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Physiology > CNS Tracts > Flashcards

CNS Tracts Flashcards

1
Q

1st order neuron of dorsal column

A
  • from mechano and proprioreceptors
  • cell bodies in dorsal root ganglion
  • enter spinal cord through dorsal root
  • enter posterior white column on same side
  • fibres from lower half form tractus gracilis and upper half form tractus cuneatus
  • synapse with nucleus gracilis and nucleus cuneatus in medulla
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2
Q

2nd order neurons of dorsal column

A 
- 2 types: external and internal arcuate
External:
- from accessory nucleus cuneatus
- ascend on same side
Internal:
- decussate to opp. side - sensory decussation
- form medial lemniscus
- synapse with VPL nucleus of thalamus
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3
Q

3rd order neurons of dorsal column

A
  • from VPL nucleus of thalamus
  • ascend through internal capsule
  • reach somatosensory areas 1 and 2 on contralateral side
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4
Q

Sensations carried by dorsal column

A
  1. Conscious and unconscious proprioception
  2. Vibration
  3. Fine touch
  4. Tactile discrimination
  5. Localization
  6. Stereognosis
  7. Deep pressure
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5
Q

Diseases affecting dorsal column

A
  1. Multiple sclerosis
  2. Brown-sequard syndrome
  3. Thalamic syndrome
  4. Tabes dorsalis
  5. Guillain-Barren syndrome
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6
Q

1st order neuron of lateral spinothalamic tract

A
  • from noci and thermoreceptors
  • cell bodies in dorsal root ganglion
  • enter spinal cord through dorsal root
  • synapse with smaller cells in posterior grey horn (Lamina 1, 2, 5)
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7
Q

2nd order neuron of lateral spinothalamic tract

A
  • from posterior grey horn
  • cross to opp. side
  • ascend in lateral white column as lateral spinothalamic tract
  • enters medulla lateral to medial lemiscus
  • terminate in VPL nucleus of thalamus
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8
Q

3rd order neurons of lateral spinothalamic tract

A
  • from VPL nucleus of thalamus
  • ascend through posterior limb of internal capsule
  • end in contralateral somatosensory area 1 and 2
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9
Q

Sensations carried by lateral spinothalamic tract

A
  1. Pain

2. Temperature

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10
Q

1st order neurons of anterior spinothalamic tract

A
  • cell bodies in dorsal root ganglion

- axons terminate in nucleus proprius

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11
Q

2nd order neurons of anterior spinothalamic tract

A
  • from nucleus proprius
  • cross to opp. side and occupy ventral white column
  • ascend to medulla
  • joins with lateral ST tract to form SPINAL LEMNISCUS
  • terminated in VPL nucleus of thalamus
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12
Q

3rd order neurons of anterior spinothalamic tract

A
  • from VPL nucleus
  • ascend through posterior limb of internal capsule
  • terminate in contralateral
    1. somatosensory area 1 and 2
    2. parietal cortex area 5, 7
    3. supramarginal gyrus area 40
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13
Q

Sensations carried by anterior spinothalamic tract

A
  1. Crude touch
  2. Crude pressure
  3. Itching
  4. Tickling
  5. Sexual senstions
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14
Q

Differences in transmission in Dorsal column pathway and anterolateral pathway

A
  1. DCML is 3 times faster
  2. Degree of spatial localization poor in AL
  3. Gradations of intensities are more accurate in DCML
  4. Ability to transmit rapidly changing/repetitive signals poor in AL
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15
Q

Origin of corticospinal (pyramidal) tracts

A

Broadmann areas 4,6 of frontal cortex (60%)

Areas 3,1,2,5,7 of parietal cortex contribute (40%)

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16
Q

Composition of corticospinal tracts

A
  • 1 million fibres
  • half are unmyelinated
  • both facilitatory and inhibitory fibres
17
Q

Course of corticospinal tracts

A
  • descend through corona radiata
  • occupy genu and ant. 2/3 of posterior limb of INTERNAL CAPSULE
  • occupy middle 3/5 of pes pedunculi in MIDBRAIN
  • splits into bundles among pontine nuclei in PONS
  • bundles join to form pyramid in MEDULLA
  • 80% fibres cross - motor decussation
  • descend into spinal cord
  • terminate on alpha motor neurons in anterior grey horn on opp. side directly, or through internuncial neuron
18
Q

Functions of corticospinal tracts

A
  1. Controls voluntary fine movements
  2. Facilitates superficial reflexes
  3. Facilitates muscle tone
  4. Controls gross voluntary movements
  5. Direct sensory motor coordination
19
Q

Effect of lesions on corticospinal tracts

A
  1. Voluntary mvmt impairment
  2. Fine skilled mvmt impairment
  3. Spasticity
  4. Clasp knife rigidity
  5. Exaggerated tendon reflexes, clonus
  6. Babinski +ve
  7. Loss of superficial reflexes
20
Q

Origin of medial longitudinal fasiculus

A
  1. Vestibular nucleus
  2. Reticular formation
  3. Superior colliculus
  4. Interstitial cells of Cajal
21
Q

Course of medial longitudinal fasiculus

A
  • descend through brainstem
  • enter spinal cord in anterior white column
  • prominent in upper cervical segments
  • end in anterior horn cells
22
Q

Functions of medial longitudinal fasiculus

A

Coordinates movements of eyes, head, neck and body in response to visual, auditory and somatic stimuli

23
Q

Origin of rubrospinal tract

A

Magnocellular division of red nucleus

24
Q

Course of rubrospinal tract

A
  • crosses to opp. side
  • descends in lateral white column
  • ends in interneurons of spinal cord
  • extend upto thoracic segments only
25
Q

Functions of rubrospinal tract

A

Controls distal muscles used for fine skilled mvmts

26
Q

Origin and course of pontine reticulospinal tract

A
  • from pontine nuclei
  • descends through ipsilateral anterior white column
  • crosses at segmental level
  • synapses in anterior horn cell
27
Q

Origin and course of medullary reticulospinal tract

A
  • from medullary reticular nuclei
  • descends as crossed and uncrossed
  • synapses in anterior horn cell
28
Q

Functions of reticulospinal tract

A
  1. Muscle tone of antigravity M
  2. Postural and equilibrium
  3. Gross postural mvmts
  4. Influence respiration, heart rate, bp
29
Q

Origin and course of tectospinal tract

A
  • from sup. colliculus
  • crosses in midbrain
  • terminates on motor neurons of cervical spinal segments
30
Q

Functions of tectospinal tract

A

Coordination of head, body, neck mvmts with visual, auditory and somatic stimuli

31
Q

Origin of vestibulospinal tract

A
  • from medial and lateral vestibular nuclei on floor of 4th ventricle
32
Q

Course of vestibulospinal tract

A 
Medial:
- reach upto thoracic segments, synapse in anterior horn cell
- connected to semicircular canals
Lateral:
- reach upto sacral segments
- connected to Otolith organs
33
Q

Functions of vestibulospinal tract

A

Medial: mvmt of head, neck, eyeball with rotational mvmts
Lateral: Postural adjustments during linear acceleration

34
Q

General functions of extrapyramidal system

A
  1. Alternate path when damage to pyramidal
  2. Control facial and eyeball mvmts
  3. Control muscle tone, posture, equilibrium
  4. Coordinate mvmts of head and neck with external stimuli
  5. Control gross complex mvmts
  6. Coordinate posture with voluntary mvmts
35
Q

Features of extrapyramidal lesions

A
  1. Immobility without paralysis
  2. Difficulty initiating voluntary mvmt
  3. Imbalance
  4. Rigidity
  5. Involuntary mvmts
  6. Resting tremor

Physiology (9 decks)

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