is involved. A conditioned reflex is a type of reflex action where the response is affected by past experience. Conditioned reflexes are acquired through learning, but can subsequently be performed without conscious thought. These reflexes are coordinated by the brain. Examples of conditional reflex action is when a dog salivates when it sees food presented to it. If a bell is rung just before food is presented to the dog routinely the dog will learn to associate bell ringing with food. In human beings conditioned reflex is seen during riding a bicycle, driving a car and typing documents on a computer or typewriter.

8. The differences between Simple Reflex action and Conditioned Reflex Action   Simple reflex Action Conditioned Reflex Action 1 Inborn response to external stimuli that is not learnt Learnt or modified patterns of behaviour gained through experience 2 Are the same in all members of a species Differ from one member to another of the same species 3 Initiated by a related stimulus Initiated by an unrelated stimulus substituted by the one which normally initiates the response 4 Single stimulus brings about response Combined stimuli that when the pattern is repeated brings about response 5 Response coordinated by spinal cord Response coordinated by the brain