Chapter FourAnatomy of the Nervous System

Divisions of the Vertebrate Nervous SystemCentral Nervous System-the brain and the spinal cordPeripheral Nervous System-the nerves outside the brain and spinal cordTwo Division of the PNSSomatic Nervous System-the nerves that convey messages from the sense organs to the CNS and from the CNS to the muscles and glandsAutonomic Nervous System-a set of neurons that control the heart, the intestines, and other organs

Figure 4.1The human nervous systemBoth the central nervous system and the peripheral nervous system havemajor subdivisions. The closeup of the brain shows the right hemisphereas seen from the midline.

The Nervous SystemThe Spinal Cord-part of the CNS found within the spinal column The spinal cord communicates with the sense organs and muscles below the level of the headBell-Magendie Law-the entering dorsal roots carry sensory information and the exiting ventral roots carry motor information to the muscles and glandsDorsal Root Ganglia-clusters of neurons outside the spinal cord

Figure 4.3Diagram of a cross section through the spinal cordThe dorsal root on each side conveys sensory information to the spinal cord; the ventral root conveys motor commands to the muscles.

Autonomic Nervous SystemSympathetic-prepares the body for arousalEx: increased breathing, increased heart rate, decreased digestive activityForm chain of ganglia just outside spinal cordShort preganglionic axons release norepinephrineLong postganglionic axons release norepinephrineParasympathetic-facilitates vegetative, nonemergency responses by the bodys organsEx: increase digestive activity, activities opposing sympathetic systemConsists of cranial nerves and nerves from sacral spinal cordLong preganglionic axons extend from the spinal cord to parasympathetic ganglia close to each internal organ; release norepinephrineShorter postganglionic fibers then extend from the parasympathetic ganglia in the organs; release acetylcholine

The BrainThe Hindbrain/rhombencephalonPosterior part of brainMedulla-controls vital reflexes like breathing, heart beat, etcPons-Area where many axons cross from one side of the brain to the otherReticular formation-control motor areas of the spinal cord and sends output to cerebral cortex increasing arousal and attentionRaphe system-sends axons to much of the forebrain, increasing or decreasing the brains readiness to respond to stimuliCerebellum-control movement, shifts of attention, balance and coordination

The BrainThe Midbrain-middle of the brainTegmentum-roof or coveringNuclei for third and fourth cranial nervesParts of Reticular formationExtensions of the pathways between the forebrain and the spinal cord or hindbrainTectum-roofSuperior Colliculus & Inferior Colliculus-important in routes of sensory information

Figure 4.8The human brain stemThis composite structure extends from the top of the spinal cord into the center of the forebrain. The pons, pineal gland, and colliculi are ordinarily surrounded by the cerebral cortex.

The BrainThe Forebrain-most anterior and most prominent part of the mammalian brainThalamusPart of the DiencephalonCenter of forebrainRelay Station for Sensory InformationHypothalamusPart of DiencephalonRegulates homeostasis, sexual behavior, fighting, feedingPituitary GlandEndocrine gland attached to the base of the hypothalamus

Figure 4.10The limbic system is a set of subcortical structures that form a border (or limbus) around the brain stem

Figure 4.12A sagittal section through the human brain

The BrainForebrain ContdBasal GangliaResponsible for motor behavior, some memory and emotional expressionBasal ForebrainLocated on the dorsal surface of the forebrainReceived input from the hypothalamus and basal gangliaSend axons to cerebral cortexImportant in arousal, wakefulness, and attentionHippocampusLocated between thalamus and cerebral cortexCritical for the formation of new memory

Figure 4.14The basal gangliaThe thalamus is in the center, the basal ganglia are lateral to it, and the cerebral cortex is on the outside.

The BrainThe Ventricles-Assists in cushioning the brainCentral Canal-fluid-filled channel in the center of the spinal cordVentricles-four fluid-filled cavities within the brainCSF-clear fluid similar to blood plasmaFormed in choroid plexusFlows from lateral to third to fourth ventricle to central canal or between meningesMeninges-membranes that surround the brain and spinal cord

Figure 4.16The cerebral ventriclesDiagram showing positions of the four ventricles.

The Cerebral CortexOrganization of the Cerebral CortexContains six distinct layers of cellsOrganized into columns-cells with similar properties; arranged perpendicular to the laminaeCells within a given column have similar or related properties

The LobesThe Occipital Lobe-posterior end of cortexContains primary visual cortexThe Parietal Lobe-between occipital love the central sulcusContains the primary somatosensory cortex-receiving touch sensation, muscle-stretch information and joint position informationThe Temporal Lobe-lateral portion of each hemisphere, near the templesContains targets for audition, essential for understanding spoken language, complex visual processes, emotional and motivational behaviorsThe Frontal Lobe-extends from the central sulcus to the anterior limit of the brainContains Primary Motor Cortex-fine movementsContributes to shifting attention, planning of action, delayed response tasks as examples

Figure 4.20Some major subdivisions of the human cerebral cortexThe four lobes: occipital, parietal, temporal, and frontal.

Brain FunctionHow Do the Pieces Work Together?Does the Brain Operate as a Whole or a Collection of Parts?Each brain area has a function but it cant do much by itselfThe Binding ProblemThe question of how the visual, auditory, and other areas of your brain influence on another to produce a combined perception of the single objectSynchronized neural activity?