Brain and Cranial Nerves PDF

Anatomy and Physiology II Review Sheet Kimberly Denise Vigee’ N.D. BRAIN AND CRANIAL NERVES - One’s brain defines who that person is b/c it records the sum of all of our experiences. One’s physical body is just the vessel that carries out the brain’s instructions. - The brain is the organ that...

Anatomy and Physiology II Review Sheet Kimberly Denise Vigee’ N.D. BRAIN AND CRANIAL NERVES - One’s brain defines who that person is b/c it records the sum of all of our experiences. One’s physical body is just the vessel that carries out the brain’s instructions. - The brain is the organ that defines life just as it defines death. i.e. One is pronounced dead when their brain dies. The brain is the only organ we have not figured out how to transplant. - Don’t forget!!! The brain and spinal cord are the 2 organs composing the CNS. They are both located in the dorsal cavity. The brain is connected to the spinal cord at the level of the foramen magnum of the occipital bone. Protection System of the Brain - The brain is protected by: 1. Cranial Bones * Compact bone - the outer layer * Spongy bone - the inner layer. If the cranial bones were made of solid compact bone then the cranium would be too heavy. 2. Cranial Meninges * Are connective tissue coverings that run continuously around the spinal cord and brain. * Bear the same names as the spinal meninges: a. Dura Mater (outermost) - gives the brain its strength - A tough white fibrous connective tissue (inelastic). - Located only inside the cranial bones and lines the vertebral canal. - The dura mater contains channels, called dural sinuses which collect venous blood to return to the cardio vascular system. b. Arachnoid (middle) - Has a coblike appearance - Has villa that produces CSF. Note that the choroid plexus also produces CSF. 1 Anatomy and Physiology II Review Sheet Kimberly Denise Vigee’ N.D. c. Pia Mater (innermost) – layer that adheres to the brain itself - can’t be dissected away from the brain without injury - closely follows contours of brain 3. Cerebrospinal Fluid (CSF) -A clear, viscous liquid. - CSF contains sodium, potassium, calcium, magnesium, chloride, and white blood cells. - (3) Functions of the CSF: 1. Circulation: Delivers nutrients from the blood to the brain and spinal cord and removes waste and toxic substances. 2. Chemical protection: provides optimal chemical environment for neuronal signaling. 3. Mechanical protection: Completely surrounds the spinal cord for protection. Acts as a cushion for the brain - CSF is found in 3 places: 1. Ventricles of the brain 2. Subarachnoid space 3. Central canal of the spinal cord - The Ventricular system - a series of spaces and canals located deep inside the cerebrum of the brain. - In the ventricles are specialized tissue known as the choroids plexuses - Choroids plexus are tiny masses of specialized capillaries from the pia mater. - 4 Ventricles: 1. 2 Lateral Ventricles - largest of the 4 ventricles * Resemble the horns of a ram. * There is 1 lateral ventricle located in each of the hemispheres (right and left) of the 2 Anatomy and Physiology II Review Sheet Kimberly Denise Vigee’ N.D. cerebrum. * Ventricle #1 is located in the left cerebral hemisphere; ventricle #2 is in the right cerebral hemisphere. * Septum Pellucidum – thin membrane separating the 2 lateral ventricles. 2. 3rd Ventricle: - The 2 lateral ventricles join at the 3rd ventricle. * The 2 openings in the third ventricle allow for communication with the lateral ventricles. 3. 4th Ventricle: * Is located between the brain stem and the cerebellum but still in the cerebrum. - Flow of the CSF: 1. CSF is made in the choroid plexuses, which are networks of capillaries in the walls of the 2 lateral ventricles. 2. CSF passes from each lateral ventricle to the 3rd ventricle through the interventricular foramina. 3. CSF then passes to the 4th ventricle via the cerebral aquaduct. 4. CSF enters the subarachnoid space through 3 openings in the roof of the 4th ventricle: the median aperture and 2 lateral aperatures. 5. CSF then circulates in the central canal of the spinal cord and in the subarachnoid space around the surface of the brain and spinal cord. 6. CSF is gradually reabsorbed in the blood through arachnoid villi, extensions of the arachnoid that project into the dural venous sinuses. - Hydrocephalus – an abnormality of CSF drainage due to brain tumors, inflammation, head injury, meningitis, etc. When excess CSF fluid accumulates in the ventricles, the CSF pressure rises. The fluid buildup compresses and damages the nervous tissue. To relieve the pressure, a neurosurgeon may implant a drain line, called a shunt, into the lateral ventricle to divert CSF into the superior vena cava or abdominal cavity. Blood Supply to the Brain and Cranial Nerves - The brain always has a backup system just in case of any blockage. 3 Anatomy and Physiology II Review Sheet Kimberly Denise Vigee’ N.D. - Main supply is from the common carotid arteries, which divide into the internal and external carotid arteries. - The internal carotid feeds the structures of the brain. - The external carotid supplies the face and neck. - Vertebral Arteries, the 2 arteries running up the vertebral column, join inside the head to form a circle. This circle is referred to as the circle of Willis or cerebral arterial circle. The circle is located at the base of the brain. The vertebral arteries are separate, one on the right and one on the left, when located outside the brain. * Circle of Willis: 1. Posterior Cerebral - supply the posterior brain 2. Posterior Communicates – makes a circle with the carotid arteries 3. Anterior Cerebral - supply the anterior brain 4. Anterior Communicates - makes a circle with the carotid arteries - The brain has no reserve of oxygen, nutrients, or glucose so it is extremely important to have constant blood supply to the brain. - One of the most metabolically active organs of the body, and the amount of oxygen it uses varies with the degree of mental activities. i.e. supply and demand - In the adult, the brain comprises only 2% of total body weight, but consumes about 20% of the oxygen used at rest. - If blood flow is impaired briefly = could result in unconsciousness If blood flow is impaired 1-2 minutes = can impair brain cells If blood flow is impaired for 4 minutes = results in permanent injury to brain - Principal source of energy for brain is glucose (principle molecule to make ATP) which is delivered by the blood. - Glucose, oxygen, carbon dioxide, water, and most lipid-soluble substances, such as caffeine, alcohol, nicotine, heroine and anesthetics, pass rapidly from the circulating blood into the brain cells. - Proteins and most antibiotics do not pass at all from the blood into brain cells. - Blood Brain Barrier- functions as a selective anatomical and physiological barrier to protect brain cells from harmful substances and pathogens. Brain capillaries are much less permeable than most other body capillaries. Substances that cross the BBB with the assistance of a transporter to cross by active transport. Principle Parts of the Brain (4) 1. Brain Stem 4 Anatomy and Physiology II Review Sheet Kimberly Denise Vigee’ N.D. 2. Diencephalon 3. Cerebellum 4. Cerebrum Brain Stem - 3 Parts of the Brain Stem: * The brain stem – connects the brain to the spinal cord 1. Midbrain (Mesencephalon) - most superior part of the brainstem - The most superior portion of the brainstem and connected to the diencephalon 2. Pons (“bridge”) - middle part of brainstem - Connects parts of the brain and other parts of the brain with each other by way of tracts. - Nuclei in the pons contain the pneumotaxic & apneustic centers, which control respiration. * Pneumotaxic Area – Portion of respiratory center in the pons that continually send inhibitory nerve impulses to the inspiratory area that limit inspiration and facilitate expiration. * Apneustic Area – Portion of the respiratory center in the pons that send stimulatory nerve impulses to the inspiratory area that activate and prolong inspiration and inhibit expiration. 3. Medulla Oblongata - or simply AKA: Medulla - Forms the inferior part of the brain stem. that is continuous with the spinal cord. - All the ascending (sensory) and descending (motor) nerve fibers connecting the brain and spinal cord pass through the medulla. – Refer to the cranial nerves that come off the medulla. - Decussation * Descending fibers cross over from side to the other. In other words, fibers descending on the left side cross over to the right and vice versa. * Neurons on the left side of the brain control skeletal muscles on the right side of the body. and neurons on the right side of the brain control skeletal muscles on the left side of the body - The medulla contains nuclei that form 3 Centers that control ANS Activities: 1. Cardiovascular Center – rate and force of HR; diameter of blood vessels; BP 5 Anatomy and Physiology II Review Sheet Kimberly Denise Vigee’ N.D. 2. Respiratory Center – acts with the centers in the pons to regulate the rate, rhythm, and depth of breathing 3. Other centers - involved in coughing, sneezing, swallowing, and vomiting. Diencephalon - “Dia” = between; “Enkephalos” = brain (Greek) - It surrounds the 3rd ventricle and is largely composed of gray matter. - 4 Parts to the diencephalon: thalmaus, hypothalamus, subthalamus, epithalamus - Thalamus * Located superior to the brain stem * Serves as relay stations for all sensory impulses, except smell, to the cerebral cortex. * Registers conscious recognition of pain, temperature, light touch and pressure. - Hypothalamus (major one) * It is a small region below the thalamus. * Infundibulum – a slender stalk extends from the floor of the hypothalamus to the pituitary gland and acts as a connector between the 2 structures. * Mamillary Bodies - two visible “bumps” on the posterior portion of the hypothalamus, they are involved in memory and emotions to different odors. * Functions of the Hypothalamus (A major regulator of homeostasis): 1. Regulator of the ANS – The ANS controls cardiac and smooth muscle and the secretions of certain glands. In this way it regulates many visceral activities such as heart rate, blood pressure, respiratory rate, contraction of the urinary bladder, and motility of the digestive tract. 2. Regulator of the Pituitary gland - The hypothalamus synthesizes and secretes 2 regulatory factors for the anterior lobe of the pituitary gland: - Releasing factors (RF’s). - Inhibiting factors ( IF’s). 3. Regulation of Emotional and Behavioral patterns – together with the limbic system, the hypothalamus i.e. rage and aggression, fear, pleasure, and sex drive. 6 Anatomy and Physiology II Review Sheet Kimberly Denise Vigee’ N.D. 4. Regulation of Eating and Drinking/Water balance – * 3 Centers in the Hypothalamus that regulate eating and drinking: 1. Feeding center – responsible for hunger sensations 2. Satiety center – sends outs impulses that inhibit the hunger center when a sufficient food amount is consumed 3. Thirst center – certain cells in the hypothalamus are stimulated by rising osmotic pressure of the extracellular fluid, they cause the sensation of thirst. The intake of water by drinking restores the osmotic pressure to normal, removing the stimulation of thirst. 5. Control of body Temperature – If the blood flowing through the hypothalamus is higher than normal, the hypothalamus directs the ANS to release heat. 6. Regulates the circadian rhythms and states of consciousness – 7. Regulates endocrine system activity – The hypothalamus is an endocrine gland. It produces 2 hormones that are stored in the posterior pituitary gland: 1.Vasopressin (Antidiuretic hormone) 2. Oxytocin * Epithalamus: - Houses the Pineal gland. : involved in with the onset of puberty, especially in males and rhythmic cycles in the body. : In animals, the pineal gland apparently directs instinctive behavior. : In humans, this gland also synthesizes and secretes 2 hormones: 1. Melatonin 2. Serotonin : It is like the biological clock. * Subthalamus: controls body movements * Limbic System - AKA “Emotional Brain” - Plays a role a primary role in a range of emotions, including pain, pleasure, affection and anger - Experiments have shown that when different areas of animals’ limbic system are stimulated, the animal’s reactions indicate that they are experiencing intense pain or extreme pleasure. Stimulation of other limbic system areas in animals produces tameness and signs of affection. - Together with the cerebrum, also functions in memory 7 Anatomy and Physiology II Review Sheet Kimberly Denise Vigee’ N.D. Cerebellum - Translates as brain in Latin. - Cerebellum is the Second largest portion of the brain - cerebrum is the largest - Located below the occipital lobes of the cerebrum and is separated from them by the Transverse fissure. - Like the cerebrum, the cerebellum consists of white matter surrounded by a thin layer of gray matter – Cerebellar Cortex. - 3 Paired Bundles of Myelinated Nerve Fibers – called Cerebellar Peduncles: * They form communication pathways between the cerebellum and other parts of the CNS, by connecting the cerebellum to the brain stem Superior Cerebellar Peduncles Middle Cerebellar Peduncles Inferior Cerebellar Peduncles - Compares intended movements with what is actually happening to smooth and coordinated complex, and skilled movements. Regulates posture and balance. Cerebrum - Largest part of the brain - Portion of the brain that occupies the upper part the cranial cavity and provides higher mental functions, reading, writing, speech, calculations, etc. - Has 2 hemispheres called “Cerebral Hemispheres” - Has a cerebral cortex – just like the cerebellum - Controls functions such as: interpreting sensory impulses, initiating muscular movements, storing memory, reasoning, and determining intelligence. -The ridges are the gyri ( sing.= gyrus). -The grooves are the sulci (sing.= sulcus). - The cerebrum is comprised of two cerebral hemispheres (right and left). * These are separated by the longitudinal fissure. -The cerebrum is subdivided into four surface lobes. The lobes and their primary functions are: 8 Anatomy and Physiology II Review Sheet Kimberly Denise Vigee’ N.D. 1. Frontal lobes Function in: a. Voluntary skeletal muscle activity. b. Mood. c. Aggressiveness. d. Other functions. 2. Temporal lobes & Function in memory. 3. Parietal lobes & Sensory functions: a. Balance. b. Taste. c. Speech. 4. Occipital lobes : Contain the visual cortex. * The lobes of the cerebrum are separated by sulci or deeper fissures: Longitudinal fissure- separates the cerebrum into left and right lobes (right & left cerebral hemispheres). Lateral fissure- separates the frontal lobe from the temporal lobe. Central sulcus- separates the frontal lobe from the parietal lobe. Brain Lateralization (Split Brain Concept) - They are connected by the corpus callosum ( a prominent white fiber tract). This is a white commissure comprised of white fiber nerve tracts. It allows for communication and exchange of neural information between the hemispheres. - Typically, the left hemisphere dominates the right hemisphere (dominant hemisphere). - Has 2 hemispheres that are not bilaterally symmetrical, either anatomically or functionally. - Left Hemisphere is important for: 1. Right-handed control 3. Numerical and scientific skills 2. Spoken and written language 4. Reasoning - Right Hemisphere is important for: 1. Left-handed control 2. Musical and artistic awareness 3. Space and pattern perception 4. Insight, Imagination, and generating mental images of sight, sound, touch, taste, and smell. 9 Anatomy and Physiology II Review Sheet Kimberly Denise Vigee’ N.D. Brain Stem and its related Cranial Nerves - Medulla = cranial nerves VIII, IX, X, XI, XII - Pons = cranial nerve V, VI, VII, VIII - Midbrain = cranial nerves III, IV * Note: Cranial nerves I and II arise from nervous tissue in the nose and eyes. CRANIAL NERVES Oh, Oh, Oh, To Touch And Feel Very Green Vegetables A H ! Some Say Marry Money But My Brother Says Big Brains Matter More ! A. Olfactory (nerve I) - sensory Function: smell B. Optic (nerve II) - sensory Function: sense of sight * Note: Olfactory and Optic does not originate in the brain stem ! C. Oculomotor (nerve III) - primarily motor Function: movement of eyeball, proprioception (muscle sense) D. Trochlear (nerve IV) - primarily motor Function: movement of eyeball, constriction of pupil in bright light or for near vision * Note: Oculomotor and Trochlear originate in the midbrain part of the brainstem ! E. Trigeminal (nerve V) - both Function: sensory for face and teeth, motor for chewing F. Abducens (nerve VI) - primarily motor Function: movement of eyeball G. Facial (nerve VII) - both Function: facial expression and secretion of saliva and tears; proprioception Clinical Application: Injury produces paralysis of the facial muscles, called Bell's Palsy; loss of taste; & loss of ability to close the eyes, even during sleep. H. Vestibulocochlear (nerve VIII) - sensory Function: associated with hearing, equilibrium 10 Anatomy and Physiology II Review Sheet Kimberly Denise Vigee’ N.D. Clinical Application: Injury may cause tinnitus (ringing) or deafness, vertigo (dizziness) * Note: Vestibule = bony chamber of the inner ear Cochlea = portion of the inner ear that contains receptors for hearing * Note: Trigeminal, Abducens, Facial, Vestibulocochlear originate in the pons part of the brain stem I. Glossopharyngeal (nerve IX) - both Function: secretion of saliva; taste and regulation of BP J. Vagus (nerve X) - both Function: visceral muscle movement and their sensation K. Accessory (nerve XI) - primarily motor Function: swallowing, movement of head L. Hypoglossal (nerve XII) - primarily motor Function: movement of tongue during speech and swallowing * Note: Glossopharygeal, Vagus, Accessory, Hypoglossal originate in the medulla part of the brainstem. * Note: Eyeball: Trochlear, Optic, Oculomotor, Abducens Key Medical Terms Associated with the Central Nervous System Analgesia ("an" = without ; "algia" = painful condition) - pain relief Anesthesia ("esthsia" = feeling) - loss of feeling Babinski Sign - abnormal reflexes Coma - Abnormally deep unconsciousness with an absence of voluntary response to stimuli and with varying degrees of reflex activity. It may be due to illness or to an injury. Dementia ("de" = away from, "mens" = mind) - An organic mental disorder that results in permanent or progressive general loss of intellectual abilities such as impairment of memory, judgment, and abstract thinking and changes in personality. Lethargy - A condition of functional torpor (limpness) or sluggishness. Nerve Block - Loss of sensation in a region, such as in local dental anesthesia, due to injection of a local anesthetic. 11 Anatomy and Physiology II Review Sheet Kimberly Denise Vigee’ N.D. Neuralgia - Attacks of pain along the entire course or branch of a peripheral sensory nerve. Paralysis - Diminished or total loss of motor function resulting from damage to nervous tissue or a muscle. Spastic ("spas" = draw or pull) - An increase in muscle tone (stiffness) associated with an increase in tendon reflexes and abnormal reflexes (Babinski sign). Tinnitus - ringing in the ear Torpor - limpness Vertigo - dizziness 12