By M. Moff. Manchester College.
The excess ﬂuid overﬂows Extensive discussion of vision and ocular anatomy is beyond the eyelids and becomes tears buy innopran xl 80 mg cheap heart attack mayo clinic. The sclera is a white buy innopran xl 40mg low cost blood pressure medication that doesn't cause ed, opaque, fibrous tis- • The eyelids and lacrimal system function to protect the sue that covers the posterior five sixths of the eyeball. The eyelid is a covering that acts as a barrier to the The cornea is a transparent, special connective tissue entry of foreign bodies, strong light, dust, and other po- that covers the anterior sixth of the eyeball. The canthi (singular, canthus) are blood vessels and connective tissue, continues forward the angles where the upper and lower eyelids meet. The iris is composed of pigmented The lacrimal system produces a ﬂuid that constantly cells, the opening called the pupil, and muscles that moistens and cleanses the anterior surface of the eye- control the size of the pupil by contracting or dilating ball. The ﬂuid drains through two small openings in the in response to stimuli. The retina is the innermost inner canthus and ﬂows through the nasolacrimal duct layer of the eyeball. The most common type of glaucoma is called primary Light rays do not travel directly to the retina. Its etiology is unknown, but contribut- they are deﬂected in various directions according to the ing factors may include advanced age, a family history of density of the ocular structures through which they pass. In addition, the inci- is the area of the retina where ophthalmic blood vessels dence of glaucoma in African Americans is about three times and the optic nerve enter the eyeball. Closed-angle glau- • The structure and function of the eyeball are further in- coma is usually an acute situation requiring emergency ﬂuenced by the lens, aqueous humor, and vitreous body. It may occur when pupils are dilated and the outﬂow The lens is an elastic, transparent structure; its function of aqueous humor is blocked. Darkness and drugs with anti- is to focus light rays to form images on the retina. It is cholinergic effects (eg, atropine, antihistamines, tricyclic anti- located behind the iris and held in place by suspensory depressants) may dilate the pupil, reduce outﬂow of aqueous ligaments attached to the ciliary body. Most of the ﬂuid ﬂows through the pupil into the anterior chamber (between the cornea and the lens Inﬂammatory or Infectious Conditions and anterior to the iris). Infections may result from production and drainage of aqueous humor are approx- foreign bodies, contaminated hands, contaminated eye med- imately equal, and normal intraocular pressure (<21 mm ications, or infections in contiguous structures (eg, nose, face, Hg) is maintained. Common inflammatory and infectious disorders causes increased intraocular pressure. The vitreous body include the following: is a transparent, jelly-like mass located in the posterior • Conjunctivitis is a common eye disorder that may be portion of the eyeball. It functions to refract light rays caused by allergens (eg, airborne pollens), bacterial or and maintain the normal shape of the eyeball. Symp- toms include redness, tearing, itching, edema, and burn- ing or gritty sensations. Bacterial conjunctivitis is often DISORDERS OF THE EYE caused by Staphylococcus aureus, Streptococcus pneu- moniae, or Haemophilus inﬂuenzae and produces mu- The eye is subject to the development of many disorders that copurulent drainage. Conjunctivitis with a purulent threaten its structure, function, or both. Some disorders in discharge is most often caused by the gonococcus; which ophthalmic drugs play a prominent role are discussed corneal ulcers and scarring may result. A hordeolum (commonly called Refractive Errors a stye) is often associated with blepharitis. Refractive errors include myopia (nearsightedness), hyper- • Keratitis (inﬂammation of the cornea) may be caused opia (farsightedness), presbyopia, and astigmatism. Ophthalmic drugs are used major symptom is pain, which ranges from mild to se- only in the diagnosis of the conditions; treatment involves vere. Pseudomonal ulcers are less common but may rapidly progress to perforation. Glaucoma, a common preventable cause of blindness, is a Fungal ulcers may follow topical corticosteroid therapy group of diseases characterized by optic nerve damage and or injury with plant matter, such as a tree branch. It is often characterized by increased ulcers are usually caused by the herpesvirus. Di- attributed to frequent use of ophthalmic antibiotics and agnostic tests for glaucoma include ophthalmoscopic exami- corticosteroids. CHAPTER 65 DRUGS USED IN OPHTHALMIC CONDITIONS 937 TYPES OF OPHTHALMIC DRUGS aqueous humor.
Organisation and pattern of connections 79 Katz purchase 80mg innopran xl visa blood pressure medication safe for pregnancy, 1989) proven 40 mg innopran xl hyperextension knee, ﬂexor carpi radialis (FCR) and ﬂexor Organisation and pattern of carpiulnaris(FCU)(Malmgren&Pierrot-Deseilligny, connections 1988), deltoid, triceps brachii, extensor carpi radi- alis (ECR), ﬂexor digitorum superﬁcialis (FDS) and The efﬁcacy of a given Ia input in discharging a extensor digitorum (ED) (Gracies et al. It must be emphasised that these investiga- inhibition and the level of post-activation depres- tions were performed during weak voluntary con- sion at Ia terminals; (iii) any limitation produced by tractions(below5%MVC),andthemotorunitsstud- inhibitory circuits activated by the test volley, and ied were all in the low-threshold range. Differences in the efﬁcacy of homonymous Homonymous monosynaptic Ia excitation Ia excitation in ﬁring motoneurones Estimate of the efﬁcacy of the Ia input in ﬁring Evidence for homonymous Ia excitation in all homonymous motoneurones motoneurone pools This efﬁcacy may be assessed by the ease with which Hreﬂex the H reﬂex can be elicited at rest and by the size of At rest, H reﬂexes can be recorded from the the peak of excitation elicited in the PSTHs of sin- soleus, quadriceps and FCR in most healthy subjects gle motor units by stimulation subthreshold for the (Fig. Generally, these subjects (e )), and rarely from other muscles ((c ),(f ), two measures are closely linked: e. However,anHreﬂexcanbeobtainedinvirtually with the ease with which the H reﬂex is obtained all limb muscles during a weak voluntary contrac- at rest in the soleus and FCR, the peak of homony- tion of the test muscle (see p. The difﬁculty in activating some motoneurone pools reﬂexly can- Homonymous monosynaptic Ia excitation not be attributed to low excitability of the motoneu- in single motor units rone pool: tibialis anterior is more excitable to corti- Stimulation of the parent nerve evokes an early peak cospinal inputs than soleus, while the reverse is true ofincreasedprobabilityofdischargeinPSTHsofsin- for Ia afferent inputs. The size of the (Bayoumi & Ashby, 1989), intrinsic foot muscles monosynaptic Ia peak should then decrease as (Marque et al. Given this preferential distribution of Ia exci- cles in which the different motor unit types have tatory inputs to motoneurones innervating slow- beeninvestigated:seconddorsalinterosseus(Buller, twitch units, it is not surprising that the soleus H Garnett & Stephens, 1980), soleus (Awiszus & Feist- reﬂex may be obtained in all healthy subjects at ner,1993),ECR(Fig. Hilton-Brown & Stalberg,˚ 1986;Semmler & Turker,¨ 1994) and in abductor digiti minimi (Mazzocchio, Heteronymous monosynaptic Ia Rothwell & Rossi, 1995), the largest responses to Ia excitation in the lower limb input have not been found in low-threshold units. Pattern and strength of distribution Inhibitory mechanisms limiting the efﬁcacy of the monosynaptic Ia input In striking contrast with data for the cat and baboon hindlimb (see pp. The constraints raised above, the conclusions advanced larger the maximal soleus H reﬂex at rest, the smaller below have generally been conﬁrmed using more the tonic on-going presynaptic inhibition of Ia ter- than one method. Grey cells represent Contamination by oligosynaptic IPSPs muscle–nerve combinations with a statistically sig- niﬁcantconnectioninhumans. This limitation could also based on the average size of the heteronymous peak contribute to the absence of a recordable H reﬂex relative to that of the homonymous peak, both in at rest in muscles, such as tibialis anterior, abduc- response to stimulation at 1 × MT. As expected, the tor pollicis brevis and ECR, though this would imply stronger the connection, the more frequently was it that the Ia/Ib balance was then shifted in favour of observed: e. In these muscles, the appearance of an trocnemius medialis to biceps femoris, ﬁve aster- Hreﬂex during a tonic voluntary contraction could isks) was observed in 21/21 (100%) units and was, involve depression of non-reciprocal group I inhibi- on average, 54% of the homonymous peak, whereas tion to the active motoneurone pool (see Chapter 6, the weakest connection (from the intrinsic plantar pp. Thresholds for α motor axons and Ia afferents Connections between close synergists operating Alternatively, if the threshold for motor axons was at the same joint closer to that of Ia afferents, the maximal H reﬂex would probably be smaller and the reﬂex more difﬁ- At knee level, strong connections exist between the cult to obtain and, with single motor units, the peak two heads of the quadriceps (vastus lateralis and 82 Monosynaptic Ia excitation Table 2. Monosynaptic heteronymous Ia excitation in the lower limb Columns: nerve stimulated: Sol (inferior soleus), GM (nerve to the gastrocnemius medialis), SP (superﬁcial pero- neal), DP (deep peroneal), FN (femoral nerve), TN (tibial nerve at the ankle). Lines: motoneurone pools (MN) investigated with the PSTH method: Sol (soleus), GM (gastrocnemius medialis), Per Brev (peroneus brevis), TA (tibialis anterior), Q (quadriceps), Bi (biceps femoris), ST (semitendinosus). Grey cells indicate the existence of signiﬁcantIaexcitationinhumans(crossedcellscorrespondtohomonymouspathways). Thenumberofasterisks indicates the average size of the heteronymous peak relative to the homonymous peak (both recorded using sti- mulationat1×MT):*<10%;**between10and20%;***between20and30%,****between30and40%;*****>40% (from Meunier, Pierrot-Deseilligny & Simonetta, 1993;Marque et al. Connections are compared to those described in the cat (cells with horizontal lines, Eccles, Eccles & Lundberg, 1957)andthebaboon(cellswithverticallines,Hongoetal. Withtheanimalexperiments,onlyconnections with a heteronymous EPSP >5% of the homonymous EPSP are shown. There is no Ia excitation from gastrocnemius medialis to soleus, There are bidirectional connections between soleus a ﬁnding conﬁrmed using different techniques: the andperoneusbrevis(Fig. Organisation and pattern of connections 83 Transjoint connections exist between all Phylogenetic adaptations muscle–nerve combinations tested In Table 2. However, it should be emphasised that cat(cellswithhorizontallines,Eccles,Eccles&Lund- conclusions based on stimuli at 1 × MT underesti- berg, 1957) and the baboon (cells with vertical lines, matethestrengthoftheconnectionsbecause,asdis- Hongo et al. These connections are not conﬁned to Connections between close synergists units in the low-threshold range investigated with Theabsenceofconnectionsbetweensomeclosesyn- the PSTH method. Many of the connections have ergists operating at the same joint in humans is pre- alsobeenobservedwithmethodsthatexplorealarge dictable because of their weakness in the baboon. Proximal-to- distal transjoint connections can be explored safely Themoststrikingdifferencesinvolvethepresenceof only from the femoral nerve, because it does not heteronymous connections that do not exist in the contain afferents from distal muscles.
Critique of the tests to study fusimotor drive Microneurography Effects of cutaneous afferents on fusimotor neurones Conclusions about fusimotor activity from record- ings of muscle spindle discharge are valid only Evidenceforreﬂexactivationof motoneuroneshas if all disturbances to the spindle are rigidly con- been found for human lower limb muscles buy innopran xl 40mg blood pressure medication beginning with h, but only trolled buy innopran xl 80mg blood pressure normal high, and this is rarely possible in human subjects; when subjects were standing without support. In the relaxed forearm extensor muscles, alargersample;themovementrepertoirethatcanbe such reﬂexes may be active even at rest. There may studied is quite limited; the technique is traumatic be some background d drive to the resting forearm and technically demanding. However, an effective discharge cannot be gener- ated without discharging motoneurones and pro- Effects of voluntary effort on fusimotor drive ducing EMG activity in the test muscle. This afferent inﬂow has an overall When applied transversely to a muscle tendon of an autogenetic excitatory effect at spinal level and con- intact subject, vibration is usually not selective for tributestomaintainingtheﬁringof motoneurones. Themajorityofhumanprimaryendingsrespond dominantly for spindles in the contracting muscle. It vigorously to tendon vibration, though often at sub- hasalimitedroleincompensatingformusclefatigue. Most cutaneous (iii) The efﬁcacy of drive in activating spindle mechanoreceptors respond to vibration, and it is endings depends on whether the contraction pro- probable that Rufﬁni endings in joints do so as well. Shortening Like any mechanical stimulus, vibration of a tendon (asinaconcentriccontraction)unloadsspindleend- will spread widely through bone, exciting receptors ings,andanincreaseinspindledischargeoccursonly in skin, muscles, fascia and joints remote from the inslowcontractionsorwhengreatereffortisrequired site of vibration. There will probably drive can enhance the spindle response to vibration, be little increase in spindle feedback from the con- butthecontractionitselfmayunloadtheendingand tracting muscle in unloaded rapid shortening move- thereby decrease the spindle discharge. Stretching a con- tracting muscle (an eccentric contraction) greatly Motor tasks and physiological enhances any fusimotor effect on spindle discharge. Performance of the Jendrassik manoeuvre poten- (iv) The exact role of the fusimotor system in nor- tiates tendon jerks in uninvolved non-contracting mal motor control remains speculative. However, it muscles, but there is now cogent evidence that this is possible that the -driven feedback from muscle is not due to widespread activation of d motoneu- spindles plays an important role in learning motor rones. References 145 Changes in fusimotor activity in patients REFERENCES There are cogent arguments against the view that Al-Falahe,N. Roleofthehumanfusimo- fusimotor dysfunction drives motor disturbances, torsysteminamotoradaptationtask. JournalofPhysiology but the database of spindle recordings from patients (London), 401, 77–95. Response proﬁles of human muscle afferents during active ﬁnger movements. Reﬂex changes for spindle afferents from triceps surae and the fore- inmusclespindledischargeduringavoluntarycontraction. Reﬂexactivationofmusclespindlesinhuman independent of the level of drive. Behavior of human muscle receptors when reliant activation drives the next clonic contraction. Journal of suggests that spinal proprioceptive reﬂexes do not Neurophysiology, 64, 661–70. Muscle spindle feedback during spa- There are, as yet, no published reports of recordings tially oriented movements. Experimental Brain Research, from spindle endings in patients with spinal spas- 134, 301–10. Journal of Physiology (London), 180, group II muscle afferents, contributes to the reﬂex 649–72. Afferent tobedominatedbymusclespindleactivityandsome andefferentactivationofhumanmusclereceptorsinvolved single-unit recordings during parkinsonian tremor. Experimental Neurol- These have revealed no evidence of selective or dis- ogy, 41, 754–68. JournalofNeurology,Neurosurgery but the question needs to be addressed quantita- and Psychiatry, 37, 1012–21. The activity of human muscle spindle endings ings from identiﬁed afferents. In International Review of Phys- ing tremor, spindle discharge occurs in two phases: iology,vol. Criticalexaminationofthecasefororagainstfusimo- stretched, a pattern similar to that seen with volun- tor involvement in disorders of muscle tone.