Nervous System


The Nervous system

: the network of nerve cells and fibres which transmits nerve impulses between parts of the body. It enables humans to react to their surroundings and coordinate their behaviour.

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Advantages of being sensitive to the environment

  • You can protect yourself from danger
  • You can detect change in temperature and reacting appropriately
  • You can move away from danger
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: a thing or event that evokes a specific functional reaction in an organ or tissue.

2 different types

physical – touching something sharp

chemical – eating a poisoned berry

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: an organ or cell able to respond to light, heat, or other external stimulus and transmit a signal to a sensory nerve.

Receptors are transducers, this means they convert one form of energy into another.

Light energy stimulates the eye and is converted into electrical energy that can be sent along a sensory neurone as an impulse.

Sense Organ                Stimulus

Ears                               Sound

Eyes                              Sight

Tongue                          Taste

Nose                             Scent

Skin                              Touch, Pressure, Pain

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The Brain

·      the cerebral cortex is concerned with consciousness, intelligence, memory and language

·      the cerebellum is concerned mainly with the coordination of muscular activity

·      the medulla is concerned with unconscious activities such as heart beat and breathing

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Nerves and neurones

This is what happens:

  1. receptor detects a stimulus - change in the environment
  2. sensory neurone sends signal to relay neurone
  3. It reaches a synapse, which triggers a chemical to diffuse across the synapse and trigger the production of another impulse.
  4. motor neurone sends signal to effector
  5. synapse
  6. effector produces a response

Stimulus---> Receptor ---> Sensory ---> Relay ---> Motor ---> Effector

Sensory neurones carry signals from receptors to the spinal cord and brain. Relay neurones carry messages from one part of the CNS to another. Motor neurones carry signals from the CNS to effectors.

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Reflex Arc

reflex arc is the nerve pathway which makes such a fast, automatic response possible.


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1.Impulse reaches the end of the first neurone

2.Initiates the release of a neurotransmitter (chemical) substance from tiny sacs at the end of the first neurone

3.the neurotransmitter diffuses across the synapse and causes a ne impulse to be generated in the second neurone


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The Endocrine system

The endocrine system is the collection of glands that produce hormones that regulate metabolism, growth and development, tissue function, sexual function, reproduction, sleep, and mood, among other things.


A gland is an organ that secretes a substance (i.e. hormone).  There are two kinds of glands:

Exocrine – secretes into a tube or duct which then passes to where it is needed. (i.e. salivary glands)

Endocrine – secretes into a blood vessel that passes through the gland.

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Hormones are chemicals, produced by endocrine or exocrine glands, which travel in the blood to a target organ and produce an effect.

Hormones only affect particular tissues or organs in the cells of that tissue or organ have special chemical receptors or that particular hormone.

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Nervous System vs Endocrine

Speed        Nervous system- milliseconds 

                  Endocrine- hours/days

Nature       Nervous system- electrical impulses

                  Endocrine- chemical

Duration    Nervous- quick, short lived

                  Endocrine- long lasting

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