Part 1
Biology 12
 An
integral part of your
body’s communication
system.
 It plays an important
role in the smooth
functioning of the
body.
 The nervous system is a
complex network of
cells which are
specialized in function.
 The
Nervous System allows the body to
respond to changes in the internal and
external environments.
 Communication comes in the form of
electrochemical messages relayed to and
from the brain, or a series of chemical
messengers carried in the blood.
 Through a series of adjustments, all systems
of the body are regulated to maintain the
internal environment within safe limits
(homeostasis).
 The
nervous system has
two main divisions:


Central Nervous System
(CNS)
Peripheral Nervous System
(PNS)
 Consists
of the nerves of the brain and spinal
cord.

Brain is known as the “cerebrum”
 Acts
as a coordinating centre for incoming
and outgoing information.
The brain consists of millions
of nerve cells that cluster
together and interact with
each other through the
process of
neurotransmission.
 It controls most of the bodily
functions like movements,
thoughts, speech, sensations
and memory.

 The
spinal cord is a
continuation of the brain
and is surrounded by the
vertebral bodies that form
the spinal column.
 The spinal cord is divided
into four main segments;
reach transferring signals to
different parts of the body.
 http://www.youtube.com/watch?v=vGxho71t
ScM&NR=1
 Consists
of nerves that carry information
between the organs of the body and the
central nervous system.
 It


can be further divided into:
Somatic nervous system
Autonomic nervous system
 Information
about your body is continuously
relayed to your brain for processing and
storage.
 The cells that transfer these messages to the
brain and around the body are nerve cells.
 Nerve
cells gather & transmits electrochemical signals.
DID YOU KNOW????
 Neurons cannot be repaired
 Some last a life time
 Approximately 1000 die each day!!!
A
nerve is a bundle of neurons attached by
connective tissue
 Average
number of neurons in the human
brain = 100 billion
 Nerve “highway” in the human body contains
100 billion neurons
 1000 impluses/sec
 SENSORY



Carries signals FROM periphery (outside) TO
central nervous system for processing
Information FROM environment
NOTE: detect external stimuli (light, sound,
touch, heat, smell, & taste) or internal
conditions (blood pressure, CO2 level & muscle
tension)
 MOTOR



Carries signals FROM central nervous system TO
body part (e.g. muscles, skin, glands)
Respond to sensory neurons
Responsible for movement
 INTERNEURONS



Connects sensory or motor neurons to central
nervous system
Carries messages in-between neurons
Majority of neurons in the brain are interneurons
 Cell

Body
Contains all organelles, including a nucleus
 Dendrites


Projections off cell bodies
Make connections with other cells
Dendrites
Cell
body
Cell body
Nucleus
Figure 27.3
 Axon


Long cable like projection off cell body
Sends messages (nerve impulses)
 Myelin



Fatty protein that covers/insulates most nerves
Increases speed of transmission
Formed by Schwann cells
 Nodes

Sheath
of Ranvier
Exposed axon between myelin sheath
Dendrites
Cell
body
Cell body
Axon
Nucleus
Nodes of
Ranvier
Myelin sheath
Figure 27.3
 Synaptic



knob
End of axon branches
Comes near dendrites of adjacent neurons
Passes messages across synapse (the space
between neurons)
Signal direction
Dendrites
Cell
body
Cell body
Nucleus
Axon
Supporting
cell
Signal
pathway
Synaptic knobs
Nodes of
Ranvier
Myelin sheath
Figure 27.3
 Moves
in only one direction
 From dendrite to cell body, axon, then
synaptic knob
Signal direction
Dendrites
Cell
body
Cell body
Nucleus
Axon
Supporting
cell
Signal
pathway
Synaptic knobs
Nodes of
Ranvier
Myelin sheath
Figure 27.3
 The
three interconnected functions of the
nervous system are carried out by the three
types of neurons
Sensory input
Sensory
neuron
Integration
Sensory receptor
Motor neuron
Interneuron
Motor output
Brain and spinal cord
Effector
Peripheral nervous
system (PNS)
Central nervous
system (CNS)
Figure 27.2
 Nervous
System explained
 Nervous System Rap
 How Neurons Work
 Draw
a large motor neuron on a
white piece of paper.
 Label
Cell body
 Nucleus
 Dendrites
 axon

 Then
Myelin sheath
 Schwann cells
 Node of Ranvier
 Synaptic knob

draw arrows to show the
message direction
 Identify the motor neuron functions
Synaptic knob