Sensation Flashcards
Where is the primary sensory cortex
Post-central gyrus
Where is the primary motor cortex
Pre-central gyrus
How much of the cortical mantle is occupied by representation of the face?
1/3 of cortical mantle within S1
Does cerebellar (proprioceptive) info come from ipsi- or contra- inputs?
Ipsilateral
Does input to S1 come from contra- or ipsi- input?
Contralateral
What are the three neurons involved in general somatasensation?
1) Primary sensory neuron outside CNS (except CN V) enter SC and travel to caudal medulla in medial-lemniscal columns ipsilaterally
2) Secondary sensory neuron in caudal medulla (or brainstem) — DECUSSATE — and go to thalamus
3) Tertiary neuron in the VPL (body) or VPM (face) thalamus goes to S1 via the internal capsule
Where do second order neurons eminate from prior to decussation in the caudal medulla?
1) Gracile nucleus (lower limb, most medial)
2) Cuneate nucleus (upper limb, most lateral)
What is the name of the pain/temp system
Anterolateral system/spinothalamic tract
Which 4 pathways are involved in nonconcious prorpioception
1) Cuneocerebellar (upper limb)
2) Posterior spinocerebellar (lower limb)
3) Anterior spinocerebellar (trunk + lower limb)
4) Rostral spinocerebellar (trunk + upper limb)
Which 2 pathways are involved in concsious prorprioception
1) Discriminative touch pathway (upper limb)
2) Collaterals of the PSCT (lower limb)
Where is the end point for CONCIOUS proprioception
S1 (via VPL)
What is the external cuneate?
Site of first synpase for non-conscious proprioception of the upper limb
Describe the neurons involved in nonconcious proprioception of the upper limb (above C8) via the cuneocerebellar tract
1; Fibres from skeletal muscle and skin receptors above C8 enter the dorsal horn and travel to rostral medulla via fasciculus cuneatus
2; Synapse in external cuneate nucleus – 2nd order neurons tracel from ECN to cerbellum via Inferior Cerebllar Peduncle
Describe the neurons involved in nonconscious proprioception of the lower limb (below C8) via the posterior spinocerebellar tract
1a) Below L3; fibres enter in the dorsal horn and travel in the fasciculus gracilis until they reach L3, where they synpase at Clark Nucleus
1b) L3 to C8; fibres enter the dorsal horn and synpase at Clark Nucleus
2) Second order neurons travel in the POSTERIOR spinocerebellar tract (PSCT) and into the ICP to reach the cerebellum
Where do the first synapses occur for nonconcious proprioception of the upper and lower limb, respectively
1) upper limb; rostral medulla in the external cuneate nucleus
2) lower limb; Clark’s nucleus in the spinal cord (L3 to C8)
Which lamina is Clarke’s nucleus in?
Lamina VII
What are three inputs to spinal border cells?
Muscle spindles and golgi tendon organs, descending modulating tracts to LMNs, flexor reflex arcs in the SC
what are the outputs of SBCs?
1) Anterior spinocerebellar tract (ASCT)
2) Rostral spinocerebellar tract (RSCT)
Synapses in ASCT
1) proprioceptive afferents enter dorsal horn and synapse with SBCs (which can also receive descending modulatory inputs)
2) SPCs cross the midline and travel to the pons in the ASCT
3) Enter the cerebellum via SCP and then cross midline again to arrive at the ipsilateral cerebellar hemisphere
Synapses in RSCT
1) proprioceptive afferents ABOVE T8 enter dorsal horn and synapse with SBCs (which can also receive descending modulatory inputs)
2) SBC fibres travel uncrossed to the ipsilateral cerebellum as the RSCT
Sensory information from the head and face is carried by which cranial nerve
Trigeminal (V)
Which nerve has the largest sensory ganglion in the skull?
Trigeminal (V)
How many cranial nerve nuclei does CN V have?
4: Chief sensory nucleus (touch); Spinal nucleus of V (pain/temp in face); motor nucleus of V (motor); mesencephalic nucleus (proprioception)
Which neurons (2) are involved in discriminative touch in the face?
1) 1st order neuron enters through ganglion of V (midpons) and synpases w/i chief sensory nucleus
2) 2nd order neuron crosses midline and ascends through the trigeminal lemniscus to VPM thalamus
Which neurons (2) are involved in pain transmission from the face?
1) 1st order neuron (c-fibres, A-delta) enter through ganglion of V (mid-pons) and DESCEND through spinal tract of V to the spinal nucleus of V (synpase here)
2) 2nd order neurons cross the midline and join the trigeminal lemniscus to the VPM thalamus
What are the three regions of the spinal tract of V
Most rostral to most caudal: oralis, interpolaris, caudal
What is carried in the spinal tract of V
Pain fibres from the face (descending to the appropriate level of the medulla)
Which cranial nuclei mediate jaw and bite reflexes
1) Mesencephalic nucleus of V; 2) Motor nucleus of V
What neurons are involved in proprioception of the face (e.g., jaw and bite reflexes)
1) A-alpha sensory neuron (cell body in the mesencephalic nucleus in the midbrain) synpases at motor nucleus of V
2) 2nd order neuron (motor efferent) goes back to face via trigeminal root
Where is the ganglion for A-alpha fibres carrying proprioceptive info from the face
In the midbrain (unlike all other primary sensory neurons, whose cell bodies are outside the CNS)
What info travels in the mesencephalic root
Face proprioceptive afferents
Where does proprioceptive info from face make its first synpase in the CNS?
Motor nucleus of V (mediated through mesencephalic nucleus)
At which level of the brainstem does the medial lemniscus FLATTEN horizontally?
Caudal pons
Where does the medial lemniscus terminate?
VPL thalamus
What are arcuate fibres and where are they found
Caudal medulla; second order neurons that cross midline carrying somatosensory info in medial-lemniscus to thalamus
What are the 2 divisions/purposes of the anterolateral tract?
1) Awareness of pain and temperature (spinal cord –> thalamus); 2) Modulation of pain and temperature (smaller tracts; spinal cord –> modulation centres)
Which tracts are involved in transmisssion of “dull, aching, poorly localized pain”
1) Paleospinothalamic tract; 2) Spinoreticulothalamic tract; final projections are in limbic areas
Which tracts carry pain information that projects to the dorsal MEDIAL and intralaminar nuclei of the thalamus?
1) Paleospinothalamic tract; 2) Spinoreticulothalamic tract; no somatotopy
What is the spinomesencephalic tract?
1) offshoots of spinothalamic tract into the PAG and superior colliculus; from their, these structures play a role in descening pain modulation
Role of A-delta fibres
Activated by mechanical and thermal stim; FAST and myelinated
Role of c fibres
Slow and unmyelinated; activated by chemical components of “inflammatory soup”; diffuse signal transmission
Role of A-beta fibres
General sensory; pain modulation
Components of inflammatory soup
1) Tissue damage releases 5-HT, bradykinin, prostaglandins and K+
2) These chemicals activate c-fibres to release CGRP and substance P
3) Mast cells release histamine
4) Local inflammation and vessel dilation
In which laminae do A-delta pain fibres synapse?
1, 2, 5
In which laminae do c-fibres synase?
1 and 2
What are the 2 dorsal horn synaptic targets?
1) Nociceptive specific cells
2) Wide dynamic range neurons
Where are nociceptive specific cells (NS) cells located in the dorsal horn?
Lamina 1, synapse with A-delta and c-fibres
Encode only for pain stimuli and project to higher centres
Where are WDR neurons located in the dorsal horn?
Lamina 5; synapse with all sensory neuron types
What are the four targets of the anterolateral tract?
1) Thalamus (spinothalamic tract)
2) Hypothalamus (spinohypothalamic tract)
3) PAG (spinomesencephalic tract)
4) Reticular formation (5-HT, NE)
What is the function of the lateral pain system
Pain localization
What is the function of the medial pain system
Dull/chronic pain; affective component
Which key structures are targets for the medial pain system
ACC, insula, hypothalamus, amygdala
Which pain system engages primary and secondary sensory cortices
Lateral pain system
In gate theory modulation, what synapse is the site of modulation
C-fibre synapsing onto WDR neuron in lamina 5; interneurons (stimulated by A-beta fibres) also release GABA and decrease pain perception
Which NTs are most involved in descending pain modulation
1) NE (from locus coeruleus); 2) 5-HT from raphe nuclei
How do opioids decrease pain transmission
Bind to opioid receptors on pre-synaptic neurons and inhibit excitation of post-synaptic neurons (e.g., decrease firing AND block release of excitatory NTs)
Pain information reaches PAG through which tract
Spinomesencephalic
Describe PAG efferent pathway with relation to pain
PAG efferents –> RF in rostral medulla/caudal pons –> dorsal horn substantia gelatinosa
Where is the chief sensory nucleus of V?
Mid-pons, posterolateral tegmentum
In which tract do ascending fibres from the Spinal Nucleus of V and Chief Sensory nucleus travel?
trigeminothalamic tract
Where does trigeminothalamic tract terminate?
VPM thalamus
3 branches of the trigeminal nerve?
V1) opthalmic; V2) maxillary; V3) mandibular
3 exit points of CN V?
1) superior orbital fissure; 2) foramen rotundum; 3) foramen ovale
Which part of Cn V carries motor information?
V3 (mandibular)
Which info is carried by the trigeminal lemniscus
Sensation (non-nociceptive) from face; from chief sensory nucleus of V
