Download Chapter 14 The Brain and Cranial Nerves

The Brain
•  100 billion neurons
•  ~1000 trillion synapses
•  Brain functions:
•  sensations
•  memory
•  emotions
•  decision making
•  behavior
Chapter 14
The Brain and Cranial Nerves
Overview:
Organization, protection, blood supply, parts of the brain and
their functions
2
1
Synaptic terminals
Dendrites
Inhibitory
Principal Parts of the Brain
Excitatory
•  Cerebrum
•  Diencephalon
–  thalamus & hypothalamus
Cerebellum
•  Brainstem
• 
–  medulla, pons & midbrain
Myelin
sheath
Receiving
cell body
Axon
Synaptic
termini
3
4
Protective Coverings of the Brain
Blood Supply to Brain
•  Uses 20% of our bodies oxygen & glucose needs
•  Bone, meninges & fluid
•  Meninges same as
around the spinal cord
–  blood flow to an area increases with activity in that area
–  because carbohydrate storage in the brain is limited, the supply of
glucose to the brain must be continuous
–  deprivation of O2 for 4 min causes permanent damage
–  dura mater
–  arachnoid mater
–  pia mater
•  Blood-brain barrier (BBB)
–  formed by tight junctions between epithelial cells, thick basement
membrane & astrocytes covering capillaries
–  allows passage of some molecules (e.g., O2, glucose, alcohol,
anesthetics)
–  but not others (e.g., proteins, antibiotics, many drugs)
–  protects cells from some toxins and pathogens
–  injury to the brain due can cause a breakdown of the BBB
•  Dura mater extensions
–  falx cerebri
–  tentorium cerebelli
–  falx cerebelli
5
6
Ventricles
Cerebrospinal Fluid (CSF)
•  80-150 ml (3-5 oz., ½ cup)
•  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
•  There are four CSF filled cavities within the brain called ventricles
–  2 lateral ventricles, one within each cerebral hemisphere
–  third ventricle
–  fourth ventricle
•  Choroid plexus = capillaries covered by ependymal cells
–  produce CSF
7
8
THE BRAIN STEM
Medulla Oblongata
•  Medulla oblongata
•  Pons
•  Midbrain (mesencephalon)
• 
• 
• 
• 
• 
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
–  sets basic rhythm of breathing
•  Reflex centers for coughing, sneezing, swallowing, etc.
9
Medulla Oblongata
10
Pons
•  Links parts of the
brain with one
another
•  Helps control
breathing
•  Cranial nerves 5
through 7
•  Decussation (crossing over) of sensory and motor fiber tracts
–  left cortex controls right muscles
•  Hard blow to the back of the head may be fatal
•  Loss of sensation or paralysis of throat or tongue;
irregularities in breathing and heart rhythm
11
12
Dorsal Surface of Midbrain
Midbrain
•  Extends from
pons to
diencephalon
•  Cerebral
aqueduct
connects 3rd
ventricle above
to 4th ventricle
below
•  Corpora quadrigemina = superior & inferior colliculi
–  coordinate eye movements with visual stimuli
–  coordinate head movements with auditory stimuli
13
Reticular Formation
14
Cerebellum
•  Second largest part of brain
•  2 cerebellar hemispheres and
vermis (central area)
•  Function
•  Scattered nuclei in medulla, pons & midbrain
•  Reticular activating system
–  alerts cerebral cortex to sensory signals (sound of
alarm, flash light, smoke or intruder) to awaken from
sleep
–  maintains consciousness & helps keep you awake
with stimuli from ears, eyes, skin and muscles
–  correct voluntary muscle contraction
and posture based on sensory data
from body about actual movements
–  sense of equilibrium & balance
–  coordinate & regulate motor
impulses initiated in cerebrum
–  govern subconscious aspects of
skeletal muscle movements
•  Helps maintain muscle tone
15
16
Diencephalon
Thalamus
•  Serves as a relay station for all sensory impulses
(except smell) to the cerebral cortex
•  Registers crude perception of some sensations
•  Plays an essential role in awareness and the
acquisition of knowledge (cognition)
•  Thalamus
•  Hypothalamus
17
Hypothalamus
18
THE CEREBRUM
•  A major regulator of homeostasis
•  Has numerous functions:
•  Largest part of the brain
•  Cerebral cortex (surface layer) is
gray matter
–  controls the ANS
–  produces hormones
–  functions in regulation of emotional and behavioral
patterns
–  regulates hunger and thirst sensations
–  aids in controlling body temperature
–  regulates circadian rhythms and states of consciousness
–  pineal gland secretes melatonin to influence diurnal
cycles
–  Folds (gyri)
–  grooves (sulci or fissures)
•  Longitudinal fissure separates
left & right cerebral hemispheres
–  Corpus callosum is a commissure
(band of white matter) connecting
left and right cerebral hemispheres
19
20
Lobes and Fissures
Lobes
•  Longitudinal fissure
•  Central sulcus
•  Each cerebral hemisphere is further subdivided into
four lobes by sulci or fissures
–  precentral &
postcentral gyrus
–  frontal, parietal, temporal, and occipital
•  Lateral sulcus
•  A fifth part of the cerebrum, the insula, lies deep to
the parietal, frontal, and temporal lobes and cannot
be seen in an external view of the brain
21
22
Basal Ganglia
Cerebral White Matter
•  The white matter is under the cortex and consists of
myelinated axons running in three principal directions
–  Association fibers between gyri in same hemisphere
–  Commissural fibers from one hemisphere to other
–  Projection fibers form descending & ascending tracts
23
•  The basal ganglia are paired masses of gray matter
in each cerebral hemisphere
24
Limbic System
Basal Ganglia
•  Control large automatic movements of skeletal
muscles
–  Arm swinging while walking
–  Laughter
•  Damage to the basal ganglia results in tremor,
rigidity, and involuntary muscle movements
–  Parkinson s disease
•  Basal ganglia also help initiate and terminate some
cognitive processes
–  Obsessive compulsive disorder, schizophrenia & chronic
anxiety are thought to involve dysfunction of the circuits
between the basal ganglia and limbic system
•  Emotional brain -- intense pleasure & intense pain
•  Strong emotions increase efficiency of memory
•  Damage to hippocampus prevents formation of new
memories
25
26
Motor Areas of Cerebral Cortex
Sensory Areas of Cerebral Cortex
•  Motor areas are the regions that govern muscular movement
•  Sensory areas of the cerebral cortex are concerned with the reception
and interpretation of sensory impulses
–  Primary motor area = 4 = precentral gyrus
•  controls voluntary contractions of skeletal muscles on other side
–  Motor speech area = 44 = Broca s area
•  production of speech -- control of tongue & airway
Primary somatosensory area = postcentral gyrus = 1, 2, 3
Primary visual area = 17
Primary auditory area = 41 & 42
27
28
Association Areas of Cerebral Cortex
Hemispheric Lateralization
•  The two cerebral
hemispheres share many
functions
•  Each hemisphere also
performs unique
functions
•  Functional specialization
of each hemisphere is
more pronounced in men
•  Females generally have
larger connections
between 2 sides
•  Association areas are concerned with complex integrative functions
such as memory, emotions, reasoning, will, judgment, personality
traits, and intelligence
•  Visual association area = 18 & 19 (recognize & evaluate)
•  Auditory association area (Wernicke s) = 22 (words become
speech)
29
Brain Injuries
Electroencephalogram (EEG)
•  Brain waves are millions of
nerve action potentials in
cerebral cortex
–  diagnosis of brain disorders
(epilepsy)
–  brain death (absence of
activity in 2 EEGs 24 hours
apart)
• 
• 
• 
• 
30
•  Causes of damage
–  displacement or distortion of tissue at impact
–  increased intracranial pressure
–  infections
–  free radical damage after ischemia
•  Concussion -- temporary loss of consciousness
–  headache, drowsiness, confusion, lack of concentration
•  Contusion -- bruising of brain
Alpha -- awake & resting
Beta -- mental activity
Theta -- emotional stress
Delta -- deep sleep
–  brief unconsciousness
–  blood in CSF
•  Laceration -- tearing of brain (fracture or bullet)
–  increased intracranial pressure from hematoma
31
32
Cerebrovascular Accident (CVA or Stroke)
Transient Ischemic Attack (TIA)
•  The most common brain disorder
•  Third leading cause of death after heart attacks and
cancer
•  CVAs are classified into two principal types:
•  Episode of temporary cerebral dysfunction
•  Cause
–  impaired blood flow to the brain
–  ischemic (the most common type), due to a decreased
blood supply
–  hemorrhagic, due to a blood vessel in the brain that
bursts
•  Common causes of CVAs are intracerebral
hemorrhage, emboli (blood clots), and
atherosclerosis
•  Tissue plasminogen activator (t-PA) used within 3
hours of ischemic CVA onset will decrease
permanent disability
•  Symptoms
–  dizziness, slurred speech, numbness, paralysis on one
side, double vision
–  reach maximum intensity almost immediately
–  persists for 5-10 minutes & leaves no deficits
•  Treatment is aspirin or anticoagulants; artery
bypass grafting or carotid endarterectomy (removal
of plaque)
33
34
Cranial Nerves
Alzheimer Disease (AD)
•  Dementia = loss of memory, reasoning, ability to
read, write, talk, eat & walk
•  Afflicts 11% of population over 65
•  Loss of neurons in specific regions (e.g.,
hippocampus and cerebral cortex)
•  Loss of neurons that release acetylcholine
•  Twelve pairs of cranial nerves originate from the brain
–  numbered by order of attachment to the brain
•  Cranial nerves I, II, VIII contain only sensory fibers
•  Cranial nerves III, IV, VI, XI, XII are motor nerves
•  The rest (V, VII, IX, X) are mixed nerves
–  they contain both sensory and motor fibers
35
36