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Mechanical receptors respond to mechanical forces (touch, hearing, balance)
o Ion channels open and release neurotransmitter or generate an action potential
(because receptors are ionotropic)
The rate of the action potentials tells the CNS the strength of the stimulus
o More stimulus = more action potentials
Merkel’s discs are one of the most important tactile receptors
o Adapt slowly and provide continuous information about anything touching the
skin
Meissner’s corpuscles are found primarily in non hairy skin
o Very sensitive
o Adapt rapidly
o Provide information about changes in things touching the skin
Ruffini endings are deeper in the skin
o Adapt slowly
o Provide information about vibrating stimuli or low frequency stimuli
Pacinian corpuscles adapt rapidly and provide information of higher frequency
vibrations
Dendrites of neurons wrap around hair follicles deep in the skin
o These neurons are stimulated when surface hairs are displaced
Receptor density is different throughout the body
o If two different things touch you right next to each other and you can discern that
there are two things, then receptor density is high
Mechanoreceptors continuously supply information to the CNS about position of limbs
and muscles and joint stress
o Controls posture and coordination
Muscle spindles are mechanoreceptors found in skeletal muscle
o They are embedded in connective tissue inside the muscle and innervated with
neurons
o When the muscles stretches, the spindle stretches and sends an action potential to
the CNS, which then alters the strength of the muscle contraction
The golgi tendon organ is the mechanoreceptor in the tendons and ligaments
o Provides information about the force generated by contracting a muscle
o If contraction is too forceful, the GTO inhibits the spinal cord motor neurons,
causing the muscle to relax
Hair cells are the mechanoreceptors for the vertebrate auditory system and vestibular
system
Stereocilia protect the surface of each hair cell and bend in response to pressure waves
o Bending in one direction depolarizes hair and the other direction hyperpolarizes
hair
§ Bending creates local electric currents near the tips because the ion
channels are at the tips
Each stereocilia is connected to its taller neighbor by filaments that act like springs that
open and close the channels
o Bent toward taller = relaxed and closed
o Bent away from taller = tight and open ****potassium flows in

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Sound is pressure waves
o Mechanoreceptors convert these pressure waves into receptor potentials
The outer ear consists of the pinnae and auditory canal
o Pinna collects waves and directs them into the auditory canal
o The tympanic membrane marks the end of the auditory canal and vibrates in
response to the pressure waves
§ Pressure wave → physical force
The middle ear consists of an air-filled cavity connected to the throat at the back of the
mouth through the eustachian tube
o Ossicles = malleus, incus, stapes
§ Transmit vibrations of tympanic membrane to oval window
§ Movement of oval window imparts pressure to the inner ear which is
transduced into action potentials
The inner ear consists of the cochlea and the vestibular system
o The cochlea is composed of 3 parallel canals separated by the vestibular
membrane and basilar membrane
§ Vestibular canal → vestibular membrane → cochlear canal → basilar
membrane → tympanic canal
§ The vestibular and tympanic canals merge when they reach the distal end
of the cochlea
• The round window is a flexible membrane at the end of the
tympanic canal
§ The organ of corti sits on basilar membrane and transduces pressure
waves into action potentials
• Contains hair cells with stereocilia
A pressure wave in the fluid displaces the fluid → stapes pushes oval window→ fluid in
vestibular canal is displaced→ pressure is dissipated by outward bulging of round
window

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