Anatomy of Touch

Question 1

What does a meissner corpuscle do?

(2 marks)

Answer 1

Senses deformation of the skin, frequency of stimulation increase

not as sensitive as pacinain corpuscle

Question 2

What des the merkel cell neurite complex do?

(1 mark)

Answer 2

• Slow responses, continue to fire to length of stimulus

Question 3

What does myelinated C-fibre LTM do?

(3 marks)

Answer 3

• Has high threshold, or noxious damage to skin stimulation
• activated for a long time (throbbing pains)
• low spatial resolution

Question 4

What does an unmyelinated C-fibre LTM do?

(4 marks)

Answer 4

• Responds to low threshold touch e.g. stroking
• Carries low threshold information
• Projects to part of brain that deals with pleasure points
• Convey mechanical and temperature information

Question 5

Through which tracts does sensory information travel?

(2 marks)

Answer 5

Dorsal Column pathway

Spinothalamic tract

Question 6

Outline the dorsal column system in the transmission of sensory information to the cortex.

(4 marks)

Answer 6

• Action potential come in through ganglion enters spinal cord at dorsal root
• Makes a turn and ascends up spinal cord
• Synapses at nucleus gracilis and cunneatus - nuclei cells project up through midbrain to somatosensory thalamus
• Reliant on low threshold receptors and high innervation sensitivity

Question 7

Outline the spinothalamic tract when transmitting sensory information to the cortex.

(4 marks)

Answer 7

• Action potential comes in through DRG and synapses at same side entered
• Cells in spinal cord project across the midline and then project up through spinal thalamic tract which is ventral and lateral
• Goes up to the somatosensory thalamus
• Carries crude tactile information, pressure, high threshold touch and temperature information

Question 8

What is the name of the PHAT nerve that innervates the face and what are its derivatives?

(4 marks)

Answer 8

Trigeminal nerve (CN V)

3 branches:

• opthalamic branch - sensory - give rise to infraorbital nerve
• maxillary branch - sensory
• mandibular branch - sensory and motor

Question 9

What nerve are the whiskers of rodents innervated by?

(2 marks)

Answer 9

Infraorbital nerve

• Sensory nerve - provides sensory input to central somatosensory pathways that process discriminative touch-related information

Question 10

Where does the information from whiskers go?

(1 mark)

Answer 10

Whiskers → thalamus → cortex

Question 11

What is each whisker represented by in the cortex?

(1 mark)

Answer 11

Corresponding patch of cells known as a ‘barrel’

Question 12

What is innervation density in the context of whiskers and the brain?

Answer 12

• Related to area of cortex thats occupied by particular area of the body

Question 13

What pathways do the receptors in the trigeminal system give rise to?

Answer 13

Principalis and Interpolaris pathways

Question 14

Where does information from the infraorbital nerve go to?

hint: not the common first initial answer you think of every single time

(3 marks)

Answer 14

• Information is FROM whiskers
• Has trigeminal ganglion and then receptor projects inot the brainstem to 2 seperate nuclei principalis (PrV) and interpolaris (SpV/Iv)
• PrV projects to VPm, and SpV projects to Pom nuclei

Question 15

What information does Prv carry?

(1 mark)

Answer 15

Fine detailed textured information about where exactly stimuli are on whiskers

Question 16

What information does SpV carry?

(1 mark)

Answer 16

Carries more ‘diffused’ roguher spatially coded information as well as noxious information and temperature information

Question 17

How would you conduct an experiment that allowed you to view where the nuclei of cells travelled to after stimulation of CN V?

(3 marks)

Answer 17

• Inject tracer into VPm
• Tracer picked up by cells and transported to nuclei of those cells
• After inject tracer to VPm, will track tracer to mainly PrV

Question 18

What would you see if you injected a fluorescent dye marker inot VPm?

(4 marks)

Answer 18

View where their axons go -

• Nerve fibres travel into internal capsule and up into cortex
• Then form distinct bundle of axons w/ little gaps inbetween
• Bundles of axons = barrels - these contain high detailed temporal and spatial acuity information about teh somatosensory surface

Question 19

Where do barrels carry afferents from?

Answer 19

VPm - carrying high tactile information

Question 20

Where does POm mainly carry its information from?

Answer 20

Spinothalamic tract

Question 21

Where does information from the POm go?

(2 marks)

Answer 21

• Layer 5 and 1 septal columns inbetween the barrels
• Septal column innervation mainly goes to motor strutures, striatum and primary motor cortex

Question 22

Where does information from the VPm go?

(1 mark)

Answer 22

• Barrel columns, and then projects to 2° somatosensory cortex which takes over higher cortical processing

Question 23

In monkeys, what is the difference between the ventral and dorsal stream?

(3 marks)

Answer 23

• Ventral stream:
  
  • ​SI and SII - project to parietal ventral cortex and then to teh entorhinal cortex
• Dorsal stream:
  
  • ​MII appears to integrate internal state with movement to produce goal directed behaviour