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Chapter 14
The Brain and Cranial Nerves
The Brain
• The Brain is part of Central Nervous
System (CNS)
• It is divided into 6 major parts:
–
–
–
–
–
–
The cerebrum
The diencephalon
The mesencephalon
The cerebellum
The pons
The medulla oblongata
Major divisions of the Brain
The real thing
Fig.14.01b
The Human Brain
• Ranges from 750 cc to 2100 cc
• Contains almost 98% of the body’s
neural tissue
• Average weight about 1.4 kg (3 lb)
Protection of the Brain
• The brain is protected by bone,
meninges, and cerebrospinal fluid
• Harmful substances are shielded
from the brain by the blood-brain
barrier
Cerebrospinal fluid
• Protects by absorbing shock (it “floats”
the brain.
• Maintains the electrochemical
environment (opitmal pH & osmolality).
• Circulates nutrients and wastes.
The Ventricles
Formation of
CSF
Choroid Plexuses
Figure 12.25a
Fig. 14.04c
Cirulaation of
CSF
Meninges
• Three connective tissue membranes lie
external to the CNS – dura mater,
arachnoid mater, and pia mater
• Functions of the meninges
– Cover and protect the CNS
– Protect blood vessels and enclose venous
sinuses
– Contain cerebrospinal fluid (CSF)
– Form partitions within the skull
The
Meninges
of the
Brain
Dura Mater
• Three dural septa extend inward and
limit excessive movement of the brain
– Falx cerebri – fold that dips into the
longitudinal fissure
– Falx cerebelli – runs along the vermis of
the cerebellum
– Tentorium cerebelli – horizontal dural
fold extends into the transverse fissure
• Falx cerebri, tentorium cerebelli, and falx cerebelli
Dural Folds
Figure 14–3b
Arachnoid Mater
• The middle meninx, which forms a loose
brain covering
• It is separated from the dura mater by the
subdural space
• Beneath the arachnoid is a wide
subarachnoid space filled with CSF and
large blood vessels
• Arachnoid villi protrude superiorly and
permit CSF to be absorbed into venous
blood
Blood flow, O2 and the BBB
• Though only 2% of body mass the brain
consumes 20% of the oxygen and glucoseof
the resting body.
• No O2 for a minute = dizziness
– 4 minutes = brain damage
– 6 minutes = death
• The brain is protected by the blood-brain
barrier.
Blood-Brain Barrier:
Functions
• Selective barrier that allows nutrients to
pass freely
• Is ineffective against substances that can
diffuse through plasma membranes
• Absent in some areas (vomiting center and
the hypothalamus), allowing these areas to
monitor the chemical composition of the
blood
• Stress increases the ability of chemicals
to pass through the blood-brain barrier
The Bloodbrain
barrier
The Brain Stem
• The brain stem is comprised of 3
main subdivisions:
– The Medulla Oblongata
– The Pons
– The Mesencephalon
The
diencephalon
& brainstem
Medulla Oblongata:
3 Groups of Nuclei
1. Autonomic nuclei:
–
control visceral activities
2. Sensory and motor nuclei:
–
of cranial nerves
3. Relay stations:
–
along sensory and motor pathways
Nuclei of
the medulla
oblongata
Summary: The Medulla Oblongata
Table 14-2
• Links cerebellum with mesencephalon,
diencephalon, cerebrum, and spinal cord
The Pons
Figure 14–6c
The Pons: 4 Groups
1. Sensory and motor nuclei of cranial
nerves V, VI, VII, VIII
2. Nuclei involved with respiration:
–
–
apneustic center and pneumotaxic
center
modify respiratory rhythmicity center
activity
The Pons: 4 Groups
3. Nuclei and tracts:
–
process and relay information to and from
cerebellum
4. Ascending, descending, and transverse
tracts:
–
transverse fibers (axons)
•
link nuclei of pons with opposite cerebellar
hemisphere
The Cerebellum
• An autonomic & motor processing center
Figure 14–7a
Functions of the Cerebellum
1. Adjusts postural muscles
2. Fine-tunes conscious and
subconscious movements
Structures of the
Cerebellum
Figure 14–7b
Structures of the
Cerebellum (1 of 2)
• Folia:
– surface of cerebellum
– highly folded neural cortex
• Anterior and posterior lobes:
– separated by primary fissure
Structures of the
Cerebellum (2 of 2)
• Cerebellar hemispheres:
– separated at midline by vermis
• Vermis:
– narrow band of cortex
• Flocculonodular lobe:
– below fourth ventricle
Summary: The Cerebellum
Table 14-3
The Mesencephalon
Figure 14–8a
Midbrain nuclei
• Substantia nigra: dopamine release, control
of subconscious muscle movents.
• Red nuclei: synapses between neurons of
cerebellum and cerebrum. Also origin of
oculomotor nerve (CN III) and trochlear
nerve (CN IV).
Some major functions mesencephalon
• Cerebral peduncles: contain motor axons
connecting cerebrum to brain stem and
sensory axons that connect medulla to
thalamus
• Tectum:
– Superior colliculi: visual reflexes, including
pupillary reflexes.
– Inferior colliculi: auditory path from ear to
thalamus.
– Startle reflex
Summary: The
Mesencephalon
Table 14-4
The Diencephalon
• The Thalamus - switch board for the
cerebrum. Includes the:
– Geniculate nuclei (part of the ventral group):
• Medial processes auditory information.
• Lateral processes visual input.
– Other ventral nuclei connect motor & sensory
areas of cortex to cerebellum & spinal cord
– Anterior & medial nuclei
• Anterior connects to limbic system & hypothalamus
• Medial connects with cortex & limbic system
The
Diencephalon
The Thalamus:
Filters ascending
sensory information for
primary sensory cortex.
Relays information
between basal nuclei and
cerebral cortex
Figure 14–9
Those
pesky
thalamic
nuclei
Fig. 14.09a-d
Fig. 14.09e
Oblique section of brain showing the
Thalamus and basal nuclei
Summary:
Thalamic
Nuclei
Table 14-5
The Hypothalamus
Functions of the hypothalamus
• ANS control
– , heart rate, respiration, sweating, digestion,
urination, stress response
• Hormones - ADH, oxytocin, GnRH et al.
• Basic emotions - rage, sex drive, fear, pain
pleasure.
• Thirst & appetite
• Temperature & sleep/wake (circadian) cycles
The Hypothalamus
• Lies below thalamus
Figure 14–10a
Summary: The Hypothalamus
Table 14-6
The Limbic System
• Is a functional grouping that:
– establishes emotional states
– links conscious functions of cerebral
cortex with autonomic functions of brain
stem
– facilitates memory storage and retrieval
The Limbic System
Figure 14–11a
The Limbic System
Figure 14–11b
Limbic System
• Structures located on the medial aspects of
cerebral hemispheres and diencephalon
• Includes the rhinencephalon, amygdala,
hypothalamus, and anterior nucleus of the
thalamus
• Parts especially important in emotions:
– Amygdala – deals with anger, danger, and fear
responses
– Cingulate gyrus – plays a role in expressing
emotions via gestures, and resolves mental
conflict
• Puts emotional responses to odors – e.g., skunks
smell bad
Limbic System: Emotion and
Cognition
• The limbic system interacts with the
prefrontal lobes, therefore:
– One can react emotionally to conscious
understandings
– One is consciously aware of emotion in
one’s life
• Hippocampal structures – convert new
information into long-term memories
Summary: The Limbic System
Table 14-7
The Cerebrum
Major divisions of the Cerebrum
• Hemispheres - left and right split down the
middle by the longitudinal fissure.
• Lobes:
– Frontal, parietal, occipital, temporal and insula
– Delineated by the sulci (singular sulcus):
• Central
• Parieto-occipital
• Lateral
Lobes of the Cerebrum
Landmarks of
the cerebrum
White Matter
of the
Cerebrum
Myelinated fibers (axons)
1. Association fibers
2. Commissural fibers
3. Projection fibers
Figure 14–13
Cerebral White Matter
The Basal Nuclei
Figure 14–14b, c
Functions of Basal Nuclei
• Are involved with:
– the subconscious control of skeletal
muscle tone
– the coordination of learned movement
patterns (walking, lifting)
Functional map of the cerebrum
Fig. 14.15
Motor and Sensory Areas of the Cortex
Figure 14–15a
Interpretive Areas of
Cortex
Figure 14–15b
Hemispheric
Lateralization
Figure 14–16
The Left Hemisphere
• In most people, left brain (dominant
hemisphere) controls:
– reading, writing, and math
– decision-making
– speech and language
The Right Hemisphere
• Right cerebral hemisphere relates to:
– senses (touch, smell, sight, taste, feel)
– recognition (faces, voice inflections)
The Electroencephalogram
Figure 14–17
Types of Brain Waves
• Alpha waves – 8 - 13 Hz, regular and rhythmic, lowamplitude, slow, synchronous waves indicating an
“idling” brain
• Beta waves – 14 - 30 Hz, rhythmic, more irregular
waves occurring during the awake and mentally
alert state
• Theta waves – 4 - 7 Hz, more irregular than alpha
waves; common in children but abnormal in adults
• Delta waves – 1 - 5 Hz, high-amplitude waves seen
in deep sleep and when reticular activating system
is damped
Brain Waves: State of the
Brain
• Brain waves change with age, sensory
stimuli, brain disease, and the chemical
state of the body
• EEGs can be used to diagnose and localize
brain lesions, tumors, infarcts, infections,
abscesses, and epileptic lesions
• A flat EEG (no electrical activity) is clinical
evidence of death
Cranial Nerves
Figure 14–18
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
On
Old
Olympus’
Towering
Top
A
Frenchman
Viewed
Greek
Villagers
At
Home
The 12
cranial
nerves
The
Olfactory
Nerve (I)
Figure 14–19
The
Optic
Nerves
(II)
Figure 14–20
The Oculomotor Nerves (III)
Figure 14–21
The Trochlear Nerves (IV)
Figure 14–21
The Abducens Nerves (VI)
Figure 14–21
The Trigeminal Nerves (V)
Figure 14–22
The Facial Nerves (VII)
Figure 14–23
The Vestibulocochlear
Nerves (VIII)
Figure 14–24
The Glossopharyngeal
Nerves (IX)
Figure 14–25
The Vagus
Nerves (X)
Figure 14–26
The Accessory Nerves (XI)
Figure 14–27
The Hypoglossal Nerves (XII)
Figure 14–27
Summary: Cranial Nerves
Table 14-9 (1 of 2)
Summary: Cranial Nerves
Table 14-9 (2 of 2)
Examples of Cranial Reflexes
Table 14-10
Clinical Stuff
• Epilepsy
• CVA & TIA
• Degenerative Diseases
– Alzheimers
– Huntington’s
– Parkinbson’s
Epilepsy
• A victim of epilepsy may lose
consciousness, fall stiffly, and have
uncontrollable jerking, characteristic of
epileptic seizure
• Epilepsy is not associated with, nor does it
cause, intellectual impairments
• Epilepsy occurs in 1% of the population
Epileptic Seizures
• Absence seizures, or petit mal – mild
seizures seen in young children where the
expression goes blank
• Grand mal seizures – victim loses
consciousness, bones are often broken due
to intense convulsions, loss of bowel and
bladder control, and severe biting of the
tongue
Control of Epilepsy
• Epilepsy can usually be controlled with
anticonvulsive drugs
• Valproic acid, a nonsedating drug, enhances
GABA and is a drug of choice
• Vagus nerve stimulators can be implanted
under the skin of the chest and can keep
electrical activity of the brain from
becoming chaotic
Cerebrovascular Accidents (Strokes)
• Caused when blood circulation to the brain is
blocked and brain tissue dies
• Most commonly caused by blockage of a cerebral
artery
• Other causes include compression of the brain by
hemorrhage or edema, and atherosclerosis
• Transient ischemic attacks (TIAs) – temporary
episodes of reversible cerebral ischemia
• Tissue plasminogen activator (TPA) is the only
approved treatment for stroke
Degenerative Brain
Disorders
• Alzheimer’s disease – a progressive
degenerative disease of the brain that
results in dementia
• Parkinson’s disease – degeneration of the
dopamine-releasing neurons of the
substantia nigra
• Huntington’s disease – a fatal hereditary
disorder caused by accumulation of the
protein huntingtin that leads to
degeneration of the basal nuclei