Sensation

Question 1

Where is the primary sensory cortex

Answer 1

Post-central gyrus

Question 2

Where is the primary motor cortex

Answer 2

Pre-central gyrus

Question 3

How much of the cortical mantle is occupied by representation of the face?

Answer 3

1/3 of cortical mantle within S1

Question 4

Does cerebellar (proprioceptive) info come from ipsi- or contra- inputs?

Answer 4

Ipsilateral

Question 5

Does input to S1 come from contra- or ipsi- input?

Answer 5

Contralateral

Question 6

What are the three neurons involved in general somatasensation?

Answer 6

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

Question 7

Where do second order neurons eminate from prior to decussation in the caudal medulla?

Answer 7

1) Gracile nucleus (lower limb, most medial)

2) Cuneate nucleus (upper limb, most lateral)

Question 8

What is the name of the pain/temp system

Answer 8

Anterolateral system/spinothalamic tract

Question 9

Which 4 pathways are involved in nonconcious prorpioception

Answer 9

1) Cuneocerebellar (upper limb)
2) Posterior spinocerebellar (lower limb)
3) Anterior spinocerebellar (trunk + lower limb)
4) Rostral spinocerebellar (trunk + upper limb)

Question 10

Which 2 pathways are involved in concsious prorprioception

Answer 10

1) Discriminative touch pathway (upper limb)

2) Collaterals of the PSCT (lower limb)

Question 11

Where is the end point for CONCIOUS proprioception

Answer 11

S1 (via VPL)

Question 12

What is the external cuneate?

Answer 12

Site of first synpase for non-conscious proprioception of the upper limb

Question 13

Describe the neurons involved in nonconcious proprioception of the upper limb (above C8) via the cuneocerebellar tract

Answer 13

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

Question 14

Describe the neurons involved in nonconscious proprioception of the lower limb (below C8) via the posterior spinocerebellar tract

Answer 14

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

Question 15

Where do the first synapses occur for nonconcious proprioception of the upper and lower limb, respectively

Answer 15

1) upper limb; rostral medulla in the external cuneate nucleus
2) lower limb; Clark’s nucleus in the spinal cord (L3 to C8)

Question 16

Which lamina is Clarke’s nucleus in?

Answer 16

Lamina VII

Question 17

What are three inputs to spinal border cells?

Answer 17

Muscle spindles and golgi tendon organs, descending modulating tracts to LMNs, flexor reflex arcs in the SC

Question 18

what are the outputs of SBCs?

Answer 18

1) Anterior spinocerebellar tract (ASCT)

2) Rostral spinocerebellar tract (RSCT)

Question 19

Synapses in ASCT

Answer 19

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

Question 20

Synapses in RSCT

Answer 20

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

Question 21

Sensory information from the head and face is carried by which cranial nerve

Answer 21

Trigeminal (V)

Question 22

Which nerve has the largest sensory ganglion in the skull?

Answer 22

Trigeminal (V)

Question 23

How many cranial nerve nuclei does CN V have?

Answer 23

4: Chief sensory nucleus (touch); Spinal nucleus of V (pain/temp in face); motor nucleus of V (motor); mesencephalic nucleus (proprioception)

Question 24

Which neurons (2) are involved in discriminative touch in the face?

Answer 24

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

Question 25

Which neurons (2) are involved in pain transmission from the face?

Answer 25

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

Question 26

What are the three regions of the spinal tract of V

Answer 26

Most rostral to most caudal: oralis, interpolaris, caudal

Question 27

What is carried in the spinal tract of V

Answer 27

Pain fibres from the face (descending to the appropriate level of the medulla)

Question 28

Which cranial nuclei mediate jaw and bite reflexes

Answer 28

1) Mesencephalic nucleus of V; 2) Motor nucleus of V

Question 29

What neurons are involved in proprioception of the face (e.g., jaw and bite reflexes)

Answer 29

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

Question 30

Where is the ganglion for A-alpha fibres carrying proprioceptive info from the face

Answer 30

In the midbrain (unlike all other primary sensory neurons, whose cell bodies are outside the CNS)

Question 31

What info travels in the mesencephalic root

Answer 31

Face proprioceptive afferents

Question 32

Where does proprioceptive info from face make its first synpase in the CNS?

Answer 32

Motor nucleus of V (mediated through mesencephalic nucleus)

Question 33

At which level of the brainstem does the medial lemniscus FLATTEN horizontally?

Answer 33

Caudal pons

Question 34

Where does the medial lemniscus terminate?

Answer 34

VPL thalamus

Question 35

What are arcuate fibres and where are they found

Answer 35

Caudal medulla; second order neurons that cross midline carrying somatosensory info in medial-lemniscus to thalamus

Question 36

What are the 2 divisions/purposes of the anterolateral tract?

Answer 36

1) Awareness of pain and temperature (spinal cord --> thalamus); 2) Modulation of pain and temperature (smaller tracts; spinal cord --> modulation centres)

Question 37

Which tracts are involved in transmisssion of "dull, aching, poorly localized pain"

Answer 37

1) Paleospinothalamic tract; 2) Spinoreticulothalamic tract; final projections are in limbic areas

Question 38

Which tracts carry pain information that projects to the dorsal MEDIAL and intralaminar nuclei of the thalamus?

Answer 38

1) Paleospinothalamic tract; 2) Spinoreticulothalamic tract; no somatotopy

Question 39

What is the spinomesencephalic tract?

Answer 39

1) offshoots of spinothalamic tract into the PAG and superior colliculus; from their, these structures play a role in descening pain modulation

Question 40

Role of A-delta fibres

Answer 40

Activated by mechanical and thermal stim; FAST and myelinated

Question 41

Role of c fibres

Answer 41

Slow and unmyelinated; activated by chemical components of "inflammatory soup"; diffuse signal transmission

Question 42

Role of A-beta fibres

Answer 42

General sensory; pain modulation

Question 43

Components of inflammatory soup

Answer 43

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

Question 44

In which laminae do A-delta pain fibres synapse?

Answer 44

1, 2, 5

Question 45

In which laminae do c-fibres synase?

Answer 45

1 and 2

Question 46

What are the 2 dorsal horn synaptic targets?

Answer 46

1) Nociceptive specific cells | 2) Wide dynamic range neurons

Question 47

Where are nociceptive specific cells (NS) cells located in the dorsal horn?

Answer 47

Lamina 1, synapse with A-delta and c-fibres | Encode only for pain stimuli and project to higher centres

Question 48

Where are WDR neurons located in the dorsal horn?

Answer 48

Lamina 5; synapse with all sensory neuron types

Question 49

What are the four targets of the anterolateral tract?

Answer 49

1) Thalamus (spinothalamic tract) 2) Hypothalamus (spinohypothalamic tract) 3) PAG (spinomesencephalic tract) 4) Reticular formation (5-HT, NE)

Question 50

What is the function of the lateral pain system

Answer 50

Pain localization

Question 51

What is the function of the medial pain system

Answer 51

Dull/chronic pain; affective component

Question 52

Which key structures are targets for the medial pain system

Answer 52

ACC, insula, hypothalamus, amygdala

Question 53

Which pain system engages primary and secondary sensory cortices

Answer 53

Lateral pain system

Question 54

In gate theory modulation, what synapse is the site of modulation

Answer 54

C-fibre synapsing onto WDR neuron in lamina 5; interneurons (stimulated by A-beta fibres) also release GABA and decrease pain perception

Question 55

Which NTs are most involved in descending pain modulation

Answer 55

1) NE (from locus coeruleus); 2) 5-HT from raphe nuclei

Question 56

How do opioids decrease pain transmission

Answer 56

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)

Question 57

Pain information reaches PAG through which tract

Answer 57

Spinomesencephalic

Question 58

Describe PAG efferent pathway with relation to pain

Answer 58

PAG efferents --> RF in rostral medulla/caudal pons --> dorsal horn substantia gelatinosa

Question 59

Where is the chief sensory nucleus of V?

Answer 59

Mid-pons, posterolateral tegmentum

Question 60

In which tract do ascending fibres from the Spinal Nucleus of V and Chief Sensory nucleus travel?

Answer 60

trigeminothalamic tract

Question 61

Where does trigeminothalamic tract terminate?

Answer 61

VPM thalamus

Question 62

3 branches of the trigeminal nerve?

Answer 62

V1) opthalmic; V2) maxillary; V3) mandibular

Question 63

3 exit points of CN V?

Answer 63

1) superior orbital fissure; 2) foramen rotundum; 3) foramen ovale

Question 64

Which part of Cn V carries motor information?

Answer 64

V3 (mandibular)

Question 65

Which info is carried by the trigeminal lemniscus

Answer 65

Sensation (non-nociceptive) from face; from chief sensory nucleus of V