Biology Chpater 45
 Mechanoreceptors
o A sense organ or cell that respond to mechanical stimuli such as touch
or sound.
 Nociceptors
o Receptors that transmit impulses perceived as pain
o They can be sensitive to noxious substances as well as tissue damage
o Many hyper stimulated sensory receptors can also produce the
perception of pain in the brain
o Most nociceptors consist of free nerve endings located throughout the
body, especially near surfaces where damage is most likely to occur
o Some respond to extreme temperatures, very intense mechanical
stimulation, or specific chemicals in the extracellular fluid
 Theremoreceptors
o Which are naked dendritic endings of sensory neurons that are
sensitive to changes in temperature
o Two types of thermoreceptors
 Cold receptors
 Located directly below the epidermis
 3 to 4 times more cold receptors than warm receptors
 Warm receptors
 Located deeper in the dermis.
 Mechanoreceptors found in the skin
o Merkle Cell
o Messner Corpuscle
o Ruffini Corpuscle
o Pacinian Corpuscle
 Merkle Cell
o Tonic receptors located near the surface of the skin that are sensitive
to touch pressure and duration
 Meissner Corpuscle
o Phasic receptors sensitive to fine touch, concentrated in hairless skin
 Ruffini Corpuscle
o Tonic receptors located near the surface of the skin that are sensitive
to touch pressure and duration
 Pacinian Corpuscle
o Pressure-sensitive phasic receptors deep below the skin in the
subcutaneous tissue
 Proprioceptiors
o Muscle spindles together with other receptors in tendons and joints
o Tehese sensory receptors provid information about the relative
positive or movement of the animal’s body parts
o The sensory neuron conduct action potentials into the spinal cord,
where they synapse with somatic motor neuron that innervate the
muscle
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Muscle spindles
o Sensory stretch receptors that lie in parallel with the rest of the fibers
in the muscle
o Each spindle consists of several thin muscle fibers wrapped together
and innervated by sensory neuron, which becomes activated when the
muscle, and therefore the spindle, is starched
Chemoreceptors
o Contain membrane proteins that can bind to particular chemical or
ligands in the extracellular fluid
o Are used in the senses of taste and smell and are also important in
monitoring the chemical composition of blood and cerebrospinal fluid
Taste buds
o Are onion-shaped structures between 50 and 100 taste cells
 Each cell has fingerlike projection called microvilli
Peripheral chemoreceptors
o Located in the aortic and carotid bodies
o Are sensitive primarily to plasma pH
Central chemoreceptors
o In the medulla oblongata of the brain, which are sensitive to the pH of
cerebrospinal fluid.
Vision
o Begins with capturing light rays with photoreceptors
Invertebrates have simple visual systems
Cornea and lens
o Help focus light onto the retina at the back of the eye, which contains
the photoreceptors
The center of each eye’s visual field is focused on the fovea
Sclara
o White of your eye
Iris
o Colored portion of the eye
Cones
o Responsible for high visual activity
o Can see better in lit up areas
Rods
o Active in dimmed areas
o Try to get the sharpest image.