The Central Nervous System: Part A

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

Functions of the Nervous System Sensory input Information gathered by sensory receptors about internal and external changes Integration Interpretation of sensory input Motor output Activation of effector organs (muscles and glands) produces a response

Sensory input Integration Motor output Figure 11.1

Divisions of the Nervous System Central nervous system (CNS) Brain and spinal cord Integration and command center Peripheral nervous system (PNS) Paired spinal and cranial nerves carry messages to and from the CNS

Peripheral Nervous System (PNS) Two functional divisions Sensory (afferent) division Somatic afferent fibers—convey impulses from skin, skeletal muscles, and joints Visceral afferent fibers—convey impulses from visceral organs

Motor (efferent) division Transmits impulses from the CNS to effector organs

Motor Division of PNS Somatic (voluntary) nervous system Conscious control of skeletal muscles

Figure 11.2 Central nervous system (CNS) Peripheral nervous system (PNS) Brain and spinal cord Cranial nerves and spinal nerves Integrative and control centers Communication lines between the CNS and the rest of the body Sensory (afferent) division Motor (efferent) division Somatic and visceral sensory nerve fibers Motor nerve fibers Conducts impulses from the CNS to effectors (muscles and glands) Conducts impulses from receptors to the CNS Somatic sensory fiber Somatic nervous system Autonomic nervous system (ANS) Skin Somatic motor (voluntary) Visceral motor (involuntary) Conducts impulses from the CNS to skeletal muscles Conducts impulses from the CNS to cardiac muscles, smooth muscles, and glands Visceral sensory fiber Stomach Skeletal muscle Motor fiber of somatic nervous system Sympathetic division Parasympathetic division Mobilizes body systems during activity Conserves energy Promotes house- keeping functions during rest Sympathetic motor fiber of ANS Heart Structure Function Sensory (afferent) division of PNS Parasympathetic motor fiber of ANS Bladder Motor (efferent) division of PNS Figure 11.2

Embryonic Development Don’t copy Neural plate forms from ectoderm Neural plate invaginates to form a neural groove and neural folds

The neural plate forms from surface ectoderm. Head Neural plate Tail 1 The neural plate forms from surface ectoderm. Figure 12.1, step 1

Neural folds Neural groove The neural plate invaginates, forming the neural groove, flanked by neural folds. 2 Figure 12.1, step 2

Embryonic Development don’t copy Neural groove fuses dorsally to form the neural tube Neural tube gives rise to the brain and spinal cord

Neural crest 3 Neural fold cells migrate to form the neural crest, which will form much of the PNS and many other structures. Figure 12.1, step 3

Head Surface ectoderm Neural tube Tail The neural groove becomes the neural tube, which will form CNS structures. 4 Figure 12.1, step 4

Anterior (rostral) Posterior (caudal) Metencephalon Mesencephalon Midbrain Diencephalon Flexures Cervical Telencephalon Spinal cord Myelencephalon (a) Week 5 Figure 12.3a

Outline of diencephalon Cerebral hemisphere Outline of diencephalon Midbrain Cerebellum Pons Medulla oblongata Spinal cord (b) Week 13 Figure 12.3b

Cerebral hemisphere Cerebellum Pons Medulla oblongata Spinal cord (c) Week 26 Figure 12.3c

*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 PLAY Animation: Rotatable brain

Parieto-occipital sulcus (on medial surface of hemisphere) Precentral gyrus Central sulcus Postcentral gyrus Frontal lobe Parietal lobe Parieto-occipital sulcus (on medial surface of hemisphere) Lateral sulcus Occipital lobe Temporal lobe Transverse cerebral fissure Cerebellum Pons Medulla oblongata Fissure Spinal cord (a deep sulcus) Gyrus Cortex (gray matter) Sulcus White matter (a) Figure 12.6a

Central sulcus Frontal lobe Gyri of insula Temporal lobe (pulled down) Figure 12.6b

Anterior Longitudinal Frontal lobe fissure Cerebral veins and arteries covered by arachnoid mater Parietal lobe Left cerebral hemisphere Right cerebral hemisphere Occipital lobe (c) Posterior Figure 12.6c

Left cerebral hemisphere Transverse cerebral fissure Brain stem 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

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

*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 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 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

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