Transcript Brain Physiology PPT

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There are four major
parts of the brain:
 The most “primitive”
part of the brain is
the brainstem
 The diencephalon is
an “outgrowth” of the
brainstem
 The cerebellum
coordinates complex
movements
 The cerebrum is the
“newest” part of the
brain, and is involved
in “higher” brain
function
The Brain
Comparative Physiology:
The Vertebrate Brain
Protective Mechanisms of the Brain
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The brain is covered
by the same three
meninges as the
spinal cord:
 Dura mater
 Arachnoid mater
 Pia mater
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Extensions of the
dura mater separate
parts of the brain:
 The falx cerebri separates the two cerebral hemispheres
 The falx cerebelli separates the two cerebellar
hemispheres
 The tentorium cerebelli separates the cerebrum and the
cerebellum
Protective Mechanisms of the Brain
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The blood brain barrier (BBB)
prevents substances in the blood
from entering the brain
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It consists in part of tight
junctions in endothelial cells of
capillaries, and a thick basement
membrane
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It also consists of processes of
astrocytes which press up
against the endothelial cells
• Glucose crosses the BBB by special transport
• Most water soluble substances cannot cross the BBB
• Most lipid soluble substances can cross the BBB
Cerebrospinal Fluid (CSF) and Ventricles
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CSF protects the brain,
and carries O2, glucose,
and ions
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CSF circulates
continuously in the
subarachnoid space of
the brain and spinal cord
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CSF fills cavities called
ventricles:
 Lateral ventricles (separated by the septum pellucidum)
 3rd ventricle (between halves of thalamus)
 4th ventricle (between brain stem and cerebellum)
• CSF is generated in the choroid plexuses
• CSF is reabsorbed into the blood through the arachnoid villi
Structures of the Brainstem
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The medulla oblongata is
continuous with the spinal
cord
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It regulates heart rate,
blood vessel diameter, and
breathing
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It controls several survival
oriented reflexes for
vomiting, coughing,
hiccuping, sneezing, and
swallowing
• It contains the pyramids and the olives
 ~90% of the descending corticospinal tracts cross in the pyramids
 This is known as the decussation of the pyramids
 The inferior olivary nuclei convey proprioceptive information
 The medulla contains nuclei for cranial nerves VIII - XII
Structures of the Brainstem
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The pons is the “bridge”
between the brain stem and the
cerebellum
 The pneumotaxic and apneustic
areas help regulate breathing
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The pons contains nuclei for
cranial nerves V - VIII
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The midbrain lies between the
pons and the diencephalon
 The tectum consists of the superior and inferior colliculi
 The superior colliculi function as visual reflex and tracking centers
 The inferior colliculi function as auditory reflex and transmission centers
 The cerebral aqueduct passes through the midbrain, connecting the 3rd and 4th
ventricles
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Structures of the Brainstem
The midbrain also contains the
substantia nigra:
 So named because of its dark
color
 Dopaminergic neurons send
axons into the putamen and
caudate nuclei
 Degeneration of these neurons
leads to Parkinson’s disease
• The midbrain also contains the red nuclei
 Once again named for their color
 Cell bodies for the rubrospinal tract, function with the cerebellum to coordinate
movements
• The midbrain contains nuclei for cranial nerves III and IV
• The ascending reticular activation system (ARAS) helps regulate sleep and
wakefulness
Structures of the Diencephalon
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The diencephalon lies superior to
the brain stem
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The thalamus is the relay station,
switchboard, or network router of
the brain
 It routes incoming sensory
information to the appropriate
locations in the cerebrum
 Involved in crude pain, temperature,
and pressure sensations
• The pineal gland releases melatonin, an indoleamine related to serotonin,
which is involved in regulating sleep
• The habenular nuclei (not shown) are involved in olfaction and emotional
responses to smell
Structures of the Diencephalon
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The hypothalamus lies
inferior to the thalamus
 Involved in the 4 F’s
 Major regulator of
homeostasis
 Monitors blood glucose,
blood pressure, and
many hormones
 Controls the ANS
 Controls circadian
rhythms
• The pituitary gland is connected to the hypothalamus by the infundibulum
• The posterior pituitary is an extension of the hypothalamus, the anterior
pituitary is the “master gland” of the endocrine system
• The pituitary is situated in the hypophyseal fossa of the sella turcica
The Cerebellum
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Posterior to the pons
and medulla
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Second largest
structure in the brain
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Accounts for only 10%
of the brain’s mass, but
50% of the neurons
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Connected to the brain
stem by the cerebellar
peduncles
• Sends feedback signals to the motor cortex to regulate balance and posture
• Monitors and coordinates complex skilled movements, such as speaking,
dancing, juggling, riding a bicycle, skipping, flipping a pancake, playing a
musical instrument, hitting a baseball, playing a video game, skating, etc.
• The cerebellum is one of the first brain structures affected by alcohol
The Cerebrum: Lobes
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Involved in
cognition, memory,
learning, problem
solving, and “higher
functions”
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Divided into two
lateral hemispheres
connected by the
corpus callosum
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Divided into 4 lobes:
 The frontal lobe is involved in planning, organizing, personality, attention, speech,
movement (motor cortex), emotions, problem solving, and more.
 The occipital lobe is the primary visual center of the brain
 The parietal lobe includes the sensory cortex and association cortex
 The temporal lobe is involved in auditory and visual processing, and memory
• Deep folds of the cerebrum, not seen from the surface, are called insula
The Cerebrum: Basal Ganglia
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Three nuclei deep within the
cerebral hemisphere
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Globus pallidus and putamen
together known as the
lentiform nucleus
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Together with caudate
nucleus known as the corpus
striatum
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Linked to substantia nigra
and subthalamic nuclei
• Regulate muscle tone and subconscious movements
• Involved in the initiation and termination of movement
• Axons from the substantia nigra synapse with neurons in the caudate nucleus
• Degeneration of these neurons lead to Parkinson’s Disease
The Cerebrum: Basal Ganglia
• Parkinson’s patients often have a stooped posture, rigid limbs, and a fixed facial
expression
• They walk with an unsteady, shuffling gait (the “Parkinson’s shuffle”), and have little
arm swing
The Cerebrum: Famous Parkinson’s Patients
The Cerebrum: White Matter
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The corpus callosum is the
largest fiber bundle in the
brain, with ~300 million
fibers
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The corpus callosum,
anterior commissure, and
posterior commissure
connect the two
hemispheres of the
cerebrum
• In the past, some patients who had various forms of epilepsy underwent a cerebral
commissurotomy, which severed the corpus callosum
• This was sometimes knows as “split brain” surgery, because patients experienced a
dissociation of the left and right sides of their brains
• This created peculiar problems for some patients in which one side of the brain
seemed not to know what the other side of the brain was doing
The Cerebrum: Split Brain Phenomenon
• In one type of procedure, split
brain patients were shown two
words, each visible to only one
visual field
• A group of objects, including
the objects corresponding to
the two words, were placed
behind a screen, out of view of
the patient
• The patient could grab the
objects with the left hand
• When asked to speak the word that was seen, the patient responded only with
the word which registered in the left hemisphere
• When asked to grab the object named by the word, the patient grabbed the
object corresponding to the word which registered in the right hemisphere
The Cerebrum: Limbic System
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A group of diverse
structures
implicated in
emotions and
memory formation
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Also involved in
sensations of
pleasure and pain
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Includes the dentate gyrus, parahippocampal gyrus, amygdala, septal
nuclei, mammilary bodies, olfactory bulbs, fornix, and hippocampus
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Damage to the hippocampus and amygdala may result in the inability
to form new memories
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This may result from physical injury, or from chemical injury (e.g.
Korsakoff’s Syndrome)
The Cerebrum: Sensory & Motor Cortex
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Incoming sensory signals
register in the primary
somatosensory cortex on
the postcentral gyrus
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Outgoing motor signals
arise from the primary
motor cortex on the
precentral gyrus
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A representation of the
body can be “mapped”
onto these cortexes
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This representation is known as a homunculus (“little man”)
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Areas such as the face and hands have disproportionately large
representations, while regions such as the back have disproportionately small
representations
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Larger area means more neurons devoted to that region, and so more
sensitivity & control
The Cerebrum: The Homunculus
The Cerebrum: Speech Areas
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Speech areas are usually
located in the left hemisphere
of the cerebrum
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Broca’s area is located in the
frontal lobe, and is associated
with the primary motor cortex
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Wernicke’s area is located in
the temporal and parietal lobes,
and is associated with other
auditory processing areas
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Broca’s area is involved in the production of speech, Wernicke’s area is
involved in speech comprehension
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Damage to Broca’s area may result in the inability to form complete sentences
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Damage to Wernicke’s area may result in the inability to understand what is
being said
An Overview of Memory
Memory
Long Term
(“permanent”)
Declarative
(Explicit)
(facts & events)
Semantic
(facts)
e.g. Who is
George Washington?
Short Term
(last 30 sec)
Procedural (Implicit)
(skills)
e.g. Knowing how to
ride a bicycle
Episodic
(events)
e.g. What did I have
for dinner yesterday?
Did you have dinner last night
with George Washington, the
first President of the United
States?
Where Is The Following Information Stored?
1. Where you left your car keys.
2. How to make your bed.
3. The meaning of the word beautiful.
4. The capital of North Carolina.
5. How to throw a curve ball.
6. When Columbus “discovered” America.
7. Your best friend in fifth grade.
8. How to drive a manual transmission.
9. Where you went on your first date.
10. When World War II ended.
A Review of Memory
Amnesia in the Movies
No short term memory???
Amnesia Humor
Amnesia Definitions
• Amnesia is the loss of
memory, the inability
to remember past
events
• In many cases,
amnesia centers
around a traumatic
event
• Retrograde amnesia is
the inability to
remember events
before the trauma
• Anterograde amnesia
is the inability to
remember events
after the trauma
Types of Amnesia
• Based on its source, amnesia can be divided into two types: organic and
psychogenic
• Organic amnesia results from some sort of physical trauma to the brain:
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Head injury
Drug toxicity
Alcohol blackout
Disease (e.g. epilepsy, encephalitis, Alzheimer’s, etc.)
ECT (electroconvulsive therapy)
Hypoglycemia
• Psychogenic amnesia results from some
sort of psychological trauma:
 War, violent crime, etc.
 Depression
 Embarrassment, public offense, etc.
• Amnesia can be transient or persistent
Types of Amnesia
• Neither type of amnesia typically affects procedural memory
 Victims can still drive a car, ride a bicycle, play a musical instrument, etc.
• Both types of amnesia may have effects on episodic and semantic memory, but they
are characteristically different
 Organic amnesia
 Most victims still know who they are
 Victims usually have continuous and systematic
gaps in episodic memory
 Psychogenic amnesia
 Victims often don’t know who they are
 Victims have selective gaps in episodic memory
• Most “movie” amnesia doesn’t exist
• Many organic amnesia victims confabulate
• Anterograde amnesia is an encoding problem, typically involving the limbic system,
particularly the hippocampus
 Information is unable to pass from short term memory into long term memory
 The memory is not forgotten, it is in fact never even formed