The Nervous system

The Nervous System

• Brain• Spinal cord• Nerves

• Enables you to control your body

• Gives you feedback about the world

What does it do?

What are its component parts?

Look away if you’re squeamish…

A dissected brain, spinal cord and sections of major nerves.

How the nervous system worksHow the nervous system works

For example;If you smell something burning…• Your nose (receptorreceptor) detects the stimulusstimulus

(smell)• Nerve fibresNerve fibres send the message to the brainbrain• Your brainbrain then sends a message to move

your body away or to put out the fire! SIMPLES RIGHT!SIMPLES RIGHT!

Lets look at some bits more closelyLets look at some bits more closelyRECEPTORSRECEPTORS

• Receptors are sensors on the body that detect stimuli• They convert stimuli into electrical signalselectrical signals (messages) called

impulses.

EFFECTORSEFFECTORSAn effectoreffector is any part of the body that produces the responseresponse.

Here are some examples of effectors:

• a muscle contracting to move the arm • a muscle squeezing saliva from the salivary gland • a gland releasing a hormonehormone into the blood

The Cells of the Nervous System - Neurones

NERVE FIBRESNERVE FIBRES• Nerve fibres are bundles of nerve cells (neurones)(neurones)

that pass on electrical signals (impulses)(impulses) to the brain.

• From the brain, nerve fibres send impulses to effectorseffectors (muscles).

NEURONESNEURONESThere are three types of neuronesThere are three types of neurones1.1. Sensory neuroneSensory neurone – carries impulses from the receptors to the

spinal cord.2.2. Relay NeuroneRelay Neurone – carries impulses to and from the spinal cord

and the brain3.3. Motor NeuroneMotor Neurone – carries impulses from the brain to the effector

The route impulses take

The route impulses take

Effectors –

Sensory neurone

Motor neurone

Relay neurones (in brain or spinal cord)

Left: sensory neurone

Right: motor neurone

Nerves – bundles of neurones

Sensory Receptors• Information from our environment is received

via our senses.• The Eye receives light and transfers this

information via our optic nerve to our brain.• Our Ear receives sound and via the auditory

nerve sends messages to our brain• Our Skin receives messages about temperature,

pain and pressure and via sensory nerves sends this information to our brain.

• The skin and body temperature – the skin helps to keep your body at a constant 37°C +/- 1˚C.

• Sweating, shivering, body hair and fat beneath the skin all help this. Also, capillaries in the skin surface open or close to lose heat or keep heat in.

• This vasodilation (opening) and vasoconstriction (closing) of blood vessels helps to lose or conserve body heat

Inside the eye

lens

focuses lighton retina

irisregulates amountof light entering eye

ciliary muscles

change shape of the lens

optic nerve

transmits impulses to the brain

cornea

protects eye surface and focuses light rays

retina

senses lighthold lens in place

suspensory ligaments

ACTIONACTION

The way the iris in our eye adjusts the size of the pupil in response to bright or dim light is a reflex action.

http://www.bbc.co.uk/schools/gcsebitesize/science/aqa/human/thenervoussystemrev3.shtml

In bright light

In dim light

•Radial muscles of the iris relax.

•Circular muscles of the iris contract.

•Less light enters the eye through the contracted pupil.

•Radial muscles of the iris contract.

•Circular muscles of the iris relax.

•More light enters the eye through the dilated pupil.

Reflex Reactions – bypassing the brain for extra speed

Reflex Reactions

Can you think of any?

• Startle reflex – moving away, contraction of arm and leg muscles, blinking, breathing changes

• Withdrawal reflex – moving away from potentially harmful influences (e.g. high temperature)

• Iris reflex – pupil becomes smaller in bright light

Knee Jerk Reflex

Why the knee jerk reflex?

• This reflex is quite useful for walking. Every time you put weight on your foot, your muscles contract to support you. Without this reflex, we would all look silly staggering around, having to consciously think about working our muscles for each step, but with the muscles reacting too hopelessly late to be useful. Chewing gum at the same time would be out of the question.

Endocrine System

• As well as sending and receiving messages using our nervous system, we also use our endocrine system to do the same job.

• Instead of using electrical impulses however, this system releases chemicals into our blood stem called hormones.

• These hormones are not a fast acting as nervous impulses but are longer lasting.

Endocrine Glands

Hormones

Pituitary gland – FSH, LH (stimulates the release and maturity of follicles during menstruation)

Thyroid gland – Thyroxine (regulates the rate of metabolism)Adrenal gland - corticosteroids and catecholamines including

cortisol and adrenaline and small amounts of testosterone (regulates stress levels)

Pancreas – peptides (regulates the production of shorter active digestive enzymes)

Ovary – oestrogen, progesterone and small amounts of testosterone (regulates the growth of eggs and stabilises the growing foetus during pregnancy)

Testis – testosterone (plays a key role in the health and well-being of the man)