Body in Action Subtopic (C) Coordination

Judging distance The judgement of distance is more accurate using two eyes rather than one eye

leftright Binocular vision CREDIT When two eyes are situated at the front of the head, facing forward……. …….. the image formed on the retina of each eye is different. This is called Binocular Vision

With binocular vision, the two images are joined together by the brain …… and a more accurate judgement of distance. ….producing a three – dimensional picture, giving an appreciation of depth, This is an advantage to predators as it allows them to judge the distance of their prey. Binocular vision CREDIT

Retina Optic Nerve Lens Iris Pupil Cornea Controls amount of light entering the eye by altering size of pupil Allows light to enter Allows light to enter and begins to bring it to a focus Focuses light on to retina Converts light to nerve impulses Carries nerve impulses from retina to brain

F F L L lenspupil Objects focussed on the retina are upside down and back to front CREDIT

Optic nerve Carries nerve impulses from retina to brain

Focussing Ciliary muscle fibres CREDIT

In bright conditions the muscles of the iris make the pupil smaller to prevent too much light entering. In dark conditions the muscles of the iris make the pupil larger to allow more light in.

The Blind Spot If light from an object lands on the retina ….. ….. we see it If light from an object lands on the optic nerve ….. …. we don’t see it Where the optic nerve leaves the eye there are no light sensitive cells, so ….. CREDIT

The Ear

Middle ear bones Semi-circular canals ♫ Outer ear canal Ear drum Cochlea Auditory nerve Eustachian tube (to back of throat) Structure Outer ear Middle ear Inner ear The outer + middle ear are air-filled, the inner ear is liquid-filled BONE Judgement of the direction of sound is more accurate with two ears rather than one

PartFunction Ear drum Vibrates when sound waves reach it Middle ear bones Carry the vibrations from the ear drum to the liquid-filled inner ear Cochlea Receptor cells convert sound vibrations in the liquid to nerve impulses Auditory nerve Carries nerve impulses from the cochlea to the brain Semi-circular canals Balance

Semi-circular canals There are 3 semi-circular canals at right angles to each other… … so whichever direction the head moves, at least 1 is stimulated.

The 3 directions detected are; 1.Up and down (nodding head) 2.Rotating (shaking head) 3.Side to side (ear down towards shoulder) CREDIT

The 3 directions detected are; 1.Up and down (nodding head) 2.Rotating (shaking head) 3.Side to side (ear down towards shoulder) CREDIT The semi circular canals are at right angles so that movement can be detected in all directions

The Nervous System The nervous system consists of the brain, spinal cord and nerves. Brain Spinal cord Nerves The brain and spinal cord make up the central nervous system (CNS).

Nerves ( neurones ) Nerves carry information from the senses to the central nervous system (CNS), and from the central nervous system to the muscles. The central nervous system sorts out information from the senses and sends instructions to muscles, which respond by contracting, and therefore make the appropriate response. Sense organ muscle CNS Sensory nerve Motor nerve (containing receptor cells) (effector)

Nerves are made up of many nerve cells. Some nerve cells are stretched out into long, thin fibres that can be over 1 metre long. Nerve impulses travel along nerve fibres in one direction. There are 3 types of nerve cells; 1. Sensory nerve cells 2. Motor nerve cells 3. Relay nerve cells

Sensory nerve cells These carry nerve impulses from the sense organs to the CNS. Receptor cell (inside sense organ) Cell body Direction of nerve impulse

Motor nerve cells These carry impulses from the CNS to the muscles, causing them to contract. Cell body Muscle (effector organ) Direction of nerve impulse

Relay nerve cell These are nerve cells in the spinal cord which connect motor nerve cells to sensory nerve cells. They are involved in reflex actions. Where they allow nerve impulses to pass straight through the spinal cord, bypassing the brain. Cell body Direction of nerve impulse

Reflex Action A reflex action is a rapid, automatic response to a stimulus. A stimulus is a factor detected by a receptor in a sense organ, that sets off the transmission of a nerve impulse. A reflex action is an involuntary action which does not always involve the brain. Reflex actions happen so fast that there is no time for the nerve impulse to reach the brain – often only the spinal cord is involved. CREDIT

Reflex arc A reflex arc is the simple arrangement of nerve cells which bring about a reflex action. Nerve cells don’t actually join together, there are gaps between them called synapses. A nerve impulse travelling from one nerve cell to another is carried across this gap by chemical messengers. CREDIT

Reflex arc Receptor detects stimulus Impulse sent along sensory nerve to spinal cord Impulse sent along motor nerve to muscle (effector) Muscle responds by contracting Impulse sent along relay nerve in spinal cord synapse CREDIT

Example of reflex arc – touching something hot; sensory nerve CREDIT

The Brain The brain controls the whole body and coordinates all nerve impulses. It sorts out information from the sense organs and sends instructions to the muscles. There are 3 main parts to the brain. cerebrum cerebellum medulla CREDIT

Longitudinal section through brain (releases hormones eg. ADH - see ‘kidney’) CREDIT

PartFunction cerebrum cerebellum medullacontrols heart rate and breathing controls muscle coordination and balance controls memory, reasoning, intelligence, imagination, it analyses sensory information and sends out motor impulses to muscles CREDIT

The cerebrum is in two parts, called the left and right cerebral hemispheres. Each performs different functions.