Download Receptors - Virtual Medical Academy

Receptors:
Receptor is the part of sense organ which receive stimulus
and convert it into nerve impulses, which travel to central
nervous system along a sensory neuron ex: rods & cones of
the eye.
Types of sensory receptors:
There are 6 major categorized based on type of stimulus energy that each type
selected:
1) Mechanoreceptors:
Detect mechanical energy associated with changes in pressure,
position (ex: touch).
2) Thermo receptors:
Detect infrared energy (heat). Not in human, but in other animals to
detect warm-blooded prey in the dark.
3) Pain receptors (nociceptors):
Detect tissue damage.
4) Chemo receptors:
Detect chemical energy of specific substances dissolved in the fluid
surrounded them e.g. taste and smell.
5) Osmoreceptors:
Detect changes in water volume (solute concentration) in the
surrounding fluid.
6) Photoreceptors:
Detect visible and ultraviolet light (not in human, but in other animals
like bees).
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Types of sensation:
There are 2 types: somatic sensation& special sensation..
a) Somatic sensation: sensory receptors present in more than one
location in the body, it includes: awareness of tough, pressure,
temperature, pain& muscle sense.
Each sensation start with receptors ending that embedded in skin or
skeletal muscle & in the wall of internal organs.
Examples:
1. touch receptors:
@ Are mechanoreceptors in the skin, are the receiving end of
sensory neurons like free endings nerve.
@ Stimulated by light pressure on skin & enables person to
distinguish between the texture.
2. Pressure receptors:
@ Pressure receptors (pacinian corpuscles) mechanoreceptors
in the skin.
@ stimulated by heavy pressure.
3. pain receptors(nociceptors):
@ detect pain.
@these receptors consist of branched free nerve endings,
which occur in nearly all body tissues, detect any stimulus
causing tissue damage.
4. temperature receptors:
@ are free nerve endings serve as heat receptors (thermo
receptors), found in the skin which fire off action potential to
the brain.
@ stimulated by sudden changes in temperature.
5. muscle sense:
@mechanoreceptors in skeletal muscle, joints, tendons,
ligament and skin are responsible for awareness of body
position and limb movement.
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b) Special sensation: sensory receptors restricted to special
locations as eye (vision), ear (hearing), tongue (taste), nose
(smell) and balance.
1) Taste:
Taste receptors on animals tongue are the taste buds.
Group of columnar epithelial cells which synapse with the dendrites of
sensory nerves.
These cells detect one of the four chemical stimuli (sweet, sour, salt, and
bitter).
These cells stimulate sensory nerve dendrites, and then the information is
sent to the central nervous system by the nerve impulse.
2) Smell:
Human have about 10 million olfactory receptors (smell receptors) in the
nose, then sensory nerve path way to primary receiving centers in the brain.
These receptors are sensitive to chemicals in air (chemoreceptor).
3) Vision:
Vision requires eyes (photoreceptor organs) that contributed to image.
In the vertebrate (e.g. human )eye there are 3 layers:
Outer layer (fibrous tunic):
Sclera:
Outer layer of eye ball, thick (through white fibrous tissue).
Protect most of the eye ball.
Maintain the eye’s rounded shape.
Cornea:
It is continuous with the sclera.
Transparent.
Has curved shape.
Focus light.
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Middle layer (vascular tunic):
Chorid:
It lines the inside of the sclera at the back of the eye.
The front edge of it from the ciliary’s body.
It is a layer of blood vessels nutritionally support wall cells, pigment
prevent light scattering.
Lens:
Consists of layers of transparent tissue.
Finely focus light on photoreceptors.
Iris:
Extension of chorids tissue.
It is the colored part of the eye.
Situated in front of the lens.
It has a hole at its center called pupil (let light enter).
It is made up of radial & circular muscles.
It control (regulate) the amount of light entering the eye (when bright
light entering, circular muscle of the iris contract and shrink (reduce)
the size of the pupil, whereas, in dim light, radial muscle contract and
so enlarge the pupil.
Aqueous humor:
The space in front of the lens is filled with a liquid called aqueous humor,
which:
1. Transmit light.
2. Maintain pressure.
Vitreous humor;
The space behind the lens is filled with a jelly called vitreous humor, which:
1. Transmit light.
2. Support lens.
3. Support eye ball.
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Inner layer (sensory tunic):
Retina:
A layer of light sensitive cells at the back of the eye on which images
are projected (light reception & transduction).
The flow of information beings as light reaches the retina. The
retina’s basement layer is a pigmented epithelium, covers the
choroids.
Resting on the epithelium are densely packed photoreceptors called
rod& cone cells.

Distinct layers of neurons are located above the rods& cones: the first are
bipolar cells & the second are ganglion cells.

Axon of ganglion cells from the optic nerves to the brain (transmit signals
towards brain).
Rod cells:
Light sensitive receptors (photoreceptors) in the retina, sensitive to
very dim light& are not sensitive to color.
Rods about 125 million.
The principal light sensitive chemical in the rod is the Rhodesian
(visual pigment in the rod cells).
Cone cells:
Light sensitive photoreceptors in the retina, operate only in bright
light& are sensitive to color.
Are about 6 million.
Rhodesian does not respond to bright light , color & day time vision
depend on red, green, blue cone cell, each with a different kinds of
visual pigments.
Fovea:
Region of the retina immediately opposite the lens.
Consist of densely packed cones.
Blind spot:
The point in the retina where the blood vessels & nerve fibers leave the
eye and form the optic nerve.
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