21: Somatosensory Tracts: PCML, Trigeminal Thalamic Pathway

Question 1

Somatosensory function

Answer 1

Transmits and analyzes touch/tactile info from external and internal locations of the body and head

Question 2

Four notable pathways of the somatosensory system

Answer 2

PCML, trigeminal thalamic pathway, spinocerebellar pathway, anterolateral system

Question 3

Receptive field

Answer 3

Area of skin innervated by somatic afferent fibers

Question 4

Small receptive field means…

Answer 4

Higher receptor density

Question 5

Speed and precision of PCML pathway

Answer 5

Fast conduction velocities + precise somatotopic organization

Question 6

What do afferent fibers of PCML detect?

Answer 6

Discriminative touch, flutter-vibration, proprioception

Question 7

Lesion in SC of PCML

Answer 7

Ipsilateral loss of discriminative, positional, and vibratory tactile sensation at/below level of injury

Question 8

Ventral posterior nuclei

Answer 8

Wedge-shaped cell group in caudal nucleus: VPL + VPM

Question 9

Generally, what do the VPL and VPM nuclei receive?

Answer 9

VPL: info from body
VPM: info from face (trigeminal)

Question 10

Blood supply to ventral posterior nuclei of thalamus

Answer 10

Thalamogeniculate branches of posterior cerebral A

Question 11

Lesion of the ventral posterior nuclei of the thalamus

Answer 11

Lose all tactile sensation over contralateral body and head

Question 12

Where is the primary somatosensory cortex (SI)?

Answer 12

Post-central gyrus + postparacentral sulcus

Question 13

Two borders of the SI

Answer 13

Central sulcus + post-central sulcus

Question 14

Brodmann’s areas in SI

Answer 14

1, 2, 3A, 3B

Question 15

Blood supply to SI (2 arteries)

Answer 15

ACA + MCA

Question 16

MCA lesion

Answer 16

Tactile loss over contralateral upper body and face

Question 17

ACA lesion

Answer 17

Contralateral tactile loss of lower limb

Question 18

Secondary somatosensory cortex (SII): location

Answer 18

Lateral sulcus upper bank

Question 19

Two places that send inputs to the SII

Answer 19

1. Ipsilateral SI cortex

2. Ventral posterior inferior nucleus (VPI) of thalamus

Question 20

Lesion to the parietal cortical regions

Answer 20

Agnosia: contralateral body regions lost from body map; limb is not recognized as part of own body

Question 21

Column of the four trigeminal nulcei

Answer 21

Form an elongated, continuous column in the brainstem

Question 22

Path of the spinal trigeminal tract

Answer 22

Extends caudally to about C3 -> becomes continuous with Lissauer’s tract

Question 23

Onion-peel sensory loss

Answer 23

Lesions of different parts of the spinal trigeminal tract cause loss of sensation around the face in different areas

Question 24

Caudal lesion of spinal trigeminal tract vs more rostral lesion

Answer 24

Caudal lesion: affects posterolateral boundaries of face

Rostral lesion: sensory loss increasingly anterior, converging on mouth

Question 25

How is there a smooth transition of sensory on the posterior head to the anterior face?

Answer 25

Trigeminal fibers end in the cervical cord overlapping the C1 and C2 dermatomes a bit

Question 26

Why is the mesencephalic nucleus unique?

Answer 26

Only nucleus in the CNS which is basically a ganglia due to its pseudounipolar neurons

Question 27

When to use a jaw jerk reflex?

Answer 27

To determine if pt has upper MN damage

Question 28

How to do the jaw jerk reflex

Answer 28

Downward tap on chin -> stretches the masseter -> causes contraction bilaterally

Question 29

Tract of the jaw jerk reflex

Answer 29

1. Afferent neuron (V3) in masseter muscle spindle -> cell body in mesencephalic nucleus -> trigeminal motor nucleus -> trigeminal motor neuron activation -> efferent action

Question 30

Symptoms of a lesion of the trigeminal nerve or nuclei (3 parts)

Answer 30

1. Anesthesia/loss of sensation in trigeminal dermatomes 2. Paralysis of muscles of mastication 3. Loss of ipsilateral afferent limb corneal reflex

Question 31

Alternating trigeminal hemiplegia: what causes this?

Answer 31

Unilateral destruction of CN 5 + CST in pons

Question 32

Sx of alternating trigeminal hemiplegia

Answer 32

Ipsilateral trigeminal anesthesia and paralysis, contralateral spastic hemiplegia

Question 33

What type of info is integrated in the SI?

Answer 33

Position sense, size, and shape discrimination

Question 34

What fissure is the SII located in?

Answer 34

Sylvian fissure

Question 35

What is the SII involved in?

Answer 35

Cognitive touch, comparing between objects, different tactile sensations, determines what becomes a memory

Question 36

Where is the parieto-temporal-occipital association cortex (PTO)?

Answer 36

Posterior parietal lobe

Question 37

PTO receives input from?

Answer 37

Multiple sensory areas

Question 38

What is the PTO involved in?

Answer 38

Analyzing spatial coordinates of self in environment, names objects, etc.