the brain structure & function. the brain most complex organ controls everything that we do, say...

THE BRAINStructure & Function

THE BRAIN• most complex organ• controls everything that we do, say &

feel• without it we would only react without

knowing or experiencing events• enables the mind• allows us to see, hear, remember,

think, feel, speak & dream

Embryonic Development• nervous system develops

from ectoderm• by week 3 neuroectoderm

developsthickens forming neural plate

• plate gives rise to all neurons & glial cells of nervous system

• plate sinks forming neural groove with raised neural folds along each side

• neural folds fuse forming a hollow tube- neural tube which contains a fluid filled cavity-neurocoel

Embryonic Development• by week 4 tube has

3 primary vesicles:

• Prosencephalon-forebrain

• Mesencephalon-midbrain

• Rhombencephalon-hindbrain

Embryonic Development• week 5-primary

vesicles become 5 secondary vesicles

• Prosencephalon telencephalon & diencephalon

• midbrain does not divide

• rhombencephalon metencephalon & myelencephalon

Ventricles• neurocoel expands forming

ventricles• each hemisphere has a lateral

ventricle• 3rd ventricle is in diencephalon• lateral ventricles communicate

with the 3rd via interventricular foramen or foramen of Munro

• mesencephalic aqueduct connects 3rd ventricle with 4th which extends into medulla oblongata

• 4th ventricle narrows becoming continuous with central canal of spinal cord

• ventricles are filled with cerebral spinal fluid (CSF)

Protection & Support• cranial bones

• cranial meninges

–dura mater

–Arachnoid

–pia mater

• cerebral Spinal Fluid

• blood-brain barrier

Meninges• outer most-dura mater

– has an outer-endosteal layer fused to periosteum of cranial bones & an inner fibrous layer or meningeal layer

• arachnoid meninge– in contact with inner

layer of dura mater

• pia mater-innermost– sticks to brain surface– extends into every fold

of brain

Dural Folds• dura mater extensions• hold brain in position• falx cerebri

– between cerebral hemispheres in longitudinal fissure

• tentorium cerebelli– separates cerebellar

hemispheres from cerebrum

• falx cerebelli– divides cerebellar

hemispheres

Cerebral Spinal Fluid• CSF surrounds & bathes all

exposed surfaces of CNS• cushions CNS from jolts &

shocks• supports brain which actually

floats in CSF• transports nutrients, chemical

messengers & waste products

• changes in CSF denote changes in function of CNS

• forms in choroid plexus of the ventricles

Blood Supply• to meet high

demands for oxygen & glucose- extensive circulatory supply

• arterial blood reaches brain through internal carotid & vertebal arteries

• venous flow leaves via internal jugular veins

Blood-Brain Barrier• isolates CNS from general circulation

– blood carries substances that might be harmful to brain • due to tight junctions between endothelial cells lining capillaries

of CNS• prevent diffusion of materials between adjacent cells• only lipid soluble compounds can diffuse across membranes into

brain & spinal cord• waste products & ions must pass through channels• restricted permeability depends on

– astrocytes– secrete chemicals– that control permeability

Brain Structure• internal parts rolled up to fit

into the skull• fit a large amount of

material into a small space• biological history of brain is

like an archeological dig• deeper you goolder

structures are found• older parts are more apt to

include basic mechanisms for survival

Brain Divisions• Brainstem

• Cerebellum

• Diencephalon

• Cerebrum

BRAIN STEMbegins where spinal

cord enters skull & swells

Medulla oblongata

Pons

Midbrain

MEDULLA• regulates autonomic functions• breathing, heartbeat, blood

pressure & digestion or vegetative processes

• cross over point where nerves come in & cross to opposite side-decussation

• groups of nuclei– cardiovascular center adjusts

heart rate & blood flow through peripheral tissues

– respiratory rhythmicity centers set basic pace for respiratory movements

– Sensory or motor nuclei of cranial nerves, VIII, IX, X, XI, XII provide motor commands to muscles of neck, pharynx & back

– Nucleus gracilis & nucleus cuneatus pass sensory information to thalamus

PONS• connects cerebellum to

brain stem• nuclei for somatic & visceral

motor control• cranial nerves V, VI, VII, VIII

– innervates jaw & face muscles, eye muscles and organs of vestibular sense

• contains nuclei for control of respiration– apneustic &

pneumotaxic centers• modify activity of

respiratory rhythmicity centers of medulla

Midbrain• connects hindbrain &

forebrain• contains cerebral

aqueduct• gives rise to cranial

nerves that control eye movements

Midbraincorpora quadrigemina– tectum or roof houses 2– superior & inferior

colliculi• Superior colliculi

– receive visual information– control reflexes related to

vision • Inferior colliculi

– receive auditory sensations

– control reflexes in relation to sound

Midbrain• red nucleus & substantia nigra are

found on each side of midbrain• red nucleus

– contains numerous blood vessels– receives information from

cerebrum & cerebellum– issues subconscious motor

commands affecting background muscle tone and limb position

• substantia nigra– inhibits activity of cerebral nuclei

by releasing dopamine• cerebral peduncles

– descending nerve fiber bundles– project to cerebellum via pons– carry voluntary motor commands

from the primary motor cortex

Reticular Formation• loosely organized area of

gray matter running vertically through all levels of brainstem

• Ascending part-Reticular Activating System (RAS)

• altertness & attention• sleep• consciousness• habituation

– process by which brain learns to ignore repetitive stimuli while remaining sensitive to others

• damaged-coma

Cerebellum• extends from rear of

brainstem• right & left cerebellar

hemispheres• connected by vermis• each hemisphere has

slender folds or pleating-folia

Cerebellar Lobes• Anterior lobe• Posterior lobe

– govern subconscious aspects of skeletal muscle movement

• Flocculonodular lobe– contributes to equilibrium &

balance

• Arbor viking or tree of life– white matter

Cerebellum• connects to brainstem by three cerebellar

peduncles• automatic processing center• responsible for adjusting ongoing

movements by comparing arriving sensations & sensations experienced previously

• adjusts postural muscles• coordinates rapid, automatic adjustments

that maintain balance and equilibrium• responsible for coordination of voluntary

movements• allows you to walk straight by monitoring

proprioceptive, visual, tactile, balance & auditory sensations

• responsible for programming & fine tuning movements controlled at conscious & subconscious levels

• refines learned movement patterns or learned motor responses

– driving a car, playing a musical instrument or any activity performed nearly unconsciously

A= cerebral peduncle

Diencephalon• links cerebrum with

brainstem

• integrates conscious & unconscious sensory information & motor commands

• three major parts

• Thalamus

• Hypothalamus

• Epithalamus

Thalamus• top of brainstem• relay station• receives information from all

senses, except smell• routes them to higher brain

regions• acts as a filter by passing on

only small amounts of arriving information

• coordinates activities of cerebral nuclei & cerebral cortex

• important in motor control by relaying signals from cerebellum to cerebrum

Thalamus• anterior nuclei

– part of limbic system– primitive brain area effecting motivation

& emotion• medial nuclei

– conscious awareness of emotional states

– connect emotional centers in hypothalamus with frontal lobes

• ventral nuclei– relay information from basal nuclei of

cerebrum & cerebellum to somatic motor areas of cerebral cortex

– relay information regarding touch, pressure, pain and temperature to sensory areas of cerebral cortex

• posterior nuclei– lateral geniculate nucleus

• receives visual information from optic tract

– medial geniculate nucleus• relays auditory information to

cerebral cortex

Hypothalamus• below thalamus• connected to pituitary

gland by infundibulum• maintenance functions

– regulates hunger, thirst, hormone production, body temperature & sexual behavior

– controls by triggering autonomic nervous system & by monitoring hormone levels in blood

Hypothalamic Nuclei• endocrine gland

– ADH or antidiuretic hormone• produced by supraoptic

nucleus• restricts water loss at kidneys

– Oxytoxin• made by paraventricular

nucleus• stimulates smooth muscle

contractions in uterus• produces emotions & behavior drives

such as hunger, thirst, and sexual desire

• coordinates voluntary & autonomic functions, preparing body for emergencies

• regulates body temperature via preoptic area

• controls circadian rhythms by suprachiasmatic nucleus

Epithalamus• Roof

• houses pineal gland– secretes melatonin– day/night cycles

• habenular nuclei– emotional response

to odors

Cerebrum• most visible & largest part

of brain-80% of brain’s weight

• right & left cerebral hemispheres

• extensive cerebral hemispheres make mammals different from other vertebrates

• releases species from genetic control & increases adaptability

Functions• conscious thoughts• higher functions• processes somatic sensory• processes motor information• ultimate control & information

processing center• responsible for conscious thought,

sensations, intellect, memory &complex movements

Cerebrum• surface is highly convoluted

– increases surface area• cortex forms elongated ridges-

gyri• separated by deep

depressions-sulci or deeper grooves-fissures

• covered by a neural or cerebral cortex– superficial layer of gray

matter composed of interconnected neural cells, pyramidal cells, stellate cells, 6 layers thick (1/8th inch)

• contains 30 billion nerve cells

Hemispheres• hemisperes are divided

by longitudinal fissure• connected by corpus

callosum

Hemisphere Lobes• each hemipshere divided

into 4 lobes made distinct by gyri

• named for bone each covers

• central sulcus separates frontal lobe from parietal lobe

• lateral sulcus separates frontal lobe from temporal lobe

• parieto-occipital sulcus separates parietal lobe from occipital lobe

Lobe Functions• Frontal lobes

– executive centers• Parietal lobes

– spatial relationships\– pre & post central gyri– movement &

sensations• Occipital lobes

– sight • Temporal lobes

– hearing

Cerebral White Matter• most of volume of cerebrum

• fibers form bundles or tracts

• Projection

• Commissural

• Association

Association Fibers• interconnect neural

cortex in one hemisphere

• shorter fibers-arcuate– curve in an arc from

one gyrus to another• longer fibers-fasciculi• longitudinal fasciculi

– connect frontal lobe to other lobes in same hemisphere

ARCUATE FIBER

Longitudinal Fasciculi

Commissural Fibers• Interconnect gyri

between cerebral hemispheres

• Corpus Callosum– thick white band– provides way for

cerebral hemispheres to communicate

• Anterior Commissure

Projection Fibers• link cerebral cortex to

lower parts of CNS

• entire collection of projective fibers is internal capsule

Gray Matter of Brain• cell bodies

• cerebral cortex

• basal nuclei

• limbic system

Basal Nuclei• masses of gray matter

embedded in white matter• globus pallidus• Putamen• Together form lentiform

nucleus• caudate nucleus– all three corpus striatum

Corpus Striatum• monitor activities occurring

at subconscious level• help initiate & terminate

movements & cognitive • subconscious control of

skeletal muscle tone– coordination of learned

movement patterns• once motion is

underway basal nuclei provide basic pattern & rhythm for movement

Basal ganglia

Limbic System•Amygdala•Hippocampus

Amygdala• Fear

• Applies emotional significance to people &things

AMYGDALA

Hippocampus• Memory

functions

• Making memories

• Retrieval of memories

Cerebral Cortex• covers hemispheres of

brain• 2-3mm thick• 6 layers• neocortex• two main neurons• Stellate cells

• receive & process information locally

• Pyramidal cells– output neuron– transmits signals to

other parts of CNS

Functions of Cerebral Cortex• higher brain functions• Sleep• Memory• Cognition• Emotion• Sensation• Motor control• Language

Functional Organization of Cerebral Cortex

• functions not responsibility of just one brain area• cortex is arranged according to function• Sensory areas

– receive sensory information– involved in perception

• conscious awareness of sensation

• Motor areas– control execution of voluntary movements.

• Association areas– deal with complex, integrative functions– memory, emotions, reasons, personality & intelligence

Location of Functions in Cerebral Hemispheres

• primary motor cortex• arch shaped region at

back of frontal lobes running from one ear to other across top of brain

• stimulate area specific muscles contract on opposite side of stimulation site

• controls voluntary movements

Primary Sensory Cortex• located behind motor

cortex at front of parietal lobes

• post central gyrus• stimulation produces

sensations of being touched on specific parts of body

• more sensitive body part more area of sensory cortex is allotted to it

Other Sensory Areas• Primary visual area

– occipital lobes • Primary auditory area

– temporal lobes • Primary olfactory area

– medial surface of temporal lobe & inferior surface of frontal lobe

• Primary gustatory area– temporal lobe– base of post central

gyrus

Primary Motor Cortex• mapped 1950s

• Forester & Penfield

• Precentral gyrus

• body parts that need precise control such as fingers & mouths had greater amount of cortical space

• seen on a homunculus

Broca’s Area• located in

frontal lobe• controls motor

cortexspeech produced

Association Areas• identification of

functions for the sensory & motor areas of brain leaves ¾ of cerebral cortex with nothing to do

• when these areas are stimulatedno observable responses

• areas not dormant• do not use 10% of our

brains• these areas represent

association areas

Association Areas• responsible for

integrating information

• associate sensory inputs with stored memories

• important in cognition or thinking

Association Areas• Somatosensory association area

– posterior to primary somatosensory area

– receives information from primary somatosensory area, thalamus & other parts of the brain

– lets us determine exact shape & texture of an object just by feeling it

– stores memory and lets us recognize objects by touching them

• Auditory association area– monitor sensory activity in auditory

cortex• Visual association area

– monitor patterns of activity in visual cortex & interpret results

• Wernicke’s area- posterior language area– left temporal & parietal lobes– interprets meaning of speech by

recognizing spoken words • Frontal lobe association area-premotor

cortex– personality, intellect & complex learning

Association Areas• facial recognition area (fusiform)

– inferior temporal lobe – receives information from visual

association area – allows us to store information about faces

&recognize individuals by their faces– primary isolated to right hemisphere

• orbitofrontal cortex– lateral part of frontal lobe– receives information from primary olfactory

area– allows us to identify odors

• frontal eye field area (between 4, 5 & 8) – frontal lobe– controls voluntary scanning movements

Association Area Comparison

Hemispheric Lateralization• right & left cerebral hemispheres are not paired • have different functions• Specialized• Left• Speech• Reasoning• Math and scientific skills

RIGHT HEMISPHERE• analyzes sensory

information• relates body to sensory

environment & identifies faces

• understands simple requests & perceives objects

• superior in drawing faces, perceiving differences, perceiving emotions & expressing emotion on left side of face

• important in understanding emotional context of conversations