Biology 232
Human Anatomy and Physiology
Chapter 14 Lecture Outline
The Brain – 100 billion neurons averaging 1000 synapses each
4 Major Regions of the Brain
cerebrum – center of thought, intellect, memory
cerebellum
diencephalon
brainstem
Protection and Nourishment of the Brain
Cranium – bones surrounding and protecting the brain
Cranial Meninges – 3 protective connective tissue membranes; continuous with
spinal meninges and similar in structure
dura mater – composed of outer and inner layers
outer layer fuses with periosteum of cranium (no epidural space)
venous sinuses – large, open veins between the 2 layers of dura
split in some regions to form venous sinuses
3 folds of inner dura mater:
falx cerebri – between hemispheres of cerebrum
superior sagittal sinus
falx cerebelli – between hemispheres of cerebellum
tentorium cerebelli – separates cerebrum from cerebellum
arachnoid mater
arachnoid villi – finger-like projections that extend into dural
sinuses
subarachnoid space – contains CSF
pia mater – adheres to surface of brain; contains blood vessels which
enter the brain
Blood-Brain Barrier – protects brain by preventing passage of many substances
from blood to brain tissue; lipid-soluble substances can cross, but others
are regulated by transport proteins
brain capillaries have epithelium with a thick basement membrane and
tight junctions between cells
astrocyte processes surround capillaries – selectively pass some
substances to neurons but inhibit others
glucose crosses by active transport – main energy supply for neurons via
oxidative phosphorylation; interruption of oxygen or glucose
supply rapidly impairs brain function
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Cerebrospinal Fluid (CSF) – clear fluid containing glucose, proteins, lactic acid,
ions, and some white blood cells
circulates through cavities in brain and spinal cord, and in subarachnoid
space
Functions of CSF:
site of chemical exchange for CNS tissue
floats and cushions delicate neurons
Formation of CSF:
ventricles – 4 cavities in brain filled with CSF
lateral ventricles (2) – in cerebral hemispheres; separated
from each other by septum pellucidum
third ventricle – midline in diencephalon
fourth ventricle – between brainstem and cerebellum
choroid plexuses – capillary networks in wall of each ventricle
produce CSF by filtration of blood
ependymal cells line ventricles and choroid plexuses
secrete CSF into the ventricles and adjust its content
tight junctions between ependymal cells
(blood – CSF barrier)
Circulation of CSF
lateral ventricles
interventricular foramina
third ventricle
cerebral aqueduct
fourth ventricle
median and lateral apertures to subarachnoid spaces
central canal of spinal cord
reabsorbed into blood through arachnoid villi into dural sinuses
reabsorption rate = formation rate
hydrocephalus – excess accumulation of CSF resulting in increased
pressure (reabsorption < formation)
DIVISIONS OF THE BRAIN - brainstem, diencephalon, cerebellum, cerebrum
1) Brainstem – between spinal cord and diencephalon
3 regions:
Medulla oblongata – continuous with spinal cord
sensory and motor tracts between brain and spinal cord
pyramids – motor tracts from cerebrum to spinal cord
decussation of pyramids – 90% of axons cross to opposite side
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vital centers – nuclei that control vital autonomic functions
cardiovascular center – regulates heart and blood vessels
respiratory rhythmicity center – controls respiratory muscles
nuclei of cranial nerves – VIII, IX, X, XI, XII
Pons – superior to medulla; attachment site for the cerebellum
sensory and motor tracts carry information to and from cerebellum
pneumotaxic and apneustic areas – regulate respiratory rhythmicity
center
nuclei of cranial nerves – V, VI, VII, VIII
Mesencephalon – superior part of brainstem
cerebral peduncles – sensory and motor tracts to and from cerebrum
tectum (roof) – corpora quadrigemina (2 pairs of nuclei)
superior colliculi – visual reflex centers
inferior colliculi – hearing, startle reflex
substantia nigra – nuclei involved in regulating subconscious
motor activity
disorders associated with Parkinson’s disease
nuclei of cranial nerves – III, IV
(Reticular formation – network of interconnected nuclei extending from upper spinal cord
to lower diencephalon; forms the reticular activating system involved in awakening and
consciousness)
2) Diencephalon – between brainstem and cerebrum
3 divisions:
thalamus – 80% of diencephalon; paired right and left oval masses
intermediate mass – bridge of gray matter between 2 halves
major relay station of brain
sensory information synapses in the thalamus before being relayed to the
appropriate region of the cerebrum
relays information involved in planning and control of movements
involved in integrating information related to emotions
hypothalamus – inferior to thalamus
has no blood-brain barrier – senses changes in composition of blood
and CSF
important regulator of homeostasis
acts as link between nervous and endocrine systems
mammillary bodies – reflexes for feeding and smell
infundibulum – stalk-like connection to pituitary gland
functions of hypothalamus:
regulates activities of ANS – regulates visceral organ functions
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produces hormones – oxytocin, antidiuretic hormone, and hormones
that regulate pituitary function
regulates eating and drinking – thirst center, feeding center
regulates body temperature via ANS
participates in emotional behavior
facial expressions, sexual arousal, stress responses
epithalamus – inferior and posterior to thalamus
pineal gland – secretes hormones
melatonin – promotes sleep, helps regulate circadian rhythm
3) Cerebellum – automatically fine-tunes body movements
coordinates of skeletal muscle movements
maintains posture, balance, and muscle tone
transverse fissure and tentorium cerebelli – separate cerebellum from cerebrum
vermis – central portion
right and left cerebellar hemispheres
cerebellar cortex – gray matter
folia – parallel ridges
arbor vitae – branching white matter deep to cortex
cerebellar peduncles – 3 large, paired tracts connecting cerebellum to pons
receive voluntary and automatic motor impulses for cerebrum, thalamus,
and mesenchephalon
receive sensory impulses related to body position and balance
the cerebellum compares intended movements with actual movements
sends feedback to cerebrum for corrections
disorders result in ataxia – loss of motor coordination
4) Cerebrum – “seat of intelligence” – language, math, thought, memory
origin of voluntary actions, site of conscious perceptions
right and left cerebral hemispheres
longitudinal fissure – divides into 2 hemispheres
falx cerebri – fold of dura mater between hemispheres
cerebral cortex – outer gray matter
gyri – folds in cortex
sulci – grooves in cortex; divide hemispheres into lobes
central sulcus
lateral sulcus
parieto-occipital sulcus
lobes of cerebrum – named for overlying bones
frontal lobes
parietal lobes
temporal lobes
occipital lobes
insula – deep to lateral cerebral sulcus
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cerebral white matter – deep to cortex; myelinated and unmyelinated axons
association fibers – conduct impulses within same hemisphere
commissural fibers – conduct impulses between the 2 hemispheres
corpus callosum – main commissural tracts
anterior commissure
projection fibers – conduct impulses to and from lower brain regions and
spinal cord
internal capsule
enter and exit through cerebral peduncles
basal nuclei – 3 paired nuclei within white matter of cerebrum
subconsciously regulate muscle tone and automatic movements
(eg. walking and swinging arms)
Functional Areas of the Cerebral Cortex
Sensory areas – receive sensory impulses
primary sensory cortex – receives somatic sensory input
“map” of body – size of region depends on number of receptors
postcentral gyrus – posterior to central sulcus
visual cortex – vision; occipital lobe
auditory cortex – sound; temporal lobe
gustatory cortex – taste; frontal lobe and insula
olfactory cortex – smell; medial temporal lobe
Motor areas – produce motor outputs to skeletal muscles
primary motor cortex – “map” of body; each region controls voluntary
contractions of specific regions; size of region depends on number
of motor units
precentral gyrus – anterior to central sulcus
Association areas – located within or near motor and sensory areas
link sensations to motor responses
somatic sensory association area – recognition of general sensations
visual association area – recognition of visual inputs
auditory association area – recognition of sounds (eg. music, speech)
somatic motor association area – generates complex, learned motor
activities (skilled movements)
integrative centers – integrate information from many association areas
perform complex motor and intellectual functions
general interpretive area – integrate many sensory impulses, allowing
interpretation and understanding of language and math
(usually found in left hemisphere)
speech center – plans and produces speech
prefrontal cortex – integrates information from all association areas
performs abstract functions – prediction, theorizing, creativity
affects emotions (frustration, anxiety)
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Hemispheric Lateralization – functional differences between 2 cerebral hemispheres
Left hemisphere functions
sensory and motor signals for right side of body
reasoning
numerical and scientific skills
language skills
Right hemisphere functions
sensory and motor signals for left side of body
musical and artistic ability
understanding patterns and spatial relationships
emotional expression and recognition of emotional expression
Limbic System – ring of structures around inner border of cerebrum
“emotional brain” – primary role in motivation, pleasure, pain, affection, anger
also involved in memory
amygdala – helps regulate “fight of flight” response
hippocampus – involved in storage and retrieval of memories
hypothalamus
Brain Waves – electrical signals (action potentials and graded potentials) generated by
brain neurons
electroencephalogram (EEG) – recording of brain waves detected by electrodes
placed on forehead and scalp; useful for studying normal brain functions
and diagnosing disorders
4 Types of Brain Waves:
alpha waves (8-13 Hz (cycles/second))
normal awake and resting pattern
beta waves (14-30 Hz) higher frequency
normal mental activity pattern
delta waves (1-5 Hz) large, low frequency
normal adult sleep pattern or awake infant pattern
theta waves (4-7 Hz)
emotionally stressed adults, or brain disorders
Cranial Nerves – 12 pairs; pass through foramina of cranium; part of PNS
sensory nerves – only sensory fibers
mixed nerves – sensory and motor fibers
Cranial nerve I – olfactory nerve
sensory – olfaction (smell)
Cranial nerve II – optic nerve
sensory – vision
Cranial nerve III – oculomotor nerve
mainly motor – most eyeball and inner eye movements
Cranial nerve IV – trochlear nerve
mainly motor – eyeball movements
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Cranial nerve V – trigeminal nerve
mixed – 3 branches
ophthalmic nerve – sensory from eye, nose, forehead
maxillary nerve – sensory from nose, upper jaw, pharynx
mandibular nerve – sensory from lower jaw and mouth
motor to muscles of mastication (chewing)
Cranial nerve VI – abducens nerve
mainly motor – eyeball movements
Cranial nerve VII – facial nerve
mixed
sensory – taste buds
motor – somatic - facial expressions
autonomic - secretion of tears, saliva, nasal secretions
Cranial nerve VIII – vestibulocochlear nerve
mainly sensory – 2 branches
vestibular nerve – equilibrium
cochlear nerve – hearing
Cranial nerve IX – glossopharyngeal nerve
mixed
sensory – taste buds, throat
motor – somatic - swallowing
autonomic - secretion of saliva
Cranial nerve X – vagus nerve
mixed
sensory – ear, throat, visceral organs, carotid artery
motor – autonomic fibers to most viscera
Cranial nerve XI – accessory nerve
mainly motor – swallowing, head and shoulder movements
Cranial nerve XII – hypoglossal nerve
mainly motor – tongue movements
Development of Nervous System
neural tube – formed by folding of ectoderm
Week 4
3 primary brain vesicles – enlargements of neural tube
prosencephalon (forebrain)
mesencephalon (midbrain)
rhombencephalon (hindbrain)
Week 6
5 secondary brain vesicles
telencephalon (from prosencephalon) forms cerebrum
diencephalon (from prosencephalon) forms thalamus, epithalamus,
hypothalamus, subthalamus
mesencephalon – forms mesencephalon
metencephalon (from rhombencephalon) forms pons and cerebellum
myelencephalon (from rhombencephalon) forms medulla oblongata
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