NERVOUS SYSTEM

Part 1Biology 12

THE NERVOUS SYSTEM 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.

HOMEOSTASIS & NERVOUS SYSTEM 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).

TWO DIVISIONS... The nervous system has

two main divisions: Central Nervous System

(CNS)Peripheral Nervous

System (PNS)

CENTRAL NERVOUS SYSTEM 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 CEREBRUM (BRAIN) 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 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.

VIDEO CLIP http://

www.youtube.com/watch?v=vGxho71tScM&NR=1

PERIPHERAL NERVOUS SYSTEM 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 systemAutonomic nervous system

NERVE CELLS

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.

CELLS OF THE NERVOUS SYSTEM Nerve cells gather & transmits electro-

chemical signals.

DID YOU KNOW???? Neurons cannot be repaired Some last a life time Approximately 1000 die each day!!!

NERVE VS NEURONS A nerve is a bundle of neurons attached

by connective tissue

NEURON NOTABLES Average number of neurons in the

human brain = 100 billion Nerve “highway” in the human body

contains 100 billion neurons 1000 impluses/sec

TYPES OF NEURONS SENSORY

Carries signals FROM periphery (outside) TO central nervous system for processing

Information FROM environmentNOTE: detect external stimuli (light, sound,

touch, heat, smell, & taste) or internal conditions (blood pressure, CO2 level & muscle tension)

TYPES OF NEURONS MOTOR

Carries signals FROM central nervous system TO body part (e.g. muscles, skin, glands)

Respond to sensory neuronsResponsible for movement

TYPES OF NEURONS INTERNEURONS

Connects sensory or motor neurons to central nervous system

Carries messages in-between neuronsMajority of neurons in the brain are

interneurons

PARTS OF A NEURON Cell Body

Contains all organelles, including a nucleus

DendritesProjections off cell bodiesMake connections with other cells

Figure 27.3

Dendrites

Cell body

Nucleus

Cell body

PARTS OF A NEURON Axon

Long cable like projection off cell bodySends messages (nerve impulses)

Myelin SheathFatty protein that covers/insulates most

nerves Increases speed of transmission Formed by Schwann cells

Nodes of RanvierExposed axon between myelin sheath

Figure 27.3

Dendrites

Cell body

Nucleus

Axon

Myelin sheath

Nodes of Ranvier

Cell body

PARTS OF A NEURON Synaptic knob

End of axon branches Comes near dendrites of adjacent neuronsPasses messages across synapse (the space

between neurons)

Figure 27.3

Signal direction Dendrites

Cell body

Nucleus

AxonSupportin

g cell

Myelin sheath

Signal pathway

Nodes of Ranvier

Synaptic knobs

Cell body

DIRECTION OF MESSAGE Moves in only one direction From dendrite to cell body, axon, then

synaptic knob

Figure 27.3

Signal direction Dendrites

Cell body

Nucleus

AxonSupportin

g cell

Myelin sheath

Signal pathway

Nodes of Ranvier

Synaptic knobs

Cell body

NEURONS IN ACTION The three interconnected functions of

the nervous system are carried out by the three types of neurons

Sensory input

Sensory receptor

Sensory neuron

Integration

Interneuron

Brain and spinal cord

Central nervous system (CNS)

Motor neuron

Motor output

Peripheral nervous system

(PNS)

Effector

Figure 27.2

LET’S REVIEW: VIDEO CLIPS Nervous System explained Nervous System Rap How Neurons Work

TASK Draw a large motor neuron on a

white piece of paper. Label

Cell bodyNucleusDendritesaxon

Myelin sheathSchwann cellsNode of RanvierSynaptic knob

Then draw arrows to show the message direction

Identify the motor neuron functions

MOTOR NEURONSynaptic knob