Somatosensory System and Thalamus

Question 1

Touch pressure vibration receptors

Answer 1

Meissner’s corpuscle, pacinian corpuscle, ruffini corpuscles, merkel’s disks

Question 2

Pain and temp reception

Answer 2

Free nerve ending

Question 3

1a Fibers
1b

AB

2

Answer 3

Muscle spindle fibers
GTO fibers

Touch, proprioception

Spindle

Large diameter, heavy myelin, fast conducting.

Question 4

Group III
AD

Group IV
C

Answer 4

Thin myelinated

Thin unmyelinated

Pain and temperature sense

Question 5

DC-ML system senses

Answer 5

Proprioception, touch, vibration

Question 6

Spinothalamic (anterolateral) tract

Answer 6

Pain and temp

Question 7

Where does DC-ML ascend?

Answer 7

Ipsilaterally in the fasciculus gracilis, fasciculus cuneatus (above T6) to their respective nuclei. (1st synapse) Then decussate at medial lemniscus in medulla.

Question 8

Where does the spinothalamic tract ascend

Answer 8

Enters 1-2 levels higher via Lissauer’s tract, (enters and synpases) then crosses immediately via ventral white commissure, then rises in the lateral spinothalamic tract to the thalamus.

Question 9

Brown sequard syndrome

Answer 9

Hemisection of spinal cord leads to ipsilateral weakness/loss of touch and position, and contralateral reduction of pain/temp.

Question 10

Mechanosensation from face

Answer 10

AB fibers from face (whose cell bodies live in trigeminal ganglion in pons) synapse in the principal sensory nucleus (pons), and ascend contralaterally in the medial lemniscus.

Question 11

Pain/temp from face

Answer 11

AD and C fibers from face (whose cell bodies live in trigeminal ganglion in pons) descend to spinal nucleus of V, then synapse, cross and ascend in spinothalamic tract.

Question 12

How is the DCML organized in the thalamus?

Answer 12

Legs lateral, trunk arm neck in VPL. Face medial in the VPM. Proportional representation, strong and faithful synapses.

Question 13

How is spinothalamic system organized in the thalamus?

Answer 13

Very little somatotopic organization, little proportional representation, large receptive fields, no convergence of info.

Question 14

Somatotopy in SI

Answer 14

Leg medial, Face lateral

Question 15

Do AD and C fibers run with AB fibers to places in S1?

Answer 15

Yes. Just not as organized in the thalamus.

Question 16

Areas 3a, 3b, 1 and 2 in S1

Answer 16

Sagitally anterior to posterior. 3A and 2 are proprioception. 3b and 1 are cutaneous. Pain and temp everywhere in S1. .

Question 17

Where do DCMLs synapse in the cortex?

Answer 17

Layer 4 on stellate cells

Question 18

Where to spinothalamic neurons synapse in the cortex?

Answer 18

Nowhere, run directly to pial layer.

Question 19

S2

Answer 19

Second somatosensory cortex, organized face rostral, legs caudal. Receives bilateral input via fibers running through corpus callosum.

Question 20

TRN

Answer 20

Thalamic reticular nucleus (Ventral Thalamus). Sheet of 100% gabaergic inhibitory neurons. Surrounds dorsal thalamus, sends axons only to dorsal thalamus relay neurons.

Question 21

Draw the circuits from sensory inputs to Dorsal Thalamus and interaction with TRN and cortex

Answer 21

Do it!

Question 22

What is the purpose of the TRN/Dorsal thalamus circuit?

Answer 22

Regulates states of consciousness

Question 23

Awake EEG

Answer 23

Low voltage, high frequency

Question 24

Spindle Waves

Answer 24

Stage 2 sleep, mid frequency

Question 25

Delta Waves

Answer 25

Stage IV sleep, low frequency, synchronized oscillations. High amplitude

Question 26

Oscillatory (burst) mode of relay cells

Answer 26

Cell hyperpolarized due to input from TRN. Hyperpolarization activated current activated, spike with Ca 2 influx, so depolarization happens. This then activates TRN neurons. Cycle repeats

Question 27

Tonic mode of relay cells

Answer 27

During consciousness. Thalamic relay cell relatively depolarized because inputs from reticular activating system depolarize the membrane of relay cells.

Question 28

Reticular activating system

Answer 28

Parabrachial nucleus, raphe, locus ceruleus, hypothalamus (produces histamine).

Question 29

Thalamic syndrome

Answer 29

Damage to posterior thalamus (which includes VPL and VPM) causes hemianesthesia with excruciating central pain.

Question 30

Tremor states

Answer 30

Rhythmic bursts in motor thalamus

Question 31

Amnesia

Answer 31

Lesions of anterior/medial thalamus

Question 32

Descending modulatory systems of pain

Answer 32

S1 -> PAG ->Raphe/LC/PBN -> Enkephalin inhibitory interneurons in dorsal horn -> Ad or C fibers which project back up to thalamus

Question 33

What does activation of opiate receptors do?

Answer 33

Decreases duration of sensory neuron AP coming from periphery, so less released onto dorsal horn projection neurons.
Decreases EPSP, hyperpolarizes projection neuron.

Question 34

Nociceptive pain

Answer 34

Physiological pain produced by noxious stimuli. Everything is correct

Question 35

Gate theory

Answer 35

Light tough decreases pain because activates inhibitory interneuron that stops dorsal horn projection neuron from firing.

Question 36

Inflammatory pain

Answer 36

Pain hypersensitivity due to peripheral inflammation. Pain with no stimulus. All stimuli more painful.

Question 37

Allodynia

Answer 37

Normally non-painful stimulus is painful

Question 38

Hyperalgesia

Answer 38

Normally painful stimulus is more painful.

Question 39

Dysfunctional Pain

Answer 39

Neither protects nor supports healing/repair (fibromyalgia).

Question 40

Neuropathic pain

Answer 40

Maladaptive plasticity cause by disease causes nociceptive processing. HUGE pain.

Question 41

Central sensitization

Answer 41

Pain felt with enhanced synaptic signalling