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The Nervous System
Chapter 13.1
Pages 408-414
Introduction
The Organization
of the Nervous System
A)
Introduction
The Organization of the Nervous System
Nervous System
Central Nervous System
Brain
Peripheral Nervous System
Spinal Cord
Autonomic Nerves
Somatic Nerves
Involuntary
Voluntary
Sensory
Motor
Sympathetic
Sensory
Motor
Parasympathetic
Sensory
Motor
Introduction
The Organization of the Nervous System

the Central Nervous System (CNS)

consists of:
 the
nerves of the brain
 the spinal cord

acts as a coordinating centre for incoming and
outgoing information
Introduction
The Organization of the Nervous System

the Peripheral Nervous System (PNS)
 consists of nerves that carry information
between the organs of the body and CNS
 is subdivided into:
 the somatic nerves
 the autonomic nerves.
Introduction
The Organization of the Nervous System

the somatic nervous system controls skeletal
muscle, bones, and skin
 sensory somatic nerves relay information
about the environment to the CNS
 motor somatic nerves initiate a response
Introduction
The Organization of the Nervous System
 the
autonomic nervous system
 controls involuntary actions of the
smooth muscles and heart and glands
 a system of two types of nerves that
oppose each in action (parasympathetic
versus sympathetic)
 Video
Anatomy of a Nerve Cell
Anatomy of a Nerve Cell

The nervous system has two different types of
cells: glial (neurological) cells and neurons.

glial cells are nonconducting cells
 important for the
structural support
and metabolism of
the nerve cells.
 glial comes from the
Greek word for
“glue”

neurons are
 the functional units of the nervous system
 a cell that conduct nerve impulses

all neurons contain:
 cell bodies
 dendrites
 axons.
Anatomy of a Nerve Cell
Anatomy of a Nerve Cell

cell body
 main part of the neuron that contains the nucleus
 processes input from the dendrites and relays it to
the axon.

dendrites
 receive information, either from the environment or
other neurons.
 is an extension of cytoplasm that conduct nerve
impulses toward the cell body
Anatomy of a Nerve Cell

axon
 is an extension of cytoplasm that
carries the nerve impulses away
from the cell body.
 a neuron has one axon that can
form many branches.
 an axon carries impulses
towards other neurons or to
effectors.
 most nerves are made up of
many axons held together by
connective tissue.
Anatomy of a Nerve Cell
Anatomy of a Nerve Cell

myelin sheath
 a white coating of fatty protein
that covers the axon.
 produced by Schwann Cells in
the PNS
 produced by oligodendrocytes
in the CNS
 acts as an insulator preventing the
loss of charged ions from the
nerve cells – signal travels faster!
 an axon is said to be myelinated if
it has a myelin coating
Anatomy of a Nerve Cell
Medical Break ~Multiple Sclerosis (MS)~
 Multiple sclerosis is a disease in which the myelin degenerates.
 It is currently thought that T cells, plays a key role in the
development of MS.
 The axons themselves can also be damaged by the attacks.
 Symptoms of MS usually appear in episodic acute periods of
worsening (relapses) or in a gradually-progressive deterioration of
neurologic function, or in a combination of both
Anatomy of a Nerve Cell
Anatomy of a Nerve Cell
Anatomy of a Nerve Cell

nodes of Ranvier
 the areas between the sections of myelin sheath
 nerve impulses jump from one node to another
which speeds up the movement of nerve impulses.
 nerve impulses move much faster along
myelinated nerve fibres than nonmyelinated ones.
 speed is also affected by axon diameter, the
larger the diameter the faster the axon.
Anatomy of a Nerve Cell

neurilemma
 a thin outer membrane
around the axon, found in all
nerves of the peripheral
nervous system
 formed by the Schwann cells
and promotes the
regeneration of the damaged
axons.
 this is how feeling returns
to areas that have been
cut (only PNS!).
Anatomy of a Nerve Cell
 white
matter (white from myelination) in
the brain and grey matter (no myelin
sheath) in the brain and spinal cord lack
neurilemmas.
 this is why CNS injuries are usually
permanent.
Anatomy of a Nerve Cell
Anatomy of a Nerve Cell
Dendrites
Stimulus
Presynaptic Cell
Nucleus
Cell
body
Axon
hillock
Axon
Synapse
Synaptic terminals
Postsynaptic Cell
Neurotransmitter
Introduction to
Information Processing
Introduction to Information Processing

there are three stages in information processing:
 sensory input
 integration
 motor output
Introduction to Information Processing

sensory input
 sensory (also called afferent) neurons
transmit information from sensory
receptors that detect external stimuli
(light, sound, touch, heat, smell and taste)
and internal stimuli
 the cell bodies of sensory neurons are
located in clusters called ganglia which are
located outside the spinal cord.
Introduction to Information Processing

Integration
 interneurons (also called association neurons)
link neurons to other neurons.
 interneurons are only found in the brain and
spinal cord.
 the majority of neurons in the brain are
interneurons.
 interneurons integrate and interpret the sensory
information and connect sensory neurons to
outgoing motor neurons.
Introduction to Information Processing

motor output
 motor neurons (efferent neurons) relay
information to the effectors.
 effectors are the cells or organs that
respond to the external stimulus.
Example: muscles, organs and
glands.

Introduction to Information Processing
Sensor
Sensory input
Integration
Effector
Motor output
Peripheral nervous
system (PNS)
Central nervous
system (CNS)
Introduction to Information Processing
Introduction to Information Processing
Reflex Arc
 reflexes are involuntary and often
unconscious
 the simplest nerve pathway is the reflex arc.
 a neural circuit through the spinal cord
that provides a framework for a reflex
action.
 usually does not involve the brain.
Introduction to Information Processing
 contains





five essential components:
a sensory receptor
sensory neurons
interneurons (found in the spinal
cord usually)
motor neurons
the effector
Introduction to Information Processing
Introduction to Information Processing
 example
of a reflex arc: Patellar Reflex
 stimulus: tapping the tendon below the
kneecap
 sensory receptors: detect the slight
stretching of the tendon.
Introduction to Information Processing
 the
impulse travels down the sensory
neuron to the spinal cord. (from the PNS 
CNS)
 the CNS relays a message back to PNS along
two motor neurons.
 the impulse causes the quadriceps to
contract and hamstring to relax.
 this causes your lower leg to rise.
C) Introduction to Information Processing
Try it!

Questions 1-5 page 414