The Nervous System Chapter 6
The Nervous system has three major functions: Sensory monitors internal & external environment through presence of receptors Integration Interprets sensory information Motor response to information processed through stimulation of effectors
Organization of the Nervous System Two Anatomical Divisions Central nervous system (CNS) Brain Spinal cord Peripheral nervous system (PNS) All the neural tissue outside CNS Afferent division (sensory input) Efferent division (motor output)
Afferent vs Efferent Afferent Nerves Efferent Nerves Sensory Nerves Receive Information Transmit sensory information gathered from the skin, muscles, and joints to the CNS Motor Nerves Send information on Carries information from the CNS out to the muscles and glands
Sensory nerve cells: Afferent pathway CNS (brain and spinal cord): Integration centers Motor nerve cells: Efferent pathway
Organization of the Nervous System Brain & spinal cord
Cells of the Nervous System Two types of neural cells in the nervous system: Neurons Process, transfer, and store information Neuroglia – (also called “glial cells”) Support and protect neurons
Structure of a Neuron
Most axons of the nervous system are surrounded by myelin The presence of myelin speeds up the transmission of signals along the axon Myelin will get laid down in segments along the axon, leaving unmyelinated gaps known as “nodes of Ranvier”
ELECTRICITY!!! Conductivity: the property of neurons that give them the ability to transmit nerve impulses Electrical impulses (action potentials) are “all-or-none” responses
Neurotransmitters are chemical messengers. Axon terminals do not actually touch the other neuron or muscle. The gap is called the synapse. Neurotransmitters are chemical messengers.
The Structure of a Typical Synapse
Classification of Neurons Structural classification based on number of processes coming off of the cell body We will talk about three neuron structures: Multipolar Bipolar Unipolar
Multipolar neuron multiple dendrites single axon most common type ALL motor neurons are multipolar
Bipolar neuron two processes coming off cell body one dendrite one axon only found in eyes, ears & nose Process sensory information
Unipolar neuron single process coming off cell body dendrites at one end axon makes up the rest of the process some sensory neurons in PNS are unipolar
Anatomical structure of Nerves Fig. 14.6
Efferent Divisions Somatic Nervous System Autonomic Nervous System Voluntary Stimulates skeletal muscles Stimulates them to contract Involuntary Controls cardiac muscle of the heart and smooth muscle of internal organs 2 Categories Sympathetic Fight or Flight response Releases adrenaline Parasympathetic Rest and digest response Day-in-day-out functions
Reflexes (Simple, rapid, involuntary, programmed responses to stimuli) Somatic Reflexes Autonomic Reflexes Stimulation of skeletal muscles Ex: Withdrawing hand from something hot before you even realize it is hot Fast because doesn’t travel to brain and back (sensory neuron spinal cord motor neuron) Send involuntary stimuli to cardiac muscle of heart and smooth muscle of internal organs Ex: Digestion, elimination, sweating, blood pressure
Nervous System Overview
Nerve Impulses
Synapses In Detail