Download 1- The central nervous system

NRVOUS SYSTEM
It has composed of central nervous system (CNS) and peripheral nervous system (PNS)
1- The central nervous system: consists of brain and spinal cord which are enclosed
by the meninges
2-The peripheral nervous system: consists of:
A-spinal, cranial nerves and the ganglia that are connected to the CNS
B- Autonomic nervous system:
Brain: is the enlarged rostral part of the CNS and its situated in the cranial cavity. It is
very closely conforms to this cavity in size and shape. The brain can be subdivided into
brainstem, cerebrum and cerebellum.
1.
The cerebrum: is the largest part of the brain, is separated from cerebellum (caudally)
by deep fissure and subdivided into two symmetrical halves (the hemispheres), by longitudinal
fissure. The hemispheres have numerous depressions (cerebral sulcus) and convolution
(cerebral gyri) on their surface. Most of the cranial nerves emerge from the basal surface of
the brain.
The brainstem: is situated on the basal side or ventral surface of the brain and is covered
by the other two parts. Its consists of the continuations of the spinal cord (medulla
oblongata) following Rostral by the transversely oriented pons, Mesencephalon and
diencephalon . Dorsally one recognizes the rhomboid fossa at the level of the pons and
medulla oblongata. This fossa represents the bottom of the 4th ventricle, which is bounded
laterally by the cerebellar peduncle, rostral to them are the corpora quadrigemina (Rostral
and caudal colliculi) and the thalamus.
The dorsal surface of the brainstem is represented by the two thalami which on the
midline to form interthalamic adhesion.
A-Medulla oblongata: related to the Rhombencephalon), is the caudal part of the
brainstem which extends to pons rostral and caudally continuous with spinal cord. There is
no visible limit between it and spinal cord. It has two surfaces (ventral and dorsal)
The ventral surface: consists of
1. ventral median fissure which bounded laterally by 2
2. ventral lateral sulcus , between 1,2 there are
3. pyramids
Arise from the ventral lateral sulcus –the cranial nerves (Abducent) and (hypoglossal).
(The cranial nerves ((glossopharyngeal, vagus and accessory)) arise from lateral border of
medulla oblongata.)
Trapezoid body: its transverse fiber tract situated in Rostral of medulla oblongata, caudal
to the pons, its passes deep to the pyramids where its fibers cross the mid line.
The dorsal surface: The caudal portion of the dorsal surface of medulla oblongata is
subdivided into two symmetrical halves by the dorsal median sulcus, a continuation of the
spinal cord dorsal median sulcus. Adjacent to it’s the dorsal funiculus which is bounded
laterally by the dorsal lateral sulcus. At this level the dorsal funiculus enlarges considerably
and passes laterally forming two small tubercles
1-the medial tubercle –is the tubercle of the gracile nucleus
2-the lateral tubercle—is the tubercle of the cuneate nucleus.
These tubercles are situated at the end of the respective fascicles of the spinal cord. The
dorsal surface of medulla oblongata takes place in the formation of 4th ventricle and
formed the rhomboid fossa.