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.

Receptors for pressure, heat, cold and pain The fingertips, mouth and tongue are the most sensitive to pressure and the chest and abdomen are the least sensitive The body contains many more cold receptors than heat receptors

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 we need saliva in order to taste because it dissolves molecules

Smell in the upper part of the nasal cavity there are olfactory cells which respond to smell olfactory cells are columnar cells with cilia which act as sensors the cilia are attached to nerves which lead to the olfactory bulb in the limbic system located in the frontal lobe.

Limbic System - Smell

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

Optic disk (blind spot) Central artery and vein of the retina Fig. 50-18 Choroid Sclera Retina Ciliary body Suspensory ligament Fovea centralis (center of visual field) Cornea Iris Optic nerve Pupil Lens Aqueous humor Optic disk (blind spot) Central artery and vein of the retina Figure 50.18 Structure of the vertebrate eye Vitreous humor

The Human Eye Structure

Choroid Layer - middle layer of the eye Choroid Layer - middle layer of the eye. Prevents reflection of light in the eye

Iris - colored portion of choroid coat Iris - colored portion of choroid coat. Circular muscles that act as a diaphram that controls amount of light entering 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

Lens - changes shape to focus image on. retina (convex shape) 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: Rods - b+w vision Cones- color vision

Rods 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 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.

Optic Nerve Transmits sensory information to the occipital lobe.

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 Cones occur in the centre (fovea centralis) of the retina

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) – caused 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. p 389

p 389

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 p 392-393

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)

c. Correction is a concave lens

3. Astigmatism - lens or cornea curved unevenly a. Like having a “chipped lens” b. Parts of the image are out of focus. C. Needs special shaped lens.

p 392-393

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. Surgery link

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 severe vitamin A deficiency.

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.