Transcript THE BRAIN - Doctor Jade

THE BRAIN
Structure & 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
developsthickens 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:
• Prosencephalonforebrain
• Mesencephalonmidbrain
• Rhombencephalonhindbrain
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 goolder
structures are found
• older parts are more apt to
include basic
mechanisms for survival
Brain Divisions
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Brainstem
Cerebellum
Diencephalon
Cerebrum
BRAIN STEM
begins where spinal
cord enters skull &
swells
Medulla oblongata
Pons
Midbrain
MEDULLA
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regulates autonomic functions
breathing, heartbeat, blood
pressure & digestion or vegetative
processes
cross over point where nerves come
in & cross to opposite sidedecussation
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
Midbrain
corpora 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 pleatingfolia
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
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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
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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
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
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
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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
Cerebrum
• surface is highly convoluted
– increases surface area
• cortex forms elongated ridgesgyri
• 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
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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
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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
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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
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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
cortexspeech
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
stimulatedno
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
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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
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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