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BIOB32H3 (80)
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Department
Biological Sciences
Course
BIOB32H3
Professor
Kenneth Welch
Semester
Fall

Description
Central Nervous System (CNS) Central Nervous System (CNS) • CNS – composed of the brain and spinal cord • Cephalization • Elaboration of the anterior portion of the CNS • Increase in number of neurons in the head • Highest level has been reached in the human brain The Brain • Composed of wrinkled, pinkish gray tissue • Surface anatomy includes cerebral hemispheres, cerebellum, and brain stem Embryonic Development • During the first 26 days of development: • Ectoderm thickens along dorsal midline to form the neural plate • The neural plate invaginates, forming a groove flanked by neural folds • The neural groove fuses dorsally and forms the neural tube Primary Brain Vesicles • The anterior end of the neural tube expands and constricts to form the three primary brain vesicles • Prosencephalon – the forebrain • Mesencephalon – the midbrain • Rhombencephalon – hindbrain Secondary Brain Vesicles • In week 5 of embryonic development, secondary brain vesicles form: • Telencephalon and diencephalon arise from the forebrain • Mesencephalon remains undivided • Metencephalon and myelencephalon arise from the hindbrain Adult Brain Structures • Fates of the secondary brain vesicles: • Telencephalon – cerebrum: cortex, white matter, and basal nuclei • Diencephalon – thalamus, hypothalamus, and epithalamus • Mesencephalon – brain stem: midbrain • Metencephalon – brain stem: pons • Myelencephalon – brain stem: medulla oblongata Adult Neural Canal Regions • Adult structures derived from the neural canal • Telencephalon – lateral ventricles • Diencephalon – third ventricle • Mesencephalon – cerebral aqueduct • Metencephalon and myelencephalon – fourth ventricle Basic Pattern of the Central Nervous System • Spinal Cord • Central cavity surrounded by a gray matter core • External to which is white matter composed of myelinated fiber tracts • Brain • Similar to spinal cord but with additional areas of gray matter • Cerebellum has gray matter in nuclei • Cerebrum has nuclei and additional gray matter in the cortex Ventricles of the Brain • Arise from expansion of the lumen of the neural tube • The ventricles are: • The paired C-shaped lateral ventricles • The third ventricle found in the diencephalon • The fourth ventricle found in the hindbrain dorsal to the pons Cerebral Hemispheres • Form the superior part of the brain and make up 83% of its mass • Contain ridges (gyri) and shallow grooves (sulci) • Contain deep grooves called fissures • Are separated by the longitudinal fissure • Have three basic regions: cortex, white matter, and basal nuclei Major Lobes, Gyri, and Sulci of the Cerebral Hemisphere • Deep sulci divide the hemispheres into five lobes: • Frontal, parietal, temporal, occipital, and insula • Central sulcus – separates the frontal and parietal lobes • Parietal-occipital sulcus – separates the parieto and occipital lobes • Lateral sulcus – separates the parietal and temporal lobes • The precentral and postcentral gyri border the central sulcus Cerebral Cortex • The cortex – superficial gray matter; accounts for roughly 40% of the mass of the brain • It enables sensation, communication, memory, understanding, and voluntary movements • Each hemisphere acts contralaterally (controls the opposite side of the body) • Hemispheres are not equal in function • No functional area acts alone; conscious behavior involves the entire cortex Functional Areas of the Cerebral Cortex • Three types of functional areas are: • Motor areas – control voluntary movement • Sensory areas – conscious awareness of sensation • Association areas – integrate diverse information Cerebral Cortex: Motor Areas • Primary (somatic) motor cortex • Premotor cortex • Broca’s area • Frontal eye field Primary Motor Cortex • Located in the precentral gyrus • Composed of pyramidal cells whose axons make up the corticospinal tracts • Allows conscious control of precise, skilled, voluntary movements • Motor homunculus – caricature of relative amounts of cortical tissue devoted to each motor function Premotor Cortex • Located anterior to the precentral gyrus • Controls learned, repetitious, or patterned motor skills • Coordinates simultaneous or sequential actions • Involved in the planning of movements Broca’s Area and Frontal Eye Field • Broca’s area • Located 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 • Located anterior to the premotor cortex and superior to Broca’s area • Controls voluntary eye movement Sensory Areas • Primary somatosensory cortex • Somatosensory association cortex • Visual areas • Auditory areas • Olfactory cortex • Gustatory cortex • Vestibular cortex Primary Somatosensory Cortex • Located in the postcentral gyrus, this area: • Receives information from the skin and skeletal muscles • Exhibits spatial discrimination • Somatosensory homunculus – caricature of relative amounts of cortical tissue devoted to each sensory function Somatosensory Association Area • Located posterior to the primary somatosensory cortex • Integrates sensory information • Forms comprehensive understanding of the stimulus • Determines size, texture, and relationship of parts Visual Area • Primary visual cortex • Located on the extreme posterior tip of the occipital lobe • Receives visual information from the retinas • Visual association area • Surround the primary visual cortex • Interprets visual stimuli (e.g., color, form, and movement) Auditory Areas • Primary auditory cortex • Located at the superior margin of the temporal lobe • Receives information related to pitch, rhythm, and loudness • Auditory association area • Located posterior to the primary auditory cortex • Stores memories of sounds and permits perception of sounds Association Areas • Prefrontal cortex • Language areas • General (common) interpretation area • Visceral association area Prefrontal Cortex • Location – anterior portions of the frontal lobe • Involved with intellect, cognition, recall, and personality • Necessary for judgment, reasoning, persistence, and conscience • Closely linked to the limbic system (emotional part of the brain) Language Areas • Located in a large area surrounding the left (or language-dominant) lateral sulcus • Major parts and functions: • Wernicke’s area – involved in sounding out unfamiliar words • Broca’s area – speech preparation and production • Lateral prefrontal cortex – language comprehension and word analysis • Lateral and ventral temporal lobe – coordinate auditory and visual aspects of language General (Common) Interpretation Area • Ill-defined region including parts of the temporal, parietal, and occipital lobes • Found in one hemisphere, usually the left • Integrates incoming signals into a single thought • Involved in processing spatial relationships Visceral Association Area • Located in the cortex of the insula • Involved in conscious perception of visceral sensations Lateralization of Cortical Function • Lateralization – each hemisphere has abilities not shared with its partner • Cerebral dominance – designates the hemisphere dominant for language • Left hemisphere – controls language, math, and logic • Right hemisphere – controls visual-spatial skills, emotion, and artistic skills Cerebral White Matter • Consists of deep myelinated fibers and their tracts • It is responsible for communication between: • The cerebral cortex and lower CNS center, and areas of the cerebrum • Types include: • Commissures – connect corresponding gray areas of the two hemispheres • Association fibers – connect different parts of the same hemisphere • Projection fibers – enter the hemispheres from lower brain or cord centers Basal Nuclei • Masses of gray matter found deep within the cortical white matter • The corpus striatum is composed of three parts • Caudate nucleus • Lentiform nucleus – composed of the putamen and the globus pallidus • Fibers of internal capsule running between and through caudate and lentiform nuclei Functions of Basal Nuclei • Though somewhat elusive, the following are thought to be functions of basal nuclei: • Influence muscular activity • Regulate attention and cognition • Regulate intensity of slow or stereotyped movements • Inhibit antagonistic and unnecessary movement Diencephalon • Central core of the forebrain • Consists of three paired structures – thalamus, hypothalamus, and epithalamus • Encloses the third ventricle Thalamus • Paired, egg-shaped masses that form the superolateral walls of the third ventricle • Connected at the midline by the intermediate mass • Contains four groups of nuclei – anterior, ventral, dorsal, and posterior • Nuclei project and receive fibers from the cerebral cortex Thalamic Function • Afferent impulses from all senses converge and synapse in the thalamus • Impulses of similar function are “sorted out,” edited, and relayed as a group • All inputs ascending to the cerebral cortex pass through the thalamus • Plays a key role in mediating sensation, motor activities, cortical arousal, learning, and memory Hypothalamus • Located below the thalamus, it caps the brainstem and forms the inferolateral walls of the third ventricle • Mammillary bodies: • Small, paired nuclei bulging anteriorly from the hypothalamus • Relay station for olfactory pathways • Infundibulum – stalk of the hypothalamus; connects to the pituitary gland • Main visceral control center of the body Hypothalamic Function • Regulates blood pressure, rate and force of heartbeat, digestive tract motility, rate and depth of breathing, and many other visceral activities • Is involved with perception of pleasure, fear, and rage • Controls mechanisms needed to maintain normal body temperature • Regulates feelings of hunger and satiety • Regulates sleep and the sleep cycle Endocrine Functions of the Hypothalamus • Releasing hormones control secretion of hormones by the anterior pituitary • The supraoptic and paraventricular nuclei produce ADH and oxytocin Epithalamus • Most dorsal portion of the diencephalon; forms roof of the third ventricle • Pineal gland – extends from the posterior border and secretes melatonin • Melatonin – a hormone involved with sleep regulation, sleep-wake cycles, and mood • Choroid plexus – a structure that secretes cerebral spinal fluid (CSF) Brain Stem • Consists of three regions – midbrain, pons, and medulla oblongata • Similar to spinal cord but contains embedded nuclei • Controls automatic behaviors necessary for survival • Provides the pathway for tracts between higher and lower brain centers • Associated with 10 of the 12 pairs of cranial nerves Midbrain • Located between the diencephalon and the pons • Midbrain structures include: • Cerebral peduncles – two bulging structures that contain descending pyramidal motor tracts • Cerebral aqueduct – hollow tube that connects the third and fourth ventricles • Various nuclei Midbrain Nuclei • Nuclei that control cranial nerves III (oculomotor) and IV (trochlear) • Corpora quadrigemina – four domelike protrusions of the dorsal midbrain • Superior colliculi – visual reflex centers • Inferior colliculi – auditory relay centers • Substantia nigra – functionally linked to basal nuclei • Red nucleus – largest nucleus of the reticular formation; red nuclei are relay nuclei for some descending motor pathways Pons • Bulging brainstem region between the midbrain and the med
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