Objectives – What you will need to know from this section

Objectives – What you will need to know from this section

Outline the nervous system components: central nervous system (CNS) and the peripheral nervous system (PNS)

Receptor messages are carried through these systems by nerve cells or neurons.

Outline the structure & function of the neuron including:cell body, dendrites, axon, myelin sheath, schwann cell, and neurotransmitter vesicles & synaptic cleft

Outline impulse movement & synapse. Explain activation & inactivation of

neurotransmitter.

Responses in the Human Nervous System

1

The structure and function of a neuron: variation in size and shape.

Neuron -- Three part structure:> dendrite(s) receive information and carry it towards the cell body,> the axon conducts nerve impulses away from the cell body,> the cell body contains the nucleus and other organelles and produces neurotransmitter chemicals.

Explain the role & position of 3 types of neuron -- sensory/motor/inter

2

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

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.

LEARNING CHECK• Co-ordination of an organism’s

activities is carried out by what body system?

• Distinguish between the CNS and PNS.

• What is a neuron?• What is an impulse?

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

The cerebrum is our conscious brain, with different parts havingdifferent jobs to do.

The pituitary ‘[master] gland secretes hormones that stimulateother glands to release their hormones.

The hypothalmus is the centre for the regulation of the internal organs.

cerebrumhypothalamus

pituitary

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.

SENSE ORGANS

Animals have specialised senses to provide them with information about their environment.

The five senses are sight, hearing, touch, taste and smell.

A receptor is a cell that can detect a stimulus A stimulus is any change in your environment, e.g. light,

sound.

Smell

Taste

Touch

Hearing

Sight

Sense

Smell

Taste

Touch

Hearing

Sight

Sense

Nose

Tongue

Skin

Ear

Eye

Organ

Smell

Taste

Touch

Hearing

Sight

Sense

Nose

Tongue

Skin

Ear

Eye

Organ

chemicals [receptors in the nasal cavity detect vapours]

chemicals [taste buds detect sweet, sour, salt and bitter].

touch, pressure, temperature and pain [receptors spread throughout body]

sound [receptors in cochlea]

light [by rods and cones in the retina]

Stimulus detected