Mechanoreceptor
A
mechanoreceptor is a
sensory receptor that responds to mechanical pressure or distortion. There are four main types in the glabrous skin of humans:
Pacinian corpuscles,
Meissner's corpuscles,
Merkel's discs, and
Ruffini corpuscles.
Mechanoreceptors are primary neurons that respond to mechanical stimuli with action potentials. Peripheral transduction is believed to occur in the end-organs. Slowly adapting type I mechanoreceptors have multiple Merkel cell end-organs. Slowly adapting type II mechanoreceptors have single Ruffini corpuscle end-organs. Rapidly adapting type I mechanoreceptors have multiple Meissner corpuscle end-organs, while Rapidly Adapting type II mechanoreceptors (usually called Pacinian) have single Pacinian corpuscle end-organs. The human work stemmed from Vallbo and Johansson's percutaneous recordings from human volunteers in the late 1970s. Work in rhesus monkeys has found virtually identical mechanoreceptors with the exception of Ruffini corpuscles which are not found in the monkey.
Cutaneous mechanoreceptors with small, accurate
receptive fields are found in areas needing accurate taction (e.g. the fingertips). Mechanoreceptors with large, less accurate
receptive fields are found in areas needing less precise taction (ie. the palm).
Cutaneous mechanoreceptors provide the senses of touch, pressure, vibration,
proprioception and others. Mechanoreceptors can also be separated into categories based on their rates of adaptivity. When a mechanoreceptor receives a stimulus it begins to fire impulses or
action potentials at an elevated frequency (the stronger the stimulus the higher the frequency). The cell, however, will soon "adapt" to a constant or static stimulus and the pulses will subside to a normal rate. Receptors that adapt quickly (i.e. quickly return to a normal pulse rate) are referred to as ‘'phasic
. Those receptors that are slow to return to their normal firing rate are called ‘'tonic. Phasic mechanoreceptors are useful in sensing such things as texture, vibrations, etc; whereas tonic receptors are useful for temperature and
proprioception among others.
In
sensory transduction, the
afferent neurons transmit the message through a
synapse in the
dorsal column nuclei, where another neuron sends the signal to the
thalamus, where another neuron sends the signal to the
somatosensory cortex.
*
Thermoreceptor*
Nociceptor*
proprioception*
