Somatosensory Function I: Sensation

Question 1

Sensory receptors

Answer 1

• Term ‘Receptor’ used in different sense
to cell biology
• Not ligand binding to protein
• Specialised cell or part of cell

Question 2

• Sensory pathways

Answer 2

• Including peripheral and cranial nerves
• Conduct sensory information from
receptors to CNS

Question 3

• Brain areas dedicated to processing

Answer 3

• Process/decode/make sense of sensory

information

Question 4

Sensory receptors detect a range of sensory stimuli, largely defined as three different sensations:

Answer 4

• Proprioception
• Touch
• Pain & Temperature

Question 5

Mechanoreceptors

Answer 5

Modality; Touch, Audition, Vestibular
Receptor; Pacinian corpuscle, Hair cell
Location; Skin, Organ of Coni Macula, semicircular canal

Question 6

Photoreceptors

Answer 6

Modality; Vision
Receptor; Rods and cones
Location; Retina

Question 7

Chemoreceptors

Answer 7

Modality; Olfaction, Taste, Anerial Po; pH of CSF
Receptor; Olfactory receptor, Taste buds
Location; Olfactory mucosa, Tongue Carotid and aortic bodies, Ventrolateral medulla

Question 8

Theroreceptors

Answer 8

Modality; Temperature
Receptor; Cold receptors, Warm receptors
Location; Skin

Question 9

Nociceptors

Answer 9

Modality; Extremes of pain and temperatUre
Receptor; Thermal nociceptors, Polymodal nociceptors
Location; Skin

Question 10

Sensory Pathways

• Function

Answer 10

• Including peripheral and cranial nerves
• Conduct sensory information from
receptors to CNS

• Conduction velocity
• Slow vs Fast

Question 11

Anatomy

Answer 11

• Myelinated vs Unmyelinated

* Axon diameter

Question 12

Anatomically, sensory pathways are found within

Answer 12

mixed neuronal bundles within spinal nerves.

Question 13

Describe receptor type, axon diameter and conduction velocity in proprioception sensory pathways

Answer 13

Muscle spindle
13-20um
80-120 m/s

Question 14

Describe receptor type, axon diameter and conduction velocity in touch sensory pathways

Answer 14

Merkel, meissner, pacinian and ruffini cells

6-12um
35-75 m/s

Question 15

Describe receptor type, axon diameter and conduction velocity in pain, temperature sensory pathways

Answer 15

Free nerve endings
1-5um
5-30 m/s

Question 16

Describe receptor type, axon diameter and conduction velocity in pain, temperature sensory pathways (unmyelinated)

Answer 16

Free nerve endings (unmyelinated)

0. 2-1.5um
1. 5-2 m/s

Question 17

Functional divisions of spinal nerves:

Answer 17

• Root
• Primary
• Peripheral

Question 18

• Spinal Nerve

Answer 18

• Mixed sensory and motor

fibre

Question 19

Dorsal Root

Answer 19

Bifurcation of sensory

fibres from spinal nerve

Question 20

Ventral Root

Answer 20

• Bifurcation of motor

fibres from spinal nerve

Question 21

Fibres of the dorsal root carry

Answer 21

sensory information.

Question 22

Lateral division of dorsal root

Answer 22

• Myelinated and unmyelinated fibres. Temperature & pain sensation.

Question 23

Medial division of medial root

Answer 23

• Myelinated fibres .
• discriminative touch, pressure,
vibration, and conscious proprioception.

Question 24

pseudounipolar

Answer 24

Sensory nerve fibres a pseudounipolar, with their cell bodies located within the dorsal root ganglion.

Question 25

Dorsal Root Ganglion

Answer 25

Sensory nerve fibres from the ANS input to the Dorsal Root Ganglion from the Grey Ramus.
Typically associated with organ pain.
Motor fibres from the ventral root input to ANS fibres via the White ramus.
Link to mechanical analgesia.

Question 26

White matter:

Answer 26

Fibre pathways

Question 27

Grey matter:

Answer 27

Neuronal nuclei

Question 28

Dorsal Horn:

Answer 28

Sensory input

Question 29

Ventral Horn:

Answer 29

Motor output

Question 30

Sensory fibres input via the dorsal horn, then:

Answer 30

• Enter the white matter tracts
and project in ascending tracts.
• Synapse with interneurone, then motor neurone, exiting via the Ventral horn.
• Decussate, before either of the above.

Question 31

Brain areas dedicated to

Answer 31

processing
• Process/decode/make sense of sensory
information

Question 32

Proprioception & Fine Touch

Answer 32

Fine touch, often referred to as discriminatory touch, enables the animal to localise.
Crude touch, often referred to as non- discriminative touch, enables sensation without localisation.
Difference between modalities a combination of both receptors activated and spinal pathways.

Question 33

Describe the pathway in the brain of fine touch, proprioceptionn, vibration, nociception, temperature and coarse Touch

Answer 33

Pain, temperature, and coarse touch cross the midline in the spinal cord.

Fine touch, vibration, and proprioception pathways cross the midline in the medulla.

Sensory pathways synapse in the thalamus.

Sensations are perceived in the primary somatic sensory cortex.

Question 34

Dorsal Column System

Answer 34

• Dorsal input enters via the dorsal root, ascending via the Fasiculus cuneatus (1st Order Neurone).
• Decussates at the medulla, ascending via the Medial leminiscus (2nd Order Neurone).
• Synapses at the Thalamus before projecting to the sensory cortex (3rd Order Neurone).

Question 35

Spinothalamic Tract

Answer 35

• Dorsal input enters via the dorsal root, synapses within the Dorsal horn (1st Order Neurone).
• Decussates, ascending via the Lateral spinothalamic tract (2nd Order Neurone).
• Synapses at the Thalamus before projecting to the sensory cortex (3rd Order Neurone).

Question 36

Thalamus

Answer 36

Incoming spinal sensory pathways synapse within the ventral posterior nucleus of the Thalamus.
Inputs stratified by sensation:
• Superior (VPS) Proprioceptive
• Inferior (VPI) Pain & Temperature
• Medial (VPM) and Lateral (VPL) Fine touch
The medial and lateral aspect are further stratified by sensory region:
• Medial (VPM) Face
• Lateral (VPL) Foot
• Middle: Hand