Download - Chapter 15 A, Sp 10
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Human Anatomy, Second Edition
McKinley & O'Loughlin
Chapter 15A Lecture Outline: Brain and Cranial Nerves
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Brain and Cranial Nerves An adult brain weighs 1.35 - 1.4 kg
(about 3 pounds) and has a volume of about 1200 cc
Brain size is not directly correlated with intelligence
It is the number of active synapses!
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The Brain’s 4 Major Regions The cerebrum, diencephalon,
brainstem, and cerebellum. Left and right cerebral hemispheres.
Each has five functional areas called lobes. Outer surface of an adult brain exhibits
folds and shallow depressions Inferior portion has 12 pairs of cranial
nerves.
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Brain Development and Tissue Organization
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Embryonic Development of the Brain
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Organization of Brain Tissue Gray matter has cell bodies,
dendrites, axon terminals, and unmyelinated axons.
White matter is composed of myelinated axons.
The gray cortex covers the surface of most of the adult brain. About 2-4 mm thick.
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Organization of Neural Tissue Areas in the Brain White matter lies deep to the
gray matter of the cortex. Within the white matter are
clusters of neuron cell bodies,cerebral nuclei.
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Support and Protection of the Brain The brain is protected and isolated
by several structures: bony cranium meninges cerebrospinal fluid (CSF) blood-brain barrier
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3 Cranial Meninges Connective tissue layers separate the
soft tissue of the brain from the cranial bones.
Enclose and protect blood vessels that supply the brain.
Contain and circulate CSF. Help form some veins that drain blood
from the brain.
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Pia Mater (“Gentle Mother”) Thin layer of delicate areolar tissue
that follows every contour of the brain surface.
Not visible except with a microscope.
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Arachnoid (Spider Web Like) Partially a delicate web of collagen
and elastic fibers, termed the arachnoid trabeculae.
Between the subdural space and the subarachnoid space.
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Dura Mater (“Tough Mother”) Strongest meninx. Two dense, irregular C.T. layers.
periosteal layer is the periosteum of the cranial bones
meningeal layer is deep to the periosteal layer
Fused, except at the dural venous sinuses.
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4 Cranial Dural Septa The meningeal layer of the dura mater
extends as flat partitions (septa) deep into the cranial cavity as the cranial dural septa.
These separate parts of the brain and give stabilization and support to the entire brain. Falx cerebri Falx cerebelli Tentorium cerebelli Diaphragma sellae
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Hematomas Epidural hematoma
Usually from a severe blow at the pterion: junction of temporal, sphenoid, frontal, and parietal bones
Fracture results in arterial hemorrhage. Typically, lose consciousness, awake and seem fairly
normal, few hours later brain damaged and neurologic injury and death if not treated
Subdural hematoma Usually from broken veins from fast or violent
rotation of the head Blood accumulates slowly, but still a serious medical
emergency
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Concussion Most common brain injury Loss of consciousness after a blow or sudden stop No obvious physical defect but many symptoms may
occur Cumulative effect
Contusion Visible bruising of the brain May be from torn pia mater Loss of consciousness briefly May have respiration abnormalities and decreased
blood pressure
Brain Injuries
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4 Brain Ventricles Cavities derived from the lumen
(opening) of the embryonic neural tube.
Continuous with one another as well as with the central canal of the spinal cord.
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Cerebrospinal Fluid A clear, colorless liquid that
circulates in the ventricles and subarachnoid space.
Performs several important functions. buoyancy protection environmental stability
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CSF Formation Formed from blood plasma by
the choroid plexus, capillaries covered by ependymal cells, in each ventricle.
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CSF Circulation 500 ml produced per day 100-160 ml total volume
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Hydrocephalus (“Water on the Brain”) Excessive CSF Prior to suture closure, head enlarges
and neurologic damage may occur After suture closure, brain compressed
and results in permanent brain damage Treatment of severe cases: shunt
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Blood-Brain Barrier There are differential rates of
passage for different substances in order to protect the brain’s neurons.
Prevents exposure of neurons in the brain to drugs, toxins, waste products in the blood, and variations in levels of normal substances (ions, hormones) that could adversely affect brain function.
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Examples Quickly pass through the barrier;
Lipid-soluble substances and water-soluble substances with a carrier by active transport
Glucose, gases such as O2 and CO2, water, and most lipid soluble substances (ethanol and anaesthetics)
Caffeine, nicotine, and heroin Slowly pass through the barrier;
Na+, K+, Cl-, creatinine, and urea Do NOT pass through the barrier:
Proteins, most antibiotics, and chemotherapeutic agents
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The Barrier The brain capillaries are the
least permeable in the body. Tight junctions A continuous basement
membrane that totally surrounds the capillaries.
Astrocytes act as “gatekeepers.”
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Barrier Missing or Lacking in Places Circumventricular organs (organs
around the 3rd and 4th ventricles) lack the BBB: hypothalamus, pituitary, pineal gland, and other nearby glands
Missing where there is a need to monitor blood chemical changes to coordinate endocrine and nervous systems. Missing in the choroid plexus where CSF made.
HIV virus may enter where the BBB is lacking.
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Damage to the BBB Trauma can damage the BBB During prolonged emotional stress, the
tight junctions are opened, so the BBB fails and toxic substances in the blood can enter the brain tissue. Implicated in the neurological symptoms associated with Gulf War syndrome.
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Tricking the BBB High glucose solutions can be used
to shrink the cells to make gaps for antibiotics to enter.
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Cerebrum Location of conscious thought
processes and origin of all complex intellectual functions
Two large hemispheres Gray cerebral cortex with inner white
matter and islands of gray cerebral nuclei
Folded ridges are gyri separated by shallow depressions called sulci or deeper grooves called fissures
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Cerebral Hemispheres Joined by white matter tracts in
some places. Hard to assign specific function to
a specific region. Usually contralateral. Anatomically almost mirror images
but some functional differences, hemispheric lateralization.
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Lobes of the Cerebrum Frontal lobe Parietal lobe Temporal lobe Occipital lobe Insula (deep to the lateral
sulcus)
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Mapping Some specific structural areas have distinct
motor and sensory functions Some higher mental functions are dispersed
over large areas Three categories of functional areas
Motor (voluntary movement) Sensory (conscious awareness of
sensation) Association (primarily integrate and
store information)
Functional Areas of the Cerebrum
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Primary motor cortex in precentral gyrus Voluntary skeletal muscle activity Motor homunculus (surface area proportional to the
number of motor units for the area) Motor speech area (Broca’s area) - left side
Regulates patterns of breathing and controls the muscle movements for speech
Frontal eye field Control and regulate eye movements for reading and
coordinating binocular vision Anterior to premotor cortex, a motor association area
Motor Areas in Frontal Lobes
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Sensory Areas Primary somatosensory cortex
General somatic sensory information (conscious)
Postcentral gyrus in parietal lobe Sensory homunculus (surface area proportional
to the number of receptors for the area) Primary visual cortex in occipital lobe Primary auditory and olfactory
cortices in temporal lobe Gustatory cortex in insula
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Association Areas Connected to primary areas - process and
interpret incoming information or coordinate a motor response. They integrate new sensory inputs with memories of past experiences.
Premotor cortex mainly coordinates learned, skilled motor activities
Somatosensory association area integrates and interprets sensations to determine the texture, temperature, pressure, and shape of objects
Auditory association area interprets the characteristics of sound and store memories of sounds heard in the past.
Visual association area analyzes color, movement, and form to ID what we see
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Wernicke’s area is involved in recognizing, understanding, and comprehending spoken or written language. Must work with Broca’s area.
Gnostic area (common integrative area or general interpretation area) integrates all sensory association area information to give a comprehensive understanding of a current activity
Multi-Association Areas
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Process incoming information from several association areas and ultimately direct either extremely complex motor activity or complicated analytical functions in response.
Examples: speech, cognition, understanding spatial relationships, and general interpretation
Higher-Order Processing Centers
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Prefrontal Cortex Most complex area
Intelligence, complex learning abilities, personality
Also: abstract ideas, judgment, reasoning, persistence, planning, concern for others, and conscience
Prefrontal lobotomy used from 1930-1950s to treat severe mental illness Epilepsy and abnormal personality changes Use drugs now
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The Case of Phineas Gage Railroad accident in 1848 drove a 3 1/2
ft. tamping rod through his frontal lobe Survived, but changed his personality
Formerly, capable, well-balanced and shrewd, etc.
After, irreverent, fitful, profane, inconsiderate, and could not make decisions
Frontal lobes important in personality and basic elements of decision making
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The Insula Not well understood The insula and anterior cingulate cortex are crucial
centers of emotional cognition. They are also necessary for attending to feelings that arise from your body and for experiencing pain.
The more viscerally aware you are, the more emotionally attuned you are.
Your ability to read and interpret sensations arising from within your own body, interoception, is essential to fundamental features of being human: sentiment, sentience, and emotional awareness.
(from Scientific American Mind, Aug./Sept. 2007)
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Central White Matter Association tracts
Connect nearby gyri within the same hemisphere
Commissural tracts Connect the two hemispheres Corpus callosum, anterior and posterior
commissures Projection Tracts
Connect the cerebral cortex to the inferior brain regions and the spinal cord
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Cerebral or Basal Nuclei Corpus striatum (largest part)
Caudate nucleus stimulates muscles to produce the pattern and rhythm of arm and leg movements associated with walking
Lentiform nucleus Putamen controls muscular movement
at the subconscious level Globus pallidus controls and adjusts
muscle tone
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