Central Nervous System (CNS) CNS consists of the brain and spinal cord Cephalization 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 Neural plate forms from ectoderm Neural plate invaginates to form a neural groove and neural folds

Regions and Organization of the CNS Adult brain regions Cerebral hemispheres Diencephalon Brain stem (midbrain, pons, and medulla) Cerebellum

Cerebral hemisphere Diencephalon Cerebellum Brain stem • Midbrain • Pons • Medulla oblongata (d) Birth Figure 12.3d

Regions and Organization of the CNS Spinal cord Central cavity surrounded by a gray matter core External white matter composed of myelinated fiber tracts

Regions and Organization of the CNS Brain Similar pattern with additional areas of gray matter Nuclei in cerebellum and cerebrum Cortex of cerebellum and cerebrum

Central cavity Cortex of gray matter Migratory pattern of neurons Inner gray matter Cerebrum Outer white matter Cerebellum Gray matter Region of cerebellum Central cavity Inner gray matter Outer white matter Gray matter Brain stem Central cavity Outer white matter Inner gray matter Spinal cord Figure 12.4

Ventricles of the Brain Connected to one another and to the central canal of the spinal cord Lined by ependymal cells

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

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

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 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 Primary motor cortex (precentral gyrus) Swallowing 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

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 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 somato- sensory cortex (postcentral gyrus) Intra- abdominal 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

Primary visual (striate) cortex 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 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

Primary auditory cortex 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

Medial aspect of temporal lobes (in piriform lobes) 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)

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 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

Myelinated fibers and their tracts Responsible for communication 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

Commissural fibers (corpus Longitudinal fissure callosum) Superior Lateral ventricle Association fibers Basal nuclei • Caudate Corona radiata • Putamen • Globus pallidus Fornix Internal capsule Thalamus Gray matter Third ventricle White matter Projection fibers Pons Decussation of pyramids Medulla oblongata (a) 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)

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

Three paired structures Diencephalon Three paired structures Thalamus Hypothalamus Epithalamus Encloses the third ventricle

Cerebral hemisphere Septum pellucidum Corpus callosum Interthalamic adhesion (intermediate mass of thalamus) Fornix Choroid plexus Thalamus (encloses third ventricle) Interven- tricular foramen Posterior commissure Pineal gland (part of epithalamus) Anterior commissure Corpora quadrigemina Mid- brain Hypothalamus Cerebral aqueduct Optic chiasma Arbor vitae (of cerebellum) Pituitary gland Fourth ventricle Mammillary body Choroid plexus Pons Cerebellum Medulla oblongata 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 dorsal Lateral posterior Pulvinar Anterior nuclear group Medial geniculate body Reticular nucleus Lateral geniculate body Ventral postero- lateral Ventral anterior Ventral lateral 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

Forms the inferolateral walls of the third ventricle 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

(b) The main hypothalamic nuclei. Paraventricular nucleus Anterior commissure Dorsomedial nucleus Fornix Preoptic nucleus Posterior hypothalamic nucleus Anterior hypothalamic nucleus Lateral hypothalamic area Supraoptic nucleus Ventromedial nucleus Supra- chiasmatic nucleus Mammillary body Arcuate nucleus Optic chiasma Pituitary gland Infundibulum (stalk of the pituitary gland) (b) The main hypothalamic nuclei. 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