Descending tracts of spinal cord

 

Tract		Situation	Origin	Course	Function
Pyramidal tracts	1. Anterior corticospinal tract	Anterior white funiculus	Betz cells and other cells of motor area	Uncrossed fibers	1. Control of voluntary  movements. 2. Upper motor Neurons functions
	2. Lateral corticospinal tract	Lateral white funiculus	Betz cells and other cells of motor area	Crossed fibers
Extra-pyramidal tracts	1. Medial longitudinal fasciculus	Anterior white fasciculus	Vestibular nucleus.  Reticular formation.  Superior colliculus and  cells of Cajal	Uncrossed fibers.  Extend up to upper cervical segments	1. Coordination of reflex ocular move- ments. 2. Integration of movements of eyes and neck.
	2. Anterior vestibulo- spinal tract	Anterior white funiculus	Medial vestibular nucleus	Uncrossed fibers. Extend up to upper  thoracic segments	1. Maintenance of muscle tone and posture. 2. Maintenance of position of head and body during acceleration
	3. Lateral vestibule- spinal tract	Lateral white funiculus	Lateral vestibular  nucleus	Mostly un- crossed.  Extend to all segments
	4. Reticulo- spinal tract	Lateral white fasciculus	Reticular formation of pons and medulla	Mostly un- crossed.  Extend upto thoracic segments	1. Coordination of  voluntary and reflex movements. 2. Control of muscle tone. 3. Control of respi- ration and blood vessels
	5. Tectospi- nal tract	Anterior white funiculus	Superior colliculus	Crossed fibers. Extend up to lower cervical segments.	Control of movement of head in response to visual and auditory impulses
	6. Rubro- spinal tract	Lateral white funiculus	Red nucleus	Crossed fibers. Extend up to thoracic seg- ments.	Facilitatory influence on flexor muscle tone
	7. Olivo- spinal tract	Lateral white funiculus	Inferior olivary  nucleus	Mostly crossed. Extent—not clear.	Control of movements due to proprioception
Termination — Fibers of all the tracts terminate in motor neurons situated in the anterior gray horn of spinal cord

Sensory pathways

Sensation	Receptor	First order neuron in	Second order neuron in	Third order neuron in	Center
Fine touch		Posterior nerve root ganglion	Nucleus gracilis and
Tactile localization, tactile discrimination, vibratory sensation, stereognosis.	Meissner's corpuscles and Merkel's disc	Ganglion – Fibers form fasciculus gracilis and fasciculus cuneatus	Nucleus cuneatus- Internal arcuate fibers	Ventral postero- lateral nucleus of thalamus	Sensory cortex
Pressure, crude touch	Pacinian corpuscle	Posterior nerve root ganglion	Chief sensory cells- Fibers form anterior spinothalamic tract	Ventral postero- lateral nucleus of thalamus	Sensory cortex
Temperature	Warmth- Raffini's end bulb, cold-Krause's end bulb	Posterior nerve root ganglion	Substantia gelatinosa-Fibers form lateral spinothalamic tract	Ventral postero- lateral nucleus of thalamus	Sensory cortex
Conscious kinesthetic sensation	Proprioceptors— muscle spindle, Golgi tendon apparatus, etc.	Posterior nerve root ganglion- -Fibers form fasciculus gracilis and fasciculus cuneatus.	Nucleus gracilis and nucleus cuneatus— Internal arcuate fibers	Ventral postero- lateral nucleus of thalamus	Sensory cortex
Subcon- scious kine-sthetic sensation	Proprioceptors— muscle spindle, Golgi tendon apparatus, etc.	Posterior nerve root ganglion	Clarke's column of cells and marginal cells— Fibers form dorsal and ventral spinocerebellar tracts		Cerebel- lum
Pain	Free nerve endings	Posterior nerve root – Ganglion –  Fast pain – A 5 fibers Slow pain – С fibers	Fast pain—marginal  cells in spinal cord. Slow pain-substantia gelatinosa	Ventral postero- lateral nucleus of thalamus. Reticular forma- tion and midbrain	Sensory cortex