Nervous System: The Senses

Where are sensory receptors located in the body?

All parts of the body, not in epidermis (upper layer of skin)

What are the 5 types of sensory receptors?

Chemoreceptors, Thermoreceptors, Mechanoreceptors, Photoreceptors, Pain receptors

Chemoreceptors

• Generate nerve impulse in presence of acid base + gases (chemical substances)

• Located in: Nose + mouth

• Responsible for: sense of taste + smell

Thermoreceptors

• Generate nerve impulse in response to temp changes (separate receptors for hot and cold)

• Located in: Hypothalamus + dermal layer of skin

Mechanoreceptors

• Generate nerve impulse in response to mechanical changes (pressure, stretch, touch)

• Located in: Cochlea + semicircular canals of ear ( responsible for balance + equilibrium)

• Also in muscular walls of stretchy organs (stomach + bladder, and arteries)

Photoreceptors

• Generate nerve impulse to wavelength of light

• Located in: rod + cone cells of retina

• Responsible for: Vision

Pain receptors

• Generate nerve impulse in response to chemicals released from damaged tissue

• Located in: all areas of body except brain

• Responsible for: body’s warning system

Sense of vision is our strongest sense. True or False?

True, primary sensory system for evaluating danger

What two things are involved in the sense of vision?

Eye + brain, 1/3 of cerebral cortex involved in visual processing

Sclera

White, fibrous outer layer of eye. Vascular and sensitive

Cornea

Transparent part of sclera, made of collagen fibers

Iris

coloured part of the eye

made of cuboidal epithelial cells

regulates amount of light entering eye by constricting circular and smooth muscles —> constrict and dilate pupil

Pupil

Hole in iris through which light travels to retina

Aqueous humour

Watery fluid behind cornea and Infront of lens

Lens

Transparent, flexible, oval body of eye which changes shape to focus

Highly elastic

main light focussing structure

Ciliary body

Thick portion of choroid, contains ciliary muscles

controls shape of lens + holds it in place

Vitreous humour

Jelly like fluid behind lens in eye cavity, maintaining its shape

Retina

Inner layer of eye behind lens maintaining eye cavity shape, absorbs light —> electrical impulse

Sensory ligaments

Attach lens to ciliary body

Fovea Centralis

Area of retina with most cone cells

Point at which refracted light is focused (vision most acute)

Choroid

Pigmented middle layer behind retina, inside sclera

absorbs light rays not absorbed by photoreceptors, preventing scattering of rays

Optic nerve

Takes visual stimulus to visual cortex of brain

blind spot occurs at area where optic nerve leaves eye, no photoreceptors here

What are the two types of photoreceptors?

Rod and cone cells

Cone cells

• Located in: fovea centralis

• Responsible for: day, clear, acute colour vision (activated by light)

• Contain: blue, green, and red cone cells, photospin, Vitamin A

Rod cells

• Located in: retina

• Responsible for: night, non-colour, peripheral vision (activated in low light levels), less acute—> blurry images

• Contain: rhodopsin

What happens to the lens when focusing on a distant vs near object?

Distant: lens becomes thinner

near: lens becomes thicker + rounder

What are the three sections of the ear?

Outer, middle, inner

Outer ear

Pinna- ear flap, collects sound waves

Auditory canal-transmits sound waves to tympanic membrane

Tympanic membrane- Ear drum, thin membrane with blood vessels and nerves, picks up vibrations—> middle ear

Middle ear

Ossicles: 3 bones of middle ear

-Malleas: First bone, sits against tympanic membrane

-Incus: Middle bone, rests between malleus and stapes

-Stapes: End bone, rests against oval window and cochlea

Oval window

Thin membrane @ entrance of cochlea

Behind window is fluid of vestibular canal of cochlea

Vibrations set this fluid in motion

Inner ear

Cochlea: responsible for hearing

Semicircular canals: responsible for equilibrium + balance

How do we hear?

Outer ear collects sound waves —> middle ear amplifies them through ossicles —> reach cochlea and fluid bends tiny hairs which trigger action potentials—> send impulse to brain via auditory nerve

What are our two weakest senses?

Taste and smell

What type of receptors do the nose and tongue contain?

Chemoreceptors sensitive to chemicals released by food and air

Olfactory cells

Chemoreceptors sensitive to water soluble or easily vaporized substances (perfumes, alcohols, deodorants)