NERVOUS SYSTEM

Structure & Function The function of the nervous system is: To sense, interpret, and respond to internal and external environmental changes to maintain a steady state in the body (homeostasis) The nervous system is divided into two major structures: Central nervous system (CNS) Peripheral nervous system (PNS)

Central Nervous System Central nervous systems includes: Brain Spinal cord *Coordinates body’s full nervous system *Contains nerves that control connections between impulses coming to and from the brain and the rest of the body

CentRAL NERVOUS SYSTEM Nervous tissues are surrounded by 3 tough membranes (Meninges) because they are extremely delicate & easily damaged Pia mater (inner) Arachnoid (middle) Dura mater (outer) The nervous tissue & meninges are further protected by bones (vertebrae & cranium)

PERIPHERAL NERVOUS SYSTEM Peripheral nervous system consists of: 12 pairs of cranial nerves -Originate in the brain 31 pairs of spinal nerves -Act independently from the brain in some reflex reactions

PERIPHERAL NERVOUS SYSTEM Organs of the peripheral nervous system contains: Afferent (sensory) neurons *Carry messages from the sensory cell of the body to the brain Efferent (motor) neurons *Carry messages from the brain to the body organs or parts *Classified as somatic (voluntary) or autonomic (involuntary) Interneurons *Connecting nerves *Carry messages from afferent to efferent nerves

PERIPHERAL NERVOUS SYSTEM Autonomic nervous system is a part of the peripheral nervous system and has two parts: Sympathetic * Stimulated in situations that require action * Example: “fight or flight” reaction Parasympathetic * Functions in response to normal, everyday situations * Example: Digestion of food

UNITS OF THE NERVOUS SYSTEM

Nerves system is the nerve, which is a bundle of * The basic structural unit of the nervous system is the nerve, which is a bundle of fibers that carries impulses * Nerve fibers consist of neuron cells

NEURONS *Neuron cells are the functional unit of the nervous system * Three main types of neuron cells: afferent, efferent, & interneuron (each carry messages, or impulses, to & from the body’s organs) * Parts of Neuron: Dendrite Cell body Axon

Dendrites: receive impulses & transmit them to the cell body Cell body: contains nucleus, transmits impulse to axon Axon: transmits impulse away from cell body to dendrite of next neuron

NEURONS * Impulse transmissions can travel more than 130 meters per second or 300 miles per hour * Myelin (white matter) - White, fatty substance covering the axon (outside CNS) - Arranged in bundles called Schwann cells - Has protective membrane called neurilemma which enables axons to repair & regenerate themselves * Gray Matter - Axons IN the CNS - Unable to repair or regenerate themselves due to NO neurilemma

NEUROGLIA (glia) * Special nervous tissue cells that act as “glue” to support, bind, repair, & protect neurons * Three major types: Astrocyte cells Oligodendroglia Microglia

SYNAPSE across the synapse to another neuron by a * Space between two neurons * Impulses from one neuron are transmitted across the synapse to another neuron by a chemical called a neurotransmitter * Two most common neurotransmitters: Acetylcholine Norepinephrine

GANGLIA of the Central Nervous System * Groups of nerve tissue located outside of the Central Nervous System * Increased ability to transmit impulses because they are clustered together in the ganglion

PLEXUS & DERMATOME Plexus * Four major networks of interwoven spinal nerves (cervical, brachial, lumbar, and sacral) * Provide impulses to specific regions of the body Dermatomes * Spinal nerves that control sensations on the skin surface

BRAIN * Largest structure of the nervous system and one of the largest organs of the body * Brain weighs about 2 to 3 pounds * The brain is covered by three layers of membranes called meninges: - Dura mater - Arachnoid - Pia mater

BRAIN * Brain cells can only survive 4-6 min without oxygen and glucose from the blood * Four major areas of the brain: - Cerebrum - Diencephalon - Cerebellum - Brain Stem