Anatomy & Physiology IChapter 10

CerebrumCerebral hemispheres

DiencephalonThalamusHypothalamus

Brain stemMidbrainPonsMedulla oblongata

Cerebellum

Corpus callosum

ThalamusHypothalamus

Midbrain

Cerebellum

Pons

Medullaoblongata

Cerebral cortex – outer layer of gray matterGyri – elevated ridgesSulci – shallow groovesFissures – deep grooves

Five LobesFrontalParietalTemporalOccipital

Insula (within the hemisphere)

External surface of the brain, superior view.

The division into two hemispheres and into lobes is visible.

Surface markingsCentral sulcus

Separates the frontal lobe and the parietal lobeLongitudinal fissure

Separates the two hemispheresLateral sulcus

Separates the temporal lobe from the frontal and parietal

Transverse cerebral fissureSeparates the cerebrum and the cerebellum

Precentral gyrusImmediately anterior to the central sulcus

Postcentral gyrusImmediately posterior to the central sulcus

Postcentral gyrus

CentralsulcusPrecentral gyrus

Frontal lobe Parietal lobe

Lateral sulcus

Transverse cerebral fissure

Occipital lobe

Temporal lobe

Cerebellum

Cortex (gray matter)

FissureGyrus

Sulcus

White matter

Figure 12.6b

CentralsulcusFrontal lobe

Temporal lobe(pulled down)

Gyri of insula

Figure 12.6c

Parietallobe

Frontal lobe

Right cerebralhemisphere

Occipitallobe

Left cerebralhemisphere

Cerebral veinsand arteriescovered byarachnoidmater

Longitudinalfissure

Posterior

Anterior

three connective tissue membranes that envelop the brain and spinal cord

lies between the nervous tissue and boneprotect the brain and provide structural framework for its arteries and veins

Dura mater – outer layerDural sinuses - collect blood circulating through brain

Arachnoid mater – middle layerPia mater – innermost layer (adheres to brain)

Subdural space

Skull

Pia mater

Dura mater

Arachnoid mater

Cerebrum:

Gray matter

White matter

Subarachnoidspace

Terminology: What’s The Meaning?

• Epidural

• Subdural

• Subarachnoid

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inflammation of the meningesserious disease of infancy & childhood; especially between 3 months and 2 years of age

caused by bacterial and virus invasion of the CNS by way of the nose and throat

bacterial meningitis can cause swelling the brain, enlarging the ventricles, and hemorrhage

signs include high fever, stiff neck, drowsiness, and intense headache and may progress to coma – death within hours of onset

diagnosed by examining the CSF for bacterialumbar puncture (spinal tap) draws fluid from subarachnoid space between two lumbar vertebrae

Clear fluid found in and around the brain and spinal cordFormed by choroid plexus in ventriclesAbsorbed into bloodstream by arachnoid villi

CSF provides these functions:BuoyancyProtectionChemical stability

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buoyancyallows brain to attain considerable size without being impaired by its own weightif it rested heavily on floor of cranium, the pressure would kill the nervous tissue

protectionprotects the brain from striking the cranium when the head is joltedshaken child syndrome and concussions do occur from severe jolting

chemical stabilityflow of CSF rinses away metabolic wastes from nervous tissue

Path of CSF through ventricles:Lateral ventriclesInterventricular foramen3rd ventricleCerebral aqueduct4th ventricleCSF then continues through the central canal (spinal cord) and outside the brain and spinal cord

About 500ml of CSF is produced and drained from the CNS daily

What happens if production and drainage are not balanced?

Choroid plexus in fourthventricle adds more CSF.

CSF flows out two lateral aperturesand one median aperture.

CSF fills subarachnoid space andbathes external surfaces of brainand spinal cord.

At arachnoid villi, CSF is reabsorbedinto venous blood of duralvenous sinuses.

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CSF is secreted bychoroid plexus ineach lateral ventricle.

CSF flows throughInterventricular foraminainto third ventricle.

Choroid plexus in thirdventricle adds more CSF.

CSF flows down cerebralaqueduct to fourth ventricle.

Arachnoid villus

SuperiorsagittalsinusArachnoid mater

SubarachnoidspaceDura mater

Choroid plexus

Third ventricle

Cerebralaqueduct

Lateralaper ture

Fourth ventricle

Median aperture

Centralcanalof spinal cord

Subarachnoidspace ofspinal cord

Frontal lobeMotor areaSpeech centers

Parietal lobeSensory areaEstimation of distances, sizes, shapes

Temporal lobeAuditory areaOlfactory area

Occipital lobeVisual receiving areaVisual association area

ZOOMING IN • What cortical

area is posterior to the central sulcus? What area is anterior to the central sulcus?

Auditory areasAuditory receiving Auditory association Speech comprehension (Wernicke area)

Motor areasMotor speech (Broca area)Written speech center

Visual areasVisual language images receiving

Short-term memoryInformation retain for few seconds to minutes; lost unless reinforced

Long-term memoryTransfer of short term memory to long term memory requires rehearsal (repetition)Information stored for later recallRequires mental alertness

Procedural MemoryMotor (physical) memory of movementsTying shoes, typing, playing instruments, sports

ThalamusSorts sensory impulsesDirects impulses within cerebral cortex

HypothalamusMaintains homeostasisControls sympathetic and parasympathetic divisions of autonomic nervous systemInfluences heartbeat, blood flow, hormone secretion

Regions of the diencephalon. The figure shows the relationship among the thalamus, hypothalamus, and pituitary gland (hypophysis).

ZOOMING IN • To what part of the brain is the pituitary gland attached?

Networks of neurons that work together and span wide areas of the brain

Limbic system – Emotional BrainIncludes the amygdala, cingulate gyrus and hippocampus

Reticular formation – Consciousness Mass of gray matter extending through the entire brainstem

Corpus callosum

Olfactory bulb

•Hypothalamus

•Cingulate gyrus

•Amygdala

•Hippocampus

Thalamic Nuclei

Includes centers for both gratification and aversiongratification – sensations of pleasure or rewardaversion – sensations of fear or sorrow

Emotional or affective brainAmygdala—recognizes angry or fearful facial expressions, assesses danger, and elicits the fear responseCingulate gyrus—plays a role in expressing emotions via gestures, and resolves mental conflictHippocampus – plays a significant role in learning and memory formation

Puts emotional responses to odorsExample: skunks smell bad

Hippocampus and amygdala—play a role in memory

plays central role in states of consciousness, such as alertness and sleep

Consciousness is a state of wakefulnessVery sensitive to the effects of certain drugs and alcohol

Combination of tranquilizers and alcohol can damage the reticular formation, causing permanent unconsciousness

Consciousness depends on the reticular activating system (RAS)

Visualimpulses

Reticular formation

Ascending generalsensory tracts(touch, pain, temperature)

Descendingmotor projectionsto spinal cord

Auditoryimpulses

Radiationsto cerebralcortex

Reticular FormationReticular Formation

RAS (reticular activating system) Sends impulses to the cerebral cortex to keep it conscious and alertFilters out repetitive and weak stimuli (~99% of all stimuli!)Severe injury results in permanent unconsciousness (coma)

Nuclei that control cranial nerves III and IVSuperior part of brain stemReflexes involving eyes and earssubstantia nigra

dark gray to black nucleus pigmented with melaninmotor center that relays inhibitory signals to thalamus & basal nuclei preventing unwanted body movementdegeneration of neurons leads to tremors of Parkinson disease

Forms part of the anterior wall of the fourth ventricleFibers of the pons

Connect higher brain centers and the spinal cordRelay impulses between the motor cortex and the cerebellum

Origin of cranial nerves V, VI, VII and VIIINuclei that help maintain normal rhythm of breathingreticular formation in pons contains additional nuclei concerned with:

sleep, respiration, and posture

cardiac center adjusts rate and force of heart

vasomotor center adjusts blood vessel diameter

respiratory centers control rate and depth of breathing

reflex centers for coughing, sneezing, gagging, swallowing, vomiting, salivation, sweating

Location of cranial nerves - IX, X, XI, XII

Three partsVermisLeft hemisphereRight hemisphere

FunctionsHelp coordinate voluntary musclesHelp maintain balanceHelp maintain muscle tone

(A) Posterior view showing the two hemispheres.

(B) Midsagittal section showing the distribution of gray and white matter.

The three parts of the brain stem (midbrain, pons, and medulla oblongata) are also labeled.

Cerebellum receives impulses from the cerebral cortex of the intent to initiate voluntary muscle contraction

Signals from proprioceptors and visual and equilibrium pathways continuously “inform” the cerebellum of the body’s position and momentum

Cerebellar cortex calculates the best way to smoothly coordinate a muscle contraction

A “blueprint” of coordinated movement is sent to the cerebral motor cortex and to brain stem nuclei

Record electric currents given off by brain nerve cellsStudy sleep patternsDiagnose diseaseLocate tumorsStudy drug effectsDetermine brain death

Scalp electrodes are used to record brain waveactivity (EEG).

Alpha waves (8–13 Hz)—regular and rhythmic, low-amplitude, synchronous waves indicating an “idling” brain

Beta waves (14–30 Hz)—rhythmic, less regular waves occurring when mentally alert

Theta waves (4–7 Hz)—more irregular; common in children and uncommon in adults

Delta waves (4 Hz or less)—high-amplitude waves seen in deep sleep and when reticular activating system is damped, or during anesthesia; may indicate brain damage

Figure 12.20b

Alpha waves—awake but relaxed

Beta waves—awake, alert

Theta waves—common in children

Delta waves—deep sleep

(b) Brain waves shown in EEGs fall intofour general classes.

1-second interval

Change with age, sensory stimuli, brain disease, and the chemical state of the body

EEGs used to diagnose and localize brain lesions, tumors, infarcts, infections, abscesses, and epileptic lesions

A flat EEG (no electrical activity) is clinical evidence of death

Hydrocephalus Abnormal CSF accumulation within brainCauses

Congenital malformationTumorInflammationHemorrhage

Encephalitis Inflammation of the brainViral causesToxic substances causesViral vaccine causes

Stroke (Cerebrovascular Accident; CVA)Most common brain disordersudden death of brain tissue caused by ischemia

atherosclerosis, thrombosis, ruptured aneurysm effects range from unnoticeable to fatal

blindness, paralysis, loss of sensation, loss of speech common

recovery depends on surrounding neurons, collateral circulation

Tumors Gliomas – tumor arising from glial cellsNeuroma – tumor arising from nervesMeningioma – tumors arising from meninges

Cerebral palsy (CP)Group of neuromuscular disorders that result from injury to an infant before, during or shortly after delivery.All forms cause impairment of skeletal muscle activityMental retardation and speech difficulty may accompany CP

EpilepsyDisorder in which neurons of the brain fire suddenly and unpredictablyMay be caused by brain tumors, toxins, trauma, or fever.Grand mal seizure - motor areas fire repeatedly causing convulsive seizures and loss of consciousnessPetit mal seizure - sensory areas affected; not accompanied by convulsions or prolonged unconsciousness

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brain is only 2% of the adult body weight, and receives 15% of the blood

750 mL/min

neurons have a high demand for ATP, and therefore, oxygen and glucose, so a constant supply of blood is critical to the nervous system

10 second interruption of blood flow may cause loss of consciousness

1 – 2 minute interruption can cause significant impairment of neural function

4 minutes with out blood causes irreversible brain damage

InjuryInjury

Head trauma can lead to injury within skullEpidural hematomaSubdural hematomaIntracerebral hematomaCerebral concussion

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the brain must communicate with the rest of the body

most of the input and output travels by way of the spinal cord

12 pairs of cranial nerves arise from the base of the brain

exit the cranium through foramina

lead to muscles and sense organs located mainly in the head and neck

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some cranial nerves are classified as motor, some sensory, others mixed

sensory (I, II, and VIII)

motor (III, IV, VI, XI, and XII) stimulate muscle but also contain fibers of proprioception

mixed (V, VII, IX, X)sensory functions may be quite unrelated to their motor function

facial nerve (VII) has sensory role in taste and motor role in facial expression

Cranial NervesCranial Nerves12 pairsRemember: all nerves (cranial and spinal) carry signals toward or away from the CNSFour categories

Special sensory impulsesGeneral sensory impulsesSomatic motor impulsesVisceral motor impulses

Cranial nerves.

The 12 pairs of cranial nerves are seen from the base of the brain.

The Cranial Nerves (functions)The Cranial Nerves (functions)I. Olfactory – sense of smell

II. Optic – vision

III. Oculomotor – eye movement (innervates most eye muscles)

IV. Trochlear – eye movement (innervates one eye muscle; so)

V. Trigeminal – facial sensation

VI. Abducens – eye movement (innervates one eye muscle; lr)

The Cranial Nerves (functions)The Cranial Nerves (functions)VII. Facial – facial movement (expressions), taste

sensation, saliva and tear secretionVIII. Vestibulocochlear – sense of hearing and

equilibrium

IX. Glossopharyngeal – tongue and throat movement (swallowing), saliva secretion

X. Vagus – regulation of viscera; muscles of larynx & pharynx

XI. Accessory – Swallowing, head, neck and shoulder movement

XII. Hypoglossal – tongue movement

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Trigeminal neuralgia (tic douloureux)recurring episodes of intense stabbing pain in trigeminal nerve area (near mouth or nose)pain triggered by touch, drinking, washing facetreatment may require cutting nerve

Bell palsydegenerative disorder of facial nerve causes paralysis of facial muscles on one sidemay appear abruptly with full recovery within 3 - 5 weeks

Decreased brain size and weightDecreased speed of information processing Slowed movementsDiminished memoryReduced blood flow to brain