By Definition these are Bundle or groups of nerve fibers used for spinal cord connections Sub classed as.. 1- Short tracts. 2-Long Tracts.
Short Tracts are just within the spinal cord for its connections with itself.Subclassed as :1- associative (Connects adjecent parts of same side spinal cord)
2- Commissural connects opposite halves of spinal cord.
LONG TRACTS connects spinal cord to other parts of CNS .Subdivided as1- Ascending tracts (Ascend fronm spinal cord to brain)2-Decending tracts(Decends from brain to spinal cord)
THE DESCENDING TRACTS OF SPINAL CORD These tracts descends from brain to spinal cord and carry motor information. These are further divided as 1- Pyramidal tracts. 2- Extrapyramidal tracts.
PYRAMIDAL TRACTS Pyramidal tracts or corticospinal tracts originate from motor area of cerebral cortex and extend to the thoracic region of spinal cord. Just a little of them goes to sacral region. Further divided as 1- Anterior 2- Lateral
Diameter of each nerve fiber is 4-22 microns They are presnt since birth but later in old age they may dissapear causing automatic shivering movements. ORIGIN : ; these originate from motor area of cerebral cortex from following cells Betz Cells – Area 4 (30%) Premotor area 6 (30%) Somatosensory area of parietal lobe (39%) Other parts of frontal lobe. (1%)
Termination : Motor neurons of gray horn. Upto mid thoracic level and least to sacral region. Function : voluntary movements Fine and skilled movements of body. Effect of Lesions : Voluntary movements Muscle tone Reflexes Weakened muscles One body side paralysis Four limbs paralysis
EXTRAPYRAMIDAL TRACTS : Other than pyramidal tracts. Medial longitudinal Fasciculus : Descends through posterior part of anterior white column. Origin : Takes origin from 4 different sites.1. Vestibular nuclei (Present in medulla – cranial nuceli for vestibular nerve)2. Reticular Formation ( Region of pons involved in sleep wake cycle)3. Superior Colliculus (Area below thalamus – surrounds pineal gland )4. Internal cells of Cajal (pace maker cells of GIT that produce Basal electrical rythem)
Course : Directly enters the spinal cord from brain stem and are well defined at cervical region only . Termination : they terminates on anterior motor neurons either directly or indirectly via internuncial neurons. Function : helps in reflex ocular movements and movement of neck. Effect of lesion : Reflex ocular and neck movements are effected.
Anterior Vestibulospinal Tracts Situated in anterior white column along its periphery. Origin: Arise from medial vestibular nuclei of M.O . and extend upto thoracic region. Termination : anterior motor neurons directly or indirectly. Function : Concerned with adjustment of position of head and body during angular and linear motion.
Lateral vestibulospinal tracts Situated in anterior part of lateral white matter. Origin : Lateral vestibular nuclei of Medulla – Dieter’s nucleus. Extent : present throughout the spinal cord. Course : Descends from Dieter’s nucleus directly in the spinal cord to its lateral white column with few being crossed before reaching spinal cord. Termination : Anterior Motor neurons directly or indirectly. Function : tht of previous one. Effect of lesion : adjustment of head and body remains no more coordinated during acceleration.
4-Reticulospinal Tracts : Situated in anterior white column , posterior to anterior vestibulospinal tracts . Origin : Reticular formation of pons and medulla. Course : . pontine are uncrossed and descends in medial part of anterior column. From medulla are crossed and uncrossed (mixed) and descends to anterior parts of anterior and lateral column. Extention : upto thoracic segments. Termination : Gamma motor neurons of anterior gray horn. Function : Controls diameter of blood vessels , breathing , movementn maintenance . Effect of lesions : disturbed movement, breathing and b.p.
Tectospinal tract : Situated in anterior white column of spinal tract . Origin : superior colliculous of mid brain. Extention : lower cervical segments. Course : after taking origin, it cross the mid line and at decussation level and then descends directly in to spinal cord. Termination : Anterior motor neurons , directly or indirectly. Function : movement of head in response to audio and video stimuli. Effect of Lesion : function is disturbed.
Rubrospinal tract : Present in lateral white column of spinal cord. Origin : Red nucleus of mid brain (Larg cell area – controls crawling of babies) Extent : upto thoracic level of spinal cord . Course : after taking origin, it cross the mid line and at decussation level and then descends directly in to spinal cord through reticular formation of midbrain . Termination : terminates at anterior motor neurons only indirectly. Function: Facilitates the function of flexor joints.
Olivospinal tract : Situated in lateral white column of spinal cord . Origin : Medulla oblongata – inferior olivary nucleus. Course : Descends directly to spinal cord from M.O . Termination : Anterior motor neurons. Function : Reflex movements of joints. Effect of lesion : Reflex movement of joints is lost .