Central Nervous SystemCh. 13

Introduction• CNS consists of brain & spinal cord• The brainstem connects the brain to spinal

cord• Communication to PNS is by way of spinal

cord

Meninges• Membranes of CNS• Protect CNS• Made up of 3 layers:

– Dura Mater: “tough mother”• Venous sinuses• Falx

– Arachnoid Mater: “spider-web like”

• Space contains cerebrospinal fluid (CSF)

– Pia Mater: “faithful mother”

• Encapsulates blood vessels

Gray matter White matter

Ventricles & Cerebrospinal Fluid

• 4 ventricles• Interconnected

cavities w/in cerebral hemispheres & brain stem

• Continuous with central canal of spinal cord

• Filled with CSF

Ventricles & CSF• Ventricles:

– Lateral ventricles(2)• Known as 1st & 2nd

ventricles

– 3rd ventricle– 4th ventricle

• Interventricular foramen• Cerebral aqueduct

Cerebrospinal Fluid• Secreted by the choroid plexus• Circulates in ventricles, central canal of spinal

cord, & subarachnoid space• Completely surrounds the brain & spinal cord

• Excess or wasted CSF is absorbed by arachnoid villi

• Clear fluid similar to blood plasma• Vol = about 120 mL• Nutritive & protective• Helps maintain stable ion

concentrations in CNS

Cerebrospinal Fluid

CSF Pressure

• CSF Pressure remains relatively constant• Infection, tumor or blood clot can incr

pressure in ventricles by interfering with fluid’s circulation

• Can cause collapsed blood vessels, injured brain tissue

CSF Pressure• Lumbar puncture (spinal tap) – bt 3rd & 4th

lumbar vertebrae; measures pressure; removes fluid to look for blood cells

CSF Pressure• Temporary drain can relieve pressure• Fetus/infant – can lead to

hydrocephalus– Shunt redirects fluid to digestive tract

Healthy CSF – Lauren Shaw <3Unhealthy CSF

Brain

• Functions of Brain– Interprets sensations– Determines perceptions– Stores memory– Reasoning– Makes decisions– Coordinates muscular movements– Regulates visceral activities– Determines personality

Major Parts of the Brain• Cerebrum

– Frontal lobes– Parietal lobes– Occipital lobes– Temporal lobes– Insula

Major Parts of the Brain

• Diencephalon• Cerebellum• Brainstem

– Midbrain– Pons– Medulla oblongata

The Brain

Structure of the Cerebrum• Corpus callosum

– Connects cerebral hemispheres (a commissure)

• Gyri– Bumps or

convolutions

• Sulci– Grooves in gray matter– Central Sulcus of Rolando

Structure of Cerebrum• Fissures

– Longitudinal: separates the cerebral hemispheres

– Transverse: separates cerebrum from cerebellum

– Lateral fissure of Sylvius

Lobes of Cerebrum• 4 lobes bilaterally:

– Frontal lobe– Parietal lobe

– Temporal lobe– Occipital lobe– and Insula aka “Island of

Reil”

Functions of Cerebrum

• Interpreting impulses• Initiating voluntary movements• Storing info as memory• Retrieving stored info• Reasoning• Seat of intelligence and personality

Functional Regions of Cerebral Cortex• Cerebral Cortex• Thin layer of gray matter that constitutes

the outermost portion of cerebrum

• Contains 75% of all neurons in nervous system

Functional Regions of Cerebral Cortex

Functions of Cerebral Lobes

Sensory Areas (post-central sulcus)• Cutaneous sensory area• Parietal lobe• Interprets sensations on skin

Sensory Areas (post-central sulcus)• Visual area• Occipital lobe• Interprets vision

• Auditory area• Temporal lobe• Interprets hearing

Sensory Areas (post-central sulcus)• Sensory area for smell• Arises from centers deep

within cerebrum

• Sensory area for speech

• Wernicke’s area

• Gnostic area – stg for complex memory patterns assoc w/sensation; dmg causes imbecilic behavior due to inability to interpret any sensation

• Gustatory cortex – sense of taste

Sensory Areas (post-central sulcus)

• Affective language area – opp of Broca’s, nonverbal emotional components of language; expression of emotions associated with speech (“lilt” of one’s voice)

Sensory Areas (post-central sulcus)

– Association fibers – connect lobes– Projection fibers – connect cortex with lower

brain or cord centers

Sensory Areas

Association Areas• Regions that are not primary motor or primary

sensory areas• Widespread throughout cerebral cortex

• Analyze/interpret sensory experiences• Provide memory, reasoning,

verbalization, judgment, emotions

Association Areas

Association Areas• Frontal lobe assoc areas• Concentrating• Planning• Complex problem solving

• Parietal lobe assoc areas• Understanding speech• Choosing words to express thought

Association Areas

• Temporal lobe assoc areas• Interpret complex sensory experiences• Store memories of visual scenes,

music, & complex patterns

Association Areas

• Occipital lobe assoc areas• Analyze & combine visual images

w/other sensory experiences

Association Areas

Motor Areas (pre-central sulcus)• Primary motor areas• Frontal lobes• Control voluntary muscles

• Broca’s Area• Anterior to primary motor cortex• Usually in left hemisphere• Controls muscles needed for speech

Motor Areas (pre-central sulcus)

• Frontal eye field• Above Broca’s area• Controls voluntary movements of eyes

& eyelids

Motor Areas (pre-central sulcus)

Motor Areas

Hemisphere Dominance• Left hemisphere is dominant in most

individuals – 91%• Related to right-handedness

Dominant hemisphere controls:• Speech• Writing• Reading• Verbal skills• Analytical skills• Computational skills

Hemisphere Dominance

• Non-dominant hemisphere controls:• Non-verbal tasks; • Holistic interpretation• Motor tasks • Spatial relations• Understanding/interpreting musical,

artistic, visual patterns• Imagination & insight • Provides emotional & intuitive thought

processes

Hemisphere Dominance

• Lateralization develops with age–females have more communication

between hemispheres (corpus callosum thicker posteriorly)

Lateralization of Cerebral Functions

Brain lesions• parietal lobe

– contralateral neglect syndrome• temporal lobe

– agnosia - inability to recognize objects– prosopagnosia - inability to recognize

faces

• frontal lobe – problems with personality (inability to

plan and execute appropriate behavior)

Lobotomy of Phineas Gage

• Ventromedial region of both frontal lobes

• Personality change – irreverent, profane

• Prefrontal cortex functions – planning, moral

judgment, and emotional control

Alzheimer Disease

• 100,000 deaths/year–11% of population over 65;

47% by age 85• Memory loss for recent events,

moody, combative, lose ability to talk, walk, and eat

• Diagnosis confirmed at autopsy–atrophy of gyri (folds) in cerebral

cortex–neurofibrillary tangles and senile

plaques• Degeneration of cholinergic neurons

and deficiency of ACh and nerve growth factors

• Genetic connection confirmed

Alzheimer Disease Effects

Memory

• Short-term memory• Working memory• Closed neuronal circuit• Circuit is stimulated over & over• When impulse flow ceases, memory does

also unless it enters long-term memory via memory consolidation

Memory• Long-term memory• Changes structure or function of neurons• Enhances synaptic transmission

Traumatic Brain Injury• Occurs by mechanical force (fall, accident,

attack, sports-related, combat)• “Blast-related brain injury” (combat) – chg

in atmospheric pressure, violent rls of energy, exposure to neurotoxin from blast (rocket-propelled grenades, incendiary dvcs, landmines) – brain is jolted fwd at >1,600 ft/sec, then 2nd wave as air in brain rushes fwd – may take a while for symptoms to appear

Basal Nuclei• Masses of gray matter• Deep within cerebral hemispheres• Caudate nucleus, putamen, & globus pallidus• Produce dopamine• Control certain muscular activities

– Primarily by inhibiting motor function

Diencephalon• Between cerebral hemispheres and above

brainstem• Surrounds 3rd ventricle

Diencephalon

• Thalamus• Epithalamus• Hypothalamus• Optic tracts• Optic chiasma

• Infundibulum• Posterior pituitary• Mammillary bodies• Pineal gland

Diencephalon• Thalamus• Gateway for sensory impulses

heading to cerebral cortex• Rcvs all sensory impulses (except

smell)• Channels impulses to appropriate part

of cerebral cortex for interpretation

• Hypothalamus• Maintains homeostasis by regulating

visceral activities• Links nervous & endocrine systems

= “neuroendocrine system”

Diencephalon

• The Limbic System• Consists of:

– Portions of frontal lobe– Portions of temporal lobe– Hypothalamus– Thalamus– Basal nuclei– Other deep nuclei

Diencephalon

• The Limbic System• Functions:

– Controls emotions– Produces feelings– Interprets sensory impulses

Diencephalon

Parkinson Disease• Causes: “designer drugs”, pesticides,

frequent blows to head, genetic factor (though usually not inherited)

• Symptoms: – Leaning while walking– Twitching– Poor small motor control– Hypomimia – mask-like expression– Hypophia – difficulty speaking– Micrographia – small writing

Parkinson Disease

• Neurons in brainstem (substantia nigra) degenerate & less dopamine reaches synapses = motor symptoms

• Non-motor symptoms – depression, dementia, constipation, incontinence, sleep problems, orthostatic hypotension (dizzy when standing)

Muhammed Ali & Michael J. Fox

Parkinson Disease• Treatments:

– levodopa – converts to dopamine• Becomes less effective over years

– Surgery – electrodes– Retinal pigment epithelium – stimulated to

produce dopamine/levodopa– Stem cells

Brainstem

• 3 parts:• Midbrain• Pons• Medulla

Oblongata

Midbrain• Between diencephalon & pons• Contains bundles of fibers that join lower

pts of brainstem & spinal cord w/higher pt of brain

• Cerebral aqueduct• Cerebral peduncles (bundles of nerve

fibers)• Corpora quadrigemina (centers for

auditory & visual reflexes)

Midbrain

Pons• Rounded bulge on underside of brainstem• Between medulla oblongata & midbrain• Helps regulate rate & depth of breathing• Relays nerve impulses to & from medulla

oblongata & cerebellum

Medulla Oblongata• Enlarged continuation of spinal cord• Conducts ascending & descending

impulses bt brain & spinal cord

Medulla Oblongata• Contains cardiac, vasomotor, & respiratory

control centers• Contains various nonvital reflex control

centers (coughing, sneezing, swallowing, vomiting)

Reticular Formation• Complex

network of nerve fibers scattered throughout the brainstem

• Extends into diencephalon

• Connects to centers of hypothalamus, basal nuclei, cerebellum, & cerebrum

Reticular Formation

• Filters incoming sensory info

• Arouses cerebral cortex into state of wakefulness

Types of Sleep• Slow Wave• Non-REM sleep• Person is tired• Decr activity of reticular

system• Restful• Dreamless

• Reduced blood pressure & respiratory rate

• Ranges from light to heavy

• Alternates with REM sleep

• Rapid Eye Movement (REM)• Paradoxical sleep• Some areas of brain active• Heart & respiratory rate irregular• Dreaming occurs

Types of Sleep

Cerebellum• Inferior to occipital lobes• Posterior to pons & medulla oblongata• 2 hemispheres

Cerebellum• Vermis connects hemispheres• Cerebellar cortex (gray matter)• Arbor vitae (white matter)

Cerebellum

• Cerebellar peduncles (nerve fiber tracts)• Dentate nucleus (largest nucleus in

cerebellum)

Cerebellum• Integrates sensory info concerning

position of body pts• Coordinates skeletal muscle activity• Maintains posture

Major Parts of Brain

Brain Waves• Recordings of fluctuating

electrical chgs in brain• Electrodes placed on sfc of

surgically exposed brain or outer sfc of head (EEG)

• Detect electrical chgs in extracellular fluid of brain in response to chgs in potential among lg grps of neurons

• Used to diagnose seizures, locating brain tumors, detect “brain death”

Brain Waves• Alpha – recorded from posterior

regions of head; frequency = 8-13 cycles/sec; awake but resting w/eyes closed

• Beta - >13 cycles/sec; anterior portion of head; actively engaged in mental activity/tension

Brain Waves• Theta – 4-7 cycles/sec; parietal &

temporal regions; normal in children (not usual in adults); some adults – early stages of sleep/times of emotional stress

• Delta - <4 cycles/sec; during sleep; cerebral cortex