Neuro Anatomy

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Neuro Anatomy

Lec.11 د.عبد الجبار الحبيـطي

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: -

  1. Anterior median fissure or groove.

  2. 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: -

  1. Anterior horn: -contains lower motor neurons arranged in 3 columns as: -

  1. Medial zone: - which supplies the muscles of the neck region & trunk (including intercostals & anterior abdominal wall musculature).

  2. Central zone: - includes: -

  1. Phrenic nucleus: - in the segments C3 – C5 of the spinal cord, it gives origin to the phrenic nerve.

  2. Accessory nucleus: - in the upper 5 cervical segments, it gives origin to the spinal root of accessory nerve.

  1. Lateral zone: - which is responsible for the formation of brachial & lumbo-sacral plexuses.

  1. Posterior horn: - contains sensory nuclei as: -

  1. 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.

  2. 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.

  3. Nucleus dorsalis (clark’s 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 clark’s nuclei gives origin to anterior spino-cerebellar tract.

  4. Visceral afferent nuclei: - in the segments T1- L3 resposible for visceral afferent information.

  1. Lateral grey horn: - in the following areas: -

  1. T1 – L3 segments: - gives off to the thoraco-lumbar outflow which is the sympathetic component.

  2. 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

  1. The tracts in the posterior white column:

  1. Gracile tract medially placed.

  2. Guneate tract laterally placed.

These tracts convey proprioceptive sensation & discriminative fine touch.

They are of first order neurone.

  1. 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 crosses to opposite side (2nd order).

ii-Descending tracts as:-

1-Anterior corticospinal from precentral is uncrossed tract.

2-Tecto-spinal tract from tectum of mid is uncrossed tract.

3-Vestibulo-spinal tract from vestibular nuclei.

4-Medial reticulospinal tract from reticular formation of brain stem & of extrapyramidal fibres.

Neuro Anatomy -12-

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