Transcript Slide 1

Diencephalon
• Three paired structures
– Thalamus
– Hypothalamus
– Epithalamus
• Encloses the third ventricle
Cerebral hemisphere
Septum pellucidum
Interthalamic
adhesion
(intermediate
mass of
thalamus)
Interventricular
foramen
Anterior
commissure
Hypothalamus
Optic chiasma
Pituitary gland
Mammillary body
Pons
Medulla oblongata
Corpus callosum
Fornix
Choroid plexus
Thalamus
(encloses third
ventricle)
Posterior commissure
Pineal gland
(part of epithalamus)
Corpora
quadrigemina MidCerebral
brain
aqueduct
Arbor vitae (of
cerebellum)
Fourth ventricle
Choroid plexus
Cerebellum
Spinal cord
Figure 12.12
Thalamus
• 80% of diencephalon
• Superolateral walls of the third ventricle
• Connected by the interthalamic adhesion
(intermediate mass)
• Contains several nuclei, named for their
location
• Nuclei project and receive fibers from the
cerebral cortex
Thalamic Function
• Gateway to the cerebral cortex
• Sorts, edits, and relays information
– Afferent impulses from all senses and all parts of the
body
– Impulses from the hypothalamus for regulation of
emotion and visceral function
– Impulses from the cerebellum and basal nuclei to help
direct the motor cortices
• Mediates sensation, motor activities, cortical
arousal, learning, and memory
Hypothalamus
• Forms the inferolateral walls of the third
ventricle
• Contains many nuclei
– Example: mammillary bodies
• Paired anterior nuclei
• Olfactory relay stations
• Infundibulum—stalk that connects to the
pituitary gland
Hypothalamic Function
• Autonomic control center for many visceral
functions (e.g., blood pressure, rate and
force of heartbeat, digestive tract motility)
• Center for emotional response: Involved in
perception of pleasure, fear, and rage and
in biological rhythms and drives
Hypothalamic Function
• Regulates body temperature, food intake,
water balance, and thirst
• Regulates sleep and the sleep cycle
• Controls release of hormones by the
anterior pituitary
• Produces posterior pituitary hormones
Epithalamus
• Most dorsal portion of the diencephalon;
forms roof of the third ventricle
• Pineal gland—extends from the posterior
border and secretes melatonin
– Melatonin—helps regulate sleep-wake cycles
Cerebral hemisphere
Septum pellucidum
Interthalamic
adhesion
(intermediate
mass of
thalamus)
Interventricular
foramen
Anterior
commissure
Hypothalamus
Optic chiasma
Pituitary gland
Mammillary body
Pons
Medulla oblongata
Corpus callosum
Fornix
Choroid plexus
Thalamus
(encloses third
ventricle)
Posterior commissure
Pineal gland
(part of epithalamus)
Corpora
quadrigemina MidCerebral
brain
aqueduct
Arbor vitae (of
cerebellum)
Fourth ventricle
Choroid plexus
Cerebellum
Spinal cord
Figure 12.12
Brain Stem
• Three regions
– Midbrain
– Pons
– Medulla oblongata
Brain Stem
• Similar structure to spinal cord but contains
embedded nuclei
• Controls automatic behaviors necessary for
survival
• Contains fiber tracts connecting higher and
lower neural centers
• Associated with 10 of the 12 pairs of
cranial nerves
Frontal lobe
Olfactory bulb
(synapse point of
cranial nerve I)
Optic chiasma
Optic nerve (II)
Optic tract
Mammillary body
Midbrain
Pons
Temporal lobe
Medulla
oblongata
Cerebellum
Spinal cord
Figure 12.14
View (a)
Optic chiasma
Optic nerve (II)
Crus cerebri of
cerebral peduncles
(midbrain)
Diencephalon
• Thalamus
• Hypothalamus
Mammillary body
Thalamus
Hypothalamus
Diencephalon
Midbrain
Oculomotor nerve (III)
Trochlear nerve (IV)
Pons
Brainstem
Medulla
oblongata
Trigeminal nerve (V)
Pons
Facial nerve (VII)
Middle cerebellar
peduncle
Abducens nerve (VI)
Vestibulocochlear
nerve (VIII)
Pyramid
Glossopharyngeal nerve (IX)
Hypoglossal nerve (XII)
Vagus nerve (X)
Ventral root of first
cervical nerve
Decussation of pyramids
Accessory nerve (XI)
Spinal cord
(a) Ventral view
Figure 12.15a
Crus cerebri of
cerebral peduncles
(midbrain)
Thalamus
View (b)
Infundibulum
Pituitary gland
Superior colliculus
Inferior colliculus
Trochlear nerve (IV)
Trigeminal nerve (V)
Pons
Superior cerebellar peduncle
Middle cerebellar peduncle
Facial nerve (VII)
Abducens nerve (VI)
Glossopharyngeal nerve (IX)
Hypoglossal nerve (XII)
Inferior cerebellar peduncle
Vestibulocochlear nerve (VIII)
Olive
Thalamus
Vagus nerve (X)
Hypothalamus
Diencephalon
Midbrain
Accessory nerve (XI)
Pons
Brainstem
Medulla
oblongata
(b) Left lateral view
Figure 12.15b
Thalamus
View (c)
Diencephalon
Pineal gland
Anterior wall of
fourth ventricle
Choroid plexus
(fourth ventricle)
Dorsal median sulcus
Dorsal root of
first cervical nerve
Midbrain
• Superior
Corpora
colliculus quadrigemina
• Inferior
of tectum
colliculus
• Trochlear nerve (IV)
• Superior cerebellar peduncle
Pons
• Middle cerebellar peduncle
Medulla oblongata
• Inferior cerebellar peduncle
• Facial nerve (VII)
• Vestibulocochlear nerve (VIII)
• Glossopharyngeal nerve (IX)
• Vagus nerve (X)
• Accessory nerve (XI)
Thalamus
Hypothalamus
Midbrain
Pons
(c) Dorsal view
Diencephalon
Brainstem
Medulla
oblongata
Figure 12.15c
Midbrain
• Located between the diencephalon and the
pons
• Cerebral peduncles
– Contain pyramidal motor tracts
• Cerebral aqueduct
– Channel between third and fourth ventricles
Pons
• Forms part of the anterior wall of the fourth
ventricle
• Fibers of the pons
– Connect higher brain centers and the spinal cord
– Relay impulses between the motor cortex and the
cerebellum
• Origin of cranial nerves V (trigeminal), VI
(abducens), and VII (facial)
• Some nuclei of the reticular formation
• Nuclei that help maintain normal rhythm of
breathing
Medulla Oblongata
• Joins spinal cord at foramen magnum
• Forms part of the ventral wall of the fourth
ventricle
• Contains a choroid plexus of the fourth
ventricle
• Pyramids—two ventral longitudinal ridges
formed by pyramidal tracts
• Decussation of the pyramids—crossover of
the corticospinal tracts
Medulla Oblongata
• Respiratory centers
– Generate respiratory rhythm
– Control rate and depth of breathing, with
pontine centers
Medulla Oblongata
• Additional centers regulate
– Vomiting
– Hiccuping
– Swallowing
– Coughing
– Sneezing
The Cerebellum
• 11% of brain mass
• Dorsal to the pons and medulla
• Subconsciously provides precise timing
and appropriate patterns of skeletal muscle
contraction
Anatomy of the Cerebellum
• Two hemispheres connected by vermis
• Each hemisphere has three lobes
– Anterior, posterior, and flocculonodular
• Folia—transversely oriented gyri
• Arbor vitae—distinctive treelike pattern of
the cerebellar white matter
Anterior lobe
Cerebellar cortex
Arbor
vitae
Cerebellar
peduncles
• Superior
• Middle
• Inferior
Medulla
oblongata
(b)
Flocculonodular
lobe
Posterior
lobe
Choroid
plexus of
fourth
ventricle
Figure 12.17b
Anterior
lobe
Posterior
lobe
(d)
Vermis
Figure 12.17d
Cerebellar Peduncles
• All fibers in the cerebellum are ipsilateral
• Three paired fiber tracts connect the
cerebellum to the brain stem
– Superior peduncles connect the cerebellum to
the midbrain
– Middle peduncles connect the pons to the
cerebellum
– Inferior peduncles connect the medulla to the
cerebellum
Cerebellar Processing for Motor
Activity
• Cerebellum receives impulses from the cerebral
cortex of the intent to initiate voluntary muscle
contraction
• Signals from proprioceptors and visual and
equilibrium pathways continuously “inform” the
cerebellum of the body’s position and momentum
• Cerebellar cortex calculates the best way to
smoothly coordinate a muscle contraction
• A “blueprint” of coordinated movement is sent to
the cerebral motor cortex and to brain stem
nuclei
Cognitive Function of the
Cerebellum
• Recognizes and predicts sequences of
events during complex movements
• Plays a role in nonmotor functions such as
word association and puzzle solving
Functional Brain Systems
• Networks of neurons that work together
and span wide areas of the brain
– Limbic system
– Reticular formation
Limbic System
• Structures on the medial aspects of
cerebral hemispheres and diencephalon
• Includes parts of the diencephalon and
some cerebral structures that encircle the
brain stem
Septum pellucidum
Diencephalic structures
of the limbic system
•Anterior thalamic
nuclei (flanking
3rd ventricle)
•Hypothalamus
•Mammillary
body
Olfactory bulb
Corpus callosum
Fiber tracts
connecting limbic
system structures
•Fornix
•Anterior commissure
Cerebral structures of the
limbic system
•Cingulate gyrus
•Septal nuclei
•Amygdala
•Hippocampus
•Dentate gyrus
•Parahippocampal
gyrus
Figure 12.18
Limbic System
• Emotional or affective brain
– Amygdala—recognizes angry or fearful facial
expressions, assesses danger, and elicits the
fear response
– Cingulate gyrus—plays a role in expressing
emotions via gestures, and resolves mental
conflict
• Puts emotional responses to odors
– Example: skunks smell bad
Limbic System: Emotion and
Cognition
• The limbic system interacts with the
prefrontal lobes, therefore:
– We can react emotionally to things we
consciously understand to be happening
– We are consciously aware of emotional
richness in our lives
• Hippocampus and amygdala—play a role
in memory
Reticular Formation
• Three broad columns along the length of
the brain stem
– Raphe nuclei
– Medial (large cell) group of nuclei
– Lateral (small cell) group of nuclei
• Has far-flung axonal connections with
hypothalamus, thalamus, cerebral cortex,
cerebellum, and spinal cord
Reticular Formation: RAS and
Motor Function
• RAS (reticular activating system)
– Sends impulses to the cerebral cortex to keep
it conscious and alert
– Filters out repetitive and weak stimuli (~99% of
all stimuli!)
– Severe injury results in permanent
unconsciousness (coma)
Reticular Formation: RAS and
Motor Function
• Motor function
– Helps control coarse limb movements
– Reticular autonomic centers regulate visceral
motor functions
• Vasomotor
• Cardiac
• Respiratory centers
Radiations
to cerebral
cortex
Visual
impulses
Auditory
impulses
Reticular formation
Ascending general
sensory tracts
(touch, pain, temperature)
Descending
motor projections
to spinal cord
Figure 12.19
Brain Waves
• Patterns of neuronal electrical activity
• Generated by synaptic activity in the cortex
• Each person’s brain waves are unique
• Can be grouped into four classes based on
frequency measured as Hertz (Hz)
Types of Brain Waves
• Alpha waves (8–13 Hz)—regular and rhythmic,
low-amplitude, synchronous waves indicating an
“idling” brain
• Beta waves (14–30 Hz)—rhythmic, less regular
waves occurring when mentally alert
• Theta waves (4–7 Hz)—more irregular; common
in children and uncommon in adults
• Delta waves (4 Hz or less)—high-amplitude
waves seen in deep sleep and when reticular
activating system is damped, or during
anesthesia; may indicate brain damage
Consciousness
• Conscious perception of sensation
• Voluntary initiation and control of
movement
• Capabilities associated with higher mental
processing (memory, logic, judgment, etc.)
• Loss of consciousness (e.g., fainting or
syncopy) is a signal that brain function is
impaired
Consciousness
• Clinically defined on a continuum that
grades behavior in response to stimuli
– Alertness
– Drowsiness (lethargy)
– Stupor
– Coma
Sleep
• State of partial unconsciousness from
which a person can be aroused by
stimulation
• Two major types of sleep (defined by EEG
patterns)
– Nonrapid eye movement (NREM)
– Rapid eye movement (REM)
Sleep
• First two stages of NREM occur during the
first 30–45 minutes of sleep
• Fourth stage is achieved in about 90
minutes, and then REM sleep begins
abruptly
Importance of Sleep
• Slow-wave sleep (NREM stages 3 and 4) is
presumed to be the restorative stage
• People deprived of REM sleep become moody
and depressed
• REM sleep may be a reverse learning process
where superfluous information is purged from the
brain
• Daily sleep requirements decline with age
• Stage 4 sleep declines steadily and may
disappear after age 60
Language
• Language implementation system
– Basal nuclei
– Broca’s area and Wernicke’s area (in the
association cortex on the left side)
– Analyzes incoming word sounds
– Produces outgoing word sounds and grammatical
structures
• Corresponding areas on the right side are
involved with nonverbal language components
Memory
• Storage and retrieval of information
• Two stages of storage
– Short-term memory (STM, or working
memory)—temporary holding of information;
limited to seven or eight pieces of information
– Long-term memory (LTM) has limitless
capacity
Outside stimuli
General and special sensory receptors
Afferent inputs
Temporary storage
(buffer) in
cerebral cortex
Automatic
memory
Data permanently
lost
Data selected
for transfer
Short-term
memory (STM)
Forget
Forget
Data transfer
influenced by:
Retrieval
Excitement
Rehearsal
Association of
old and new data
Long-term
memory
(LTM)
Data unretrievable
Figure 12.22
Transfer from STM to LTM
• Factors that affect transfer from STM to
LTM
– Emotional state—best if alert, motivated,
surprised, and aroused
– Rehearsal—repetition and practice
– Association—tying new information with old
memories
– Automatic memory—subconscious information
stored in LTM
Categories of Memory
1. Declarative memory (factual knowledge)
– Explicit information
– Related to our conscious thoughts and our
language ability
– Stored in LTM with context in which it was
learned
Categories of Memory
2. Nondeclarative memory
– Less conscious or unconscious
– Acquired through experience and repetition
– Best remembered by doing; hard to unlearn
– Includes procedural (skills) memory, motor
memory, and emotional memory
Brain Structures Involved in
Declarative Memory
• Hippocampus and surrounding temporal
lobes function in consolidation and access
to memory
• ACh from basal forebrain is necessary for
memory formation and retrieval