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