Somatosensory Flashcards
Types of afferent fibres and the modality?
Aalpha - proprioception
Abeta - pressure/vibration
Adelta- thermal sensation/nociception
Cfibres - nociception and itch
How is stimulus intensity detected?
Graded response can be produced
Variance in receptive fields can by tested through
2-point descrimination
Muscle spindles lie
In parallel with fibres
GTOs lie
In series with fibres
A alpha fibres synapse in which laminae
VI, VII and IX
A beta fibres synapse in which laminae?
III, IV, V (nucleus proprius)
Spinocerebellar afferents synapse in
VII, Clarke’s column and project to inferior cerebellar peduncle
Clarkes column is associated with which ascending path?
Spinocerebellar
Substantia gelatinosa is associated with which modality and ascending path?
Pain, anterolateral spinothalamic tract C fibres
Nucleus proprius is associated with which, fibres and modality?
A delta carrying pain
A beta carrying general sensation
Lamina 1 received input from
Lissauer’s tract (pain and temp)
Dorsal column sends information to
VP thalamus and S1
Proprioception S1
3a
Touch S1
3b
Rapidly adapting fibres
Stop firing action potentials as soon as the produced skin indentation is stationary
Slowly adapting fibres
Respond to steady skin indentation with sustained discharge of action potentials.
Which touch fibres (1 or 2 ) are superficial and deep?
1 superficial
2 deep
SA1, SA2, RA1, RA2 types
Merkel’s discs
Ruffini
Meissner’s
Pacinian
Type 1 sensory receptors better at
Small details
Type 2 better at
Pressure and vibration
Sensitive to edges and corners
Merkel’s discs
Meissner’s structure
Encapsulated unmyelinated nerve endings, surrounded by Schwann cells.
Good for microdetection of detailed surface features
Meissener’s (rapid adapting good for high acuity)
Ruffini corpuscles located?
Palmar folds and finger joints
Pacinian corpuscles structure
Wrapped in successive layers of connective tissue and myelin called lamellae separated by fluid-filled space.
Ruffini sensitive to
Skin stretch, stereognosis
Good for pressure and vibration
Pacinian corpuscles
TRPV1
Hot painful capsaicin receptor
TRPV2
Hot, not responding to chemicals (very hot >52 degrees)
TRPV8
Extreme cold receptor
A alpha fibres synapse on
Motor neurons, motor Ia inhibitory interneurons and sensory (lamina 6) interneurons
A beta proprioception primarily from
Static bag and chain fibres
A alpha proprioception primarily from
Both dynamic and static information
Touch receptors afferent neuron
A beta (and static proprioception)
Thermosensitive a delta project to
Nucleus proprius
A delta pain synapses in
Laminae I
C fibre pain synapses in
Laminae II interneurons
Adelta touch is?
Crude touch
Sensory afferents go to ipsilateral/contralateral thalamus
Contralateral
Spinal level above which cuneate tract
T6 up
Spinal level below which gracile tract
T7 down
Gracile is medial/lateral to cuneate
Medial
Sensory decussation occurs
Lower medulla (medial lemniscus forms)
In medial lemniscus are lower limb medial or lateral
Lateral
Mesencephalic nucleus of trigeminal
Midbrain, proprioception
A alpha
Principle nucleus of trigeminal
Pons, touch, A beta
Spinal nucleus of trigeminal
Medulla, pain/temp, a delta
Where does principle trigeminal nucleus axons go?
Cross to join medial lemniscus and terminating in VPm
Where do mesencephalic trigeminal nucleus axons go?
Motor nucleus V
Where does spinal trigeminal nucleus axons go?
Anterolateral tract
Area 1
Receives large amounts of input from RA1/2 and is thus important in integrating texture
Area 2
Receives inputs from 3a in addition to 3b and therefore is key in combining proprioception with touch information, this underpins stereognosis
S2
Tactile memory
Areas 5&7 posterior parietal
Tactile memory and sensory integration
Brown sequard
Loss of ipsilateral sensation and proprioception
Contralateral loss of pain and temperature
LMN lesion at the level of the lesion
UMN lesion below level of the lesion
ANS loss
Central cord syndrome
Medial corticospinal tract (upper limb/axial muscles) UMN lesion
Progressive loss of sensations
Anterior cord syndrome
Preserve proprioception and touch
Crossing anterolateral pain fibres - loss of pain and temperature sensation
Loss of corticospinal fibres
White matter, the higher the vertebrae?
White matter increases as more fibres
Until T6 there is only one…
Dorsal column (gracilis)
Intermediate horn is much larger where?
Thoracic spine (T1-T12) lots of visceral output
and Clarke’s column
Larger ventral horns where?
(L2-S2), shows where there are large amounts of motor neurons for innervation of the lower limb.
Upper limb is in the cervical segments C4-T2
