Transcript chapt08_lecture

Chapter 08
Lecture Outline
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I. Structural Organization of
the Brain
A.
Central Nervous System
1. Composed of the brain and spinal cord
a. Receives input from sensory neurons and
directs activity of motor neurons that innervate
muscles and glands
b. Association neurons integrate sensory
information and help direct the appropriate
response to maintain homeostasis and respond
to the environment.
Central Nervous System
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Gyrus
Sulcus
Corpus
callosum
Cerebrum
Meninges
Spinal cord
Central canal
Tentorium
cerebelli
Cerebellum
B.
Embryonic Development
1. From the ectoderm comes a groove that will
become the neural tube around 20 days after
conception. This will eventually become the CNS.
2. Between the neural tube and the developing
epidermis, a neural crest forms. This will become
PNS ganglia.
Embryonic Development of the CNS
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Neural crest
Neural groove
Neural crest
Cranial neuropore
Neural canal
Neural tube
Caudal neuropore
Neural crest
Neural groove
Neural groove
Neural crest
Waldrop
Wall of
yolk sac
Embryonic Development, cont
3. By week 4 after conception, three distinct swellings
are seen on the neural tube:
a. Prosencephalon (forebrain)
b. Mesencephalon (midbrain)
c. Rhombencephalon (hindbrain)
Embryonic Development, cont
4. By week 5, these regions differentiate into five
regions.
a. The forebrain divides into the telencephalon
and diencephalon.
b. The mesencephalon remains the midbrain
c. The hindbrain divides into the metencephalon
and myelencephalon.
5. These terms are still used to describe regions of
the adult brain.
Developmental Sequence of the Brain
Weeks 4 and 5
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Three primary vesicles
Wall
Five secondary vesicles Adult derivatives of
Walls
Cavities
Cavity
Telencephalon
Prosencephalon
(forebrain)
Mesencephalon
(midbrain)
Diencephalon
Mesencephalon
Cerebral
hemisphere
Thalamus
Hypothalamus
Lateral
ventricles
Midbrain
Aqueduct
Pons
Rhombencephalon
Metencephalon
(hindbrain)
Third
ventricle
Upper
portion
Cerebellum
Myelencephalon
Medulla
oblongata
Spinal cord
of fourth
ventricle
Lower
portion
6.
Later development
a. Telencephalon – get two cerebral hemispheres
and the two lateral ventricles (remnant of the tube)
b. Diencephalon – get the thalamus, hypothalamus,
and the third ventricle
c. Mesencephalon – get the midbrain and cerebral
aqueduct
d. Metencephalon – get the pons, cerebellum, and
upper fourth ventricle
e. Myelencephalon – get the medulla oblongata and
lower fourth ventricle
f. The posterior neural tube becomes the spinal cord
C.
Choroid plexuses and cerebrospinal fluid
1. Consists of simple cuboidal to columnar epithelium
in close association with blood capillaries
2. Project into the roofs of the ventricles
3. Secrete cerebrospinal fluid (CSF) into the
ventricles and central canal of the cord.
4. CSF is made from blood and is returned to blood
Ventricle of the Brain
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Lateral ventricle
Interventricular
foramen
Lateral ventricle
Third ventricle
Third ventricle
Interventricular
foramen
Mesencephalic
aqueduct
Mesencephalic
aqueduct
Fourth ventricle
Fourth ventricle
(a)
To central canal
of spinal cord
(b)
To central canal
of spinal cord
D.
Brain statistics
1. Gray matter forms the cortex and deep nuclei;
white matter is deep forming tracts
2. The adult brain has 100 billion neurons.
3. It weighs about 1.5 kg (3−3.5 pounds).
4. It receives 15% of the total blood flow to the body
per minute.
5. Scientists have demonstrated neurogenesis (the
formation of new brain cells from neural stem cells)
in adult brains within the subgranular zone of the
hippocampus and subventricular zone of the
lateral ventricles
II. The Cerebrum
A.
1.
2.
3.
4.
Introduction
Derived from the telencephalon
Largest portion of the brain - 80% of the mass
Responsible for higher mental functions
Consists of a right and left cerebral hemisphere
connected internally by the corpus callosum
B.
Cerebral Cortex
1. The outer region of the cerebrum composed of
2−4 mm gray matter with underlying white matter.
2. Characterized by raised folds called gyri separated
by depressed grooves called sulci; together called
convolutions
3. Each hemisphere is divided by deep sulci or
fissures into 5 lobes - Frontal , Parietal, Temporal,
Occipital, Insula
Lobes of the Cerebrum
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Precentral gyrus
Superior frontal
gyrus
Superior
frontal
sulcus
Frontal poles
Central
sulcus
Superior
frontal gyrus
Postcentral
gyrus
Parietal lobe
Central
sulcus
Frontal
lobe
Lateral sulcus
Superior
frontal
sulcus
Longitudinal
fissure
Occipital
lobe
Temporal lobe
Parietal
lobe
Cerebellar
hemisphere
Occipital poles
(a)
(b)
4.
Frontal and Parietal Lobes
a. Separated by the central sulcus
b. The precentral gyrus is located in the frontal lobe
and is responsible for motor control; neurons
called upper motor neurons
c. The postcentral gyrus is in the parietal lobe and is
responsible for somatesthetic sensation (coming
from receptors in the skin, muscles, tendons, and
joints); called the somatosensory cortex
Maps of the Precentral and Postcentral Gyri
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Central sulcus
Somatosensory cortex
Motor cortex
Thumb,
fingers,
and hand
Lower
arm
Facial
expression
Upper
arm
Upper
leg
Trunk
Lower
leg
Pelvis
Pelvis Trunk Neck
Upper
arm Lower
arm
Hand, fingers,
and thumb
Upper leg
Salivation
Vocalization
Mastication
Lower leg
Foot
and toes
Foot
and toes
Genitals
Upper
face
Lips
Teeth
and gums
Swallowing
Tongue
and pharynx
Longitudinal
fissure
Insula
Insula
Parietal lobes
Central sulcus
Motor cortex
Somatosensory cortex
Frontal lobes
(a)
(b)
5.
Temporal, Occipital, and Insula Lobes
a. Temporal lobe: auditory centers
b. Occipital lobe: vision and coordination of eye
movements
c. Insula: encoding of memory and integration of
sensory information with visceral responses;
receives olfactory, gustatory, auditory, and pain
information
Functional Regions of the Cerebrum
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Central sulcus
Primary motor cortex involved
with the control of voluntary
muscles
Somatosensory cortex for
cutaneous and
proprioceptive senses
Frontal lobe
Parietal lobe
Motor speech area
(Broca’s area)
General
interpretive area
Auditory area
Lateral sulcus
Occipital lobe
Interpretation of sensory
experiences, memory of
visual and auditory patterns
Combining visual images,
visual recognition of objects
Cerebellum
Temporal
lobe
Brain stem
Functions of the Cerebral Lobes
6.
Mirror Neurons
a. Found in frontal and parietal lobes to integrate
sensory and motor neural activity
b. Connected through the insula and cingulate gyrus
to emotion centers in the brain
c. May be involved in the ability to learn social skills
and language
d. Have been implicated in autism (autism spectrum
disorder)
7.
Visualizing the Brain
a. X-ray computed tomography (CT): looks at soft
tissue absorption of X-rays
b. Positron emission tomography (PET):
radioactively labeled fluoro-deoxyglucose
injected into the blood; emits gamma rays in
active tissues
1) Used to monitor cancer
2) Used to study brain metabolism, drug
distribution in the brain, and changes in
blood flow following activity
Visualizing the Brain, cont
c. Magnetic resonance imaging (MRI): Protons in
tissues are aligned by powerful magnets. The
chemical composition of different tissues results in
differences in proton alignment.
1) Can be amplified using MRI contrast agents
injected before imaging
2) Shows clear definition between gray matter,
white matter, and cerebrospinal fluid
Visualizing the Brain: MRI
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Lateral
ventricle
Third
ventricle
White
matter of
cerebrum
Gray
matter of
cerebrum
Courtesy of Dr. Llinas, New York University Medical Center
Visualizing the Brain, cont
d. Functional magnetic resonance imaging (fMRI):
visualizes increased neuronal activity in different
brain regions indirectly by looking at blood flow
1) Release of the neurotransmitter glutamate
increases vasodilation of blood vessels in the
area.
2) Active brain regions receive more
oxyhemoglobin; called the BOLD response for
blood oxygenation level dependent contrast
Visualizing the brain, cont
e. Magnetoencephalogram (MEG)
1) Based on magnetic fields produced by
postsynaptic currents
2) Sensors are SQUIDS – superconducting
quantum interference devices
3) More accurate than EEGs
Visualizing the Brain, cont
f. Electroencephalogram (EEG): Electrodes on the
scalp detect synaptic potentials produced by cell
bodies and dendrites in the cerebral cortex.
1) Four patterns are usually seen:
a) Alpha waves: active, relaxed brain. Seen
most in frontal and parietal lobes
b) Beta waves: produced with visual stimulation
and mental activity. Seen most in frontal
lobe
EEG, cont
c) Theta waves: seen during sleep; most from
occipital and temporal lobes
d) Delta waves: also seen in sleep, from all over the
cerebrum
EEG Wave Patterns
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Alpha
Beta
Theta
Delta
1 sec
Techniques for Visualizing Brain Function
8.
Sleep
a. May be genetically controlled, although sleep is
affected by environmental factors
b. Neurotransmitters involved
1) Histamine – wakefulness
2) Adenosine & GABA – sleep
3) Serotonin – induces REM sleep and stimulates
non-REM sleep
Sleep, cont
c. Two recognized categories:
1) REM: rapid eye movement; state when dreams
occur. Theta waves are seen here.
2) Non-REM: also called resting sleep; divided
into four stages, determined by EEG waves
seen. Stages 3 and 4 are often called slowwave sleep, characterized by delta waves.
d.
Sleep pattern
1) When people first fall asleep, they enter non-REM
sleep and progress through the four stages.
2) Next, a person ascends back up the stages of nonREM sleep to REM sleep.
3) This cycle repeats every 90 minutes, and most
people go through five per night.
4) If allowed to awaken naturally, people usually do
so during REM sleep.
5) Slow-wave is prominent in the first part of sleep,
while REM is prominent in the second half
e.
REM Sleep
1) Some brain regions are more active during REM
sleep than during the waking state.
2) The limbic system (involved in emotion) is very
active during REM sleep.
3) Breathing and heart rate may be very irregular.
4) Benefits consolidation of nondeclarative memories
f.
Non-REM Sleep
1) As you fall asleep, neurons decrease their firing
rates, decreasing blood flow and energy
metabolism.
2) Breathing and heart rate are very regular.
3) Non-REM sleep may allow repair of metabolic
damage done to cells by free radicals and allows
time for the neuroplasticity mechanisms needed to
store memories.
4) Benefits consolidation of spatial and declarative
memories
C.
Basal Nuclei
1. Masses of gray matter located deep in the white
matter of the cerebrum
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Motor cerebral cortex
Thalamus
Claustrum
Putamen
Basal nuclei
Lentiform
nucleus
Globus
pallidus
Corpus
striatum
Caudate
nucleus
Cerebellum
Spinal cord
Basal Nuclei, cont
2. Most prominent is the corpus striatum; composed
of:
a. Caudate nucleus
b. Lentiform nucleus; made up of the putamen and
the globus pallidus
3. Also includes subthalamic nucleus of the
diencephalon and substantia nigra of the midbrain
4. Degeneration of dopaminergic neurons from the
substantia nigra to the corpus striatum causes
Parkinson’s disease
5.
Motor circuit
a. The neurons from motor regions of the frontal lobe
release glutamate (stimulatory) in the putamen.
The putamen then releases GABA (inhibitory) to
other regions of the basal nuclei.
b. The globus pallidus sends GABA-releasing
(inhibitory) neurons to the thalamus, which sends
excitatory axons to the motor cortex of the
cerebrum.
c. This completes a motor circuit. This circuit
stimulates appropriate movements and inhibits
unwanted movement.
The Motor Circuit
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Glutamate neurotransmitter
(excitatory)
Caudate
Dopamine neurotransmitter
(excitatory)
Putamen
GABA neurotransmitter
(inhibitory)
Thalamus
Globus pallidus
Subthalamic
nucleus
Substantia nigra
D.
Cerebral Lateralization (Dominance)
1. Each side of the precentral gyrus controls
movements on the contralateral (opposite) side of
the body due to decussation of fibers.
2. Somatesthetic sensation from each side of the
body projects to contralateral sides of the
postcentral gyrus.
3. Communication between the sides occurs through
the corpus callosum; this is severed in severe
forms of epilepsy.
Cerebral Lateralization, cont
4. Some tasks seem to be performed better by one
side of the brain than the other.
a. Right hemisphere: visuospatial tasks,
recognizing faces, composing music,
arranging blocks, reading maps
b. Left hemisphere: Language, speech, writing,
calculations, understand music
Cerebral Lateralization
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Olfaction
Olfaction
Speech, writing
Left ear
Right ear
Simple
language
comprehension
Main language
center
Spatial
concepts
Calculation
Left visual
half
field
Right visual
half
field
Split
brain
E.
Language
1. Most of the knowledge of how the brain controls
language has come from studying people with
speech problems called aphasias.
2. Two areas are identified as important :
a. Broca’s area
b. Wernicke’s area
3.
Broca’s Area
a. Located in left inferior frontal gyrus
b. Broca’s aphasia involves slow, poorly articulated
speech. There is no impairment in understanding.
1) Interestingly, other actions of the tongue, lips,
and larynx are not affected; only the production
of speech is affected.
c. Controls motor aspects of speech
4.
Wernicke’s Area
a. Located in left superior temporal gyrus
b. Wernicke’s aphasia involves production of rapid
speech with no meaning, called “word salad.”
Language (spoken and written) comprehension is
destroyed.
c. Controls understanding of words.
d. Information about written words is sent by the
occipital lobe (visual cortex).
5.
Speech
a. To speak, word comprehension originates in
Wernicke’s area and is sent to Broca’s area along
the arcuate fasciculus.
b. Broca’s area sends information to the motor cortex
to direct movement of appropriate muscles.
Speech
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Motor cortex
(precentral gyrus)
Motor speech area
(Broca’s area)
Wernicke’s
area
6.
Angular Gyrus
a. Located at the junction between the parietal,
occipital, and temporal lobes
b. Center for integration of sensory information
c. Damage here also produces aphasias involved
in reading and writing
F.
The Limbic System
1. Group of brain regions responsible for emotional
drives
a. Areas of the cerebrum included: cingulate
gyrus, amygdala, hippocampus, septal nuclei,
anterior insula
b. The hypothalamus and thalamus (in the
diencephalon) are also part of this system
The Limbic System, cont
2. Papez circuit
a. The fornix connects the hippocampus to the
mammillary bodies of the hypothalamus,
which sends neurons to the thalamus.
b. The thalamus sends neurons to the
cingulate gyrus, which sends neurons to the
hippocampus, completing the circuit.
The Limbic System
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Corpus
callosum
Thalamus
Cingulate
gyrus
Fornix
Mammillary
body
Septal
nucleus
Amygdala
Preoptic
nucleus
Hippocampus
Olfactory bulb
Olfactory tract
Cortex of right
hemisphere
Hypothalamus
Limbic System, cont
3. Once called the rhinencephalon, or “smell brain,”
because it deals with olfaction.
4. There are few synaptic connections between the
limbic system and the cerebral cortex, which is
why it is hard to control your emotions.
Limbic System, cont
5. Emotions controlled by the limbic system:
a. Aggression: areas in the amygdala and
hypothalamus
b. Fear: amygdala and hypothalamus
c. Hunger/satiety: hypothalamus
d. Sex drive: the whole system
e. Goal-directed behaviors: hypothalamus and
other regions
G.
Memory
1. Brain areas
a. Studies of people with amnesia reveal that
areas of the temporal lobe, hippocampus,
caudate nucleus, and dorsomedial thalamus are
involved in memory.
b. The amygdala is important in learning fear
responses.
c. The prefrontal cortex may be involved in
complex problem solving and working memory–
very short-term memory.
d. Left inferior frontal lobe – mathematical
calculations
Brain areas, cont
e. Hippocampus is the critical component
1) Acquire new information
2) Consolidation of short-term memory to longterm memory
f. Inferior temporal lobe – storage of long-term visual
memories
2.
Types of Memory
a. Short-term memory: recent events; transferred to
long-term memory through process of memory
consolidation
1) Memory consolidation occurs in the medial
temporal lobe, hippocampus, and amygdala.
2) Sleep is needed for optimum memory
consolidation.
b.
Long-term memory
1) Requires actual structural change - Activation of
genes, synthesis of mRNA, production of proteins,
and formation of new synapses
2) Long-term memory can be classified into:
a) Nondeclarative (implicit): memory of simple
skills, how to do things
b) Declarative (explicit): memory of things that can
be verbalized. People with amnesia have
impaired declarative memory; further broken into:
1) Semantic: facts
2) Episodic: events
Categories of Memory
3.
Alzheimer’s Disease
a. Most common form of dementia
b. Characteristics
1) Loss of cholinergic fibers in hippocampus and
cerebral cortex
2) Accumulation of extracellular proteins called
senile plaques
3) Accumulation of intracellular proteins forming
neurofibrillary tangles
Alzheimer’s Disease, cont
c. Amyloid precursor protein (APP) is broken down
into peptides called amyloid beta (Aβ)
1) Aβ forms dimers and oligomers that join to form
the fibers in the β-pleated sheet structure that
forms the amyloid senile plaques
2) Soluble dimers and oligomers of the 42-amino
acid form of Aβ causes Alzheimer’s
3) Forms 1% of early onset Alzheimer’s have a
mutation in the APP gene or the presentlin
gene; most have “sporadic” form with
environmental and genetic interactions
Alzheimer’s Disease, cont
d. Tau protein
1) Normal tau proteins bind to and stabilize
microtubules in axons
2) In Alzheimer’s, they aggregate and become
insoluble forming the neurofibrillary tangles
3) Soluble, intermediate tau proteins are more
toxic
e.
Toxic changes in Alzheimer’s Disease
1) Loss of synapses and dendritic spines
2) Reduced LTP
3) Reduced excitotoxicity leading to neuron
apoptosis
4) Mitochondrial release of reactive oxygen
species causing oxidative stress and apoptosis
f. People with APOe4 gene have an increased
chance of developing Alzheimer’s
g.
1)
2)
3)
4)
Current treatments
Acetylcholinesterase inhibitors
Antagonists of glutamate
Drugs for depression
Many others are in clinical trials
4.
Synaptic Changes in Memory
a. Short-term memory involves a recurrent circuit
(reverberating circuit) where neurons synapse
on each other in a circle.
1) Interruption of the circuit destroys the
memory because there was no structural
change.
b. Long-term memory requires a relatively
permanent change in neuron chemical structure
and synapses.
Synaptic Changes in Memory, cont
c. Long-term potentiation (LTP) in the hippocampus
is a good example.
1) Synapses that are stimulated at a high
frequency exhibit increased excitability.
2) In these synapses, glutamate is secreted by
the presynaptic neuron.
3) The postsynaptic neuron has both AMPA and
NMDA receptors for glutamate.
4) Glutamate binds to AMPA receptor, allowing
Na+ in.
Long-term potentiation, cont
5) This depolarizes the cell and activates NMDA
receptor channels (which were inactive due to a
Mg+ blocking the pore).
6) NMDA allows Ca2+ and Na+ in.
7) The Ca2+ binds to a protein called calmodulin,
which in turn activates an enzyme called CaMKII.
8) CaMKII causes more AMPA receptors to fuse to
the plasma membrane. This alone strengthens the
synapse–it becomes more sensitive to glutamate
release (EPSP).
Long-term potentiation, cont
9) Rise in Ca2+ also causes long-term changes in
postsynaptic neurons
a) Ca2+ enters the nucleus and binds to calmodulin
b) Activates protein kinase that activates a
transcription factor called CREB (cyclic AMP
response element binding protein
c) Activates genes to produce mRNA and
proteins, including dendritic spines with AMPA
receptors inserted.
Synaptic Changes in Memory
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(a)
(b)
(both): Reprinted from Esther A. Nimchinsky, Bernardo L. Sabatini, and Karel Svoboda, “Structure and Function of Dendritic Spines,”
Annual Review of Physiology, Volume 64: 313–353 © 2002 by Annual Reviews, www.annualreviews.org
Synaptic Changes in Memory, cont
d. A retrograde messenger (likely NO) is released
into the synapse, and the presynaptic axon is
changed so that more glutamate can be released
and increase LTP
e. Endocannabinoids may lift inhibition from GABAreleasing neurons on the synapse, further
strengthening it.
Synaptic Changes in Memory
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Presynaptic axon
Glutamate
4. Increased release
of glutamate from
presynaptic axon
AMPA
receptor
Na+
Na+
Ca2+
3. Increased Na+
diffusion through
more AMPA
receptors
1. Glutamate binds to
AMPA and NMDA
receptors
NMDA
receptor
Postsynaptic membrane
of dendrite
CaMKII
Nitric
LTP
Ca2+
oxide
induction
as retrograde
messenger
2. Ca2+ goes through
NMDA receptors into
cytoplasm, activates
CaMKII
5.
Neural Stem Cells in Learning
a. Neural stem cells have been found in the
hippocampus, and scientists suspect that
neurogenesis is part of learning.
b. In mice, physical activity and an enriched
environment promote neurogenesis.
c. Aging and stress reduce neurogenesis.
H.
Emotions and Memory
1. Emotions sometimes strengthen and other times
weaken memory formation.
a. If the memory has an emotional component, the
amygdala is involved in memory formation.
b. Stress impairs memory consolidation in the
hippocampus and working memory function of
the prefrontal cortex.
c. Posttraumatic stress disorder may result in
hippocampal atrophy.
d. Memories are stored but retrieval is hindered
Emotions and Memory, cont
2. The amygdala and hippocampus have
receptors for stress hormones, such as cortisol.
a. It is thought that cortisol may strengthen
emotional memory formation via the
amygdala but weaken hippocampal memory
formation and memory retrieval.
Brain Regions Involved in Emotion
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(a)
(b)
(both): Reprinted Figure 2 (1st and 3rd panels) with permission from RJ Dolan, “Emotion, Cognition, and Behavior”
Science 298: 1191–1194. Copyright 2002 AAAS
a. Yellow = prefrontal cortex; mint green = cingulate gyrus
b. Purple = insula; mint green = cingulate gyrus; red = amygdala
3.
Prefrontal Cortex
a. Orbitofrontal region: ability to consciously
experience pleasure and reward; receives input
from all the senses and the limbic system
1) Damage here results in severe impulsive
behavior.
b. Lateral prefrontal area: motivation, sexual desire,
and cognitive functions
III. Diencephalon
A.
Introduction
1. Part of the forebrain that includes the epithalamus,
thalamus, hypothalamus, part of the pituitary
gland, and the third ventricle
2. Surrounded by the cerebral hemispheres
Diencephalon
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Intermediate mass
Corpus callosum
Choroid plexus of third ventricle
Septum pellucidum
Genu of corpus
callosum
Splenium of corpus callosum
Thalamus
Pineal body
Anterior commissure
Corpora quadrigemina
Hypothalamus
Cortex of cerebellum
Optic chiasma
Infundibulum
Arbor vitae of cerebellum
Pituitary gland
Medulla oblongata
Mammillary body
(a)
Pons
Telencephalon
Forebrain
Diencephalon
Midbrain
Hindbrain
(b)
b: © The McGraw-Hill Company, Inc./Karl Rubin, Photographer
B.
Thalamus and Epithalamus
1. Thalamus
a. Paired masses of gray matter
b. Relay center through which all sensory
information, except smell, is passed to the
cerebrum
c. Intralaminar nuclei promote a state of arousal
from sleep and alertness
2.
Epithalamus
a. Contains the choroid plexus over the third ventricle
where cerebrospinal fluid is produced
b. Also contains the pineal gland, which secretes the
hormone melatonin that helps regulate circadian
rhythms
C.
Hypothalamus and Pituitary Gland
1. Hypothalamus
a. Very important for maintaining homeostasis and
regulating the autonomic system. Contains centers for:
1) Hunger/satiety and thirst
2) Regulation of body temperature
3) Regulation of sleep and wakefulness
4) Sexual arousal and performance
5) Emotions of fear, anger, pain, and pleasure
6) Control of the endocrine system
7) Controls hormone secretion from the pituitary gland
b.
Regions of the Hypothalamus & Functions
1) Lateral region: hunger
2) Medial region: satiety
3) Preoptic-anterior: shivering, hyperventilation,
vasodilation, sweating
4) Supraoptic: produces antidiuretic hormone, which
helps control urine formation
5) Paraventricular: produces the hormone oxytocin,
which stimulates childbirth
Regions of the Hypothalamus
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Paraventricular nucleus
Dorsomedial nucleus
Posterior nucleus
Anterior nucleus
Ventromedial nucleus
Preoptic area
Mammillary body
Suprachiasmatic nucleus
Supraoptic nucleus
Median eminence
Optic chiasma
Anterior pituitary
(adenohypophysis)
Posterior pituitary
(neurohypophysis)
Pituitary gland
c.
Regulation of the Pituitary Gland
1) ADH and oxytocin are transported along the
hypothalamo-hypophyseal tract to the posterior
pituitary gland, where they are stored until needed.
2) The hypothalamus also produces releasing hormones
and inhibiting hormones that are transported along the
adenohypophysis to the anterior pituitary to regulate
the secretion of pituitary hormones.
d.
Regulation of Circadian Rhythms
1) Suprachiasmatic nuclei (SCN): contain about
20,000 “clock cells” with activity that oscillates
every 24 hours – main control of circadian rhythms
2) Entrained by information about day length via
tracts from retinal ganglion cells with the
photopigment melanopsin by way of
retinohypothalamic tracts
3) Controls the secretion of melatonin from the pineal
gland which is the major regulator of circadian
rhythms; secreted mainly at night
Regulation of Circadian Rhythms, cont
4) Circadian clock genes are found in cells of the
SCN, other brain areas, heart, liver, kidneys,
skeletal muscle, adipose tissue, and other organs
IV. Midbrain and Hindbrain
A.
Midbrain
1. Also called the mesencephalon. Includes:
a. Corpora quadrigemina
1) Superior colliculi: visual reflexes
2) Inferior colliculi: auditory reflexes
b. Cerebral peduncles: ascending and descending
tracts
c. Red nucleus: connects the cerebrum and
cerebellum; involved in motor coordination
Midbrain, cont
d. Substantia nigra: important part of the motor
circuit; part of the dopaminergic nigrostriatal
system
1) Ventral tegmental area (VTA): Part of the
dopaminergic mesolimbic system that sends
neurons to the limbic system and nucleus
accumbens in the forebrain
2) Involved in the behavioral reward system and
has been implicated in addiction and psychiatric
disturbances
Dopaminergic Pathways
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Caudate
nucleus (tail)
Corpus callosum
Putamen
Ventral
tegmental area
Substantia nigra
Caudate
nucleus
(head)
Locus ceruleus
Fourth
ventricle
Nucleus
accumbens
Corpus striatum
Mesolimbic
dopamine system
Nigrostriatal
dopamine system
Prefrontal
cortex
Cerebellum
Medial
forebrain
bundle
Pons
B.
Hindbrain
1. Introduction
a. Also called the rhombencephalon
b. Composed of the metencephalon and
myelencephalon
2.
Metencephalon
a. Composed of the pons and cerebellum
b. The pons houses sensory and motor tracts
heading from/to the spinal cord.
1) The trigeminal, abducens, facial, and
vestibulocochlear nerves arise from the pons
2) Two respiratory control centers are found here:
a) Apneustic
b) Pneumotaxic
3) Surface fibers connect to the cerebellum
c.
Cerebellum
1) Second largest brain structure; gray matter
outside, white matter inside
2) Receives input from proprioceptors in joints,
tendons, and muscles
3) Works with the basal nuclei and motor cortex to
coordinate movement
a) Fibers from the cerebellum pass through the
red nucleus to the thalamus and then to the
motor cortex
Cerebellum, cont
4) The cerebellum is needed for motor learning and
the proper timing and force required to move limbs
in a specific task.
5) The cerebellum influences motor coordination
through inhibition on the motor cortex from
Purkinje cells.
6) May have roles in acquisition of sensory data,
memory, emotion, and other higher functions
3.
Myelencephalon
a) Made up of the medulla oblongata
b) All ascending and descending tracts between
the brain and spinal cord pass through the
medulla.
1) Tracts cross sides in the pyramids.
2) Cranial nerves VIII, IX, X, XI, and XII come
off the medulla.
Medulla Oblongata, cont
c) Contains nuclei required for regulation of
breathing and cardiovascular response = vital
centers
1) Vasomotor center controls blood vessel
diameter.
2) Cardiac control center controls heart rate.
3) Respiratory center works with areas in the
pons to control breathing.
Respiratory Control Centers in the Brain Stem
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Midbrain
Pons
Brain stem
respiratory
centers
Pneumotaxic area
Apneustic area
Rhythmicity area
Reticular formation
Medulla oblongata
C.
Reticular Activating System
1. To fall asleep, we must tune out sensory stimuli.
When awake, we are alert to sensory stimuli.
2. This depends on the activation and inhibition of
the reticular activating system (RAS).
a. Includes the pons and reticular formation of
the midbrain
Structures of the RAS
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Thalamus
Hypothalamus
Pons
Medulla
Cerebellum
Brainstem
Reticular Activating System, cont
3. Arousal from sleep and alertness:
a. Neurons from the pons release ACh on the
thalamus. This enhances passing of sensory
information to the cerebral cortex.
b. Neurons from the hypothalamus and basal
forebrain release monoamines onto the
cerebrum, further enhancing alertness.
c. Neurons from the lateral hypothalamic area
release arousing polypeptide hormones, orexin
and hypocretin-1
1) Loss of these neurons leads to narcolepsy.
Reticular Activating System, cont
4. Sleep
a. Neurons from the ventrolateral preoptic nucleus
(VLPO) of the hypothalamus release GABA into
other areas of the RAS.
b. This inhibits the RAS and allows sleep.
c. This activity is increased with depth of sleep.
5. Many drugs act on the RAS to promote either
sleep or wakefulness
V. Spinal Cord Tracts
A.
Introduction
1. The spinal cord is composed of white matter
surrounding a gray matter core
a. The gray matter is arranged with a left and right
dorsal horn and a left and right ventral horn.
Introduction, cont
2. The white matter is composed of ascending and
descending fiber tracts.
a. Arranged into six columns called funiculi
b. Ascending tracts carry sensory impulses and
are given the prefix spino- with a suffix that
indicates the brain region it synapses on; ex –
lateral spinothalamic tract
c. Descending tracts carry motor impulses and are
given the suffix -spinal, and the prefix indicates
the brain region they come from; ex – anterior
corticospinal tract
B.
Ascending Tracts
1. Convey sensory information from receptors in the
skin, muscles, joints, and organs
2. Crossover of tracts (decussation) may occur in the
spinal cord or in the medulla. This means that the
origin of the input and the brain area are
contralateral.
Ascending Tracts
Ascending Tracts
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Postcentral gyrus
Axons of
third-order
neurons
Thalamus
Cerebral
cortex
Medial lemniscal tract
(axons of second-order
neurons)
Medulla oblongata
Fasciculus cuneatus
(axons of first-order
sensory neurons)
Lateral spinothalamic tract
(axons of second-order neurons)
Joint stretch receptor
(proprioceptor)
Pain receptor
Spinal cord
Axons of first-order
neurons (not part of
spinothalamic tract)
Fasciculus gracilis
(axons of first-order
sensory neurons)
Temperature
receptor
(a)
Touch receptor
(b)
C.
Descending Tracts
1. Two major groups:
a. Corticospinal or pyramidal: descend directly without
synaptic interruption from the cerebral cortex to the
spinal cord
1) Cell bodies of these neurons are located in the
precentral gyrus (Primary motor cortex) and superior
frontal gyrus (Supplementary motor complex).
2) 80−90% cross in the medulla pyramids and descend
as lateral corticospinal tracts.
3) Those that do not cross in the medulla, descend as
anterior corticospinal tracts and cross in the spinal
cord at the level that the nerves leave the cord.
Descending Motor Tracts
Descending Pyramidal Tracts
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Primary motor
area of cerebral
cortex
Internal
capsule
Thalamus
Medulla
oblongata
Pyramid
Anterior
corticospinal
tract
Lateral
corticospinal
tract
Cervical
spinal
cord
Lumbar
spinal
cord
Skeletal
muscle
Descending Tracts, cont
b. Extrapyramidal tracts: originate in the brain
stem and are controlled by the motor circuits of
the corpus striatum, substantia nigra, and
thalamus
1) Symptoms of Parkinson disease reveal the
importance of these tracts for initiating body
movements, maintaining posture, and
controlling facial expression.
Extrapyramidal Tracts, cont
2) Reticulospinal tracts are the major descending
extrapyramidal tracts.
3) These originate in the reticular formation of the
brain stem. This area is stimulated or inhibited by
neurons from the cerebellum, basal nuclei, and
cerebrum.
4) Vestibulospinal tracts arise from the vestibular
nuclei in the medulla oblongata
5) Rubrospinal tracts arise from the red nuclei.
Higher Motor Neuron Control of Skeletal Muscles
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Cerebral cortex
Cerebellum
Red nucleus
Vestibular nucleus
Lower motor neurons
Vestibulospinal
tract
Brain stem
reticular
formation
Rubrospinal
tract
Basal nuclei
Reticulospinal
tract
Pyramidal (corticospinal) tracts
Thalamus
VI. Cranial and Spinal Nerves
A.
1.
2.
3.
4.
Cranial Nerves
Part of the PNS
Nerves that arise directly from nuclei in the brain
Twelve pairs
Most are mixed nerves with both sensory and
motor neurons (somatic and parasympathetic)
5. Those associated with vision, olfaction, and
hearing are sensory only and have their cell bodies
in ganglia located near the sensory organ.
Cranial Nerves
B.
Spinal Nerves
1. Part of the PNS
2. Nerves that arise directly from the spinal cord
3. 31 pairs: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral,
1 coccygeal
4. All are mixed nerves that separate near the spinal
cord into a dorsal root carrying sensory fibers and
a ventral root carrying motor fibers.
a. The dorsal root ganglion houses the sensory
neuron cell bodies.
b. Motor neuron cell bodies are in the ventral gray
horns
Distribution of Spinal Nerves
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Cranial nerves
(12 pairs)
Cervical plexus
Brachial plexus
Cervical
(8 pairs)
Thoracic
(12 pairs)
Spinal
nerves
Lumbar plexus
Sacral plexus
Some peripheral
nerves:
Ulnar
Median
Radial
Femoral
Lateral femoral
cutaneous
Sciatic
Lumbar
(5 pairs)
Sacral
(5 pairs)
Coccygeal
(1 pair)
C.
Reflex arc
1. Unconscious motor response to a sensory
stimulus
2. Parts of an arc
a. Sensory receptor
b. Sensory neuron
c. Association neuron in CNS
d. Motor neuron
e. Effector – muscle or gland that responds
3.
Types of arcs
a. Somatic reflex – effectors are skeletal muscles
b. Autonomic reflex – effectors are smooth muscle,
cardiac muscle, or glands
Reflex Arc
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Upper motor neuron
(association neuron
in brain)
Dorsal root
ganglion
Cell body
of neuron
Dorsal
root
Sensory
neuron
Somatic
motor neuron
Spinal
nerve
Association neuron
Spinal cord
Ventral
root
Skeletal muscle