clinicalmed - Ambika K on Diigo

Endolymph is very similar to intracellular
fluid: it is high in potassium and low in sodium. The ionic composition
is necessary for vestibular and auditory hair cells to function
optimally. The space between the membranous and bony labyrinths
is filled with perilymph, which is very much like normal
cerebral spinal fluid.
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- As the stapes vibrates the oval window, the perilymph
  sloshes back and forth, vibrating the round window in a complementary
  rhythm. The membranous labyrinth is caught between the two, and
  bounces up and down with all this sloshing
- As with almost all sensory neurons (the exception is in the retina),
  its cell body lies outside the CNS in a ganglion. In this case,
  the ganglion is stretched out along the spiralling center axis
  of the cochlea, and is named the spiral ganglion.
- basilar membrane is actually thinner and narrower
  at the base of the cochlea than at the tip (apex), which seems
  backwards given that the cochlea is widest at the base. The properties
  of the basilar membrane change as its shape changes; just as with
  guitar strings, thin things vibrate to high pitches, and thick
  things vibrate to low pitches. This means that the basilar membrane
  vibrates to high frequencies at the base of the cochlea and to
  low frequencies at the apex. A hair cell at the base of the cochlea
  will respond best to high frequencies, since at those frequencies
  the basilar membrane underneath it will vibrate the most. The
  key idea is that although the hair cells are arranged in order
  along the basilar membrane, from high-frequency to low-frequency,
  it is the properties of the basilar membrane that set up this
  gradient, not the properties of the hair cells.
- outer hair cells help to "sharpen the tuning".
  Outer hair cells can actually move (change length) in response
  to nerve stimulation. If they could push the basilar membrane
  up and down, they could amplify or damp vibrations at will, making
  the inner hair cells more or less responsive. (Just like you
  can push a child higher and higher on a swing or bring her to
  a halt - it's all in when you push.)
- Something about this tight connection allows the timing of the
  signal to be preserved to the microsecond (action potentials are
  on the order of milliseconds, so it is no mean feat). The ventral
  cochlear nucleus cells then project to a collection of nuclei
  in the medulla called the superior olive. In the superior
  olive, the minute differences in the timing and loudness of the
  sound in each ear are compared, and from this you can determine
  the direction the sound came from. The superior olive then projects
  up to the inferior colliculus via a fiber tract called
  the lateral lemniscus.
- The second stream of information starts in the dorsal
  cochlear nucleus. Unlike the exquisitely time-sensitive localization
  pathway, this stream analyzes the quality of sound. The dorsal
  cochlear nucleus, with fairly complex circuitry, picks apart the
  tiny frequency differences which make "bet" sound different
  from "bat" and "debt". This pathway projects
  directly to the inferior colliculus, also via the lateral lemniscus.
- Notice that both pathways are bilateral. The consequence
  of this is that lesions anywhere along the pathway usually have
  no obvious effect on hearing. Deafness is essentially only caused
  by damage to the middle ear, cochlea, or auditory nerve.
- From the inferior colliculus, both streams of information
  proceed to sensory thalamus. The auditory nucleus of thalamus
  is the medial geniculate nucleus. The medial geniculate
  projects to primary auditory cortex, located on the banks
  of the temporal lobes.
- Fibers from the cochlear nuclei
  and the superior olive (not the inferior) travel up the
  lateral lemniscus (not the medial) to the inferior
  colliculus (not the superior), and then to the medial geniculate
  (not the lateral). Try remembering the mnemonic,
  
  "S-L-I-M" .
- You must be able
  to detect rotation, such as what happens when you shake or nod
  your head. In physics, this is called angular acceleration.
  You must also be able to detect motion along a line - such as
  what happens when the elevator drops beneath you, or on a more
  subtle note, what happens when your body begins to lean to one
  side. This is called linear acceleration. The vestibular
  system is divided into two receptor organs to accomplish these
  tasks.
- semicircular canals detect angular acceleration
- continuous endolymph-filled
  hoop. The actual hair cells sit in a small swelling at the base
  called the ampula.
- hair cells are arranged as a single tuft that
  projects up into a gelatinous mass, the cupula. When you
  turn your head in the plane of the canal, the inertia of the endolymph
  causes it to slosh against the cupula, deflecting the hair cells.
  Now, if you were to keep turning in circles, eventually the fluid
  would catch up with the canal, and there would be no more pressure
  on the cupula. If you stopped spinning, the moving fluid would
  slosh up against a suddenly still cupula, and you would feel as
  though you were turning in the other direction.
- Each tuft of hair cells is polarized
  - if you push it one way, it will be excited, but if you push
  it the other way, it will be inhibited. This means that the canals
  on either side of the head will generally be operating in a push-pull
  rhythm; when one is excited, the other is inhibited
- if both sides push at once,
  then you will feel debilitating vertigo and nausea. This is the
  reason that infections of the endolymph or damage to the inner
  ear can cause vertigo. However, if one vestibular nerve is cut,
  the brain will gradually get used to only listening to one side
  - this can actually be a treatment for intractable vertigo.
- semicircular canals exert direct control over
  the eyes, so they can directly compensate for head movements.
  Recall that the eye is controlled by three pairs of muscles;
  the medial and lateral rectus, the superior and inferior rectus,
  and the inferior and superior oblique. You may also remember
  that their directions of motion seemed to be at crazy diagonals.
  Those same crazy diagonals are matched closely by the three planes
  of the semicircular canals, so that a single canal (in general)
  interacts with a single muscle pair. The entire compensatory
  reflex is called the vestibulo-ocular reflex (VOR).
- If you move your head to the left, you will excite
  the left horizontal canal, inhibiting the right. To keep
  your eyes fixed on a stationary point, you need to fire the right
  lateral rectus and the left medial rectus, to move the eyes to
  the right.
- The pathway is as follows: the vestibular nerve
  enters the brainstem and synapses in the vestibular nucleus.
  Cells that received information from the left horizontal canal
  project to the abducens nucleus on the right side, to stimulate
  the lateral rectus. They also project to the oculomotor nucleus
  on the left side, to stimulate the medial rectus. Although not
  shown on the diagram, the same vestibular cells also inhibit the
  opposing muscles (in this case, the right medial rectus, and the
  left lateral rectus).
- right horizontal
  canal is wired to the complementary set of muscles. Since it
  is inhibited, it will not excite its target muscles (the right
  medial rectus and the left lateral rectus), nor will it inhibit
  the muscles you want to use
- A great deal of the VOR axon traffic travels via
  a fiber highway called the MLF (medial longitudinal fasciculus).
  The integrity of this tract is crucial for the VOR to work properly.
  It is occasionally damaged by medial brainstem strokes.
- The utricle and saccule detect linear acceleration.
  Each organ has a sheet of hair cells (the macula) whose cilia
  are embedded in a gelatinous mass, just like the semicircular
  canals. Unlike the canals, however, this gel has a clump of small
  crystals embedded in it, called an otolith (yes, all along you've
  had rocks in your head). The otoliths provide the inertia, so
  that when you move to one side, the otolith-gel mass drags on
  the hair cells. Once you are moving at a constant speed, such
  as in a car, the otoliths come to equilibrium and you no longer
  perceive the motion.
- single
  sheet of hair cells can detect motion forward and back, side to
  side. Each macula can therefore cover two dimensions of movement.
  The utricle lays horizontally in the ear, and can detect any
  motion in the horizontal plane. The saccule is oriented vertically,
  so it can detect motion in the sagittal plane (up and down, forward
  and back).
  
  A major role of the saccule and utricle is to keep
  you vertically oriented with respect to gravity. If your head
  and body start to tilt, the vestibular nuclei will automatically
  compensate with the correct postural adjustments. This is not
  just something that happens if the floor tilts - if you watch
  someone trying to stand still, you will notice constant small
  wavers and rocking back and forth.

04 Nov 09

Welcome to Hansen Nursing

acid-base balance

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clinicalmed

29 Oct 09

Diabetic Microvascular Complications: Slideshow

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endocrinology clinicalmed

19 Oct 09

Bedside Rounds: How Do You Diagnose and Treat Diabetic Neuropathy | Clinical Correlations

assess vibration sense.
Rx- insulin,tricyclic antidepressants,traditional anticonvulsants[VA,CBZ].

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clinicalmed

neuropathic pain in a “glove and stocking” distribution with the earliest signs in the feet. Night time complaints of “my feet are on fire”
physical examination centers on assessment of vibration since it is often one of the earliest neurological signs
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- 128-Hz tuning fork is applied to the bony prominence on the dorsal aspect of the first toe just proximal to the nail bed, over the interphalangeal joint. The patient is asked what he or she feels. If impairment exists at this distal bony prominence, the examiner can proceed to test more proximal prominences (such as the malleollus, patella, etc) to assess the extent. Testing the Achilles reflex is also useful.
- intensive insulin therapy in type I DM reduced the risk of developing clinical neuropathy by 61%. The treatment goal is to slow the progression of neuropathy rather than to overcome pain.
- tricyclic antidepressants (amitriptyline, desipramine and imipramine)
- traditional anticonvulsants (sodium valproate, carbamazepine)

12 Oct 09

Common skin infections in children -- Sladden and Johnston 329 (7457): 95 -- BMJ

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clinicalmed dermatology

self limiting
2-5 year age
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- whobathe together, and who are immunosuppressed
- umbilication
- Tinea capitis should be confirmedby mycological analysis before an eight week course of griseofulvin
- Acidified nitrite cream has been reportedas effective and painless.⁸ Topical imiquimod cream may be usefulin widespread or recalcitrant mollusca, but it has not beentested in controlled trials.⁹
- peaks in adolescence
- Resolution canbe preceded by the appearance of blackened thrombosed capillaryloops
- widespread and persistent in patients whoare immunocompromised
- hands and feet
- hyperkeratotic
- at sites of injury (Koebner phenomenon
- verrucae
- soles
- painful
- Mosaic
- densely packed individual warts. They are often resistantto treatment
- Plane warts
- face,
- resolve spontaneously within two years
- Salicylic acid breaks down hyperkeratoticskin but does irritate children's skin. Topical salicylic acidshould be regarded as first line treatment.
- Staphylococcus aureus or Streptococcuspyogenes
- golden
- 2-6years of age
- highly contagious
- more common in children with atopic dermatitis,in those living in tropical climates, and in conditions of overcrowdingand poor hygiene. Nasal carriage of organisms may predisposeto recurrent infection
- Bullousimpetigo is invariably caused by toxin-producing S aureus.
- Impetigo contagiosa is the most common form
- (bullae). These are painful, spread rapidly, andproduce systemic symptoms
- topicalmupirocin and fusidic acid are safe and effective treatmentsfor mild impetigo
- serious or extensive disease; they are easier to use buthave more side effects than topical agents. Flucloxacillin isconsidered the treatment of choice
- (scalp ringworm) is a highly contagious
- M canis, but now Trichophyton tonsurans
- shaving the scalp, plaiting, and using hair oils mayincrease spread.
- patchy alopecia, but specific clinicalpatterns can be varied. Six main patterns
- erythema
- scaling
- Kerion

09 Oct 09

Pediatrics | Paediatrics - Virtual Pediatric Patients - Virtual Pediatric Hospital

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case studies clinicalmed pediatrics

08 Oct 09

Beta-blockers for hypertension: Are they going out of style? — Cleveland Clinic Journal of Medicine

in younger patients,newer beta-blockers, nebivolol[highest beta-1 selectivity] & carvedilol, which are vasodilatory are superior than atenolol & also have better maintenance of glycemic control.

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clinicalmed antihypertensives

Current evidence suggests that older beta-blockers
may not be the preferred first-line antihypertensive drugs for hypertensive patients who have no compelling indications for
them (eg, heart failure, myocardial infarction, diabetes, high risk of coronary heart disease). However, newer beta-blockers
with vasodilatory properties should be considered in cases of uncontrolled or resistant hypertension, especially in younger
patients.
Beta-blockers with peripheral vasodilatatory effects act either via antagonism of the alpha-1 receptor, as with labetolol (Normodyne) and carvedilol (Coreg),¹⁰ or via enhanced release of nitric oxide, as with nebivolol (Bystolic).⁸
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- Atenolol and nadolol are eliminated by the kidney and require dose adjustment in patients with impaired renal function.^12,13
  
  On the other hand, propranolol, metoprolol, labetalol, carvedilol, and nebivolol are excreted primarily via hepatic metabolism.¹³
- beta-blockers may not be as effective as diuretics in preventing
  cardiovascular events when used as first-line antihypertensive therapy in elde
- lower in the losartan group than in the atenolol group. The difference was mainly due to a 25% lower incidence of stroke,
  which was statistically significant. The rates of myocardial infarction and death from cardiovascular causes were not significantly
- when atenolol was compared with other antihypertensives in five other randomized controlled trials that included
  more than 14,000 patients, those treated with atenolol had a higher risk of stroke
- amlodipine-plus-perindopril group had significantly fewer strokes
- relative risk of stroke was 16% higher. Atenolol
- atenolol, when taken once daily, leaves the patient unprotected in the last 6 hours of a 24-hour
- Hemodynamic characteristics of younger hypertensive patients include a high cardiac output and hyperdynamic circulation with
  a low pulse pressure, while older patients have lower arterial compliance with an elevated vascular resistance.
- similar in efficacy to other antihypertensive agents in younger patients (1,515 events in 30,412 patients,
  RR 0.97, 95% CI 0.88–1.07) but not in older
- In healthy people with normal arteries, the reflected wave merges with the forward-traveling wave in diastole and augments
  coronary blood flow. In patients whose arteries are stiff due to aging or vascular comorbidities, the reflected wave returns
  faster and merges with the incident wave in systole, resulting in higher left ventricular afterload and less coronary perfusion
- Older beta-blockers, and especially atenolol, have well-known metabolic adverse effects, particularly impairment of glycemic
  control. This adverse effect appears to occur only with beta-blockers that do not possess vasodilatory properties and thus
  increase peripheral vascular resistance, which results in lower glucose availability and reduced uptake by skeletal muscles
- Preliminary data from studies of newer beta-blockers that possess beneficial vasodilatory properties are encouraging. Animal
  studies and preliminary human studies find that these new-generation beta-blockers cause fewer adverse metabolic effects and
  improve endothelial function, measures of arterial stiffness, and cardiovascular outcomes.
- carvedilol increased endothelial vasodilation
  and reduced inflammation and platelet aggregation. These effects may be achieved though antioxidant actions, thereby preserving
  nitric oxide bioactivity
- carvedilol was associated with better maintenance of glycemic control in diabetic hypertensive patients
- Among all the beta-blockers in clinical use today, nebivolol has the highest selectivity for beta-1 receptors.⁸
- Endothelial dysfunction is characterized by decreased
  bioavailability of nitric oxide and has been shown to be a strong predictor of cardiovascular outcomes. By generating nitric
  oxide, nebivolol reduces peripheral vascular resistance, overcoming a significant side effect of earlier beta-blockers
- nebivolol significantly reduced the pulse-wave velocity (a measure of arterial stiffness), while atenolol had no effect
- nebivolol was associated with a better metabolic profile than atenolol, with none of
  the adverse effects on insulin sensitivity that atenolol had
- Large, prospective hypertension outcome trials, particularly to evaluate primary
  prevention of cardiovascular outcomes, are needed for an evidence-based approach to using the newer beta-blockers as preferred
  first-line therapy for hypertension.

Varicose veins: newer, better treatments available. — Cleveland Clinic Journal of Medicine

They increase in frequency with age. They are rare in childhood but, when present, they are more commonly associated with an underlying vascular malformation (eg, Klippel-Trénaunay syndrome). other than legs - vulva, hemarrhoids, esophageal varices, varicoceles, reticular veins, telangiectasias. Hyperpigmentation and ulceration are more common on the medial side of the ankle.These conditions develop as a result of venous hypertension. Pigmentation is due to extravasation. Lipodermatosclerosis[stasis cellulitis] and atrophieblanche[star shaped ulcers] are painful.

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clinicalmed