The Sensory System

awareness of and response to our surroundings through the sense organs

OB28 recall five sense organs in the human (eyes, ears, nose, skin, and tongue) and understand how these enable humans to gather information from their surroundings

there is a hidden link in the OB above, dont worry about finding it ...... cos its here ..... Sense organs

Response times

from the BBC

The nervous system allows the body to respond, through effectors, to changes in the environment detected by receptors. The process involvesneurones, and is usually coordinated by the brain. A reflex action is an extra-rapid response to a stimulus, and this process also involves the nervous system, but it bypasses the brain.

The iris of the eye is a receptor, which adjusts itself according to the amount of light entering the eye. Accommodation is the ability of the eye to bring objects into focus.

The brain can be damaged by accidents or illness, such as strokes and Parkinson's disease.

Receptors and effectors


Receptors are groups of specialised cells. They can detect changes in the environment, which are called stimuli, and turn them into electrical impulses. Receptors are often located in the sense organs, such as the ear, eye and skin. Each organ has receptors sensitive to particular kinds of stimulus.

We have 5 main types of Receptors, can you name them?


An effector is any part of the body that produces the response. Here are some examples of effectors:

Muscles are the usual Effectors (they cause an effect)

  • Muscles cause motion of the limbs.
  • Muscles squeeze glands to secrete the hormones.
  • Glands release hormones.

sensory and motor function of nerves

communication between the sense organs and the brain

structure of the eye and functions of the parts of the eye

OB29 describe the role of the central nervous system and the sensory and motor functions of nerves

The Nervous system

1. The central nervous system (CNS) consists of

• the brain

• the spinal cord

2. The peripheral nervous system (PNS) consists of nerves that carry impulses to and from the CNS.


A neuron is a nerve cell.

There are three types of neurons

1. Sensory neurons: carry impulses from sense organs to the CNS

2. Motor neurons: carry impulses away from the CNS to muscles and glands.

3. Interneurons: carry impulses within the CNS.

Neurones are nerve cells, there are 3 different types of nerve cells that transmit messages from one part of the body to another part of the body

  • Sensory neurones
  • Relay neurones
  • Motor neurones

Sensory neurones

Detect changes in our environment and send a message to the brain. Messages come from your eyes, ears, nose and skin to our brains, our brains make decisions based on the information it gets.

Relay neurones

Messages travel to & from the brain along Relay Neurones

Motor neurones

Sends messages back to muscles to cause motion.

A map of the nerves in the body!


Where two neurones meet, there is a tiny gap called a synapse. Signals cross this gap using chemicals. One neurone releases the chemical into the gap. The chemical diffuses across the gap and makes the next neurone transmit an electrical signal

Reflex actions

When a receptor is stimulated, it sends a signal to the central nervous system, where the brain co-ordinates the response. But sometimes a very quick response is needed, one that does not need the involvement of the brain. This response is known as a reflex action.

Reflex actions are rapid and happen without us thinking. For example, you would pull your hand away from a hot flame without thinking about it.

This is what happens:

  • Receptor detects a stimulus (change in the environment).
  • Sensory neurone sends signal to relay neurone.
  • Motor neurone sends signal to effector.
  • Effector produces a response.

The brain - higher

The brain can be damaged by accidents or illness. When this happens, its functions can be impaired. For example, a bang on the head can cause concussion and blurred vision.

Brain tumours

A brain tumour happens when cells in the brain grow and divide uncontrollably or when cancer cells from cancer cells from other parts of the body, such as the lung or the breast, spread to the brain. The tumour damages the brain and causes it to press against the skull. This causes symptoms such as headaches, double vision, trembling and personality changes.


A stroke happens when a part of the brain does not get enough oxygen and is damaged. This can happen if a blood vessel in the brain bursts or gets a blood clot. Unlike most other cells, brain cells cannot re-grow and permanent damage and even death can be caused.

The symptoms depend on which part of the brain was damaged. They can include:

  • numbness and poor reflexes
  • difficulty in walking
  • loss of speech, memory or use of limbs - usually on one side of the body


During a party, a friend stumbled and took a little fall - she assured everyone that she was fine and just tripped over a brick because of her new shoes. (they offered to call ambulance)

They got her cleaned up and got her a new plate of food - while she appeared a bit shaken up, Ingrid went about enjoying herself the rest of the evening. Ingrid's husband called later telling everyone that his wife had been taken to the hospital - (at 6:00pm , Ingrid passed away.)

She had suffered a stroke at the party . Had they known how to identify the signs of a stroke, perhaps Ingrid would be with us today.

Some don't die. They end up in a helpless, hopeless condition instead. It only takes a minute to read this...


A neurologist says that if he can get to a stroke victim within 3 hours he can totally reverse the effects of a stroke...totally. He said the trick was getting a stroke recognized, diagnosed, and then getting the patient medically cared for within 3 hours, which is tough.


Remember the '3' steps, STR . Read and Learn!

Sometimes symptoms of a stroke are difficult to identify. Unfortunately, the lack of awareness spells disaster.

The stroke victim may suffer severe brain damage when people nearby fail to recognize the symptoms of a stroke.

Now doctors say a bystander can recognize a stroke by asking three simple questions :

S * Ask the individual to SMILE ..

T * = TALK. Ask the person to SPEAK A SIMPLE SENTENCE (Coherently) (eg 'It is sunny out today').

R * Ask him or her to RAISE BOTH ARMS .

If he or she has trouble with ANY ONE of these tasks, call the ambulance and describe the symptoms to the dispatcher.

NOTE : Another 'sign' of a stroke is

1. Ask the person to 'stick' out their tongue.

2. If the tongue is 'crooked', if it goes to one side or the other that is also an indication of a stroke.

Parkinson's disease

Parkinson's disease is caused by a reduced amount of dopamine, a chemical involved in transmitting nerve impulses from one neurone to another in the brain. It gradually gets worse and symptoms include:

  • trembling and stiffness
  • slowed movements
  • difficulty speaking and swallowing

A Nervous System Disorder:

Parkinson’s Disease


A failure to produce a neurotransmitter called dopamine causes Parkinson’s disease.

This failure occurs in a tiny section of the brain that controls muscle movment.

The reasons for failing to produce dopamine are not known.

The disease is most common in older people and males.


• Trembling hands and legs

• Stiff muscles

• Difficulty walking


Because the cause is unknown there is no way to prevent or cure the disease.


Treatment involves exercises and the use of special aids.

Drug treatment works only for a short time and is not always effective.

There are hopes that stem cells may provide a cure.


Epilepsy is caused by sudden bursts of unusual activity in the brain. This makes the brain stop working properly for a short time. It can cause the person to become unconscious and their body shakes repeatedly. This type of seizure is called a tonic-clonic seizure, which used to be called a grand mal seizure.