By A. Sinikar. Medical College of Georgia. 2018.
The majority of the conducting passages are held permanently open by muscle or a bony or cartilaginous framework purchase 4 mg zofran visa symptoms 3 days after embryo transfer. Nose The nose includes an external portion that protrudes from the face and an internal nasal cavity for the passage of air cheap 8mg zofran visa keratin smoothing treatment. The external portion of the nose is covered with skin and supported by paired nasal bones, which form the bridge, and pliable cartilage, which forms the distal portions (fig. The septal cartilage forms the anterior portion of the nasal septum, and the paired lateral carti- lages and alar cartilages form the framework around the nostrils. The nasal vestibule is the anterior expanded portion of the nasal fossa (fig. There are several openings into the nasal cavity, including the openings of the various paranasal sinuses, those of the nasolacrimal ducts that drain from the eyes, and those of the audi- tory tubes that drain from the tympanic cavities. Respiratory System © The McGraw−Hill Anatomy, Sixth Edition Body Companies, 2001 606606 Unit 6 Maintenance of the Body Simple squamous epithelium (lining pulmonary alveoli) FIGURE 17. The roof of the nasal cavity is formed anteriorly by the frontal bone and paired nasal bones, medially by the cribriform plate of the ethmoid bone, and posteriorly by the sphenoid bone (see figs. In the trachea and bronchi, there are The anterior openings of the nasal cavity are lined with stratified squa- about 300 cilia per cell. The cilia move mucus-dust particles toward mous epithelium, whereas the conchae are lined with pseudostratified the pharynx, where they can either be swallowed or expectorated. Mucus-secreting gob- let cells are present in great abundance throughout both regions. Dust, pollen, smoke, and other fine particles are trapped • The nasal epithelium covering the conchae serves to warm, along the moist mucous membrane lining the nasal cavity. The nasal epithelium is highly vascular and covers an extensive surface • The olfactory epithelium in the upper medial portion of area. This is important for warming the air but unfortu- the nasal cavity is concerned with the sense of smell. Respiratory System © The McGraw−Hill Anatomy, Sixth Edition Body Companies, 2001 Chapter 17 Respiratory System 607 FIGURE 17. There are several drainage openings into the nasal cavity (see Pharynx fig. An excessive secretion of tears causes the nose to run as the tears drain into the nasal cavity. The supporting walls of the pharynx are com- accessory connections, it is no wonder that infections can spread so posed of skeletal muscle, and the lumen is lined with a mucous easily from one chamber to another throughout the facial area. To avoid causing damage or spreading infections to other areas, one membrane. Within the pharynx are several paired lymphoid or- must be careful not to blow the nose too forcefully. Commonly referred to as the “throat” or “gul- let,” the pharynx has both respiratory and digestive functions. Paranasal Sinuses The pharynx is divided on the basis of location and function into three regions (see fig. Paired air spaces in certain bones of the skull are called paranasal • The nasopharynx serves only as a passageway for air, be- sinuses. These sinuses are named according to the bones in cause it is located above the point of food entry into the which they are found; thus, there are the maxillary, frontal, body (the mouth). It is the uppermost portion of the phar- sphenoidal, and ethmoidal sinuses (fig. Each sinus com- ynx, positioned directly behind the nasal cavity and above municates via drainage ducts within the nasal cavity on its own the soft palate. These sinuses are responsible ditory (eustachian) tubes connect the nasopharynx with for some sound resonance, but most important, they function to the tympanic cavities. The pharyngeal tonsils, or ade- decrease the weight of the skull while providing structural noids, are situated in the posterior wall of the nasal cavity. During the act of swallowing, the soft palate and uvula You can observe your own paranasal sinuses.
Some of the cranial nerves buy 8mg zofran with visa treatment tendonitis, however order 8mg zofran free shipping symptoms before period, are composed either of sensory neurons only (sensory nerves) or of motor neurons only (motor nerves). Sensory nerves serve the special senses, such as taste, smell, sight, and hearing. Motor nerves conduct impulses to mus- cles, causing them to contract, or to glands, causing them to secrete. A myelin layer is formed by the wrapping of neurolemmocytes around the axon of a neuron. Nervous Tissue and the © The McGraw−Hill Anatomy, Sixth Edition Coordination Central Nervous System Companies, 2001 Chapter 11 Nervous Tissue and the Central Nervous System 353 1. Nervous Tissue and the © The McGraw−Hill Anatomy, Sixth Edition Coordination Central Nervous System Companies, 2001 354 Unit 5 Integration and Coordination (a) (b) (c) (d) (e) FIGURE 11. Visceral motor (efferent) fibers, also called according to the area of innervation into the following scheme autonomic motor fibers, are part of the autonomic nervous (fig. Sensory receptors within the skin, bones, muscle, glands, and smooth muscle within the visceral organs. Impulses from the CNS travel through so- axons and distinguish between bipolar, pseudounipolar, matic motor (efferent) fibers and cause the contraction of and multipolar neurons. Explain the nature of the blood-brain barrier and describe CNS for integration. Nervous Tissue and the © The McGraw−Hill Anatomy, Sixth Edition Coordination Central Nervous System Companies, 2001 Chapter 11 Nervous Tissue and the Central Nervous System 355 Astrocyte Nucleus Cytoplasm Mitochondrion Astrocyte foot processes Capillary Basement membrane (continuous) Nucleus Overlapping endothelial cells Erythrocyte Waldrop (a) (b) FIGURE 11. Nervous Tissue and the © The McGraw−Hill Anatomy, Sixth Edition Coordination Central Nervous System Companies, 2001 356 Unit 5 Integration and Coordination Pseudounipolar Dendritic branches Bipolar Dendrite Multipolar Dendrites Axon FIGURE 11. Pseudounipolar neurons have one process, which splits; bipolar neurons have two processes; and multipolar neurons have many processes (one axon and many dendrites). Sensory Motor Motor (afferent) (efferent) Sensory ending ending Receptors within joints, integument, Skeletal muscle Neurofibril Dendrite skeletal muscles, tissue node and inner ear Myelin sheath Perineurium Intrafascicular blood Somatic Somatic vessel (sensory fibers) (motor fibers) Endoneurium (supports the fasciculi) Central nervous Epineurium Fasciculus system (bundle of nerve fibers) Visceral Visceral (sensory fibers) (autonomic motor fibers) Interfascicular blood vessels Smooth muscle Sensory receptors tissue, cardiac muscle within tissue, and glandular visceral organs Nerve epithelial tissue FIGURE 11. Nervous Tissue and the © The McGraw−Hill Anatomy, Sixth Edition Coordination Central Nervous System Companies, 2001 Chapter 11 Nervous Tissue and the Central Nervous System 357 Dendrite Stimulus Depolorization applied ++++++++++++ Axon ++ ++ (a) ++++++++++++ Stimulus Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ + + + + + + + + + + Nerve +++ + + + + + + + + + Na Na Na K K K K K K K fiber ++ + + + + + + + + + + ++ Na Na Na K K K K K K K (b) Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ +++ + + + + + + + + + Region of depolarization + + + + + + + + + + + + FIGURE 11. Direction of action potential ++ (c) + + + + + + + + + + + + TRANSMISSION OF IMPULSES FIGURE 11. Synaptic transmission is facilitated by the secretion of a neurotransmitter chemical. Objective 8 Explain how a nerve fiber first becomes depolarized and then repolarized. When a Objective 9 Describe the structure of a presynaptic nerve stimulus of sufficient strength arrives at the receptor portion of fiber ending and explain how neurotransmitters are the neuron, the polarized nerve fiber becomes depolarized, and an released. Once depolarization has started, a sequence of ionic exchange occurs along the axon, and the action potential is transmitted (fig. After the axon Action Potential membrane has reached maximum depolarization, the original Two functional properties of neurons are irritability and conduc- concentrations of sodium and potassium ions are reestablished in tivity, both of which are involved in the transmission of a nerve a process called repolarization. Irritability is the ability of dendrites and cell bodies to re- and the nerve fiber is now ready to send another impulse. Conductivity An action potential travels in one direction only and is an is the transmission of an impulse along the axon or a dendrite of all-or-none response. An action potential (nerve impulse) is the actual move- will invariably travel the length of the nerve fiber and proceed ment, or exchange, of sodium (Na+) and potassium (K+) ions without a loss in voltage. The speed of an action potential is de- along the length of a nerve fiber, resulting in the creation of a termined by the diameter of the nerve fiber, its type (myelinated stimulus that activates another neuron or another tissue. A polarized nerve fiber has an abundance of sodium eters conduct impulses at the rate of about 0. Nervous Tissue and the © The McGraw−Hill Anatomy, Sixth Edition Coordination Central Nervous System Companies, 2001 358 Unit 5 Integration and Coordination Direction of action potential Vesicle releasing neurotransmitter Synaptic vesicles chemical Axon Axon membrane Mitochondrium Neurotransmitter chemical Membrane of postsynaptic cell Axon terminal Synaptic cleft FIGURE 11. When an action potential reaches the axon terminal, neurotransmitter chemicals are released into the synaptic cleft. Synaptic transmission occurs if sufficient amounts of the neurotransmitter chemicals are released. Define the terms depolarization and repolarization and illus- axon terminal of a presynaptic neuron and a dendrite of a post- trate these processes graphically. The axon terminal (synaptic knob), is the distal portion of the presynaptic neuron at the end 9.
Chemical Buffers Are the First to Defend pH The Bicarbonate/Carbon Dioxide Buffer Pair When an acid or base is added to the body proven zofran 8mg symptoms zoloft dosage too high, the buffers just Is Crucial in pH Regulation mentioned bind or release H purchase 4 mg zofran treatment laryngomalacia infant, minimizing the change in pH. Acids or For several reasons, the HCO3 /CO2 buffer pair is espe- bases also enter cells and bone, but this generally occurs cially important in acid-base physiology: more slowly, over hours, allowing cell buffers and bone to 1) Its components are abundant; the concentration of share in buffering. In the ECF, phosphate is present as inorganic phos- 3) It is controlled by the lungs and kidneys. Its concentration, however, is low (about 1 mmol/L), so it plays a minor role in extracellular buffering. CO2 exists in the body in sev- Phosphate is an important intracellular buffer, how- eral different forms: as gaseous CO2 in the lung alveoli, and 2– ever, for two reasons. First, cells contain large amounts of as dissolved CO2, H2CO3, HCO3 , carbonate (CO3 ), phosphate in such organic compounds as adenosine and carbamino compounds in the body fluids. Although these compounds primarily rather alkaline solutions, and so we will ignore it. We will function in energy metabolism, they also act as pH also ignore any CO2 that is bound to proteins in the car- buffers. The most important forms are gaseous CO2, the pH of ECF and is closer to the pK of phosphate. Dissolved CO in Phosphate is, thus, more effective in this environment 2 2 3 3 2 than in one with a pH of 7. Bone has large phosphate pulmonary capillary blood equilibrates with gaseous CO2 salt stores, which also help in buffering. Consequently, the partial pressures of CO2 (PCO2) in alveolar air and systemic arterial blood are normally identical. The concentration of dissolved CO2 ([CO2(d)]) is related to the PCO2 by Henry’s law (see Chap- ter 21). Buffer Reaction In aqueous solutions, CO2(d) reacts with water to form H2CO3: CO2(d) H2O H2CO3. The reaction to the Extracellular fluid Bicarbonate/CO CO H O→←H CO →←H right is called the hydration reaction, and the reaction to 2 2 2 2 3 HCO the left is called the dehydration reaction. These reactions 3 Inorganic phosphate H PO →←H HPO 2 are slow if uncatalyzed. In many cells and tissues, such as 2 4 4 Plasma proteins (Pr) HPr→←H Pr the kidneys, pancreas, stomach, and red blood cells, the re- Intracellular fluid actions are catalyzed by carbonic anhydrase, a zinc-con- Cell proteins (e. At equilibrium, CO is greatly favored; 2(d) hemoglobin, Hb) at body temperature, the ratio of [CO2(d)] to [H2CO3] is Organic phosphates Organic-HPO →←H 4 about 400:1. H2CO3 dissociates instantaneously into Bicarbonate/CO CO H O→←H CO →←H 2 2 2 2 3 H and HCO3 : H2CO3 H HCO3. The Hender- HCO 3 son-Hasselbalch expression for this reaction is Bone Mineral phosphates H PO →←H HPO 2 2 4 4 [HCO ] Mineral carbonates HCO →←H CO 2 3 3 3 pH 3. Using the low concentration in body fluids lessens its impact on acidity. From the reaction H HCO3 H2CO3 H2O CO2, we [HCO3 ] predict that the [HCO3 ] will fall by 10 mmol, and that 10 6. If the system were closed and no CO2 could escape, the new pH would be We can also use 0. This form of the Henderson-Hasselbalch equation is Fortunately, however, the system is open and CO2 can escape via the lungs. If all of the extra CO2 is expired and useful in understanding acid-base problems. Therefore, this equation is [24 10] valid only if CO2(d) and H2CO3 are in equilibrium with pH 6. The following expression results if we take antiloga- Although this pH is low, it is compatible with life. In the body, an acidic blood pH stimulates breathing, which [H ] 24 PCO2/[HCO3 ] (16) can make the PCO2 lower than 40 mm Hg.
From the cerebral cortex proven 4mg zofran medications mexico, the corticospinal tract axons descend through the brain along a path located between the basal ganglia and the thalamus zofran 8mg cheap treatment kidney stones, known as the internal capsule. They then continue along the ventral brainstem as the cerebral peduncles and on through the pyramids of the medulla. Most of the corticospinal axons cross the midline in the medullary pyramids; thus, the motor cortex in each hemisphere controls the muscles on the contralateral side of the body. After crossing in the medulla, the corticospinal Lower motor axons descend in the dorsal lateral columns of the spinal neuron cord and terminate in lateral motor pools that control dis- tal muscles of the limbs. Axons arising from cortical neurons, including the primary motor cross in the medulla and descend in the ventral spinal area, descend through the internal capsule, decussate in the columns. These axons terminate in the motor pools and ad- medulla, travel in the lateral area of the spinal cord as the lateral jacent intermediate zones that control the axial and proxi- corticospinal tract, and terminate on motor neurons and interneu- mal musculature. Note the upper The corticospinal tract is estimated to contain about 1 and lower motor neuron designations. The largest-diameter, heavily myelinated axons are between 9 and 20 m in diameter, but that population accounts for only a small fraction of the total. Most corticospinal axons are small, 1 to 4 m in diameter, and half are unmyelinated. CHAPTER 5 The Motor System 103 In addition to the direct corticospinal tract, there are Cerebral other indirect pathways by which cortical fibers influence cortex motor function. Some cortical efferent fibers project to the reticular formation, then to the spinal cord via the reticu- lospinal tract; others project to the red nucleus, then to the spinal cord via the rubrospinal tract. Despite the fact that these pathways involve intermediate neurons on the way to Caudate the cord, volleys relayed through the reticular formation can nucleus Direct reach the spinal cord motor circuitry at the same time as, or Thalamus Striatum earlier than, some volleys along the corticospinal tract. Putamen GPe Indirect THE BASAL GANGLIA AND MOTOR CONTROL GPi The basal ganglia are a group of subcortical nuclei located SNc SNr primarily in the base of the forebrain, with some in the di- SUB encephalon and upper brainstem. The striatum, globus pal- lidus, subthalamic nucleus, and substantia nigra comprise the basal ganglia. Input is derived from the cerebral cortex MBEA SC and output is directed to the cortical and brainstem areas concerned with movement. The cir- the entire motor system and plays a role in the preparation cuit of cerebral cortex to striatum to GPi to and execution of coordinated movements. Note the direct and indirect pathways involving the striatum, GPi, GPe, and subthalamic nu- ganglia consist of the striatum, which is made up of the cleus. GPi output is also directed to the midbrain extrapyramidal caudate nucleus and the putamen, and the globus pallidus. The SNr to SC pathway is important in eye move- The caudate nucleus and putamen are histologically identi- ments. Excitatory pathways are shown in red, inhibitory pathways cal but are separated anatomically by fibers of the anterior are in black. GPe and GPi, globus pallidus externa and interna; limb of the internal capsule. The globus pallidus has two SUB, subthalamic nucleus; SNc and SNr, substantia nigra pars subdivisions: the external segment (GPe), adjacent to the compacta and pars reticulata; SC, superior colliculus. The other main nuclei of the basal ganglia are the subthalamic nucleus in the dien- similar to the GPi. The output is directed to the superior col- cephalon and the substantia nigra in the mesencephalon. The GPi and SNr output is inhibitory via neurons that use GABA as the neurotransmitter. The Basal Ganglia Are Extensively Interconnected The internal pathway circuits link the various nuclei of Although the circuitry of the basal ganglia appears complex the basal ganglia. The globus pallidus externa (GPe), the at first glance, it can be simplified into input, output, and subthalamic nucleus, and the pars compacta region of the internal pathways (Fig. Input is derived from the substantia nigra (SNc) are the nuclei in these pathways. The cerebral cortex and is directed to the striatum and the sub- GPe receives inhibitory input from the striatum via GABA- thalamic nucleus. The output of the GPe is also inhibitory striatum is termed the medium spiny neuron, based on its via GABA release and is directed to the GPi and the sub- cell body size and dendritic structure. The subthalamic nucleus output is excita- receives input from all of the cerebral cortex except for the tory and is directed to the GPi and the SNr. The input is roughly so- GPe-subthalamic nucleus-GPi circuit has been termed the matotopic and is via neurons that use glutamate as the neu- indirect pathway in contrast to the direct pathway of stria- rotransmitter.