Diencephalon

• Three paired structures– Thalamus– Hypothalamus– Epithalamus

• Encloses the third ventricle

Figure 12.12

Corpus callosum

Choroid plexusThalamus(encloses third ventricle)

Pineal gland(part of epithalamus)

Posterior commissure

CorporaquadrigeminaCerebralaqueductArbor vitae (ofcerebellum)Fourth ventricleChoroid plexusCerebellum

Septum pellucidum

Interthalamicadhesion(intermediatemass of thalamus)Interven-tricularforamenAnteriorcommissure

Hypothalamus

Optic chiasma

Pituitary gland

Cerebral hemisphere

Mammillary bodyPonsMedulla oblongata

Spinal cord

Mid-brain

Fornix

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

Figure 12.12

Corpus callosum

Choroid plexusThalamus(encloses third ventricle)

Pineal gland(part of epithalamus)

Posterior commissure

CorporaquadrigeminaCerebralaqueductArbor vitae (ofcerebellum)Fourth ventricleChoroid plexusCerebellum

Septum pellucidum

Interthalamicadhesion(intermediatemass of thalamus)Interven-tricularforamenAnteriorcommissure

Hypothalamus

Optic chiasma

Pituitary gland

Cerebral hemisphere

Mammillary bodyPonsMedulla oblongata

Spinal cord

Mid-brain

Fornix

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

Figure 12.14

Frontal lobeOlfactory bulb(synapse point ofcranial nerve I)Optic chiasmaOptic nerve (II)Optic tractMammillary body

Pons

MedullaoblongataCerebellum

Temporal lobe

Spinal cord

Midbrain

Figure 12.15a

Optic chiasmaView (a)

Optic nerve (II)

Mammillary body

Oculomotor nerve (III)

Crus cerebri ofcerebral peduncles (midbrain)

Trigeminal nerve (V)

Abducens nerve (VI)Facial nerve (VII)

Vagus nerve (X)

Accessory nerve (XI)

Hypoglossal nerve (XII)

Ventral root of firstcervical nerve

Trochlear nerve (IV)

PonsMiddle cerebellarpeduncle

Pyramid

Decussation of pyramids

(a) Ventral view

Spinal cord

Vestibulocochlearnerve (VIII)

Glossopharyngeal nerve (IX)

Diencephalon• Thalamus• Hypothalamus

Diencephalon

Brainstem

Thalamus

Hypothalamus

Midbrain

Pons

Medullaoblongata

Figure 12.15b

View (b)

Crus cerebri ofcerebral peduncles (midbrain)

InfundibulumPituitary gland

Trigeminal nerve (V)

Abducens nerve (VI)

Facial nerve (VII)

Vagus nerve (X)

Accessory nerve (XI)

Hypoglossal nerve (XII)

Pons

(b) Left lateral view

Glossopharyngeal nerve (IX)

Diencephalon

Brainstem

Thalamus

Hypothalamus

Midbrain

Pons

Medullaoblongata

Thalamus

Superior colliculusInferior colliculusTrochlear nerve (IV)

Superior cerebellar peduncle

Middle cerebellar peduncle

Inferior cerebellar peduncle

Vestibulocochlear nerve (VIII)Olive

Figure 12.15c

View (c)

Diencephalon

Brainstem

Thalamus

Hypothalamus

Midbrain

Pons

Medullaoblongata

Pineal gland

Diencephalon

Anterior wall offourth ventricle

(c) Dorsal view

Thalamus

Dorsal root offirst cervical nerve

Midbrain• Superior

colliculus• Inferior

colliculus• Trochlear nerve (IV)• Superior cerebellar peduncle

Corporaquadrigeminaof tectum

Medulla oblongata• Inferior cerebellar peduncle• Facial nerve (VII)• Vestibulocochlear nerve (VIII)• Glossopharyngeal nerve (IX)• Vagus nerve (X)• Accessory nerve (XI)

Pons• Middle cerebellar peduncle

Dorsal median sulcus

Choroid plexus(fourth ventricle)

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

Figure 12.17b

(b)

Medullaoblongata

Flocculonodularlobe

Choroidplexus offourth ventricle

Posteriorlobe

Arborvitae

Cerebellar cortex

Anterior lobe

Cerebellarpeduncles• Superior• Middle• Inferior

Figure 12.17d

(d)

Anteriorlobe

Posteriorlobe

Vermis(d)

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

Figure 12.18

Corpus callosum

Septum pellucidum

Olfactory bulb

Diencephalic structuresof the limbic system

•Anterior thalamic nuclei (flanking 3rd ventricle)•Hypothalamus•Mammillary body

Fiber tractsconnecting limbic system structures

•Fornix•Anterior commissure

Cerebral struc-tures of the limbic system

•Cingulate gyrus•Septal nuclei•Amygdala•Hippocampus•Dentate gyrus•Parahippocampal gyrus

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

Figure 12.19

Visualimpulses

Reticular formation

Ascending generalsensory tracts(touch, pain, temperature)

Descendingmotor projectionsto spinal cord

Auditoryimpulses

Radiationsto cerebralcortex

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

Figure 12.22

Outside stimuli

General and special sensory receptors

Data transferinfluenced by:

ExcitementRehearsalAssociation ofold and new data

Long-termmemory(LTM)

Data permanentlylost

Afferent inputs

Retrieval

Forget

Forget

Data selectedfor transfer

Automaticmemory

Data unretrievable

Temporary storage(buffer) in cerebral cortex

Short-termmemory (STM)

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