Anatomy Chapter 13 -The Brain


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Anatomy Chapter 13 -The Brain

  1. 1. Anatomy Chapter 13 -The Brain & Cranial NervesAnatomy Chapter 13 -The Brain & Cranial Nerves BrainBrain Principle PartsPrinciple Parts the brain stem diencephalon cerebrum cerebellum Protection & CoveringsProtection & Coverings cranial bones meninges - continuous w/ s.c. meninges; dura, arachnoid, & pia mater. Cerebrospinal FluidCerebrospinal Fluid Production: CSF - formed by filtration of blood from networks of capillaries called choroid plexuses (found in the ventricles). CSF circulates through the subarachnoid space, ventricles, & central canal of the s.c. CSF provides: mechanical protection chemical protection circulation of nutrients & wastes products Ependymal Cells w/ many tight junctions prevents CSF leaks. Provides a Blood/Brain (CSF) Barrier : permits certain substances to enter the fluid but excludes others An injury to the brain due to trauma, inflammation, or toxins, causes a breakdown of the BBB, permitting normally restricted substances into brain tissue.It also prevents entry of drugs that could be used as therapy for brain cancer or other CNS disorders. Reabsorption: most CSF is absorbed by the arachnoid villi of the superior sagittal blood sinus HydrocephalusHydrocephalus “water on the brain” - results when CSF cannot circulate or drain properly. Causes increased pressure & may damage nervous tissue. A shunt to the subclavian vein can be implanted surgically. Blood SupplyBlood Supply via the cerebral arterial circle (circle of Willis) Although the brain is only 2% of the total body weight, it utilizes ~ 20% of the bodies oxygen, one of the most metabolically active organs depending on the amount of mental activity. An interruption of the O2 supply to the brain can result in weakening, permanent damage, or death of brain cells
  2. 2. Disruption at childbirth can result in paralysis, mental retardation, epilepsy, or death Because carbohydrate storage in the brain is limited, the supply of glucose must be continuous. Glucose deficiency may produce mental confusion, dizziness, convulsions, and unconsciousness Brain StemBrain Stem 1. Medulla - or medulla oblongata - continuous w/ the upper part of the s.c. & contains portions of both motor & sensory tracts. Decussation of pyramids occurs here - where ascending and descending tracts cross. contains nuclei that are reflex centers for regulation of heart rate, respiration rate, vasoconstriction's, swallowing, coughing, sneezing, vomiting, and hiccuping contain nuclei of origin for cranial nerves VIII-XII also contains olivary and vestibular nuclei olive - insure precise, voluntary movements & maintain equilibrium vestibular nuclei - maintain equilibrium 2. Pons - superior to the medulla - connects s.c. w/ brain relays nerve impulses related to voluntary skeletal movements from the cerebral cortex to the cerebellum contains the nuclei for cranial nerves V through VII Contains pneumotaxic & apneustic areas, which help control respiration along w/ the respiratory center of the medulla. 3. Reticular Formation - a lg. portion of the brain stem (medulla, pons, & midbrain) consists of sm areas of gray matter interspersed among fibers of white matter; it has both sensory & motor functions It helps regulate muscle tone, alerts the cortex to incoming sensory signals (reticular activating sys, or RAS), and is responsible for maintaining consciousness & awakening from sleep. 4. Midbrain or mesencephalon - connects pons and diencephalon It conveys motor impulses from the cerebrum to the cerebellum & s.c., sends sensory impulses from the s.c. to the thalamus, and regulate auditory and visual reflexes The midbrain contains red nucleus (coordinates muscle movements) & nuclei of origin for c.n.’s III & IV
  3. 3. DiencephalonDiencephalon Thalamus & Hypothalamus Thalamus - located superior to the midbrain & contains nuclei that serve as relay stations for all sensory impulses, except smell, to the cerebral cortex. Also registers conscious recognition of pain and temperature & some awareness of light touch & pressure Hypothalamus - inferior to the thalamus, has four major regions (mammilary, tuberal, supraoptic, & preoptic), controls many body activities, & is one of the major regulators of homeostasis. Functions of hypothalamusFunctions of hypothalamus Controls & integrates the ANS, which regulates contractions of smooth muscle, cardiac muscle, & secretions of many glands Principle intermediary btn the nervous sys and the endocrine sys - the 2 major control systems of the body. When the hypothalamus detects certain changes in the body, it releases a variety of chems called regulating hormones (or factors) that stimulate or inhibit specific cells in the anterior pituitary gland. fs in the feelings of rage and aggression aides in controlling body temperature Regulates food intake through 2 centers, the feeding (hunger) center and the satiety center It contains the thirst center which initiates drinking when ECF osmotic pressure rises above normal It is one of the centers that maintains the waking state & sleep patterns (part of RAS) CerebrumCerebrum largest part of the brain Cerebral Cortex - surface layer - 2-4mm thick & is composed of gray matter. Contains billions of neurons. cortex contains gyri (convolutions), deep groves called fissures and shallower sulci Below the cortex lies the cerebral white matter, tracts which connect parts of the brain with itself and other parts of the nervous system The cerebrum is nearly divided into left & right halves called hemispheres, by the longitudinal fissure Internally it remains connected by the corpus callosum, a bundle of transverse white fibers.
  4. 4. Lobes - each hemisphere is further subdivided into 4 lobes by sulci or fissures (frontal, parietal, temporal, & occipital a 5th part (lobe) of the cerebrum, the insula, lies deep to the parietal, frontal, and temporal lobes & cannot be seen in an external view of the brain White MatterWhite Matter under the cortex & consists of myelinated axons running in three principal directions association fibers - connect & transmit nerve impulses btn gyri in the same hemisphere commissural fibers - connect gyri in one hemisphere to corresponding gyri in the opposite hemisphere projection fibers - form ascending & descending tracts that transmit impulses from the cerebrum to other parts of the brain and s.c. Basal GangliaBasal Ganglia (cerebral nuclei) - paired masses of gray matter in each cerebral hemisphere responsible for helping control muscular movements Limbic SystemLimbic System found in the cerebral hemispheres & diencephalon f’s in emotional aspects of behavior and memory, and is associated w/ pain & pleasure Functional Areas of the Cerebral CortexFunctional Areas of the Cerebral Cortex Specific types of sensory, motor, & integrative signals are processed in certain regions. Sensory areas are concerned w/ interpretation of sensory impulses Motor areas govern muscular movements Association areas are concerned w/ complex integrative f’s such as memory, emotions, reasoning, will judgment, personality traits, & intelligence Brain LateralizationBrain Lateralization the two hemisphere are not bilaterally symmetrical, either anatomically or functionally Left Hemisphere - is more important for right-handed control, spoken & written language, & numerical & scientific skills. Right Hemisphere - left handed control, musical & artistic awareness, space and pattern perception, insight, imagination, & generating images of sight, sound, touch, taste, & smell CerebellumCerebellum inferior & posterior to cerebrum in cranial cavity Consists of 2 hemispheres & central constricted vermis attached to the brain stem by 3 pairs of cerebellar peduncles coordinate skeletal muscle contractions & in maintaining normal muscle tone, posture, &
  5. 5. balance **may also play a role in discrimination of the shape of an object Cranial NervesCranial Nerves 12 pairs named primarily on the basis of distribution and numbered by their order of attachment, Some are sensory nerves, some are motor, the rest are mixed FunctionsFunctions olfactory-special sensory- smell optic-special sensory- vision oculomotor- motor- eye movements trochlear- motor- eye movements trigeminal - mixed (s&m) to face abducens- motor- eye movements VII - facial - mixed (s&m) to face auditory or vestibulocochlear- special sensory- balance, equilibrium, and hearing glossopharyngeal - mixed (s&m) - head and neck vagus- mixed (s&m) - thorax & abdomen spinal accessory - motor- neck & upper back hypoglossal- motor- tongue movements VI. Homeostatic ImbalancesVI. Homeostatic Imbalances Cerebrovascular AccidentCerebrovascular Accident CVA - aka stroke - Ischemic (most common type) due to decreased blood supply or Hemorrhagic - due to b.v.’s in the brain that burst Transient Ischemic Attack - TIA - temporary - caused by impaired blood flow. Dizziness, weakness, numbness, or paralysis in a limb or in 1/2 the body. Drooping of 1 side of face headache, slurred speech, partial loss of vision or double vision. few minutes, rarely 24 hrs. common forerunner of CVA Alzheimer’s disease - (AD) - 11% of people over 65. Cause is genetic. Effects irreversible & devastating. Great loss of neurons in specific regions. Plaques of abnormal proteins deposited outside neurons. Tangled protein filament w/i neurons Brain tumor - benign or malignant cancerous growth w/i the cranium Cerebral Palsy - (CP) - muscular incoordination & loss of muscle control cause - damage to motor areas of the brain during fetal life, birth, or infancy Parkinson’s Disease (PD) - victims usually around 60. Toxic environmental factors suspected that effects neurotransmitters. unnecessary skeletal muscle contractions result Drug therapy to return neurotransmitters to homeostasis Multiple Sclerosis - (MS) progressive destruction of myelin sheaths of CNS Dyslexia - brains inability to translate images received from the eyes into understandable language
  6. 6. Headaches - cause: brain tumors, b.v. abnormalities, inflammation of brain or meninges, decrease in O2 supply to the brain, damage to brain cells, & infections of eyes, ears, nose, or sinuses Tension Headaches - assoc w/ stress, fatigue, & anxiety & usually occur in occipital & temporal muscles Migraine - sometimes respond to drugs that constrict b.v.’s
  7. 7. Headaches - cause: brain tumors, b.v. abnormalities, inflammation of brain or meninges, decrease in O2 supply to the brain, damage to brain cells, & infections of eyes, ears, nose, or sinuses Tension Headaches - assoc w/ stress, fatigue, & anxiety & usually occur in occipital & temporal muscles Migraine - sometimes respond to drugs that constrict b.v.’s