Human Responses 3

Senses

SENSE ORGANS

Animals have specialised senses to provide them with information about their environment.

The five senses are sight, hearing, touch, taste and smell.

A receptor is a cell that can detect a stimulus

A stimulus is any change in your environment, e.g. light, sound.

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Smell

Taste

Touch

Hearing

Sight

Sense

Smell

Taste

Touch

Hearing

Sight

Sense

Nose

Tongue

Skin

Ear

Eye

Organ

Smell

Taste

Touch

Hearing

Sight

Sense

Nose

Tongue

Skin

Ear

Eye

Organ

chemicals [receptors in the nasal cavity detect vapours]

chemicals [taste buds detect sweet, sour, salt and bitter].

touch, pressure, temperature and pain [receptors spread throughout body]

sound [receptors in cochlea]

light [by rods and cones in the retina]

Stimulus detected

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Eyelids can cover and protect the eyes.

The EYE

Conjunctiva — thin transparent lining protecting the cornea.

Conjunctiva

Eyelid

Cornea—front transparent part of the sclera. It focuses light rays on the retina.

Cornea

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Sclera—tough fibrous outer layer – the ‘white’ of the eye; it maintains the shape of the eyeball.

Choroid—contains blood vessels supplying food and oxygen to the cells of the eye.

Retina—the innermost layer that contains the receptor cells [rods and cones].

Sclera

Choroid

Retina

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The front region of the choroid is specialised into the iris

Iris—contains blood vessels and melanin [giving us our eye colour], and controls the amount of light entering the eye [through the pupil].

Iris

The fovea is where our best vision is [mainly cones] Fovea

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Pupil

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In bright light, pupil constricts to protect the retina

due to circular muscles contracting in iris.

In dim light, the pupil dilates to allow more light in

Due to radial muscles

contracting in the iris.

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Ciliary body [muscle] — thickened edge of the choroid that controls the shape of the lens

Lens—like a magnifying glass, it focuses the light rays on the retina.

Suspensory ligaments —hold the lens in place.

Ciliary muscle

Suspensory ligaments

Lens

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Lens—focuses the light rays on the retina.

Accommodation is the ability of the lens to change its shape (focal length) to form a clear image. 11

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

For close vision, the ciliary muscle contracts, the suspensory ligaments relax, the lens becomes thicker.

Close Vision

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

Distant Vision

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

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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.

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Aqueous humour—watery liquid that supplies the lens and cornea with nutrients and helps keep the shape of the cornea and lens.

Vitreous humour—gel that helps maintain the shape of the eye.

Aqueous humour Vitreous humour

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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)

Blind spot—where the optic nerve fibres pass through the retina and there is no room for receptors.

Optic nerve

Blind Spot

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Long-sighted :You are long-sighted if you can clearly see objects a long way off, but you cannot see things close by.

Reading glasses [convex lenses] can correct the problem.

Eye Defects

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Short-sightedYou are short-sighted if you can clearly see objects close to you, but you cannot see things in the distance.

Glasses with concave lenses can correct the problem.

Eye Defects

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NOTE

You have to learn either eye defect or

Ear defect – recommend this ….

Eye Defects

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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?

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Pinna—outer visible ear, funnels sound into the ear canal.

The EAR

Ear canal —tube leading to the ear drum. It has hairs and wax glands to trap dirt and germs.

Eardrum—membrane of skin that vibrates when sound waves hit it.

EardrumPinna

Ear Canal

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Middle ear—air-filled cavity containing three small bones [ossicles] and the Eustachian tube

Eustachian tube—keeps air pressure equal on each side of the eardrum.

It opens when we swallow, cough, etc.

Ossicles— 3 small bones [hammer, anvil and stirrup], that amplify the sound.

Middle Ear

Ossicles

Eustachian tube

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Inner ear—contains a coiled, fluid-filled tube called the cochlea and the semi-circular canals.

Semi-circular canals—help us keep our balance and posture.

Cochlea—contains nerves that convert sound vibrations into electrical impulses.

Inner Ear

Cochlea

Semi-circular canals

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In turn, this vibrates the hammer, anvil and stirrup bones, which amplify the sound.

The pinna (ear lobe) channels the sound (vibrations in the air) towards the eardrum, which then vibrates.

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The brain interprets these as sounds, and we ‘hear’.

The stirrup pushes on the oval window of the cochlea, moving the liquid inside.

Special hairs on 30,000 receptor cells detect the movement and send signals to the brain along the auditory nerve.

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Semi-circular canals—help us keep our balance and posture.

The three semicircular canals are curved tubes, each about 15mm long and filled with fluid. 29

Head movements are detected by nerves inside the canals.

This helps us keep our whole body balanced as we move.

The brain responds by sending messages through the cerebellum, which trigger reflex actions in our muscles.

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Deafness

Deafness can be caused by long exposure to a high level of noise, drugs, or ear infections.

Damage to the eardrum, ossicles [bones], and cochlea, which can be caused by loud sounds, produces incurable deafness.

Ear Defects

Workers exposed to prolonged sounds of over 90 decibels [dB] are obliged by law to wear ear protection.

Any exposure to 140 dB causes immediate damage to hearing. 31

The SKIN as a Sense Organ

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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?

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Objectives – What you will need to know from this section

Outline the nervous system components: central nervous system (CNS) and the peripheral nervous system (PNS)

Receptor messages are carried through these systems by nerve cells or neurons.

Outline the structure & function of the neuron including:cell body, dendrites, axon, myelin sheath, schwann cell, and neurotransmitter vesicles & synaptic cleft

Outline impulse movement & synapse.

Explain activation & inactivation of neurotransmitter.

3.5.3 Responses in the Human

Nervous System

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The structure and function of a neuron: variation in size and shape.

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.

Explain the role & position of 3 types of neuron -- sensory/motor/inter

Movement of nerve impulse.(Detailed knowledge of electrochemistry not required.)

Knowledge that the conduction of nerve impulses along a neuron involves movement of ions (details not required).

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State location & function of cerebrum / hypothalamus / pituitary gland / cerebellum / medulla oblongata

Label &/or draw diagrams of spinal cord (cross section) indicating : white matter, grey matter, central canal, 3 layer protective tissue-meninges.

Spinal nerves containing dorsal and ventral roots that project from the spinal cord

Outline the senses with the brain as an interpreting centre.

 Outline the CNS, brain & spinal cord.

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Outline disorders from NS disorders: paralysis or

Parkinson's including: Cause/Prevention/Treatment

Outline PNS including the location nerve fibres & cell bodies.

State the role, structure & mechanism of the Reflex arc/action.

The sense organs contain receptors, with the brain as an interpreting centre for received information.

Knowledge of the five senses and related organs.

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.

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