Neuro Anatomy
Lec.11 د.لمى العلاف تشريحعدد الاوراق ( ) م\2\موصل 28\2\2018
The spinal cord consists of a central core of grey matter (bodies of neurons) as H-shaped in appearance (2 anterior & 2 posterior horns with grey commissure) & an outer layer of white matter (nerve fibers) occupied by tracts.
The cord is divided into R. & L. halves by: -
Anterior median fissure or groove.
Posterior median sulcus or septum.
The 2 halves are connected together by a horizontal band of grey commissure traversed by the central canal.
In transverse section, the grey matter is H-shaped having the following horns: -
Anterior horn: -contains lower motor neurons arranged in 3 columns as: -
Medial zone: - which supplies the muscles of the neck region & trunk (including intercostals & anterior abdominal wall musculature).
Central zone: - includes: -
Phrenic nucleus: - in the segments C3 C5 of the spinal cord, it gives origin to the phrenic nerve.
Accessory nucleus: - in the upper 5 cervical segments, it gives origin to the spinal root of accessory nerve.
Lateral zone: - which is responsible for the formation of brachial & lumbo-sacral plexuses.
Posterior horn: - contains sensory nuclei as: -
Substantia gelatinosa: - at the apex of the posterior horn responsible for pain, temperature & touch sensation. It is seen along the entire length of the spinal cord. It gives origin to the lateral spino-thalamic tract.
Nucleus proprius: -in the middle of the horn, just anterior to substantia gelatinosa. It gives origin to the anterior spino-thalamic tract responsible for position & movement (proprioception), two points discrimination & vibration sensation.
Nucleus dorsalis (clarks column): - at the of the posterior horn from the level of segments C8 L3 (or L4) it gives origin to posterior spino-cerebellar tract. Some cells just medial to the clarks nuclei gives origin to anterior spino-cerebellar tract.
Visceral afferent nuclei: - in the segments T1- L3 resposible for visceral afferent information.
Lateral grey horn: - in the following areas: -
T1 L3 segments: - gives off to the thoraco-lumbar outflow which is the sympathetic component.
S2 S4 segments: - gives off to sacral outflow as part of cranio-sacral outflow (parasympathetic).
Tracts: -
Means a bundle of nerve fibers having a specific function, is also known as funiculi
The tracts in the posterior white column:
Gracile tract medially placed.
Guneate tract laterally placed.
These tracts convey proprioceptive sensation & discriminative fine touch.
They are of first order neurone.
Lateral white column tracts:-
i-Ascending tracts:-
1-lateral spino thalamic (2nd order venoues).
They cross to the opposite side in the white commissure.
2-posterior spino cerebellar tract (2nd order) carries proprioceptive sensations to cerebellum,its fibres do not cross.
3-Anterior spino-cerebellar tract (2nd order).its fibres are both crossed (mainly) and uncrossed,carries proprioceptive to cerebellum.
4-Dorsolateral tract of Lissauer (1st order) arises in the dorsal root ganglia and carries pain & temperature sensations.
ii-Descending tracts:-
1-Lateral cortico-spinal arises from precentral gyrus & relay on anterior horn cells of s.c.
Its of the crossed fibres.
2-Rubro-spinal tract arises from red nucleus of mid brain and are crossed fibres.
3-Olivospinal tract arises from olivary nucleus of m.o.
4-Lateral reticulo-apinal tract from the reticular formation of the brain stem 2,3,4 Belongs to Extrapyramidal system.
5-Descending autonomic tracts arises in the hypothalamus and relay on the autonomic cells Located in the lateral grey horn.
Anterior white column tracts:-
i-Ascending tracts includes:
Anterior spino-thalamic for crude non-discriminative touch & hight pressure.it crosses to opposite side (2nd order).
ii-Descending tracts as:-
1-Anterior corticospinal from precentral gyrus.it is uncrossed tract.2-Tecto-spinal tract from tectum of mid brain.it is uncrossed tract.
3-Vestibulo-spinal tract from vestibular nuclei.
4-Medial reticulospinal tract from reticular formation of brain stem & of extrapyramidal fibres.
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