PERIPHERAL NERVOUS SYSTEM

1. PERIPHERAL NERVOUS SYSTEM -PNS is made up of nerves. -it is divided into two: Somatic nervous system b. Aotunomic nervous system -somatic nervous system transmits impulses from receptors to the CNS and from CNS to the skeletal muscles. -autonomic nervous ststemis divided into two: Sympathetic system- has spinal nerve only. b. Parasympathetic system- has spinal and cranial nerves.

2. FUNCTIONS OF SYMPATHETIC SYSTEM Increases heart beat. Dilates blood vessels. Increases spleen output. Increases blood pressure. Iincreases rate of breathing. Dilates pupils of the eye. FUNCTIONS OF PARASYMPATHETIC SYSTEM Decreases heart beat. Constrict blood vessels. Decreases spleen output. Decreases blood pressure. Decreases rate of breathing. Constricts pupils of the eye. NEURONES -Neurones are the basic structural and functional units of the nervous system. -A neurone or nerve cell has four parts: The cell body or cyton. Dendrites Axon. The fatty sheath.

3. THE CELL BODY OR CYTON • The cell body consists of: • - The nucleus • The cytoplasm • SYNAPSE • - Neurones are connected to one another directly. • There are slight gaps (about 20nm across) between the axon ending (synaptic knobs) of one neurone and the dendrites of the surface of the cell body of the neighbouring neurone. • These junctions between the neighbouring neurones are known a synapse. • Nerve impulses are able to cross synapse. • Information transfer across a synapse either by the passage of electrical signal or more commonly by a chemical called neurotransmitter. • Often, there may be about 6000 synapses between the dendrites and the body cell of a single motor neurone and other neurones. • CLASSIFICATION OF NEURONES • There are two classifications of neurones. • Classification based on the number of processes neurones have. • Classification based on the functions of neurones. • CLASSIFICATION OF BASED ON THE NUMBER OF PROCESSES NEURONES HAVE • There three types of neurones based on the number of processes they have. These are: • Unipolar neurones: These are with one process. Mainly found in invertebrates.

4. 2. Bipolar neurones: They are with two separate processes. They are mainly found in the retina of the eye. • 3. Multipolar neurone: These are with more than two processes. Mainly found in most vertebrates. • CLASSIFICATION OF NEURONES BASED ON THE FUNCTIONS • In vertebrates, there are three categories of neurones based on their functions. They are: • 1. Sensory (afferent) neurones: They receive impulses or connects receptors to the CNS. • 2. Motor (efferent) neurones: they conduct information away from the CNS to the effectors. E.g, glands and muscles. • 3. Relay/connectors/association/intermediate/internuncial neurones: They connect two or more neurones, usually lie within the CNS. • FUNCTIONS OF NEURONES • Neurones are connected with receiving and relaying nervous impulses in reflex and voluntary actions. • TRANSMISSION OF NERVE IMPULSES • An electric or nerve impulse is never a flow of electrons like an electric current.

5. -It is a wave of electrical activity travelling along the neurone. • To do this, a neurone must be able to generate electricity. • RESTING NEURONE • A resting neurone is so called because it does not convey a nerve impulse and not because it is inactive. • On the contrary, a resting neurone expends much energy in maintaining a potential difference across its membranes. • This is called the resting potential and measures about -70 millivolts. • MECHANISM OF TRANSMISSION OF IMPULSES • - The transmission of impulses along the fibre is characterized by change in electrical potential. • - At rest, the outside of the nerve is positively charged and the inside is negatively charged. • Chemically, the nerve fibres have potasium ions concentrated inside the fibre while sodium ions are concentrated more on the outside. • When the fibre is stimulated, there is a change in the permeability of the membrane. • - Sodium ions enter the nerve while potasium ions move out to the outside. • The change in permeability along the nerve or the change in the electrical potential along the fibre causes the movement of electrical current along the fibre. • In this way, the impulse is propagated or transmitted. • The original resting stage of the nerve is restored as soon as the impulses pass.

6. TRANSMISSION OF IMPULSES ACROSS THE SYNAPSES BY ELECTRICAL MEANS • In an electric synapse, the presynaptic membranes are close together, with pores made of proteinlinking the cytoplasm of the two cells. • This enables electrical signals to jumprelativelyunchanged from the pressynaptic cell to the postsynaptic cell. • Transmission is veryfast because there is no intervening chemical, therefore electrical synapses are found when responses have to be very quick. • Electrical synapses are found in pathways that control the escape responses of someanimals. • In mammals, they occur on nerve pathways which control rapid eye movement; they are alsocommon in the heart. • TRANSMISSION OF IMPUSES ACROSS THE SYNAPSE BY CHEMICAL MEANS • Chemical transmission at the synapse involves the process of neurosecretion and chemoreception. • The arrival of a nerve impulse at the axon terminal stimulates the release of a specific chemical substance, which has been synthesized in cell body and stored in the tip of the axon into the narrow synaptic space between the adjacent neurones. • This process constitute neurosecretion. • The chemical secreted, known as neurotransmitter, can cause local depolarization of the membrane of the postsynapticregion and thus transmit the exitation to the adjacent neurone. • Chemoreception is the process in which the neurotransmitter becomesattached to specificmolecules sites on the membrane of the dendrite(postsynapticregion), producing a change in the properties of the cell

7. Membrane so that a new impulse is established. 6. The chemical transmitter, i.e; acetylcholine, passes from the presynaptic axon to the postsynaptic dendrites by simple diffusion across the narrowspace, called synaptic clefts, separating the two neurones involved in the synapse. 7. The synaptic cleft have been measured under the electron microscope to be about 200A in width. After the neurotransmitter has exerted its effect on the postsynaptic membrane. It is promptly dectroyed by an enzyme called cholinesterase. 8. This destruction is of critical importance because if the acetylcholine were not destroyed, it would continue its stimulatory action indefinitely and all controls ould be lost. ACTIONS AND BEHAVIOURS Actions are responses to stimulus which involves both the neurones and endocrine system. TYPES OF ACTION. There are two types of actions: -Reflex/involuntary actions. -Voluntary actions. FEATURES OF REFLEX/ INVOLUNTARY ACTIONS They are automatic responses to stimuli. They occur in a stereotyped manner ,i.e; the same way always. Higher centres of the brain are not involved. They are involuntary action. They are protective responses which guard us from dangerous stimuli. Examples are: jerking of the lower arm when the knee cap is tapped.

8. b. Blinking responses of the eyes when object move across it. • c. Contraction of the pupils in bright light.e.t.c. • RELEX ARC • It is the path traced by the impulses in a simple relex action. It involves the following structures: • a. sensory receptor • b. Sensory neurone or afferent neurone. • c. relay neurone. • d. motor neurone or efferent neurone. • e. Effectors i.e; muscles and glands. • -Most reflex arcs involve three or more neurones • TYPES OF SIMPLE REFLEX ACTION. • There are two types of simple reflex action. • a. Spinal Reflex: This involves only the spinal cord e.g Knee-jerk • b. Cranial Reflex: This involves only the brain e.g contraction of the pupils when light is shone into the eyes. • COMPLEX REFLEX ACTION. • This involves neurones at various levels of the spinal column and the brain. Just like simple reflexes, it is quick, automatic and produce stereotyped responses. • MECHANISM OF REFLEX ACTION • When the nerve endings of a sense organ (receptor) are stimulated say by touching a hot object, impulses are transmitted through the sensory nerve (efferent) passing through the dorsal root into the spinal cord. • In the spinal cord, the impulses are relayed via the synapse, into the intermediate neurone through another synapse to the motor or effector nerve.

9. -This passes through the ventral root, to the effect or organ(muscle) which brings about response. • In the above case, the muscle contract and relax. The object is quickly dropped and the hand is withdrawn. • VOLUNTARY ACTIONS • Features: • These are conscious actions. • Higher centres of the brain are involved. • They involve most of the components of reflex arc. • The responses are not stereotyped, but vary with circumstance. • WEEK TWO ASSIGNMENT • In a tabular form, state five differences between reflex and voluntary actions. • What is behaviour? • State the types of behaviour. • Make a well labelled drawing of the various types of neurones.