Somatic Sensation Flashcards
Speed of adaptation of Meissner’s corpuscle?
Complete and rapid
What happens to number of Meissner’s with age?
Declines
How many Meissner’s corpuscles does each axon branch innervate?
15
How many axon branches may each Meissner’s corpuscle contain?
3
What is Meissner’s stimulated by?
Sideways displacement of the skin - slipping?
What do Meissner’s show phase locking to?
Vibration frequency
Which fibres from Meissner’s corpuscles?
RA1
Size of receptive field of Merkel’s disc?
Small
Are Merkel’s rapidly or slowly adapting?
Slowly
Where are Merkel’s discs found?
Epidermal ridges of glabrous skin and touch zone of hairy skin
How are Merkel’s discs attached to epidermal keratinocytes?
Desmosomes
What do Merkel’s discs respond to?
Light steady pressure
What is the structure of a Meissner’s corpuscle?
Layers of Schwann cells with a perineural outer sheath
Where are Pacinian corpuscles found?
In the deep dermis of the glabrous skin between tendons and close to the periosteum
What are lamellae in Pacinian corpuscle for?
Act as mechanical filter which completely adapts under steady displacement
Which fibres do Pacinian corpuscles use?
RA2
What do Pacinian corpuscles detect?
High frequency vibration
How many nerve fibres supply each receptor?
One
What is Ruffini/Golgi tendon organ capsule divided into?
Compartments of endoneural connective tissue
Which fibres do Ruffini and Golgi tendon organs use?
SA2
How does tension activate Ruffini/Golgi tendon organ ?
Tension tightens the spirals and squashes the nerve endings
Which fibres respond to mechanical damage, heat and temperature?
Polymodal C fibres
Above which temperature is all fibres firing nociceptors?
46
What is background discharge of nociceptors?
None
Where are free ending intraepidermal?
Cornea, trachea and bronchi
Which fibres are labelled line?
Cold and hot
Why/where are gracile and cuneate ipsilateral?
Crosses over in brain not spine
Where does somatic signal go from VPN of thalamus?
SI and SII
Which parts of brain does somatic sensation go to?
Thalamus, reticular formation, PAG, amygdala, hypothalamus, superiory colliculus
Where does somatic sensation go from thalamus?
ACC, insula, SI
What is SI for?
Localisation of pain response
How is gate control theory involved in pain?
Descending influence on pain response from PAG
What is astereognosia?
can’t identify objects by touch
What is Pacinian receptive field like?
Large
How many receptors per afferent fibres are there in Pacinian corpuscle?
One
Speed of adaptation in Pacinian?
Rapid
What is the highest frequency Pacinian can reconstruct?
300-400Hz
How many Meissners converge to form 1 afferent?
Up to 20
Size of Meissners receptive field?
Small
How many receptors to one afferent in Merkels?
20
Which fibre type do Merkels use?
SA1
How many receptors per fibre in Ruffini?
1
What do Ruffini respond to?
Skin stretch
Which fibre is faster out of C and Adelta?
C is slower
WHich fibre is more myelinated out of C and Adelta?
Adelta
Which fibres are affected first during hypoxia?
Large - Abeta then Adelta
Which fibres does local anaesthetic affect?
Small - C and Adelta
Do Aalpha and Abeta fibres go ipsilateral or contralateral?
Ipsilateral
Do pain fibres travel ipsilateral or contralateral?
Contralateral
Which tract to pain fibres travel in?
Spinothalamic
What happens in posterior column syndrome?
Lose mechanoreceptors, can still feel pain and temperature
Is the mandibular branch sensory or motor?
Mixed
Are ophthalmic and maxillary sensory or motor?
Sensory
What part of the thalamus is to respond to pain?
Posterior part of VMN
Where is the somatosensory cortex
Postcentral gyrus
What is Brodman’s area?
S1 (3a, 3b, 1,2 )
Where is S1 input from?
VP in thalamus
Which area of cortex shows direction selectivity?
Area 2
What enhances response of neurones in S2?
Attention
What is SI for in pain?
Discriminative
What is insula for?
Homeostatic
What is ACC for?
Emotion and empathy
What does rubbing around injury stimulate?
Abeta fibres
What are cold receptors called?
Trpm8
Which fibres does Trpm8 receptors use?
A delta and C
Which fibres do TRPV1 use?
C
When do you get myoclonus?
Hypoxia
What happens to corticospinal cord in primates?
Spreads ventrally
What is the human equivalent of the rubrospinal tract?
Corticospinal
What are the two parts of the corticospinal tract?
Large lateral and smaller ventromedial
What happens to receptors as temperature increases?
More are activated
What are wide dynamic range neurones for?
Intensity
Which receptors rapidly adapt?
Meissners and Pacinian
Which receptors slowly adapt?
Merkel and Ruffini
What are the otolith organs?
Saccule and utricle
How is intensity shown in rapidly adapting cells?
Recruitment
What is the PAG for?
Analgesic response, back to spinal cord to modulate -GATE CONTROL
Which vibration receptors does topical anaesthetic reach?
Meissner
Are Ad and C myelinated or unmyelinated?
C is unmyelinated, Ad slightly myelinated
Where do A fibres cross to get to the somatosensory cortex?
Medial lemniscus
Where does the spinothalamic tract go to?
Reticular formation, SI, ACC or insula
What does syringomyelia cause?
Loss of nociception and thermoreceptors bilaterally, can still feel touch
Whcih kind of fibres are in teh DC-ML?
A d and b
Which part of the thalamus do DC-ML fibres end up in?
VPN
WHich lamina is a disctint nociceptive pathway?
I
Which part of the thalamus responds to pain and temperature?
Posterior part of the VMN
What kind of of input do lamina I spinothalamic neurones give?
Topographical
Which layer do thalamic afferent terminate?
IV
WHich layers goes back to thalamus?
VI
Which layers go to other cortical regions?
II and III
WHich layer goes back to subcortical structures?
V (basal ganglia and brainstem)
How does area 2 get directional selectivity?
Overlapping excitatory and inhibitory zones
What is an emergent property?
Not seen in lower pathway
Which lamiae do Ad fibres synapsee?
1 and 5
Which laminae do C fibres synapse?
1 and 2
Which laminae do Ab (mechanoreceptors) synpase?
4 and 5
Which fibres show wind-up?
Adelta
How do Ab fibres mediate lateral inhibition?
Inhibitory interneurones
In which laminae are the narrow dynamic range fibres?
1
Which area does PAG integrate input from?
Cortex, thalamus, hypothalamus
What can be stimulated for surgery without anaesthesia?
PAG
What blocks the PAG without surgery effect?
Opioid antagonists