Anatomy 4.

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Practice Examinations

Upper Limb Practice Written Exam

Head and Neck Practice Written Exam

Head and Neck Practice Practical

Head and Neck Practice practical for Netscape users

Thorax Practice Written Exam

Abdomen Practice Written Exam

Pelvis and Perineum Written Exam

Lower Limb Practice Written Exam

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The primary divisions of the developing brain

1stry division	Sub division	Adult structures
1)      Fore brain	Telencephalon	Cerebral hemispheres Basal ganglia Hippocampus
	Diencephalon	Thalamus Hypothalamus Pineal body Infundibulum
2)      Mid brain	Mesencephalon	Tectum Tegmentum Crus cerebri
3)      Hind brain	Metencephalon	Pons & Cerebellum
	Myelencephalon	Medulla oblongata

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A. Development of the medulla oblongata

1) There are basal & alar plates in the hind brain, separated by the sulcus limitans

2) As the 4^th ventricle enlarges, the alar plate comes lateral to the basal plate

3) Basal plate forms the motor nuclei of IX, X, XI & XII cranial nerves (They are situated medial to the sulcus limitans)

4) Alar plate forms the sensory nuclei of the V, VIII, IX & X cranial nerves, gracile & cuneate nuclei and Olivary nuclei

5) As the roof plate becomes stretched into a thin layer, tela choroidea projects into the cavity of the 4^th ventricle to form the choroid plexus

6) During the 4^th & 5^th months, foramina of Luschka & foramen of Magendie are formed

7) Descending motor fibers from the cortex produce a prominent swelling in the anterior aspect of MO called the pyramids

 

B. Development of the pons

1) It’s formed from the anterior part of the Metencephalon

2) It has also cellular contributions from the alar part of the Myelencephalon

3) Basal plate forms the motor nuclei of V, VI & VII cranial nerves

4) Alar plate forms

1. Sensory nucleus of V & VII

2. Vestibular cochlear nuclei of VIII

3. Pontine nuclei

5) Axons of the pontine nuclei go to the developing cerebellum of the opposite side (Rhombic lip) & form

1. Transverse pontine fibers

2. Middle cerebellar peduncle

C. Development of the cerebellum

1) It’s formed from the posterior part of the alar plate of the Metencephalon

2) On each side, alar plates bend medially to form the rhombic lip

3) As the lips enlarges, they project over the roof plate of the 4^th ventricle & unite with each other to form the cerebellum

4) At 12^th week, vermis & 2 cerebellar hemispheres can be recognized

5) Matrix cells situated close to the ventricle form neuroblasts & migrate to the cerebellum to form the cerebellar cortex

6) Neuroblasts that remained close to the ventricles differentiate into dentate & other cerebellar nuclei

D. Development of the midbrain

1) Mid brain develops from the midbrain vesicle

2) Cavity becomes much small to form the cerebral aqueduct

3) Basal plate forms

1. Motor nuclei of the 3^rd & 4^th cranial nerves

2. Red nuclei

3. Substantia nigra

4. Reticular formation

4) The marginal zone of basal plates on each side enlarges to form basis pedunculi (The descending motor tracts are situated in that region – Cortico pontine, corticobulbar & corticospinal tracts)

5) The 2 alar plates & the roof plate forms the Tectum

6) The alar plate forms the sensory neurons of the superior & inferior colliculi

 

E. Development of the forebrain

The division of the forebrain vesicle into the Telencephalon & the diencephalon

1) Lateral diverticulum appears from each side of the forebrain called optic vesicle

2) Optic vesicle & the stalk will form the retina & the optic nerve

3) 2 cavities are formed inside the cerebral hemispheres on either side & they are called lateral ventricles

4) The 3^rd ventricle is formed by Telencephalon (Anterior part) & diencephalon (Posterior part) and its openings to the lateral ventricles form the interventricular foramen

5) On each side of the lateral ventricle, alar plate forms:

1. A thickening to form the thalamus

2. Medial & lateral geniculate bodies

6) Lower part of the alar plate on each side will differentiate into hypothalamic nuclei

 

Development of the cerebral hemispheres

 

1) Each cerebral hemisphere arises at the beginning of the 5^th week of development

2) Cerebral hemispheres grow & expand,

1. Anteriorly : Form frontal lobes (1^st)

2. Laterally & superiorly : Parietal lobes (2^nd)

3. Posteriorly & inferiorly : occipital & temporal lobes (Last)

3) The matrix cells lining the floor of the forebrain proliferate to produce neuroblasts, they collectively forms corpus striatum; Later corpus striatum differentiate into caudate & lentiform nuclei

4) Longitudinal thickening of the wall of the forebrain which protrudes into the lateral ventricle forms the hippocampus

5) Many axons leave & arrive the differentiating cerebral hemispheres (Ascending & descending tracts)

6) They pass between the thalamus & caudate nucleus medially and lentiform nucleus laterally, the compact bundle of ascending & descending tracts is called the internal capsule

7) The differentiation matrix cells

1. The matrix cells lining the cavity of the cerebral hemispheres produce large number ofneuroblasts & neuro glial cells (They migrate to the marginal zone)

2. The remaining matrix cells will form the ependyma (Lines the lateral ventricle)

8.) At the 12^th week, cortex become very cellular due to migrating neuroblasts; different areas of the cortex will show specific cell types due to the influence of the ascending & descending tracts

1. Motor cortex : Pyramidal cells

2. Sensory areas : Granular cells

 

Development of the commisures

 

1) Lamina terminalis (The cephalic end of the neural tube) forms a bridge between the 2 cerebral hemispheres & enables nerve fibers to move from one to the other

2) Anterior commisures

1. 1^st commisure to develop

2. Runs in the lamina terminalis

3. Connects olfactory bulbs of the temporal lobes on either side with each other

3) The fornix

1. 2^nd commisure to develop

2. Connects hippocampus in each hemisphere

4) Corpus callosum

1. 3^rd commisure to develop

2. It’s the largest & most important

3. It connects frontal lobes (Initially) & parietal lobes (Later) of both sides

4. As it develops, it arches over the roof of the developing 3^rd ventricle

 

5) The remaining of the lamina terminalis (Lies between the corpus callosum & the fornix) form theseptum pellucidum

6) Optic chiasma is formed by the inferior part of the lamina terminalis

 

Myelination of the CNS

 

1) The myelin sheath of the CNS is formed & maintained by oligodendrocytes (PNS axons are myelinated by Schwann cells)

2) Myelination of the spinal cord begins initially in the cervical region in the 4^th month & extends downwards

3) Sensory fibers myelinate first & descending motor fibers at last

4) Myelination of the brain begins in the 6^th month & confined to the fibers of the basal ganglia

5) At birth the brain is largely unmyelinated (In new born there’s very little cerebral function as most of the action are reflexes)

6) After birth, descending tracts starts to myelinate