The Nervous System: Structure, Function, and Components, Lecture notes of Anatomy

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CNS

• (^) By the end of this session students are expected to be able to:
• (^) Define the Nervous system, Autonomic Nervous system, Somatic nervous system, and Nerves
• (^) List Components of the Nervous System
• (^) Explain the Structure of Central Nervous System.
• (^) State Functions of Nervous System

• (^) Somatic Nervous System The part of the peripheral nervous system that transmits signals from the central nervous system to skeletal muscle and from receptors of external stimuli, thereby mediating sight, hearing and touch.

• (^) Nerves
• (^) Nerves are bundles of axons in the peripheral nervous system (PNS) that act as information highways to carry signals between the brain and spinal cord and the rest of the body.

• (^) Nerve tissue is made up of nerve cells called neurons or nerve fibers
• (^) All neurons have the same physical parts.
• (^) The cell body contains the nucleus and is essential for the continued life of the neuron.
• (^) Dendrites are processes (extensions) that transmit impulses toward the cell body.
• (^) The one axon of a neuron transmits impulses away from the cell body.

• (^) It is the cell membrane of the dendrites, cell body, and axon that carries the electrical nerve impulse.
• (^) Axons and dendrites are collectively called Schwann cells in the peripheral nervous system and are covered by a membrane called myelin sheath.

• (^) Synapse.
• (^) It is the small gap or space between the axon of one neuron and the dendrites/cell body of the next neuron.
• (^) The synaptic knob of presynaptic axon contains chemical neurotransmitters that are released to the synapse on the arrival of an impulse.

• (^) Synapses ensure one way impulse transmission
• (^) neurotransmitter diffuses across the synapse, combines with specific receptor sites on the cell membrane of the postsynaptic neuron, and there generates an electrical impulse that is, in turn, carried by this neuron’s axon to the next synapse.
• (^) Example of neurotransmitter is acetylcholine found at the neuromuscular junction.

• (^) Sensory neurons
• (^) Carry impulses from receptors to the central nervous system.
• (^) Receptors detect external or internal changes and send the information to the CNS in the form of impulses by way of the afferent neurons.
• (^) The central nervous system interprets these impulses as a sensation

• (^) Motor neurons
• (^) Carry impulses from the central nervous system to effectors.
• (^) The two types of effectors are muscles and glands.
• (^) In response to impulses, muscles contract or relax and glands secrete

• Central Nervous

System

• (^) The spinal cord extends from the foramen magnum of the occipital bone to the disc between the first and second lumbar vertebrae.
• (^) The internal grey matter is shaped like the letter H
• (^) Grey matter consists of the cell bodies of motor neurons and interneurons

• (^) The external white matter is made of myelinated axons and dendrites of interneurons.
• (^) Emerging from the spinal cord are spine nerves.
• (^) Spinal cord reflexes are those that do not depend directly on the brain, although the brain may inhibit or enhance them.
• (^) A reflex arc is the pathway that nerve impulses travel when a reflex is elicited, and there are five essential parts: