1 - Structure and Function of Peripheral Sensory Receptors Flashcards
What does the somatosensory system allow our body to sense?
Touch: pressure against skin
Temp of skin, heat and cold stimuli
Proprioception: position of joints and muscles
Pain: tissue-damaging stimuli
The somatosensory system is distributed throughout what parts of the body?
Skin, muscles, joints, and bone.
What is the basic sensory pathway that the stimulus travels to get to the brain?
Stimulus > sensory receptors > spinal cord > medulla/brainstem > thalamus >cortex
Cell bodies of sensory neurons of the PNS are located where? What do these innervate?
The dorsal root ganglia, they innervate the neck and below.
What is the basic anatomy of the dorsal root ganglia? How many cell bodies does each house?
1 at each spinal level on each side of the spinal cord.
1 DRG has 10,000-20,000 cell bodies in the thoracic level (can be 50,000 at cerv or lumbar).
Length of axons up to 1 meter in leg.
What are the three general categories for sensory receptors?
- Exteroreceptive
- Proprioceptive
- Interoceptive
Where are exteroreceptive sensory receptors located? What are some receptors that fall into this category?
Receptors that sense the external world on the skin:
- mechanoreceptors sense non-painful touch and vibration
- thermoreceptors sense warning and cooling
- nociceptors sense pain (sharp, dull, pinch, painful heat, -20F wind chill).
What is the function of proprioceptive sensory receptors?
Sense muscle length, tension, and joint angle.
- Muscle afferents: muscle spindles sense muscle length and golgi tendon organs sense tension.
- Joint tendon afferents
Where are interoceptive sensory receptors located? Give some examples.
In internal organs.
Responsible for visceral afferents (localize sensation and pain poorly)
Ex: baroreceptors, blood pressure, pH
What are the characteristics of an encode stimulus?
Quality: brush, pressure, vibration, temp, pain
Intensity: light stroke v. intense pressure
Duration
Location
What is the receptive field?
The area in the periphery (ew. skin) where an adequate stimulus causes response from a neuron
What are two ways that the intensity of a sensory stimulus is encoded?
Rate code: freq of AP firing per neuron
Spatial summation code: number of neurons firing (info to spinal cord is summated)
What two things impact the conduction velocity (speed) of an AP?
Axon diameter: large diameter is faster
Myelination: thicker myelin is faster
What are the differences in myelination thickness and their impact on conduction velocity?
- Large myelin = very fast:
- Aalpha muscle spindles, golgi tendon organ –> fastest
- Abeta skin: light tough, vibration, pressure –> a little slower than Aalpha - Thin: Adelta = medium:
- Nociceptors (fast pain)
- cooling receptors - Unmyelinated C fibers: slow
- nociceptors (slow pain); warm receptors
Describe the sensory receptors in the skin?
They have specialized ending that tune sensory neurons to respond to specific physical stimuli
What are characteristics that determine the sensitivity and function of the sensory receptor?
- Location: superficial v. deep
- Ending: encapsulated v. non-encapsulated
- Slowly adapting v. rapidly adapting response
- Spatial resolution
What is the difference between a slowly adapting receptor and a rapidly adapting receptor?
Slowly adapting: have sustained, unchanging stimulus.
-encode pressure and shape of objects
Rapidly adapting: changing stimulus
- fire at onset and offset NOT throughout
- encode impact and motion of objects
- important for things moving across skin
What does spatial resolution depend on? What is a 2 pt discrimination threshold? What does a sensitive area consist of?
Depends on receptive field size of each neuron and innervation density.
The minimum distance between two detectable stimuli.
High density of receptors and small size of receptive fields.
What type of stimuli do mechanoreceptors respond to? What don’t they respond to? How is their info transmitted?
Touch pressure, vibration, and very sensitive to force.
They are silent without stimulation and don’t respond to painful stim
Sent via myelinated axons with fast conduction velocity so signal reaches sp cord fast.
What is the function of Merkel disks - superficial (1st type of mechanoreceptor)? Describe their receptive field and location?
Fine touch, 2 pt discrimination, and sense sustained pressure
Receptive field: several small, sensitive spots: touch dome
High density in finger tips, lips, and mouth
What are the charactieristics of 2 pt discrimination that the Merkel disks are capable of? What type of response do these receptors have?
Sharpest resolution of texure, surface of objects (bumpy v. smooth), braille.
Slowly adapting response: number of APs fired ~ indentation force
Several disks are innervated by a single axon.
What is the function of Meissner’s corpuscles- superficial (2nd type of mechanoreceptors)? Where are they located? What is the receptive field?
Fine touch, 2 pt discrimination, sense abrupt changes in edges, bumps, and corners; adjust grip and release when lifting objects.
In glabrous skin only (thick skin on sole of feet or palms). High density in finger tips, lips, and mouth.
Receptive field is a single spot.
What are the histological characteristics of Meissner’s corpuscles? Describe their response to stimuli?
They enclose a stack of schwann cells; Axon is myelinated.
Rapidly adapting response based on onset and offset of indentation.
APs fired ~ # times the skin is indented, low frequency.
What is the function of Ruffini corpuscles (3rd type of mechanoreceptor)? Where are they located and what is their receptive field?
Sense the stretch of skin and gravity force against skin.
Located in the dermis of the skin.
Large and diffuse receptive field.
