The CNS is composed of the mind and spinal cord, i m sorry are situated in the dorsal body cavity. The mind is surrounded by the cranium, and the spinal cord is safeguarded by the vertebrae. The mind is constant with the spinal cord at the foramen magnum. In enhancement to bone, the CNS is surrounding by connective tissue membranes, called meninges, and also by cerebrospinal fluid.

You are watching: The _______ is a tough protective sheath that covers the brain and that lies closest to the skull.

Meninges

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There are three class of meninges roughly the mind and spinal cord. The outer layer, the dura mater, is tough white fibrous connective tissue. The center layer that meninges is arachnoid, which resembles a cobweb in appearance, is a slim layer with countless threadlike strands that attach it to the innermost layer. The room under the arachnoid, the subarachnoid space, is filled through cerebrospinal fluid and contains blood vessels. The pia mater is the innermost layer of meninges. This thin, vulnerable membrane is tightly bound to the surface of the brain and spinal cord and cannot it is in dissected far without damaging the surface.

Meningiomas room tumors that the nerve tissue spanning the brain and spinal cord. Return meningiomas are usually not most likely to spread, physicians frequently treat them together though they to be malignant come treat symptoms that may build when a tumor uses pressure to the brain.

Brain

The brain is split into the cerebrum, diencephalons, brain stem, and cerebellum.

Cerebrum

The largest and most obvious part of the mind is the cerebrum, which is separated by a deep longitudinal fissure into two cerebral hemispheres. The two hemispheres are two separate entities however are connected by one arching band of white fibers, called the body callosum that offers a interaction pathway between the 2 halves.

Each cerebral hemisphere is separated into 5 lobes, 4 of which have the exact same name together the bone over them: the fontal lobe, the parietal lobe, the occipital lobe, and also the temporal lobe. A fifth lobe, the insula or Island of Reil, lies deep in ~ the lateral sulcus.

Diencephalon

The diencephalons is centrally located and also is almost surrounded by the cerebral hemispheres. It consists of the thalamus, hypothalamus, and also epithalamus. The thalamus, about 80 percent of the diencephalons, is composed of two oval masses the gray matter that serve as relay stations for sensory impulses, other than for the feeling of smell, going to the cerebral cortex. The hypothalamus is a small an ar below the thalamus, which plays a key role in keeping homeostasis since it regulates countless visceral activities. The epithalamus is the most dorsal section of the diencephalons. This little gland is connected with the beginning of puberty and rhythmic cycles in the body. That is prefer a biological clock.

Brain Stem

The mind stem is the an ar between the diencephalons and the spinal cord. It consists of 3 parts: midbrain, pons, and also medulla oblongata. The midbrain is the most superior portion of the brain stem. The pons is the bulging middle section of the brain stem. This region primarily consists of nerve yarn that kind conduction tracts between the higher brain centers and spinal cord. The medulla oblongata, or merely medulla, expand inferiorly native the pons. It is constant with the spinal cord at the foramen magnum. All the ascending (sensory) and also descending (motor) nerve fibers connecting the brain and spinal cord pass v the medulla.

Cerebellum

The cerebellum, the 2nd largest part of the brain, is located below the occipital lobes that the cerebrum. Three paired bundles of myelinated nerve fibers, called cerebellar peduncles, type communication pathways between the cerebellum and other components of the main nervous system.

Ventricles and also Cerebrospinal Fluid

A collection of interconnected, fluid-filled cavities are discovered within the brain. This cavities room the ventricles of the brain, and also the liquid is cerebrospinal liquid (CSF).

Spinal Cord

The spinal cord extends native the foramen magnum in ~ the base of the skull to the level that the an initial lumbar vertebra. The cord is constant with the medulla oblongata at the foramen magnum. Prefer the brain, the spinal cord is surrounding by bone, meninges, and cerebrospinal fluid.

The spinal cord is separated into 31 segments v each segment offering rise come a pair the spinal nerves. In ~ the distal end of the cord, many spinal nerves extend past the conus medullaris to type a collection that each other a horse"s tail. This is the cauda equina. In overcome section, the spinal cord appears oval in shape.

The spinal cord has actually two key functions:

Serving together a conduction pathway for impulses going to and from the brain. Sensory impulses travel to the brain on ascending tracts in the cord. Motor impulses travel on descending tracts.Serving together a reflex center. The reflex arc is the useful unit of the worried system. Reflexes space responses come stimuli that do not require aware thought and consequently, castle occur more quickly 보다 reactions that need thought processes. Because that example, v the tap the money reflex, the reflex action withdraws the affected component before friend are conscious of the pain. Many reflexes are mediated in the spinal cord without going to the higher brain centers.

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Brain Tumor

Glioma refers to tumors the arise native the support cells that the brain. This cells are called glial cells. This tumors encompass the astrocytomas, ependymomas and also oligodendrogliomas. This tumors are the most usual primary brain tumors.