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HUMAN ANATOMY
LECTURE ELEVEN
BRAIN AND SPINAL
CORD
BRAIN
Part of CNS contained in cranial cavity
• Control center for many body functions
• Divided into (i) midbrain (brainstem)
- connects spinal cord to brain
- reflexes necessary for survival
(ii) hindbrain
- control of locomotion, balance, posture
(iii) forebrain
- higher level processes, autonomic functions,
thoughts, memories, intellectual functions
• Covered by neural cortex with elevated ridges (GYRI), shallow
depressions (SULCI) and deep grooves (FISSURES)
SAGITTAL SECTION OF BRAIN
PARTS OF THE BRAIN
BRAINSTEM
• Connects spinal cord to brain - all signal must pass through
• Controls life-sustaining processes
Medulla Oblongata
• Continuous with spinal cord
• All communication to and from brain through ascending and
descending nerve tracts
• Contains control centers:
cardiovascular - heart rate, blood vessel diameter
respiration – breathing
reflex centers - swallowing, vomiting, hiccupping, coughing,
sneezing
Pons
• Superior to medulla oblongata
• Links cerebellum to rest of
brain
• Contains sleep centers
• Respiratory center coordinates
with medulla
Midbrain (mesencephalon)
• Superior to pons
• Ascending and descending nerve tracts
• Four mounds on dorsal surface called CORPORA
QUADRIGEMINA
- two inferior COLLICULI are auditory nerve pathways
- two superior COLLICULI are involved in visual reflexes
• Contains a black mass called SUBSTANTIA NIGRA that is
involved with regulation of general body movements
HINDBRAIN
Cerebellum
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Attached to brainstem, posterior to pons
Gray matter (cortex) folded in ridges
with white matter inbetween resembles
tree (ARBOR VITAE)
CEREBELLAR PEDUNCLES - tracts that
communicate with other areas of brain
FLOCCULONODULAR LOBE -controls
balance and eye movements
VERMIS - controls posture, fine motor
coordination, smooth movements
LATERAL HEMISPHERES - works with
cerebrum to plan, practice, learn
complex movements
FOREBRAIN - DIENCEPHALON
• Between brainstem and
cerebrum
• Integrates conscious and
unconscious sensory info
and motor commands
Thalamus
• Right and left halves are
separated by the 3rd ventricle of
the brain
• Receives sensory info - filtered
and relayed to cerebrum
• Emotional awareness, mood
regulation, motivation
Epithalamus
• Superior and posterior to
thalamus
PINEAL BODY - endocrine
gland that helps regulate
biological clock, causes
sleepiness, may influence
puberty
HABENULAR NUCLEUS emotional and visceral
responses to odors
Hypothalamus
• Collection of fibers under
thalamus
• Controls secretion of hormones
from posterior pituitary gland
• Maintains homeostasis, central role
in control of body temperature,
hunger, thirst, urination
• “feel good” emotions like sexual
pleasure, satiation also rage and
fear
MAMMARY BODIES - process
emotional responses and memories
to odor
INFUNDIBULUM - stalk extending
from floor to posterior pituitary
gland
Hypophysis (Pituitary Gland)
• Pea sized gland that rests in the depression (sella turica) of the
sphenoid bone
• Divided into anterior and posterior halves and attached to
hypothalamus by infundibulum
• Both halves secrete hormones
FOREBRAIN - CEREBRUM
• Largest portion of the brain
• Divided into right and left
hemispheres
• Higher level functions, memory,
conscious thought, language
Cerebral Cortex (gray matter)
• Outer surface with gyri, sulci and
fissures:
LATERAL FISSURE separates
hemispheres
LATERAL SULCUS separates
temporal lobe from frontal and
parietal lobe
CENTRAL SULCUS separates
frontal and parietal lobes
• Hemispheres divided into lobes:
FRONTAL LOBE - voluntary motor function, motivation, mood,
aggression
PARIETAL LOBE - reception and evaluation of some sensory info
OCCIPITAL LOBE - visual input
TEMPERAL LOBE - sound, smell, memory, abstract thought
Cerebral Medulla
• White matter found under cortex
ASSOCIATED FIBERS -connections within the same hemisphere
COMMISSURAL FIBERS – connects the hemispheres
PROJECTION FIBERS - tracts between cerebrum and rest of brain
and spinal cord
Basal Nuclei (Basal Ganglia)
• Masses of gray matter deep within white matter of hemispheres
• Linked to all other areas of brain
• Function in subconscious motor control and coordination
STRUCTURES OF THE BRAIN
Cranial Meninges
• Continuous with spinal meninges
• Surround and protect brain – stability
and shock absorption
(i) Dura Mater - superficial double
layer, elastic, dense collagen fibers
- outer layer connected to periosteum
of skull
- inner layer folds into:
FALX CEREBRI - inbetween cerebral
hemispheres
TENTORIUM CEREBELLI - inbetween
cerebellum and cerebrum
FALX CEREBELLI – between
cerebellar hemispheres
(ii) Arachnoid Mater/Subdural Space
• Thin, wispy layer over brain surface - not following folds
• Projections allow CSF to be reabsorbed into blood
• Subdural space inbetween dura and arachnoid layer - small
amount of fluid
(iii) Pia Mater/Subarachnoid Space
• Thin, delicate membrane closely attached to brain and spinal cord
• Follows contours of brain
• Highly vascularized - brings blood to ependymal cells lining
ventricles
• Subarachnoid space - contains weblike strands of arachnoid
mater, blood vessels, cerebrospinal fluid
Ventricles
• Fluid filled cavities in the brain
• Lined with EPENDYMAL CELLS
(produce CSF)
LATERAL VENTRICLES - within cerebral
hemispheres
- separated by SEPTUM PELLUCIDUM
THIRD VENTRICLE - within diencephalon
INTERVENTRICULAR FORAMINA
- join lateral and third ventricles
FOURTH VENTRICLE - base of
cerebellum
CEREBRAL AQUADUCT - joins third and
fourth ventricles
- continuous with spinal cord and
connected to subarachnoid space through
holes (formamina) in walls and roof of
4th ventricle
Cerebrospinal Fluid (CSF)
• Bathes brain and spinal cord forming protective cushion
• Transports nutrients, chemical messengers and waste products
CHOROID PLEXUS – within ventricles, produces CSF
- composed of ependymal cells, support tissues and blood vessels
- removes waste products from CSF
ARACHNOID GRANULATIONS - masses of arachnoid tissue in
dural sinus where CSF passes into blood stream
Flow of CSF
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CSF from lateral ventricles flows through foramina to 3rd ventricle
CSF flows from 3rd ventricle through cerebral aquaduct to 4th ventricle
CSF exits 4th ventricle into subarachnoid space - some enters central canal of spinal cord
CSF flows through subarachnoid space to arachnoid granulations in superior sagittal
sinus where it enters venous circulation
Flow of Cerebrospinal Fluid
• From lateral ventricles through
foramina to 3rd ventricle
• 3rd ventricle through cerebral
aquaduct to 4th ventricle
• Exits 4th ventricle into subarachnoid
space - some enters central canal of
spinal cord
• Subarachnoid space to arachnoid
granulations in superior sagittal sinus
where it enters venous circulation
BRAIN BLOOD SUPPLY
• Brain requires tremendous amount of blood
• Receives blood through arteries - internal carotids and vertebral arteries
which join to form basilar artery. Carotids plus basilar form CIRCLE OF
WILLIS (cerebral arterial circle)
• Blood leaves brain through internal jugular veins
Blood-Brain Barrier
• Separates neural tissue from general blood supply
• Endothelial cells lining capillaries interconnected by tight junctions preventing diffusion of materials into brain
• Astrocytes release chemicals that control permeability of endothelium
- only lipid soluble materials diffuse - CO2, O2, nicotine, ethanol, heroin
- water soluble materials mediated transport – A.A., glucose, H2O
Arteries of the Brain
SPINAL CORD
• Extends from foramen magnum to second
lumbar vertebra
• Gives rise to 31 pairs of spinal nerves
• Divided into specialized areas:
CERVICAL ENLARGEMENT - supplies
upper limbs
LUMBOSACRAL ENLARGEMENT supplies lower limbs
CONUS MEDULLARIS - tapered inferior
end
CAUDA EQUINA - origins of spinal nerves
extending from lumbosacral enlargement
and conus medullaris
Spinal Cord
Cross Section of a Spinal Cord
Cross Section of a Spinal Cord
Cross Section
ANTERIOR MEDIAN FISSURE and POSTERIOR MEDIAN SULCUS - deep
clefts partially separating left and right halves
White Matter (outside area)
• myelinated axons form ascending and descending nerve tracts or columns (dorsal,
ventral and lateral columns)
Gray Matter (inside area)
• unmyelinated axons, cell bodies/nuclei, dendrites surrounding central canal
• divided into horns:
- posterior horn (sensory neurons)
- anterior horn (motor neurons)
- lateral horn (sympathetic autonomic neurons)
Commissures - connections between the left and right halves of the white
matter and the gray matter
Roots - spinal nerves arise as rootlets and combine to form roots that exit
through intevertebral foramen
• DORSAL ROOT - afferent neurons (coming into spinal cord)
• VENTRAL ROOT - efferent neurons (leaving the spinal cord)
• Dorsal and ventral roots combine to form spinal nerves
Dorsal Root Ganglion
• collections of cell bodies from afferent (sensory) neurons form dorsal roots
• efferent (motor) neuron cell bodies are found in anterior and lateral horns of
gray matter
anterior horn - somatic motor neurons
lateral horn - autonomic neurons
• axons of efferent neurons form ventral roots and pass into spinal nerves