Human Responses 3 Senses SENSE ORGANS Animals have

Human Responses 3 Senses

SENSE ORGANS Ø Animals have specialised senses to provide them with information about their environment. Ø The five senses are sight, hearing, touch, taste and smell. Ø A receptor is a cell that can detect a stimulus Ø A stimulus is any change in your environment, e. g. light, sound. 2

Sense Organ Sight Eye Hearing Ear Touch Skin Taste Tongue Smell Nose Stimulus detected light [by rods and cones in the retina] sound [receptors in cochlea] touch, pressure, temperature and pain [receptors spread throughout body] chemicals [taste buds detect sweet, sour, salt and bitter]. chemicals [receptors in the nasal cavity detect vapours] 3

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The EYE Ø Eyelids can cover and protect the eyes. Eyelid Conjunctiva Cornea Ø Conjunctiva — thin transparent lining protecting the cornea. Ø Cornea—front transparent part of the sclera. It focuses light 5 rays on the retina.

Sclera Choroid Retina Ø Sclera—tough fibrous outer layer – the ‘white’ of the eye; it maintains the shape of the eyeball. Ø Choroid—contains blood vessels supplying food and oxygen to the cells of the eye. Ø Retina—the innermost layer that contains the receptor cells [rods and cones]. 6

Ø The fovea is where our best vision is [mainly cones] Ø The front region of the choroid is specialised into the iris Fovea Iris Ø Iris—contains blood vessels and melanin [giving us our eye colour], and controls the amount of light entering the eye [through the pupil]. 7

Pupil 8

Ø In bright light, pupil constricts to protect the retina Ø due to circular muscles contracting in iris. Ø In dim light, the pupil dilates to allow more light in Ø Due to radial muscles contracting in the iris. 9

Ø Ciliary body [muscle] — thickened edge of the choroid that controls the shape of the lens Ø Suspensory ligaments — hold the lens in place. Ciliary muscle Suspensory ligaments Lens Ø Lens—like a magnifying glass, it focuses the light rays on the retina. 10

Ø Lens—focuses the light rays on the retina. Ø Accommodation is the ability of the lens to change its shape 11 (focal length) to form a clear image.

LEARNING CHECK • Name the 5 senses and the organs involved. • Name the 3 main layers of the eye and the function of each. • Which part of the eye is only an opening – a hole in another part? • What is the function of the [a] iris, • [b] lens, • [c] cornea, • [d] fovea • What is accommodation? 12

Close Vision Ø For close vision, the ciliary muscle contracts, the suspensory ligaments relax, the lens becomes thicker. 13

Distant Vision Ø When the eye is at rest, the lens is thin, has a long focal length and is adapted for seeing distant objects. 14

Ø Accommodation is the ability of the lens to change its shape (focal length) to form a clear image. 15

Seeing things at different distances For distant objects, the ciliary muscle relaxes and so the suspensory ligaments pull tight, pulling the lens thinner – the light doesn’t bend as much. For close objects the ciliary muscle contracts, allowing the lens to go fat, thus bending the light more. 16

Ø Aqueous humour—watery liquid that supplies the lens and cornea with nutrients and helps keep the shape of the cornea and lens. Aqueous humour Vitreous humour Ø Vitreous humour—gel that helps maintain the shape of the 17 eye.

Ø When light rays focus on the retina, receptor cells are stimulated and impulses are carried along the optic nerve to the brain. (optic nerve = communication between eye and brain) Optic nerve Blind Spot Ø Blind spot—where the optic nerve fibres pass through the 18 retina and there is no room for receptors.

Eye Defects Ø Long-sighted : You are long-sighted if you can clearly see objects a long way off, but you cannot see things close by. Ø Reading glasses [convex lenses] can correct the problem. 19

Eye Defects Ø Short-sighted You are short-sighted if you can clearly see objects close to you, but you cannot see things in the distance. Ø Glasses with concave lenses can correct the problem. 20

Eye Defects Ø NOTE Ø You have to learn either eye defect or Ø Ear defect – recommend this …. 21

LEARNING CHECK • Explain how the ciliary body and suspensory ligaments alter the lens. • What is the function of the [a] humours, [b] optic nerve? • If you are longsighted, what does it mean? • What could be a possible cause? • What type of lens can rectify it? 22

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The EAR Ø Pinna—outer visible ear, funnels sound into the ear canal. Ø Ear canal —tube leading to the ear drum. It has hairs and wax glands to trap dirt and germs. Ø Eardrum—membrane of skin that vibrates when sound waves hit it. Eardrum Pinna Ear Canal 24

Ø Middle ear—air-filled cavity containing three small bones [ossicles] and the Eustachian tube Middle Ear Ossicles Ø Ossicles— 3 small bones [hammer, anvil and stirrup], that amplify the sound. Ø Eustachian tube—keeps air pressure equal on each side of the eardrum. Ø It opens when we swallow, cough, etc. Eustachian tube 25

Ø Inner ear—contains a coiled, fluid-filled tube called the cochlea and the semi-circular canals. Inner Ear Semi-circular canals Ø Cochlea—contains nerves that convert sound vibrations into electrical impulses. Ø Semi-circular canals—help us keep our balance and posture. Cochlea 26

Ø The pinna (ear lobe) channels the sound (vibrations in the air) towards the eardrum, which then vibrates. Ø In turn, this vibrates the hammer, anvil and stirrup bones, 27 which amplify the sound.

Ø The stirrup pushes on the oval window of the cochlea, moving the liquid inside. Ø Special hairs on 30, 000 receptor cells detect the movement and send signals to the brain along the auditory nerve. Ø The brain interprets these as sounds, and we ‘hear’. 28

Ø Semi-circular canals—help us keep our balance and posture. Ø The three semicircular canals are curved tubes, each about 29 15 mm long and filled with fluid.

Ø Head movements are detected by nerves inside the canals. Ø The brain responds by sending messages through the cerebellum, which trigger reflex actions in our muscles. Ø This helps us keep our whole body balanced as we move. 30

Ear Defects Deafness ØDeafness can be caused by long exposure to a high level of noise, drugs, or ear infections. ØDamage to the eardrum, ossicles [bones], and cochlea, which can be caused by loud sounds, produces incurable deafness. ØWorkers exposed to prolonged sounds of over 90 decibels [d. B] are obliged by law to wear protection. ØAny exposure to 140 d. B causes immediate damage to hearing. 31

The SKIN as a Sense Organ 32

LEARNING CHECK • What is the function of the [a] pinna, [b] 3 ossicles, [c] cochlea, [d] semi-circular canals, [e] eustachian tube? • Outline how vibrations in the air are eventually “heard” by our brain. • Name a common ear defect. • Give some possible causes & treatments. • How might you reduce your risks of this defect? 33

3. 5. 3 Responses in the Human Nervous System Objectives – What you will need to know from this section Ø Outline the nervous system components: central nervous system (CNS) and the peripheral nervous system (PNS) Ø Receptor messages are carried through these systems by nerve cells or neurons. Ø Outline the structure & function of the neuron including: cell body, dendrites, axon, myelin sheath, schwann cell, and neurotransmitter vesicles & synaptic cleft Ø Outline impulse movement & synapse. Ø Explain activation & inactivation of neurotransmitter. 34

Ø The structure and function of a neuron: variation in size and shape. Ø Neuron -- Three part structure: > dendrite(s) receive information and carry it towards the cell body, > the axon conducts nerve impulses away from the cell body, > the cell body contains the nucleus and other organelles and produces neurotransmitter chemicals. Ø Explain the role & position of 3 types of neuron -- sensory/motor/inter Ø Movement of nerve impulse. (Detailed knowledge of electrochemistry not required. ) Ø Knowledge that the conduction of nerve impulses along a neuron involves movement of ions (details not required). 35

Ø Outline the senses with the brain as an interpreting centre. Ø Outline the CNS, brain & spinal cord. ØState location & function of cerebrum / hypothalamus / pituitary gland / cerebellum / medulla oblongata ØLabel &/or draw diagrams of spinal cord (cross section) indicating : white matter, grey matter, central canal, 3 layer protective tissue-meninges. Ø Spinal nerves containing dorsal and ventral roots that project from the spinal cord 36

Ø Outline disorders from NS disorders: paralysis or Parkinson's including: Cause/Prevention/Treatment Ø Outline PNS including the location nerve fibres & cell bodies. Ø State the role, structure & mechanism of the Reflex arc/action. Ø The sense organs contain receptors, with the brain as an interpreting centre for received information. Ø Knowledge of the five senses and related organs. Ø Study the eye and the ear – recognition and fuction of the main parts. • Corrective measures for long and short sight or for a hearing defect. 37