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The Nervous System NEURONS AND THE NERVOUS SYSTEM Structure and Functions System A physical organ system The main cell of the Nervous System is: The NEURON! Organs of the nervous system form two subsystems Central Nervous System (CNS) Peripheral Nervous System (PNS) The PNS delivers information to the CNS and carries messages from the CNS to other organs via NERVES Nerves Nerves Collections of neurons that are joined together by connective tissue. Responsible for transferring impulses (a message carried by neurons) from receptors to CNS and back to effectors. CNS & PNS The CNS is made up of: The Brain The Spinal Cord The PNS is made up of All nervous tissue outside of the CNS Sensory Neurons Motor Neurons (sensory & autonomic) Break It DOWN! The Nervous System Central Nervous System (CNS) Brain Peripheral Nervous System (PNS) Spinal Cord • Motor Neurons Somatic Nervous System Voluntary movements via skeletal muscles Sympathetic - “Fight-or-Flight” responses • Sensory Neurons Autonomic Nervous System Organs, Smooth muscles Parasympathetic - maintenance Divisions of the Autonomic Nervous System The Sympathetic division of the nervous system prepares the body for action The Parasympathetic division returns the body to a resting state Neurons Made up of a cell body and branches called dendrites and axons Dendrites receive messages from other neurons and send them to the cell body Axons carry messages away from the cell body A message carried by a neuron is called an impulse Functions 1. 3. 2. Neurons have 3 functions: Reception, Conduction, Transmission Types of Neurons 1. Sensory Neurons Neurons located near receptor organs (skin, eyes, ears). Function: receive incoming stimuli from the environment. 2. Motor Neurons Neurons located near effectors (muscles and glands) Function: Carry impulses to effectors to initiate a response. 3. Interneurons Neurons that relay messages between other neurons such as sensory and motor neurons. (Found most often in Brain and Spinal chord). Types of Neurons Sensory Vs. Motor Sensory Nerve Neurons that send signals from the senses, skin, muscles, and internal organs to the CNS e.g., skin Motor Nerve Neurons that transmit commands from the CNS to the muscles, glands, and organs e.g., muscle Gray’s Anatomy 38 1999 The Withdrawal Reflex Parts of a Neuron Dendrite Fine hair-like extensions on the end of a neuron. Function: receive incoming stimuli. Receive messages from other neurons and send them to the cell body Cell Body or Soma The control center of the neuron. Function: Directs impulses from the dendrites to the axon. Nucleus Control center of the Soma. Function: Tells the soma what to do. Neuron Structure Extra Extra! Dendrite The bushy, branching extensions of a neuron that receive messages and conduct impulses toward the cell body Axon The extension of a neuron, ending in branching terminal fibers, through which messages are sent to other neurons or to muscles or glands Parts of a Neuron Continued Axon Pathway for the nerve impulse (electrical message) from the soma to the opposite end of the neuron. Carries messages away from the cell body Myelin Sheath An insulating layer around an axon. Made up of Schwann cells. Nodes of Ranvier Gaps between Schwann cells. Function: Conduction of the impulse. (Situation where speed of an impulse is greatly increased by the message ‘jumping’ the gaps in an axon). Myelin Sheath & Nodes of Ranvier Myelin Sheath Fatty material made by glial cells Insulates the axon Allows for rapid movement of electrical impulses along axon Multiple sclerosis is a breakdown of myelin sheath Nodes of Ranvier: gaps in myelin sheath where action potentials are transmitted Speed of neural impulse Ranges from 2 – 200+ mph Neurons Dendrites Cell Body Myelin Sheath Axon of another neuron Axon Dendrites of another neuron