By T. Karlen. York College of Pennsylvania. 2017.
Cardiac Muscle Like skeletal muscle fibers buy discount ampicillin 500 mg online, cardiac muscle fibers are striated. Damage to an autonomic nerve, in fact, makes its target spread to all cells in the mass that are joined by intercalated muscle more sensitive than normal to stimulating agents. Because all of the cells in the myocardium are physiologi- Van De Graaff: Human V. Autonomic Nervous © The McGraw−Hill Anatomy, Sixth Edition Coordination System Companies, 2001 Chapter 13 Autonomic Nervous System 437 TABLE 13. Origin of electrical activity Spontaneous activity of myogenic fibers Not spontaneously active; neurogenic action potentials Type of stimuli Action potentials Graded depolarizations Response to stretch By contraction; not dependent on action potentials No inherent response Presence of gap junctions Numerous gap junctions join all fibers together Few (if any) gap junctions electrically Type of muscle contraction Slow and sustained Slow and sustained cally joined, the myocardium behaves as a single functional unit, half times their resting length. Unlike skeletal muscles, their ability to contract when the sarcomeres are stretched to the which can produce graded contractions with a strength that de- point where actin and myosin no longer overlap. Single-Unit and Multiunit Smooth Muscles Furthermore, whereas skeletal muscle fibers require stimu- Smooth muscles are often grouped into two functional cate- lation by action potentials through somatic motor neurons before gories: single-unit and multiunit. Single-unit smooth muscles they can contract, cardiac muscle fibers are able to produce ac- have numerous gap junctions (electrical synapses) between adja- tion potentials automatically. Multiunit smooth muscles have few, if any, gap cally independent from stimulation from action potentials. Car- junctions; thus, the individual cells must be stimulated separately diac action potentials normally originate in a specialized group of by autonomic action potentials through motor neurons. However, the rate of similar to the control of skeletal muscles, in which numerous this spontaneous depolarization, and thus the rate of the heart- motor units are activated. Single-unit smooth muscles display pacemaker activity, in which certain cells stimulate others in the mass. Single-unit Smooth Muscles smooth muscles also display intrinsic, or myogenic, electrical ac- Smooth (visceral) muscle tissue is arranged in circular layers tivity and contraction in response to stretch. For example, the around the walls of blood vessels, bronchioles (small air passages stretch induced by an increase in the luminal contents of a small in the lungs), and in the sphincter muscles of the GI tract. How- artery or a section of the GI tract can stimulate myogenic con- ever, both circular and longitudinal smooth muscle layers are traction. Such contraction does not require stimulation by auto- found in the tubular GI tract, the ureters (which transport urine), nomic nerves.
Label the myofibril ampicillin 250 mg on-line, sarcomeres, A bands, (a) I bands, H bands, and Z lines. Draw three successive sarcomeres in a myofibril of a con- tracted fiber. Indicate which bands get shorter during con- traction and explain how this occurs. Describe how the antagonistic muscles in the brachium can be exercised through both isotonic and isometric contractions. Explain why sarcomeres are considered the basic structural components of skeletal muscles, and motor units are considered the basic functional units of muscle contraction. NAMING OF MUSCLES (a) An isometric contraction, in which the muscle stays the same length and (b) an isotonic contraction, in which the muscle shortens. Skeletal muscles are named on the basis of shape, location, at- tachment, orientation of fibers, relative position, or function. Objective 9 Use examples to describe the various ways in which muscles are named. Skeletal muscles are voluntary in that they can be con- sciously contracted. The magnitude of the task determines the One of your tasks as a student of anatomy is to learn the names number of motor units that are activated. Although this may seem task, such as lifting a book, requires few motor units, whereas overwhelming, keep in mind that most of the muscles are paired; lifting a table requires many. Muscles with pennate architecture that is, the right side is the mirror image of the left. To help you have many motor units and are strong and dexterous; however, further, most muscles have names that are descriptive. Identify the muscle on the figure referenced in the text nar- athletic feat involves voluntary activation of more motor units rative and locate it on your own body as well. Feel it contracting beneath your skin and note motor units within a muscle, the secretion of epinephrine (ep'ı˘- the movement that occurs at the joint. Shape: rhomboideus (like a rhomboid); trapezius (like a testes, and ovaries.
Attritional tendinosis is associated tion can be seen between the glenoid margin and the with a narrow bicipital groove and hence it affects the ex- labrum buy ampicillin 250mg lowest price. In contrast to the Bankart lesion, the ALPSA le- tracapsular portion of the tendon. Magnetic resonance sion can heal, leaving a deformed and patulous labrum. After the acute episode of dislocation, Complete rupture of the LBT more often occurs prox- the arm frequently remains locked in adduction and in- imally, at the level of the proximal portion of the extra- ternal rotation. Posterior instability caused by repeated capsular segment, within the groove. MRI demonstrates micro-trauma, without frank dislocation, may cause per- the absence of the LBT in the groove and its distal dis- sistent shoulder pain in young athletes. Intracapsular tears of the LBT are seen more ion and internal rotation are the mechanism involved in often in patients with rotator cuff tears. This nosis affecting the intertubercular portion of the LBT can may be also associated with posterior capsular laxity. A bifid LBT (normal tear, posterior capsular stripping or laxity, fracture, ero- variant) should not be confused with a partial longitudi- sion, or sclerosis and ectopic bone formation of the pos- nal tear. In the first type, the insertional sions involve the superior part of the labrum with vary- fibers of the subscapularis tendon are intact. Pain, click- ond type, the subscapularis tendon is detached and the ing, and occasional instability in a young patient are the LBT is medially displaced, becoming entrapped intra-ar- typical clinical manifestations. Shoulder 5 Compressive Neuropathies rial mixed with hyperintense cartilage may mimic pig- mented villonodular synovitis, especially if bone erosions The suprascapular nerve and its branches can become are present. Other differential diagnostic considerations compressed or entrapped by stretching due to repetitive include entities that can produce multiple intra-articular scapular motion, or they can be damaged by scapular bodies, such as osteocartilaginous loose bodies related to fractures, overhead activities, soft-tissue masses or direct osteoarthritis or osteochondral trauma, and “rice bodies”, trauma. T2-weighted images can show hyperintensity of such as those seen in rheumatoid arthritis and tuberculo- the involved muscle.
Oligodendrites are glial cells which are involved in myelin formation and although they also have long processes buy ampicillin 250 mg without a prescription, these are spirally bound rather than extending out as in the astocytes. Neurons and glia are bathed in an ion-containing protein-free extracellular fluid which occupies less of the tissue volume (20%) in the brain than in other organs because of the tight packing of neurons and glia. In fact the whole brain is really suspended in fluid within its bony casing. The brain and spinal cord are covered by a thin close-fitting membrane, the pia mater and a thicker loose outer membrane, the dura mater. In the space between them, the subarachnord space, is the cerebrospinal fluid (CSF). This also flows into a series of ventricular spaces within the brain as well as a central canal in the cord and arises mainly as a secretion (ultra filtrate) of blood from tufts of specialised capillaries (the choroid plexus), which invaginate the walls of the ventricles. While the CSF is contiguous with the extracellular fluid within the brain and contributes to it, much of this fluid comes directly from the copious network of capillaries found throughout the brain. In fact neurons are never far from a capillary and their high metabolic rate means that despite contributing only 2% towards body weight, the nervous system receives 15% of cardiac output. In most parts of the body, substances, other than large molecular ones like proteins, are filtered from the blood into the extracellular space through gaps between endothelial cells in the capillary wall. Such gaps are much narrower, almost non- existent, in brain capillaries and it is likely that any filtering is further reduced by the manner in which astrocytes pack around the capillaries. This constraint is known as the NEUROTRANSMITTER SYSTEMS AND FUNCTION: OVERVIEW 11 blood±brain barrier (BBB). It protects the brain from inappropriate substances, including all NTs and many drugs. To enter the brain as a whole is therefore almost as difficult for a substance as entering a neuron and again it has to be either very lipid soluble, when it can dissolve in and so pass through the capillary wall, or be transported across it.
Home | Contact | Rates | Appraisals | Articles & Info | Links | Cars for Sale