Lecture 18; Somatosensory receptor cells, receptors, primary afferents Flashcards
What are some characteristics of receptor cells?
Rapidly or slowly adapting
Small or large receptive fields
What are somatic sensations?
touch
pain,
temperature,
body position
List examples of receptor cells?
Exteroceptors Interoceptors Proprioceptors Mechanoreceptors Thermoreceptors Nociceptors Encapsulated nerve endings Free nerve endings
What do encapsulated receptor cells consist of? (1)
Meissner’s corpuscles – sensitive to tactile
stimulation, small RFs and rapidly adapting.
Pacinian corpuscles – sensitive to vibrations,
large RFs, rapidly adapting.
Merkels discs – sensitive to slow deformation
of skin, small RFs, slowly adapting.
What do encapsulated receptor cells consist of? (2)
Ruffini cylinders – sensitive to tactile stimulation, large RFs, slowly adapting. Dogiel body, Golgi-Mazzoni body, Endbulbs of Krause, Genital corpuscle etc.
What are nocioceptors?
signal painful stimulation
What are the 4 major types of touch mechanoreceptors?
- Merkel discs
- Meissner corpuscles
- Ruffini cylinders
- Pacinian corpuscles.
How do the 4 major types of touch mechanoreceptors differ?
in regard to 5 features;
- location in the skin
- physical appearance
- speed of adaptation
- size of their receptive fields
- tuning to stimulus
What is the Meisner corpuscle?
is composed of flattened cells located in the dermis, near the epidermis. A single nerve fiber winds its way through these cells.
What is the Merkel Disc?
is a disk-shaped receptor that is located near the epidermis and dermis border.
What is the Ruffani cylinder?
is located in the dermis and has many branched fibers inside a cylindrical capsule.
What is the Pacinian Corpuscle?
is a layered, onion-like capsule surrounding a nerve fiber.
It is located deep in the dermis, in the subcutaneous fat. They are also found in the intestines and joints as proprioceptors.
What is two point discrimination?
is the ability to discern that two nearby objects touching the skin are truly two distinct points, not one.
What are proprioceptors?
are located in skeletal muscles, tendons, ligaments
and joints.
They are sensitive to muscle stretch, muscle tone and position of joints
What do proprioceptors consist of?
Free nerve endings
Pacinian and paciniform endings
Muscle spindles
Golgi tendons
What is reflexive behavioural circuits in muscle spindles and golgi tendons?
Sensors in the tendon, the Golgi tendon organ, are activated upon stretch of the tendon, which requires considerable force.
These sensors synapse on interneurons in the spinal cord that inhibit further activity of the motor neurons innervating the muscle. This relaxation of the muscle prevents damage from excess force.
Who was Thomas Graham Brown?
he was the first to propose a half-centre model of motor neurons in which two groups of spinal neurons that are both reciprocally organized and mutually inhibiting are capable of producing basic rhythmic movement
Explain Henrik Ehrsson’s out of body experience?
subject is shown their peripheral view, in which the camera they see out of is prodded and so is their chest
What does TRP stand for?
Transient Receptor Potential (TRP) channels
of sensory afferents
In persistent injury what do central and peripheral pain pathways exhibit?
exhibit tremendous plasticity, producing
hypersensivity (hyperalgesia/allodynia)
What are the stimuli that lead to tissue damage but also activate nociceptors?
Strong mechanical stimulation
Extreme temperature
Oxygen deprivation
Exposure to certain chemicals
What are nociceptors described as?
Nociceptors are polimodal or they respond exclusively to thermal stimuli or some chemicals.
They are usually C fibres and lightly myelinated delta fibres.
There are also molecular pain receptors.
What does damaged tissue leak?
Damaged tissue leaks several chemicals: ATP and K+ , but also proteases (like kininogen to form bradykinin).
Bee venom causes histamine release from mast cells, which in turn sensitizes nociceptors.
Histamine causes blood capillaries to become leaky…hence causing redness and swell.
What is Hyperalgesia?
Primary (mechanical and heat stimuli) and secondary hyperalgesia (mechanical stimuli only)
Peripheral and central hyperalgesia
Sensitizing chemicals: bradykinin, substance P and prostaglandins
List the primary afferent axons?
Aα, Aβ, Ad, C
What fibres are involved in slow pain?
C fibres
1um in diameter
1 sec to travel to brain
What fibres are involved in fast pain?
Ad fibres
mylinated
5um in diameter
30 msec to travel to brain
