By S. Hengley. University of Montevallo.
Spinocerebellar pathways carrying somatosensory information terminate in the vermis and intermediate zones in somatotopic arrange- Climbing Mossy ments generic 10 mg doxepin free shipping. The auditory purchase doxepin 25mg line, visual discount doxepin 25mg without prescription, and vestibular systems and sen- fiber fiber sorimotor cortex also project to this portion of the cerebel- lum order doxepin 75mg with mastercard. Output from the vermis is directed to the fastigial nuclei, which project through the inferior cerebellar pe- FIGURE 5. The cell types and ac- duncle to the vestibular nuclei and reticular formation of tion potential pathways are shown. Output from the intermediate zones fibers bring afferent input from the spinal cord and the cerebral goes to the interposed nuclei and from there to the red nu- cortex. Climbing fibers bring afferent input from the inferior olive cleus and, ultimately, to the motor cortex via the ventrolat- nucleus in the medulla and synapse directly on the Purkinje cells. It is believed that both the The Purkinje cells are the efferent pathways of the cerebellum. Mossy fibers make complex multicontact Lesions Reveal the Function of the Cerebellum Lesions synapses on granule cells. The granule cell axons then as- of the cerebellum produce impairment in the coordinated cend to the molecular layer and bifurcate, forming the action of agonists, antagonists, and synergists. These travel perpendicular to and synapse ment is clinically known as ataxia. The control of limb, ax- with the dendrites of Purkinje cells, providing excitatory ial, and cranial muscles may be impaired depending on the input via glutamate. Limb ataxia might manifest as rates, 50 to 100 Hz, which increases further during vol- the coarse jerking motions of an arm and hand during untary movement. When mossy fiber input is of sufficient reaching for an object instead of the expected, smooth ac- strength to bring a Purkinje cell to threshold, a single ac- tions. This jerking type of motion is also referred to as ac- tion potential results. The swaying walk of an intoxicated individual Climbing fibers arise from the inferior olive, a nucleus is a vivid example of truncal ataxia. Each climbing fiber synapses directly on the Cerebellar lesions can also produce a reduction in mus- dendrites of a Purkinje cell and exerts a strong excitatory cle tone, hypotonia. One action potential in a climbing fiber pro- decrease in the low level of resistance to passive joint duces a burst of action potentials in the Purkinje cell called movement detectable in normally relaxed individuals. Climbing fibers also synapse with basket, otatic reflexes produced by tapping a tendon with a reflex Golgi, and stellate interneruons, which then make in- hammer reverberate for several cycles (pendular reflexes) hibitory contact with adjacent Purkinje cells. This circuitry because of impaired damping from the reduced muscle allows a climbing fiber to produce excitation in a single tone. The hypotonia is likely a result of impaired process- Purkinje cell and inhibition in the surrounding ones. The cerebellar cortical output (Purk- cerebellar function, we are left without a firm idea of what inje cell efferents) is inhibitory to the cerebellar and the cerebellum does in the normal state. Cerebellar func- vestibular nuclei, but the ultimate output of the cerebellar tion is sometimes described as comparing the intended nuclei is mostly excitatory. A smaller population of neurons with the actual movement and adjusting motor system out- of the deep cerebellar nuclei produces inhibitory outflow put in ongoing movements. Other putative functions in- directed mainly back to the inferior olive. REVIEW QUESTIONS DIRECTIONS: Each of the numbered (A) Finger flexion (C) Spinocerebellar items or incomplete statements in this (B) Elbow flexion (D) Rubrospinal section is followed by answers or by (C) Shoulder abduction (E) None completions of the statement. What is the location of the primary ONE lettered answer or completion that is (E) No muscles would become abnormal motor area of the cerebral cortex? Tapping the patellar tendon with a (A) Upper parietal lobe reflex hammer produces a brief (B) Superior temporal lobe 1. Concurrent flexion of both wrists in (A) Low threshold, fatigue-resistant connective tissue response to electrical stimulation is (B) High threshold, fatigable (B) Golgi tendon organ response characteristic of which area of the (C) Intrafusal, gamma controlled (C) Muscle spindle activation nervous system? The cyclical flexion and extension (C) Dentate nucleus provides information about the force of motions of a leg during walking result (D) Primary motor cortex muscle contraction? If you could histologically examine the (B) Nuclear chain fiber (A) Cerebral cortex spinal cord of a patient who had (C) Golgi tendon organ (B) Cerebellum experienced a viral illness 10 years (D) Bare nerve ending (C) Globus pallidus before in which only the neurons of (E) Type Ia ending (D) Red nucleus the primary motor area of the cerebral 3. If a patient experiences enlargement of (E) Spinal cord cortex were destroyed, what findings the normally rudimentary central canal 6.
Because cannabis may be Some individuals experience adverse abused in combination with other drugs buy 75mg doxepin with amex, effects from LSD cheap 25 mg doxepin with visa, such as a panic state treatment may occasionally be multifocal with severe anxiety discount doxepin 75mg free shipping. The physical consequences of hallucino- gen abuse in and of themselves are not sig- Hallucinogens niﬁcant doxepin 10mg mastercard. Adverse effects of Sometimes called psychedelics, hallu- hallucinogens vary from acute psychosis to cinogens are drugs that, at some dosage, self-mutilation or suicide. Accidents can produce hallucinations or distortions in per- result from misjudgment or impairment. Individuals under the Some individuals experience “ﬂashbacks” influence of hallucinogens report in- in which hallucinations reappear brieﬂy creased awareness of sensory input and a even months after the last drug dose. An subjective feeling of enhanced mental overdose of hallucinogens can result in activity. Common hallucinogens are LSD, exceedingly high body temperatures, PCP (angel dust), and mescaline. Controlled substance analogues, or Because hallucinogens produce no designer drugs, can have dangerous, perma- physical dependence, there is no speciﬁc nent effects. Adverse drugs, the methamphetamines such as effects such as panic episodes are usually MDMA (ecstasy) or MDA (street name treated with a supportive environment Adam), may be especially susceptible to and observation. Designer derivatives Substances that cause perceptible of amphetamines (MDMA) produce eu- changes in brain function through inhala- phoria but can also have hallucinogenic tion are called inhalants. Inhalants are gen- effects; they may also cause cerebral hem- erally classiﬁed into four categories: orrhage (stroke), hyperthermia (elevated • Aerosols body temperature), altered mental status, • Gases panic, and psychosis. Their use is now often concurrent A wide variety of substances are abused with the use of other drugs. One of the in this way, often because they are readily most powerful hallucinogens is LSD. For example, effects vary with the individual, the dose, commonly used inhalants are airplane and the environment in which the drug glue, typewriter correction ﬂuid, marking pen- is used. Generally, the effects develop cils, industrial and household chemicals, Medical Consequences of Abuse of Other Drugs and Substances 219 gasoline, nitrites (poppers, snappers, or rush), ten to crimes committed to obtain drugs or and nitrous oxide. Sub- all age groups practice inhalant abuse, it stance abuse also has medical consequences. Drug-Related Illness Although the effects of inhalants are brief, they can be serious, especially with Dermatologic Complications prolonged or long-term use. Adverse ef- fects of inhalants vary according to the Many of the medical complications type of substance inhaled. Organic sol- related to drug abuse result from nonster- vents such as airplane glue can produce ile injections or from adulterants, rather cardiac arrhythmia, bone marrow depression, than from the drug itself. Abscess Prolonged use of nitrites is thought to suppress the immune system, increasing the Bacterial infection may cause pus to col- individual’s susceptibility to infection. In Nitrites are frequently used to enhance association with drug use, improper sexual pleasure; consequently, individuals cleansing of the skin before injection or the who use nitrites in this way and are also use of a nonsterile needle may lead to an exposed to human immunodeﬁciency abscess. Skin at the site becomes warm, red, virus (HIV) may be at greater risk for devel- swollen, and painful with a purulent (pus) oping HIV infection because of their sup- discharge. Skin around the area frequent- pressed immune system and subsequent ly becomes necrotic (dies). Treat- senses, driving during intoxication is haz- ment of an abscess consists of draining the ardous. Even though the effects of purulent material and debriding (remov- inhalants are brief, their use can result in ing) the area of dead tissue. No speciﬁc medical treat- usually prescribed, especially if individu- ment is usually indicated for inhalant als demonstrate systemic symptoms. An acute inﬂammation of the tissues without necrosis (tissue death) is called cellulitis. When associated with intra- MEDICAL CONSEQUENCES OF venous drug abuse, cellulitis is caused by ABUSE OF OTHER DRUGS AND the invasion of a variety of organisms or SUBSTANCES by irritation of the tissues from the drug itself.
Somatic Reflexes reflex is initiated as a person encounters a painful stimulus doxepin 10 mg with visa, such as a hot or sharp object cheap doxepin 75mg on-line. As a receptor organ is stimulated order 75mg doxepin fast delivery, sen- Somatic reflexes are those that result in the contraction of skele- sory neurons transmit the impulse to the spinal cord quality 10 mg doxepin, where asso- tal muscles. The three principal kinds of somatic reflexes are ciation neurons are activated. Here, the impulses are directed named according to the response they produce. Simultaneously, antagonistic muscles are inhibited (re- synapse in the pathway; it is therefore called a monosynaptic reflex laxed) so that the traumatized extremity can be quickly arc. Slight stretching of the neuromuscular spindle receptors (de- withdrawn from the harmful source of stimulation. In an intersegmental reflex arc, ron occurs in the anterior gray column, and activation of a motor motor units from several segments of the spinal cord are acti- unit causes specific muscle fibers to contract. In an tor and effector organs of the stretch reflex involve structures on intersegmental reflex arc, more than one effector organ is the same side of the spinal cord, the reflex arc is an ipsilateral re- stimulated. This type of reflex is A flexor reflex, or withdrawal reflex, involves a polysynap- called a crossed extensor reflex (fig. Flexor reflexes involve association neu- for maintaining body balance while a flexor reflex is in rons in addition to the sensory and motor neurons. Peripheral Nervous © The McGraw−Hill Anatomy, Sixth Edition Coordination System Companies, 2001 Chapter 12 Peripheral Nervous System 429 FIGURE 12. Peripheral Nervous © The McGraw−Hill Anatomy, Sixth Edition Coordination System Companies, 2001 430 Unit 5 Integration and Coordination TABLE 12. However, Babinski’s reflex is present in infants up to 12 months of age because of the immaturity of their corticospinal tracts. For example, withdrawal of one leg, after stepping on broken glass, requires extension of the other in order to keep Clinical Case Study Answer from falling. The reflexive inhibition of certain muscles to The radial nerve lies in the radial groove of the humerus as it extends contract, called reciprocal inhibition, also helps maintain bal- through the brachial region toward the arm and hand. In this position, ance while either flexor or crossed extensor reflexes are in the radial nerve is susceptible to injury in the case of a fracture to the progress. The muscles innervated by the radial nerve in- Certain reflexes are important for physiological functions, clude those of wrist extension (extensor carpi radialis longus and brevis, whereas others are important for avoiding injury. Some of the extensor carpi ulnaris); wrist adduction (extensor carpi ulnaris); wrist abduction (extensor carpi radialis brevis and longus); supination more common reflexes are described in table 12. Several reflexes are used to assess certain fected, however, because of the more proximal branching point of its neurological conditions, including functioning of the synapses. The radial nerve is a mixed nerve, carrying both some portion of the nervous system has been injured, the testing of motor and sensory fibers; therefore, a sensory deficit would be present. Decreased sensation would be detectable on the posterolateral aspect of Also, an anesthesiologist may try to initiate a reflex to ascertain the the hand (see fig. Define the following terms: visceral reflex, somatic reflex, stretch reflex, flexor reflex, crossed extensor reflex, ipsilateral reflex, and contralateral reflex. Peripheral Nervous © The McGraw−Hill Anatomy, Sixth Edition Coordination System Companies, 2001 Chapter 12 Peripheral Nervous System 431 (a) Glabellar reflex (b) Biceps reflex (c) Triceps reflex (d) Supinator (brachioradialis) reflex (e) Knee-jerk (patellar) reflex (f) Ankle (Achilles) reflex (g) Babinski’s reflex (h) Plantar reflex (i) Abdominal reflex FIGURE 12. Peripheral Nervous © The McGraw−Hill Anatomy, Sixth Edition Coordination System Companies, 2001 432 Unit 5 Integration and Coordination CLINICAL PRACTICUM 12. She has normal knee and ankle sudden onset of back pain 2 weeks ago while reflexes, but her skin is relatively numb over lifting a heavy object. The back pain is ac- the anterior tibia (“shin”) and superior sur- companied by a burning pain that spreads face of the foot. Her left great toe extensor is from the left buttock down the posterior left weak. Sneezing or cough- of the lumbar spine even though you proba- ing sends shooting pains down the leg in the bly know what’s causing the problem. She has not experienced L4 any change in urinary bladder or bowel con- QUESTIONS: trol. In your office she prefers to stand be- L5 cause sitting only makes her leg hurt worse. S1 On examination you note only minimal tenderness to palpation of the lower back, 2.
The relative importance of each buffer depends on its amount cheap 25 mg doxepin otc, pK generic doxepin 10mg overnight delivery, and availability buy discount doxepin 75 mg on line. Systemic The isohydric principle underscores the fact that it is the pH concentration ratio for any buffer pair buy doxepin 10mg line, together with its pK, that sets the pH. The addition of an exoge- their ratios according to the pH and their pK values. A base load, by raising pH, stimulates buffers, however, are present and active. Protection of acid-base balance by pH regulation of (lungs and kidneys) regulate pH by acting on components acid production. CHAPTER 25 Acid-Base Balance 433 RESPIRATORY REGULATION OF PH loss of acid or base (e. By loss of H in the urine can be calculated from the following changing the PCO2 and, hence, [H2CO3] of the blood, the equation, which shows typical values in the parentheses: respiratory system can rapidly and profoundly affect blood pH. As discussed in Chapter 22, a fall in blood pH stimu- Renal net acid excretion (70 mEq/day) lates ventilation, primarily by acting on peripheral urinary titratable acid (24 mEq/day) chemoreceptors. An elevated arterial blood PCO2 is a pow- urinary ammonia (48 mEq/day) erful stimulus to increase ventilation; it acts on both periph- urinary HCO3 (2 mEq/day) (22) eral and central chemoreceptors, but primarily on the latter. Urinary ammonia (as NH4 ) ordinarily accounts for CO2 diffuses into brain interstitial and cerebrospinal fluids, about two thirds of the excreted H , and titratable acid for where it causes a fall in pH that stimulates chemoreceptors about one third. Therefore, it must be the lungs blow off more CO2, making the blood less acidic. If the Conversely, a rise in blood pH inhibits ventilation; the con- urine contains significant amounts of organic anions, such sequent rise in blood [H2CO3] reduces the alkaline shift in as citrate, that potentially could have yielded HCO3 in blood pH. Respiratory responses to disturbed blood pH be- the body, these should also be subtracted. RENAL REGULATION OF PH Hydrogen Ions Are Added to Urine as The kidneys play a critical role in maintaining acid-base It Flows Along the Nephron balance. If there is excess acid in the body, they remove As the urine flows along the tubule, from Bowman’s capsule H , or if there is excess base, they remove HCO3. The on through the collecting ducts, three processes occur: fil- usual challenge is to remove excess acid. As we have tered HCO3 is reabsorbed, titratable acid is formed, and learned, strong acids produced by metabolism are first ammonia is added to the tubular urine. The involve H secretion (urinary acidification) by the tubular kidneys then must eliminate H in the urine and restore the epithelium. For example, if the urine has its lowest pH value shows ammonia movements in various nephron segments. With a typical daily urine output of 1 to 2 L, the amount of acid the body must Acidification in the Proximal Convoluted Tubule. The dispose of daily (about 70 mEq) obviously is not excreted pH of the glomerular ultrafiltrate, at the beginning of the in the free form. Most of the H combines with urinary proximal tubule, is identical to that of the plasma from buffers to be excreted as titratable acid and as NH4. H ions are secreted by the prox- Titratable acid is measured from the amount of strong imal tubule epithelium into the tubule lumen; about two base (NaOH) needed to bring the urine pH back to the thirds of this is accomplished by a Na /H exchanger and pH of the blood (usually, 7. It represents the amount about one third by H -ATPase in the brush border mem- of H ions that are excreted, combined with urinary brane. The largest component of titratable acid is normally The drop in pH is modest for two reasons: buffering of phosphate, that is, H2PO4. The glomerular filtrate and tubule bine with the free base NH3 and are excreted as NH4. The NH4 ) is produced by the kidney tubule cells and is se- proximal tubule epithelium is rather leaky to H , so that creted into the urine. Because the pKa for NH4 is high any gradient from urine to blood, established by H secre- (9.