Week 5 Lecture 12: Ascending Pathways

Question 1

What sensations is the spinothalamic pathway responsible for?

Answer 1

crude touch
pressure
pain
temperature

Question 2

What sensations is the dorsal column medial lemniscus pathway responsible for?

Answer 2

proprioception
discriminative touch 
vibration 
pressure
(ipsilateral)

Question 3

What is a dermatome?

Answer 3

a specific region of skin of the BODY innervated by the sensory fibres of a single segmental spinal nerve

Question 4

How are sensory roots of specific spinal nerves affected in herpes zooster

Answer 4

• infection of the sensory roots of specific spinal nerves
• virus can remain dormant in specific sensory root of specific cranial nerve
• these dormant viral vesicles can then reactivate in later life as shingles

Question 5

Which modalities are essential to survival and how are they conducted?

Answer 5

• pain and temperature
• some touch and pressure
• carried via thin, poorly myelinated or unmyelinated fibres
• conduction slow

Question 6

Which modalities increase detail and how are they conducted?

Answer 6

• discriminative touch
• vibration
• proprioception
• carried via large diameter, heavily myelinated fibres
• fast conduction

Question 7

What does ipsilateral mean?

Answer 7

occurring at same side of body

Question 8

Explain the 3 neuron chain

Answer 8

1. 1st neuron:
   - pseudounipolar
   - brings information from the receptor
   - cell bodies located in the dorsal root ganglion
2. 2nd neuron:
   - at the level of the spinal cord, the 1st neuron makes contact with the 2nd neuron
   - the axon of the 2nd neuron crosses the midline and travels to the ventroposterior nuclei in the thalamus on the opposite side
3. 3rd neuron
   - relays information from thalamus to primary sensory cortex

Question 9

If information is coming from the body, where in the thalamus does it travel to?

Answer 9

VPL

Question 10

If information is coming from the face, where in the thalamus does it travel to?

Answer 10

VPM

Question 11

Which order neurones transfer info from the PNS to CNS and have their cell bodies in the peripheral ganglia?

Answer 11

first order neurone

Question 12

Where do the cell bodies of 2nd order neurones reside?

Answer 12

CNS ipsilateral grey matter

Question 13

Where do the cell bodies of 3rd order neurones reside?

Answer 13

in the thalamus

Question 14

Explain the pathway in the spinothalamic tract? (5 steps)

Answer 14

1. thin, slow fibre from receptor in periphery reaches 1st neurone with cell bodies in dorsal root ganglion
2. sensory fibres enter the dorsal horn of the spinal cord by travelling through the Lissauer’s tract
3. Fibres synapse with the 2nd order neurone in the dorsal grey horn
4. crossing over of fibres of the 2nd order neurone occurs at the white ventral commissure
5. 2nd order fibres ascend in spinothalamic tract to the opposite side of the thalamus

Question 15

When fibres reach the thalamus, how are they organised?

Answer 15

somatotopically

• fibres containing information from the arm travel more medially
• fibres containing information from the legs travel more laterally

Question 16

Which lamina is the substantial gelatinosa found in?

Answer 16

lamina II

Question 17

Which modality is the substantia gelatinosa nucleus responsible for?

Answer 17

pain and temperature

Question 18

Except from the substantia gelatinosa, which nuclei contain synapses from the spinothalamic tract?

Answer 18

1. marginal zone (lamina I)

2. Nucleus proprius (lamina III and IV)

Question 19

Why do different modalities travel through slightly different pathways? e.g different lamina

Answer 19

so we can differentiate whether the impulse is is pain, touch, pressure or temperature

Question 20

At the level of the medulla, the spinothalamic tract changes name to what?

Answer 20

spinal lemniscus

Question 21

Where in the post central gyrus are the fibres projected?

Answer 21

to the body region of the sensory homunculus
e.g if the fibres are coming from the hand, they will end in the hand region of the post central gyrus (somatotropin map)

Question 22

What is a lamina?

Answer 22

a region of the dorsal grey horn that contains specific composition of cells

Question 23

Explain the 3 neuron chain in the dorsal column medial lemniscus (6 steps)

Answer 23

1. 1st order neuron brings information from the periphery of touch, vibration, proprioception and pressure to the cell body at the DRG
2. Enters dorsal aspect of cord using lissauers tract but doesn’t synapse
3. jumps out to join the white matter to ascend ipsilaterally in the cord
4. 2nd order neurone send axon to midline at level of medulla and now ascending fibres travel through a region called the medial lemniscus
5. if information comes from above T6, it will travel in the cuneate fascicle. if information travels in the gracile fascicle, it is from below T6
6. travels to thalamus
7. 3rd order neurones project to the post central gyrus

Question 24

What do the gracile and cuneate fascicules contain?

Answer 24

axons

Question 25

What do the gracile and cuneate tubercles contain?

Answer 25

cell bodies

Question 26

In the DCML pathway, what are the fibres that cross the midline called?

Answer 26

internal arcuate fibres

Question 27

How are the medial lemniscus fibres organised?

Answer 27

somatotopically

Question 28

A 1st order neuron from the leg would travel through which fascicle?

Answer 28

gracile fascicle because it is below T6

Question 29

What is meant by somatotopic mapping?

Answer 29

different areas of the body are perceived by specific regions on the post central gyrus

Question 30

What does contralateral mean?

Answer 30

the side of the body opposite to that on which a particular structure or condition occurs

Question 31

What is the difference between the spinothalamic pathway and the dorsal column medial lemniscus pathway?

Answer 31

Spinothalamic pathway: - travel contra laterally in cord - fibres cross at the level of spinal cord entry Dorsal column medial lemniscus: - travel ipsilaterally in cord - cross at the level of the closed medulla

Question 32

What is a diverging circuit?

Answer 32

if the first neuron is modified, the following neurone all become modified

Question 33

What is a converging circuit?

Answer 33

many neurone have an input on one neuron

Question 34

What structure do ascending sensory axons travel through on their way to the post central gyrus?

Answer 34

posterior limb of the internal capsule

Question 35

What is thermoanaesthesia?

Answer 35

inability to feel changes in temperature

Question 36

What is somatotopy?

Answer 36

the point-for-point correspondence of an area of the body to a specific point on the central nervous system. Typically, the area of the body corresponds to a point on the primary somatosensory cortex (postcentral gyrus).

Question 37

Which cranial nerves carry general somatic sensation from the head?

Answer 37

CN V, VII, IX and X

Question 38

Which cranial nerve is the major carrier of general sensory information from the face, nose, scalp and dura?

Answer 38

trigeminal , CN V

Question 39

CN VII carries somatic sensation from which part of face?

Answer 39

external ear

Question 40

CN VIII carries somatic sensation from which part of face?

Answer 40

posterior 1/3rd tongue pharynx middle ear

Question 41

CN X carries somatic sensation from which part of face?

Answer 41

Auditory canal larynx pharynx oesophagus

Question 42

Which pathway does sensory information from the face travel in?

Answer 42

trigeminal sensory pathway

Question 43

What is the association between cranial nerves and cranial nerve nuclei?

Answer 43

for each fibre type a cranial nerve has, there is a specific cranial nerve nuclei associated to it

Question 44

What are the 4 trigeminal nuclei and where is each located?

Answer 44

1. mesencephalic nucleus (in the midbrain) 2. pontine/ chief sensory nucleus (in the pons) 3. spinal nucleus (medulla) 4. motor nucleus

Question 45

Where are all first order cranial nerve neuron cell bodies found? (with one exception)

Answer 45

in the trigeminal ganglion (instead of a dorsal root ganglion for dorsal root nerves) so cell bodies from V1, V2 and V3 go through the trigeminal ganglion

Question 46

Which sensory nucleus is associated with proprioception?

Answer 46

``` mesencephalic nucleus (this pathway is an exception to the generalisation that 1st order cell bodies are in the peripheral ganglia) ```

Question 47

Which sensory nucleus is associated with discriminative touch?

Answer 47

pontine nucleus

Question 48

Which sensory nucleus is associated with simple touch and pressure?

Answer 48

rostral part of spinal nucleus

Question 49

Which sensory nucleus is associated with pain and temperature?

Answer 49

caudal part of spinal nucleus

Question 50

Pain and temperature fibres that travel through the spinal tract of the trigeminal travel to which part of the thalamus?

Answer 50

VPM (because from face)

Question 51

Explain the pathway for pain and temperature fibres in the face (5 steps)

Answer 51

1. 1st order neuron travels through trigeminal ganglion 2. 1st order fibres run caudally in spinal tract of trigeminal 3. fibres synapse with 2nd order neurones in caudal spinal nucleus 4. 2nd order axons cross and ascend in trigeminothalamic tract 5. ascend to VPM of thalamus

Question 52

What is the difference between the pathway for pain and temperature, and the pathway for crude touch and pressure?

Answer 52

Same process but the 1st order neurones from crude touch and pressure reach the rostral part of the spinal nucleus (not the caudal)

Question 53

Where are the 1st order neurone cell bodies in the proprioception pathway?

Answer 53

in the mesencephalic nucleus (not in the trigeminal ganglion)