Q. Jerek. Indiana Institute of Technology.
The anterior spi- they give off two thin posterior spinal arter- nal artery supplies the anterior horns cheap 100 mg suhagra with amex, the ies that form a network of small arteries bases of the posterior horns generic suhagra 100 mg with visa, and the largest along the posterior surface of the spinal part of the anterior lateral funiculi (E9) buy suhagra 100mg. At the level of the pyramidal decussa- posterior funiculi and the remaining parts tion buy generic suhagra 100 mg line, two additional branches of the verte- of the posterior horns are supplied by the bral arteries join to form the anterior spinal posterior spinal arteries (E10). The marginal artery (AD2) which runs along the anterior zone of the anterior lateral funiculus is sup- surface of the spinal cord at the entrance to plied by the plexus of the vasocorona (E11). Their posterior which one anterior spinal vein and two pos- branches(C4)andthevertebralarteriesgive terior spinal veins stand out. The efferent off spinal branches (C5) which enter through veins run along the spinal roots and open the intervertebral foramina and divide at into the epidural venous plexus (see vol. Of the 31 spinal arteries, only 8 to 10 extend to the spinal cord and C12 Aorta. The levels at which the radicular arteries approach the spinal cord vary, and so do the sizes of the vessels. The largest vessel approaches the spinal cord at the level of the lumbar en- largement between T12 and L3 (large radicu- lar artery) (A6). The anteriorspinalartery is widest at the level of the cervical and lumbar enlargements. Its diameter is much reduced in the mid- thoracic region of the spinal cord. As this re- gion is also the border area between two supplyingradiculararteries,thissegmentof the spinal cord is especially at risk in case of circulatory problems (A, arrow). Depending on the variation of the radicular arteries, this may also apply to other segments of the spinal cord. The anterior spinal artery gives off numer- ous small arteries into the anterior sulcus, the sulcocommissuralarteries (D7). In the cer- vical and thoracic spinal cords, they turn al- ternately to the left and right halves of the spinal cord; in the lumbar and sacral spinal cords, they divide into two branches. Spinal Blood Vessels 61 1 C 1 2 5 C 3 C 5 3 4 T 1 12 T 3 C Afferent blood vessels T 5 T 8 8 T10 7 2 D Vascularization of the spinal cord 6 L 2 10 L 5 11 9 A B Arteries and veins E Areas supplied by the spinal cord of the spinal cord arteries (according to Gillilan) Kahle, Color Atlas of Human Anatomy, Vol. It contains fibers of various cali- bers, two-thirds of them being poorly my- The posterior spinal root contains a spindle- elinated or unmyelinated fibers. The thin shaped bulge, the spinal ganglion (A), an poorly myelinated and unmyelinated fibers, accumulation of cell bodies of sensory neu- which transmit impulses of the protopathic rons; their bifurcated processes send one sensibility (p. They lie thick myelinated fibers transmit impulses as cell clusters or as cell rows between the of the epicritic sensibility and enter through bundles of nerve fibers. This zone is regarded as the boundary Hence, the spinal ganglia can be regarded as between the central and the peripheral gray matter of the spinal cord that became nervous systems (Redlich–Obersteiner zone) translocated to the periphery. In the electron-microscopic image (H), tives of the neural crest are the cells of the however, this boundary does not exactly autonomic ganglia, the paraganglia, and the coincide with the Redlich–Obersteiner adrenal medulla. Foreachaxon,theboundaryismarked by the last node of Ranvier prior to the en- From the capsule (A3) of the spinal gan- trance into the spinal cord. Up to this point, glion,whichmergesintotheperineuriumof the peripheral myelin sheath is surrounded the spinal nerve, connective tissue extends by a basal membrane (blue in H). The next to the interior and forms a sheath around internode no longer has a basal membrane. The innermost sheath, however, also marked by the basal membrane of the is formed by ectodermal satellite cells (BE5) enveloping Schwann cell. Thus, the basal and is surrounded by a basal membrane membranes around the spinal cord form a comparable to that around the Schwann boundary that is only penetrated by the cellsoftheperipheralnerve. The remainder consists of medium-sized and small ganglion cells with poorly myeli- nated or unmyelinated nerve fibers which arethoughttoconduct pain signals and sen- sations from the intestine. During development, however, the two processes fuse to form a single trunk which then bifurcates in a T-shaped man- ner. Spinal Ganglion and Posterior Root 63 A Spinal ganglion B Detail of A 3 5 6 4 1 2 2 C Development of the spinal ganglion 5 D Development of the pseudounipolar ganglion cell 8 E Spinal ganglion cell and satellite cells 7 F Posterior root G Redlich–Obersteiner zone H Posterior root, electron-micro scopic diagram (according to Andres) Kahle, Color Atlas of Human Anatomy, Vol. The pia mater contains numerous small blood vessels that penetrate from the The spinal dura mater forms the outermost surface into the spinal cord. A connective sheath which is separated from the perios- tissue plate, the denticulate ligament (A17), teum-like lining of the vertebral canal, the extends on both sides of the spinal cord endorhachis (A4), by the epidural space (A5).
These cell groups linked and share a seven-membrane-spanning segment are functionally dissimilar suhagra 100mg with amex. The parasympathetic and sympathetic the striatum or involved in language construction suhagra 100mg without prescription. Although not known for certain suhagra 100 mg overnight delivery, it is ceptor at the neuromuscular junction purchase suhagra 100 mg on-line. Circulating leptin levels are sensed by retrieval of stored declarative memory does not require neurons in the arcuate nucleus, which does not possess the hippocampus. While some other regions of the the formation or retrieval of procedural memory. Wernicke’s area is responsible for the gions do not contain leptin-sensing cells. Circadian rhythms are entrained by when it is damaged, the individual speaks but the con- the SCN to the external day/night cycle. Damage to Broca’s area results in an information reaches the SCN directly by an optic inability to speak clearly because it controls the motor nerve projection from the retina. The internal clock re- patterns required to speak; the little speech that is pro- sides in the SCN and regulates the production of mela- duced is grammatically and syntactically correct. Reticular formation and vi- hippocampus and corpus callosum are not involved in sual cortical inputs are not directly involved in the the generation of speech. Magnocellular neurons of the par- generated in the Wernicke’s area would not be con- aventricular and supraoptic nuclei of the hypo- veyed to Broca’s area. Mania is an affective disorder char- the hypothalamo-hypophyseal tract, secrete the poste- acterized by increased transmission through noradren- rior pituitary hormones. Other transmitter systems may play a from the hypothalamus to the pituitary gland is associ- role, but effective treatments are targeted at the nora- ated with the anterior pituitary. Acetylcholine is critical for cognitive reticular activating system, or emotional state, none of function because of the cholinergic neurons in the these directly mediates posterior pituitary hormone se- basal forebrain that relay hippocampal information to cretion. The only effective drugs for the treatment of dle connecting Broca’s and Wernicke’s areas. The cognitive deficits in Alzheimer’s disease are choliner- fornix connects the hippocampus with the hypothala- gic, although cognition clearly involves neurons in mus and basal forebrain. The thalamocortical tract many regions of the brain that utilize a variety of trans- connects the thalamus with the cortex and the reticu- mitters. In all muscle types, the interaction be- symptoms of psychosis in disorders such as schizophre- tween actin and myosin provides the forces that result nia. Skeletal and cardiac muscle have repeat- derstood and many transmitter systems may be in- ing sarcomeres, but smooth muscle does not. The width of the I band changes be- ing system and convey information to the cortex. These nuclei are critical for the maintenance of arousal The Z lines move closer together. Without the intralaminar nuclei, band width and the moving of the Z lines together are beta rhythms and attention would be severely compro- proportional, but there is no change in A band dimen- mised. ATP must bind to the myosin heads the reticular activating system and its input. Relaxed skeletal muscle is in a state of which does not generate language. The enzymatic activity of myosin what the object is, the information must cross to the is greatly enhanced by its interaction with actin. This crossing occurs through the cor- role of calcium is as an activator, not an inhibitor; at rest, pus callosum. The fornix and hippocampus would be the concentration of free calcium is low. Neither the primary so- ament space into the sarcoplasmic reticulum (not the matic sensory cortex on the left side nor the visual cor- extracellular space) is an absolute requirement for nor- tex on either side plays a role in identifying an object mal relaxation. A reduction of ATP would promote placed in the left hand by tactile cues.
Ganglia and nerve occasionally by some fibers from C4 plexuses are also part of the PNS purchase suhagra 100mg amex. Each of the 31 pairs of spinal nerves is (a) The brachial plexus is divided into and the spinal nerves arise from the spinal formed by the union of an anterior roots buy suhagra 100mg fast delivery, trunks purchase 100mg suhagra free shipping, divisions discount suhagra 100 mg otc, and cords. Sensory (afferent) nerves convey impulses root that emerges from the spinal cord musculocutaneous, ulnar, and median toward the CNS, whereas motor through an intervertebral foramen to are the five largest nerves arising from (efferent) nerves convey impulses away innervate a body dermatome. The lumbar plexus is formed by the composed of both sensory and motor to the levels of the spinal column from anterior rami of L1 through L4 and by fibers. Twelve pairs of cranial nerves emerge consisting of a posterior root of sensory (b) The femoral and obturator are two from the inferior surface of the brain fibers and an anterior root of motor fibers. The sacral plexus is formed by the anterior the foramina of the skull to innervate rami of L4, L5, and S1 through S4. The names of the cranial nerves indicate T12, the anterior rami of the spinal (b) The sciatic nerve, composed of the their primary function or the general nerves combine and then split again as common fibular and tibial nerves, distribution of their fibers. The olfactory, optic, and (a) There are four plexuses of spinal (c) The lumbar plexus and the sacral vestibulocochlear cranial nerves nerves: the cervical, the brachial, the plexus are collectively referred to as are sensory only; the trigeminal, lumbar, and the sacral. Peripheral Nervous © The McGraw−Hill Anatomy, Sixth Edition Coordination System Companies, 2001 Chapter 12 Peripheral Nervous System 433 Reflex Arc and Reflexes (pp. A reflex arc is the simplest type of nerve (a) The stretch reflex is a monosynaptic motor neuron and its innervation in the pathway. Visceral reflexes cause smooth or cardiac (b) The flexor reflex is a polysynaptic more association neurons in the CNS. The reflex arc enables a rapid, automatic Review Activities Objective Questions 7. A person with quadriplegia from a spinal (b) It contains components of the (e) the sacral plexus cord injury at the level of C5 can speak, autonomic nervous system. Roots, trunks, divisions, and cords are digest food, breath, and regulate his or her (c) Sensory receptors, nerves, ganglia, characteristic of heartbeat, yet the person cannot move and plexuses are all part of the PNS. Which cranial nerve innervates the (c) axillary/brachial appointment with the company doctor muscle that raises the upper eyelid? Following a routine physical exam, (b) the oculomotor nerve ligament is tapped is an example of the physician scheduled the man for a (c) the abducens nerve (a) a visceral reflex. Discuss (b) the facial nerve Essay Questions the possible treatment of this condition. Explain the structural and functional (You may have to refer to medical (d) the vagus nerve relationships between the central nervous textbooks in your library to find the system, the autonomic nervous system, answer. Which cranial nerve passes through the and the peripheral nervous system. List the cranial nerves and describe the punch during the world featherweight (a) the facial nerve major function(s) of each. How is each championship fight, the ringside (b) the glossopharyngeal nerve cranial nerve tested for dysfunction? List the roots of each of the spinal damage when his right zygomatic bone 6. Describe where each plexus is located and state the nerves that originate symptoms might the boxer have displayed fibers? Autonomic Nervous © The McGraw−Hill Anatomy, Sixth Edition Coordination System Companies, 2001 Autonomic Nervous System 13 Introduction to the Autonomic Nervous System 435 Structure of the Autonomic Nervous System 438 Functions of the Autonomic Nervous System 444 Control of the Autonomic Nervous System by Higher Brain Centers 448 CLINICAL CONSIDERATIONS 450 Clinical Case Study Answer 451 Chapter Summary 451 Review Activities 452 Clinical Case Study A low-flying crop duster sprays a field worker. Within the hour, he develops blurry vision, ex- cessive salivation, and a runny nose. As the minutes pass, he begins to experience nausea, vom- iting, abdominal cramping, and coughing up of copious mucus. An observant paramedic called to the scene makes a diagnosis of organophosphate poisoning and promptly initiates therapy. Can you account for each of the symptoms this man suffered by describing the normal response of individual organs to parasympathetic stimuli? What effect would this drug have on the eyes, salivary glands, and nose?
At the right are the analogous biological steps in- transformed into a corresponding action potential frequency discount 100 mg suhagra free shipping, and volved in the same process order 100mg suhagra with visa. CNS processes decode the nerve activity into biologically useful cated composite modalities of itch generic suhagra 100mg visa, tickle buy cheap suhagra 100mg on line, wet, and so on. Ruffini of pressure, vibration, heat, or cold, the distribution of cu- endings (located in the dermis) are also slowly adapting re- taneous receptors over the skin can be mapped. Merkel’s disks in areas of hairy skin are grouped areas of skin used in tasks requiring a high degree of spatial into tactile disks. Nonmyelinated nerve endings, also usually specific receptors, and these areas are correspondingly well found in hairy skin, appear to have a limited tactile function represented in the somatosensory areas of the cerebral cor- and may sense pain. Several receptor types serve the sensa- warm and cold represent values along a temperature contin- tions of touch in the skin (Fig. In regions of hairless uum and do not differ fundamentally except in the amount skin (e. However, the familiar subjec- Meissner’s corpuscles, and pacinian corpuscles. Merkel’s tive differentiation of the temperature sense into “warm” and disks are intensity receptors (located in the lowest layers of “cold” reflects the underlying physiology of the two popula- the epidermis) that show slow adaptation and respond to tions of receptors responsible for thermal sensation. Meissner’s corpuscles adapt more rapidly Temperature receptors (thermoreceptors) appear to be to the same stimuli and serve as velocity receptors. The naked nerve endings supplied by either thin myelinated Pacinian corpuscles are very rapidly adapting (accelera- fibers (cold receptors) or nonmyelinated fibers (warm re- tion) receptors. They are most sensitive to fast-changing ceptors) with low conduction velocity. In regions of hairy skin, small form a population with a broad response peak at about 70 PART II NEUROPHYSIOLOGY range, steady temperature sensation depends on the ambi- ent (skin) temperature. At skin temperatures lower than Hairless skin Hairy skin 17 C, cold pain is sensed, but this sensation arises from pain receptors, not cold receptors. At very high skin tem- Horny peratures (above 45 C), there is a sensation of paradoxical layer cold, caused by activation of a part of the cold receptor Epidermis population. Temperature perception is subject to considerable pro- cessing by higher centers. While the perceived sensations reflect the activity of specific receptors, the phasic compo- nent of temperature perception may take many minutes to Dermis be completed, whereas the adaptation of the receptors is complete within seconds. The familiar sensation of pain is not limited to cu- Subcutaneous taneous sensation; pain coming from stimulation of the tissue body surface is called superficial pain, while that arising from within muscles, joints, bones, and connective tissue is called deep pain. Visceral pain arises from internal organs and is often due to strong contractions of visceral muscle or its forcible deformation. Pain is sensed by a population of specific receptors Meissner’s called nociceptors. In the skin, these are the free endings of Hair-follicle Merkel’s corpuscle receptor disks thin myelinated and nonmyelinated fibers with characteris- tically low conduction velocities. They typically have a high threshold for mechanical, chemical, or thermal stimuli (or a combination) of intensity sufficient to cause tissue de- struction. The skin has many more points at which pain can be elicited than it has mechanically or thermally sensitive Tactile Pacinian Ruffini sites. Because of the high threshold of pain receptors (com- disks corpuscle ending pared with that of other cutaneous receptors), we are usu- Tactile receptors in the skin. Both sets of receptors share some common mediated by different nerve fiber endings. In addition to features: • They are sensitive only to thermal stimulation. The density of temperature receptors differs at different places on the body surface. They are present in much lower numbers than cutaneous mechanoreceptors, and there are many more cold receptors than warm receptors. The perception of temperature stimuli is closely related to the properties of the receptors.