Friday, March 23, 2012

Fractures

break in continuity of bone
  • Traumatic-sustained due to excessive force-a qualified fracture usually means traumatic fracture
  • Pathological-usually trivial-bone already weak by underlying disease
  • Displaced fracture may occur due to fracturing force/muscle pull on fracture filaments/gravity-displacement may be shift/angulation/rotation
  • Simple/closed
  • Compound/open-
  1. internal compounding-piercing of sharp fracture end
  2. external compounding-lacreation+fracture from outside

  • Transverse # fracture line perpendicular to long axis of bone, caused by tapping/bending force
  • Oblique #line of # oblique, caused by a bending force which in addition has component along the long axis of the bone
  • Comminuted #with miltiple fragments,caused by crushing/compression force along the long axis of the bone
  • Segmental # two fractures in same bone@different levels

Fractures with Eponyms
  • Monteggia #dislocation #proximal 1/3rd of ulna + dislocation of head of radius
  • Galeazzi #dislocation # distal 1/3rd of radius with dislocation of distal radio-ulnar joint
  • Night stick # isolated # shaft of ulna
  • Colles' # occuring in adults@cortico-cancellous junction of distal end of radius + dorsal tilt & other displacements
  • Smith's # occur in adults@cortico-cancellous junction of distal end of radius with ventral tilt & other displacements (reverse Colles')
  • Barton's (marginal) # intra-articular# through distal articular surface of radius, taking a margin, anterior/posterior of the distal radius with the carpals displaced anteriorly/posteriorly
  • Chauffeur's # intra-articular oblique # of styloid process of radius
  • Bennet's # dislocation-oblique,intra-articular # of base of 1st metacarpal with sublaxation of trapezio-metacarpal joint
  • Rolando # extra articular # of base of 1st metacarpal
  • Boxer's # a ventrally displaced # through the neck of the 5th metacarpal-common in boxers
  • Side swipe # an elbow injury, combination of #distal end of humerus with # proximal end of radius &/or ulna (baby car #)
  • Bumper # comminuted depressed type-lateral condyle of tibia
  • Pott's # bimalleolar ankle
  • Cotton's # trimalleolar ankle
  • Massonaise's # ankle with # neck of fibula
  • Pilon # comminuted, depressed intra-articular # distal end of tibia
  • Aviator's # neck of talus
  • Chopart # dislocation # dislocation through inter tarsal joints
  • Jone's # Avulsion # base of 5th metatarsal
  • Jeffersen's # 1st cervical vertebra
  • Whiplash Injury- cervical spine injury involving sudden flexion followed by hyperextension
  • Chance # also called seat belt #, line of # runs horizontally through the body of vertebra through & through to the posterior elements
  • March # fatigue # of shaft of 2nd & 3rd metatarsal
  • Burst # comminuted # of vertebral body where fragments burst out in different directions
  • Clay-Shoveller's # an avulsion # of spinous process of one or more of the lower cervical or upper thoracic vertebra
  • Hangman's # pedicle & lalamina of C2 vertebra, with sublaxation of C2 over C3-sustained in hanging
  • Dashboard # posterior lip # of acetabulum, often associated with posterior dislocation of hip
  • Straddle # bilateral superior & inferior pubic rami #
  • Malgaigne's # a type of pelvis # in which there is a combination of #s- pubic rami anteriorly & SI joint/ilium posteriorly, on the same side
  • Mallet Finger- a finger flexed at the DIP joint d/t avulsion or rupture of extensor tendon@base of distal phallanx

Skin: Histology

Continually renewing stratified squamous epithelium-keratinizes & gives rise to derivative structures called appendages (pilosebaceous units, nails & sweat glands)

Cell Cycle-G0-G1-S-G2-M

Keratinocyte-ectodermally derived cell constituting 80% of epidermal cells-keratin filaments are hallmarks of keratinocytes & other epithelial cells

Immigrant cells- Melanocytes& Langerhans cells(migrate into epidermis during embryonic development), Merkel cells(differentiate in situ)

Melanocytes- located in stratum basale(stratum germinativum)- project their dendrites into epidermis- transfer their melanosomes (melanin packed membrane bound organelles) to keratinocytes which contains majority of melanin pigment - 36 keratinocytes per melanocytes- epidermal melanin unit



Keratinization- genetically programmed, carefully regulated, complex series of morphological changes & metabolic events that occur progressively in postmitotic keratinocytes & involve-

  • increased cell size & flattening
  • appearance of new cellular organelles & structural reorganization of those present
  • change from generalized cellular metabolism to a more focussed metabolism associated with the synthesis of molecules related to keratinization(structural proteins & lipids)
  • alterations in properties of plasma membrane, cell surface antigen & receptors
  • eventual degradation of cellular organelles including internucleosomal chromatin fragmentation characteristic of apoptosis
  • dehydration

Epidermal Layers
  • Basal layer/stratum germinativum-attached to basement membrane-contains mitotically active keratinocytes-contains house keeping organelles(RER,golgi complex, mitochondria, lysosomes & ribosomes)-gives rise to superficial layer
  • Spinous layer/Stratum spinosum-named for spine like appearance of cell margins in histological sections. Spines are abundant desmosomes, calcium dependent cell surface modifications that promote adhesion of epidermal cells & resistance to mechanical stress.Upper spinous layer cells have organelles called lamellar granules
  • Malpighian layer-includes both basal & spinous layer
  • Granular layer/stratum granulosum-characterised by buildup of components necessary for the process of programmed cell death & formation of a superficial water impermeable layer.The most apparent structures within these cells are-basophilic keratinohyaline granules-composed of profilaggrin,keratin intermediate filament & loricrin. Conversion of profilaggrin to filaggrin(filament aggregating protein)-occurs during transition of granular to cornified cells
  • Corny layers or Stratum corneum- formed of cornified or horny cells which is the largest of epidermis & have highest concentration of free amino acids,esp in mid layers.Stratum corneum cells retain some metabolic function (not just an inert covering)
Normal turnover time of epidermis/skin doubling time-- 4wks
VLBW/premature infants lack-stratum corneum

Sunday, March 18, 2012

Carpal Tunnel

  • Carpal tunnel or carpal canal is the passageway on the palmar side of the wrist that connects the forearm to the middle compartment of the deep plane of the palm

  • The canal is narrow and when any of the nine long flexor tendons passing through it swells or degenerates, the narrowing of the canal often results in the median nerve becoming entrapped or compressed, a medical condition known as carpal tunnel syndrome

  • The structures passing through it are
  1. flexor digitorum profundus (four tendons)
  2. flexor digitorum superficialis (four tendons)
  3. flexor pollicis longus (one tendon)
A single nerve passes through the tunnel: the median nerve between tendons of flexor digitorum profundus and flexor digitorum superficialis

The carpus, the bony elements of the wrist, form an arch which is convex on the dorsal side of the hand and concave on the palmar side. The groove on the palmar side, the sulcus carpi, is covered by the flexor retinaculum, a sheath of tough connective tissue, thus forming the carpal tunnel. The flexor retinaculum is attached radially to the scaphoid tubercle and the ridge of trapezium, and on the ulna side to the pisiform and hook of hammate

The narrowest section of the tunnel is located a centimetre beyond the mid-line of the distal row of carpal bones where the sectional area is limited to 1.6 cm2

The tendons of the flexor digitorum superficialis and profundus pass through a common ulnarsheath, while the tendon of the flexor pollicis longus passes through a separate radial sheath. Themesotendon shared by these tendons is attached to the radial and palmar walls of the carpal tunnel

Superficial to the carpal tunnel and the flexor retinaculum, the ulnar artery and ulnar nerve pass through the ulnar tunnel

Movements in the wrist affects the shape and width of the carpal tunnel. The width decreases considerably during normal range of motion in the wrist and because the carpal bones move in relation to each other with every motion of the hand the bony walls of the tunnel are not rigid. Both flexion and extension increase compression in the carpal tunnel:

  • Flexing the wrist causes the flexor retinaculum to move closer to the radius which considerably decreases the cross section of the proximal opening of the tunnel. Additionally, the distal end of the capitate presses into the opening.
  • In extreme extension. the lunate constricts the passage as it is pressed toward the interior of the tunnel.




File:Carpal-Tunnel.svg

Thursday, March 15, 2012

Biosimilar Insulins

Biocon is conducting Phase-3 trials of recombinant human insulin (biosimilar of Novo Nordisk’s Novolog) in Europe and global Phase-1 trials for glargine (biosimilar of Sanofi-Aventis’ Lantus). Biocon will continue to develop other biosimilars — aspart (biosimilar of Novo Nordisk’s Novolog) and lispro (biosimilar of Eli Lilly’s Humulog)

Eye: Anatomy



Outer Layer- cornea/sclera






anterior part of sclera covered by mcous menbrane-the conjunctiva

Cornea:
  • 3 layers-epithelium, substantia propria(stroma),Descemet's membrane with endothelium
  • epithelium-stratified, basal cells lie on Bowman's membrane
  • stroma-90% of corneal thickness - regularly arranged thin fibrils of collagen ensheathed by acid mucopolysaccharides set in a ground substance- form ribbon like bundles & give the stroma a laminated appearance- fibrils circular in CS-spaced equidistant- hexagonal lattice
  • transparency related to regularity of stromal components-interfibrilar spacing less than a wavelength of light-tangential rows of fibres act as diffraction gratting resulting in destructive interference of scattered rays
  • Descemet's membrane-thin elastic membrane-covered on posterior surface by endothelium
  • stromal hydration maintained by endothelium- electrolytes removed & water flows passively
  • endothelium examined by 500x specular microscope
  • endothelial cells decrease in number with age-residual individual cells enlarge to compensate
  • corneoscleral junction- limbus- cornea set into a sclera like a watch glass
  • nerve supply-trigeminal
  • no blood vessels- minute arcades @ limbus (1mm)
  • corneal nourishment- diffusion of aqueous humour & peripheral vessels
Lining the Inner Aspect of Sclera-
  1. Uveal Tract-highly vascular-for nutrition
  2. Retina

Uveal Tract:
  • Choroid
  • Ciliary Body
  • Iris- anteriormost
Anterior Chamber:
  • aquous humour
  • between cornea & iris 2.5 mm deep in centre
  • peripheral recess- angle of anterior chamber
  • canal of Schlemm- circular venous sinus in inner layer of sclera- often more than one lumen
  • trabecular meshwork between canal of Schlemm & recess of anterior chamber
Iris:
  • anterior surface-single layer endothelium-not continuous@crypts
  • stroma contains branched connective tissue cells
  • iris stroma usually pigmented-unpigmented in blue sclera
  • blood vessels in iris-radial
  • tissue spaces communicate directly with anterior chamber through crypts@ ciliary border
  • thinnest@attachment to ciliary body
  • posterior surface-2 pigmented epithelium-developmentally from retina-continuous@pupillary margin-anterior layer flattened cells-posterior layer cuboidal cells
  • pupillary smooth muscles derived from from anterior epithelial cells
  • sensory- trigeminal
  • sphincter pupillae-occulomotor
  • dilator pupillae-sympathetic (cervical chain)
Ciliary Body:
  • like isosceles triangle- base forwards
  • chief mass-ciliary muscle-unstriped-3 parts-circumferential-blends with scleral spur
  • most muscles meridional in anteroposterior direction, 2nd portion v-shaped interdigitating concentrically@base of iris, 3rd portion -insertion@ root of iris-just anterior to pigmentary epithelium-closely related to dilator muscle
  • anterior surface-corrugated-pars plicata-contains ciliary processes(tufts of blood vessels-like glomeruli) in between
  • posterior part-smooth-pars plana
  • covered on inner surface by 2 layers of epithelium-belongs to retina-only outer layer pigmented
  • posterior extent-ora serrata-transition from ciliary body to choroid gradual
  • ora serrata more anterior on nasal side than temporal
  • sensory-trigeminal
  • motor-occulomotor & sympathetic
Choroid:
  • extremely vascular membrane in contact everywhere with sclera with a potential space-epichoroidal/suprachoroidal space in between
  • inner side lamina vitrea/membrane of Bruch
  • blood vessels increase in calibre from inside to outside-choriocapillaries(fenestrated vessels) immediately beneath membrane of Bruch
  • sensory-trigeminal
  • autonomic supply-for vasomotor
Retina:
  • Outer layer epithelium-hexagonal single layer pigment epithelium
  • Inner layer epithelium-suddenly changes@ora serrata into highly complex visual retina
Retina formed by 3 strata of cells & their synapses:
  • visual cells-externally
  • relay layer of bipolar cells-intermediate
  • ganglion cells-internally

  1. pigment epithelium-hexagonal cells-single layer-assist metabolism of retina- products of metabolism are freely exchanged between receptor cells & pigment epithelium-melanin granules prominent(absorbs light)-phagosomes present-
  2. rods & cones-neural epithelium-discs renewed continuously-rod discs have limited life,eventually lost to pigment epithelium
  3. external limiting membrane-perforated by rods & cones
  4. outer nuclear layer-nuclei of rods & cones
  5. outer plexiform layer-synaptic layer-transmissive region
  6. inner nuclear layer-nuclei of bipolar cells-
  7. inner plexiform layer-synaptic
  8. ganglion cell layer
  9. nerve fibre layer-axons of ganglion cells running centrally to optic nerve
  10. internal limiting membrane-separates retina from vitreous


  • Fibres of Muller-better developed vertical cells-supportive neuroglial cell- nutritive function

  • Fovea Centralis- at posterior pole (3mm in the temporal side of the optic disc)-only cones present- other layers almost completely absent- most sensitive part of retina

  • Macula lutea(yellow spot)-surrounds fovea centralis-nuclear layers get thinned out-plexiform layer present-ganglion cells heaped up into several layer(in stead of consisting of a single row of cells)-no blood vessels present-nourishment entirely by choroid)-more sensitive than other parts of retina,less than fovea

  • Optic Disc-fibres of nerve fibre layer pass into the optic nerve-other layers of retina stop abruptly@ the edge of the aperture in the scleral canal- spanned by transverse layer of connective tissue containing much elastic tissue(lamina cribrosa)-through its meshes the optic nerve fibres pass-on posterior side the nerve fibres abruptly become surrounded by medullary sheaths
Lens:

Biconcave mass of peculiarly differentiated epithelium-developed from invagination of surface ectoderm of the fetus(compare with plantar corns)-original surface goes inside@centre-peripheral cells correspond to the basal cells of epidermis-inner old cells undergo sclerosis-changes analogous to that of stratum granulosum in epidermis-becomes massed together in the form of nucleus-Lens is devoid of nerve supply


  1. Accommodation is one of the focusing mechanisms of the eye.
    Accommodation
  2. In order to focus rays from objects at varying distances, the lens must change it's refractive power.
  3. To change it's refractive power, the lens changes shape
  4. The exact shape of the lens is determined by seventy or so suspensory ligaments.
  5. The suspensory ligaments attached to the lens are called zonula.
  6. The zonula are attached radially around the lens.
  7. The zonula pull the edges of the lens towards the clilary body.
  8. When the eye is accommodated for distant vision, both the circular and meridional fibres of the ciliary muscle are relaxed. (a)
  9. When both the circular and meridional fibres of the ciliary muscle are relaxed, the zonula is stretched.
  10. When the zonula is stretched it pulls the elastic lens into a flattened shape.
  11. When the eye is accommodated for near vision, both the circular and meridional fibres of the ciliary muscle contract. (b)
  12. When both the circular and meridional fibres of the ciliary muscle contract, the tension in the zonula is released.
  13. When the ciliary muscle contracts, the ciliary process and choroid move forward toward the lens.
  14. When the tension in the zonula is released, it allows the the elastic lens to bulge.
  15. The lens of the eye is elastic.
  16. Because the lens is elastic, it bulges, shortens, and thickens.
  17. The ciliary process is the aqueous humor factory.
  18. The aqueous humour is drained out of the scleral venous sinus.


Tuesday, March 13, 2012

Sound Dynamics & Tests of Hearing

Decible Levels

Whisper 30 dB
Normal Conversation 60 dB
Shout 90 dB
Discomfort in ear 120dB
Pain in ear 130dB

Pitch is sensation of a particular frequency, dB is that of intensity

stapedial reflex is elicted with a sound of 70-100 dB
normal person can hear 20-20000 Hz
audiometric testing done 125-8000Hz

white noise-all frequencies if sound-comparable to white light

Narrow band noise-used in masking-it's a white noise without certain frequencies (above & below some patricular frequency having been filtered out)-used in pure tone audiometry

speech noise-noise having frequencies in speech range(300-3000 Hz)-all other frequencies filtered out

Masking-essential for all bone conduction tests-for air conduction test is required only when the difference in hearing between the two ears exceeds 40dB

Clinical Tests of Hearing

1.Finger Friction Test
2.Watch Test-practically obsolete
3.Speech (Voice Test)-conversational/forced whisper (use of spondee words by examiner)
4.Tuning Fork Tests- tests AC/BC

a)-Rinne Test (AC>BC is normal-positive Rinne)
BC>AC negative Rinne-minimum air-bone gap of 15-20 dB
  • Rinne test equal or negative for 256 Hz but positive for 512 Hz=> air bone gap 20-30 dB
  • Rinne negative for 256 & 512 Hz but positive for 1024 Hz => air bone gap 30-45 dB
  • Rinne negative for 256, 512 & 1024 Hz => air bone gap of 45-60 dB
Negative Rinne for 256, 512 & 1024 Hz indicates minimum AB gap of 15,30&45 dB respectively

False negative Rinne-in severe unilateral SNHL-correct diagnosis made by masking non test ear Barany's noise Box while testing for bone conduction-Weber lateralzation also helps

b)-Weber Test-done with 512 Hz (detects 15-20 dB)
  • lateralized to worse ear in conductive deafness
  • to better ear in sensorineural hearing loss
c)-ABC- cochlear function- comparison with examiner
d)-Schwabach's-ABC with an occluded meatus (reduced in SNHL, lengthened in CHL)

e)-Bing Test- effect of occlusion of meatus
  • Bing Positive-normal person/SNHL hear louder with occlusion of meatus
  • Bing Negative-CHL appreciates no change

f)- Gelle's Test- test of bone conduction, examined is the effect of increased air pressure in ear canal on hearing-has been replaced by tympanometry to find out stapes fixation
  • Positive in normal persons & SNHL-decreased hearing on increased pressure
  • Negative in fixed/disconnected ossicular chain

Audiometric Tests

1. Pure Tone Audiometry:
-Measure of cochlear function
-Air Conduction Threshold measured for tones 125,250,500,1000,2000,4000 & 8000 Hz
-Bone conduction threshold measured for 250,500,1000,2000 & 4000 Hz
-AB gap measured (normal individual has no AB gap in audiometry)

Shadow Curve- obtained from non-test better ear when difference between two ears is 40dB or more above air conduction thresholds-Masking is required if difference is>40dB(done by employing narrow band noise to the non-test ear)

2.Speech Audiometry:
-patient's ability to hear & understand speech is measured.parameters studied are
  • Speech Reception Threshold-normally SRT is within 10 dB of the average pure tone threshold of 3 speech frequencies(500,1000 & 2000 dB).SRT better than pure tone average by more than 10 dB suggests a functional hearing loss

  • Discrimination Score(DS) or Speech Recognition Score (SRS)
Normal 90-100%
Slight Difficulty 76-88%
Moderate difficulty 60-74%
Poor 40-58%
Very Poor <40%


Optimum Discrimination Score (ODS)-expressed in %
Half Peak Level (HPL) expressed as dB-a derived figure from audiogram

  • Normal- ODS 100% @30 dB,HPL-15 dB
  • Conductive Deafness of 40 dB-ODS100% @70 dB,HPL-55 dB
  • SNHL of 40 dB-ODS never reaches 100%, constant beyond a level
  • Retrocochlear loss- Roll over curve obtained, score falls below ODS beyond a frequency
3.Bekesy Audiometry-no longer used
4.Tympanometry-220 Hz tone delivered

  • Type A-normal tympanogram
  • As-fixation of sosicles-otosclerosis/malleus fixation-lower compliance@ambient air pressure
  • Ad-ossicular discontinuity/thin & lax TM -high compliance at or near ambient pressure
  • Type B-flat or dome shaped graph- no change in compliance with pressure changes-seen in middle ear fluid or thick TM
  • Type C-maximum compliance occurs with negative pressures in excess of 100 mm H2O-seen in retracted TM & may show some fluid in middle ear
Acoustic Reflex: Presence of stapedial reflex @ lower intensities (40-60 dB) than usual 70-100dB indicates recruitment & thus a cochlear type of hearing loss

Stapedial Reflex Decay- VIII th nerve lesion - if a sustained tone of 500-1000 Hz delivered 10dB above the acoustic reflex threshold,for a period of 10 seconds, brings the reflex amplitude to 50%, shows abnormal adaptation

Absence of stapedial reflex when hearing is normal indicates lesion of facial nerve, proximal to the nerve to stapedius.

Special Tests of Hearing


  1. Recruitment:
  • phenomenon of abnormal growth of loudness
  • the ear which doesn't hear low intensity sounds begins to hear greater intensity sounds as loud or even louder than normal hearing ear
  • poor candidates of hearing aid
  • cochlear lesions (Menier's Disease,presbycusis)
  • Alternate binaural loudness balance test- used to detect recruitment in unilateral cases
2. Short Increment Sensitivity Index
  • Patients with cochlear lesions distinguish smaller changes in intensity of pure tone better than normal persons & those with CHL or retrocochlear lesions
  • CHL- SISI score<15%
  • Cochlear Lesion-SISI score 70-100%
  • Nerve Deafness- SISI score 0-20%
3. Threshold Tone Decay Test:
  • measure of nerve fatigue
  • normal person can hear a tone continuously for 60 seconds, nerve fatigue-it's less
  • result expressed as dB decay
  • decay> 25dB=> retrocochlear lesion
4. Evoked Response Audiometry:
  • Electrocochleography (EcoG)-measures electrical potentials arising in the cochlea & CN VIII in response to auditory stimuli within 5 mili seconds, the response is in the form of cochlear microphonics,summating potentials & action potentials of VIII th nerve-finds threshold of hearing in young infants & children to within 5-10 dB
  • Auditory Brain Stem Responses-non-invasive- ECOLI,MA-7 wave forms I to VII-wates are studied for absolute latency, inter wave latency, amplitude
5.Otoacoustic Emissions: produced by outer hair cells of cochlea
6.Central Auditory Tests:designed to find defects in central auditory pathways & temporal cortex
7. Hearing Assessment ininfants & Children:
  • Screening procedures- arousal test & auditory response cradle
  • Behaviour Observation Audiometry- Moro's Reflex, Cochleo Palpebral Reflex & Cessation Reflex
  • Distraction techniques
  • Coonditioning Techniques
  • Objective Tests

Sunday, March 11, 2012

Vitamin A

pre formed-retinol
pro vitamin-beta carotene-some converted into retinol in intestinal mucosa
IU of vit A is equivalent to .3 microgram of retinol
1mcg retinol=1mcg of RE
1mcg of B-carotene=.167 mcg of RE
1mcg of other carotenoids=.084 mcg of RE

Functions:
-indispensable for normal vision-production of retinal pigments
-necessary for maintaining normal integrity & normal function of glandular & epithelial tissues
-supports growth, especially skeletal growth
-anti infective
-may protect against epithelial cell cancres like bronchial cancers

Sources:
-animal foods-halibut liver oil richest> cod liver oil
-plant foods-carrot>green leaves
-fortified foods-vanaspati,margarine,milk

Storage:
liver-retinol palmitate
well fed person-normal circumstances-reserves may last 6-9months
retinol binding protein-produced in liver-production decreases in deficiency

Deficiency:
-night blindness
-conjunctival xerosis
-bitot's spots-bilateral-triangular-foamy-in children deficiency-in older indicates earlier disease
-corneal xerosis- serious
-keratomalacia-liquefaction of cornea- rapid-most serious-medical emergency

Treatment:
-all early stages of xerophthalmia-2,00,000 IU-on 2 successive days
-all children of corneal ulcer should take vit A

Prophylaxis:
-NIN,Hyderabad-200,000 IU every 6 monthly in preschool kids(1-6yrs)
-100,000 IU to children of 6months-1yr

Recomended alllowance:
600 microgram for adult men/women/pregnancy/children>6yrs
950 microgram for lactating mother
350 for 0-12 minths
400 for 1-6yrs

Toxicity:
-nausea, vomiting,anorexia,sleep disorders, papillar edema

Saturday, March 10, 2012

Cranial Nerves

12 pairs in total-all originate from brain except for spinal accessory nerve

(LPK-trOI-AFA-GVAH)



general somatic afferent(GSA)- V,VII,IX,X
general visceral afferent(GVA)-IX,X
special afferent(SA)-I,II,VII,VIII,IX,X
general somatic efferent(GSE)-motor III, IV, VI, XI,XII
general visceral efferent(GVE)-III,VII,IX,X
branchial efferent (BE)-V,VII,IX,X-motor to skeletal muscles derived from pharyngeal arch mesoderm

  • Olfactory-SA- exit through cribriform plate of ethmoid bone -smell-
  • Optic-SA -exit thru optic canal -vision
  • Occulomotor-superior orbital fissure-
  1. GSE-innervates levator palpebrae superioris,superior rectus,inferior rectus,medial rectus,inferior oblique (LR6SO4rest3)
  2. GVE-innervates sphincter pupillae for pupillary constriction,ciliary muscles for accomodation of lens for near vision
  • Trochlear-superior orbital fissure-GSE-superior oblique muscles
  • Trigeminal-superior orbital fissure-ophthalmic division(V1), foramen rotundum-maxillary nerve(V2), foramen ovale-mandibular division(V3)
  1. GSA-sensory from:V1(ophthalmic division)-eyes, conjunctiva, orbital contents, nasal cavity, frontal sunus, ethmoidal sinus, upper eyelid, dorsum of nose, anterior part of scalp, dura in anterior cranial fossa, superior part of tentorium cerebelli -------------V2(maxillary nerve)-dura in middle cranial fossa, nasopharynx, palate, nasal cavity, upper teeth, maxillary sinus, skin covering the side of nose, lower eyelid, cheek, upper lip------V3(mandibular division)-skin of lower face, cheek, lower lip, anterior part of external ear, part of external acoustic meatus, temporal fossa, anterior 2/3rd of tongue, lower teeth, mastoid air cells, mucous membranes of cheek, mandible, dura in middle cranial fossa
  2. BE- innervates temporalis, masseter, medial & lateral pterygoids, tensor tympani, tensor veli palatini, anterior belly of digastric, myohyoid muscles
  • Abducent-superior orbital fissure- GSE- innervates lateral rectus muscle
  • Facial-stylomastoid foramen(nerve leaves cranial cavity through internal acoustic meatus)
  1. GVA-sensory from part of external acoustic meatus & deeper parts of auricle
  2. SA-taste from ant2/3rd of tongue
  3. GVE-innervates lacrimal gland, submandibular & sublingual salivary glands & mucous membranes of nasal cavity, hard & soft palates
  4. BE-innervates muscles of face(muscles of facial expression) & scalp derived from the second pharyngeal arch & stapedius, posterior belly of digastric, stylohyoid muscles
  • Vestibulocochlear-nerve leaves cranial cavity through internal acoustic meatus- vestibular division-balance, cochlear-hearing
  • Glossopharyngeal-jugular foramen
  1. GVA-sensory from carotid body & sinus
  2. GSA-posterior 1/3rd of tongue, palatine tonsils, oropharynx, mucosa of middle ear & pharyngotympanic tube
  3. SA-taste from posterior 1/3rd of tongue
  4. GVE-innervates parotid salivary gland
  5. BE-innervates stylopharyngeus muscle
  • Vagus-jugular foramen-
  1. GSA-sensory from larynx, laryngopharynx, deeper parts of auricle, part of external acoustic meatus & dura in posterior cranial fossa
  2. GVA-sensory from aortic body chemoreceptors & aortic arch baroreceptors, esophagus, bronchi, lungs, heart & abdominal viscera of the foregut & midgut
  3. SA-taste from epiglottis & pharynx
  4. GVE-innervates smooth muscle & glands in the pharynx, larynx, thoracic viscera & abdominal viscera of the foregut & midgut
  5. BE-innervates one tongue muscle(palatoglossus), muscles of the soft palate ( except tensor veli palatini), pharynx (except stylopharyngeus) & larynx
  • Accessory-jugular foramen-GSE-innervates sternocleidomastoid & trapezius muscle
  • Hypoglossal-hypoglossal canal-GSE-innervates hypoglossus, genioglossus & styloglossus muscles & all intrinsic muscles of tongue

Physiology of Hearing & Vestibular System

Physiology of Hearing

@ 20 degree C, sound travels@ 344 m/s in air
sound signal collected by pinna-passes through external auditory canal-strikes TM-transmitted through chain of ossicles- pressure changes in labyrinthine fluids-movement of basilar membrane-stimulation of hair cells in organ of corti-conversion of electrical energy into electrical impulses-travels along auditory nerve

1.conductive apparatus-mechanical conduction of sound
2.sensory system of cochlea- transduction of mechanical energy to electrical impulses
3.neural pathways-conduction of electrical impulses to brain

Conduction of Sound:
Impedence matching/Transformer action- middle ear converts sound of greater amplitude & lesser force to that of lesser amplitude & greater force-
a-lever action of ossicles-handle of malleus is 1.3 tmes longer then long process of incus-providing a mechanical advantage of 1.3
b-hydraulic action of TM-the area of TM(67.5 square mm):area of stapes footplate(3.2 square mm)=21:1
effective vibratory area is 2/3rd(45 square mm), hence the ratio reduces to 14:1(areal ratio), the product of this ratio & liver action of ossicles = 18:1
c-curved membrane effect-movements of TM are more @ periphery than @ centre where malleus handle is attached

Phase differential between oval & round window:
-sound waves striking the TM don't reach the oval & round window simultaneously. There is a preferential pathway to the oval window because of the ossicular chain. Thus, when oval window is receiving wave of compression, the round window is at phase of rarefaction. If the sound waves were to strike both the windows simultaneously, they would cancel each other's effect with no movement of perilymph & no hearing. The acoustic separation of windows is achieved by the presence of intact TM & cushion of air in the middle ear around the round window.

Natural resonance of external(3000Hz) & middle ear(800Hz):
-inherent anatomic & physiologic properties of the external & middle ear allow certain frequencies of sound of sound to pass more easily to the inner ear due to their natural resonances-frequencies most efficiently transmitted by ear ossicles are between 500-2000 Hz while that by TM is 800-1600Hz.Thus, greatest sensitivity of sound transmission is between 500-3000 Hz & these are the most important frequencies in day to day conversation


Transduction of Mechanical Energy to Electrical Impulses:
-movements of stapes footplate-transmits to cochlear fluid-moves basilar membrane-setting up of shearing force between tectorial membrane & hair cells. The distortion of hair cells gives rise to cochlear microphonics to which triggers the nerve impulse.
-sound wave, depending upon its frequency,reaches maximum amplitude on a particular place on the basilar membrane & stimulates that segment-travelling wave theory of Bekesy-higher frequencies are represented in the basal turn of cochlea & the progressively lower ones towards apex.

Neural Pathways:
-hair cells get innervation from the bipolar cells of spiral ganglion
-central axons of these cells collect to form cochlear nerve-goes to ventral & dorsal nuclei
-from there, both crossed & uncrossed fibres travel to the superior olivary nucleus-lateral leminiscus-inferior colliculus-medial geniculate body-auditory cortex of temporal lobe

Physiology of Vestibular System

Vestibular system divided as:

-Peripheral-membranous labyrinth(semicircular ducts, utricles & saccules) and vestibular nerve
-Central-made up of nuclei & fibre tracts in the central nervous system to integrate vestibular impulses with other systems to maintain body balance

Semicircular Canals:
-respond to angular acceleration & deceleration-3 canals lie @ right angles to each other, but one which lies@ right angles to the axis of rotation is stimulated the most.
-horizontal canal responds maximum to rotation on the vertical axis & so on. Due to this arrangement of the 3 canals in 3 different planes, any change in position of head can be detected
-stimulation of semicircular canals produces nystagmus & the direction of nystagmus can be determined by the plane of canal being stimulated
-horizontal nystagmus- horizontal canal
-rotatory-superior canal
-vertical -posterior canal

The stimulus to semicircular canal is flow of endolymph which displaces the cupula. The flow may be towards the cupula-ampullopetal(utriculopetal), or away from it-ampullofugal(utriculofugal). Ampullopetal flow is more effective than ampullofugal for the horizontal canal-The quick component of nystagmus is always opposite to the direction of flow of endolymph.
Thus, if a person is rotated to the right for sometime & then abruptly stopped, the endolymph continues to move to the right due to the inertia- ampullopetal for the left canal- nystagmus horizontal-directed to left

Utricle & Saccule:
-utricle stimulated by linear acceleration & deceleration or gravitational pull during the head tilts-the sensory hair cells in the macula lie in the different planes & stimulated by displacement of otolith membrane during head tilts
-the function of the saccule is similar to that of the utricle as the structure of maculae in the two organs is similar but experimentally, the saccule is also seen to respond sound vibrations

-vestibular system registers changes in head position, linear or angular acceleration & deceleration & gravitational effects-information sent to CNS where information from other systems- visual,auditory,somatosensory (muscles, joints, tendons,skin)-also received.All this information is integrated & used in the regulation of equilibrium & body posture. Cerebellum, which is also connected to vestibular end organs, further co-ordinates muscular movements in their rate, range, force & duration- maintenance of equilibrium

Maintenance of body equilibrium:
-the balance system-vestibular,visual,somatosensory- a two sided push-pull system
-in static neural position, each side contributes equal sensory information
-during movements- like turning,tilt etc, ther's temporary change in push & pull system which is corrected by appropriate reflexes & motor outputs to the eyes(vestibulo-ocular reflex), neck(vestibulocervical reflex), trunks&limbs(vestibulospinal reflex) to maintain new position of head & body, but if any component of push & pull system of one side is disturbed for a longer period due to disease- vertigo & ataxia develop.

Vertigo & Dizziness:
-Disorientation in space causes vertigo or dizziness & can arise from disorders of any of the 3 systems- notably vestibular, somatosensory or visual
-Normally, the impulses reaching the brain from the 3 systems are equal & opposite.
-if any component on one side inhibited/stimulated, the information reaching the cortex is mismatched, resulting in disorientation & vertigo. The vestibular inhibition on one side (like acute vestibular failure, labyrinthectomy, Meniere's disease, CN VIII section) causes vertigo. Dizziness can similarly results from ocular causes,(e.g. high errors of refraction/acute extraocular muscle paralysis with diplopia)

Motion Sickness:
-characterised by nausea, vomiting, pallor, sweating during sea,air,bus/car travel-in certain susceptible individuals
-can be induced by both by real & apparent motion & is thought to arise from mismatch of information reaching the the vestibular nuclei & cerebellum from visual, labyrinthine & somatosensory systems- can be controlled by labyrinthine sedatives

Friday, March 9, 2012

Eye: Development



1.Neural Groove- Invaginates to form neural tube, longitudinal, dorsal
2.Optic Plate- thickening from either side of lateral aspect the precursor of forebrain
3. Primary Optic Vesicle-when optic plate grows outwards as a diverticulum towards the surface
4.Optic Cup(secondary optic vesicle)-forms after meeting surface ectoderm, primary optic vesicle invaginates from below
5.Embryonic fissure-the line of invagination during formation of optic cup
6. Inner layer of optic cup- forms main structure of retina-nerve fibres grow from it
7.Outer layer of retina- forms single layer of pigment epithelium
8.The space between retina & pigment epithelium- original primary optic vesicle
9.From anterior border of original optic vesicle develops parts of the ciliary body & iris
10.At the meeting point of neural ectoderm & surface ectoderm, the surface ectoderm thickens to form the lens plate
11.The lens plate invaginates to form lens vesicle & then separates to form lens
12.The hyaloid artery enters the optic cup through embryonic fissure & grows forward to meet the lens, bringing temporary nourishment to the developing structures before it eventually atrophies & disappears-replaced by vitreous-largely secreted by surrounding neural ectoderm
13.The mesoderm surrounding the optic cup differentiates to form the coats of eye & orbital structures, that between the lens & surface ectoderm becomes hollowed to form the anterior chamber, lined by mesodermal condensations which forms the anterior layers of the iris, the angle of anterior chamber & the main structures of cornea.
14.Surface ectoderm remains as corneal & conjunctival epithelium.
15.In the surrounding region, folds grow over in front of the cornea, unite & separate again to to form the lids.



Major Milestones in development of Eye after the Corresponding Periods of Conception:

3wks-Optic groove appears

4th wk-optic pit develops into optic vesicle-lens plate forms-embryonic fissure develops

1month-lens pit & then lens vesicle form-hyaloid vessels develop

11/2 month-closure of embryonic fissure-differentiation of retinal pigment epithelium-proliferation of neural retinal cells-appearance of eyelid folds & nasolacrimal ducts

7th week-formation of embryonic nucleus of lens-sclera begins to form-migration of waves of neural crest(1st wave-corneal & trabecular endothelium,2nd wave-formation of corneal stroma,3rd wave-formation of iris stroma)

3rd month-Differentiation of precursors of rods & cones-anterior chamber appears-fetal nucleus starts developing-sclera condenses-eyelid folds lengthen & fuse

4th month-beginning of formation of retinal vasculature-hyaloid vessel begins to regress-formation of optic disc cup & lamina cribrosa-canal of Schlemm appears-Bowman's membrane develops-formation of major arterial circle & sphincter muscles of iris

5th month-photoreceptors differentiate-eyelid sepration begins

6th month-differentiation of dialator pupillae muscle-nasolacrimal system becomes patent-cones differentiate

7th month-rods differentiate-myelination of optic nerve begins-posterior movement of anterior chamber angle-retinal vessels start reaching nasal peripheri

8th month-completion of anterior chamber angle formation-hyaloid vessels disappear

9th month-retinal vessels reach temporal periphery, pupillary membrane disappears

After Birth-Macular region of the retina develops further




Precursors & Corresponding Derivatives of Eye structures:

Neural Ectoderm- smooth muscle of iris-optic vesicle & cup-iris epithelium-part of vitreous-retina-retinal pigment epithelium,fibres of optic nerve

Surface Ectoderm-conjunctival epithelium,corneal epithelium,lacrimal glands,tarsal glands & lens

Mesoderm-extraocular muscles,corneal stroma,sclera,iris,vascular endothelium of eye & orbit,choroid, part of vitreous

Neural Crest-corneal stroma,keratocytes & endothelium; sclera; trabecular meshwork endothelium, iris stroma, ciliary muscles, choroidal stroma, part of vitreous, uveal & conjunctival melanocytes, meningeal sheaths of optic nerve,ciliary ganglion,Schwann cells of ciliary nerves,orbital bones,orbital connective tissue,connective tissue sheath & muscular layer of ocular & orbital vessels

Thursday, March 8, 2012

Hyoid Bone

A small, U-shaped bone situated centrally in the upper part of theneck, beneath the mandible but above the larynx near the level of the third cervical vertebra. It can be felt by pressing one's finger into the crease where the chin becomes the neck. The hyoid bone consists of three separate parts – the body, and the left and right greater and lesser cornu (horns) – which fuse in early adulthood.

The function of the hyoid is to provide an anchor point for the muscles of the tongue and for those in the upper part of the front of the neck.

The hyoid is (uniquely in the vertebrate skeleton) not joined to any other bone but is suspended in position by muscles that connect it to the mandible, to the styloid process of each temporal bone at the base of the skull, to the thyroid cartilage, to the sternum, and to the scapula.



Thyroid storm

Thyroid storm is a rare and sudden onset condition that occurs when thyroid hormones levels in the body jump dramatically. This is an extremely serious condition that warrants immediate medical care. Failure to treat thyroid storm usually means the condition is fatal quickly. However, symptoms are so grave, they are unlikely to be ignored.

Having too much of thyroid hormone can occur in several types of disease. It sometimes happens as a consequence of thyroid surgery but more commonly occurs in present day due to underlying conditions like Grave’s disease, which causes elevated thyroid levels at a slower pace. Sometimes other diseases such as Hashimoto’s thyroiditis are also responsible for a sudden thyroid storm, though this autoimmune disorder is more commonly associated with below normal thyroid hormone levels. Other conditions that have been associated with “storm” include lupus, goiter or tumors on the thyroid.

Many symptoms can present with thyroid storm. These include fever, usually of at least 101.3 degrees F (38.5 C) or higher. In many cases, fever is at least or higher than 105.8 degrees F (41 C). Sweating and difficulty breathing may be noted too. Nausea or vomiting can occur, and other stomach symptoms like diarrhea could be present. Jaundice or yellowing of the skin and whites of the eyes is sometimes present too. Behavior could change and people could be anxious or altered, and they might exhibit a visible tremor or shakiness.

On examination of the heart, heart rate is usually much quicker than normal and may exhibit sudden arrhythmia. Initially blood pressure may be elevated, but as thyroid storm progresses it can become too low (hypotensive). The longer this illness is allowed to progress the greater the potential damage. Seizures often develop and without treatment, people will ultimately lapse into a coma and die.

Given the mortality rate of untreated thyroid storm, emphasis is on treating right away, and also making sure that people with certain illnesses like Graves are aware of its potential to occur. As with any form of hyperthyroid disorder, most common treatment is to give medications to stop thyroid production, and these may vary. Other medical support could be needed, including administration of fluids to help with fluid loss due to high body temperature or vomiting and diarrhea. Fever may need to be brought down too with cooling packs or ice. Cardiac stability might require continued assessment

Once stability is achieved, patients may be released from the hospital, but they will usually need to follow up with an endocrinologist. Release could be delayed by necessity of treating underlying conditions or causes. Outlook tends to be good for those who get early treatment, though they may need additional inpatient or outpatient treatment to prevent reoccurrence of a thyroid storm.