The Nervous System

The nervous system coordinates all body functions, enabling a person to adapt to changes in internal and external environment  The nervous system is composed mainly of the nerve cells (neurons) and supporting cells (neuroglia). 

 This

is the basic conducting cell of the nervous system  Highly specialized but cannot reproduce itself  Main parts are the :  cell body (soma),  the fibers: axon and dendrites.

The axon is a long process with myelin sheath. This conducts impulses away from the cell body. •The

dendrites are short, thick, diffuse branching processes that receive impulses and conduct them towards the cell body.

MYELIN SHEATH - It is lipid protein complex covering axons . FUNCTION : - It increases velocity of impulse conduction. SYNAPSE - This is the region where communication occurs between 2 neurons or between a neuron and a target cell

These are the supporting cells  They supply nutrients to the neurons and help maintain the electrical potential  They also form part of the blood-brain barrier 

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Support Insulation Nutrition

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Types: CNS - Oligodendroglia,

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Astrocytes, Ependymal

Cells, Microglia PNS - Satellite Cells, Neurolemma (Schwann Cells)

Oligodendrocytes produce myelin sheath in the CNS  Schwann cells produce myelin sheath in the peripheral NS. 

1. Myelinated Nerve Fibers - continuous series of Schwann Cells

2. Unmyelinated Nerve Fibers - enclosed as a group by neurolemmal sheath - seen in cutaneous nerve

1.

CRANIAL NERVES (12 Pairs) I II III IV V VI

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Olfactory VII Optic VIII Oculomotor IX Trochlear X Trigeminal XI Abducens XII

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Facial VestibuloCochlear Glossopharyngeal Vagus Spinal Accessory Hypoglossal

a.

General Somatic Afferent Division (Sensory)

b. General Somatic Efferent Division (Motor) ** found both in CNS & PNS ** innervates all parts of the body (motor & sensory) EXCEPT visceral organs smooth muscles glands

2.a. General Visceral Afferent Division (Sensory) - provides info on body’s internal environment - transmits visceral pain (hunger, spasms, ischemia, distension & chemical irritations.

innervates smooth muscles, cardiac muscle & glands - regulates visceral functions - uses both Norepinephrine & Acetylcholine. as neurotransmitters.

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Sensory fibres terminate in the periphery as bare unmyelinated endings or in the form of specialised capsulated structures called

receptors.

It is the junction where the axon or some other portion of one cell terminates on the dendrites or some other portion of another cell.  Neuron which sends messages is called PRESYNAPTIC NEURON.  Neuron which receive messages is called the POSTSYNAPTIC NEURON. 

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