4.36 Mechanoreceptors and Chemoreceptors

General Senses

" Widely distributed throughout the body and include touch, pressure,pain, temperature, vibration, itch ,and pro perception" 1- somatic 2- visceral * maintaining homeostasis

Classification of Sensory Receptors

1- general senses : located throughout the body 2- special senses : all located in the head

Special Senses

1- smell (olfactory) 2- taste (gustatory) 3-vision (optic), 4-hearing (auditory) 5-equilibrium or balance (vestibular) * maintaining homeostasis

3 types of sensory receptors by location

1. Exteroceptors 2. Interoceptors 3. Propioceptors

Functional Category of sensory receptors

1. Mechanoreceptors 2. Thermoreceptors 3. Photoreceptors 4. Chemoreceptors 5. Nociceptors

sensation and components of sensation

Conscious and subconscious awareness of changes in the external or internal environment. Stimulation of the sensory receptor → transduction of the stimulus → generation of nerve impulses → integration of sensory input. 1. Stimulation of the sensory receptor. 2. Transduction of the stimulus. 3. Generation of nerve impulses. 4. Integration of sensory input.

Ruffini Endings (Bulbous Corpuscle )

Deeper in the dermis, near the base, are Ruffini endings, which are also known as bulbous corpuscles. They are found in both glabrous and hairy skin. These are slow-adapting, encapsulated mechanoreceptors that detect skin stretch and deformations within joints; they provide valuable feedback for gripping objects and controlling finger position and movement. Thus, they also contribute to proprioception and kinesthesia. Ruffini endings also detect warmth. Note that these warmth detectors are situated deeper in the skin than are the cold detectors. It is not surprising, then, that humans detect cold stimuli before they detect warm stimuli. SKIN SENSIBLE TO STRETCHING: RUFFINI ENDINGS

Meissner's (Tactile Corpuscle)

Meissner's corpuscles, also known as tactile corpuscles, are found in the upper dermis, but they project into the epidermis. They are found primarily in the glabrous skin on the fingertips and eyelids. They respond to fine touch and pressure, but they also respond to low-frequency vibration or flutter. They are rapidly- adapting, fluid-filled, encapsulated neurons with small, well-defined borders which are responsive to fine details. Merkel's disks and Meissner's corpuscles are not as plentiful in the palms as they are in the fingertips. LIGHT TOUCH

Pacinian (Lamellar) Corpuscle

Pacinian corpuscles, located deep in the dermis of both glabrous and hairy skin, are structurally similar to Meissner's corpuscles. They are found in the bone periosteum, joint capsules, pancreas and other viscera, breast, and genitals. They are rapidly-adapting mechanoreceptors that sense deep, transient (not prolonged) pressure, and high-frequency vibration. Pacinian receptors detect pressure and vibration by being compressed which stimulates their internal dendrites. There are fewer Pacinian corpuscles and Ruffini endings in skin than there are Merkel's disks and Meissner's corpuscles.

Free-Nerve Endings (dendrites)

Pain and thermal receptors in skin

root hair plexus (hair follicle receptor)

Root Hair Plexus = free nerve endings (dendrites) surrounding hair root. Allows sensation of touch

Stimulus

a detectable change in the internal or external environment

THERMORECEPTORS

detect changes in temperature

PHOTORECEPTORS

detect light; the rods and cones of the retina

mechanoreceptors

detect mechanical deformation e.g. touch or pressure in the skin; stretch receptors in muscles (stretch or compression). * mechanoreceptor cells respond to a change in the external stimulus (pressure, temperature, etc) by producing voltage pulses across neurons (i.e. generator potentials) . * Of all the receptors, the mechanoreceptors are the most varied - they include free nerve endings, tactile hair cells and complicated ENCAPSULATED END-ORGANS; - mechanoreceptors may be found in any part of the body such as the skin, muscle, gut; - you have already looked at the HAIR CELLS in the ear

free nerve endings

in tissues that detect pain, temperature and light touch (Merkel's disc).

NOCICEPTORS

pain receptors stimulated by, for example, pinching, tearing or burning -are all free nerve endings;

Transducer

part of the body that converts sensory stimulus form one form to another. Visual Transducer: rods, detect light intensity and cones detect color in retina Auditory Transducer: Hair cells within cochlea. detect frequencies of sound waves Olfactory Transducer: olfactory receptor neurons, detects odorants in auir Gustatory Transducer: gustatory papillae within tongue, taste buds detect if sweet/salt/sour/bitter Tactile Transducer: skin, detects pressure, texture, nerves, hot/cold, pain

Interoceptor

receive sensory information from inside the body

Exteroceptor

receive sensory information from outside of the body. Ex: visual, auditory, tactile LOCATION:

CHEMORECEPTORS

respond to chemical stimuli; e.g. taste, smell, changes in blood gases or pH.

Peripheral Nervous System

the sensory and motor neurons that connect the central nervous system to the rest of the body

Sensory receptor

these are nerve endings or specialised cells which convert stimuli from the external and internal environment into afferent nerve impulses which pass into the CNS