Partial depolarization: impulse from one excitatory fiber has excitatory and inhibitory nerve fibers ending close to it caused partial below firing threshold depolarization of motor neuron Excitatory fibers mV Excitatory fibers mV —70 —70 Axon Axon Inhibitory fibers Inhibitory fibers C. Temporal excitatory summation: a series of impulses in one D. Spatial excitatory summation: impulses in two excitatory fibers excitatory fiber together produce a suprathreshold depolarization cause two synaptic depolarizations that together reach firing that triggers an action potential threshold triggering an action potential Excitatory fibers mV Excitatory fibers mV —70 —70 Axon Axon Inhibitory fibers Inhibitory fibers E.
Spatial excitatory summation with inhibition: impulses from E. Tempo- tial panel D. Both temporal and spatial summation can be modu- ral summation occurs when a series of subthreshold impulses in lated by simultaneous inhibitory input panel E. Spatial summation occurs when subthreshold which are summarized here. This allows small changes in space surrounding the brain and spinal cord.
Most of the CSF is system and pia mater. CSF bathes the cord and to the central nervous system from the skin, skeletal muscles, and is found in the subarachnoid space. Cell bodies of the motor neurons are tems. The PNS consists of somatic and autonomic components. The found in the anterior horn gray matter, whereas the cell bodies of somatic component innervates skeletal muscle and skin and is sensory neurons are located in the dorsal root ganglia.
Postganglionic axons of the auto- parasympathetic division derived from four of the cranial nerves nomic nervous system innervate smooth muscle, cardiac muscle, and CN III, VII, IX, and X and the S2-S4 sacral spinal cord levels, and the glands. The autonomic nervous system is a two- homeostatic functions. Normally, both divisions work in concert to neuron chain, with the preganglionic neuron arising from the central regulate visceral activity respiration, cardiovascular function, diges- nervous system and synapsing on a postganglionic neuron located in tion, and associated glandular activity.
Although acetylcholine and noradrenaline are the autonomic ganglion. Acetylcholine is the neurotransmitter in both chief transmitter substances, other neuroactive peptides often are the sympathetic and parasympathetic ganglia. The parasympathetic colocalized with them and include such substances as gamma- division of the ANS releases acetylcholine at its postganglionic aminobutyric acid GABA , substance P, enkephalins, histamine, synapses and is characterized as having cholinergic C effects, glutamic acid, neuropeptide Y, and others.
It tion of the functions listed. The limbic system functions in linking emo- interconnected structures in the telencephalon cingulate, parahip- tion and motivation amygdala , learning and memory hippocam- pocampal, and subcallosal gyri , as well as the amygdala and hip- pal formation , and sexual behavior hypothalamus. General cortical cerebral cortex participates in advanced intellectual functions, areas associated with these functions are illustrated.
The anterior horn cells and their associated axons constitute skilled movements of distal muscles of the limbs.
All structures the lower portion of the system lower motor neuron. The called vestibulocerebellum paleocerebellum also called spinocere- neocerebellum is the largest portion of the cerebellum, and it coordi- bellum and the neocerebellum also called the cerebrocerebellum. It receives The archicerebellum is primarily involved in controlling posture and input from the cerebral cortex and thus helps in the planning of balance, as well as the movement of the head and eyes.
It receives motor activity e. The archicerebellum is primarily involved descending motor pathways. The neocerebellum coordinates the in controlling posture and balance and movement of the head and movement of the distal portions of the limbs. It helps in the plan- eyes.
The paleocerebellum primarily controls movement of executing the movement of the arm and hand to pick it up. Free at low frequency i. The pacinian corpuscles are located nerve endings respond to pain and temperature. Pressure at central core Central core and, accordingly, generator potentials are rapidly dissipated by viscoelastic properties of capsule Action potentials may Unmyelinated axon terminal be blocked by pressure at a node or by drugs Pressure To amplifier Generator potential B.
In absence of capsule, axon responds to slow as well as to rapid changes in pressure. As the vis- mechanical force while the concentric lamellae dissipate slow coelastic lamellae are displaced, the unmyelinated axon terminal changes in pressure.
If the muscle tension is too great e. Passive stretch. Both intrafusal and extrafusal muscle fibers stretched; Golgi spindles activated. Reflex via Ia fibers and alpha motor neurons causes tendon secondary contraction basis of stretch reflexes, such as knee jerk.
Active contraction. Central excitation of alpha motor neurons only causes contraction of extrafusal muscle fibers with consequent relaxation of intrafusal fibers; spindles not activated. Tension is low; Golgi does not adjust to increased resistance. Active contraction with gamma coactivation. Intrafusal as well as Golgi extrafusal fibers contract; spindles activated, reinforcing contraction tendon stimulus via Ia fibers in accord with resistance.
Stretch reflex A. Recurrent inhibition D. The fasciculus gracilis and cuneatus of the spinal pathways. Maxillary n. Pons Sensory root and Motor root of mandibular n.
Neuronal cell bod- tral gyrus of the cerebral cortex, where they are somatotopically ies mediating proprioception reside in the mesencephalic nucleus represented. Variability and overlap occur, so all dermatome segments roots sensory nerve cell bodies reside in the corresponding dorsal are only approximations. Eyeball B. Rod in dark D. Thus, in the ization of the receptor cell membrane.
Fibers synapse in the lateral geniculate acuity. The colliculi of the tioned. The primary fissure, located on the superior midbrain are in view, with CN IV exiting posteriorly. The other functional easily recognizable by its surface which is composed of area that can be visualized — on the ventral view of the narrow ridges of cortex, called folia singular is folium. In the inferior view of the brainstem and The cerebellum is involved with motor control and is cerebellum see Figure 4 , two of them can be seen: the part of the motor system, influencing posture, gait, and inferior cerebellar peduncle attaching the medulla and voluntary movements discussed in more detail with the the cerebellum, and the prominent middle cerebellar pe- motor system.
Its function is to facilitate the perfor- duncle from the pons to the cerebellum. These are also mance of movements by coordinating the action of the shown from the dorsal perspective in Figure 7. Details various participating muscle groups. The superior cerebellum pe- the cerebellum does in motor control, damage to the duncle is located in Figure 7 on the dorsal aspect of the cerebellum leads to quite dramatic alterations in ordi- brainstem, in the roof of the fourth ventricle.
Lesions of the cerebellum result in the decomposition of the activi- Clinical Aspect ty, or fractionation of movement, so that the action is no The cerebellar lobule adjacent to the medulla is known longer smooth and coordinated.
Certain cerebellar as the cerebellar tonsil see ventral view of the cerebel- lesions also produce a tremor which is seen when per- lum, Figure 4. The tonsils are found just inside the forming voluntary acts, better known as an intention foramen magnum of the skull. Should there be an in- tremor.
This pressure may and force the cerebellar tonsils into the foramen magnum, 2. The compression, if discussion of the cerebellum as part of the motor severe, may lead to a compromising of function of the system Section B. The complete syndrome is known as Anatomically, the cerebellum can be described by tonsillar herniation, or coning, and is a life-threatening looking at its appearance in a number of ways.
The central portion is known The pineal is discussed with Figure 9. In addition, the limbic system also has circuits that involve the thalamus. Parts of the thalamus play an important encephalon is composed of both thalamus and hypotha- role in the maintenance and regulation of the state of lamus as well as some other subparts. It is situated consciousness, alertness, and also possibly attention. During develop- D. The pineal visible in Figure 8 is sometimes consid- ment of the human brain the enormous growth of the ered a part of the diencephalon.
The subthalamus is an area between the thalamus Figure It is important to note that there are two and midbrain; the subthalamic nucleus, located in this thalami; these are often connected across the midline by small zone, is an important nucleus involved with the the massa intermedia as seen in Figure 3.
The thalamus makes up the bulk of the diencephalon. It has many nuclei which are strongly linked with the cere- Additional Detail bral cortex, even during development. This feature The following topographic information will be under- becomes clearer in one of the principles of thalamic stood only after studying the hemispheres see Figures function, namely that most thalamic nuclei that project 11— It is recommended that students review this ma- to the cerebral cortex also receive input from that area terial at that time.
As shown in the diagram, the dien- — these are called reciprocal connections. This principle cephalon is situated within the brain below the level of does not apply, however, to all of the nuclei see below. In a horizontal section of information before forwarding it to the select area of the the hemispheres, the two thalami are located at the same cerebral cortex.
This is especially true for all the sensory level as the lentiform nucleus see Figures 27, 28A, and systems, except the olfactory. Likewise, two subsystems of the Figures 8 and 20B. There are two ways of dividing up the nuclei of the VA ventral anterior motor thalamus: topographically and functionally. VL ventral lateral motor 1. Topographically, the thalamus is subdivided by VPL ventral posterolateral somatosensory bands of white matter into a number of compo- VPM ventral posteromedial trigeminal nent parts.
It divides Association nuclei and association cortex the thalamus into a lateral mass, a medial mass, These nuclei are reciprocally connected to association and an anterior group of nuclei. Included with these are the medial and lateral geniculate bodies, relay Nonspecific nuclei nuclei for the auditory and visual systems. In These nuclei relay to widespread areas of the cerebral addition, motor regulatory information from cortex.
CM centromedian not illustrated — see Figures These nuclei are located in the lateral nuclear 51 and 61 mass. One of the most important nuclei ic nuclei, which is also shown in a number of textbooks, of this group is the dorsomedial nucleus, is quite usable.
A more histological view of the thalamus located in the medial mass of the thalamus. Some of these nuclei are located within the in- The student should learn the names and understand the ternal medullary lamina and are often re- general organization of the various nuclei at this point. This The student should also consult this diagram as the cere- functional group of nuclei does not have the bral cortex is described see the following figures.
Each strong reciprocal connections with the cortex of the specific relay nuclei involved in one of the path- like the other nuclei. Some of these nuclei form ways is discussed again with the functional system part of the ascending reticular activating system Section B , and at that point the student should return which is involved in the regulation of our state to this and the previous illustration.
Various nuclei are of consciousness and arousal discussed with involved with the limbic system Section D. After Figure 40A. The reticular nucleus which lies studying all of these systems, it is worthwhile returning on the outside of the thalamus is also part of again to Figures 9 and 10 for better understanding and this functional system. The brains of the higher apes and humans are dominated by the cerebral hemispheres.
The nervous Each of the hemispheres is divided into four lobes: tissue of the hemispheres, particularly the outer layer of frontal, parietal, temporal, and occipital. Two prominent neurons — the cerebral cortex — is responsible for con- fissures allow this subdivision to be made — the central sciousness, language, thinking, memory, movements, fissure and the lateral fissure. The central fissure, which sensory perceptions, and certain aspects of emotion. In is easier to identify on the right side of the specimen in short, neuronal activities in the cerebral cortex deter- Figure 11, divides the area anteriorly, the frontal lobe, mine to a large extent our capabilities.
It is not that the from the area posteriorly, the parietal lobe. The parietal other parts of the CNS are not important, but working lobe extends posteriorly to the parieto-occipital fissure, in and adapting to our complex modern world depends which is more easily seen on other views see Figure The brain area behind the parieto-occipital fissure is the occipital lobe.
The temporal lobe and the lateral fissure The hemispheres are organized in the following way: bil- cannot be seen on this view of the brain see Figure Most of the cerebral cortex is organized in six motor function. The most anterior parts of the frontal layers, the neocortex, with the neurons of each layer lobe are the newest in evolution and are known as the having a different function.
In formalin-fixed material, prefrontal cortex. The parietal often referred to as the gray matter. The occipital lobe is concerned with the pro- other species is thrown into irregular folds. These ridges cessing of visual information see Figure A very deep The meningeal layers arachnoid and pia have not been sulcus is called a fissure. This arrangement allows for a removed from this specimen, which means that the greater surface area to be accommodated within a con- blood vessels are also present.
Under the arachnoid fined space, the skull. The cerebral hemispheres occupy membrane is the subarachnoid space, which is collapsed the interior of the skull, the cranial cavity, which is in this fixed specimen; it is normally filled with cere- divided into the three cranial fossa.
This photographic view shows some coral-like The surface of the cerebral hemispheres can be visual- whitish material lying adjacent to the interhemispheric ized from a number of perspectives: from above dorsal fissure; this material is collectively called the arachnoid view, as seen in Figure 11 , from the side the dorsolater- granulations and is part of the CSF circulation, return- al view, as in Figure 12 , and from below inferior view, ing the CSF to the venous circulation discussed with as in Figures 13 and In addition, dividing the two Figure The photograph in Figure 11 shows the cerebral hemispheres from above, a dorsal view.
With the meninges removed, it is possible to identify the sulci and fissures with more certainty. The central fissure The lateral fissure fissure of Sylvius divides the tem- often called the fissure of Rolando is now seen more poral lobe below from the frontal and parietal lobes completely, dividing the frontal lobe anteriorly from the above. Extending the line of the lateral fissure parietal lobe posteriorly.
In the parietal lobe there are Some cortical areas are directly connected functionally two gyri whose association type of function is known; with either a sensory or motor system; these are known they have been labeled the supramarginal and angular as the primary areas. The gyrus in front of the central gyri.
These areas, particularly on the nondominant side, fissure is called the precentral gyrus see also Figure 51 seem to be involved in visuo-spatial activities. The frontal eye field, The temporal lobe is a large area of association cortex an area in the frontal lobe outlined , has a motor func- whose function is still being defined.
The areas exposed tion related to eye movements. The gyrus behind the on this dorsolateral view — other than the portions in- central fissure, the postcentral gyrus see also Figure volved with the auditory system and language on the 34 , has a somatosensory function for information from dominant side — are, in fact, still to be assigned a func- the skin and joints.
Other sensory primary areas are tional role. Other portions of the temporal lobe include identified where appropriate. The area in front of the frontal eye fields previ- The specialized cortical areas for audition are located ously mentioned, the prefrontal cortex, is a typical within the lateral fissure as shown in Figure It example of an association area.
Large parts of the pari- should be noted that the lateral fissure has a large etal and temporal lobes are association cortex.
They The cortex has been studied by many people using dif- have been removed from the specimen in the figure. It is possible to recognize distinct his- tological microscopic features between different The location of the parieto-occipital fissure is indicated cortical areas, and these might reflect the differing func- on this photograph.
This fissure separates the parietal tions of each particular area. One of the most commonly lobe from the occipital lobe, which can be seen in Figure used sub-parcelations of the cerebral cortex is that of The cerebellum lies below the occipital lobe, with the Brodmann who divided brain areas numerically.
Some large dural sheath — the tentorium cerebelli — separat- of these numbers are sometimes used interchangeably ing these parts of the brain see Figure This forms the for the lateral premotor cortex in-between see also basis for understanding the possible clinical implications Figure 51 , and areas 3, 1, and 2 which are synonymous of lesions in the various parts of the brain, a task be- for the postcentral somatosensory gyrus.
One hemisphere is therefore said CT and magnetic resonance imaging MRI — see, for to be dominant for that function. This is the case for example, Figure Olfactory information Figure 13 is a photographic view of the intact brain, in- is then carried in the olfactory tract to the uncal region cluding the brainstem and the cerebellum, seen from of the temporal lobe.
The optic nerves exit from the below. The medulla and pons, parts of the brainstem, orbit and continue to the optic chiasm where there is a can be identified, but the midbrain is mostly hidden partial crossing of visual fibers see Figures 39A and from view. The cranial nerves are still attached to the 39B.
Posterior to the chiasm is the area of the hypo- brainstem, and the arteries to the brainstem and cerebel- thalamus, part of the diencephalon, which can be seen lum are also present. The inferior surface of the frontal lobe extends from the The brainstem and cerebellum occupy the posterior part frontal pole to the anterior tip of the temporal lobe and the posterior cranial fossa and obscure the visualiza- the beginning of the lateral fissure.
These gyri rest on tion of the occipital lobe shown in Figure Various the roof of the orbit and are sometimes referred to as cranial nerves can be identified as in Figure 4.
The the orbital gyri. The has strong connections with the limbic system dis- trigeminal nerve, CN V, exits along the middle cerebellar cussed in Section D.
The temporal lobe extends medially towards the The arterial system is also seen in this illustration. The midbrain and ends in a blunt knob of tissue which is two vertebral arteries unite to form the basilar artery known as the uncus. The arterial supply to the brainstem and seen clearly on the right side of the photograph in cerebellum comes from these arteries.
There are three Figure It demarcates the parahippocampal gyrus, pairs of cerebellar arteries — posterior inferior, anterior part of the limbic system discussed with Figure 74 , inferior, and superior. The basilar artery gives off the which is the most medial gyrus of the temporal lobe.
It two superior cerebellar arteries at the upper level of the should be noted that the uncus is the most medial pro- pons, and ends by dividing into the posterior cerebral trusion of this gyrus. The clinical significance of the arteries to supply the occipital regions of the brain. Parts uncus and the discussion of uncal herniation are dis- of the arterial Circle of Willis are also seen on this speci- cussed with Figure The arterial supply to the hemispheres is fully Parts of the olfactory and visual sensory afferent systems described in Section C see Figure The tentorium divides the cranial cavity into an In Figure 14, the brainstem has been sectioned at the area above it, the supratentorial space, and an area level of the midbrain, and most of the brainstem itself below, the infratentorial space, which is the posterior and the attached cerebellum have been removed.
The cut cranial fossa. The sheath of dura splits to allow the surface of the midbrain exposes for view the pigmented brainstem to pass through; this split in the tentorium is cells of the substantia nigra; since this specimen has not called the tentorial notch hiatus. Note that it lies just above the free edge of the shown with the cross sections of the midbrain in Figure tentorium cerebelli.
The occurrence of a tumor or a It is not possible to creased tissue mass in the cranial cavity above the tento- define the boundary between these two lobes on this rium, accompanied by increased intracranial pressure view. Some of these gyri are involved with the processing ICP. As the volume of brain tissue increases, the hemi- of visual information, including color, as well as facial spheres are forced out of their supratentorial space and recognition.
The parahippocampal gyri should be noted the only avenue is in a downward direction, through the on both sides, with the collateral sulcus demarcating the tentorial notch. The uncus becomes the leading edge of lateral border of this gyrus discussed with Figure The whole process is clinically referred to as uncal herniation.
Since the edges of the The optic nerves lead to the optic chiasm. Behind the tentorium cerebelli are very rigid, the extra tissue in the optic chiasm is the median eminence and the mammil- area causes a compression of the brain matter, leading to lary bodies, both of which belong to the hypothalamus. CN III is usually compressed as well, damag- tains some hypothalamic nuclei. The pituitary stalk is at- ing it and causing a fixed and dilated pupil on that side, tached to the median eminence and connects the an ominous sign in any lesion of the brain.
The pupil- hypothalamus to the pituitary gland. The pituitary stalk lary light reflex is discussed with the introduction to the is not present in this photograph.
Behind are the paired midbrain in Section C. The interhemispher- bundles, as well as the latest in evolution. This is the ic fissure is opened. The dura between the hemispheres, anatomic structure required for each hemisphere to be the falx cerebri, has been removed from the interhemi- kept informed of the activity of the other hemisphere. This thick sheath of dura holds the two Functionally, the axons connect to and from the lower halves of the hemispheres in place within the cranial layers of the cerebral cortex, and in most cases the con- cavity.
The superior sagittal venous sinus has also been nections are between homologous areas and are reciprocal. A whitish structure is seen in the depths of the If the brain is sectioned in the sagittal plane along this fissure — the corpus callosum. This sectioning will reveal the the number of neurons devoted to communicating with medial aspect of the brain. It is difficult from the view in other neurons of the cortex.
These interneurons are es- Figure 15 to appreciate the depth of the corpus callo- sential for the processing and elaboration of informa- sum. In fact, there is a considerable amount of cortical tion, whether generated in the external world or tissue on the medial surface of the hemispheres, as rep- internally by our thoughts.
This intercommunicating resented by the frontal, parietal, and occipital lobes. It network is reflected in the vast interconnections between should be noted that the cerebral ventricles are located cortical areas.
Therefore, one would expect to find below i. Note on the safe handling of brain tissue: These interconnecting axons are located within the Figure 15 shows a rather old photograph of a brain depths of the hemispheres. They have a white coloration specimen. Current guidelines recommend the use of dis- after fixed in formalin, and these regions are usually posable gloves when handling any brain tissue as is seen called the white matter see Figures 27 and The pineal body sectioned is understanding the gross anatomy of the brain, brain- located off the posterior aspect of the diencephalon see stem, and ventricles.
In this figure, the brain has been also Figure 8. The three parts of the brainstem can be distinguished from this view — the midbrain, the pons with its bulge The medial aspects of the lobes of the brain are in view. Through the midbrain is a narrow brain although not as deep, usually, as on the dorsolat- channel for CSF, the cerebral aqueduct, also known as eral surface. The medial surface of the frontal lobe is the aqueduct of the midbrain or the aqueduct of Sylvius situated anteriorly, with the parietal lobe behind.
The posterior aspect of the midbrain Moving posteriorly, the parieto-occipital fissure has behind the aqueduct consists of the superior and infe- been opened. The occipital lobe is visible, divided by a rior colliculi see Figure 8. This aqueduct opens into the deep fissure, the calcarine fissure, into upper and lower fourth ventricle, which separates the pons and medulla portions.
The primary visual area, the cortical area from the cerebellum. The fourth ventricle is said to have where the visual fibers first arrive in the cerebral cortex, a floor, which is the brainstem, and a roof see Figure is located along the banks of the calcarine fissure. This 20A. The roof is divided into an upper and lower area is commonly called area 17 described with Figures portion. The upper part consists of a band of white 39A and 39B. The adjacent areas of the occipital lobe matter known as the superior medullary velum see also are visual association areas, also known as areas 18 and The lower part of the roof of this ventricle is The corpus callosum in this particular specimen does occupied by choroid plexus, which has not been pre- not have the usual white matter appearance that would served on this specimen.
The septum pellucidum, a membrane The cerebellum lies behind or above the fourth which divides the lateral ventricle of one hemisphere ventricle. It has been sectioned through its midline from that of the other side see Figure 28A , has been portion, the vermis. Although it is not necessary to removed, thereby exposing one of the lateral ventricles name all of the various parts of the vermis, it is useful to which is seen to be situated inferior to the corpus callo- know two of them: the lingula and the nodulus.
The sum. Above the corpus callosum is an important gyrus reason for knowing these is evident when describing which is part of the limbic system, the cingulate gyrus the cerebellum; see Figure The lingula is that part see Figures 74 and The nodulus is that part of the vermis paired diencephalon see Figures 3, 4, and 9. The thala- lying adjacent to the lower portion of the roof of the mic portion is separated from the hypothalamic part by fourth ventricle.
MRI imaging is the brain after a series of views are taken from many the way the brain is seen in clinical settings. The view perspectives. In this view the bones of the skull are presented in this figure is a T1-weighted image see bright, the CSF is dark, and the brain tissue gray, not below. Note that the cerebrospinal fluid is dark in this clear. This image can be obtained in several seconds, image, including the subarachnoid space and cisterns even with a very sick patient.
It uses an extremely tissue of the scalp are well demarcated. Again there is By comparing this view with the photographic view of a computer reconstruction of the images. The three parts of the brainstem — midbrain, An intermediate setting allows the structures of the pons and medulla — can be identified, with the tectum interior of the brain to be seen; this method produces colliculi seen behind the aqueduct of the midbrain. With MRI, the bones of the The fourth ventricle separates the cerebellum from the skull are dark, while fatty tissue including bone brainstem.
The location of the cerebellar tonsil s should marrow is bright. Functional of the skull see discussion on tonsillar herniation with MRIs allow us to see which areas of the brain are partic- Figure 8.
The location of the cerebello-medullary ularly active during a certain task, based upon the cistern the cisterna magna behind the medulla and just metabolic rate oxygen saturation.
They are becoming above the foramen magnum is easily seen see Figure more widely available. Other techniques also visualize the living brain and its The remaining structures are those of the nose and activity, such as the positron emission tomography mouth, which are not within the subject matter in PET scan.
PET uses a very short-acting radioactive this Atlas. Its use is usually restricted to specialized neurologic centers Note on radiological imaging involved in research on the human brain. Corpus callosum 2. Thalamus 3. Tectum of midbrain 4. Optic chiasm 5. Pons 6. Tonsil of cerebellum 7. Cisterna magna 8. In a DISSECTED VIEW sagittal section, the thickened anterior aspect of the Structures within the depths of the cerebral hemispheres corpus callosum is called the genu, and the thickened include the white matter, cerebral ventricles, and basal posterior portion the splenium neither has been labeled ganglia, all of which are described in the following figures.
The white matter consists of the myelinated axonal Clinical Aspects fibers connecting brain regions. In the spinal cord these In a clinical setting, the corpus callosum is sectioned are called tracts; in the hemispheres these bundles are surgically in individuals with intractable epilepsy classified in the following way also discussed with epilepsy that could not be controlled with anti-convul- Figure 15 : sant medication. Under laboratory conditions, it has been possible to demonstrate in these individuals how the two In the dissection of this specimen, the brain is again hemispheres of the brain function independently, after seen from the medial view.
Its anterior aspect is on the the sectioning of the corpus callosum. These studies right side of the photograph. Cortical tissue has been show how each hemisphere responds differently to removed as shown in Figure 16 , using blunt dissection various stimuli, and the consequences of information techniques. If done successfully, the fibers of the corpus not being transferred from one hemisphere to the other. These fibers intermingle with the other fiber bundles which make up the mass of white matter in the depth of the hemisphere.
Under the cerebral cortex is the white matter of the processing, allowing for integration of activities for brain.
Various fiber bundles can be dissected not easily example, sensory with motor and limbic. The various using a blunt instrument e. Some of these, functionally, are the association much importance in a general introduction to the CNS bundles, fibers that interconnect different parts of the except as in Figure 19B.
The only deficit is an inability to repeat The arcuate bundle is a specific group of association what has been heard. This is usually tested by asking the fibers of some importance, particularly on the side patient to repeat single words or phrases whose meaning dominant for language the left hemisphere in most cannot be readily understood e.
The formation, circulation, and duct of the midbrain, the cerebral aqueduct, or the locations of the CSF are explained with Figure In the hind- brain region, the area consisting of pons, medulla, and The ventricles of the brain are what remain of the origi- cerebellum, the ventricle widens again to form the nal neural tube, the tube that was present during devel- fourth ventricle see Figures 16 and The channel opment.
The cells of the nervous system, both neurons continues within the CNS and becomes the very narrow and glia, originated from a germinal matrix adjacent to central canal of the spinal cord Figure 2A. The cells multiply and migrate away from the walls of the neural tube, forming the Within the ventricles is specialized tissue, the choroid nuclei and cortex.
As the nervous system develops, the plexus. It is made up of the lining cells of the ventricles, mass of tissue grows and the size of the tube diminishes, called the ependyma, and pia with blood vessels dis- leaving various spaces in different parts of the nervous cussed with Figure The choroid plexus is the tissue system. It is found in the body and inferior horn of the lateral ventri- The parts of the tube that remain in the hemispheres cle, in the roof of the third ventricle, and in the lower are called the cerebral ventricles, or the lateral half of the roof of the fourth ventricle.
The tissue forms ventricles. In Figure 20A, the lateral ventricle of one large invaginations into the ventricles in each of these hemisphere is shown from the lateral perspective. The exit points are temporal lobes. The major exit is the In addition, there may be an extension into the occipital foramen of Magendie in the midline. There are two ad- lobes, called the occipital or posterior horn. These ditional exits of the CSF laterally from the fourth ventri- lateral ventricles are also called ventricles I and II cle, the foramina of Luschka seen in Figure 20B.
From the foramen of Magendie, the CSF then enters one Each lateral ventricle is connected to the midline third of the enlargements of the subarachnoid space, called a ventricle by an opening, the foramen of Monro inter- cistern, in this case the cisterna magna, the cerebello- ventricular foramen — seen in the medial view of the medullary cistern.
It lies below the cerebellum and is brain, Figure The third ventricle is a narrow, slit- found inside the skull, just above the foramen magnum like ventricle between the thalamus on either side and is see Figure 1B.
The CSF then flows in the subarachnoid also called the ventricle of the diencephalon see also space downwards around the spinal cord and upwards Figure 8. Sectioning through the brain in the midline around the brain discussed with Figure Both lateral ventricles and the such as developmentally, following a meningitis, or by a short interventricular foramen of Monro are visible on tumor in the region.
The result is an enlargement of the both sides, connecting each lateral ventricle with the ventricles, called hydrocephalus, which can be seen with midline third ventricle. It is important to note that the imaging techniques e. Not uncommonly, hydrocephalus in infancy occurs spontaneously, for unknown reasons. Clinical assessment lateral ventricles within the hemispheres see Figure Untreated hydrocephalus eventually spaces of the lateral and third ventricles see Figure Clinical treatment of this condition, after evaluation of The ventricular channel continues through the aqueduct the causative factor, includes shunting the CSF out of of the midbrain.
CSF then enters the fourth ventricle, the ventricles into one of the body cavities. The fourth ventricle is In adults, hydrocephalus caused by a blockage of the diamond-shaped, and the lateral recesses carry CSF into CSF flow leads to an increase in intracranial pressure, the cisterna magna through the foramina of Luschka, since the sutures are fused and skull expansion is not the lateral apertures, one on each side.
The cause in adults is usually a tumor, and, in Clinical Aspects addition to experiencing the specific symptoms, the The flow of CSF can be interrupted or blocked at patient will usually complain of headache, often in the various key points within the ventricular system.
One of early morning. The CSF is formed within the ventricles, This slow circulation is completed by the return of flows through the various channels, exits from within CSF to the venous system. The return is through the the brain, circulates in the subarachnoid space and cis- arachnoid villi which protrude into the venous sinuses terns around the brain and spinal cord, and is finally re- of the brain, particularly the superior sagittal sinus absorbed into the venous system the venous sinuses.
These can be The physiological barriers between the various compart- seen as collections of villi, called arachnoid granula- ments is also indicated in the illustration.
The ventricles of the brain are lined with a layer of cells known as the ependyma. In certain loci within each of There is no real barrier between the intercellular tissue the ventricles the ependymal cells and the pia meet, thus of the brain and the CSF, either through the ependyma forming the choroid plexus, which invaginates into the at all sites other than the choroid plexus or the pia.
Functionally, the choroid plexus has a vascular This lack of barrier is depicted by the arrows, which in- layer, i. The blood vessels of the choroid ments. Therefore, substances found in detectable plexus are freely permeable, but there is a cellular barrier amounts in the intercellular spaces of the brain may be between the interior of the choroid plexus and the ven- found in the CSF.
The barrier consists of tight junctions and functional, between the blood vessels and the brain between the ependymal cells that line the choroid tissue. This is called the blood-brain barrier BBB and plexus. CSF is actively secreted and an enzyme is in- is situated at the level of the brain capillaries. Only volved. The ionic and protein composition of CSF is oxygen, carbon dioxide, glucose, and other select, small different from that of serum.
CSF leaves the ventricular system from the fourth ven- Sampling of CSF for clinical evaluation, including in- tricle, as indicated schematically in the diagrams.
In the flammation of the meninges meningitis , is performed intact brain, this occurs via the medially placed foramen almost always in the lumbar cistern discussed with of Magendie and the two laterally placed foramina of Figures 1A and 1B.
Luschka described in the previous illustrations. There are two aspects to this involvement. It longing to the forebrain. This neuronal mass is found seems that different parts of the basal ganglia are con- deep within the cerebral hemispheres.
Our understand- cerned with the speed and magnitude of a movement. In ing of the functional role of the basal ganglia is derived addition, some of the structures that make up the basal largely from disease states affecting these neurons. In ganglia are thought to influence cognitive aspects of general, humans with lesions in the basal ganglia have motor control, helping to plan the sequence of tasks some form of motor dysfunction movement disorder needed for purposeful activity.
This process is some- — dyskinesia. From the strictly anatomical point of view, the basal Clinical Aspects ganglia are collections of neurons located within the The functional role of this large collection of neurons is hemispheres. Traditionally, this would include the best illustrated by clinical conditions affecting this neu- caudate nucleus, the putamen, the globus pallidus, ronal system — abnormal movements, such as chorea and the amygdala. Although the caudate and putamen jerky movements , athetosis writhing movements , are separated from each other anatomically, they are and tremors rhythmic movements.
The most common histologically the same neurons, and are known as the condition that affects this group of neurons is striatum. A person with this disease has diffi- ically found together and are called the lentiform or culty initiating movements, loses facial expressiveness lenticular nucleus.
From the functional point of view taking on a mask-like appearance, and has muscular and based upon the complex pattern of interconnec- rigidity, slowing of movements bradykinesia , and a tions, two other nuclei should be included with the de- tremor of the hands when at rest that goes away with scription of the basal ganglia: the subthalamic nucleus purposeful movements and in sleep.
The amygdala is now The other major disease that affects the basal ganglia is included with the limbic system see Section D. Overall, the basal ganglia receive much of their input Note on terminology: The term ganglia refers to a col- from the cortex, the motor areas of the cortex, as well as lection of cells in the peripheral nervous system. There are intricate con- Therefore, the anatomically correct name for this group nections between the various parts of the system in- of neurons should be the basal nuclei.
Few texts use this volving different neurotransmitters , and the output is term. Most clinicians would be hard-pressed to change directed via the thalamus mainly to premotor, supple- to the use of this term, so the traditional name remains mentary motor, and frontal cortical areas. Neuroanatomy Atlas in Clinical Context is unique in integrating clinical information, correlations, and terminology with neuroanatomical concepts. It provides everything students need to not only master the anatomy of the central nervous system, but also understand its clinical relevance — ensuring preparedness for exams and clinical rotations.
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