Your 5 Senses and YouWith special focus on eyes and ears

Unit Outcomes

 Explain other ways that humans sense their environment and their spatial orientation in it› olfactory receptors, proprioceptors, taste receptors, receptors

in the skin

Describe the structure and function of the parts of the human eye› cornea, lens, sclera, choroid, retina, rods and cones, fovea

centralis, pupil, iris, and optic nerve

Describe the structure and function of the parts of the human ear › pinna, auditory canal, tympanum, ossicles, cochlea, organ of

Corti, auditory nerve, semicircular canals, and Eustachian tube

Receptors

Table 1 pg 446

Figure 2 pg 447

Taste Taste receptors are concentrated in

taste buds on our tongues

Specific chemicals stimulate receptors› 5 types: sour, salty, sweet, bitter and

savoury

each cell (each taste bud)can detect all tastes, but is particularly responsive to a certain type/chemical

Tongue Mapping

Eye Structure

Has 3 separate layers› Sclera › Choroid Layer› Retina

Sclera

This is the white of your eye It is the outermost layer and its

function is to protect and maintain the shape of the eye

It includes the cornea and aqueous humour

Cornea

Front portion of sclera Clear Strongly curved Starts to focus light

Aqueous Humour

Clear Supplies nutrients to cornea Fills front (anterior) eye cavity

Choroid Layer

This is the middle layer of your eye It contains the blood vessels for the

retina It includes the iris, pupil, lens, vitreous

humour, and ciliary muscles

Iris and Pupil

Iris is the coloured part that makes up the front of choroid layer

It contains muscles to change pupil diameter› Circular muscles close pupil› Radial muscles open pupil

The pupil is just a hole in the iris that light comes through

Ciliary Muscles (body)

Smooth muscle that changes lens shape

Attaches to ligaments which are connected to lens

Muscle contraction changes shape of lens

Secretes aqueous humour

Lens

Focuses light on retina Controlled by muscles of ciliary body Lens flattens for distant objects

› Image is inverted when light passes through Image is projected on retina upside-down.

The changing shape of the lens will focus the image on the retina

Vitreous Humour

Cloudy, jelly-like material Maintains the shape of the eyeball Helps focus light onto the retina

Retina

This is the innermost layer of your eye It contains photoreceptors and has 4

different layers of cells› Pigmented epithelium› Light-sensitive cells (sensory receptors)› Bipolar cells› Cell of the optic nerve

More Retina

Light-sensitive cells (sensory receptors)› Rods which are cells for low-intensity light› Cones which are cells for high-intensity light

and identify colours› Cones are concentrated in the fovea

centralis located at the back of the eye› Rods are located around the periphery of the

fovea.› There are no receptors (rods and cones)

where the optic nerve and retina join blind spot

Path of Light

Light enters the retina through the pigmented epithelium, which helps focus the light onto the rods and cones.

The signal is then sent through the bipolar cells to the cells of the optic nerve which transmit the message to the brain.

Chemistry of Vision Rods contain rhodopsin, a light senstive

pigment› Light hits the rhodopsin and causes an

Action Potential in the rod. › Neurotransmitters communicate this

stimulus (AP) to the bipolar cells and then to the optic neurons

› Rhodopsin is sensitive to light and breaks down in high light intensity, so it works best in low light intensity situations

› Negatively affected by Vitamin A deficiency.

Chemistry of Vision

Cones have a less sensitive pigment, so they work better in high intensity situations, allowing you to see colours.

Each cone is sensitive to one of the three primary colours of source light› Red› Blue› Green

Seeing Colour

Combinations of cones being stimulated by different wavelengths allows you to perceive different colours

Colour Blind

This happens when one or more types of cones are defective

The most common type is red-green colourblindness where the red sensitive cones are defective

Afterimages

Positive = you can see the shape of a camera’s flash after you close your eyes.› Image has been “burned” onto your retina

Negative = color reversal› caused by fatigue of cones responsible for

particular colors, while others continue to fire

Focusing Near and Far

Note how the shape

of the lens changeswith distance from

object.

Accommodation

Normal focusing of light› Cornea bends light to pupil: light slows

down as it travels through the cornea (dense material) = refraction of light inward toward lens. Lens is thicker in middle than edges, so light bends to a focal point (center of retina)

Accommodation Viewing close up

› ciliary muscle contracts and lens becomes thicker = additional bending of light. Pupil constricts to focus the image (light is focused more onto the fovea centralis)

Viewing farther away› Relaxaion of ciliary muscle causes lens to

thin out. Pupil dilates to let in more light. As you age: layers of protein cover the

lens, hardening it so it is less flexible; more difficulty accommodating for close up (reading).

Defective Vision

Near-Sightedness (Myopia) Eyeball is TOO LONG Rays from distant objects focus in front of

the retina

Myopia can be corrected using a concave lens.

Far-Sightedness-Hypermetropia Eyeball is TOO SHORT Rays from near objects focus behind the

retina

Hypermetropia can be corrected with a convex lens

Glaucoma› Buildup of aqueous humour› Increases pressure in the eye which causes

retinal ganglion cells (nerve cells) to die› Results in loss of vision

Cataracts› Lens becomes opaque

(can’t see through it)› Light can’t pass

through› Can remove the lens

and wear strong prescription glasses

Astigmatism› Lens or

cornea is irregularly shaped

› Light doesn’t focus on back center of retina (fovea centralis)

Lets Look at an Eye Dissection!!

Ear Structure The ear is made up of three main

structures› Outer Ear

Gathers sound waves Transfers sound waves to middle ear

› Middle Ear Amplifies sound waves Transfers sound waves to inner ear

› Inner Ear Turns vibration signals (from sound waves)

into electrical impulses which are sent to the brain through the auditory nerve

Outer Ear

The outer ear consists of the pinna and the auditory canal

Pinna› External ear flap› Collects sound

Auditory Canal› Carries sound to the eardrum› Has sweat glands that produce ear wax

Outer Ear meets Middle Ear

Tympanic membrane (Ear Drum)› Thin tissue layer that receives sound

vibrations› Sends the vibrations from the sound waves

into the middle ear

Middle Ear

The middle ear consists of the ossicles and eustachian canal

Ossicles› Consists of three small bones that amplify

and carry sound from tympanic membrane to the oval window of the cochlea Malleus (hammer) Incus (anvil) Stapes (stirrup)

Sound through the ossicles

Sound vibrations transfer from the tympanic membrane to the malleus, which then hits the incus which hits the stapes which vibrates against the membrane covering the oval window of the cochlea

Sound is amplified by concentrating the sound energy from the tympanic membrane to the smaller oval window

Middle Ear

Eustachian tube› Does not help with hearing› It is an air-filled tube that equalizes

pressure between the external and internal ear

› Where your ears “pop”

Inner Ear

Inner Ear

The inner ear consists of the vestibule, semicircular canals and the cochlea

Vestibule (for balance)› Involved in static equilibrium/head

positiion Semicircular canals (for balance)

› Involved in dynamic equilibrium/body movement

Inner Ear

Cochlea (hearing)› Coiled structure that turns sound waves

into nerve impulses› Contains the Organ of Corti

Has sound receptors where waves become impulses

Hair cells attached to basilar membrane

Cochlea

Movement of fluid in the cochlea causes the basilar membrane to vibrate› Different pitches of notes make different

areas of membrane vibrate Small hairs (cilia) are attached to the

basilar membrane The hairs rub and bend against the

tectorial membrane The bending generates a sensory nerve

impulse that is sent to the brain

Overview of Hearing

http://www.nelson.com/ABbio20-30/student/protect/animations/unit30Ach14.html#14.2

Sound Waves

Tympanic membrane

Hammer

Anvil

Stirrup

Oval window

Fluid inside a coiled tube (cochlea)

Round window

Hearing Summary So FarSound Waves initiate a series of movements within the ear:

Hearing Summary

Sound waves push against tympanic membrane; these vibrations are passed onto the ossicles (malleus then incus and finally stapes).

The ossicles concentrate and amplify the vibrations (exerting greater force by concentrating the energy in a very small area).

Oval window receives vibrations from stapes which causes the oval window to move in and out. This results in the round window (below it) to also move in and out (in alternation with oval window). The two windows moving in and out cause fluid to move in the inner ear.

The cochlea receives fluid waves and converts them into electrical impulses.

Fluid waves move the basilar membrane, the hairs on the membrane brush against tectorial membrane and bend. This stimulates sensory nerves in the basilar membrane impulses to auditory nerve then to brain.

Ear Safety

Small muscles in your ears help protect your hearing

When loud noises are around:› Muscles attached to the malleus (hammer)

contract and restrict intense movements› A second muscle contracts, pulling the

stapes (stirrup) away from the oval window, limiting inner ear damage

This doesn’t work for sudden loud noises

Hearing Loss

Conductive Hearing Loss› Sound waves can’t enter inner ear› caused by wax buildup, middle ear infection,

or punctured eardrum› Fixed by medical/surgical procedures

Sensorineural Hearing Loss› Auditory nerve is severed or damaged or hair

cells of the cochlea are damaged or dead.› caused by aging, loud noises, head trauma or

genetic conditions

Hearing Loss

Hearing Aids› pick up sound (microphone), amplify it and

transmit it to eardrum› won’t work for Sensorineural hearing loss

(vibrations can’t be transmitted to brain)

Hearing Loss Cochlear Implants

› does not make sounds louder or clearer› bypasses damaged parts and converts sounds into

electrical impulses that are sent to the brain.› has a microphone (picks up sounds), a speech processor

(selects and arranges sounds), a transmitter and receiver/stimulator receive signals from the speech processor and convert into electrical impulses. Electrodes send them to the auditory nerves.

* Doesn’t replicate exact sounds (like we hear them), provides sounds that allow person to interpret their environment. Over time, person learns to decipher impulses and can understand speech.*

Equilibrium and Balance

Static equilibrium (Am I upside down)› Detected by the vestibule

Inner Ear

Equilibrium and Balance

Static equilibrium (Am I upside down)› Movement along one plane (vertical or

horizontal)› Detected by the vestibule› Involves two other structures

Utricle Saccule

› Fluid filled› Contains tiny hairs (cilia)

Static Equalibrium

When the head is upright: calcium carbonate crystals in the fluid (otoliths) don’t move = fluid doesn’t move = cilia don’t move

- When the head is bent forward: the otoliths shift downward, pulling on the fluid.

This causes the cilia to bend which stimulates the nerve cell.

Sends a nerve impulse to brain (cerebellum) informing of head position relative to gravity

Inner Ear

Equilibrium and Balance

Dynamic Equilibrium (Moving forwards or backwards, spinning, flipping around)

Detected by the semicircular canals› Has 3 different fluid filled rings

Vertical Horizontal Diagonal

Dynamic Equilibrium

Each canal has an ampulla (pocket) that holds a cupula

When you move, fluid in the semicircular canals moves, bending cilia (that are on hair cells found in the cupula).› Results in nerve signals sent to brain.

Rapid, continuous movement of the fluids causes motion sickness