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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



Sensory Nerves
Receive Information
Transmit sensory
information gathered from
the skin, muscles, and
joints to the CNS
Efferent Nerves



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

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:
1. Multipolar
2. Bipolar
3. 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
 Voluntary
 Stimulates skeletal
muscles
 Stimulates them to
contract
Autonomic Nervous System
 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
 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)
Autonomic Reflexes
 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