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Questions and Answers
Where do the fibres of the fasciculus gracilis terminate?
Where do the fibres of the fasciculus gracilis terminate?
Where are the second order neurons of the anterior and lateral spinothalamic tracts located?
Where are the second order neurons of the anterior and lateral spinothalamic tracts located?
What type of sensations does the lateral spinothalamic tract carry?
What type of sensations does the lateral spinothalamic tract carry?
Which tract carries proprioceptive impulses arising in muscle spindles and Golgi tendon organs?
Which tract carries proprioceptive impulses arising in muscle spindles and Golgi tendon organs?
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What percentage of fibres in the anterior spinothalamic tract are uncrossed?
What percentage of fibres in the anterior spinothalamic tract are uncrossed?
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Where do the central processes of the first order neurons of the spinothalamic tract terminate?
Where do the central processes of the first order neurons of the spinothalamic tract terminate?
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Where do the fibres of the fasciculus cuneatus originate from?
Where do the fibres of the fasciculus cuneatus originate from?
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Where do the fibres of the anterior spinothalamic tract lie in the spinal cord?
Where do the fibres of the anterior spinothalamic tract lie in the spinal cord?
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What type of sensations does the anterior spinothalamic tract carry?
What type of sensations does the anterior spinothalamic tract carry?
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Where do the fibres of the posterior spinocerebellar tract terminate?
Where do the fibres of the posterior spinocerebellar tract terminate?
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Study Notes
Postganglionic Fibres
- Arise in ganglia and supply smooth muscles and glands
- Are short in length
Descending Tracts
- Connect grey matter in the central nervous system
- Can be ascending or descending
- Examples: Lateral and Anterior Corticospinal Tracts, Rubrospinal Tract, Tectospinal Tract, and Descending Autonomic Fibres
Lateral and Anterior Corticospinal Tracts
- Made up of axons from neurons in the motor area (area 4) of the cerebral cortex
- Some fibres arise from premotor area (area 6) and somatosensory area (areas 3, 1, 2)
- Pass through the internal capsule, crus cerebri, and pons to enter the pyramids in the medulla
- About 80% of fibres cross to the opposite side in the lower medulla and enter the lateral funiculus of the spinal cord
Rubrospinal Tract
- Made up of axons from neurons in the red nucleus (midbrain)
- Fibres cross to the opposite side in the lower part of the midbrain tegmentum
- Pass through the pons and medulla to enter the lateral funiculus of the spinal cord
- Facilitatory to flexors and inhibitory to extensors
Tectospinal Tract
- Fibres arise from neurons in the superior colliculus (midbrain)
- Cross to the opposite side in the upper part of the midbrain tegmentum
- Descend through the pons and medulla into the anterior funiculus of the spinal cord
Descending Autonomic Fibres
- Hypothalamospinal fibres arise from the paraventricular nucleus of the hypothalamus
- Descend uncrossed in the dorsolateral funiculus
- Some noradrenergic fibres descend from the locus coeruleus and adrenergic fibres from the medulla to the intermediolateral grey column
Ascending Tracts
- Pathways by which afferent impulses are conveyed to the brain
- First-order neurons are located in spinal ganglia
- Central processes enter the spinal cord through dorsal nerve roots and terminate in spinal grey matter
- Second-order neurons are located in spinal grey matter and cross the midline
- Third-order neurons are located in the thalamus and carry sensations to the cerebral cortex
Fasciculus Gracilis and Fasciculus Cuneatus (Posterior Column)
- Occupy the posterior funiculus of the spinal cord
- Formed by central processes of neurons in dorsal root ganglia
- Fibres derived from the lowest ganglia are situated most medially, while those from the highest ganglia are most lateral
- Fasciculus gracilis (Tract of Goll) lies medially and consists of fibres from the coccygeal, sacral, lumbar, and lower thoracic dorsal root ganglia
- Fasciculus cuneatus (Tract of Burdach) lies laterally and consists of fibres from upper thoracic and cervical dorsal root ganglia
- Fibres extend upwards as far as the lower part of the medulla and terminate in the nucleus gracilis and nucleus cuneatus
Anterior and Lateral Spinothalamic Tracts
- First-order neurons are located in spinal ganglia
- Central processes enter the spinal cord and terminate in relation to spinal grey matter
- Ascend in the dorsolateral tract before ending in grey matter
- Second-order neurons are located in laminae II to V in substantia gelatinosa of Rolando and nucleus proprius
- Cross to the opposite side of the spinal cord in the white commissure
- Carry some uncrossed fibres (about 10%)
- Anterior spinothalamic tract carries sensations of crude touch and pressure
- Lateral spinothalamic tract carries sensations of pain and temperature
Anterior and Posterior Spinocerebellar Tracts
- Carry proprioceptive impulses arising in muscle spindles, Golgi tendon organs, and other receptors to the cerebellum
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Description
This quiz covers the structure and function of nerve fibres, ganglia, and tracts in the central nervous system.
