Exam 2 week 8 ppt 2 Cutaneous Receptors of the Somatic Sensory System Flashcards
Cutaneous Receptors: Primary Afferents and theire receptors
Four characteristics
- •1st degree afferent fiber carry information from the receptor to the CNS
- •May be myelinated or unmyelinated
- •Classification by conduction velocities & fiber diameter
- •Of course conduction velocity depend on degree of myelination and diameter of fiber
Cutaneous Receptors: Primary Afferents and theire receptors
where do 1 degree affferent fibers carry information?
•1 degree afferent fibers carry information from the receptor to the CNS
Cutaneous Receptors: Primary Afferents and theire receptors
how are they classified?
•Classified by conduction velocities & fiber diameter
Cutaneous Receptors: Primary Afferents and theire receptors
what does conduction velocity depend on?
•Of course conduction velocity depend on degree of myelination and diameter of fiber
Cutaneous Receptors: Primary Afferents and theire receptors
are they myelinated or unmyelinated?
•May be myelinated or unmyelinated
list the fiber types by conduction velocity (7)
- A-alpha (Ia diameter)
- A-alpha (Ib diameter)
- A-beta
- A-gamma
- A-delta
- B
- C
Type A - alpha fibers
what diameter?
(Dr. Lake said we don’t need to know, but I don’t trust him on this)
Ia or Ib
Type A - alpha fibers (Ia)
Function
- primary muscle spindle afferents
- Motor efferents to extrafusal muscle
Type A - alpha fibers
size
12-22 micrometers
Type A - alpha fibers (Ib)
Function
Golgi tendon organ afferents: contractile tension (force)
Type A - beta fibers
diameter
(Dr L said we don’t need to know, but I don’t trust that)
II
Type A - beta fibers
function
Mechanoreception: discriminative touch, pressure, joint rotation
Secondary muscle spindle afferents (static muscle length)
Type A - gamma fibers
function
Motor efferents to muscle spindle intrafusual fibers
Type A - gamma fibers
size
2-8 micrometers
Type A - beta fibers
size
5-12 micrometers
Type A - delta fibers
Fiber diameter
(Dr L said we don’t need to know, but I don’t trust that)
III
Type A - delta fibers
function
Mechanoreception: touch
Nociception: discriminative pain
Type A - delta fibers
size
1-5 micrometers
List the 5 types of cutanious mechanoreceptors in the skin and Subcutanious Tissues
- •Peritrichial endings - or hair follicle receptors
- •Meissner’s corpuscle
- •Merkel cell–neurite complex
- •Pacinian corpuscle
- •Ruffini ending
Peritrichial endings (4)
•Peritrichial endings
- –Around base of hair in hair follicle
- –Respond to hair movement
- –Light touch, breeze
- –Rapidly adapting
Peritrichial endings are the endings Around base of hair in hair follicle and they respond to hair movement. These are Rapidly adapting receptors that respond to the Light touch of what has been described as a loving caress, or a wafting breeze
Meissner’s Corpuscle (4)
- –Found is superficial cutaneous layers at base of epidermis
- –Nerve endings surrounded by connective tissue capsule
- –Responds to light touch
- –Low threshold and fast adapting
Meissner’s corpuscle are Low threshold and fast adapting that are Found is superficial cutaneous layers at base of epidermis
Nerve endings surrounded by connective tissue capsule. These receptors are specialized to respond to the light touch of passing your hand over an object to get a sense of it s size and shape
•Merkel cell–neurite complex (4)
- –At base of epidermal ridges in superficial cutaneous layers
- –Clustered together in “touch-domes” (lower picture)
- –Function in sustained light touch
- –Low threshold and slow adapting
Merkel cell–neurite complex are Low threshold and slow adapting cutaneous receptors located at the base of epidermal ridges in superficial cutaneous layers. These are Clustered together in “touch-domes” (as seen in the lower picture) and function in sustained light touch. These are the receptors you use to get a real sense of the texture of an object or to read braille. As David Linden described in his book Touch: The Science of Hand, Heart, you shouldn’t try to read braille with you lips as lips have very few if any Merkel’s touch domes. So even though the lips are highly sensitive and have a high receptor density they do not have these receptors
•Meissner & Merkel receptors
- –Meissner respond to onset & release of touch
- –Merkel respond for entire duration of touch
- –Both widely distributed but heaviest density at areas of greatest sensitivity - finger tips
- –Ab or group II afferents
- –Ascend in dorsal columns
Meissner & Merkel receptors are both widely distributed but heaviest density at areas of greatest sensitivity - finger tips and face with Meissner corpuscles responding to onset & release of touch and Merkel receptors responding for entire duration of touch and are responsible for the fine discriminative touch which ascends in the dorsal columns. They both utilize A-beta or group II afferent fibers.
•Pacinian corpuscles
- –Found in deeper cutaneous layers
- –Ab nerve endings surrounded by multiple connective tissue layers
- –Responds to vibratory pressure
- –High threshold and fast adapting afferents
Pacinian corpuscles are High threshold and fast adapting cutaneous receptors found in the deeper cutaneous layers. These are A-beta Nerve ending surrounded by multiple connective tissue layers. These are most sensitive to vibratory pressures felt say through a steering wheel when driving over rough pavement or the lack of vibration when going over ice. It has been speculated that these are useful when using tools to say feel the click of a screwdriver into the notch on the head of the screw or the variation in the vibration felt as a hammer it’s the nail or misses the nail and hits wood.
•Ruffini ending
- –Spindle shaped, encapsulated Ab endings
- –Found is deep cutaneous layers
- –Function in sustained pressure & stretch of skin (object slippage along skin)
- –High threshold and slow adapting
Ruffini ending is a Spindle shaped, encapsulated endings also Found is deep cutaneous layers. It is High threshold and slow adapting A-beta endings and is thought to function in Function in sustained pressure & stretch of skin. Some have speculated that it serves an important role to assess object slippage across the skin such as when you are gripping an object. You need to grip the object enough to prevent slippage of that object but not too hard to cause fatigue
•Pacinian vs Ruffini receptors
- –Pacinian respond to onset & release of pressure (vibration)
- –Ruffini respond for entire duration of pressure
- –Both widely distributed
- –Pacinian afferents ascend in dorsal columns
- –Ruffini afferents ascend in spinothalamic tracts
Pacinian respond to onset & release of pressure (vibration) while Ruffini respond for entire duration of pressure
Both widely distributed but less densely distributed than the Meissner’s corpuscles and Merkel touch domes. So these may also play a role in non-discriminative touch. The vibratory sense from Pacinian afferents ascend in dorsal columns and the non-discriminative touch and pressure sensations of Ruffini afferents and Pacinian afferents ascend in spinothalamic tracts
Pain and Thermal Receptors
about them in general
- Unencapsulated nerve endings throughout body, most numerous in skin
- Are lightly myelinated or unmyelinated primary afferents
There are also Pain and thermal receptors. These are Unencapsulated nerve endings which are seen throughout body, but most numerous in skin. They are the terminals of lightly myelinated or unmyelinated primary afferents. Thermal receptors respond to temperature changes of the skin and Nociceptors respond to stimuli that damage tissue.
