Download The Senses

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



sensation occurs when the neural
impulses arrive at the cerebral cortex.


blood pH, blood pressure
blood volume, osmolarity
 these sensors send signals about your internal
environment to your brain to help you maintain
homeostasis.
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 environment
 sensory 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
Sclera
Ciliary body
Choroid
Retina
Fovea centralis
Suspensory
ligament
(center of visual field)
Cornea
Iris
Optic
nerve
Pupil
Aqueous
humor
Lens
Vitreous humor
Central artery and
vein of the retina
Optic disk
(blind spot)
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 Differences
between Dogs and Humans
by Jennifer Davis
http://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
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.)
A Closer Look at Rods and Cones



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/
A Closer Look at Rods and Cones

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
Organ meats (liver, giblets), various, cooked, 3 oza
Vitamin A
(μg RAE)
Calories
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 restored
 the 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 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.


The adjustment of the lens is known as the accommodation reflex,
objects 6 meters away from the viewer need no accommodation.

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

Hearing and Equilibrium
Hearing and Equilibrium
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 Equilibrium
The 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.
Hearing and Equilibrium

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
Hearing and Equilibrium

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.

Hearing and Equilibrium



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.
Hearing and Equilibrium
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
Hearing and Equilibrium


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)
Hearing and Equilibrium

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 and Equilibrium
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 and Equilibrium


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.
Hearing and Equilibrium

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.
Hearing and Equilibrium
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.
Hearing and Equilibrium

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.
Hearing and Equilibrium
Hearing and Equilibrium

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.
Hearing and Equilibrium
Hearing and Equilibrium

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
