Coordination and Response (Bio IGCSE)

IGCSE biology

Central nervous system

Coordinates the messages travelling along the nervous system

Neurons (as electrical impulses)

Information carried by the Nervous system travel through

Dendrites

Short fibers that pick up electrical signals from the other neurons lying nearby

Axon

Long fiber carrying information away from body cells

Cell body

Controls the metabolism of nerve cell

Myelin sheath

Layers of fats covering axon

Why does the Mylin sheath cover the axon?

• Speeds up nerve impulse

• Protects nerve fiber

• Prevent leakage of electrical signals

Motor end plate

Passes the electrical signals to another nerve cell

Synapse

The junction between two nerve cells with a minute gap between the nerve cells across which impulses pass by diffusion of neurotransmitters

How does synapse act like a one-way valve?

As there are neurotransmitters and receptors on only one side of the synapse, so the impulse can only pass from that side. This prevents the backward flow of impulses

Sensory Neuron

• Carries electrical impulses from receptors to the Central Nervous system

• One direction

• Myelin sheath

• Cell body in the middle of the cell

• Short Axons

Sensory neuron location

Present in Ganglion (group of neuron cell bodies in P.N.S)

Relay neuron

• Carries electrical impulses from sensory neuron to motor neuron in C.N.S

• No Myelin Sheath

Relay neuron location

C.N.S present in grey matter in spinal cord

Why doesn’t the Relay neuron have Myelin sheath?

So the impulses can be carried slowly across spinal cord

Motor Neuron

• Carries electrical signal from the C.N.S to the effector organ showing response

• Myelin sheath

• Cell body present at one end of the cell

Motor neuron location

grey matter of the spinal cord

Stimulus

change in the internal or external environment of the body

Receptors

Parts of the body that can detect the Stimulus and convert it to an electrical impulse

Effector organ

• Muscle to contract

  OR

• Gland to secrete

Reflex Action

It’s involuntary, protective and rapid response to a stimulus. The Reflex Action message gets from the receptors to the effector very quickly. The function of the reflex action is protection of the body from mechanical damage or injury. The center is located in the spinal cord.

Examples of Reflex Actions

• Stimulus —→ Hot Pan

  Response —→ Muscles in arm contract so the hand pulls away

• Stimulus —→ Bright light falling on Retina

  Response —→ Contraction of circular muscles of Iris

Voluntary Action

Non-automatic action that requires a conscious decision by the Brain

Involuntary Action

Automatic action that doesn’t involve a conscious decision by the brain

Sense organs

Organs containing group of receptor cells responding to a specific stimulus

Sense organs examples

1. Eyes

   Receptor —→ Photo receptors

   stimulus —→ Light

2. Ear

   Receptor —→ Sound receptors

   stimulus —→ Sound

3. Nose/Tongue

   Receptor —→ Chemoreceptors

   stimulus —→ Chemicals

4. Skin

   Receptor —→ Skin receptors

   stimulus —→ Temperature, Touch, Pressure and Pain

Conjunctiva

Thin, transparent membrane that protects the cornea

Cornea

Transparent layer which allows light to penetrate eye and bends the light rays that enter

Aqueous humor

Water fluid that supports the Cornea and Front chamber of eye

Iris

Colored part of the eye that controls the amount of light that enters by controlling the pupil’s diameter to protect the retina from excess light

Pupil

Circular opening that allows light to enter, appears black because the choroid is visible

Sclera

Tough outer layer that protects eye from damage

Lens

Changes shape to focus light into the retina

Accommodation

A reflex that changes the refractive power of the lens