STRUCTURE: NERVOUS SYSTEM

Question 1

Fasciculus gracilis, what information does this tract carry?

Answer 1

carries information from the lower body extremities (Gracilis = Ground)

Question 2

Fasciculus cuneatus, what information does this tract carry?

Answer 2

carries information from the upper body extremities

Question 3

Dorsal/ventral spinocerebellar tracts, what information does this tract carry?

Answer 3

carry proprioceptive information from the muscle spindles (dorsal) and golgi organs (ventral)

Question 4

Spinothalamic tracts (anterolateral system), what information does this tract carry?

Answer 4

principally pain

Question 5

Describe the route of the dorsal column median lemniscus from the 1st order neurone to the cerebral cortex

Answer 5

1st order neurons ascend ipsilaterally in dorsal columns known as the:
- Fasciculus gracilis (enters up to T6)
- Fasciculus caneatus (enters above T6)
At the gracilis and caneate nuclei in the brainstem they synapse with 2nd order neurons to the medial lemniscus contralaterally
These then decussate from the medial lemniscus and project to the ventral posterolateral lobe (VPL) of the thalamus. Then projects up to the cerebral cortex

Question 6

Dorsal column-medial lemniscus pathway: What type of information does it carry? and is made up of which fibres?

Answer 6

Pathway for: MECHANICAL STIMULI, conscious proprioception, discriminative touch, vibration and pressure
Composed of large diameter (fast A-beta fibres, sensory)
Note: contains the fasiculus gracilis and cuneatus

Question 7

Spinothalamic pathway: What type of information does it carry? What type of fibres does it contain?

Answer 7

Pathway for: NOCICEPTIVE STIMULI, mechanical +chemical + thermal detection of coarse/non-discriminative touch, pain, temperature
The fibres:
- Composed of smaller diameter (slow: either A-delta or C fibres) with no specialized sensory endings
- Myelinated fibres which are ‘quick to cross’
- A-delta fibres detect non-discriminative touch (strong stimuli that does not damage the skin, heat/cold and sharp pain
- C fibres detect dull aching pain and itch (histamine sensitive) plus thermal and mechanical sensation

Question 8

What is the route for the spinothalmic tract?

Answer 8

1. 1st order neurones synapse with 2nd order neurones at the dorsal horn
2. These then ascend in the ventral or lateral spinothalamic tract
3. Synapse with 3rd order neurones at the thalamus
4. project up to sensory cortex

Question 9

What are the names of the two spinothalamic routes and how do they differ?

Answer 9

Lateral and lateral spinothalamic tract
Ventral: C fibres only, carries information regarding coarse + non-discriminating touch
Lateral: A-delta and C fibres, carries information about pain and temperature

Question 10

Describe the general route of neurons in the spinocerebellar pathway?

Answer 10

1. Cell bodies of 2nd orders ascend in the dorsal horn of the spinal cord
2. They terminates at the vermis of the cerebellum

Question 11

What is the different between the routes of the ventral and dorsal spinocerebellar tracts?

Answer 11

Dorsal: neurons ascend ipsilaterally and enter cerebellum via the inferior peduncle
Ventral: neurons ascend contralaterally and enter cerebellum via the superior peduncle

Question 12

What are the 4 different types of nociceptor?

Answer 12

Polymodal nociceptors: Unmyelinated C fibres, mechanicals, chemical and thermal
Mechanical nociceptors: lightly myelinated a-delta fibres, sensitive to high pressure
Chemical nociceptors: lightly myelinated a-delta fibres, sensitive to histamine (gives itch feeling_
Thermal nociceptors: lightly myelinated a-delta fibres, sensitive to high/low temperature

Question 13

What is the purpose of substance P in pain neurons?

Answer 13

The peripheral neuronal response to noxious stimuli is modulated by Substance P (SP)
SP is released from pain neurons when they are stimulated in fast succession. SP increases sensitivity to noxious stimuli

Question 14

What is the mechanism for referred pain?

Answer 14

Signals of noxious stimuli and normal cutaneous stimuli enter the spinal cord at the same point
Cross talk in the dorsal horn between modalities is common
Signals from viscera get picked up by ascending nerve fibres that are mapped cortically to the dermis.

Question 15

What sensory inputs are utilised in controlling posture?

What are the two principle pathways involved?

Answer 15

Information is integrated from…

1. Muscle proprioceptors (detect changes in muscle length and/tension)
2. Sense of balance derived from movements of the head relative to the earth’s gravitational field
3. Visual inputs (detecting movements in visual field representing movement of the body)

2 principle pathways controlling posture: VESTIBULOSPINAL and RETICULOSPINAL

Question 16

Which pathway does the vestibulospinal pathway branch from?

Answer 16

The ventromedial pathway

Question 17

What are the two branches of the vestibulospinal

pathway and what are their main functions?

Answer 17

Lateral pathway: increase antigravity muscle tone

Medial pathway: controls head and eye movements

Question 18

Reticulospinal pathway: Function?

Answer 18

Co-ordinates movement and posture by receiving information from multiple sources

Question 19

What does the corticospinal tract branch?

Answer 19

Corticobulbar tract: Reticulospinal, vestibular spinal tract
Pyramidal decussation: The anterior ipslaterial corticospinal tract
the Lateral contralateral corticospinal tract

Question 20

What are the positive and negative signs of a lesion being present in the UMN’s of the corticospinal tract?

Answer 20

Signs of lesions are presented as positive or negative signs
o Negative: loss of function
o Positive: the appearance of an abnormal response (e.g. extensor plantar reflex aka babinki sign
No atrophy or fasciculation but painful increased muscle tone

Question 21

What is caused when lesions appear in LMNs?

Answer 21

-	Lesions of axons from these neurons cause:
o	Muscle paralysis
o	Reduced motor tone
o	Reduced stretch reflex
o	Fasciculation
o	Atrophy

Question 22

Describe the anterior ipsilateral corticospinal tract:
Function:
Length:
Innervates: Bilateral/unilateral

Answer 22

Function: provides postural compensation for movements contralaterally
Length: Ends at L2
Innervates: Bilaterally

Question 23

Describe the Lateral contralateral corticospinal tract:
Function:
Length:
Innervates: Bilateral/unilateral

Answer 23

Function: Provides fine motor control over distal muscles
Length: Length of the cord
Innervates: Unilaterally

Question 24

What are the major classes of descending pathways?
What tracts do they involve?
What proximity of muscle is innervated?

Answer 24

1. Conscious movement via corticospinal tracts (anterior and lateral). Mainly associated with distal muscles
2. Unconcious movement: Ventromedial pathways. (including main tracts: reticulospinal and vestibulospinal) Principally controlled by brainstem and is mainly associated with axis and proximal muscles