Chapter 12 The Central Nervous System Part A Shilla Chakrabarty, Ph.D.

Central Nervous System (CNS) CNS consists of the brain and spinal cord During the course of evolution, cephalization has occurred Evolutionary development of the rostral (anterior) portion of the CNS Increased number of neurons in the head Highest level is reached in the human brain

Embryonic Development Of Neural Tube The neural plate forms from surface ectoderm. 1 Head Tail Surface ectoderm Neural plate The neural plate invaginates, forming the neural groove, flanked by neural folds. 2 Neural folds Neural groove Neural fold cells migrate to form the neural crest, which will form much of the PNS and many other structures. 3 Neural crest The neural groove becomes the neural tube, which will form CNS structures. 4 Neural tube

Embryonic Development Of Neural Tube Neural plate forms from ectoderm Neural plate invaginates to form a neural groove and neural folds Neural groove fuses dorsally to form the neural tube Neural tube gives rise to the brain and spinal cord (CNS) Neural crest cells segregate and either move in a lateral direction to form melanocytes in skin (1), or move ventrally to form neurons and glial cells of PNS(2,3)

Embryonic Development Of Human Brain Neural tube (b) Primary brain vesicles Anterior (rostral) Posterior (caudal) Rhombencephalon (hindbrain) Mesencephalon (midbrain) Prosencephalon (forebrain) Anterior end of the neural tube gives rise to three primary brain vesicles Prosencephalon—forebrain Mesencephalon—midbrain Rhombencephalon—hindbrain

Embryonic Development Of Human Brain Primary vesicles give rise to five secondary brain vesicles Telencephalon and diencephalon arise from procencephalon Telencephalon  cerebrum (two hemispheres with cortex, white matter, and basal nuclei) Diencephalon  thalamus, hypothalamus, epithalamus, and retina Mesencephalon remains undivided Mesencephalon  brain stem (midbrain) Metencephalon and myelencephalon arise from rhombencephalon Metencephalon  brain stem (pons) and cerebellum Myelencephalon  brain stem (medulla oblongata) Central canal of the neural tube enlarges to form fluid-filled ventricles

Embryonic Development Of Human Brain

Effect of Space Restriction on Brain Development Metencephalon Anterior (rostral) Posterior (caudal) Mesencephalon Diencephalon Midbrain Cervical Spinal cord Flexures Telencephalon Myelencephalon (a) Week 5 Cerebellum Pons Medulla oblongata Cerebral hemisphere Outline of diencephalon (b) Week 13 Medulla oblongata Cerebral hemisphere (c) Week 26 Midbrain flexure and cervical flexure cause forebrain to move toward the brain stem Cerebral hemispheres grow posteriorly and laterally Cerebral hemisphere surfaces crease and fold into convolutions

Regions and Organization of the CNS Adult brain regions Cerebral hemispheres Diencephalon Brain stem (midbrain, pons, and medulla) Cerebellum Cerebellum Diencephalon Cerebral hemisphere (d) Birth Brain stem • Midbrain • Pons • Medulla oblongata

Development Of The Human Brain

Pattern Of Gray And White Matter In The CNS Spinal cord Central cavity surrounded by a gray matter core External white matter composed of myelinated fiber tracts Brain Similar pattern with additional areas of gray matter Both cerebral hemispheres and cerebellum have outer layer or “bark” of gray matter called a cortex With descent through brain stem cortex disappears, scattered gray matter nuclei seen within white matter

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, develops from the lumen of the neural tube

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 Posterior horn Inferior horn Interventricular foramen Lateral aperture Median aperture Third ventricle Inferior horn Lateral aperture Cerebral aqueduct Fourth ventricle Central canal (a) Anterior view (b) Left lateral view Figure 12.5

Cerebral Hemispheres Surface markings Ridges (gyri), shallow grooves (sulci), and deep grooves (fissures) Five lobes Frontal Parietal Temporal Occipital Insula Postcentral gyrus Central sulcus Precentral Frontal lobe (a) Parietal lobe Parieto-occipital sulcus (on medial surface of hemisphere) Lateral sulcus Transverse cerebral fissure Occipital lobe Temporal lobe Cerebellum Pons Medulla oblongata Spinal cord Cortex (gray matter) Fissure (a deep sulcus) Gyrus Sulcus White matter Central sulcus (b) Frontal lobe Temporal lobe (pulled down) Gyri of insula

Surface Markings Of The Brain 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 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 Three types of functional areas: 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 Gustatory cortex (in insula) Primary motor cortex Premotor cortex Frontal eye field Working memory for spatial tasks Executive area for task management Working memory for object-recall tasks Broca’s area (outlined by dashes) Solving complex, multitask problems (a) Lateral view, left cerebral hemisphere Motor areas Prefrontal cortex Sensory areas and related association areas Central sulcus Primary somatosensory cortex Somatosensory association cortex Somatic sensation Taste Wernicke’s area Primary visual Visual association area Vision Auditory association area Primary auditory cortex Hearing Motor association cortex Primary sensory cortex Sensory association cortex Multimodal association cortex

Motor Areas: 1. Primary Motor Cortex Toes Swallowing Tongue Jaw Primary motor cortex (precentral gyrus) Motor Motor map in precentral gyrus Posterior Anterior 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

Motor Areas 2. Premotor Cortex 3. Broca’s Area 4. Frontal Eye Field 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 3. 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 4. 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 Gustatory cortex (in insula) Primary motor cortex Premotor cortex Frontal eye field Working memory for spatial tasks Executive area for task management Working memory for object-recall tasks Broca’s area (outlined by dashes) Solving complex, multitask problems (a) Lateral view, left cerebral hemisphere Motor areas Prefrontal cortex Sensory areas and related association areas Central sulcus Primary somatosensory cortex Somatosensory association cortex Somatic sensation Taste Wernicke’s area Primary visual Visual association area Vision Auditory association area Primary auditory cortex Hearing Motor association cortex Primary sensory cortex Sensory association cortex Multimodal association cortex

Sensory Areas 2. Somatosensory Association Cortex Genitals Intra- abdominal Primary somato- sensory cortex (postcentral gyrus) Sensory Sensory map in postcentral gyrus Posterior Anterior 1. 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 2. 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

Sensory Areas 3. 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 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

Sensory Areas 4. Auditory Areas 5. Olfactory Cortex 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 5. Olfactory 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

Sensory Areas 6. Gustatory Cortex 7. Visceral Sensory Area In the insula Involved in the perception of taste 7. Visceral Sensory Area Posterior to gustatory cortex Conscious perception of visceral sensations, e.g., upset stomach or full bladder 8. Vestibular Cortex Posterior part of the insula and adjacent parietal cortex Responsible for conscious awareness of balance (position of the head in space)

Sensory areas and related association areas Primary motor cortex Motor areas Central sulcus Sensory areas and related association areas Primary motor cortex Primary somatosensory cortex Premotor cortex Somatic sensation Frontal eye field Somatosensory association cortex Broca’s area (outlined by dashes) Gustatory cortex (in insula) Taste Prefrontal cortex Working memory for spatial tasks Wernicke’s area (outlined by dashes) Executive area for task management Working memory for object-recall tasks Primary visual cortex Visual association area Vision Solving complex, multitask problems Auditory association area Hearing Primary auditory cortex (a) Lateral view, left cerebral hemisphere Primary motor cortex Motor association cortex Primary sensory cortex Sensory association cortex Multimodal association cortex Figure 12.8a

Primary somatosensory cortex Cingulate gyrus Primary motor cortex Premotor cortex Central sulcus Corpus callosum Primary somatosensory cortex Frontal eye field Parietal lobe Somatosensory association cortex Prefrontal cortex Parieto-occipital sulcus Occipital lobe Processes emotions related to personal and social interactions Visual association area Orbitofrontal cortex Olfactory bulb Olfactory tract Primary visual cortex Fornix Temporal lobe Uncus Calcarine sulcus Primary olfactory cortex Parahippocampal gyrus (b) Parasagittal view, right hemisphere Primary motor cortex Motor association cortex Primary sensory 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 Three parts Anterior association area (prefrontal cortex) Posterior association area Limbic association area

Multimodal Association Areas 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 (Prefrontal Cortex) 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