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Define the terms preganglionic and postganglionic neurons in sympathetic division of the ANS and the adrenal medulla order 50 mg imipramine with mastercard. Distinguish between single-unit and multiunit smooth parasympathetic neurons and the location of the muscles purchase 50mg imipramine free shipping. Explain how the two categories are regulated dif- parasympathetic ganglia purchase imipramine 50 mg on line. Objective 7 Describe the distribution of the vagus nerve and comment on its significance within the parasympathetic division of the ANS cheap 75mg imipramine with visa. Autonomic Nervous © The McGraw−Hill Anatomy, Sixth Edition Coordination System Companies, 2001 Chapter 13 Autonomic Nervous System 439 FIGURE 13. Conver- of the ANS because its preganglionic neurons exit the vertebral gence is apparent also when a postganglionic neuron receives column from the first thoracic (T1) to the second lumbar (L2) synaptic input from a large number of preganglionic neurons. Most sympathetic neurons, however, separate from the so- divergence of impulses from the spinal cord to the ganglia and the matic motor neurons and synapse with postganglionic neurons convergence of impulses within the ganglia usually results in the within chains of sympathetic trunk ganglia located on either side mass activation of almost all the postganglionic neurons. Postganglionic neurons from here innervate the postganglionic neurons located at their same level in the chain of smooth muscles and glands of the head and neck. Other preganglionic neurons travel up or down within the sympathetic chain before synapsing with postgan- glionic neurons. Because the postganglionic sympathetic neurons Peripheral Ganglia are unmyelinated and thus appear gray, they form the gray rami Many preganglionic neurons that exit the spinal cord below the communicantes. Postganglionic axons in the gray rami extend di- level of the diaphragm pass through the sympathetic trunk without rectly back to the anterior roots of the spinal nerves and travel dis- synapsing. Beyond the sympathetic trunk, these preganglionic neu- tally within the spinal nerves to innervate their effector organs. Autonomic Nervous © The McGraw−Hill Anatomy, Sixth Edition Coordination System Companies, 2001 440 Unit 5 Integration and Coordination Vagus nerve CI (cut) Superior cervical sympathetic ganglion CII Gray rami External carotid CIII artery and plexus CIV Carotid sinus CV CVI Middle cervical sympathetic ganglion CVII Intermediate cervical sympathetic ganglion CVIII Common carotid artery Inferior cervical sympathetic ganglion Subclavian artery Lew FIGURE 13. The adrenal cortex secretes steroid The greater splanchnic nerve arises from preganglionic sym- hormones; the adrenal medulla secretes the hormone epineph- pathetic neurons T4–T9 and synapses in the celiac ganglion. The lesser whose cells are derived from postganglionic sympathetic neurons. The cells of the adrenal medulla are innervated by preganglionic Postganglionic neurons from here innervate the small intestine sympathetic neurons originating in the thoracic level of the and colon. The lumbar splanchnic nerve synapses in the inferior spinal cord; they secrete epinephrine into the blood in response mesenteric ganglion, and the postganglionic neurons innervate to sympathetic stimulation. The effects of epinephrine are com- the distal colon and rectum, urinary bladder, and genital organs. Adrenal Glands The paired adrenal glands are located above each kidney (see fig. Each adrenal is composed of two parts: an outer Parasympathetic (Craniosacral) Division adrenal cortex and an inner adrenal medulla. These two parts The parasympathetic division is also known as the craniosacral di- vision of the autonomic system. This is because its preganglionic neurons originate in the brain (specifically, the midbrain, pons, adrenal: L. Autonomic Nervous © The McGraw−Hill Anatomy, Sixth Edition Coordination System Companies, 2001 Chapter 13 Autonomic Nervous System 441 Celiac ganglion Adrenal gland Superior mesenteric ganglion Left kidney Renal plexus First lumbar sympathetic Aortic ganglion plexus Inferior mesenteric ganglion Pelvic sympathetic chain FIGURE 13. Another group of neurons in the fa- parasympathetic ganglia, which are called terminal ganglia, supply cial nerve terminate in the submandibular ganglion, which the postganglionic neurons that synapse with the effector cells. Preganglionic neurons of the glossopharyngeal nerve the sympathetic and parasympathetic divisions. It should be synapse in the otic ganglion, which sends postganglionic neurons noted that, unlike sympathetic neurons, most parasympathetic to innervate the parotid gland. Cutaneous effectors Nuclei in the medulla oblongata contribute preganglionic (blood vessels, sweat glands, and arrector pili muscles) and blood neurons to the very long vagus nerves, which provide the most vessels in skeletal muscles thus receive sympathetic but not extensive parasympathetic innervation in the body (see parasympathetic innervation. As the paired vagus nerves pass through the thorax, Four of the twelve pairs of cranial nerves contain pregan- they contribute to the cardiac plexus and the pulmonary plexuses glionic parasympathetic neurons.

Note the diagrammatic representa- tion showing the direction of possible movement discount 75mg imipramine with visa. Note the diagrammatic repre- sentation showing the direction of possible movement discount 25 mg imipramine visa. Note the diagrammatic representation showing the direc- bone articulates with the cavity of another generic imipramine 50mg free shipping. Articulations © The McGraw−Hill Anatomy generic imipramine 75 mg without prescription, Sixth Edition Companies, 2001 Chapter 8 Articulations 205 FIGURE 8. Note the diagrammatic representation showing the direction of with the base of the first metacarpal bone. Suture Edges of articulating bones frequently jagged; None Sutures between bones of the skull separated by thin layer of fibrous tissue 2. Syndesmoses Articulating bones bound by interosseous ligament Slightly movable Joints between tibia-fibula and radius-ulna 3. Gomphoses Teeth bound into dental alveoli of bone by Slightly movable Dentoalveolar joints (teeth secured in periodontal ligament dental alveoli) Cartilaginous Joints Skeletal elements joined by fibrocartilage or hyaline cartilage 1. Symphyses Articulating bones separated by pad of fibrocartilage Slightly movable Intervertebral joints; symphysis pubis 2. Synchondroses Mitotically active hyaline cartilage located None Epiphyseal plates within long bones; between skeletal elements costal cartilages of rib cage Synovial Joints Joint capsule containing synovial membrane and synovial fluid 1. Gliding Flattened or slightly curved articulating surfaces Sliding Intercarpal and intertarsal joints 2. Hinge Concave surface of one bone articulates with Bending motion in one plane Knee; elbow; joints of phalanges convex surface of another 3. Pivot Conical surface of one bone articulates with Rotation about a central axis Atlantoaxial joint; proximal depression of another radioulnar joint 4. Condyloid Oval condyle of one bone articulates with Movement in two planes Radiocarpal joint; elliptical cavity of another metacarpophalangeal joint 5. Saddle Concave and convex surface on each Wide range of movements Carpometacarpal joint of thumb articulating bone 6. Ball-and-socket Rounded convex surface of one bone articulates Movement in all planes and Shoulder and hip joints with cuplike socket of another rotation Van De Graaff: Human IV. Articulations © The McGraw−Hill Anatomy, Sixth Edition Companies, 2001 Developmental Exposition cleft eventually enlarges to become the joint cavity. Thin pads of The Synovial Joints hyaline cartilage develop on the surfaces of the epiphyses that contact the joint cavity. As the joint continues to develop, a EXPLANATION highly vascular synovial membrane forms on the inside of the The sites of developing synovial joints (freely movable joints) are joint capsule and begins secreting a watery synovial fluid into the discernible at 6 weeks as mesenchyme becomes concentrated in joint cavity. At this In certain developing synovial joints, the mesenchymal stage, the future joints appear as intervals of less concentrated cells do not migrate away from the center of the joint cavity. As cartilage cells develop within a forming Rather, they give rise to cartilaginous wedges called menisci, as bone, a thin flattened sheet of cells forms around the cartilagi- in the knee joint, or to complete cartilaginous pads called articu- nous model to become the perichondrium. Most synovial joints have formed completely by the end Surrounding the gap, the flattened mesenchymal cells differenti- of the third month. Shortly thereafter, fetal muscle contrac- ate to become the joint capsule. During the early part of the third month of development, the Joint movement enhances the nutrition of the articular carti- mesenchymal cells still remaining within the joint capsule begin to lage and prevents the fusion of connective tissues within migrate toward the epiphyses of the adjacent developing bones. At 12 weeks, the synovial joints are formed and have either (c) a free joint cavity (e. Articulations © The McGraw−Hill Anatomy, Sixth Edition Companies, 2001 Chapter 8 Articulations 207 Extension MOVEMENTS AT SYNOVIAL JOINTS In extension, which is the reverse of flexion, the joint angle is Movements at synovial joints are produced by the contraction of increased (fig. Extension returns a body part to anatomi- skeletal muscles that span the joints and attach to or near the cal position. In an extended joint, the angle between the articu- bones forming the articulation. An exception is the ankle joint, in which levers, the muscles provide the force, and the joints are the fulcra, there is a 90° angle between the foot and leg in anatomical posi- or pivots.

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It has also been shown that at I I very short lengths imipramine 25mg on line, the effectiveness of some of the steps in A A A the excitation-contraction coupling process is reduced generic imipramine 25mg mastercard. These include reduced calcium binding to troponin and some loss of action potential conduction in the T tubule system discount imipramine 25 mg on-line. Some of the consequences for the muscle as a whole are apparent when the mechanical behavior of mus- Most overlap cle is examined in more detail (see Chapter 9) purchase 50 mg imipramine. The overall shortening is the sum of Events of the Crossbridge Cycle the shortening of the individual sarcomeres. Drive Muscle Contraction The process of contraction involves a cyclic interaction be- tween the thick and thin filaments. The steps that comprise amount of force that can be produced, since a shorter the crossbridge cycle are attachment of thick-filament length of thin filaments interdigitates with A band thick fil- crossbridges to sites along the thin filaments, production of aments and fewer crossbridges can be attached. Thus, over a mechanical movement, crossbridge detachment from the this region of lengths, force is directly proportional to the thin filaments, and subsequent reattachment of the cross- degree of overlap. At lengths near the normal resting bridges at different sites along the thin filaments (Fig. Most of our knowledge of this process comes from studies on skeletal muscle, but the same basic steps are followed in all muscle types. Initially, the crossbridges extend at right angles from each thick filament, but they rapidly undergo a 1. An ATP molecule bound to each crossbridge supplies the energy for this step. The myosin head to which the ATP is bound is called “charged myosin” (M*ADP*Pi in step 1). When charged myosin interacts with actin, the association is represented as A*M*ADP*Pi (step 2). The force a muscle can produce depends sociated with the final hydrolysis of the bound ATP and re- on the amount of overlap between the thick and thin filaments lease of the hydrolysis products (step 3), an inorganic phos- because this determines how many crossbridges can interact ef- phate ion (P ) and ADP. An impor- tant series of these steps, called excitation-contraction coupling, takes place deep within a muscle fiber. This is the Hydrolysis subject of the remainder of this chapter; the very early Product events (communication between nerve and muscle) and the A M*ADP release and very late events (actual mechanical activity) are discussed Detachment power in Chapter 9. The SR controls the internal concentration of these ions, and changes in the internal calcium ion concentration have The events of the crossbridge cycle in profound effects on the actions of the contractile proteins FIGURE 8. Undesired contraction is prevented by a spe- new ATP molecule binds to the myosin head and is ⑦ subse- quently hydrolyzed. These cyclic reactions can continue as long cific inhibition of the interaction between actin and as the ATP supply remains and activation (via Ca2 ) is main- myosin. The long tropomyosin molecules, lying in the grooves of the en- twined actin filaments, interfere with the myosin binding tion pulls the actin filaments past the myosin filaments, a sites on the actin molecules. Following this tions increase, the ions bind to the Tn-C subunit associated movement (which results in a relative filament displace- with each tropomyosin molecule. Through the action of ment of around 10 nm), the actin-myosin binding is still Tn-I and Tn-T, calcium binding causes the tropomyosin strong and the crossbridge cannot detach; at this point in molecule to change its position slightly, uncovering the the cycle, it is termed a rigor crossbridge (A*M, step 5). The myosin detachment to occur, a new molecule of ATP must bind to (already “charged” with ATP) is allowed to interact with the myosin head (M*ATP, step 6) and undergo partial hy- actin, and the events of the crossbridge cycle take place un- drolysis to M*ADP*Pi (step 7). Once this new ATP binds, the newly recharged myosin head, momentarily not attached to the actin fila- The Switching Action of Calcium. An effective switching ment (step 1), can begin the cycle of attachment, rota- function requires the transition between the “off” and “on” tion, and detachment again. This can go on as long as the states to be rapid and to respond to relatively small changes muscle is activated, a sufficient supply of ATP is avail- in the controlling element. The calcium switch in skeletal able, and the physiological limit to shortening has not muscle satisfies these requirements well (Fig. If cellular energy stores are depleted, as curve describing the relationship between the relative force happens after death, the crossbridges cannot detach be- developed and the calcium concentration in the region of cause of the lack of ATP, and the cycle stops in an at- the myofilaments is very steep.

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