Thursday, April 14, 2011

Neuroanatomy- Post #6- The Skull, the Ventricles, and the Spaces

     As you probably already know there are many components of the body that serve as protective mechanisms. Within the realm of neuroanatomy this is especially true. This blog is going to be covering the Skull, the ventricles, and the spaces of the brain. All of these to some extent contribute to protection of the brain. At this point, I'm not going to delve into the specifics of the skull itself, but rather what passes into it.
    The skull (cranium), surrounds the brain and meninges completely and forms a strong mechanical protection.Essential structures (eg, cranial nerves, blood vessels) travel to and from the brain through various openings (fissures, canals, foramens) in the skull and are especially subject to compression as they traverse these small passageways.

Table 11–3 Structures Passing through Openings in the Cranial Floor.

Cribriform plate of ethmoid
Olfactory nerves
Optic foramen
Optic nerve, ophthalmic artery, meninges
Superior orbital fissure
Oculomotor, trochlear, and abducens nerves; ophthalmic division of trigeminal nerve; superior ophthalmic vein
Foramen rotundum
Maxillary division of trigeminal nerve, small artery and vein
Foramen ovale
Mandibular division of trigeminal nerve, vein
Foramen lacerum
Internal carotid artery, sympathetic plexus
Foramen spinosum
Middle meningeal artery and vein
Internal acoustic meatus
Facial and vestibulocochlear nerves, internal auditory artery
Jugular foramen
Glossopharyngeal, vagus, and spinal accessory nerves; sigmoid sinus
Hypoglossal canal
Hypoglossal nerve
Foramen magnum
Medulla and meninges, spinal accessory nerve, vertebral arteries, anterior and posterior spinal arteries
     One of the more obvious problems or pathologies associated with the skull would be fractures of the skull. This can lead to many problems such as brain damage or morphological changes in the skulls shape. Leaving the person more suseptible to future damage. These fractures can occur in many places, but the most common places are referred to as Le Forts I, II, and III. See the image below.

Red = I ; Blue = II, & Green = III

The next topic I would like to focus on are the ventricles of the brain. Within the brain there is a communicating system of cavities that are lined with ependyma and filled with cerebrospinal fluid (CSF): There are two lateral ventricles, the third ventricle (between the halves of the diencephalon), the cerebral aqueduct, and the fourth ventricle within the brain stem.
         The lateral ventricles are the largest of the ventricles. They each include two central portions (body and atrium) and three extensions (horns).
          The third ventricle is a narrow vertical cleft between the two halves of the diencephalon. And the fourth ventricle is a pyramid-shaped cavity bounded ventrally by the pons and medulla oblongata.
          The last structure to point out is the cerebral aqueduct. The cerebral aqueduct is a narrow, curved channel running from the posterior third ventricle into the fourth. It contains no choroid plexus.
See the image below for details.
Lastly , I would like to talk about the spaces and meningies in the brain.
Three membranes, or meninges, envelop the brain: the dura, the arachnoid, and the pia. The dura, the outer membrane, is separated from the thin arachnoid by a potential compartment, the subdural space, which normally contains only a few drops of CSF. An extensive subarachnoid space containing CSF and the major arteries separates the arachnoid from the pia, which completely invests the brain.  The pia, together with a narrow extension of the subarachnoid space, accompanies the vessels deep into the brain tissue; this space is called the perivascular space.
         The dura, is a tough, fibrous structure with an inner (meningeal) and an outer (periosteal) layer. The dural layers over the brain are generally fused, except where they separate to provide space for the venous sinuses and where the inner layer forms septa between brain portions. The outer layer is firmly attached to the inner surface of the cranial bones and sends vascular and fibrous extensions into the bone itself; the inner layer is continuous with the spinal dura.
        The arachnoid, a delicate avascular membrane, covers the subarachnoid space, which is filled with CSF. The inner surface of the arachnoid is connected to the pia by fine arachnoid trabeculae.
     The pia is a thin connective tissue membrane that covers the brain surface and extends into sulci and fissures and around blood vessels throughout the brain.

      Damage to any of the meningeal coverings can be fatal. That is why most of the coverings are very strong and durable. They are able to withstand massive wear and tear, and are very rarely ruptured, unless intracranial pressure is increased dramatically.

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