By A. Grimboll. Southwest Florida College.
The small size of the SR also limits its cal- muscles safe viagra jelly 100mg, in cardiac muscle buy viagra jelly 100 mg without a prescription, it is the basis of the remarkable cium storage capacity, and the other source of calcium en- capacity of the heart to adjust to a wide range of physio- try and exit, the sarcolemma, has an important role in the logical conditions and requirements. The sarcomeres appear essentially like those of skeletal muscle, with similar A bands and I bands, Z lines, and M PHYSIOLOGICAL SPECIALIZATIONS lines. Myofilaments make up almost half the cell volume and OF CARDIAC MUSCLE are bathed in the cytosol. Numerous mitochondria comprise another 30 to 40% of the cell volume, reflecting the highly Cardiac muscle is a striated muscle, but it functions rather aerobic nature of cardiac muscle function. The lack of skeletal at- cell volume, about 15%, consists of cytosol, containing nu- tachments provides a wider range of lengths over which it merous enzymes and metabolic products and substrates. Special features of the excitation-contraction coupling process allow a subtle degree of control at the level of the muscle that is largely independent of the cen- Cardiac Muscle Cells Are Linked in a tral nervous system (CNS). Functional Syncytium Electron microscopy reveals that in the region of the inter- Specialized Electrical and Metabolic Properties calated disk, each cardiac myocyte sends processes deep Control Cardiac Muscle Contraction into its neighboring cell to form an interdigitating junction with a large surface area. Gap junctions in the intercalated A more detailed treatment of the electrical properties of car- disks function like those of smooth muscle, allowing close diac muscle is given in Chapter 13. Also plentiful in cuses on the electrical properties most closely related to con- the intercalated disk region are desmosomes, areas where trolling the mechanical function of cardiac ventricular muscle. This mode of attachment, rather than an extensive extracellular The Cardiac Action Potential. As in other types of mus- connective tissue matrix as in smooth muscle, allows the cle and in nerve, the muscle cells of the heart have an ex- transmission of force from cell to cell. The intercalated citable and selectively permeable cell membrane that is re- disk, therefore, allows cardiac muscle to form a functional sponsible for both resting potentials and action potentials. The conduction of action poten- diverse and complex than in skeletal muscles and are much tials is solely a function of the muscle tissue. Impulse prop- more closely linked to the actual form of the mechanical agation is aided by the branched nature of the cells, the in- contraction.
Amanda eration has given me the opportunity to make the improvements seen Ellis generic viagra jelly 100mg otc, B generic viagra jelly 100 mg free shipping. I am indebted to the following individuals for their careful review Last, but certainly not least, I would like to express a special thanks of previous editions of the book: Drs. Dietrichs, in progress, carefully reviewed all changes in the text and all ques- J. The goal is not Abooks are becoming available to students and instruc- only to show external and internal structure per se but also tors, it is appropriate to brieﬂy outline the approach used in to demonstrate that the relationship between brain anatomy this volume. Most books are the result of 1) the philosophic and MRI/CT, the blood supply to speciﬁc areas of the CNS approach of the author/instructor to the subject matter and and the arrangement of pathways located therein, the neu- 2) students’ needs as expressed through their suggestions roactive substances associated with pathways, and examples and opinions. The present atlas is no exception, and as a re- of clinical deﬁcits are inseparable components of the learn- sult, several factors have guided its further development. An effort has been made to provide a for- These include an appreciation of what enhances learning in mat that is dynamic and ﬂexible—one that makes the learn- the laboratory and classroom, the inherent value of corre- ing experience an interesting and rewarding exercise. The goal is to make considering that approximately 50% of what goes wrong in- it obvious to the user that structure and function in the CNS side the skull, producing neurological deﬁcits, is vascular- are integrated elements and not separate entities. To emphasize the value of this information, the dis- Most neuroanatomic atlases approach the study of the tribution pattern of blood vessels is correlated with external CNS from fundamentally similar viewpoints. These atlases spinal cord and brain anatomy (Chapter 2) and with inter- present brain anatomy followed by illustrations of stained nal structures such as tracts and nuclei (Chapter 5), re- sections, in one or more planes. Although variations on this viewed in each pathway drawing (Chapter 7), and shown in theme exist, the basic approach is similar. This approach atlases do not make a concerted effort to correlate vascular has several advantages: 1) the vascular pattern is immediately patterns with external or internal brain structures. Also, related to the structures just learned, 2) vascular patterns most atlases include little or no information on neurotrans- are shown in the sections of the atlas in which they belong, mitters and do not integrate clinical examples and informa- 3) the reader cannot proceed from one part of the atlas to tion with the study of functional systems. Following a brief period The ability to diagnose a neurologically compromised pa- devoted to the study of CNS morphology, a signiﬁcant por- tient is speciﬁcally related to a thorough understanding of tion of many courses is spent learning functional systems. This pathway structure, function, blood supply, and the rela- learning experience may take place in the laboratory because tionships of this pathway to adjacent structures.
The NspRTN and other thalamic nuclei receive reciprocal inputs from the cortex and it is possible that it is the ensuing oscillations in neuronal activity in this circuit between the cortex and thalamus that give rise to the sleep spindle waves in stages 2±4 discount viagra jelly 100 mg without a prescription. In fact viagra jelly 100mg visa, it has been suggested that the stronger and clearer these oscillations become, the more likely it is that there will be loss of consciousness. Apart from neuronal inputs originating in the cortex, thalamic afferents (see Fig. Because these neurons are themselves activated by sensory inputs transmitted along the spinothalamic tract, this provides one way in which sensory stimuli can influence cortical activity generally, as well as specifically. As described below, these seem to be particularly important and probably disrupt the thalamo-cortical synchrony. SLEEP AND WAKING CENTRES One of the first experiments to investigate the brain mechanisms that might be involved in regulation of sleep and waking showed that after transection of the brain of cats, so that the cerebrum was separated from the brainstem, the animal displayed continuous sleep. Conversely, transection that separated the entire brain, including the brainstem, from the spinal cord (at the level of Cl) caused continuous arousal. Jouvet (1974) extended this work by showing that a lesion at a specific site in the pons abolished REM sleep, together with the associated muscle atonia and EEG changes, but did not affect SWS. Later studies confirmed the existence of these brain centres in that stimulation of the anterior hypothalamus, at a frequency similar to that of the sleep spindles in the EEG, induced sleep whereas stimulation of a zone of the brainstem, that came to be known as the ascending reticular activating system (ARAS), induced arousal (Moruzzi and Mayoun 1949). The generally accepted view is that the stimulatory drive for the ARAS comes from collaterals of the classical ascending sensory pathways. Indeed, this is another way in which sensory stimuli can affect our state of arousal (Fig. The ascending reticular activating system (ARAS) extends from the cephalic medulla through the pons and mid- brain to the thalamus (see Moruzzi and Mayoun 1949). It is activated by impulses in collaterals of the spinothalamic sensory pathway running to specific thalamic nuclei (SpThNc) and in turn activates much of the cortex, partly through the non-specific thalamic nuclei (NspThNc), which also receive inputs from SpThNc and also via the nucleus basalis (NcB). It is probable that reciprocal links between cortical areas and the thalamus, particularly NspThN, lead to slow-wave (8 Hz) cortical EEG synchrony and, in the absence of appropriate sensory input and ARAS activity, a sleep state system ensures that all sensory stimuli, whatever their strength or modality, contribute collectively to cortical arousal. This is possible because part of any sensory input is diverted to the ARAS and so prevents the cortex from reverting to its basic slow-wave oscillating rhythm.