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The Central Nervous System Chapter 12 Regions and Organization of the CNS Adult brain regions 1. 2. 3. 4. Cerebral hemispheres Diencephalon Brain stem (midbrain, pons, and medulla) Cerebellum Cerebral hemisphere Diencephalon (d) Birth Cerebellum Brain stem • Midbrain • Pons • Medulla oblongata Figure 12.3d Ventricles of the Brain • Connected to one another and to the central canal of the spinal cord • Lined by ependymal cells • 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 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 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 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 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 and sends output to multiple areas • Allow us to give meaning to information received, store it as memory, compare it to previous experience, and decide on action to take • 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 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 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 • Includes: cingulate gyrus, parahippocampal gyrus, and hippocampus • Provides emotional impact that helps establish memories Lateralization of Cortical Function • Lateralization – Division of labor between hemispheres – Left hemisphere • Controls language, math, and logic – Right hemisphere • Insight, visual-spatial skills, intuition, and artistic skills • Cerebral dominance – Designates the hemisphere dominant for language (left hemisphere in 90% of people) Cerebral White Matter • Myelinated fibers and tracts • Communication between cerebral areas, and between cortex and lower CNS – Association fibers— horizontal; connect different parts of same hemisphere – Commissural fibers— horizontal; connect gray matter of two hemispheres – Projection fibers— vertical; connect hemispheres with lower brain or spinal cord Basal Nuclei (Ganglia) • Subcortical nuclei (caudate nucleus, putamen, globus pallidus) • Functionally associated with subthalamic nuclei (diencephalon) and substantia nigra (midbrain) Figure 12.9b Basal nuclei. Anterior Cerebral cortex Cerebral white matter Corpus callosum Anterior horn of lateral ventricle Head of caudate nucleus Putamen Globus pallidus Thalamus Tail of caudate nucleus Third ventricle Inferior horn of lateral ventricle Posterior © 2013 Pearson Education, Inc. Functions of Basal Nuclei • Functions thought to be: – Influence muscle movements – Role in cognition and emotion – Regulate intensity of slow or stereotyped movements – Filter out incorrect/inappropriate responses – Inhibit antagonistic/unnecessary movements Diencephalon • Three paired structures – Thalamus – Hypothalamus – Epithalamus • Encloses the third ventricle Thalamus (encloses third ventricle) Pineal gland (part of epithalamus) Hypothalamus Figure 12.12 Thalamus • 80% of diencephalon • 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 to help direct the motor cortical areas • Mediates sensation, motor activities, cortical arousal, learning, and memory Hypothalamus • Autonomic control center for many visceral functions • Center for emotional response • 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 • Pineal gland—extends from the posterior border and secretes melatonin – Melatonin—helps regulate sleep-wake cycles Brain Stem • Controls automatic behaviors necessary for survival • Associated with 10 of the 12 pairs of cranial nerves • Three regions – Midbrain – Pons – Medulla oblongata Midbrain Pons Medulla oblongata 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 Midbrain • Located between the diencephalon and the pons • Cerebral aqueduct – Channel between third and fourth ventricles • Nuclei that control cranial nerves III (oculomotor) and IV (trochlear) • Releases dopamine from the substantia nigra Pons • 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) • Nuclei that help maintain normal rhythm of breathing Medulla Oblongata • Joins spinal cord at foramen magnum • Crossover of the corticospinal tracts (decussation of the pyramids) • Cranial nerves VIII, X, and XII are associated with the medulla • 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 • Additional centers regulate – Vomiting – Hiccupping – Swallowing – Coughing – Sneezing Cerebellum 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 The Cerebellum • 11% of brain mass • Dorsal to the pons and medulla • Subconsciously provides precise timing and appropriate patterns of skeletal muscle contraction • Two hemispheres connected by vermis • Folia—transversely oriented gyri • Arbor vitae—distinctive treelike pattern of the cerebellar white matter 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 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 • 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 • Motor function – Helps control coarse limb movements – Reticular autonomic centers regulate visceral motor functions 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) 1-second interval Alpha waves—awake but relaxed Alpha: 8-13 Hz Beta waves—awake, alert Beta: 14-30 Hz Theta waves—common in children Theta: 4-7 Hz Delta waves—deep sleep Delta: ≤ 4 Hz (b) Brain waves shown in EEGs fall into four general classes. Figure 12.20b 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) is a signal that brain function is impaired 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 Patterns • Alternating cycles of sleep and wakefulness reflect a natural circadian (24-hour) rhythm (via Hypothalamus) • Typical = alternates b/w REM and NREM Language • Language implementation system – 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 Categories of Memory 1. Declarative (fact) memory – – – Explicit information Related to conscious thoughts and language ability Stored in LTM with context in which learned 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 Figure 12.21a Proposed memory circuits. Sensory input Thalamus Basal forebrain Touch Prefrontal cortex Hearing Vision Hippocampus Declarative memory circuits Thalamus Taste Smell Association cortex Medial temporal lobe (hippocampus, etc.) ACh released by basal forebrain Prefrontal cortex Figure 12.21b Proposed memory circuits. Premotor cortex Sensory and motor inputs Association cortex Basal nuclei Dopamine released by substantia nigra Basal nuclei Thalamus Substantia nigra Procedural (skills) memory circuits © 2013 Pearson Education, Inc. Thalamus Premotor cortex Protection of the Brain • • • • Bone (skull) Meninges Cerebrospinal fluid Also…..Blood-brain barrier Major Protective Structures Meninges • Cover and protect the CNS • Protect blood vessels and enclose venous sinuses • Contain cerebrospinal fluid (CSF) • Form partitions in the skull • Three layers – Dura mater – Arachnoid mater – Pia mater Dura Mater • Two layers of fibrous connective tissue – Periosteal and meningeal layers – Layers separate to form dural venous sinuses • Dural septa limit excessive movement of the brain Skin of scalp Periosteum Bone of skull Periosteal Dura Meningeal mater Arachnoid mater Pia mater Arachnoid villus Blood vessel Superior sagittal sinus Subdural space Falx cerebri (in longitudinal fissure only) Subarachnoid space Dural septa! Figure 12.24 Arachnoid Mater • Middle layer with weblike extensions • Subarachnoid space contains CSF and blood vessels • Arachnoid villi protrude into the superior sagittal sinus and permit CSF reabsorption Pia Mater • Layer of delicate vascularized connective tissue that clings tightly to the brain Cerebrospinal Fluid (CSF) • Composition – Watery solution – Less protein and different ion concentrations than plasma • Functions – Gives buoyancy to the CNS organs – Protects the CNS from blows and other trauma – Nourishes the brain and carries chemical signals Choroid Plexuses • Produce CSF at a constant rate • Hang from the roof of each ventricle 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 Blood-Brain Barrier • Helps maintain a stable environment for the brain • Separates neurons from some bloodborne substances Blood-Brain Barrier • Composition – Continuous endothelium of capillary walls – Basal lamina – “Feet of astrocytes” Blood-Brain Barrier: Functions • Selective barrier – Allows nutrients to move by facilitated diffusion – Allows any fat-soluble substances to pass, including alcohol, nicotine, and anesthetics • Absent in some areas, e.g., vomiting center and the hypothalamus, where it is necessary to monitor the chemical composition of the blood Spinal Cord • Location – Begins at the foramen magnum, ends (conus medullaris) at L1 • Functions • Two-way communication to/from the brain, spinal reflex centers • Protection – Bone, meninges, and CSF Cervical enlargement Dura and arachnoid mater Lumbar enlargement Conus medullaris Cauda equina Filum terminale (a) The spinal cord and its nerve roots, with the bony vertebral arches removed. The dura mater and arachnoid mater are cut open and reflected laterally. Cervical spinal nerves Thoracic spinal nerves Lumbar spinal nerves Sacral spinal nerves Figure 12.29a Spinal Cord • Spinal nerves – 31 pairs • Cervical and lumbar enlargements – The nerves serving the upper and lower limbs emerge here • Cauda equina – The collection of nerve roots at the inferior end of the vertebral canal Cross-Sectional Anatomy • Two lengthwise grooves divide cord into right and left halves – Ventral (anterior) median fissure – Dorsal (posterior) median sulcus • Gray commissure—connects masses of gray matter; encloses central canal Dorsal median sulcus Dorsal funiculus White Ventral funiculus columns Lateral funiculus Dorsal root ganglion Gray commissure Dorsal horn Gray Ventral horn matter Lateral horn Spinal nerve Dorsal root (fans out into dorsal rootlets) Ventral root (derived from several ventral rootlets) Central canal Ventral median fissure Pia mater Arachnoid mater Spinal dura mater (b) The spinal cord and its meningeal coverings Figure 12.31b Dorsal root (sensory) Dorsal root ganglion Dorsal horn (interneurons) Somatic sensory neuron Visceral sensory neuron Visceral motor neuron Somatic motor neuron Spinal nerve Ventral root (motor) Ventral horn (motor neurons) Interneurons receiving input from somatic sensory neurons Interneurons receiving input from visceral sensory neurons Visceral motor (autonomic) neurons Somatic motor neurons Figure 12.32 Pathway Generalizations • Pathways decussate (cross over) • Most consist of two or three neurons (a relay) • Most exhibit somatotopy (precise spatial relationships) • Pathways are paired symmetrically (one on each side of the spinal cord or brain) See figures 12.30 and 12.31, Table 12.2 Spinal Cord Trauma • Functional losses – Parasthesias (abnormal sensation) – Paralysis (loss of motor function) • Transection – Cross sectioning of the spinal cord at any level – Results in total motor and sensory loss in regions inferior to the cut – Paraplegia—transection between T1 and L1 – Quadriplegia—transection in the cervical region