sensory & eye structure.pptx

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Collect a handout from the front.

What are the 5 different senses?

Sensory Receptors

– input to the nervous system is in the form of our

five senses: touch, taste, smell, sight and sound

– sight, taste, smell and sound are known as the

special senses controlled by the autonomic system.

– touch (pain, temperature, pressure) is known as

the voluntary senses controlled by the somatic system.

Touch

The skin contains receptors for pressure, heat, cold and pain

Pressure receptors are not evenly distributed in the skin, nor are they equally sensitive

The fingertips, mouth and tongue are the most sensitive to

pressure and the back, chest and abdomen are the least sensitive The body contains many more cold receptors than heat receptors Different body parts have different sensitivities to temperature (eg. the mouth can withstand more than the skin)

Taste

The tongue contains chemoreceptors

Small bumps on the tongued called papillae and contain taste buds

There are five types of specialized taste receptors: salty, sweet, bitter, sour, and umami.

Tastes buds are actually buried in the tissue, a small pore lets solutions into stimulate the receptors in the taste bud

Smell

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in the upper part of the nasal cavity

there are olfactory cells which respond

to smell

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olfactory cells are columnar cells with

cilia which act as sensors

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the cilia are attached to nerves which

lead to the olfactory bulb in the limbic

system located in the frontal lobe.

THE HUMAN EYE

I. The Eye is a Photoreceptor - Composed of:

A. Sclera - tough, white outer layer that supports and protects eyeball

B. Cornea - clear front part of sclera which admits light into the eye and bends it into the lens. Protected by the

conjunctiva. This region has no blood vessels to allow light into the eye unimpeded

Fig. 50-18 Pupil Aqueous humor Lens Vitreous humor Optic disk (blind spot)

Central artery and vein of the retina

Optic nerve

Fovea centralis

(center of visual field)

Choroid Sclera _Retina Ciliary body Suspensory ligament Cornea Iris

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Choroid Layer - middle layer of the eye.

Pupil - opening in iris

Aqueous Humor - fluid filling space between lens and cornea. Nourishes cells. If it fails to drain can lead to glaucoma

Vitreous Humor - transparent gel gives shape to eye

Iris -

Circular

muscles

Lens - changes shape to focus image on retina

(convex shape). Suspended by suspensory ligaments. When they contract lens is more spherical, when

relaxed lens is flattened

Retina - inner layer of eye. Contains 2 types of photo receptors:

1. Rods - b+w vision 2. Cones- color vision

a. Very light sensitive and can be stimulated in very dim light

b. Relies on Rhodopsin - pigment partially formed from vitamin A

i. Rhodopsin breaks down when stimulated by light into two smaller molecules: (retinene and opsin)

ii. Results in a nerve impulse in the sensory neuron attached to the rod.

c. Many rod cells are connected to one sensory neuron ---> vision produced by stimulation of rod cells is not very clear.

d. Rod cells are concentrated in the

peripheral regions of vision --> blind at night in center of vision.

2. Cones - colour vision.

a. About 300 times less sensitive to light than the rod cells. ---> functional in bright light only.

b. There are three different types sensitive to one of three colours of light: (Blue, Green, Red)

c. Fewer cone cells are attached to one neuron = greater resolution

d. Concentrated directly behind the lens in the fovea centralis

Blind Spot - where optic nerve exits eye. No rods or cones

AKA Optic Disk

Fovea Centralis - near centre of retina. All cones, no rods. Very sensitive, good detail but nightblind. A.K.A maculla. Each cone is connected to an optic neuron.

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Optic Nerve

– Transmits sensory information to the

II. The Lens

A. The lens is a convex lens, which focuses light rays at a focal point.

B. The light from an object is focused so that the image is upside-down and reversed.

C. The lens changes shape when viewing near objects as compared to distant objects.

1. The ciliary body attaches the lens by

ligaments to its smooth muscles.

The human eye can detect light in the 400-700nm range, which really is only a small portion of the

electromagnetic spectrum:

What makes a colour a colour is because that wavelength is what is being reflected and every other color is being absorbed

White light – all colours are being reflected

This explains why you get hot when you wear dark clothes, because dark colors absorb all wavelengths of light

Light enters the pupil and passes through the lens onto the retina at the back of the eye.

The ciliary muscles stretch or relax to accommodate and focus the lens on the object

There are rods and cones in the retina that detect the image Rods are used to see movement and objects in dim light Cones are used to see colour and fine detail

There are three types of cones, each sensitive to a different color of light: red, green and blue (Primary colours of light. If mixed, get white light. Not like mixing paint – we would get brown paint.)

Rods are more common in a circular zone, near the edge of the eye

Light reaching the rods causes a breakdown of the light sensitive pigment rhodopsin, which in turn causes a

membrane potential in the neurons. See Pg. 391

Cones contain a similar pigment, but are less sensitive to light. Like rhodopsin, this pigment contains vitamin A & opsin component.

this action potential transfers to synapsed neurons that connect to the optic nerve, which in turn connects to the occipital lobe in the brain

Eye Disorders

astigmatism – caused by the uneven

surface of the lens and creates image

distortion

myopia (near-sightedness) – caused by

the eyeball being too long and the

image is focused in front of the retina

Hypermetropia (far-sightedness) –

by the eyeball being too short and the image is focused behind the retina

2. When muscles are completely

relaxed, the lens is flat and focuses

distant objects.

3. To focus on a near object:

a. The muscles contract and shorten.

b. The lens then becomes more spherical

(fatter) in shape which bends light more.

D.

Errors in Refraction

1. Far-sightedness (hyperopia) - The lens

when in the relaxed position focuses beyond

the retina.

a. Can view distant objects, but unable

to view near objects.

b. Usually caused by an eyeball that is

too short or a lens that is too flat in the

relaxed position.

c.Correction is

with a convex

lens

2. Myopia (near-sighted) - The lens in the

relaxed state focuses light in front of the

retina.

a. Can view near objects , but unable to

see objects clearly at a certain distance

b. Usually caused by an eyeball that is

too long (can be due to a lens that is too

spherical at the relaxed position)

3.

Astigmatism - lens or cornea

curved unevenly

a. Like having a “chipped lens”

b. Parts of the image are out of

focus.

5. Glaucoma - pressure increases in the

aqueous humour.

a. This eventually decreases blood flow to

the retinal cells.

b. The cells die from lack of oxygen

and

nutrients resulting in blindness.

4. Cataracts - The proteins of the lens become

denatured.

a. They coagulate to

form cloudy areas of

the lens.

b. The lens is

completely removed

and replaced with an

artificial lens if

cataracts impair vision

greatly.

6. Colour blindness

a. One or more of the pigments in the different cone cells cannot be produced = colour

deficiency

7. Night blindness

a. Inability to form sufficient quantities of pigment for the rod and cone cells due to

Conjunctivitis:

Sometimes called “pink eye”

Irritation of the conjunction membrane over the cornea which acts as a barrier against infection

Strabismus

The lack of coordination of the ocular muscles

which causes a cross eyed or lazy eye condition. In most cases people need eye therapy

III.

Distance determination

A. The brain relates size of objects to

the size of known objects to

determine size.

B. Stereoscopic vision - vision is due

to two eyes which can use the

overlapping of vision to determine

distance of an object.