30Sense organs

📚
EYE
▢ Introduction:

An eye is a sensory organ that allows an organism to perceive visual information. It detects light and converts it into electro-chemical impulses in neurons (neurones). It is part of an organism's visual system.

▢ Accessory structures:
Image 1
❖ Eyebrow:
❖ Eyelids/ Palpebra:
◉ Glands:
◈ Glands:
■ At the base of Hair follicle:
● Gland of Moll: Sweat gland
● Gland of Zeis:
⟣ Modified form of: Sebaceous gland
⟣ Inflammation of gland of moll and gland of zeis is called Stye:
■ On the Tarsal plate:
● Tarsal glands/ Meibomian glands:
⟣ Inflammation: Chalazion
◉ Palpebral fissure: Opening between the upper and lower eyelid.
◉ Nictitating membrane/ Third eyelid:
◈ Supported by Harderian gland: Frog and Birds
◈ Supported by Meibomian gland: Rabbit
◈ Vestigial in human: Plica semilunaris
❖ Eyelashes:
❖ Conjunctiva:
◉ Palpebral conjunctiva:
◈ Location: Lining the eyelids/ Palpebra
◈ Clinical significance: Pallor for Anaemia is seen here
◉ Bulbar conjunctiva:
◈ Location: Lining the eyeball(sclera only)
◈ Clinical significance: Jaundice for hepatitis is seen here
❖ Lacrimal gland:
Image 1
◉ Function: Secrete tear which contain salts and lysozyme (bactericidal) and is isotonic to blood and normal saline (0.9% NaCl solution)
◉ Drainage pathway:
  1. Lacrimal gland
  2. Lacrimal duct
  3. Lacrimal punctum
  4. Lacrimal canal
  5. Lacrimal sac
  6. Nasolacrimal duct
  7. Nasal cavity
◉ Inflammation: Dacrocystitis/ Dacroadenitis
❖ Extrinsic eye Muscles:
  1. Superior rectus
  2. Inferior rectus
  3. Lateral rectus
  4. Medial rectus
  5. Superior oblique
  6. Inferior oblique
Image 1
1 / 2
❖ Muscle defect: Strabismus/ Squint eyes
❖ Nerves:
◉ Cranial nerves involved: 6 out of 12 cranial nerves (II, III, IV, V, VI and VII)
◉ Muscle control: 3 control extrinsic muscles (LR_6 SO_4 Rest_3)
▢ Eyeball:
Image 1
❖ Tunica fibrosa:
◉ Cornea:
◈ Location: Anterior part
◈ Structure: Transparent layer made up of 5 layers
◈ Epithelium: Non-keratinized stratified squamous epithelium
◈ Function: Major site of refraction
◈ Vascularity: Avascular layer (used in eye donation - Keratoplasty)
◈ Inflammation: Keratitis
◉ Sclera:
◈ Origin: Mesodermal
◈ Composition:
■ Frog: Cartilage
■ Rabbit and Human: White, hard, opaque thick fibrous connective tissue
❖ Tunica vasculosa:
◉ Description: Highly vascularized layer
◉ Iris:
◈ Pigmentation:
■ Cause: Melanin pigment produced by Melanocytes
■ Rabbit: Red eye due to Red melanin
■ Human: Green, Blue, Brown or Black eye
◈ Pupil: Aperture formed by Iris
◈ Muscles:
■ Outer Radial Muscle: Contraction causes Dilation of pupil (Mydriasis)
■ Inner Circular muscle: Contraction causes Constriction of pupil (Miosis)
◉ Ciliary body:
Image 1
◈ Components:
  1. Ciliary muscle
  2. Ciliary process (Produces Aqueous humor)
  3. Suspensory ligament/ Zonules of Zinn (Holds the lens)
◈ Chambers:
Image 1
■ Aqueous chamber:
● Contents: Aqueous humor
● Subdivisions:
⟣ Anterior aqueous chamber:
⟣ Posterior aqueous chamber:
● Drainage:
⟣ Canal of Schlemm:
➢ Function: Aqueous humor drains out through it
➢ Disorder: Glaucoma (Blockage causes increased intraocular pressure)
■ Vitreous chamber:
● Contents: Vitreous humor
● Hyaloid canal/ Cloquet's canal:
⟣ Location: From blind spot to Central point of lens
⟣ Function: Provides nourishment to the developing lens
◉ Choroid:
◈ Description: Pigmented vascular layer which prevents the internal reflection of light inside the eyeball
◈ Tapetum lucidum: Reflecting layer between retina and choroid found in carnivores (cat, dog, lion, etc.) that causes eyes to glow at night
❖ Tunica nervosa/ Retina:
Image 1
◉ Origin: Ectodermal
◉ Landmark: Orra serrata
◉ Layers:
◈ Pigmented layer (Outer): Retinal pigment epithelium
◈ Nervous tissue layer/ Neural layer (Inner):
■ Components:
  1. Rods and cones (photoreceptors)
  2. Outer limiting membrane
  3. Outer nuclear layer
  4. Outer plexiform layer
  5. Inner nuclear layer (Bipolar cell, Horizonal cell, Amacrine cell, Muller cell)
  6. Inner plexiform layer
  7. Ganglion cell layer
  8. Nerve fiber layer
  9. Inner limiting membrane
Image 1
■ Photoreceptors:
● Rod cells:
⟣ Number: 120 million
⟣ Function: Dim light vision
⟣ Pigment: Rhodopsin (Visual purple)
⟣ Specialization: Only rods in Nocturnal animals (Owl, rats, bats)
▢ Disorders of eye:
Disorder
Defects
Cause
Correction
Myopia/ Short sightdness
Can see near object only/ Can't see far object
Decrease in focal length/ Increased eyeball size
Concave lens
Hypermetropia/ Long sightedness
Can see far object only/ Can't see near object
Increased focal length/ Decreased eyeball size
Convex lens
Astigmatism
Blurred vision
Irregular curvature of Cornea
Cylindrical lens
Presbyopia
Blurred vision
Loss of accomodating power in Old age
Bifocal lens
Cataract
Increased opacity of lens
Glaucoma
Increased intraocular pressure
Blockage of Canal of Schlemm
Trachoma (IOM 2004)
Inflammation of Conjunctiva
Chlamydia trachomatis
Xerophthalmia/ Dry eye
Keratinisation of conjunctiva and cornea/ Decreased tear production
Vitamin A deficiency
Photophobia
Difficulty seeing in bright light
📚
EAR
Image 1
▢ External Ear:
❖ Distribution: Well developed in Mammals only (absent in whale, seal, ornithorinchus, etc.)
❖ Pinna:
◉ Components:
◈ Helix: Elastic cartilage (includes Antihelix)
◈ Lobule: Auricular muscles (vestigial in human, functional in Rabbit; includes Antilobule)
❖ External auditory canal:
◉ Length: 24 mm
◉ Parts:
◈ Outer cartilaginous part:
■ Structures:
  1. Hair follicles
  2. Ceruminous gland (secretes Cerumen/earwax)
  3. Sebaceous glands
◈ Inner bony part:
▢ Middle Ear:
❖ Tympanic bulla: Part of temporal bone surrounding the tympanic cavity
❖ Tympanic cavity: Air filled cavity of middle ear
❖ Tympanic membrane/ Eardrum/ Myringo:
◉ Origin: All three germ layers
◉ Inflammation: Myringoplasty
❖ Ear ossicles:
Image 1
Ear ossicles
Shapes
Joints (Synovial joints)
Muscles attached
Malleus
Hammer
Hinge joint
Tensor tympani
Incus
Anvil
Ball and Socket joint
Stapes
Stirrup
Stapedius (Smallest muscle)
◉ Eustachian/ Auditory/ Pharyngo-tympanic tube:
◈ Function: Connects middle ear and nasopharynx (opens during swallowing and yawning)
◈ Clinical note: More prone to Otitis media in infants due to shorter and more horizontal tube
Image 1
▢ Internal Ear:
Image 1
❖ Vestibular apparatus:
◉ Bony labyrinth:
◈ Contents: Perilymph is the fluid present
◈ Components:
■ Semicircular canal (SCC): Dynamic equilibrium (Rotational motion) . Three semicircular structure perpendicular to each other
■ Vestibule: Static equilibrium (motion in a linear acceleration)
■ Cochlea: Hearing
◉ Membranous labyrinth:
◈ Contents: Endolymph
◈ Components:
■ Semicircular duct (SCD):
■ Utricle and Sacule:
■ Cochlear duct:
Image 1
● Structure:
⟣ Scala vestibule:
➢ Boundary: Reissner's membrane
⟣ Scala media/ Cochlear duct:
➢ Basilar membrane: Fused to form Organ of Corti
➢ Tectorial membrane: Stereocilia are embedded in it
⟣ Scala tympani:
➢ Connection: Meets Scala vestibule at Helicotrema
◉ Sensory structures:
Structure
Sensory cells
Supporting cells
Membrane
Cristae ampullaris
Hair cell with Stereocilia
Supporting cells
Cupula
Macula
Hair cell with Stereocilia and Kinocillium
Supporting cells
Otolithic membrane (contains CaCO3 crystals)
Organ of Corti
Hair cell with Stereocilia
Pillar cell, Boettcher cell, Claudius cell, Deiter's cell, Hensen's cell
Tectorial membrane
Image 1
📚
NOSE
▢ Membrane: Schneiderian membrane
▢ Cells:
  1. Bipolar olfactory nerve cells
  2. Supporting cells
  3. Basal cells
▢ Disorder: Anosmia (loss of sense of smell)
📚
Key
📚
SKIN
▢ Layers of epidermis:
❖ Epidermis:
◉ Layers:
Layer
Presence
Cell Features
Other features
Stratum corneum
Keratin
Composed of hardened, flattened and cornified cells
Nail is derived from this layer
Stratum lucidium
Eleidin
Nuclei absent but cell outlines distinct
present in only thick skin of palm and soles
Stratum granulosum
Keratohyalin, Abundant granules
Stratum spinosum
Provides firmness and rigidity
Stratum germinativum/Malpighian layer/stratum basale
Single layer of columnar cells on basement membrane
Innermost layer, constantly produces new cells
◉ Features:
◈ Vascularity: No blood vessels but has nerve fibres
◈ Pigmentation:
■ Melanocytes: Contain melanin pigment
■ Skin color factors: Combined effect of melanin, carotene and haemoglobin
■ Disorders:
● Albinism: Absence of melanin (recessive genetic character)
◈ Derivatives: Claws present on digits are derivatives of the epidermis
❖ Dermis:
◉ Origin: Mesodermal
◉ Thickness: Two or three times as thick as epidermis
◉ Composition:
  1. Fibrous connective tissue
  2. Unstriped muscle fibres
  3. Blood capillaries
  4. Nerve fibres
  5. Fat cells
◉ Structures:
  1. Hair follicles
  2. Sweat glands
  3. Sebaceous glands
▢ Skin derivatives:
❖ Types:
  1. Hair
  2. Claws
  3. Nails
  4. Hoofs
  5. Cutaneous glands
❖ Hair:
◉ Distribution: Found only in mammals
◉ Muscles: Arrector pili muscles (unstriped) attached to hair follicle and stratum germinativum
◉ Color: Black or brown due to melanin in cortex
▢ Cutaneous glands:
❖ Sweat glands:
◉ Location: Around lips (mostly merocrine), axillary regions (apocrine)
❖ Sebaceous gland:
◉ Product: Sebum
◉ Type: Holocrine
❖ Modified glands:
Gland
Type
Location
Note
Meibomian glands
Modified sebaceous gland
Dermis of eye-lid
Near edge and close to eye-lashes
Zeis gland
Modified sebaceous gland
Dermis of eye-lid
Opens into hair follicles of eye lashes
Ceruminous or Wax gland
Modified sweat gland
External auditory meatus
Mammary glands
Modified sweat glands
Produce milk in female mammal
Perineal glands
Modified sweat gland
Associated with reproductive organs
▢ Receptors:
❖ Types:
  1. Pain receptors
    2. ◈ Tactile receptors:
    1. Meisseners corpuscles
    2. Merckel's disc
    3. Pacinian corpuscles
    4. Genital corpuscles
    5. Vibrioreceptors on vibrissae
    ◈ Thermoreceptors:
      ● End bulbs of Krause (Frigidoreceptor): Cold receptor
      ● End bulbs of Ruffini (Caloreceptor): Heat receptors
Q1.
Acoustic spot in each ampula of human ear is known as:
📅MOE 2069•MOE 2009
Q2.
In internal ear, sensory patches are situated in:
📅IOM 2011
Q3.
The disease caused by bacteria in human eye is known as:
📅MOE 2011
Q4.
Organ of Corti cells are related to:
📅IOM 1996•IOM 2010
Q5.
Which part of ear is responsible for hearing?
📅BPKIHS 2010
Q6.
Cristae is present in:
📅KU 2010
Q7.
The sensory neurons of a vertebrate retina are its:
📅IE 2009
Q8.
Eustachian tube connects:
📅MOE 2008•IOM 2009
Q9.
Meibomian glands are present in:
📅IOM 2009
Q10.
A person (>55 years) cannot see the near objects, the defect is:
📅IOM 2009•MOE 2008
Q11.
In Retina, yellow spot contains:
📅BPKIHS 2009
Q12.
Hensen's cell is found in:
📅BPKIHS 2008
Q13.
Ceruminous glands are situated:
📅BPKIHS 2007
Q14.
A person who cannot see the near objects clearly is likely to use:
📅BP 2007
Q15.
What are thigmoreceptors?
📅MOE 2063
Q16.
Tear from eye is drained into:
📅IOM 2006
Q17.
Rods & Cones assist to:
📅IE 2006
Q18.
Which is the correct sequence of transmission of vibrations from the air to the auditory nerve in mammal?
📅MOE 2058
Q19.
Long sightedness is caused by:
📅KUMET
Q20.
The enzyme that is present in tears is:
📅KUMET
Q21.
Organ of Corti lies inside the:
📅BPKIHS 2005
Q22.
The part of the ear that distinguish different pitches is the:
📅IOM 2004
Q23.
Meissner's corpuscles are located in:
📅BPKIHS 2004
Q24.
Cochlea is mainly responsible for:
📅BPKIHS 2004
Q25.
Short sightedness or myopic vision is corrected by wearing:
📅BP 2004
Q26.
The tears of healthy girl would have osmotic pressure isotonic to NaCl solution of:
📅BPKIHS 2003
Q27.
The focusing of lens is done by:
📅MOE 2002
Q28.
Which cell is used to see colour?
📅IOM 2001
Q29.
A man was suddenly jerked but he managed to balance his body. What worked there?
📅BPKIHS 2001
Q30.
Point of greatest visual acuity:
📅IOM 1999
Q31.
Tectorial membrane is present in:
📅IOM 1998
Q32.
Yellow spot is found in:
📅IOM 1996
Q33.
The portion of head where most portions of ear lie is called:
📅IOM 1994
Q34.
All of the following structures are found in dermis except:
📅IOM 1993
Q35.
Person suffering from night blindness lacks:
📅BPKIHS 2013
Q36.
Ora serrata is present in:
📅IOM 2014
Q37.
The sensory receptors present on the surface of skin giving sensation of touch are:
📅BPKIHS 2015
Q38.
A boy is wearing spectacles having concave lens. When the spectacles are not in use, the image in boy's eyeball is formed:
📅BPKIHS
Q39.
Rejection of transplanted organs is due to:
📅IOM 2015
Q40.
Cancers arising from connective tissues are called:
📅IOM 2015
Q41.
Pigment related to observe grasses by the herbivore eyes is:
📅MOE 2012
Q42.
Acoustic spot in each ampula of human ear is known as:
📅MOE 2012
Q43.
The organ of Corti in mammals is found in:
📅KU 2011