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THE BRAINStructure & Function
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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
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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
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Embryonic Development• by week 4 tube has
3 primary vesicles:
• Prosencephalon-forebrain
• Mesencephalon-midbrain
• Rhombencephalon-hindbrain
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Embryonic Development• week 5-primary
vesicles become 5 secondary vesicles
• Prosencephalon telencephalon & diencephalon
• midbrain does not divide
• rhombencephalon metencephalon & myelencephalon
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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)
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Protection & Support• cranial bones
• cranial meninges
–dura mater
–Arachnoid
–pia mater
• cerebral Spinal Fluid
• blood-brain barrier
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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
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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
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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
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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
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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
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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
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Brain Divisions• Brainstem
• Cerebellum
• Diencephalon
• Cerebrum
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BRAIN STEMbegins where spinal
cord enters skull & swells
Medulla oblongata
Pons
Midbrain
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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
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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
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Midbrain• connects hindbrain &
forebrain• contains cerebral
aqueduct• gives rise to cranial
nerves that control eye movements
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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
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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
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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
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Cerebellum• extends from rear of
brainstem• right & left cerebellar
hemispheres• connected by vermis• each hemisphere has
slender folds or pleating-folia
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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
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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
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Diencephalon• links cerebrum with
brainstem
• integrates conscious & unconscious sensory information & motor commands
• three major parts
• Thalamus
• Hypothalamus
• Epithalamus
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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
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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
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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
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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
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Epithalamus• Roof
• houses pineal gland– secretes melatonin– day/night cycles
• habenular nuclei– emotional response
to odors
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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
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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
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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
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Hemispheres• hemisperes are divided
by longitudinal fissure• connected by corpus
callosum
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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
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Lobe Functions• Frontal lobes
– executive centers• Parietal lobes
– spatial relationships\– pre & post central gyri– movement &
sensations• Occipital lobes
– sight • Temporal lobes
– hearing
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Cerebral White Matter• most of volume of cerebrum
• fibers form bundles or tracts
• Projection
• Commissural
• Association
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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
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Commissural Fibers• Interconnect gyri
between cerebral hemispheres
• Corpus Callosum– thick white band– provides way for
cerebral hemispheres to communicate
• Anterior Commissure
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Projection Fibers• link cerebral cortex to
lower parts of CNS
• entire collection of projective fibers is internal capsule
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Gray Matter of Brain• cell bodies
• cerebral cortex
• basal nuclei
• limbic system
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Basal Nuclei• masses of gray matter
embedded in white matter• globus pallidus• Putamen• Together form lentiform
nucleus• caudate nucleus– all three corpus striatum
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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
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Basal ganglia
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Limbic System•Amygdala•Hippocampus
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Amygdala• Fear
• Applies emotional significance to people &things
AMYGDALA
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Hippocampus• Memory
functions
• Making memories
• Retrieval of memories
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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
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Functions of Cerebral Cortex• higher brain functions• Sleep• Memory• Cognition• Emotion• Sensation• Motor control• Language
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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
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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
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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
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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
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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
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Broca’s Area• located in
frontal lobe• controls motor
cortexspeech produced
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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
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Association Areas• responsible for
integrating information
• associate sensory inputs with stored memories
• important in cognition or thinking
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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
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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
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Association Area Comparison
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Hemispheric Lateralization• right & left cerebral hemispheres are not paired • have different functions• Specialized• Left• Speech• Reasoning• Math and scientific skills
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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
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