Unit Six The Nervous System I. Introduction A. Definition a coordinating system of the body, composed of highly specialized cells that conduct nerve impulses to a center so responses can be made. The nervous system provides a control for the rapid activities of the body. B. Functions of the Nervous System a. Uses special cells to help the body communicate with body parts b. Allows one to be aware of his environment c. Allows one to respond to his environment C. Two Major Subdivisions of the Nervous System 1. (CNS) a. Brain b. Spinal cord 2. (PNS) a. Cranial nerves b. Spinal nerves D. Terminology 1. special name for a nerve cell 2. a bundle of neurons 3. specially designed neurons used to interpret stimuli for the nervous system (vision, hearing, smell, taste, touch, temperature, pain, pressure).
II. Structure of a Neuron (aka a Nerve Cell) A. Shape long and thin, one cell thick and up to 1 meter long, similar to electrical wires. B. A neuron consists of two parts 1. Cell body containing a nucleus and cytoplasm 2. Cell processes the ends of neurons having branching fibers of two types a. short projections, usually more than one, receive impulses b. a very long projection, usually one, send impulses c. Nerve fiber does not mean nerve cell; a nerve fiber is any long process of a neuron and usually refers to a long axon C. Classification of Nervous Tissue Based on Function 1. Neurons a. is a neuron that conducts a nerve impulse from a receptor to the CNS b. is a neuron that conducts a nerve impulse away from the CNS to an effector c. is a neuron that conducts a nerve impulse from one part of the CNS to another part of the CNS
III. Physiology of a Neuron A. The pathway that carries a message from the brain to the toe is not the same pathway that carries a message from the toe to the brain. B. Neurons do not communicate by actually each other. C. the open space between the axon of one neuron and the dendrite of another neuron. D. Messages move along a neuron from one to another. The flow always goes from dendrite end to axon end. E. Messages must the open space from axon end to dendrites end. F. the name of the chemical crossing the synapse
IV. Structure of a Nerve A. A collection of nerve fibers (cells) that are surrounded by all of their connective tissue coverings B. Types of Nerves a. made up entirely of sensory neurons b. made up entirely of motor neurons c. made up of both sensory and motor neurons C. Construction of a Nerve 1. a. A substance that surrounds a nerve fiber b. Not present in very small nerve fibers (non-myelinated) c. Found in both the CNS and PNS 2. (Schwann s sheath) a. Found only in the PNS, not the CNS b. Necessary for the regeneration of nerve fibers 3. Endoneurium Connective tissue sheath that surrounds the nerve fiber, myelin and neurolemma in both the PNS and CNS 4. Perineurium Connective tissue covering that surrounds the fasciculus (a number of nerve fibers with their endoneural sheath) 5. Epineurium Connective tissue covering that surrounds the fasciculi and their sheaths
Diagram of a Nerve and its Coverings:
V. Physiology of a Nerve A. Nerves are bundles of nerve fibers carrying messages to and from the central nervous system. B. Nerves may carry all sensory neurons, all motor neurons or a mixture of sensory and motor neurons (mixed nerve). VI. Functional Overview of the Nervous System Reflex Arc -
VII. Diagrams of the Nervous System A. Central Nervous System B. Peripheral Nervous System 1. Brain 1. Cranial nerves 2. Spinal cord 2. Spinal nerves
VIII. Central Nervous System A. 1. The organ that receives and sends messages to all body parts 2. Made up of 3. Messages enter and leave the brain by way of the spinal cord cranial nerves 4. Parts of the brain (3 main parts although there are others) a. (known as the higher brain) (1) controls thoughts, reasons, senses (2) largest part of the brain (3) receives all messages from the sense organs (4) stores messages (memory) (5) center for muscle control (6) divided into two parts right and left hemispheres (7) most of the cerebrum functions are voluntary (8) the cerebrum is divided into four regions (lobes) (a) frontal lobe (b) parietal lobe (c) temporal lobe (d) occipital lobe b. (1) found below cerebrum at the back of the head (2) helps make our movements smooth and graceful (3) nerves that enter or leave the brain on the way to and from the muscles pass through the cerebellum
c. (part of the brain stem) (1) extends downward from the bottom of the brain until it unites with the spinal cord (2) controls some important visceral reflexes (a) regulates heart rate (b) regulates blood pressure by varying the diameter of blood vessels (c) respiration by controlling the depth and rhythm of breathing B. 1. A long, slender bundle of nervous tissue that extends about 1.5 feet 2. Protected by the vertebral column, cerebrospinal fluid and by several layers of membrane called the meninges 3. Serves two major functions A. Provides a conduction pathway for two way traffic the spinal cord carries motor messages down and sensory messages up, connecting the brain to the spinal nerves of the peripheral nervous system B. Serves as a reflex center (1) a reflex is a rapid way of responding to an emergency (2) a reflex occurs so quickly because the impulse does not travel all the way to the brain IX. Peripheral Nervous System A. 1. Connected to the spinal cord 2. 31 pairs joining the cord 3. Each spinal nerve mixed in function B. 1. Connected directly to the brain 2. 12 cranial nerves