Sensory organs

Sensory Organs
By
Dr. Luay Obed Hamza
University of Baghdad / College of
Veterinary Medicine / Department of
Anatomy and Histology

The sense organ
 The sense is defined as system that consists
of a group of sensory cell types that responds
to a specific physical phenomenon. The
special senses including vision, hearing, taste
and olfaction.

Sensations
 Pain
 Temperature
 Pressure
 Touch
 Special Senses
 Vision
 Hearing
 Taste
 Smell or olfaction

Receptors
 Exteroceptors
 Interoceptors
 Proprioceptors

Exteroceptors
 Detect stimuli near outer body surface
 Cold
 Warmth
 Touch
 Pressure
 Special senses
 Hearing
 Vision

Interoceptors
 Detect stimuli from inside the body
 Taste
 Smell
 pH
 Distension
 Spasm

Proprioceptors
 Detect stimuli deep within the body
 Located in skeletal muscles, tendons,
ligaments, and joint capsules.
 Provide information to CNS on posture,
orientation in space, pressure, etc.
 Fibers are heavily myelinated for rapid
transmission.

The Eye
is the organ that responsible for the
sense of vision. Light entering the eye
is refracted by the cornea and the lens
so that an image is focused on the
retina.

The Eye
The eye is consist of
(1) eyeball
(2) Accessory structure such as:
(a)The ocular muscles that move the eyeball,
(b)The lids that protect it
(c)The lacrimal gland that keep its exposed
parts moist.

The Eye
a) The external fibrous layer that gives form to and protects the
eyeball. It gives the eye shape and stiffness. It consists of the
sclera and cornea.
b) b) The middle vascular layer that consists largely of blood
vessels and smooth muscle and is related with the nutrition of the
eyeball and the regulation of the shape of the lens and size of
pupil. It lies deep to the sclera and consists of three zones:
choroid, ciliary body and iris.
* Tapetum lucidum: Specialized reflective area of the choroid. It is
the reason animals eyes glow when light is shined in them at
night, not present in man and pig.

The Eye
c) The internal nervous layer that consists
largely of nervous tissue, the layer most
directly related with vision that is
translation of visual stimuli into nerve
impulses for interpretation by the brain. It
contains the light- sensitive receptor cells
and is known as the retina.

The Eye
The retina has cones and rods, the
cones are respond best to bright light
and are responsible for sharpness of
vision and color vision, while the rods
responsible for best to low levels of
light (night vision).

The Eye
The inability to see is called blindness.
Blindness may result from damage to
the eyeball, especially to the retina,
damage to the optic nerve that connects
each eye to the brain.

The refractive media of the eyeball.
The cornea aqueous humor, the lens
vitreous body.
* anterior chamber: between cornea
and iris (aqueous humor)
* posterior chamber: between iris and
lens (aqueous humor)
The Eye

The muscle of the eyeball responsible for the
movement of the eyeball, which consists of four
rectus muscles, two oblique muscles and a
retractor bulbi.
Innervation:
Trochlear nerve (IV) : innervates dorsal oblique
muscle
Abducens nerve (VI) : innervates Retractor bulbi
muscle and lateral rectus
Oculomotor nerve (III) : innervates all the rest
The Eye

The Ear
Is the organ responsible for hearing and
balance, which divided into three parts:
1. External ear consist of auricle and tympanic
membrane
2. Middle ear consist of malleus, incus and stapes
3. Inner ear labyrinth: consist of cochlea and
semicircular canal

External Ear
 Outer visible part
 Tube (external acoustic meatus) which
extends from the pinna or auricle into the
substance of the skull to the middle ear
(tympanic cavity).
 The sound waves enter through the auricle
and external auditory meatus of the external
ear funnel to the tympanic membrane.

Middle Ear
 Middle ear communicates with the pharynx
by way of the auditory tube (Eustachian
tube), which allows for pressure
equalization.


Middle Ear
 Within the middle ear, a mechanical
linkage is provided between the tympanic
membrane and the membrane closing the
vestibular window by three auditory
ossicles (bones).
1. Malleus – hammer
2. Incus – anvil
3. Stapes – stirrup

Middle Ear
Amplification of sound waves is
provided by leverage of the ossicles
and by the greater surface area of
the tympanic membrane which
transmits sound to the smaller
surface area of the vestibular
window

Inner Ear
 Can be divided into tow parts according to
function
1. Vestibular portion which is sensory for
position and balance and receives branch of
cranial nerve VIII (vestibulocochlear)
2. Cochlear portion which is sensory for sound
and receives the cochlear nerve, a branch of
cranial nerve VIII

Sound Reception
 In the middle ear, the ear ossicles transmit
vibrations of the tympanic membrane to the
perilymph of the inner ear. Sound waves in
the perilymph cause the vestibular
endolymph of the cochlear duct. These
waves cause the basilar membrane to vibrate,
producing action potentials in the spiral
organ of Corti.

Taste
 Sense of taste is called gustation
 The receptor organ is the taste bud
 Taste buds are found on the tongue, palate,
pharynx, and larynx.
 Taste buds have gustatory cells and
supporting cells.
 Gustatory cells are receptors for taste.

Taste Reception
 Taste bud pit communicates with the oral cavity by
way of the pore.
 Any substance tasted must get into solution and
enter the pore of the taste bud.
 Hair of the gustatory cell is affected causing
stimulation of the gustatory cell.
 The impulse is transmitted by cranial nerves Facial
(VII) and Glossopharyngeal (IX) to the brain.

Taste Sensations
 Classified as sour, salty, sweet or bitter.
 Each taste sensation is some combination of
the above.
 Taste perception by animals is based on
preference.
 Considerable variation within a species

Smell
 Sensation of smell is known as olfaction. Olfactory
cells adapt to odors.
 Cell bodies of 1st
Cranial Nerve (olfactory) are
found in the mucous membrane of the nasal cavity.
 This location is known as the olfactory region.
 The size of this region is directly related to the
development of the sense of smell.
 Dogs can detect substances 1:1000 of that
detectable by humans.

Smell
 Animals with greatly developed sense of
smell are macrosmatic.
 Animals with less developed sense are
microsmatic. (e.g. humans and monkeys)
 Animals with no sense of smell are
anosmatic. (many aquatic animals)

Phermones
 Animals use odors to communicate with each
other.
 A chemical secreted by one animal which
influences the behavior of another is called a
pheromone.
 Pheromones are used to identify species,
mark territories, emit alarms, mark food
location, and identify animals in estrus.

Sensory organs

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Editor's Notes