Somatosensation 1 Flashcards
cutaneous sensations vs proprioception and kinesthesis
- cutaneous sensations = stimulation of skin
- proprioception and kinesthesis = sense of limb positions and movement
What are the 3 cutaneous sensations?
- tactile perception (pressure and vibration)
- temperature
- pain
What is glabrous skin?
non-hairy
What are the mechanoreceptor cells in the mammalian glabrous skin?
- meissner corpuscle
- pacinian corpuscle
- ruffini’s corpuscle
- merkel’s disks
- free nerve endings
tonic vs phasic receptor
- tonic receptor = train of impulses CONTINUES during a prolonged stimulus
- phasic receptor = train of impulses CEASES during a prolonged stimulus
classify the following receptors as tonic or phasic:
- merkel
- meissner
- ruffini
- pacinian
- tonic = merkel, ruffini
- phasic = meissner
- extremely phasic = pacinian
classify the following as slowly adapting (SA) I/II or rapidly adapting (RA) I/II receptor fibers:
- merkel disks
- meissner corpuscles
- ruffini cylinder
- pacinian corpuscles
- merkel = SA I
- meissner = RA I
- ruffini = SA II
- pacinian = RA II
What is the size of the receptive field (large/small) of the following receptors:
- merkel disks
- pacinian corpuscles
- ruffini cylinder
- meissner corpuscles
- small = merkel, meissner
- large = ruffini, pacinian
TRUE or FALSE: RA fibers correspond with phasic receptors whereas SA fibers correspond with tonic receptors
TRUE
What is a second burst of activity in RA fibers associated with?
release of stimulus
TRUE or FALSE: merkel disks and ruffini cylinders are surface mechanoreceptors; meissner and pacinian corpuscles are deep mechanoreceptors
FALSE:
- surface = merkel and meissner
- deep = ruffini and pacinian
Where are merkel receptors high in density? What are they specialized for?
- fingertip ridges
- tactile acuity –> FINE DETAILS
Where are meissner corpuscles high in density? What are they specialized for?
- lips, palms, fingers, soles of feet
- initial contact, moving stimuli, and low frequency vibrations –> HANDGRIP CONTROL
Where are ruffini corpuscles high in density? What are they specialized for?
- base of finger/toenails, palm, skin overlying joints/ligaments
- balance on feet, firmness of grasp –> STRETCH
What are pacinian corpuscles specialized for?
high frequency vibrations –> VIBRATION, FINE TEXTURE BY MOVING FINGERS
What kind of channels do somatosensory mechanoreceptors have?
piezo 2 channels
Describe the structure of a piezo 2 channel.
- homotrimer (3 blades)
- 38 transmembrane domains on each blade
TRUE or FALSE: the piezo 2 channel is a dimer with 4 transmembrane domains on each blade
FALSE:
- homotrimer
- 38 transmembrane domains on each blade
TRUE or FALSE: the N-terminus intracellular domain blocks a pore of the piezo 2 channel
FALSE: the C-terminus extracellular domain (CED) blocks a pore of the piezo 2 channel
How does the piezo 2 channel open? What does opening cause?
- blades force the cap to twist
- opens to let cations in
- voltage-gated Ca2+ channels open via beta2 GPCR and adneylyl cyclase
Draw a diagram for the SAI response, the neuron-initiated dynamic firing, and merkel-mediated firing.
slide 11
Which neurons in the RAI are recruited? What kind of stimulus do they respond to?
- respond to indentations
- TrkB+ neuron responds to every indentation at LOWER threshold
- Ret+ neuron responds to intense touch at HIGHER threshold
TRUE or FALSE: when the onion layers of the RAII fibers are removed, there is less adaptation
TRUE
Explain why RAII fibers are phasic based on their structure.
- pressure (stimulus) causes deformation in layers of connective tissue with viscous gel between
- stretching opens sodium channels and creates a generator potential –> AP in neuron
- but b/c it is gel-like, the channels will close soon after (PHASIC)
- when the probe is released, the membrane will rebound out, OPENING AGAIN, and then return to normal (closed)
Draw 2 graphs to compare voltage change in RAII fibers when the onion layers are normal vs when they are removed.
slide 13; less adaptation when layer removed; 2 peaks bc of adaptation
Draw a graph to show how RAII fibers respond to indentation, in terms of temporal resolution.
slide 14; high temporal resolution
What is the human detection threshold for skin indentation in RAII fibers? What vibration frequency range are humans extremely sensitive? Does the range match meissner, pacinian, or merkel?
100 micrometers; 100-300 Hz (match pacinian corpuscle detection)
What vibration frequency are Pacinian corpuscles most sensitive to? Meissner? humans?
- pacinian = 50-300 Hz
- meissner = 50 Hz
- humans = 100-300 Hz
What are the 5 types of low threshold mechanoreceptors (LTMRs) in hairy skin? what kind of endings do they have?
- A-beta SA1 (Merkel cells)
- A-beta RA (Lanceolate endings)
- A-beta Field (Circumferential endings)
- A-delta (Lanceolate endings)
- C (Lanceolate endings)
Which LTMRs respond to indentation? movement of hairs? skin stroke?
- indentation: A-beta SA1
- movement of hairs: A-beta RA, A-delta, C
- skin stroke: A-beta field
TRUE or FALSE: skin stroke LTMRs are directionlally sensitive
FALSE: movement of hairs LTMRs
TRUE or FALSE: hairs and whiskers have a similar detection mechanism
FALSE: the whisker is like an organ
Which somatosensory receptor is found in whiskers? What do they respond to?
- merkel disks
- respond to: whisker touch AND whisking (when animal moves the whisker)
What do free nerve endings respond to?
temperature, pain (nociception), itch (pruriception)
Which channels on free nerve endings respond below 25 degrees celsius? above?
- below 25 degrees: TrpA1, Trpm8
- above 25 degrees: Trpv1, Trpv2, Trpv3, Trpv4
Describe the structure of the TrpV1 channel.
- tetramer
- each subunit has 6 transmembrane segments
- ankyrin repeats
What is the function of ankyrin?
binds to cytoskeleton
What cellular mechanism doe TRP channels in free nerve endings use?
GPCR
why is it important not to scratch an itchy wound?
- scratching releases 5HT
- 5HT opens TRP channels
- exacerbate pain/itch
What factors cause TRP channels to open, causing pain to worsen?
- bradykinin (B2R)
- histamine (H1R)
- serotonin (5HTR)
TRUE or FALSE: sensory receptors are like neurons
FALSE: they can have free nerve endings or enclosed nerve endings
Where are the cell bodies of sensory neurons located?
in the dorsal root ganglia
Which lamina in the spinal cord innervate pain? temperature? touch?
- pain & temperature = lamina II (more superficial)
- touch = lamina III-V (deeper)
Describe the pathway of info transmission in somatosensation.
- SENSORY RECEPTOR is stimulated
- AP travels down SENSORY NEURON via dorsal root
- sensory neuron synapses with INTERNEURON
- interneuron synapses with MOTOR NEURON via ventral root
- motor neuron synapse on EFFECTOR organ
Which lamina do the following LTMRs synapse in? (C, A-delta, A-beta RA, A-beta SA1)
- C = lamina II
- A-delta = lamina III
- A-beta RA & A-beta SA1 = lamina IV-V
9TRUE or FALSE: cell bodies of sensory neurons in the head are in the DRG
FALSE: found in ganglia in the pons and medulla (e.g. trigeminal ganglion)
