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Chapter 14
The Brain and Cranial Nerves
Lecture Outline
Principles of Human Anatomy and Physiology, 11e
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INTRODUCTION
• The brain receives sensory input, integrates it, makes
decisions, and regulates movement.
• It is also the center for intellect, emotions, behavior,
and memory.
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Chapter 14
The Brain and
Cranial Nerves
• One of the largest organs in the body at almost 3 lb.
• Brain functions in sensations, memory, emotions, decision
making, behavior
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Blood Flow in the Brain
• An interruption of blood flow for 1 or
2 minutes impairs neuronal
function.
– A total deprivation of oxygen for
4 minutes causes permanent
injury.
• Because carbohydrate storage in
the brain is limited, the supply of
glucose to the brain must be
continuous.
– Glucose deficiency may produce
mental confusion, dizziness,
convulsions, and
unconsciousness.
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BBB
• A blood-brain barrier (BBB) protects brain cells from harmful
substances and pathogens by serving as a selective barrier
to prevent passage of many substances from the blood to
the brain.
• An injury to the brain due to trauma, inflammation, or toxins
causes a breakdown of the BBB, permitting the passage of
normally restricted substances into brain tissue.
•
The BBB may also prevent entry of drugs that could be
used as therapy for brain cancer or other CNS disorders, so
research is exploring ways to transport drugs past the BBB.
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Protective Covering of the Brain
• The brain is protected by the cranial bones and the
cranial meninges.
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CEREBROSPINAL FLUID
• Cerebrospinal fluid (CSF) is a clear, colorless liquid that
protects the brain and spinal cord against chemical and
physical injuries.
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Cerebrospinal Fluid (CSF)
• 80-150 ml (3-5oz)
• Clear liquid containing glucose, proteins, & ions
• Functions
– mechanical protection
• floats brain & softens impact with bony walls
– chemical protection
• optimal ionic concentrations for action
potentials
– circulation
• nutrients and waste products to and from
bloodstream
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Origin of CSF
• Choroid plexus = capillaries covered by ependymal cells
– 2 lateral ventricles, one within each cerebral hemisphere
– roof of 3rd ventricle
– fourth ventricle
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Hydrocephalus
• Blockage of drainage of CSF (tumor, inflammation,
developmental malformation, meningitis, hemorrhage or injury)
– Continued production cause an increase in pressure --hydrocephalus
– In newborn or fetus, the fontanels allow this internal
pressure to cause expansion of the skull and damage to the
brain tissue
• Neurosurgeon implants a drain shunting the CSF to the veins of
the neck or the abdomen
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XII = Hypoglossal Nerve
• Controls muscles of
tongue during speech
and swallowing
• Injury deviates tongue
to injured side when
protruded
• Mixed, primarily motor
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XI = Spinal Accessory Nerve
• Cranial portion
– arises medulla
– skeletal mm of throat &
soft palate
• Spinal portion
– arises cervical spinal cord
– sternocleidomastoid and
trapezius mm.
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X = Vagus Nerve
• Receives sensations
from viscera
• Controls cardiac muscle
and smooth muscle of
the viscera
• Controls secretion of
digestive fluids
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IX = Glossopharyngeal Nerve
• Stylopharyngeus m.
(lifts throat during
swallowing)
• Secretions of parotid
gland
• Somatic sensations &
taste on posterior 1/3 of
tongue
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VIII = Vestibulocochlear Nerve
• Cochlear branch begins in
medulla
– receptors in cochlea
– hearing
– if damaged deafness or
tinnitus (ringing) is
produced
• Vestibular branch begins in
pons
– receptors in vestibular
apparatus
– sense of balance
– vertigo (feeling of rotation)
– ataxia (lack of coordination)
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VII = Facial Nerve
• Motor portion
– facial muscles
– salivary & nasal and
oral mucous glands
& tears
• Sensory portion
– taste buds on
anterior 2/3’s of
tongue
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VI = Abducens Nerve
• Lateral rectus eye
muscle
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V = Trigeminal Nerve
• Motor portion
– muscles of
mastication
• Sensory portion
– touch, pain, &
temperature
receptors of the face
• ophthalmic
branch
• maxillary branch
• mandibular
branch
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IV = Trochlear Nerve
• Superior oblique eye
muscle
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III = Oculomotor Nerve
• Levator palpebrae raises
eyelid (ptosis)
• 4 extrinsic eye muscles
• 2 intrinsic eye muscles
– accomodation for near
vision (changing
shape of lens during
reading)
– constriction of pupil
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II = Optic Nerve
• Completely sensory
• Contains axons that
conduct nerve impulses
for vision
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I = Olfactory Nerve
• Completely sensory
• Contains axons that
conduct nerve impulses
for olfaction, which is the
sense of smell
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The Brain – The 3 Main Parts
Cerebrum: The thinking center of the brain. (memory,
planning, calculating, consciousness)
Cerebellum: The coordination center for muscles.
(Balance, Sports)
Medulla: The autonomic (automatic) control center.
(Breathing, heart beat, digestion)
Medulla Oblongata
•
•
•
•
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Continuation of spinal cord
Ascending sensory tracts
Descending motor tracts
Nuclei of 5 cranial nerves
Cardiovascular center
– force & rate of heart beat
– diameter of blood vessels
• Respiratory center
– medullary rhythmicity area sets basic rhythm of
breathing
• Information in & out of cerebellum
• Reflex centers for coughing, sneezing, swallowing etc.
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Pons
• The pons is located superior to the medulla. It connects the
spinal cord with the brain and links parts of the brain with
one another by way of tracts
– relays nerve impulses related to voluntary skeletal
movements from the cerebral cortex to the cerebellum.
– contains areas, which help control respiration along with
the respiratory center in the medulla
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Physiology, 11e
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Cerebellum
• 2 hemispheres
• Function
– correct voluntary muscle contraction and posture based
on sensory data from body about actual movements
– sense of equilibrium and balance
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Cerebellum Structure
• Cerebellar cortex (outside) & central nuclei are grey matter
• Arbor vitae = tree of life = white matter (inside)
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THE CEREBRUM
• The cerebrum is the largest part of the brain .
– The surface layer, the cerebral cortex, is 2-4 mm thick
and is composed of gray matter. The cortex contains
billions of neurons.
– The cortex contains gyri (convolutions), deep grooves
called fissures, and shallower sulci. Beneath the cortex
lies the cerebral white matter, tracts that connect parts of
the brain with itself and other parts of the nervous
system.
• The cerebrum is nearly separated into right and left halves,
called hemispheres, by the longitudinal fissure.
– Internally it remains connected by the corpus callosum, a
bundle of transverse white fibers.
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Hemispheric Lateralization
• Segments the brain into 2 parts.
• Lateralization literally means that certain functions are
located on one side of the brain.
– Left Brain: known for rational and logical thinking
– Right Brain: known for creative and intuitive thinking
– Left side controls right side of body and right side
controls left side of body.
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Brain Waves
• Rapid fluctuations of voltage between parts of the cerebral
cortex that are detectable with an electroencephalograph
• Can often tell the mental state of a person
• Frequency measured in Hz, when activity is slower there is
slower brain activity
• 4 Types of Waves:
– Delta Waves: below 4 Hz occur during sleep
– Theta Waves: (4-7 Hz) are associated with sleep, deep
relaxation, and visualization
– Alpha Waves: (8-13 Hz) occur when we are relaxed and
calm
– Beta Waves: (13-38 Hz) when we are actively thinking
and problem solving
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Brain Waves
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Memory
• The brain is an enormously complex network of billions of
neurons connected by more than 90,000 miles of fibers
• With memory, your brain needs to form association
between a complex visual image and a name, which are
encoded by different groups of neurons in various parts of
your brain
Learning
• Learning mainly takes place at synapses: the junctions
between neurons where information is relayed.
• A synapse’s performance changes when we learn
something new
• Plasticity is the capability for change associated with
learning.
Wakefulness and Sleep
• We sleep and wake up in a 24-hour cycle called a
Circadian Rhythm
• To wake up, the reticular activating system (RAS) must be
stimulated.
– Either by: Touch, Light, Noise, Movement
• The cerebral cortex responds to the RAS and causes you to
wake up.
• Sleep is a state of altered consciousness which you can be
awakened from. When we are sleeping we are in REM.
• Sleep occurs when the RAS activity is low.
Aging and the Nervous System
• The older we get, the more the Nervous System gets weaker
– # of synaptic contacts declines
– Decrease in brain mass and nerve cells
– Decreased capacity for sending nerve impulses
• Processing of info decreases
• Conduction velocity decreases
• Voluntary motor movement decreases
• Reflex times increase
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Cerebral Palsy
• Neuromuscular disability
• Infants and toddlers affected and diagnosed
• Voluntary muscles are poorly controlled or paralyzed
• Caused by brain damage either genetics or accidental
• 2 out of every 1000 newborn affected
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Alzheimer’ Disease
• Most common form of dementia (weakening of mind due to
age)
• Mind literally deteriorates alongside the brain
• Causes not well understood
• Old people mainly affected
• 1 in 8 older Americans affected by AD
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•
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Symptoms usually reveal during or after age 65:
Confusion
Mood Swings
Trouble with language
Long term memory loss
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