Section 4

Astrocytes

(a type of glial cell) envelop brain capillaries and reduce capillary permeability (except for 3 locations) -this helps prevent hazardous materials from diffusing across the capillary wall.

The 4 Ventricles of the Brain

*1&2. Lateral Ventricles* -in the cerebrum (the first is in the right cerebral hemisphere while the second is in the left cerebral hemisphere) and are separated by a thin medial partition called the "septum pellucidum" *3. Third Ventricle* -a smaller chamber located within the diencephalon. -each lateral ventricle communicates with the 3rd ventricle *4. Fourth Ventricle* -shaped like a tetrahedron and is located between the pons and the cerebellum. -the 4th ventricle narrows at its inferior end before it merges with the "central canal" in the spinal cord.

Functions of the Medulla Oblongata

-Acts as a sensory relay for several cranial nerves -Acts as a relay to the thalamus -Serves as a cardiac center by regulating the heart's rate and the strength of its contractions -Serves as the vasomotor center by controlling the contraction and relaxation of the smooth muscle in the walls of the smallest arteries to alter vessel diameter and blood pressure -Acts as the respiratory center and is also influenced by the pons. -It is also involved in coughing, sneezing, salivation, swallowing, gagging, and vomiting

Sequence of Rostrocaudal Brain Deterioration

-As pressure builds up in cranial cavity, about 50 cc of CSF can be squeezed out of the cranium to allow more room. -Some blood can also be squeezed out, but this quickly leads to progressive loss of oxygen ("hypoxia") which will then lead to increased brain swelling. -Pressure on the RAS will soon lead to unconsciousness. -As the cerebrum pushes down on the midbrain, "decorticate posturing" (like holding a cord of wood) will occur. -If not stopped, the cerebrum and midbrain will push down on the upper pons and "decerebrate posturing" (like a waiter with his arm at his side reaching for a tip) will occur. this is the last reversible phase of rostrocaudal brain deterioration. -As everything continues to shift caudally and compresses the lower pons and medulla, brain death will occur. The cerebellum may even begin to herniate out of the foramen magnum. -Treatments include: high flow oxygen, barbiturate-induced coma, diuretics, or Decompressive cranectomy.

Functions of the Cerebellum:

-It coordinates muscle contractions and ensures that skeletal muscle contraction follows the correct pattern leading to smooth, coordinated movements. (The cerebellum stores muscle memory) -Impulses for voluntary muscular movement originate in the cerebral cortex as a "rough draft" and then are coordinated by the cerebellum -ex: a pianist's controlled movements are due to the cerebellum. -it adjusts skeletal muscle activity to maintain equilibrium and posture. -Receives sensory info from nerve endings ("proprioceptors") in muscles and joints and uses info to regulate body's position. -Maintains resting muscle tone by interacting with "muscle spindle fibers" in skeletal muscles -Has a broader role in some cognitive functions (attention, processing of language, music, and other sensory stimuli)

Functions of the Hypothalamus

-The master control of the autonomic nervous system. Projects descending axons to the inferior brain stem that influence heart rate, blood pressure, digestive activities, and respiration. -master control of the endocrine system. Secretes hormones that control the secretory activities of the anterior pituitary gland. Also produces 2 hormones (Antidiuretic hormone (ADH) and oxytocin) that are transported through axons in the infundibulum and stored in the posterior pituitary. -The body's thermostate, controls body temp. regulates shivering and sweating. -It is located at the center of the limbic system, the part of the brain that controls emotional responses (pleasure, aggression, fear, rage, contentment, and sex drive) -Monitors nutrients (glucose and amino acids) and controls hunger -Continuously monitors blood solute concentration and stimulates thirst or release of fluid -Regulates sleep-wake (circadian) rhythms by acting in conjunction with the pineal gland.

Summary of CSF

-produced by the choroid plexi in the ventricles, -flows through the ventricles, -enters into the subarachnoid space and the central canal, -and is eventually drained back into the blood via the arachnoid villi that empty into the dural venous sinuses.

Important Functions of CSF

-provides buoyancy so that the brain floats, reducing its weight by more than 95% and preventing it from being crushed under its own weight (brain has consistency of jello) -provides protection by creating a liquid cushion to protect the brain from sudden movements -provides environmental stability by transporting nutrients, chemical messengers, and by removing wastes. (wastes and excess CSF are eventually transported into the venous circulation)

The 4 Cranial Dural Septa

1. Falx Cerebri 2. Tentorium Cerebelli 3. Falx Cerebelli 4. Diaphragma Sellae

3 Points to be kept in mind regarding the Cerebral Hemispheres

1. In most cases, it is difficult to assign a precise function to a specific region of the brain; there is considerable overlap of function. 2. with few exceptions, both hemispheres receive their sensory information from and project motor commands to the opposite side of the body 3. while the 2 hemispheres appear as mirror images, one hemisphere may play a greater role in controlling certain body activities (i.e. the left hemisphere is frequently more important in controlling speech and understanding the spoken word)

2 Layers of the Dura Mater

1. Meningeal Layer -deep to periosteal layer -usually fused to the periosteal layer, except in specific areas where the 2 layers separate to form "dural venous sinuses" 2. Periosteal Layer -the more superficial layer, forms the periosteum on the internal surface of the cranial bones

The 3 Meninges

1. Pia Mater 2. Arachnoid 3. Dura Mater

2 Functional Brain Systems

1. The Reticular Formation 2. The Limbic System

Meninges

3 connective tissue membrane layers that separate the soft tissue of the brain from the bones of the cranium, enclose and protect blood vessels that supply the brain, and contain and circulate cerebrospinal fluid. In addition, some parts of the cranial meninges form some of the veins that drain blood from the brain.

The Brainstem

A bidirectional passageway for all nerve tracts extending between the cerebrum and the spinal cord. -it contains many autonomic centers required for our survival. -it is composed of 3 regions: the mesencephalon, pons, and medulla oblongata

Cerebrospinal Fluid (CSF)

A clear, colorless liquid that circulates in the ventricles and subarachnoid space. -CSF bathes the exposed surfaces of the CNS and completely surrounds it.

Cerebellar Cortex

A complex, highly convoluted outer layer of gray matter. (Layer of the cerebellum)

The Sensory Component

A component of the reticular formation that is responsible for alerting the cerebrum to incoming sensory information. -This component is also known as the "reticular activating system" or "RAS" and it contains sensory axons that project to the cerebral cortex. -The RAS is responsible for maintaining a state of awareness or consciousness. -The RAS processes visual, auditory, and touch stimuli and uses this information to keep us in a state of mental alertness. -Additionally, the RAS arouses us from sleep, such as when an alarm clock wakens us because it receives stimulatory sensory info and sends it to the cerebrum, thereby arousing it. Conversely, if there is little or no stimui while in bed with the lights out, you sleep because the RAS is not stimulated to act.

The Motor Component

A component of the reticular formation which communicates with the spinal cord and is responsible for regulating muscle tone (especially when the muscles are at rest.) -This component also assists with the autonomic centers in the medulla and pons to help control respiration, blood pressure, and heart rate.

The Reticular Formation

A loosely organized core of gray matter that projects vertically through the core of the midbrain, pons, and medulla. It also extends slightly into the diencephalon and the spinal cord as well. -It has 2 components: the motor component and the sensory component

The Insula

A small lobe that can be visualized by pulling aside the temporal lobe. Its function is apparently involved in: -Memory -Interpretation of taste

Rostrocaudal Brain Deterioration

A well-known medical sequence of events that occurs when the cerebrum pushes down through the tentorial incisure (tentorial notch) because of head trauma, intracranial bleeding, tumors, inflammation, or cerebral edema. -One step in this process is called transtentorial brain herniation.

CSF Formation

CSF is formed by the *choroid plexi* in each of the four ventricles -The choroid plexi are formed by the ependymal cells that line the ventricles and by the nearby blood capillaries. -CSF is essentially a filtrate of plasma, in that it contains proteins and salts (ions) -There are cilia on the surface of ependymal cells that line the ventricles and the central canal of the spinal cord that help circulate the CSF.

Brain Ventricles

Cavities or expansions within the brain that are derived from the lumen (opening) of the embryonic neural tube. -The ventricles are contiguous with one another as well as the central canal of the spinal cord. -There are 4 ventricles in the brain, all of which contain cerebrospinal fluid.

Arachnoid Villi

Fingerlike extensions of the arachnoid project through the dura mater into the dural venous sinuses to form "arachnoid villi" -Collections of arachnoid villi form visible "arachnoid granulations"

The Occipital Lobe

Forms the posterior region of each hemisphere and immediately underlies the occipital bone -Processing incoming visual information -Storing visual memories -Integration of eye movements

5 Lobes of each Cerebral Hemisphere

Four of the lobes are visible, the 5th is not visible at the surface 1. Frontal Lobe 2. Parietal Lobe 3. Temporal Lobe 4. Occipital Lobe 5. Insula

The Mesencephalon

Greek for "midbrain" The rostral (superior) portion of the brainstem. -it is a short section of the brain between the diencephalon and the pons -it is concerned with *visual and auditory reflexes* and *control of posture and movement

Subfalcine Brain Herniation

If there is swelling, a tumor, or bleeding on one side of the brain, it may cause pressure to shift a portion of one cerebral hemisphere under the falx cerebri. Such a movement under the falx cerebri is called "subfalcine brain herniation" and can result in severe brain injury. (manifested by unconsciousness and perhaps abnormal posturing.)

Subarachnoid Space

Immediately deep to the Arachnoid; the web-like trabeculae of the arachnoid extend through this space from the arachnoid to the underlying pia mater. -Within the subarachnoid space, cerebral arteries and veins are supported by the arachnoid trabeculae and surrounded by cerebrospinal fluid.

Coup-Contrecoup

Injuries to the cerebrum that occur when a blow to the head caused the brain to shift towards the area of impact and injure itself by hitting the inner surface of the skull, and then rebounding in the opposite direction and injuring itself again by hitting the skull on the opposite side of the skull where the original blow was delivered.

The Limbic System

Is composed of multiple cerebral and diencephalic structures that collectively process and experience emotions. -The Limbic System is sometimes referred to as the "emotional brain" -The structures of the limbic system form a ring or border around the diencephalon. the limbic system exerts an important influence upon the endocrine and autonomic motor systems; its fuctions also appear to affect motivational and mood states. (fear, happiness, and sadness) -with the help of this system, particular odors can provoke certain emotions or be associated with certain memories.

Diencephalon

Is sandwiched between the inferior regions of the cerebral hemispheres and includes the epithalamus, the thalamus, and the hypothalamus.

The Cerebrum

Is the location of conscious thought processes and the origin of all complex intellectual functions. -Identified as the 2 large hemispheres on the superior aspect of the brain. -The center of your *intelligence, reasoning, sensory perception, thought, memory, and judgement as well as your voluntary motor, visual, and auditory activities*

The Pons

Latin for "bridge" A bulging region on the anterior part of the brainstem that forms from part of the metencephalon -The pons acts to relay impulses -The pons also helps regulate breathing by influencing and modifying the respiratory center in the medulla oblongata.

The Cerebellum

Latin for "little brain" The second largest part of the brain, and it develops from the metencephalon -Has 2 primary layers: the cerebellar cortex & arbor vitae -Is composed of left and right "cerebellar hemispheres"

The Medulla Oblongata

Latin for "marrow" and "rather long" Sometimes just called the "medulla", is formed from the myelencephalon and is the most caudal (inferior) part of the brainstem and is continuous with the spinal cord inferiorly. -The caudal portion of the medulla resembles the spinal cord with its rounded shape and narrow central canal. -As the central canal extends superiorly towards the pons, it enlarges and becomes the fourth ventricle. -All communication between the brain and spinal cord involves tracts of nerve fibers that ascend or descend through the medulla oblongata.

Arbor Vitae

Latin for "tree of life" An internal region of white matter that resembles the branches of a tree.

The Frontal Lobe

Lies deep to the frontal bone and forms the anterior part of the cerebral hemisphere. Primary functions: -Voluntary motor functions of skeletal muscles -Concentration -Verbal Communications -Decision Making -Planning -Personality

Arachnoid

Lies immediately internal to the dura mater. -"arachnoid" = "like a spider's web" because it's partially composed of a delicate web of collagen and elastic fibers. ("trabeculae") -Immediately deep to the arachnoid is the subarachnoid space. -Between the arachnoid and the overlying dura mater is a potential space called the "subdural space"

The Parietal Lobe

Lies internal to the parietal bone and forms the superoposterior part of each cerebral hemisphere -General sensory functions, such as evaluating the shape and texture of objects being touched -Understanding speech and formulating words to express thoughts and emotions

The Temporal Lobe

Lies internal to the temporal bone. -Hearing -Interpreting speech and language -Smell (olfaction)

Why is White Matter White?

Myelin (Oodendricytes)

Blood-Brain Barrier

Nervous tissue is protected from the general circulation by the blood brain barrier. -it is markedly reduced or missing in 3 distinct locations in the CNS: 1. the choroid plexi (so they have necessary permeability to produce CSF) 2. the hypothalamus 3. the pineal gland (both of these so the endocrine glands have access to the blood stream to release their hormones into the plasma)

Chiari Malformation

Poor formation of the floor of the occipital bone or premature fusion of a suture (craniosynostosis, particularly of the lambdoid suture) can lead to inadequate room for the cerebellum of the brain. This causes the inferior projections of the cerebellum (cerebellar tonsils) to be pushed out of the foramen magnum. -associated with headaches, nausea, muscle weakness, difficulty swallowing, impaired coordination, and blockage of the normal flow of spinal fluid, particularly in the central canal of the spinal cord -can be treated with decompressive surgery (removing the lamina of the 1st and sometimes 2nd or 3rd cervical vertebrae and part of occipital bone to relieve the pressure) -thought to be every 1 per 1,000, but is likely higher

Epidural Space

Potential space that separates the dura mater and the overlying bones of the skull, contains the arteries and veins that nourish the meninges and bones of the cranium. -under normal (healthy) conditions, the potential space is not a space at all. -However, it has the *potential* to become a real space and fill with fluid or blood as a result of trauma or disease.

The Hypothalamus

The anterioinferior region of the diencephalon -The thin, stalk-like "infundibulum" extends inferiorly from the hypothalamus to the pituitary gland -The hypothalamus has numerous functions

Central White Matter

The ascending and descending tracts between the brain and spinal cord mostly cross over ("decussate") to the opposite side at the level of the medulla oblongata.

Cerebral Hemispheres

The cerebrum is composed of 2 halves called the left and right "cerebral hemispheres" -These are separated by a deep "longitudinal fissure" that extends along the midsagittal plane. -They are also separate from one another, except at a few locations where tracts of white matter allow for communication between them. (the corpus callosum being the largest)

Decussation

The crossover of the nerve tracts in the caudal region of the medulla to the opposite side of the brain. (why the right hemisphere of your brain controls the left part of your body, and vice versa)

Cerebral Medulla

The inner white layer of the cerebrum

Falx Cerebri

The largest of the 4 dural septa, located in the midsagittal plane, and projects into the longitudinal fissure between the left and right cerebral hemispheres. -the *anterior* attachment site for the falx cerebri is the *crista galli* of ethmoid -the *posterior* attachment site is the superior portion of the *tentorium cerebelli* -within the margins of the falx cerebri are several dural venous sinuses. if there's swelling, a tumor, or bleeding on one side of the brain, it may cause pressure to shift a portion of one cerebral hemisphere under the falx cerebri

The Corpus Callosum

The largest of the white matter tracts which connects the hemispheres and provides the main method of communication between them

Cranial Dural Septa

The meningeal layer of the dura mater extends as flat partitions (septa) into the cranial cavity at several locations; these double layers of dura mater are called *"cranial dural septa"* -These membranous partitions separate specific parts of the brain and provide additional stabilization and support for the entire brain. *there are 4 cranial dural septa*

Dura Mater

The most external of the meninges and is composed of tough, dense irregular connective tissue that has 2 fibrous layers. -It is the strongest of the meninges

Cerebral Cortex

The outer gray layer of the cerebrum

The Thalamus

The paired oval masses of gray matter that lie on either side of the 3rd ventricle -forms the superolateral walls of the 3rd ventricle -*the principal and final relay point for all sensory information*, EXCEPT for the sense of smell (olfaction), that is processed and projected to the cerebral cortex. -

Diaphragma Sellae

The smallest of the dural septa, it forms a "roof" over the sella turcica of the sphenoid bone. -A small opening within it allows for the passage of a thin stalk ("infundibulum") that attaches the pituitary gland within the sella turcica to the base of the hypothalamus located just above.

Falx Cerebelli

a sickle-shaped bertical partition extending into the midsagittal line inferior to the tentorium that divides the left and right cerebellar hemispheres. -a tiny dural venous sinus runs in its posterior vertical border.

Infundibulum

a thin stalk that attaches the pituitary gland within the sella turcica to the base of the hypothalamus located just above. Passes through a small opening in the diaphragma sellae.

Tentorial Notch

also called the "tentorial incisure", it is a small gap or opening in the anterior surface of the tentorium cerebelli which allows passage of the brainstem.

Dural Venous Sinuses

large, blood-filled spaces formed by the meningeal layer and the periosteal layer separating. -They're typically triangular in cross section, and unlike most other veins, they do not have valves to regulate venous flow. -They are in essence large veins that drain blood from the brain and transport the blood to the internal jugular veins.

Tentorium Cerebelli

latin for "tent" and "little brain" A horizontally oriented fold of dura mater that separates the occipital lobe and temporal lobes of the cerebrum from the cerebellum. -There is a dural venous sinus that runs within its posterior border. -The anterior surface of the tentorium cerebelli has a small gap or opening called the "tentorial notch" ("tentorial incisure") to allow for the passage of the brainstem. -separates the cerebrum from the cerebellum

The Epithalamus

partially forms the posterior roof of the diencephalon and covers the 3rd ventricle -The posterior portion houses the "pineal gland" which is an endocrine gland which secretes melatonin (which helps regulate day-night cycles known as the body's "circadian rhythm")

Cerebrovascular Accident (CVA) and Transient Ischemic Attack (TIA)

pg 159

Pia Mater

the innermost of the cranial meninges -it is composed of delicate connective tissue that is highly vascularized and which tightly adheres to the brain and follows every contour of the brain surface

what do police snipers aim for?

the medulla oblongata in order to disconnect the brain from the spinal cord *external landmark for frontal shot*: tip of the nose *external landmark for side shot*: base of the ear lobe