The Brain and Cranial NervesLargest organ in the body at almost 3 lb.Brain functions in sensations, memory, emotions, decision making, behavior

The Cerebrum

Figure 1412a The Brain in Lateral View.

Principal Parts of the BrainCerebrumDiencephalonthalamus & hypothalamusCerebellumBrainstemmedulla, pons & midbrain

Protective Coverings of the BrainBone, meninges & fluidMeninges same as around the spinal corddura materarachnoid materpia mater

Brain Protection and Support

Figure 2123 Arteries of the Brain.

Blood Supply to BrainArterial blood supply is branches from circle of Willis on base of brainVessels on surface of brain----penetrate tissueUses 20% of our bodies oxygen & glucose needsblood flow to an area increases with activity in that areadeprivation of O2 for 4 min does permanent injuryat that time, lysosome release enzymesBlood-brain barrier (BBB)protects cells from some toxins and pathogensproteins & antibiotics can not pass but alcohol & anesthetics dotight junctions seal together epithelial cells, continuous basement membrane, astrocyte processes covering capillaries

Cerebrospinal Fluid (CSF)80-150 ml (3-5oz)Clear liquid containing glucose, proteins, & ionsFunctionsmechanical protection floats brain & softens impact with bony wallschemical protectionoptimal ionic concentrations for action potentialscirculationnutrients and waste products to and from bloodstream

Origin of CSFChoroid plexus = capillaries covered by ependymal cells2 lateral ventricles, one within each cerebral hemisphereroof of 3rd ventriclefourth ventricle

Drainage of CSF from VentriclesOne median aperture & two lateral apertures allow CSF to exit from the interior of the brain

Flow of Cerebrospinal Fluid

Reabsorption of CSFReabsorbed through arachnoid villigrapelike clusters of arachnoid penetrate dural venous sinus20 ml/hour reabsorption rate = same as production rate

HydrocephalusBlockage of drainage of CSF (tumor, inflammation, developmental malformation, meningitis, hemorrhage or injuryContinued production cause an increase in pressure --- hydrocephalusIn newborn or fetus, the fontanels allow this internal pressure to cause expansion of the skull and damage to the brain tissueNeurosurgeon implants a drain shunting the CSF to the veins of the neck or the abdomen

Medulla OblongataContinuation of spinal cordAscending sensory tractsDescending motor tractsNuclei of 5 cranial nervesCardiovascular centerforce & rate of heart beatdiameter of blood vesselsRespiratory centermedullary rhythmicity area sets basic rhythm of breathingInformation in & out of cerebellumReflex centers for coughing, sneezing, swallowing etc

Ventral Surface of Medulla OblongataVentral surface bulge pyramidslarge motor tractdecussation of most fibersleft cortex controls right musclesOlive = olivary nucleusneurons send input to cerebellumproprioceptive signalsgives precision to movements

Dorsal Surface of Medulla OblongataNucleus gracilis & nucleus cuneatus = sensory neuronsrelay information to thalamus on opposite side of brain5 cranial nerves arise from medulla -- 8 thru 12

XII = Hypoglossal NerveControls muscles of tongue during speech and swallowingInjury deviates tongue to injured side when protrudedMixed, primarily motor

XI = Spinal Accessory NerveCranial portionarises medullaskeletal mm of throat & soft palateSpinal portionarises cervical spinal cordsternocleidomastoid and trapezius mm.

X = Vagus NerveReceives sensations from viscera Controls cardiac muscle and smooth muscle of the visceraControls secretion of digestive fluids90% Parasympathetics

Cranial Nerves

Figure 1426 The Vagus Nerve.

IX = Glossopharyngeal NerveStylopharyngeus m. (lifts throat during swallowing)Secretions of parotid glandSomatic sensations & taste on posterior 1/3 of tongue

VIII = Vestibulocochlear NerveCochlear branch begins in medullareceptors in cochleahearingif damaged deafness or tinnitus (ringing) is producedVestibular branch begins in ponsreceptors in vestibular apparatussense of balancevertigo (feeling of rotation)ataxia (lack of coordination)

Cranial Nerves

Figure 1424 The Vestibulocochlear Nerve.

PonsOne inch longWhite fiber tracts ascend and descendPneumotaxic & apneustic areas help control breathingMiddle cerebellar peduncles carry sensory info to the cerebellumCranial nerves 5 thru 7

VII = Facial NerveMotor portionfacial musclessalivary & nasal and oral mucous glands & tearsSensory portiontaste buds on anterior 2/3s of tongue

VI = Abducens NerveLateral rectus eye muscle

V = Trigeminal NerveMotor portionmuscles of masticationSensory portiontouch, pain, & temperature receptors of the faceophthalmic branchmaxillary branchmandibular branch

Cranial Nerves

Figure 1422 The Trigeminal Nerve.

MidbrainOne inch in lengthExtends from pons to diencephalonCerebral aqueduct connects 3rd ventricle above to 4th ventricle below

Midbrain in SectionCerebral peduncles---clusters of motor & sensory fibersSubstantia nigra---helps controls subconscious muscle activityRed nucleus-- rich blood supply & iron-containing pigmentcortex & cerebellum coordinate muscular movements by sending information here from the cortex and cerebellum

Dorsal Surface of MidbrainCorpora quadrigemina = superior & inferior colliculicoordinate eye movements with visual stimulicoordinate head movements with auditory stimuli

IV = Trochlear NerveSuperior oblique eye muscle

III = Oculomotor NerveLevator palpebrae raises eyelid (ptosis)4 extrinsic eye muscles2 intrinsic eye musclesaccomodation for near vision (changing shape of lens during reading)constriction of pupil

Cranial Nerves

Figure 1421 Cranial Nerves Controlling the Extra-Ocular Muscles.

Lecture 2 Reticular Formation

Scattered nuclei in medulla, pons & midbrainReticular activating systemalerts cerebral cortex to sensory signals (sound of alarm, flash light, smoke or intruder) to awaken from sleepmaintains consciousness & helps keep you awake with stimuli from ears, eyes, skin and musclesMotor function is involvement with maintaining muscle tone

Cerebellum2 cerebellar hemispheres and vermis (central area)Functioncorrect voluntary muscle contraction and posture based on sensory data from body about actual movementssense of equilibrium

CerebellumTransverse fissure between cerebellum & cerebrumCerebellar cortex (folia) & central nuclei are grey matterArbor vitae = tree of life = white matter

Thalamus1 inch long mass of gray mater in each half of brain (connected across the 3rd ventricle by intermediate mass)Relay station for sensory information on way to cortexCrude perception of some sensations

Hypothalamus

Major regulator of homeostasisreceives somatic and visceral input, taste, smell & hearing information; monitors osmotic pressure, temperature of blood

Functions of HypothalamusControls and integrates activities of the ANS which regulates smooth, cardiac muscle and glandsSynthesizes regulatory hormones that control the anterior pituitaryContains cell bodies of axons that end in posterior pituitary where they secrete hormonesRegulates rage, aggression, pain, pleasure & arousalFeeding, thirst & satiety centersControls body temperatureRegulates daily patterns of sleep

EpithalamusPineal glandendocrine gland the size of small peasecretes melatonin during darknesspromotes sleepiness & sets biological clockHabenular nucleiemotional responses to odors

Cerebrum (Cerebral Hemispheres)Cerebral cortex is gray matter overlying white matter2-4 mm thick containing billions of cellsgrew so quickly formed folds (gyri) and grooves (sulci or fissures)Longitudinal fissure separates left & right cerebral hemispheresCorpus callosum is band of white matter connecting left and right cerebral hemispheresEach hemisphere is subdivided into 4 lobes

Lobes and FissuresLongitudinal fissure (green)Frontal lobeCentral sulcus (yellow)precentral & postcentral gyrusParietal lobeParieto-occipital sulcusOccipital lobeLateral sulcus (blue)Temporal lobeInsula

The Cerebrum

Figure 1412b The Brain in Lateral View.

The Cerebrum

Figure 1413b Fibers of the White Matter of the Cerebrum.

Basal GangliaConnections to red nucleus, substantia nigra & subthalamusInput & output with cerebral cortex, thalamus & hypothalamusControl large automatic movements of skeletal muscles

Limbic SystemParahippocampal & cingulate gyri & hippocampusEmotional brain--intense pleasure & intense painStrong emotions increase efficiency of memory

Brain InjuriesCauses of damagedisplacement or distortion of tissue at impactincreased intracranial pressureinfectionsfree radical damage after ischemiaConcussion---temporary loss of consciousnessheadache, drowsiness, confusion, lack of concentrationContusion--bruising of brain (less than 5 min unconsciousness but blood in CSF)Laceration--tearing of brain (fracture or bullet)increased intracranial pressure from hematoma

Sensory Areas of Cerebral CortexReceive sensory information from the thalamusPrimary somatosensory area = postcentral gyrus = 1,2,3Primary visual area = 17Primary auditory area = 41 & 42Primary gustatory area = 43

The Cerebrum

Figure 1415a Motor and Sensory Regions of the Cerebral Cortex.

Motor Areas of Cerebral CortexVoluntary motor initiationPrimary motor area = 4 = precentral gyruscontrols voluntary contractions of skeletal muscles on other sideMotor speech area = 44 = Brocas areaproduction of speech -- control of tongue & airway

Association Areas of Cerebral CortexSomatosensory area = 5 & 7 (integrate & interpret)Visual association area = 18 & 19 (recognize & evaluate)Auditory association area(Wernickes) = 22(words become speech)Gnostic area = 5,7,39 & 40 (integrate all senses & respond)Premotor area = 6 (learned skilled movements such as typing)Frontal eye field =8 (scanning eye movements such as phone book)

AphasiaLanguage areas are located in the left cerebral hemisphere of most peopleInability to use or comprehend words = aphasianonfluent aphasia = inability to properly form wordsknow what want to say but can not speak damage to Brocas speech areafluent aphasia = faulty understanding of spoken or written wordsfaulty understanding of spoken or written wordsword deafness = an inability to understand spoken wordsword blindness = an inability to understand written wordsdamage to common integrative area or auditory association area

Hemispheric LateralizationFunctional specialization of each hemisphere more pronounced in menFemales have larger connections between 2 sidesDamage to left side produces aphasiaDamage to same area on right side produces speech with little emotional inflection

The CerebrumThe Left HemisphereIn most people, left brain (dominant hemisphere) controlsReading, writing, and mathDecision makingSpeech and language The Right HemisphereRight cerebral hemisphere relates toSenses (touch, smell, sight, taste, feel)Recognition (faces, voice inflections)

The Cerebrum

Figure 1416 Hemispheric Lateralization.

Electroencephalogram (EEG)

Figure 1417a-d Brain Waves.

Electroencephalogram (EEG)Brain waves are millions of nerve action potentials in cerebral cortexdiagnosis of brain disorders (epilepsy)brain death (absence of activity in 2 EEGs 24 hours apart)Alpha -- awake & restingBeta -- mental activityTheta -- emotional stressDelta -- deep sleep

II -- Optic NerveConnects to retina supplying vision

Cranial Nerves

Figure 1420 The Optic Nerve.

I -- Olfactory NerveExtends from olfactory mucosa of nasal cavity to olfactory bulbSense of smell

Cranial Nerves

Figure 1419 The Olfactory Nerve.

Cranial Reflexes

Developmental Anatomy of the NSBegins in 3rd weekectoderm forms thickening (neural plate)plate folds inward to form neural grooveedges of folds join to form neural tubeNeural crest tissue forms: spinal & cranial nervesdorsal root & cranial nerve gangliaadrenal gland medullaLayers of neural tube form:marginal layer which forms white mattermantle layer forms gray matterependymal layer forms linings of cavities within NS

Cerebrovascular Accident (CVA)Third leading cause of death after heart attacks and cancer2 types of strokesischemic due to decreased blood flowhemorrhagic due to rupture of blood vesselRisk factorshigh blood pressure, high cholesterol, heart disease, diabetes, smoking, obesity, alcoholTissue plasminogen activator (t-PA) used within 3 hours of onset will decrease permanent disability

Transient Ischemic Attack (TIA)Episode of temporary cerebral dysfunctionCauseimpaired blood flow to the brainSymptomsdizziness, slurred speech, numbness, paralysis on one side, double visionreach maximum intensity almost immediatelypersists for 5-10 minutes & leaves no deficitsTreatment is aspirin or anticoagulants; artery bypass grafting or carotid endarterectomy

Alzheimer Disease (AD)Dementia = loss of reasoning, ability to read, write, talk, eat & walkAfflicts 11% of population over 65Loss of neurons that release acetylcholinePlaques of abnormal proteins outside neuronsTangled protein filaments within neuronsRisk factors -- head injury, heredityBeneficial effects of estrogen, vitamin E, ibuprofen & ginko biloba