Ascending Spinal Pathways

Question 1

What are some of the general senses?

Answer 1

• nociceptors (pain)
• thermoreceptors (temp, change in temp)
• mechanoreceptors (tactile and proprioception)

Question 2

Where are the sensor receptors for the general senses found?

Answer 2

• throughout the body, mainly in the skin

Question 3

What are the special senses?

Answer 3

• olfaction (smell: chemoreceptors)
• gustation (taste: chemoreceptors)
• vision (sight: photoreceptors)
• hearing and equilibrium (balance: mechanoreceptors)

Question 4

Where are the sensory receptors for the special senses found?

Answer 4

• in the head

Question 5

What are the function of the special senses, and via what nervous system does there information transmit?

Answer 5

• they are specialised to respond to one kind of stimulus: act as interface between environment and body/brain
• information only transmitted via CNS

Question 6

What is the process involved in perceiving stimuli (from PNS to CNS)?

Answer 6

• PNS receives sensations from external world and internal environment that have been detected by sensory receptors
• PNS conducts the information to CNS as an AP for awareness

Question 7

Define crude touch (pain, temp and itch) and discuss its purpose + features of its perception.

Answer 7

• the ‘protective senses
• ‘older system’
• slow system - conveyed by small and less/un-myelinated axons
• conveyed to brain via anterolateral (spinothalamic) pathways

Question 8

Define fine touch and proprioception, and discuss features of their perception.

Answer 8

• ‘explorative’ senses
• ‘new system’
• fast system (conveyed by large and highly myelinated axons)
• conveyed to brain via dorsal-column (medial-lemniscus) pathway

Question 9

How do spinal nerves receive sensory input?

Answer 9

• outside the cell, via dorsal root ganglion (where the cell body is contained within the (pseudo) unipolar neuron
• then through the dorsal root and dorsal rootlets, into dorsal horn where it there travels to the ventral motor horn

Question 10

How do spinal nerves output motor information?

Answer 10

• the cell body is contained in the motor neuron (inside grey matter of cell), information then travels through the ventral rootlets, roots and then back into the spinal nerve

Question 11

How does the difference in diameter of an axon correlate to the speed of reaction?

Answer 11

• thin = slow (protective receptors)
• thick = fast (mechanoreceptors)

Question 12

What are the functions of the enlargements on the spinal cord (cervical and lumbar), and what is a distinguishing difference between them?

Answer 12

• cervical - control + supply of upper limb and shoulder
• lumbar - control + supply of lower limb and pelvis (much more grey matter because of number of neurons required to innervate the number of muscles in the legs)

Question 13

Where do dorsal rootlets enter the spinal cord, and where do ventral rootlets exit the spinal cord?

Answer 13

Dorsal rootlets enter at the dorsolateral sulcus
Ventral rootlets exit at the ventrolateral sulcus

Question 14

What is the cauda equina?

Answer 14

• the bundle of spinal nerve roots below the conus medullaris

Question 15

What pathway is responsible for receiving proprioception and fine touch information?

Answer 15

• the dorsal column-medial Lemniscus

Question 16

What fascicles comprise the dorsal columns, and at what thoracic level are they both present?

Answer 16

• gracile (contains fibres from lower body)
• cuneate (contains fibres from upper body)
• below T6, only gracile fascicle
• from T6 and above, fibres also form cuneate fascicle

Question 17

Which fascicles forming the dorsal column are thicker, and why?

Answer 17

• cuneate much thicker because more somatotopic representation in sensory cortex

Question 18

Where does the medial lemniscus a) originate from and b) decussate, and c) how does this distinguish the locations of the 1st and 2nd order neurons?

Answer 18

a) originates from dorsal column nuclei (gracile + cuneate nuclei)
b) decussates in the medulla to connect to contralateral thalamus (VPL - ventral posterior lateral nucleus)
c) - 1st order neurons - ipsilateral
- 2nd order neurons - axon cross midline (contralateral)

Question 19

Describe the pathway of the dorsal-column medial lemniscus once it terminates in the dorsal column nuclei.

Answer 19

1. sensory decussation in lower brainstem (internal arcuate fibres)
2. forms medial lemniscus
3. to VPL
4. to primary somatosensory cortex (via posterior limb of internal capsule)

Question 20

Outline the anterolateral pathway

Answer 20

• dorsal root ganglion axons terminate in marginal zone, substantia gelatinosa
• crossover ventral white commissure
• ascend in lateral spinothalamic tract
• then via VP thalamus to somatosensory cortex

Question 21

Crude touch sensation is received by which ascending pathway?

Answer 21

• the anterolateral system (spinothalamic pathway)

Question 22

At what location do the two ascending systems come together?

Answer 22

• pons (in brainstem)

Question 23

Summarise differences between the dorsal-column medial Lemniscus pathway and the anterolateral (spinothalamic) system, in regards to the order of their neurons.

Answer 23

Both originate from sensory organ
1st order neurons:
- DCML: in dorsal root ganglion
- Spino: in dorsal root ganglion
2nd order neurons (decussate to contralateral in both pathways)
- DCML: in dorsal column nuclei
- Spino: in spinal cord, posterior horn)
3rd order neurons:
- DCML: in thalamus
- Spino: in thalamus

Question 24

What 3 centres in the cortex does the spinothalamic pathway relay information, where it is further relayed to what 3 thalamic nuclei?

Answer 24

Cingulate gyrus -> medial dorsal nucleus
Insula -> ventral medial posterior nucleus
Primary somatosensory cortex -> ventral posterior lateral nucleus