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The Brain Muse spring 2430 lecture 15 7/12/10 Embryonic Development • Neural plate forms from ectoderm • Neural plate invaginates to form a neural groove and neural folds Surface ectoderm Head Neural plate Tail 1 The neural plate forms from surface ectoderm. Figure 12.1, step 1 (a) Neural tube Anterior (rostral) (b) Primary brain vesicles Prosencephalon (forebrain) Mesencephalon (midbrain) Rhombencephalon (hindbrain) Posterior (caudal) Figure 12.2a-b (d) Adult brain structures (e) Adult neural canal regions Telencephalon Cerebrum: cerebral hemispheres (cortex, white matter, basal nuclei) Lateral ventricles Diencephalon Diencephalon (thalamus, hypothalamus, epithalamus), retina Third ventricle Mesencephalon Brain stem: midbrain Cerebral aqueduct Metencephalon Brain stem: pons (c) Secondary brain vesicles Cerebellum Myelencephalon Brain stem: medulla oblongata Spinal cord Fourth ventricle Central canal Figure 12.2c-e Anterior (rostral) Metencephalon Mesencephalon Diencephalon Telencephalon Myelencephalon (a) Week 5 Posterior (caudal) Midbrain Cervical Flexures Spinal cord Figure 12.3a Cerebral hemisphere Outline of diencephalon Midbrain Cerebellum Pons Medulla oblongata (b) Week 13 Spinal cord Figure 12.3b (c) Week 26 Cerebral hemisphere Cerebellum Pons Medulla oblongata Spinal cord Figure 12.3c Cerebral hemisphere Diencephalon (d) Birth Cerebellum Brain stem • Midbrain • Pons • Medulla oblongata Figure 12.3d Ventricles of the Brain • Contain cerebrospinal fluid • Two C-shaped lateral ventricles in the cerebral hemispheres • Third ventricle in the diencephalon • Fourth ventricle in the hindbrain, dorsal to the pons, develops from the lumen of the neural tube Lateral ventricle Septum pellucidum Anterior horn Inferior horn Lateral aperture Interventricular foramen Third ventricle Inferior horn Cerebral aqueduct Fourth ventricle Central canal (a) Anterior view (b) Left lateral Posterior horn Median aperture Lateral aperture view Figure 12.5 Cerebral Hemispheres • Surface markings • Ridges (gyri), shallow grooves (sulci), and deep grooves (fissures) • Five lobes • Frontal • Parietal • Temporal • Occipital • Insula Cerebral Hemispheres • Surface markings • Central sulcus • Separates the precentral gyrus of the frontal lobe and the postcentral gyrus of the parietal lobe • Longitudinal fissure • Separates the two hemispheres • Transverse cerebral fissure • Separates the cerebrum and the cerebellum PLAY Animation: Rotatable brain Precentral gyrus Frontal lobe Central sulcus Postcentral gyrus Parietal lobe Parieto-occipital sulcus (on medial surface of hemisphere) Lateral sulcus Occipital lobe Temporal lobe Transverse cerebral fissure Cerebellum Pons Medulla oblongata Spinal cord Fissure (a deep sulcus) Gyrus Cortex (gray matter) Sulcus White matter (a) Figure 12.6a Frontal lobe Central sulcus Gyri of insula Temporal lobe (pulled down) (b) Figure 12.6b Anterior Longitudinal fissure Frontal lobe Cerebral veins and arteries covered by arachnoid mater Parietal lobe Right cerebral hemisphere Occipital lobe Left cerebral hemisphere (c) Posterior Figure 12.6c Left cerebral hemisphere Brain stem Transverse cerebral fissure Cerebellum (d) Figure 12.6d Cerebral Cortex • Thin (2–4 mm) superficial layer of gray matter • 40% of the mass of the brain • Site of conscious mind: awareness, sensory perception, voluntary motor initiation, communication, memory storage, understanding • Each hemisphere connects to contralateral side of the body • There is lateralization of cortical function in the hemispheres Functional Areas of the Cerebral Cortex • The three types of functional areas are: • Motor areas—control voluntary movement • Sensory areas—conscious awareness of sensation • Association areas—integrate diverse information • Conscious behavior involves the entire cortex Motor Areas • Primary (somatic) motor cortex • Premotor cortex • Broca’s area • Frontal eye field Motor areas Central sulcus Primary motor cortex Premotor cortex Frontal eye field Broca’s area (outlined by dashes) Prefrontal cortex Working memory for spatial tasks Executive area for task management Working memory for object-recall tasks Solving complex, multitask problems (a) Lateral view, left cerebral hemisphere Sensory areas and related association areas Primary somatosensory cortex Somatic Somatosensory sensation association cortex Gustatory cortex (in insula) Taste Wernicke’s area (outlined by dashes) Primary visual cortex Visual association area Auditory association area Primary auditory cortex Vision Hearing Motor association cortex Primary sensory cortex Primary motor cortex Sensory association cortex Multimodal association cortex Figure 12.8a Primary Motor Cortex • Large pyramidal cells of the precentral gyri • Long axons pyramidal (corticospinal) tracts • Allows conscious control of precise, skilled, voluntary movements • Motor homunculi: upside-down caricatures representing the motor innervation of body regions Posterior Motor Motor map in precentral gyrus Anterior Toes Jaw Tongue Swallowing Primary motor cortex (precentral gyrus) Figure 12.9 Premotor Cortex • Anterior to the precentral gyrus • Controls learned, repetitious, or patterned motor skills • Coordinates simultaneous or sequential actions • Involved in the planning of movements that depend on sensory feedback Broca’s Area • Anterior to the inferior region of the premotor area • Present in one hemisphere (usually the left) • A motor speech area that directs muscles of the tongue • Is active as one prepares to speak Frontal Eye Field • Anterior to the premotor cortex and superior to Broca’s area • Controls voluntary eye movements Sensory Areas • Primary somatosensory cortex • Somatosensory association cortex • Visual areas • Auditory areas • Olfactory cortex • Gustatory cortex • Visceral sensory area • Vestibular cortex Motor areas Central sulcus Primary motor cortex Premotor cortex Frontal eye field Broca’s area (outlined by dashes) Prefrontal cortex Working memory for spatial tasks Executive area for task management Working memory for object-recall tasks Solving complex, multitask problems (a) Lateral view, left cerebral hemisphere Sensory areas and related association areas Primary somatosensory cortex Somatic Somatosensory sensation association cortex Gustatory cortex (in insula) Taste Wernicke’s area (outlined by dashes) Primary visual cortex Visual association area Auditory association area Primary auditory cortex Vision Hearing Motor association cortex Primary sensory cortex Primary motor cortex Sensory association cortex Multimodal association cortex Figure 12.8a Primary Somatosensory Cortex • In the postcentral gyri • Receives sensory information from the skin, skeletal muscles, and joints • Capable of spatial discrimination: identification of body region being stimulated Posterior Sensory Anterior Sensory map in postcentral gyrus Genitals Primary somatosensory cortex (postcentral gyrus) Intraabdominal Figure 12.9 Somatosensory Association Cortex • Posterior to the primary somatosensory cortex • Integrates sensory input from primary somatosensory cortex • Determines size, texture, and relationship of parts of objects being felt Visual Areas • Primary visual (striate) cortex • Extreme posterior tip of the occipital lobe • Most of it is buried in the calcarine sulcus • Receives visual information from the retinas Visual Areas • Visual association area • Surrounds the primary visual cortex • Uses past visual experiences to interpret visual stimuli (e.g., color, form, and movement) • Complex processing involves entire posterior half of the hemispheres Auditory Areas • Primary auditory cortex • Superior margin of the temporal lobes • Interprets information from inner ear as pitch, loudness, and location • Auditory association area • Located posterior to the primary auditory cortex • Stores memories of sounds and permits perception of sounds OIfactory Cortex • Medial aspect of temporal lobes (in piriform lobes) • Part of the primitive rhinencephalon, along with the olfactory bulbs and tracts • (Remainder of the rhinencephalon in humans is part of the limbic system) • Region of conscious awareness of odors Gustatory Cortex • In the insula • Involved in the perception of taste Visceral Sensory Area • Posterior to gustatory cortex • Conscious perception of visceral sensations, e.g., upset stomach or full bladder Vestibular Cortex • Posterior part of the insula and adjacent parietal cortex • Responsible for conscious awareness of balance (position of the head in space) Motor areas Central sulcus Primary motor cortex Premotor cortex Frontal eye field Broca’s area (outlined by dashes) Prefrontal cortex Working memory for spatial tasks Executive area for task management Working memory for object-recall tasks Solving complex, multitask problems (a) Lateral view, left cerebral hemisphere Sensory areas and related association areas Primary somatosensory cortex Somatic Somatosensory sensation association cortex Gustatory cortex (in insula) Taste Wernicke’s area (outlined by dashes) Primary visual cortex Visual association area Auditory association area Primary auditory cortex Vision Hearing Motor association cortex Primary sensory cortex Primary motor cortex Sensory association cortex Multimodal association cortex Figure 12.8a Premotor cortex Corpus callosum Cingulate gyrus Primary motor cortex Frontal eye field Prefrontal cortex Processes emotions related to personal and social interactions Orbitofrontal cortex Olfactory bulb Olfactory tract Fornix Temporal lobe (b) Parasagittal view, right hemisphere Uncus Primary olfactory cortex Central sulcus Primary somatosensory cortex Parietal lobe Somatosensory association cortex Parieto-occipital sulcus Occipital lobe Visual association area Primary visual cortex Calcarine sulcus Parahippocampal gyrus Motor association cortex Primary sensory cortex Primary motor cortex Sensory association cortex Multimodal association cortex Figure 12.8b Multimodal Association Areas • Receive inputs from multiple sensory areas • Send outputs to multiple areas, including the premotor cortex • Allow us to give meaning to information received, store it as memory, compare it to previous experience, and decide on action to take Multimodal Association Areas • Three parts • Anterior association area (prefrontal cortex) • Posterior association area • Limbic association area Anterior Association Area (Prefrontal Cortex) • Most complicated cortical region • Involved with intellect, cognition, recall, and personality • Contains working memory needed for judgment, reasoning, persistence, and conscience • Development depends on feedback from social environment Posterior Association Area • Large region in temporal, parietal, and occipital lobes • Plays a role in recognizing patterns and faces and localizing us in space • Involved in understanding written and spoken language (Wernicke’s area) Limbic Association Area • Part of the limbic system • Provides emotional impact that helps establish memories Lateralization of Cortical Function • Lateralization • Division of labor between hemispheres • Cerebral dominance • Designates the hemisphere dominant for language (left hemisphere in 90% of people) Lateralization of Cortical Function • Left hemisphere • Controls language, math, and logic • Right hemisphere • Insight, visual-spatial skills, intuition, and artistic skills • Left and right hemispheres communicate via fiber tracts in the cerebral white matter Cerebral White Matter • Myelinated fibers and their tracts • Responsible for communication • Commissures (in corpus callosum)—connect gray matter of the two hemispheres • Association fibers—connect different parts of the same hemisphere • Projection fibers—(corona radiata) connect the hemispheres with lower brain or spinal cord Longitudinal fissure Lateral ventricle Superior Commissural fibers (corpus callosum) Association fibers Basal nuclei • Caudate • Putamen • Globus pallidus Corona radiata Thalamus Internal capsule Fornix Gray matter Third ventricle White matter Pons Projection fibers Medulla oblongata (a) Decussation of pyramids Figure 12.10a Basal Nuclei (Ganglia) • Subcortical nuclei • Consists of the corpus striatum • Caudate nucleus • Lentiform nucleus (putamen + globus pallidus) • Functionally associated with the subthalamic nuclei (diencephalon) and the substantia nigra (midbrain) Fibers of corona radiata Caudate nucleus Lentiform Corpus nucleus striatum • Putamen • Globus pallidus (deep to putamen) Projection fibers run deep to lentiform nucleus (a) Thalamus Tail of caudate nucleus Figure 12.11a Anterior (b) Posterior Cerebral cortex Cerebral white matter Corpus callosum Anterior horn of lateral ventricle Caudate nucleus Putamen Lentiform Globus nucleus pallidus Thalamus Tail of caudate nucleus Third ventricle Inferior horn of lateral ventricle Figure 12.11b (1 of 2) Cerebral cortex Cerebral white matter Corpus callosum Anterior horn of lateral ventricle Caudate nucleus Lentiform nucleus Thalamus Third ventricle Inferior horn of lateral ventricle (b) Figure 12.11b (2 of 2) Functions of Basal Nuclei • Though somewhat elusive, the following are thought to be functions of basal nuclei • Influence muscular control • Help regulate attention and cognition • Regulate intensity of slow or stereotyped movements • Inhibit antagonistic and unnecessary movements Diencephalon • Three paired structures • Thalamus • Hypothalamus • Epithalamus • Encloses the third ventricle PLAY Animation: Rotatable brain (sectioned) 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 Dorsal nuclei Medial Lateral Lateral dorsal posterior Pulvinar Anterior nuclear group Reticular nucleus Ventral Ventral Ventral posteroanterior lateral lateral Medial geniculate body Lateral geniculate body Ventral nuclei (a) The main thalamic nuclei. (The reticular nuclei that “cap” the thalamus laterally are depicted as curving translucent structures.) Figure 12.13a 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 Paraventricular nucleus Anterior commissure Preoptic nucleus Anterior hypothalamic nucleus Supraoptic nucleus Suprachiasmatic nucleus Fornix Arcuate nucleus Pituitary gland Optic chiasma Infundibulum (stalk of the pituitary gland) (b) The main hypothalamic nuclei. Dorsomedial nucleus Posterior hypothalamic nucleus Lateral hypothalamic area Ventromedial nucleus Mammillary body Figure 12.13b 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 Midbrain Nuclei • Nuclei that control cranial nerves III (oculomotor) and IV (trochlear) • Corpora quadrigemina—domelike dorsal protrusions • Superior colliculi—visual reflex centers • Inferior colliculi—auditory relay centers • Substantia nigra—functionally linked to basal nuclei • Red nucleus—relay nuclei for some descending motor pathways and part of reticular formation Tectum Periaqueductal gray matter Oculomotor nucleus (III) Medial lemniscus Red nucleus Substantia nigra Fibers of pyramidal tract (a) Midbrain Dorsal Superior colliculus Cerebral aqueduct Reticular formation Ventral Crus cerebri of cerebral peduncle Figure 12.16a 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 Fourth ventricle Superior cerebellar peduncle Trigeminal main sensory nucleus Trigeminal motor nucleus Middle cerebellar peduncle Trigeminal nerve (V) Medial lemniscus (b) Pons Reticular formation Pontine nuclei Fibers of pyramidal tract Figure 12.16b 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 • Inferior olivary nuclei—relay sensory information from muscles and joints to cerebellum • Cranial nerves VIII, X, and XII are associated with the medulla • Vestibular nuclear complex—mediates responses that maintain equilibrium • Several nuclei (e.g., nucleus cuneatus and nucleus gracilis) relay sensory information Medulla Oblongata • Autonomic reflex centers • Cardiovascular center • Cardiac center adjusts force and rate of heart contraction • Vasomotor center adjusts blood vessel diameter for blood pressure regulation 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 Reticular formation Fourth ventricle Choroid Hypoglossal nucleus (XII) plexus Dorsal motor nucleus of vagus (X) Inferior cerebellar peduncle Lateral nuclear group Medial nuclear group Raphe nucleus Medial lemniscus (c) Medulla oblongata Solitary nucleus Vestibular nuclear complex (VIII) Cochlear nuclei (VIII) Nucleus ambiguus Inferior olivary nucleus Pyramid Figure 12.16c 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 Electroencephalogram (EEG) • Records electrical activity that accompanies brain function • Measures electrical potential differences between various cortical areas (a) Scalp electrodes are used to record brain wave activity (EEG). Figure 12.20a 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, lowamplitude, 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 1-second interval Alpha waves—awake but relaxed Beta waves—awake, alert Theta waves—common in children Delta waves—deep sleep (b) Brain waves shown in EEGs fall into four general classes. Figure 12.20b Brain Waves: State of the Brain • Change with age, sensory stimuli, brain disease, and the chemical state of the body • EEGs used to diagnose and localize brain lesions, tumors, infarcts, infections, abscesses, and epileptic lesions • A flat EEG (no electrical activity) is clinical evidence of death Epilepsy • A victim of epilepsy may lose consciousness, fall stiffly, and have uncontrollable jerking • Epilepsy is not associated with intellectual impairments • Epilepsy occurs in 1% of the population Epileptic Seizures • Absence seizures, or petit mal • Mild seizures seen in young children where the expression goes blank • Tonic-clonic (grand mal) seizures • Victim loses consciousness, bones are often broken due to intense contractions, may experience loss of bowel and bladder control, and severe biting of the tongue Control of Epilepsy • Anticonvulsive drugs • Vagus nerve stimulators implanted under the skin of the chest can keep electrical activity of the brain from becoming chaotic 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 Awake REM: Skeletal muscles (except ocular muscles and diaphragm) are actively inhibited; most dreaming occurs. NREM stage 1: Relaxation begins; EEG shows alpha waves, arousal is easy. NREM stage 2: Irregular EEG with sleep spindles (short high- amplitude bursts); arousal is more difficult. NREM stage 3: Sleep deepens; theta and delta waves appear; vital signs decline. (a) Typical EEG patterns NREM stage 4: EEG is dominated by delta waves; arousal is difficult; bed-wetting, night terrors, and sleepwalking may occur. Figure 12.21a Sleep Patterns • Alternating cycles of sleep and wakefulness reflect a natural circadian (24-hour) rhythm • RAS activity is inhibited during, but RAS also mediates, dreaming sleep • The suprachiasmatic and preoptic nuclei of the hypothalamus time the sleep cycle • A typical sleep pattern alternates between REM and NREM sleep Awake REM Stage 1 Stage 2 Non REM Stage 3 Stage 4 Time (hrs) (b) Typical progression of an adult through one night’s sleep stages Figure 12.21b 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 Sleep Disorders • Narcolepsy • Lapsing abruptly into sleep from the awake state • Insomnia • Chronic inability to obtain the amount or quality of sleep needed • Sleep apnea • Temporary cessation of breathing during sleep 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 • 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 • 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 Thalamus Basal forebrain Touch Prefrontal cortex Hearing Vision Taste Smell Hippocampus Sensory input (a) Declarative memory circuits Association cortex Thalamus Medial temporal lobe (hippocampus, etc.) Prefrontal cortex ACh ACh Basal forebrain Figure 12.23a Brain Structures Involved in Nondeclarative Memory • Procedural memory • Basal nuclei relay sensory and motor inputs to the thalamus and premotor cortex • Dopamine from substantia nigra is necessary • Motor memory—cerebellum • Emotional memory—amygdala Sensory and motor inputs Association cortex Basal nuclei Thalamus Dopamine Premotor cortex Premotor cortex Substantia nigra Thalamus Basal nuclei Substantia nigra (b) Procedural (skills) memory circuits Figure 12.23b Molecular Basis of Memory • During learning: • Altered mRNA is synthesized and moved to axons and dendrites • Dendritic spines change shape • Extracellular proteins are deposited at synapses involved in LTM • Number and size of presynaptic terminals may increase • More neurotransmitter is released by presynaptic neurons Molecular Basis of Memory • Increase in synaptic strength (long-term potentiation, or LTP) is crucial • Neurotransmitter (glutamate) binds to NMDA receptors, opening calcium channels in postsynaptic terminal Molecular Basis of Memory • Calcium influx triggers enzymes that modify proteins of the postsynaptic terminal and presynaptic terminal (via release of retrograde messengers) • Enzymes trigger postsynaptic gene activation for synthesis of synaptic proteins, in presence of CREB (cAMP response-element binding protein) and BDNF (brain-derived neurotrophic factor) Meninges • Three layers • Dura mater • Arachnoid mater • Pia mater Superior sagittal sinus Subdural space Subarachnoid space Skin of scalp Periosteum Bone of skull Periosteal Dura Meningeal mater Arachnoid mater Pia mater Arachnoid villus Blood vessel Falx cerebri (in longitudinal fissure only) Figure 12.24 Dura Mater • Strongest meninx • Two layers of fibrous connective tissue (around the brain) separate to form dural sinuses Dura Mater • Dural septa limit excessive movement of the brain • Falx cerebri—in the longitudinal fissure; attached to crista galli • Falx cerebelli—along the vermis of the cerebellum • Tentorium cerebelli—horizontal dural fold over cerebellum and in the transverse fissure Superior sagittal sinus Straight sinus Crista galli of the ethmoid bone Pituitary gland Falx cerebri Tentorium cerebelli Falx cerebelli (a) Dural septa Figure 12.25a Arachnoid Mater • Middle layer with weblike extensions • Separated from the dura mater by the subdural space • Subarachnoid space contains CSF and blood vessels • Arachnoid villi protrude into the superior sagittal sinus and permit CSF reabsorption Superior sagittal sinus Subdural space Subarachnoid space Skin of scalp Periosteum Bone of skull Periosteal Dura Meningeal mater Arachnoid mater Pia mater Arachnoid villus Blood vessel Falx cerebri (in longitudinal fissure only) Figure 12.24 Pia Mater • Layer of delicate vascularized connective tissue that clings tightly to the brain Superior sagittal sinus 4 Choroid plexus Arachnoid villus Interventricular foramen Subarachnoid space Arachnoid mater Meningeal dura mater Periosteal dura mater 1 Right lateral ventricle (deep to cut) Choroid plexus of fourth ventricle 3 Third ventricle 1 CSF is produced by the Cerebral aqueduct Lateral aperture Fourth ventricle Median aperture Central canal of spinal cord (a) CSF circulation 2 choroid plexus of each ventricle. 2 CSF flows through the ventricles and into the subarachnoid space via the median and lateral apertures. Some CSF flows through the central canal of the spinal cord. 3 CSF flows through the subarachnoid space. 4 CSF is absorbed into the dural venous sinuses via the arachnoid villi. Figure 12.26a Choroid Plexuses • Produce CSF at a constant rate • Hang from the roof of each ventricle • Clusters of capillaries enclosed by pia mater and a layer of ependymal cells • Ependymal cells use ion pumps to control the composition of the CSF and help cleanse CSF by removing wastes Ependymal cells Capillary Section of choroid plexus Connective tissue of pia mater Wastes and unnecessary solutes absorbed CSF forms as a filtrate containing glucose, oxygen, vitamins, and ions (Na+, Cl–, Mg2+, etc.) (b) CSF formation by choroid plexuses Cavity of ventricle Figure 12.26b Blood-Brain Barrier • Composition • Continuous endothelium of capillary walls • Basal lamina • Feet of astrocytes • Provide signal to endothelium for the formation of tight junctions Capillary Neuron Astrocyte (a) Astrocytes are the most abundant CNS neuroglia. Figure 11.3a