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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