Download The Peripheral Nervous System

The Peripheral Nervous System
Sensory Organs
The Eye
 The eye is the sensory organ related to vision.
 It detects light variations, colours, and can adapt to
light intensity.
 Normal eyes can differentiate 2,000 colours.
Structures of the Eye
Sclera
Rigid, opaque membrane of the eye. Protects the eye from shock and
gives it shape. The white part.
Choroid
Middle layer of the eye. Blood vessels connect here to nourish the eye.
Retina
Innermost layer at the back of the eye. Covered in millions of lightsensitive nerve cells that transform incoming data into nerve impulses.
Cornea
Clear and rigid membrane that is an extension of the sclera
Iris
The extension of the choroid. This membrane is pigmented, giving eyes
colour. There is an opening that regulates the amount of light entering.
Lens
Flattened sphere that focuses light information on the retina. The part
we can see is the pupil.
Aqueous
humour
Transparent liquid that fills the space between the cornea and the lens.
Vitreous
humour
Transparent jelly-like substance that fills the space between the lens and
the retina.
How the eye works
 The lens of the eye works
similar to a camera lens.
It can adjust its size so as
to see things at different
distances.
 When objects are at a
distance, the lens
flattens. When they are
up close, the lens is
rounded.
…
 Once colours and light enter the eye, the retina
converts the information into nerve impulses, and
sends it from neuron to neuron until it reaches the
brain.
 Information is sent from the optic nerve, ultimately
to the brain.
 The brain analyzes the information and allows us to
make judgements on the colours that we see, the
distances of things, their shapes and their relative
sizes.
…
 Nerve cells on the retina convert light and
colours into nerve impulses.
 Some of the nerve cells are called cones.
 Only able to distinguish colours.
 Other nerve cells are called rods.
 Only distinguish variations in light intensity.
 Nerve impulses from the retina are
transmitted through the optic nerve and sent
to the brain. The brain superimposes the
images from each eye into one image that we
see.
The Ear
 The ears pick up sounds and convert them
into nerve impulses.
 The ear is divided into three sections:
 The Outer Ear
 The Middle Ear
 The Inner Ear
Structure
Pinna
Outer Ear
Middle Ear
Description
The visible part of your ear. It is funnel shaped
so as to pick up sound vibrations from the air.
Slightly curved, 2.5 cm long Canal that carries
sound vibrations to the eardum. It is lined with
Auditory
Canal
hairs and sebaceous glands that produce wax,
preventing debris from entering the ear.
The eardrum. It is a thin, flexible membrane
Tympanic
Membrane that moves to the rhythm of sound vibrations.
Ossicles,
(bones)
Miniature bones located in the temporal bone.
The three, the hammer, the anvil and the
stirrup, move in relation to one another.
Canal that links the middle ear to the pharynx.
Eustachian
It equalizes pressure on either side of the
Tube
eardrum during swallowing.
Structure
Semi-Circular Tubes
Inner Ear
Vestibule
Cochlea
Description
Canals that are filled with liquid. They
regulate balance when the body is in
motion and are linked to the vestibular
nerve.
Liquid-filled structure that links the
semi-circular canals to the cochlea.
Plays a role in balancing the body when
not in motion and is also linked to the
vestibular nerve.
Liquid-filled structure whose walls are
covered with auditory neurons and are
linked to the auditory nerve. This is
where sounds get transmitted from
neurons to send to the brain.
How the Ear Works
 Sounds are created by vibrations in the air. Sound
waves cause changes in the air pressure surrounding
us, creating sound waves that our ears can pick up.
 Sound waves are channeled by the pinna and sent
down the auditory canal until they reach the cochlea.
 In the cochlea, the sound vibrations are transformed
into nerve impulses and sent to the brain via the
auditory nerve.
 In the brain, these nerve impulses are analyzed,
causing us to hear.
Path of Sound
1. Sound vibrations reach the eardrum, causing it
to vibrate.
2. This sets the ossicles in motion. The stirrup
transmits the vibrations to the vestibular canal.
3. After passing this canal, vibrations are sent to
the cochlea, which transmits the vibrations into
nerve impulses.
4. Nerve impulses travel via the auditory nerve to
the brain.
Another Important Role
 The ear also plays an important role in our balance.
 The ossicles, (hammer, anvil and stirrup), are each responsible
for knowing when our heads are tilting, moving from side to
side, or up and down.
 The ossicles are activated by the small hairs that they have.
When the fluid within them moves, it activates the hair cells.
 They can then situate our bodies by sending nerve impulses
from the vestibular nerve to the brain.
 This is why we know where we are in space, and why we don’t
fall down when we walk, dance, play sports, etc…
The Nose
 The nose is a sensory organ that has multiple
functions, as it is crucial in the respiratory system.
 Nerve cells that are sensitive to smells are located in
the upper wall of the nasal cavity. They are found on
a small surface of only 5 cm², called the olfactory
epithelium.
 Around 15 million nerve cells are found on the
olfactory bulb. This bulb transmits the odours into
nerve impulses that are sent to the brain for analysis.
Olfactory Epithelium
Small, (5 cm²), location where the nerve cells related to
smell are found.
Olfactory Bulb
Located above the nasal cavity, this bulb transmits
odour information into nerve impulses.
Olfactory Nerve
Nerve responsible for the transmission of odour nerve
impulses to the brain.
The Skin
 The skin is the sensory organ associated with
touch.
 This is the bodies largest organ, as it covers
the entire surface of the body.
 Skin has three distinct layers: the epidermis,
the dermis and the hypodermis.
Layer
Structures
Description
Dead Layer
Outer skin layer. Atmospheric pressure causes
these skin cells to die.
Living Layer
Layer of constantly dividing cells, (mitosis). New
cells push older cells to the surface.
Sensory
Receptors
Structures that pick up stimuli, (pressure,
heat/cold).
Blood Vessels
Vessels that nourish the skin cells with oxygen and
nutrients.
Sebaceous
Glands
Glands that secrete sebum, and oily substance that
keeps skin waterproof.
Sweat Glands
Glands that produce sweat, carried to the skin
surface through pores.
Hair
Arise from the dermis and protrude out of the skin.
Epidermis
Dermis
Hypodermis Fat Cells
Layer of fat-containing cells that act as an energy
reserve and insulators.
How Skin Works
 The sensory receptors, (neurons), in the skin allow us to
experience:
 Tactile sensations, (touch, pressure).
 Thermal sensations, (heat and cold).
 Painful sensations
 The nerve endings in the skin are either free or protected and
each one is responsible for different stimuli.
 The different sensory receptors are not equally spread out in the
body. This is why parts of our bodies experience more pain than
others, and why some are more sensitive to cold.
The Tongue
 The tongue is a sensory receptor related to
taste.
 The tongue is covered in papillae, (one
papilla), and within each are the taste buds.
 There are three nerves that carry nerve
impulses created by the taste buds to the
brain.
 There are 5 tastes that humans can detect:
 Sweet, sour, salty, bitter and umami.
How the Tongue Works
 All taste buds experience all five tastes, regardless of
their position on the tongue.
 Taste and smell work together. The taste itself only
accounts for about 10% of the taste experience. This
is because the smell of food often helps us to identify
what we are eating.
 Other tongue receptors distinguish temperature,
discomfort, (prickly feeling), and the textures of
foods.
Image Credits
 http://www.therapearl.com/wpcontent/uploads/2013/07/dry_eye.jpeg
 http://www.wpclipart.com/medical/anatomy/eye/eye_diagr
am_2.png
 http://www.webrnmaculardegeneration.com/images/macular-degenerationtest-dilated-eye-exam.jpg
 http://www.hearinglink.org/image/audiograms---generaluse/HEARING-LOSSES-800.jpg
 http://michaelfriel.net/images/anatomy_nose.gif
 http://www.cidpusa.org/I10-85-papillae.jpg