18. Posterior funiculus is a portion of the white matter, which lies between the posterior median sulcus and the posterolateral sulcus.
19. Lateral funiculus is a portion of the white matter, which lies between the posterolateral sulcus and the anterolateral sulcus.
20. Anterior white commissure is a bundle of transverse fibers, anterior to the gray commissure.
21. Near the lower end of medulla oblongata, most descending fibers of the pyramidal tract cross over the midplane; these decussating fibers are called the decussation of pyramid.
22. The transverse fibers of the pons which across the median plane of it and converge to form the lateral part of the pons, is called the middle cerebellar peduncle.
23. On the dorsal aspect of the midbrain four rounded eminences are called the corpora quadrigemina, which include a pair of superior colliculus and a pair of inferior colliculus.
24. The rhomboid fossa is formed by the dorsal surface of both the pons and the upper part of medulla oblongata. It is the floor of fourth ventricle and rhomboidal in shape. The superolateral borders of the fossa are the superior cerebellar peduncles; the inferolateral borders are the gracile tubercle, cuneate tubercle and inferior cerebellar peduncles from medial to lateral.
25. The nucleus of facial nerve gives off efferent fibers which firstly proceed dorsomedially and round the nucleus of abducent nerve to form the genu of facial nerve.
26. Most of the efferent fibers of cochlear nuclei cross the median plane of lower part of pons to form the trapezoid body.
27. The medial lemniscus is formed by the secondary-order sensory fibers arising from the contralateral gracile and cuneate nuclei. The fibers firstly pass forwards, laterally round the central gray matter and then decussate in the midplane with the corresponding fibers of the opposite side. After that the fibers turn upwards to form the medial lemniscus conducting the deep sense of the body.
28. The pretectal area is at the junction of midbrain and diencephalon, just rostral to the superior colliculus. The pretectal area receives the fibers from the ipsilateral optic tract, visual cortex and the lateral geniculate body. The efferent fibers project to the bilateral accessory nucleus of oculomotor nerve.
29. The substantia nigra is situated between the tegmentum and crus cerebri of midbrain, extends through the whole length of the midbrain and into the caudal diencephalon. In section the substantia nigra is divided into two parts, a dorsal compact part and a ventral reticular part.
30. The nucleus of hypoglossal nerve is in the hypoglossal triangle. It receives the afferent fibers from the contralateral corticonuclear tract and gives off efferent fibers to form the hypoglossal nerve which innervates the ipsilateral muscles of the tongue.
31. It is a prominence of cerebellar hemispheres adjacent to the great occipital foramen. The cerebellar tonsillar hernia will occur if tonsil of cerebellum is protruded to the great occipital foramen because of intracranial hypertension. This condition can pose a threat to life since the respiratory and cardiovascular centers in the medulla could be compressed in the protruded cerebellar tonsil.
32. The archicerebellum consists of the flocculonodular lobe. It is also known as the vestibulocerebellum because of connecting with the vestibular nuclei and vestibular nerves. It regulates muscle movement of trunk, playing an important role in the maintenance of body equilibrium.
33. The paleocerebellum is composed of the vermis (medial zone) and intermedial zone of the hemispheres, receives the afferents from the spinal cord, also called the spinocerebellum. It modulates the muscular tension and motor coordination of extremities.
34. The neocerebellum consists of the lateral zone, connects with the cerebral cortex, also termed as the cerebrocerebellum. It affects the modulation of initiation, planning and coordination of limbs fineness movement, including determination of movement strength, direction and amplitude.
35. It is the largest of the subarachnoid cisterns between the undersurface of the cerebellum and the dorsal surface of the medulla oblongata. Subarachnoid space stabbing can be carried out here in clinic.
36. The diencephalon is located between the midbrain and telencephalon, develops from the forebrain vesicle. It is mostly surrounded by the cerebral hemispheres, left the optic chiasm, optic tracts, tuber cinereum, infundibulum, hypophysis and mamillary body exposed ventrally. The diencephalon is subdivided into five parts: dorsal thalamus, epithalamus, hypothalamus, subthalamus and metathalamus.
37. The third ventricle is a narrow midplane cavity within the diencephalon. It is bordered superiorly by the choroid plexus of third ventricle, inferiorly by the optic chiasm, gray tubercle, and mamillary, anteriorly by the lamina terminalis, laterally by the dorsal thalami and hypothalami. Inferoposteriorly, the third ventricle is communicated with the fourth ventricle via the cerebral (mesencephalic) aqueduct.
38. It is a small groove and extends from the interventricular foramen to the cerebral aqueduct on the lateral wall of the third ventricle, separating the dorsal thalamus dorsally and the hypothalamus inferiorly.
39. The medial geniculate body, belonging to metathalamus, a relay station of the auditory conducting pathway, receives acoustic fibers from the inferior colliculus and the brachium of inferior colliculus. It projects fibers, via the acoustic radiation, to the auditory center of temporal cortex.
40. The pineal body is an endocrine gland that secretes a hormone, melatonin, which plays an important role in the control of sexual glands and biological clock of the body. After the age of 16, the pineal body is gradually calcified, hence usually taken as an imageological mark clinically. Pineal body is also belongs to epithalamus.
41. The internal capsule is a broad band of myelinated fibers that separates the lentiform nucleus from the medial caudate nucleus and thalamus. It has an anterior limb, genu, and a posterior limb.
42. The cerebral cortex is the highest level of the central nervous system. It is composed of gray matter and forms complete covering of the cerebral hemisphere. The surface area of the cortex has been increased by throwing it into convolution, or gyri, separated by fissures or sulci.
43. The basal ganglia refers to masses of gray matter deep within the cerebral hemispheres. Anatomically, the basal ganglia include the corpus striatum (caudate nucleus and lentiform nucleus), the claustrum, and the amygdaloid body.
44. The projection fibers connect the cerebral cortex with lower portions of the brain or the spinal cord. They are composed of afferent and efferent nerve fibers, form a compact band known as the internal capsule, which is flanked medially by the caudate nucleus and the thalamus and laterally by the lentiform nucleus.
45. The septal area is an area of gray matter lying above the lamina terminalis near and around the anterior commissure. It includes paraterminal gyms and paraolfactory area.
46. The fornix is composed of myelinated nerve fibers and constitutes the efferent system of the hippocampus that passes to the mammillary bodies of the hypothalamus.
47. The corpus callosum comprises the largest bundle of myelinated and nonmyelinated fibers, the
great white commissure that crosses under the longitudinal cerebral fissure and interconnects the hemisphere& It is the largest of the interhemispheric commissures and is largely responsible for coordinating the activities of the two cerebral hemispheres.
48. The Wernicke's area is localized in the left "dominant" hemisphere, mainly in the superior temporal gyms, with extensions around the posterior end of the lateral sulcus into the parietal lobe. It permits the understanding of the written and spoken language and enables a person to read a sentence with understanding and loudly.
49. The primary sensory areas and the primary motor areas form only a small part of the total cortical surface area. The remaining areas are referred to as association cortex. These areas of the cortex have multiple inputs and outputs and are very much concerned with behavior, discrimination, and interpretation of sensory.
50. The forms the transition between the archicortex and neocortex. It contains three to six layers and is found in such regions as the subicular complex, the cingulate gyrus and the insula.
Answer the Following Questions
1. Their receptors of the fasciculus gracilis and the fasciculus cuneatus are situated in the skin, joints and tendons. The two fasciculi are large proportion of the heavily myelinated fibers of posterior root that enter the ipsilateral posterior funiculus of the spinal cord. The fibers arising from the sacral, lumbar and lower eight thoracic segments make up the fasciculus gracilis, while the fibers arising from the upper four thoracic and cervical segments make up the fasciculus cuneatus. The fibers of these two tracts are somatotopically organized in their course, i.e., from the lateral to medial they are in cervical, thoracic, lumbar and sacral segmental order. After reaching the medulla oblongata, the fasciculus gracilis and the fasciculus cuneatus terminate upon the nuclei gracilis and nuclei cuneatus respectively. These two tracts conduct the kinesthetic senses (sense of position and movement) and the discriminating tactile (to recognize the size, shape and texture).
2. The posterior spinocerebellar tract is situated along the posterolateral periphery of the lateral funiculus of the spinal cord. It arises from the ipsilateral nucleus thoracicus and ascends through the spina! cord to the medulla oblongata in which it becomes incorporated in the inferior cerebellar peduncle. It conveys the subconscious proprioceptive impulses (controls muscular tension and coordination).
3. The anterior spinocerebellar tract is located along the lateral periphery of the lateral funiculus of the spinal cord, anterior to the posterior spinocerebellar tract. Its fibers arise from the lateral part of the laminae Ⅴ-Ⅸ and most of the fibers cross the spinal cord and ascend through the spinal cord, medulla oblongata and pons, then enter the cerebellum by coursing along the dorsal surface of the superior cerebellar peduncle. Its function is the same as that of the posterior spinocerebellar tract.
4. The lateral spinothalamic tract is closely inner to the anterior spinocerebellar tract. The nucleus proprius receives the thin myelinated fibers associated with pain and thermal senses from the dorsolateral fasciculus and gives rise to most of the axons that cross in the anterior white commissure and ascend in the opposite lateral funiculus as lateral spinothalamic tract. This tract passes through the brain stem and ends directly in the thalamus. Fibers of the lateral spinothalamic tract are somatotopically organized in their course, i.e. from the lateral to medial they are in sacral, lumbar, thoracic and cervical segmental order.
5. The anterior spinothalamic tract arises from the nucleus proprius, crossing the anterior white commissure, and ascending contralaterally anterior to the lateral spinothalamic tract. A small number of uncrossed fibers may ascend in the ipsilateral anterior spinothalamic tract. The spinothalamic tract transmits the pain and thermal sensation of trunk and limbs.
6. The lateral corticospinal tract arises from the motor and premotor area of the cerebral cortex and decussates in the medulla oblongata and descends medially to the posterior spinocerebellar tract in the spinal cord. The tract extends to the most caudal part of the spinal cord and progressively diminishes in size as more and more fibers leave to terminate in the motor neurons (lateral motor neuron column) of the anterior horn of the gray matter. This tract has somatotopical arrangement from the lateral to medial, that is in sacral, lumbar, thoracic and cervical segmental order.
7. The anterior corticospinal tract arises from the motor and premotor area of the cerebral cortex and occupies a strip adjacent to the anterior median fissure and normally extends only to the upper thoracic spinal segments. Most of these fibers decussate in the anterior white commisure before they terminate in the motor neurons (medial motor neuron column) of the anterior horn.
8. The rubrospinal tract lies anterior to and partially intermingled with the fibers of the lateral corticospinal tract. The fibers of this tract arise from the red nucleus of the midbrain, and cross the midbrain raphe immediately, and then to the spinal level. Their terminals contact cells in the posterior horn and intermediate zone through which they facilitate flexor motor neurons and control the muscular tone of the flexor muscle group.
9. The tectospinal tract arises from the neurons in the superior collieulus, and then decussates to the opposite side and descends through the pons and medulla oblongata to reach the cervical spinal segments. In the spinal cord, it's in the anterior part of the anterior funiculus near the anterior median fissure. The fibers of this tract innervate the motor neurons of anterior horn and excite the muscles of the neck of the opposite side and inhibit the ipsilateral cervical muscles.
10. The medial longitudinal fasciculus is formed by a small compact tract of nerve fibers, situated close to the medial plane and ventral to the hypoglossal nucleus. It is continuous upward throughout the pons and the midbrain and downwards in the anterior funiculus of the spinal cord. This fasciculus is the main pathway that connects the vestibular and cochlear nuclei with the nuclei controlling the extraocular muscles and the cervical anterior gray matter, principally the neurons innervating the muscles of the neck. It's chief function is to ensure the coordinate movement of the eyes and head response to stimulation of the vestibular-cochlear nerve.
11. The spinal cord occupies the upper two-thirds of the adult spinal canal within the vertebral column. It begins as a continuation of the medulla oblongata, and extends from the foramen magnum of the occipital bone to the inferior margin of the L1 level of the vertebral column in adults, and to the one of the L3 level in new-born. The length of the adult spinal cord ranges from 42 to 45cm.
The spinal cord is a long cylindrical structure that is slightly flattened anteriorly and posteriorly. The diameter of the spinal cord varies at different levels. When the spinal cord is viewed externally, two conspicuous enlargements can be seen. The enlargements of the spinal cord contain increased numbers of motor neurons and provide the origins of the nerves of the upper and lower extremities. The superior enlargement, the cervical enlargement, extends from the fourth cervical to the first thoracic segments. Nerves that supply the upper extremities arise from the cervical enlargement. The inferior enlargement, called the lumbosacral enlargement, extends from the second lumbar to the third sacral segments. Nerves that supply the lower extremities arise from the lumbosacral enlargement. Below the lumbosacral enlargement, the spinal cord tapes to form a conical portion known as the conus medullaris. Arising from the conus medullaris is the filum terminale, a nonnervous fibrous tissue of the spinal cord that extends inferior to attach to the coccyx. The filum terminale is long about 20 cm and consists mostly of pia mater, the innermost of three membranes that cover the spinal cord and brain. It becomes invested by dura mater, the outermost of three membranes that cover the spinal cord and brain, at the level of the second sacral vertebra and attaches to the posterior surface of the coccyx. On the surface of the spinal cord, six longitudinal grooves can be observed. A deep anterior median fissure and a shallow posterior median sulcus divide the spinal cord into symmetric right and left halves. There are two pairs of the shallow anterolateral sulci and postlateral sulci. The ventral roots and the dorsal roots of the spinal nerves are attached to the spinal cord along the grooves respectively. Besides the six longitudinal grooves, in the cervical and upper thoracic segments, a pair of smaller, less definite posterior intermediate sulci are present between the posterior median sulcus and the postlateral sulci.
The spinal cord is divided into 31 segments, 8 cervical segments, 12 thoracic segments, 5 lumbar segments, 5 sacral segments and 1 coccygeal segment. The spinal segment refers to a region of the spinal cord from which a pair of spinal nerves arises.
12. The spinal cord consists of both gray and white matter. A cross section of the spinal cord shows an H-shaped internal mass of gray matter surrounded by white matter. The gray matter consists primarily of nerve cell bodies, unmyelinated axons and dendrites of association and motor neurons. The white matter surrounds the gray matter and consists of bundles of myelinated axons of motor and sensory neurons. In the center of the gray matter, the gray commissure forms the cross bar of the H connecting the right and left portions. In the center of the gray commissure is a small space called the central canal, which runs the length of the spinal cord. It contains cerebrospinal fluid and is enlarged in the conus medullaris to form the 8-10cm long terminal ventricle. The anterior gray commissure and posterior gray commissure occupy the anterior and posterior halves of the gray commissure. The anterior (ventral) horn or anterior column is the enlarged protrusion in the front of the gray matter of each side. It contains the cells of origin of the fibers of the anterior roots, including alpha and gamma motor neurons. The posterior (dorsal) horn or posterior column is the narrow protrusion nearly reaching to the posterolateral sulcus. The posterior horn can be divided into a head, a neck and a relatively broad base. It represents the sensory part of the gray matter. The region between the anterior horn and posterior horn is the intermediate zone. The lateral horn or lateral column is a prominent lateral triangular projection of gray matter between the anterior and posterior horn or column in the thoracic and upper lumbar regions. It contains preganglionic cells for the autonomic nervous system. Within spinal segments T1-L3, preganglionic sympathetic neurons within the lateral column give rise to sympathetic axons that leave the spinal cord within the anterior roots and then travel to the sympathetic ganglia via the white rami communicantes. Within spinal segments S2-S4, there are sacral parasympathetic neurons within the lateral column. These neurons give rise to preganglionic parasympathetic axons that leave the spinal cord within the sacral anterior roots.
The form and quantity of the gray matter vary at different levels of the spinal cord. The proportion of gray to white matter is greatest in the lumbar and cervical enlargements. In the cervical region, the posterior column is comparatively narrow and the anterior column is broad and expansive, especially in the four lower cervical segments. In the thoracic region, both the posterior and anterior columns are narrow, and there is a lateral column. In the lumbar region, the posterior and anterior columns are broad and expanded. In the conus medullaris, the gray matter looks like two oval masses, one in each half of the spinal cord, connected by a wide gray commissure. The spinal cord has three white funiculi anterior (ventral), lateral and posterior (dorsal) funiculus around the spinal gray columns. The anterior funiculus lies between the anterolateral sulcus and the anterior median fissure. The posterior funiculus lies between the posterior median sulcus and the posterolateral sulcus. In the cervical and upper thoracic regions, the posterior funiculus is divided into a medial portion (the fasciculus gracilis) and a lateral portion (the fasciculus cuneatus). The posterior intermediate sulcus is the boundary between the fasciculus gracilis and fasciculus cuneatus. The lateral funiculus lies between the posterolateral sulcus and the anterolateral sulcus. Anterior to the gray commissure is a bundle of transverse fibers, the anterior white commissure.
The reticular formation is a field of intermingled gray and white matter collectively and is present in the area between lateral side of the base of the posterior horn and the white matter, especially obvious in the cervical segments. It is the important integration center for the vital activity.
13. Ascending tracts of the spinal cord
Name Location Origin Termination Function
Fasciculus Posterior Skin, joints, Nucleus gracilis and nucleus Finetouch
Medial longitudinal Anterior funiculus Vestibular nuclei Cervical Coordination of
Fasciculus gray matter head and
15. The stretch reflexes are also called tendon reflexes or deep tendon reflexes. The stretch reflex is based on a monosynaptie reflex arc. Only two neurons are involved, and there is only one synapse in the pathway. This reflex results in the contraction of a muscle when it is stretched. Slight stretching of a muscle stimulates receptors in the muscle called neuron musclar spindles. The spindles monitor changes in the length of the muscle. Once the spindle is stimulated, an impulse is sent along a sensory neuron to the spinal cord. The sensory neuron lies in the posterior root of a spinal nerve and synapses with a motor neuron in the anterior gray horn. The sensory neuron generates an impulse at the synapse that is transmitted along the motor neuron. The motor neuron lies in the anterior root of the spinal nerve and terminates in a skeletal muscle. Once the impulse reaches the stretched muscle, it contracts. Thus the stretch is counteracted by contraction. One such reflex is the knee-jerk, or patellar reflex. Stretch reflexes provide a feedback mechanism for maintaining appropriate muscle tone. The stretch reflex depends on specialized sensory receptors (muscle spindles), afferent nerve fibers (primarily Ia fibers) extending from these receptors via the dorsal roots to the spinal cord, two types of lower motor neurons (alpha and gamma motor neurons) that project back to muscle, and specialized inhibitory interneurons (Renshaw cells).