The Senses Jon Paul Cooper Biology 30. Introduction

The Senses

Jon Paul Cooper Biology 30

Introduction

Introduction

your external senses such as sight, hearing, taste, smell and touch send signals about your outside world to your brain.

your internal senses monitor: blood pH, blood pressure blood volume, osmolarity

these sensors send signals about your internal environment to your brain to help you maintain homeostasis.

Introduction

Category and type of Receptor Examples of Receptor Stimulus

Photoreceptors

Vision rods and cones in the eye visible light

Chemoreceptors

taste taste buds on the tongue food particles in saliva

smell olfactory receptors in the nose odour molecules

internal sense receptors in the carotid artery and aorta

blood pH

Mechanoreceptors

touch/pressure/pain receptors in the skin mechanical pressure

hearing hair cells in the inner ear sound waves

balance hair cells in the inner ear fluid movement

body position proprioceptors in the muscles and tendons, and the joints

muscle contraction, stretching, and movement

Thermoreceptors

Temperature heat and cold receptors in the skin

change radiant energy

Introduction

blood pH, blood pressure blood volume, osmolarity

these sensors send signals about your internal environment to your brain to help you maintain homeostasis.

sensation occurs when the neural impulses arrive at the cerebral cortex. different stimuli will be picked up and trigger a

neural impulse that is sent to the brain for interpretation.

perception is the interpretation of sensory information by the cerebral cortex.

Introduction

perception is the interpretation of sensory information by the cerebral cortex.

we are constantly over stimulated by the environment we live in our receptors become accustomed to the

stimulus and adapt. sensory adaptation occurs once you have

adjusted to a change in the environmentsensory receptors become less

sensitive when stimulated repeatedly.

Sensory Information

sensory adaptation occurs once you have adjusted to a change in the environment

sensory receptors become less sensitive when stimulated repeatedly.

sensory neurons supply the central nervous system with information about the external and internal environment.

there are many different types of sensors found in the body. sometimes many different types of receptors work

at the same time in one place. your skin has pressure, and temperature receptors.

THE EYE

Structure of the Eye

Main parts of the vertebrate eye: The sclera: white outer layer, including cornea The choroid: pigmented layer The iris: regulates the size of the pupil The retina: contains photoreceptors The lens: focuses light on the retina The optic disk: a blind spot in the retina where the

optic nerve attaches to the eye

The retina: contains photoreceptors The lens: focuses light on the retina The optic disk: a blind spot in the retina where the optic nerve attaches to

the eye the eye is divided into two cavities separated by the lens

and ciliary body: The anterior cavity is filled with watery aqueous

humor The posterior cavity is filled with jellylike vitreous

humor the ciliary body produces the aqueous humor

Fig. 50-18

Pupil

Aqueoushumor

Lens

Vitreous humorOptic disk(blind spot)

Central artery andvein of the retina

Opticnerve

Fovea centralis (center of visual field)

ChoroidSclera RetinaCiliary body

Suspensoryligament

Cornea

Iris

Photoreception

the innermost layer of the eye is the retina which comprises of four different layers of cells:- pigmented epithelium

- light-sensitive cells

- bipolar cells

- cell of the optic nerve

- Pigmented Epithelium is positioned between the choroid layer

and the light sensitive cells pigmented granules in this layer

prevent light that has entered the eye from scattering.

is positioned between the choroid layer and the light sensitive cells

pigmented granules in this layer prevent light that has entered the eye from scattering.

- Light Sensitive Cells there are two types of light sensitive cells

called the rods and the cones. The rods respond to low-intensity light The cones that require high intensity light,

identify colour. both rods and cones act as sensory receptors

Evolutionarily however, the dog and the human each developed the visual system that worked best for them. Humans have depended on their diurnal ability and a sense of color throughout time to help them find food. Dogs on the other hand, were not originally diurnal animals, until humans domesticated them. Consequently, the ability to see at night was originally more important to the dog than color. After all, their prey is often camouflaged with the surroundings, so they are unable to rely on color vision cues as heavily as humans do to find food. The retina of the eye is lined with both rods and cones in humans and dogs. The rods are much more prevalent in both species, but even more so in the dog than the human. The rods are adapted to work best in low light and are used for motion detection. The central retina of the canine eye contains about 20% cones, while humans have an area of 100% cones called the fovea. The cones work best in mid to high levels of light and have the ability to detect color.

Color and Acuity Differencesbetween Dogs and Humans

by Jennifer Davishttp://www.uwsp.edu/psych/dog/LA/davis2.htm

- Bipolar Cells and Optic Nerves once excited, the nerve message is

passed from rods and cones to the bipolar cells.

the bipolar cells then relay the message to the cells of the optic nerve.

the optic nerve then carries the nerve impulse to the central nervous system.

A Closer Look at Rods and Cones


the bipolar cells then relay the message to the cells of the optic nerve.

the optic nerve then carries the nerve impulse to the central nervous system.

rods and cones are unevenly distributed on the retina. in the centre of the retina there is a tiny depression referred to

as the fovea centralis. the fovea centralis

is the most sensitive part of the eye. has many cones packed very close together. when you look at an object most of light falls here. is surrounded by rods

(often you can see things in your peripheral vision without being able to identify its colour.)


when you look at an object most of light falls here. is surrounded by rods

(often you can see things in your peripheral vision without being able to identify its colour.)

There are no rods and cones in the area which the optic nerve comes in contact with the retina. because there is no photosensitive cells we call this

area the “blind spot”http://serendip.brynmawr.edu/bb/blindspot/


There are no rods and cones in the area which the optic nerve comes in contact with the retina. because there is no photosensitive cells we call this area the

“blind spot” there are three types of cones each which absorb

different wavelengths of light. the combination of cones that can detect red, blue

and green wavelengths of light allows us to see range of colours.

colour blindness is an inherited condition (occurs more in males) is a deficiency in particular cones, usually red or green

Simulated Color Blind Vision

Chemistry of Vision

the combination of cones that can detect red, blue and green wavelengths of light allows us to see range of colours.

colour blindness is an inherited condition (occurs more males) is a deficiency in particular cones, usually red or green

there are about 160 million rods surrounding the colour-sensitive cones in the centre of the eye. The rods contain a light-sensitive pigment called

rhodopsin. The cones contain a similar pigment but they are

less sensitive to light. Rhodopsin is composed of a form of vitamin A and

large protein called opsin

Chemistry of Vision

The cones contain a similar pigment but they are less sensitive to light.

Rhodopsin is composed of a form of vitamin A and large protein called opsin

when a single photon of light strikes a rhodopsin molecule it divides into two components

Retinene, the pigment portion Opsin, the protein portion.

this division alters the cell membrane of the rods and produces an action potential.

neurotransmitters are released from the end plates of the rods and the nerve message is conducted across the synapse to the bipolar cells and to a neuron of the optic nerve.

Chemistry of Vision

a terminal vitamin A deficiency can damage the rods.

Food, Standard Amount Vitamin A(μg RAE)

Calories

Organ meats (liver, giblets), various, cooked, 3 oza 1490-9126 134-235

Carrot juice, ¾ cup 1692 71

Sweetpotato with peel, baked, 1 medium 1096 103

Pumpkin, canned, ½ cup 953 42

Carrots, cooked from fresh, ½ cup 671 27

Spinach, cooked from frozen, ½ cup 573 30

Collards, cooked from frozen, ½ cup 489 31

Kale, cooked from frozen, ½ cup 478 20

Mixed vegetables, canned, ½ cup 474 40

Turnip greens, cooked from frozen, ½ cup 441 24

Chemistry of Vision

neurotransmitters are released from the end plates of the rods and the nerve message is conducted across the synapse to the bipolar cells and to a neuron of the optic nerve.

rhodopsin is extremely sensitive to light. in bright light rhodopsin is broken down faster than it

is restoredthe opsins used for colour vision are much less

sensitive and operate best with greater light intensity.

only rods are active during periods of limited light intensity, this is why images appear in shades of grey.

(rods are most effective at dusk and dawn)

Afterimages

an example of an after image is the blue or green lines that stay in your vision after a camera flash has gone off. there are two types of after images, positive

and negative ones. a positive afterimage occurs after you look

into a bright light and close your eyes. a negative afterimage occurs when the eyes

are exposed to bright coloured light for long periods of time.

cone cells adapt from the over stimulation and lose sensitivity

Focusing the Image

a negative afterimage occurs when the eyes are exposed to bright coloured light for long periods of time.

cone cells adapt from the over stimulation and lose sensitivity

As light enters the eye it is bent towards the pupil by the cornea. as light enters the more dense medium it

is refracted (bent). light is bent to a focal point and an

inverted image is projected on the light sensitive retina.

Focusing the Image

light is bent to a focal point and an inverted image is projected on the light sensitive retina.

Ciliary muscles control the shape of the lens. Suspensory ligaments maintain a constant tension.

when close objects are viewed the ciliary muscles contract and the lens becomes thicker.

the thicker lens provides additional bending of the light for near vision.

When far away objects are viewed, the ciliary muscles relax causing the lens to be thinner.

The adjustment of the lens is known as the accommodation reflex, objects 6 meters away from the viewer need no accommodation.

Focusing the Image

The adjustment of the lens is known as the accommodation reflex, objects 6 meters away from the viewer need no accommodation.

The importance of the accommodation reflex becomes more pronounced with age.

as the years add up so does layers of transparent protein covering the lens making it harder.

by the age of 40 near point accommodation has reduced so much people usually have problems reading.

a secondary adjustment occurs during the accommodation reflex. when objects are viewed from a distance, the pupil dilates

letting in as much light as possible. when objects are viewed close up the pupil constricts in an

attempt to bring the object into focus.

a constricted pupil makes it so light passes through a small opening and falls on the most sensitive part of the retina, the fovea centralis.Ex. The Inuit’s Snowblindness Glasses

Visual Defects

Glaucoma caused by a buildup of aqueous

humour in the anterior chamber of the eye.

tiny ducts usually drain out any excess liquid that is produced every day.

if the ducts get blocked, the fluid builds up and pressure inside the eye increases.

the retinal ganglion cells slowly die from the increased pressure, which leads to vision loss.

Visual Defects

Cataract the lens becomes opaque and

prevents some of the light from passing through.

the traditional solution is to remove the lens and fit the patient with strong eye glasses.

Visual Defects

Astigmatism for most people the lens and cornea

are symmetrical. incoming light is refracted along

identical angles for both the dorsal (back) and ventral (front) surfaces,

this forms a sharp focal point. in some people, the lens or cornea are

irregularly shaped leading to astigmatism.

Visual Defects

Nearsightedness Also known as myopia

occurs when the eyeball is too long. The lens cannot flatten enough to project

the image on the retina The distant image is brought into focus in front

of the retina. Someone who is nearsighted is able to

focus close objects but has difficulty seeing objects at a distance.

Glasses with concave lens can correct nearsightedness.

Visual Defects

Farsightedness Also known as hyperopia

is caused by an eyeball that is too short. distant images are brought into focus

behind the retina, instead of on it. A farsighted person can focus on

distant objects, but has trouble seeing objects that are close up. Can be corrected by glasses that have a

convex lens.

Hearing and

Equilibrium

Hearing and Equilibrium

the ear is associated with two separate

functions: hearing equilibrium

can be divided into three sections the outer ear the middle ear the inner ear



The Outer Ear comprised of the

pinna the external ear flap collects the sound

auditory canal carries sound to the eardrum. lined with specialized sweat glands that

produce earwax. earwax traps foreign particles and

prevents them entering the ear.

Hearing and EquilibriumThe Middle Ear

begins at the tympanic membrane and extends toward the oval and round windows.

Hearing and Equilibrium the tympanic membrane is a thin layer

of tissue that receives sound vibrations, also known as the eardrum.


the air filled chamber of the middle ear contains three small bones called ossicles, which include the:

mallus (the hammer) incus (anvil) stapes (stirrup)

the ossicles amplify and carry sound in the middle ear.

Hearing and Equilibrium sound vibrations that strike the

eardrum and are first concentrated within the solid malleus.

vibrations are then transmitted to the incus and finally to the stapes


the stapes strikes the membrane covering the oval window in the inner wall of the middle ear

the oval window is an oval shaped hole in the vestibule of the inner ear, covered by a thin layer of tissue

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


the oval window is an oval shaped hole in the vestibule of the inner ear, covered by a thin layer of tissue

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

the eustachian tube an air-filled tube of the middle ear that equalizes

pressure between the external and internal ear. approximately 40 mm in length and 3 mm in

diameter. extends from the middle ear to the mouth and

chambers of the nose. equalizing your ears on a plane by yawning or

swallowing allows air to leave your middle ear through the eustachian tube.


The Inner Ear has three distinct structures, the:

vestibule semicircular canals cochlea

Hearing and Equilibrium the vestibule

a chamber found at the base of the semicircular canals that provides information about static equilibrium

involved in balance connected to the middle ear by the oval

window. houses two sacs

the utricle the saccule

Hearing and Equilibrium the vestibule

a chamber found at the base of the semicircular canals that provides information about static equilibrium

involved in balance connected to the middle ear by the oval

window. houses two sacs

the utricle the saccule


the utricle and saccule contain granules called otoliths that allow us to detect gravity (linear movement) and head movement.

three semicircular canals arranged at different angles helps identify body movement

(3 canals for 3 axis of movement)(Three semicircular canals contain fluid and allow us to detect angular acceleration such as the turning of the head)


The cochlea a coiled structure of the inner ear that

responds to various sound waves and converts them to nerve impulses.

shaped like a spiralling snail’s shell. contains rows of specialized hair cells that

run the length of the inner cannal. the hair cells respond to sound waves and

convert them into nerve impulses.


Hearing sound like light must be converted into

an electrical impulse before you can interpret it.

you ear is so sensitive that you can hear a mosquito even though the sound energy reaching you ear is less than one quadrillionth of watt. The average light in the house uses a 60 watt bulb.


hearing begins when sound waves push against the eardrum, or tympanic membrane.

the vibrations of the eardrum are passed on to the three bones of the middle ear: the malleus, the incus, and the stapes

arranged in a lever system the three bones are held together by muscles and ligaments.


the bones concentrate and amplify the vibrations received from the tympanic membrane (they can triple the force)

during excessive noise a protection reflex mechanism goes into effect.

the muscles that join the bones together contract and restrict the movement of the malleus reducing the intensity of movement.

at the same time a second muscle contracts pulling the stapes away from the oval window.


the oval window receives vibrations from the ossicles.

as the oval window pushes inwards, the round window, located immediately below the oval window moves outward.

this triggers waves of fluid within the inner ear.

the cochlea receives the fluid waves and converts them into electrical impulses, which you interpret as sound.


the hearing apparatus within the cochlea is known as the organ of Corti.

it comprises a single inner row and three outer rows of specialized hair cells anchored to a basilar membrane.

the hair cells respond to vibrations of the basilar membrane.

vibrations in the fluid on either side of the basilar membrane cause the membrane to move.

the hairs on the cells bend as they brush against the tectorial membrane.



the movement of the hair cells stimulates sensory nerves in the basilar membrane

Auditory information is the sent to the temporal lobe of the cerebrum via the auditory nerves.



The ear conveys information about: Volume, the amplitude of the sound wave Pitch, the frequency of the sound wave

The cochlea can distinguish pitch because the basilar membrane is not uniform along its length

Each region vibrates most vigorously at a particular frequency and leads to excitation of a specific auditory area of the cerebral cortex

Taste

in humans, receptor cells for taste are modified epithelial cells organized into taste buds

there are five taste perceptions: sweet sour salty bitter umami (elicited by glutamate)

each type of taste can be detected in any region of the tongue

Taste

Smell

Smell

Smell

Olfactory receptor cells are neurons that line the upper portion of the nasal cavity

Binding of odorant molecules to receptors triggers a signal transduction pathway, sending action potentials to the brain

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The Senses Jon Paul Cooper Biology 30. Introduction