Anatomy of the Nervous System

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