Structure & Function of Peripheral Sensory Receptors Flashcards
(42 cards)
What is the role of the somatosensory system?
It allows us to sense: Touch: pressure against skin Temperature of skin Proprioception: position of joints and muscles with respect to body Pain: Tissue-damaging stimuli
How is the somatosensory system different from other sensory systems?
Somatosensory receptors are distributed throughout body.
Other sensory systems (vision, audition, olfaction, taste) are concentrated in small, specialized areas.
What is the basic pathway for all sensory stimuli to be perceived:
Stimulus ⇒ sensory receptors ⇒ spinal cord ⇒ medulla/brainstem ⇒ thalamus ⇒ cortex
Which direction do sensory pathways travel? Which direction do motor pathways travel?
Sensory pathways go up (periphery to cortex)
Motor pathways go down (cortex to muscles)
What is the DRG?
Cell bodies of sensory neurons innervating the neck on down
There is _______ DRG at each level of the spinal cord on each side.
1
DRG possesses __________ cell bodies with ____________ and _____________ process axons
pseudounipolar; peripheral; central
How are sensory receptors generally categorized?
Exteroreceptive
Proprioceptive
Interoceptive
Describe exteroreceptive receptors:
Code information from the external world, mainly via skin
a) Mechanoreceptors: touch
b) Thermoreceptors: warming and cooling
c) Nociceptors: sharp and burning pain
Describe proprioceptive receptors:
Code information about muscle length, muscle tension, joint angles
a) Muscle afferent receptors: Golgi Tendon Organs and Muscle Spindles
b) Joint and tendon afferents
Describe interoceptive receptors:
Code information about changes inside the body
a) Visceral afferent receptors: Localize sensation and pain very poorly
Functions of sensory neuron:
A. Encode stimulus quality, intensity, duration, location
B. Receptive field
C. Stimulus transduction
D. Intensity of the stimulus
E. Speed of action potential transmission
What is the receptive field?
The area in the periphery where application of an adequate stimulus causes response
Describe the example of stimulus transduction: Pacinian corpuscle
⇒ At peripheral terminal stimulus activates receptors and ion channels
⇒ Generates receptor potential
⇒ If receptor potential strong enough, generates action potentials
⇒ Signal (action potentials) are conveyed to spinal cord
Intensity of the stimulus is encoded by:
1) Each neuron: Frequency of action potential firing: rate code
2) Many neurons: Number of neurons firing: spatial summation code
Speed of action potential transmission (conduction velocity) depends on:
⇒ Axon diameter
⇒ Thickness of myelin
–Large myelinated Aα, Aβ fibers conduct APs very fast
–Thin myelinated Aδ fibers conduct APs moderately fast
–Unmyelinated C fibers conduct APs slowly
What is the use of the Compound Action Potential (whole peripheral nerve)?
To determine whether:
axons are missing, damaged or demyelinated
Used to diagnose peripheral neuropathies: Diabetes Herpes zoster infection (shingles) Nerve entrapment Multiple sclerosis Complications from drug treatments Nutritional deficiencies
Environment for receptive terminals:
a) skin
b) muscle
c) joint
Characteristics that set the sensitivity and function of different receptors:
a) Location: superficial vs. deep
b) Type of ending encapsulated or non-encapsulated
c) Slowly adapting vs. rapidly adapting response of the receptor
d) Spatial resolution for stimulus
What is the significance of slowly adapting vs. rapidly adapting responses?
Determines sensitivity to constant vs. changing stimuli:
1) Slowly adapting— Respond best to a sustained, unchanging stimulus. Sense pressure and shape of objects
2) Rapidly adapting— Respond only when stimulus changes (i.e. on and offset). Sense impact and motion of objects on skin
Spatial resolution for a stimulus depends on:
Receptive field size and innervation density
1) Superficial receptors: small receptive field size
Deep receptors: large receptive field size
2) Innervation density: Density is high in very sensitive areas; low in insensitive areas. 2-point discrimination best for fingers, mouth; worst for back, calves.
Mechanoreceptors:
mediate tactile/touch sensation
a) Very sensitive to force (low threshold); don’t respond to noxious stimuli
b) Silent without stimulation
c) Have myelinated axons; fast conduction velocities; signal reaches spinal cord quickly
Where would superficial mechanoreceptors be found? What are types of these receptors?
Superficial receptors: Found in border between epidermis and dermis
1) Merkel disks
2) Meissner’s corpuscles
Characterstics of Merkel disks:
- Fine touch, 2-point discrimination; Sharpest resolution of surface texture; bumpy vs. smooth
- Receptive field: Multiple small spots. High density in finger tips, around mouth; Low density on back
- Several Merkel disks innervated by single myelinated axon.
- Slowly Adapting response, encodes amount of force
