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WHAT IS COMMUNICATION?

• Communication involves an interaction that transmits information from one organism to another.

• Communication is most developed in social species such as humans.

• Humans and other animals are able to detect a range of stimuli from the external environment, some of which are useful for communication

RESPONSE TO A STIMULUS

Stimulus ReceptorMesseng

er Effector Response

Stimulus ----- change in the environment

Receptor ----- detects the stimulus. Each sensor receptor is responsible for detecting a certain stimulus (smell, taste, sound, light, etc.)

Messenger ----- receptors change the energy of the stimulus that is used to start a nerve impulse. The nerve impulse is the messenger.

Effector ----- organs that receive the messages and carry out the Response

HERE’S AN EXAMPLE OF A RESPONSE PATHWAY:

STIMULUS

Light reflected off the food entering the rabbit’s eye.

RECEPTOR

Receptor cells within the eye convert the light energy into a chemical signal.

MESSENGER

Chemical signal sent through the optic nerve to nerve cells around the body.

EFFECTOR

Nerve cells send message to muscles in the body to contract and flex.

RESPONSE

Rabbit hops towards food.

SENSESThe importance of each of the senses

differs from animal species to animal species. The range of senses include:

• Visual (sight)

• Olfactory (smell)

• Auditory (sound)

• Tactile (touch)

• Taste

• Other senses – senses to detect electric fields (platypus bill), magnetic fields and polarized light (bees) and gravity.

VISUAL COMMUNICATION

STRUCTURE OF THE EYE

FUNCTIONS OF THE STRUCTURES

conjunctiva - membrane; protects the cornea at the front of the eyeball against friction

cornea - transparent to admit light; refracts light to help form an image on the retina

sclera - the white of the eye, a tough coat of fibres; protects the eyeball against mechanical damage, maintains shape of eyeball

choroid - a membrane containing pigment and blood vessels; nourishes retina and prevents internal reflection

retina - contains light-sensitive receptor cells connected to sensory neurones; detects light

iris - a pigmented muscular structure; contracts and dilates to adjust the amount of light entering the eye

lens - a flexible transparent structure which allows light to enter the rear of the eye; refracts light to allow fine focusing of an image onto the retina

aqueous humor - a watery fluid; maintains the shape of the eye

vitreous humor - a jelly-like fluid; maintains the shape of the eye

ciliary body - contains muscles; supports the lens and alters the shape of the lens

optic nerve - consists of bundles of sensory neurons; transmits impulses generated in the retina to the brain

OUR VISUAL SPECTRUM

• The human eye can detect wavelengths between 380nm (violet light) and 750 nm (red light).

ANIMAL SPECTRUM

• Other vertebrates can detect different ranges of electromagnetic ranges compared to humans, however many cannot distinguish different colours.

• Pit vipers can detect infra-red radiation and therefore can hunt at night and detect endothermic prey.

ANIMAL SPECTRUMS

• Some invertebrates can also detect different ranges, for example, bees can detect UV light and as a result can often see patterns on flowers that humans cannot.

REFRACTION OF LIGHT

• Refection occurs when light passes from one medium to another at an angle other than 90 degrees.

• If light rays pass from the air into a denser transparent medium (e.g. glass) they will slow down.

REFRACTIVE MEDIA IN THE EYE

• The cornea, aqueous humour, lens and vitreous humour are all refractive medias that cause light to bend when it enters them.

ACCOMODATION

• Accommodation is focusing on objects at different distances. It is achieved by changing the shape and curvature of the lens.

• It enables the organism to see very close objects or distant objects, e.g. detecting predators, food sources etc.

LENS TYPES

MYOPIA

Myopia is short-sightedness. A person with myopia sees objects that are close clearly but objects in the distance are out of focus. Rays from distant objects are focused in front of the retina rather than on the retina.

HYPEROPIA

Hyperopia is long-sightedness. A person with hyperopia sees objects that are in the distance clearly but close objects are out of focus. Rays from distant objects are focused behind the retina rather than on the retina.

MYOPIA CORRECTION

Myopia can be corrected with concave lenses worn for distance viewing. These lenses cause parallel rays to diverge slightly before they enter the eye so that the lens can focus them on the retina.

HYPEROPIA CORRECTION

Hyperopia can be corrected with convex lenses worn for viewing close objects. These lenses cause parallel light rays to converge slightly before entering the eye so that the lens can then converge the rays to a point on the retina.

PHOTORECEPTOR CELLS

• Photoreceptor cells contain light sensitive pigments.

• These cells convert light into electrochemical signals that the brain can interpret.

• An electrochemical signal consists of a wave of sodium and potassium ions which move across the cell membrane of the neurone.

ROD CELLS

Rods are long rod-shaped cells, which are sensitive to low levels of light but are unable to discriminate between colours.

The image formed by the brain using information from rod cells lacks detail.

CONE CELLS

• Cones are conical cells which contain a pigment which is only sensitive to high intensities of light but exist in three different forms so that these cells can distinguish between colours.

• They have extensive nerve connections with the brain and produce a more detailed image.

• The number of cones increases towards the centre of the back of the retina.

RHODOPSIN

• Rhodopsins are light-sensitive pigments.

• When light enters a rod cell, it splits rhodopsin molecules into its two components. This reaction results in an impulse in the neurone attached to the rod or cone.

• The two products slowly recombine, ready to be split again by more light. This is known as the visual cycle.

THE CONE CELLS

• The cones contain three different photopigments.

• Each is sensitive to a different range of wavelengths, corresponding to the three primary colours red, blue and green.

• The sensitivity of these photopigments is broad enough to allow them to cover the full spectrum of visible light.

• Each pigment is thought to be located in different cones, and different colours are perceived in the brain from the sensory input from combinations of the three cone types.

COLOUR BLINDNESS

• Colour blindness in humans occurs because one or more of the three types of photopigments in cones is either absent or does not function properly.

• Complete inability to distinguish colours is rare.

• The most common form of colour blindness is the failure to discriminate between brown, red and green.

Missing Red cone Missing Green cone Missing Blue cone or defective or defective or defective

NOT EXAMINABLE, just interesting to see!