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255Gross Anatomy of theBrain and Cranial NervesE X E R C I S E14O B J E C T I V E SList the elements of the central and peripheral divisions of the nervoussystem.Discuss the difference between the sensory and motor portions of thenervous system, and name the two divisions of the motor portion.Recognize the terms that describe the development of the human brain,and discuss the relationships between the terms.As directed by your instructor, identify the bold terms associated withthe cerebral hemispheres, diencephalon, brain stem, and cerebellum on adissected human brain, brain model, or appropriate image, and state theirfunctions.State the differences among gyri, fissures, and sulci.Describe the composition of gray matter and white matter in the nervoussystem.Name and describe the three meninges that cover the brain, state theirfunctions, and locate the falx cerebri, falx cerebelli, and tentorium cerebelli.Discuss the formation, circulation, and drainage of cerebrospinal fluid.Identify the cranial nerves by number and name on a model or image,stating the origin and function of each.Identify at least four key anatomical differences between the human brainand sheep brain.P R E - L A B Q U I Z1.Circle the correct underlined term. The central nervous system / peripheralnervous system consists of the brain and spinal cord.2.Circle the correct underlined term. The most superior portion of the brainincludes the cerebral hemispheres / brain stem.3.Circle True or False. Deep grooves within the cerebral hemispheres areknown as gyri.4.On the ventral surface of the brain, you can observe the optic nerves andchiasma, the pituitary gland, and the mammillary bodies. These externallyvisible structures form the floor of the:a. brain stemc. frontal lobeb. diencephalond. occipital lobe5.Circle the correct underlined term. The inferior region of the brain stem,the medulla oblongata / cerebellum houses many vital autonomic centersinvolved in the control of heart rate, respiratory rhythm, and bloodpressure.6.Directly under the occipital lobe of the cerebrum is a large cauliflower-likestructure known as the:a. brain stemb. cerebellumc. diencephalonM A T E R I A L SHuman brain model (dissectible)Preserved human brain (if available)Three-dimensional model of ventriclesFrontally sectioned or cross-sectionedhuman brain slice (if available)Materials as needed for cranial nervetesting (see Table 14.2): aromatic oils(e.g., vanilla and cloves); eye chart;ophthalmoscope; penlight; safety pin;blunt probe (hot and cold); cotton;solutions of sugar, salt, vinegar, andquinine; ammonia; tuning fork, andtongue depressorPreserved sheep brain (meninges andcranial nerves intact)Dissecting instruments and trayDisposable glovesText continues on next page.
256Exercise 14When viewed alongside all Earth’s animals, humansare indeed unique, and the key to our uniquenessis found in the brain. Each of us is a reflection ofour brain’s experience. If all past sensory input could mysteri-ously and suddenly be “erased,” we would be unable to walk,talk, or communicate in any manner. Spontaneous movementwould occur, as in a fetus, but no voluntary integrated func-tion of any type would be possible. Clearly we would ceaseto be the same individuals.For convenience, the nervous system, is consideredin terms of two principal divisions: the central nervoussystem and the peripheral nervous system. Thecentralnervous system (CNS)consists of the brain and spinalcord, which primarily interpret incoming sensory informa-tion and issue instructions based on that information andon past experience. Theperipheral nervous system (PNS)consists of the cranial and spinal nerves, ganglia, and sen-sory receptors.The PNS has two major subdivisions: thesensoryportion,which consists of nerve fibers that conduct impulsesfrom sensory receptors toward the CNS, and themotorportion,which contains nerve fibers that conduct impulsesaway from the CNS. The motor arm, in turn, consists of thesomatic division(sometimes called thevoluntary system),which controls the skeletal muscles, and the other subdivi-sion, theautonomic nervous system (ANS),which controlssmooth and cardiac muscles and glands.This exercise focuses on the brain (CNS) and cranialnerves (PNS) because of their close anatomical relationship.The Human BrainDuring embryonic development of all vertebrates, the CNSfirst makes its appearance as a simple tubelike structure, theneural tube,that extends down the dorsal median plane. Bythe fourth week, the human brain begins to form as an expan-sion of the anterior or rostral end of the neural tube (the endtoward the head). Shortly thereafter, constrictions appear,dividing the developing brain into three major regions—forebrain, midbrain,andhindbrain(Figure 14.1). Theremainder of the neural tube becomes the spinal cord.The central canal of the neural tube, which remainscontinuous throughout the brain and cord, enlarges in fourregions of the brain, forming chambers calledventricles(seeFigure 14.8a and b, page 265).

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