The Central Nervous System : Let's Think About It

the brain and spinal cord are protected primarily by the bone coverings of the skull and spinal column, respectively, yet there are more protections underneath the bone

the meninges are the three tissue layers that lie just external to the brain and spinal cord. They protect the brain and spinal cord, they protect and enclose the venous sinuses of the brain, contain CSF and form partitions within the skull the dura mater is the most external layer. It is double layered (periosteal and meningeal), and in certain places, the dural sinuses are formed between the two layers the arachnoid layer is a loose covering, which does not dip into the sulci of the brain. The subdural space separates it from the dura mater and the subarachnoid space separates it from the next layer down. The subarachnoid space is spanned by threadlike extensions and is filled with CSF and arteries the pia mater is the deepest, most delicate membrane, clinging tightly to the surface of the brain. It contains small arteries. in several places, the dura mater extends inward into the brain to form dural septa that anchor the brain to the skull. The falx cerebri runs along the longitudinal fissure. The falx cerebelli is found within the vermis of the cerebellum. The tentorium cerebelli extends into the transverse fissure.

Meningitis is an inflammation of the meninges, either caused by bacteria or virus. It is dangerous for two reasons: 1) the bacteria or virus can easily spread to the brain, causing encephalitis (brain inflammation), or 2) the swelling of the meninges causes pressure on the brain and/or spinal cord, possibly causing death.

general anatomy of the brain

	the adult brain is typically considered in terms of the following subdivisions : cerebral hemispheres diencephalon brain stem cerebellum
	the basic pattern of the CNS is a central cavity surrounded by a gray matter core (neural nuclei), external to which is white matter (myelinated fiber tracts).

the cerebral cortex

	the main control center of perception, communication, memory, comprehension, appreciation, and conscious behavior in general
	it consists of neuron cell bodies, dendrites and unmyelinated axons (gray matter), but no fiber tracts
	~2-4mm thick (1/8 inch), but due to the convolutions, it has a great surface area and accounts for ~40% of total brain mass
	motor and sensory functions are localized into discrete cortical areas (domains), but higher functions (memory, language) are diffusely located
	three generalizations regarding the cortex each hemisphere "controls" the opposite side of the body the hemispheres are not entirely equal in function our approach to cortical function is grossly oversimplified
	motor areas of the cortex primary motor cortex : the precentral gyrus; each part of the body is represented by a different area of the gyrus premotor cortex : just anterior to the precentral gyrus; controls learned motor skills that are repititious or patterned Broca's area : found anterior to the inferior region of the premotor area, typically in the left hemisphere only, and it is generally considered a motor speech area Frontal eye field : located anterior to the premotor cortex and superior to Broca's; controls movement of the eyes
	sensory areas of the cortex primary somatosensory cortex : postcentral gyrus; similar to the primary motor cortex in that different areas of the body are coded differently somatosensory association area : located just posterior to the primary somatosensory cortex; responsible for integrating and analyzing different somatic sensations visual areas : composed of the primary visual cortex (the extreme posterior tip of the occipital lobe, in the calcarine sulcus) and the visual association area. The visual cortex is the largest of the sensory areas and receives all of the information gathered by the retinas. The association area surrounds the primary visual cortex and covers much of the occipital lobe. It is responsible for interpretation of the visual stimuli. auditory areas : there are two primary auditory cortices, each located where the temporal lobe abutts the lateral sulcus. Like the visual areas, the auditory cortex receives the sound impulses from the cochlea, but the auditory association areas interpret what is heard as speech, music, or whatever. olfactory areas : the olfactory cortices are in the medial part of the temporal lobes and are considered part of the rhinencephalon, which is part of the limbic system gustatory cortex : located deep to the temporal lobe in the parietal lobe. It perceives taste stimuli.
	association areas of the cortex (any area without primary in its name) prefrontal cortex : anterior portions of the frontal lobes; involved in intellect, personality and complex learning and thought. The most complex cortical region, it is necessary for abstract ideas, judgement, reasoning, and many other higher thinking skills. Linked to the limbic system. prefrontal lobotomy used to be used as a treatment for mental illness. gnostic area : also called the general interpretation area, a poorly-defined region including parts of the temporal, parietal and occipital lobes, only in one hemisphere (usually the left). Evidently a storage site for sensory memories, but also integrates all incoming sensory signals to send to the prefrontal cortex for final interpretation. injury to the gnostic area causes one to become an imbecile language areas : include Wernicke's area (speech area) and the affective language areas. Wernicke's is typically found only in one hemisphere (left), in the posterior, temporal lobe and it seems to be the dominant area responsible for interpretation written and spoken language, possibly mostly unfamiliar words. The affective language areas appear in the hemisphere opposite Broca's and Wernicke's and act in the emotional overtones and gestures of "body language." visceral association area : the cortex of the insula, possibly involved in visceral sensations (upset stomach, full bladder, etc.).
	cerebral dominance refers to the side of the brain used for language. This is typically the left, and the right side is used for more visual-spatial skills, intuition, emotion, appreciation of art and music, etc. most people with left-side dominance are right-handed in the others (~10%), the hemispheres' roles are switched. most right-side people are left-handed in left-handed people with bilaterally functioning cortices, ambidexterity is usually the case dyslexia may arise from lack of cerebral dominance