Organisms must be aware of what is happening around them,as this affects their survival chances.

The Nervous System

A nervous system allows an organism to detect and respond to stimuli in its internal or external environment.

e.g. a flash of light, a noise, a fly landing on your nose.

A stimulus is any change in your environment

Co-ordination of an organism’s activities is carried out by the nervous system and the endocrine system.

The nervous system relies on electrical signals, carried byspecialised cells [neurons], and is involved in fast responses.

The brain keeps a check on internal organs and activities, such as the level of carbon dioxide or water in the blood.

The central nervous system (CNS) is your brain and spinal cord.

The peripheral nervous system (PNS) is the nerves branchingfrom the CNS to all parts of the body.

Comparison of the endocrine and nervous systems - 1

Target organReceived by

BloodCarried by

GlandCells involved

Cells throughout the body

Message sent to

Chemical (Hormone)

Message

Endocrine

Comparison of the endocrine and nervous systems - 1

Endocrine NervousCells involved Gland Sense receptor

Message Chemical (Hormone)

Electrical(Impulse)

Carried by Blood Nerve cell

Message sent to Cells throughout the body

A specific cell or tissue

Received by Target organ Effector (muscle or gland)

long-lasting (hours)

Duration

Can be widespreadEffects

Usually slowSpeed of transmission

Endocrine

Comparison of the endocrine and nervous systems -- 2

Endocrine NervousSpeed of transmission

Usually slow Rapid

Effects Can be widespread Localised usually

Duration long-lasting (hours)

Usually brief (seconds)

Comparison of the endocrine and nervous systems -- 2

LEARNING CHECK• Co-ordination of an organism’s activities is

carried out by what 2 body systems?• Distinguish between the CNS and PNS.• What is a neuron?• What is an impulse?• List the main differences between the

endocrine and nervous systems.

NS ----- Co-ordination & Response

An impulse is an electrical message that is carried along aneuron.

A neuron is a specialised cell that carries electrical messages(impulses) around the body.

A stimulus is any change in your environment

A receptor is a nerve cell that detects the stimulus

The cell body contains the nucleus and other organelles andproduces neurotransmitter chemicals.

The axon is a very long fibre that conducts impulses away from the cell body.

Neuron structure

A dendron is a short fibre that receives information and carries it towards the cell body.

Dendrites are small branches of a dendron.

A dendron is a short fibre that receives information and carry it towards the cell body.

Many Schwann cells wrap their fatty cell membranes around an axon, forming a myelin sheath.

The myelin sheath insulates the neuron from electrical impulses flowing in other neurons.

There are three types of Neuron :

Motor neuron –carries impulses from the CNS to muscles and glands.

Interneuron –connects sensory and motor neurons and so carries messages within the CNS.

Sensory neuron –carries messages from the sense organ to the central nervous system (CNS).

Synapse—region where two neurons come into close contact.

Synaptic cleft—the gap between two neurons, bridged by chemicals (neurotransmitters).

Neurotransmitter—chemical released across a synaptic cleft tocarry a signal from one neuron to another.

SYNAPSE

The chemical is then destroyed or removed

LEARNING CHECK• What is a stimulus?• What is a receptor?• Name the main parts of a neuron and give

one function of each.• Distinguish between a sensory and motor

neuron.• Distinguish between synapse and synaptic

cleft.• What are neurotransmitters?

The brain is composed of over 100 billion neurons, eachreceiving messages simultaneously from thousands of otherneurons.

The brain is protected by the skull bones, meninges (three membranes) and cerebrospinal fluid.

The Brain

Conscious actionsA conscious action is one where the brain makes a considered response. Here’s what happens:

Stimulus Receptor Sensory Neuron Coordinator Motor Neuron Effector Response

1) Receptors in your skin detect a stimulus

3) Here another sensory neuron carries the signal to the brain

4) The brain decides to move away the hand

5) This impulse is sent by MOTOR NEURONS to the hand muscles (the effectors) via the spinal chord…

2) The impulse is carried by SENSORY NEURONS to the spinal chord

6) Which then moves the hand away

The cerebellum co-ordinates processes that we have learned to do automatically, such as speaking.

The medulla oblongata co-ordinates involuntary, automatic processes — such as breathing, heartbeat.

cerebellumMedulla oblongata

LEARNING CHECK• Name the 3 main parts of the brain and one

function of each.• How is the brain protected?• What is meant by “conscious action”?• What does the term “involuntary” mean?• Distinguish between the cerebrum and the

cerebellum.

The spinal cord is well protected by the vertebrae, meninges (three membranes) and cerebrospinal fluid.

It transmits impulses to and from the brain and controls many reflex actions.

A cross-section through the spinal cord shows a small central canal, filled with cerebrospinal fluid, surrounded by an area of grey matter, shaped somewhat like the letter H.

Outside the grey matter, the spinal cord consists of white matter (containing axons only).

Grey matter contains cell bodies and dendrites (regions of a neuron that have no white myelin covering).

In humans, 31 pairs of spinal nerves branch off from the spinal cord.

The dorsal root ganglion is a swelling that consists of the cell bodies of the sensory neurons.

Each spinal nerve has a dorsal root and a ventral root.

The dorsal root consists of nerve fibres carrying information into the spinal cord from the senses.

The ventral root consists of nerve fibres carrying information out from the spinal cord, to the muscles and glands.

The cell bodies of the motor neurons are positioned within the grey matter of the cord.

The spinal cord transmits impulses to and from the brain and controls many reflex actions.

A reflex action is a quick, automatic response to a particular stimulus.

Interneuron

REFLEX ACTION --- The Reflex Arc

Suppose you touch a hot flame.

In this brief instant, a message has been carried by a sensory neuron from pain receptors in the skin to the spinal cord.

Almost instantly you pull your hand away.

Interneuron

REFLEX ACTION --- The Reflex Arc

In the spinal cord, the message is passed on to an interneuron and then to a motor neuron, and so into muscles that respond by contracting and pulling your hand from the flame.

Interneuron

The response is called a reflex action, as it does not involve conscious control, and is predictable and automatic.

Many of the activities of the body, such as breathing and keeping our balance, are regulated by reflex actions.

This response saves the body from injury.

Interneuron