SOMATOSENSATION-TOUCH Flashcards
What is another word for pain?
Nossiseption
How can we quantitatively test touch perception?
- Two point discrimination threshold
- Letter identification
Where are mechanically gated cation channels found?G
Found in spike generating zones of the axons of mechanoreceptors
What happens when stretch is detected?
Stretch or lipid tension in membrane causes Na+ channels to open thus depolarising the cell
Can strucutral proteins also be stretched to open channel?
YES!
What can G protein coupled receptors be involved in?
PAIN SENSATION
because receptors are slow to activate and LONG LASTING
What are the 4 types of mechanoreceptors?
Merkel cells, Messiner corpuscle, ruffini endings, and Pacinian corpuscle
What are merkel cells?
SA1 (slowly adapting)
- 3 mechanoreceptors associated with a single axon
- Hairy and glaborous skin
- Is SUPERFICIAL layer
What are messiner cells?
2 mechanoreceptros associated with a single axon
- Rapidly adapting (RA1)
- GLABOROUS SKIN (palms of hands-fine touch tasks)
- SUPERFICIAL LAYER in dermal papillae
What are ruffini endings?
- SA2 (slowly adapting)
- hairy AND glaborous skin
- DEEP tissue- dermis
What are pacinian corpuscles?
- RA2 (rapidly adapting)
- DEEP tissue (dermis)
- Hairy and glaborous skin type
What are free nerve endings in the skin cross section associated with?
PAIN SENSATION
Do unipolar neurons have dendrites?
NO! Just all axons
The size of the receptive fields in mechanoreceptors is…
Reflected in their relative position in the skin
Why do messiners corpuslces have much smaller receptive fields than the RFs of pacinian corpuslces?
Because pacinian corpuslces are much deeper in the skin so LARGER receptive field
Why can we sometimes not feel that we are wearing clothes?
Because the rate of AP evoked by the original stimuli can DECREASE
- we adapt stimuli that are unimportant
What happens to the firing rate of messiner and pacinian corpuslces with a SUSTAINED STIMULOUS?
The firing rate drops (both RA-rapidly adapting)
Do merkel cells and ruffini endings show adaptation?
NO (not as much)
What type of RF do ruffini endings have?
- Directional RF (stretching skin from =objects slipping through fingers)
- so more elongated RFs
What is a feature of Meciners corpuscles?
Have lots off different hotspots due to multiple accessory strucutres associated with SINGLE AXON
What is the most sensitive mechanoreceptor?
Pacinian corpuscles
- Rapidly adapt to sustained pressure
- Respond to high vibration frequencies
- Concentric fluid filled layers of connective tissue around the axon terminal
- Onion like strucutre- good for vibration, not good for sustained
What accounts for the human perceptual thresholds?
Frequency of sensitivity of Pacinian Corpuscles
What is the difference between the human threshold and the neural threshold?
- Human threshold is lowest amp of vibration rthat can be readily detected
- Neural threshold is lowest stimulus intensity that reliably evokes 1 AP per cycle
What completely accounts for human sensitivity?
RA1 and RA2
What do merkel disks (SA1) ecode?
Shape and size of objects touching the hand
- smaller stimuli activate a smaller number of receptors MORE STRONGLY
- higher AP firing rate
What are merkel (SA1) cells really good for?
- edge detection, precise and spacial localisation, have good surround inhibition (like in the visual system)
- For constant force, smaller probes evoke larger responses
Which mechanorceptors provide the most information about braile?
Merkel disks (SA1) - Due to small RF and SLOW adaptation
What is the dorsal pathway to the brain?
- Abeta axons from sensory receptors enter spinal cord via dorsal root
- Axons branch, snyapsing onto neurons with the dorsal horns
- Other branch ascends S.C in dorsal column, synapsing in dorsal column nuclei
- Dorsal column neurons targert neurons in VP (ventral posterior) nucelus of thalamus–> projects to S1
What occurs in area 3b (S1)?
- Receives dense inputs from VP nucleus in thalamus
- In this area neurons responsive to somatosensory stimuli
- Lesions impair touch sensation
- Electrical stimulation evokes touch stimuli
How is area 17 V1 different to area 3b (S1)?
- receives inputs from LGN of thalamus
- neurons responsible for VISUAL STIMULI
- Lesions impair VISUAL SENSATION
What does an inhibitory surround allow for?
The size and position of stimulus to be encoded
Can a neuron with no surround still encode size and position of stimulus?
NO! not well at all.
- Large stimulus slightly displaced from the centre will evoke the same firing rate as small stimulus centred on RF centre
