Anatomy essays (chunk 11)

64. Gustatory organ. Gustatory sensory pathway

structure responsible for taste.

main sensory receptors - taste buds (specialized structures, detect dissolved chemicals in food and send nerve impulses)

mainly found in

• Fungiform papillae → tip of tongue

• Vallate papillae → back of tongue

• Foliate papillae → sides of tongue

also present in: Soft palate, Pharynx, Epiglottis

Each taste bud contains:

• Taste receptor cells

• Supporting cells

• Basal cells (replace old cells)

surface; taste pore, microvilli contact dissolved chemical

taste types; Sweet, Sour, Salty, Bitter, Umami

Gustatory Pathway —

stimulation → receptor → impulse → nerve

• CN VII → anterior 2/3

• CN IX → posterior 1/3

• CN X → epiglottis/ pharynx

• Nucleus tractus solitarius (medulla)

• Thalamus

• Gustatory cortex (insula)

65. Organ of vision - general remarks. The eyeball - shape, position, size. Outer (fibrous) coat – general characteristics, ontogenesis

Organ responsible for converting light stimuli to nerve impulses, which are interpreted by the brain as vision. The organ of vision contains: 

• Eyeball

• Optic nerve 

• Accessory organs– extraocular muscles, eyelids, conjunctiva, lacrimal apparatus

Eyeball

spherical in shape, 1 inch or 24mm diameter, in the eye socket below eyebrows

Layers of the eyeball:

1. Outer fibrous layer

2. Middle vascular layer (uvea)

3. Inner nervous layer (retina)

Outer fibrous layer– protective layer, maintains shape, attachment for extraocular muscles

Consists of - Sclera and cornea

Sclera:

• White opaque part of the eyeball made of dense connective tissue, prevents light entering the eye except through the cornea 

• Forms supporting wall of the eye, rigid to give shape to the eye

• Covered by conjunctiva that lubricates the eye

Cornea:

• Transparent, avascular, smooth structure that acts as a window of the eye.

• Refracts light into the lens so images can be focused on the retina 

Layers of the Cornea 

1. Corneal epithelium

2. Bowmans capsule

3. Stroma

4. Basement membrane

5. Corneal endothelium 

Corneoscleral junction (limbus): contains Schlemm’s canal (drainage of aqueous humor)

Ontogenesis

Sclera → Mesenchyme 

Cornea 

• epithelium → surface ectoderm

• stroma + endothelium → mesenchyme

66. The eyeball - middle (vascular) coat - parts, description.

The middle coat of the eyeball is called the vascular layer or uvea. 

• Highly vascular

• Rich in pigment (melanin)

• Dark colored (bcz of the pigment duh)

contains 3 parts:

1. Iris

2. Ciliary body

3. Choroid 

1. Iris

• Thin circular structure in the eye, made of smooth muscle fibers

• Regulates amount of entering light, protects retina from excessive light

Muscles of the iris 

• sphincter pupillae → constriction of pupil (in bright light)

• dilator pupillae → dilation of pupil in darkness or fear/stress

2. Ciliary body

• Circular ring of tissue located behind iris

• Consists of ciliary muscle and ciliary processes

Functions:

• lens accommodation 

(near vision → contracts and lens becomes convex, far vision → relaxes and flattens) 

• production of aqueous humor.

3. Choroid

• Posterior vascular layer 

• Nourishes retina

• Melanin absorbs light

67. Retina. Optic nerve. (and visual pathway)

Retina is the inner nervous coat of the eye.

Part of the eye responsible for: Receiving light stimuli → turn into nerve impulses 

Develops from neuroectoderm 

Consists of – pigmented layer and nervous (neural) layer

1. Pigmented layer

Outer thin layer, contains melanin

• Absorbs excess light, prevents light reflection inside eye

2. Nervous (neural) layer

Contains neurons responsible for vision/ visual pathway:

1. Photoreceptors - rods (black and white, dim light) and cones (color and sharp)

2. Bipolar cells

3. Ganglion cells - axons form the optic nerve (CN II), caries visual information from retina to brain

Macula lutea - contains fovea centralis (no blood vessels, only cones, highest visual acuity)

Optic disc - ‘blind spot’ , no photoreceptors, exit of optic nerve

Visual pathway

Retina → Optic nerve → Chiasm → Tract → LGN → Radiations → Primary visual cortex

 → Rods & cones
→ Bipolar cells
→ Ganglion cells
→ Optic nerve (CN II)
→ Optic chiasm (fibers from nasal half of retina cross, temporal half stay on same side)
→ Optic tract (right tract carries left visual field, and vice versa)
→ Lateral geniculate nucleus (thalamus) main relay station
→ Optic radiations
→ Primary visual cortex (occipital lobe, calcarine sulcus)

68. Internal nucleus of the eyeball. (mention cornea along with components)

Internal nucleus of the eye refers to the transparent internal structures of the eye that allow light to pass through and be focused onto the retina. Also called the dioptric (refractive) media of the eye.

Main functions:

• Refract light and ensure clear image is formed. 

Components:

1. Aqueous humor

2. Lens

3. Vitreous body

1. Aqueous humor

Clear liquid that nourishes the cornea and lens.

Produced in the ciliary body by process of diffusion and active transport.

Flows through pupil and fills anterior chamber of the eye. Produced by schlemm’s canal. Contains immunoglobulins for defence.

Functions: 

• Maintains intraocular pressure

• Nourishment of cornea and lens

• Removal of metabolic waste

2. Lens

Transparent, elastic, biconvex structure located behind iris

Completely avascular

Function: accommodation 

            can change shape to focus:

• Near objects → becomes thicker

• Distant objects → becomes flatter

3. Vitrous body

Gel-like transparent substance

 mostly water, contains collagen fibers and hyaluronic acid

Fills posterior segment of the eyeball

Function: 

• Maintains shape of eyeball

• Supports internal structures of the eye (i.e, keeps retina pressed against choroid)

69. Accessory organs of the eyeball - extraocular muscles.

Extraocular muscles are responsible for:

• Eye movements

• Binocular vision 

• Fixation of gaze 

There are 7 extraocular muscles:

• 4 rectus muscles; superior, inferior, medial, lateral

• 2 oblique muscles; superior, inferior 

• 1 eyelid muscle; levator palpebrae superioris 

Origin of muscles:

All from common tendinous ring located around optic canal 

Except: inferior oblique, originates from anterior orbital floor

Insertion: into sclera 

Innervation: 

Oculomotor - all except the following

Trochlear - superior oblique

Abducens - lateral rectus

70. Accessory organs of the eyeball – eyebrows, eyelids, conjunctiva. Lacrimal apparatus.

Eyebrows: arched elevations with hair above orbit

Functions:

• Protect eyes from sweat 

• Reduce sunlight

• Facial expression 

Eyelids: 

Muscles:

• Orbicularis oculi (innervated by facial nerve) - closes eyelid

• Levator palpebrae superioris (innervated by oculomotor nerve) - opens upper eyelid

Functions: 

• Protect eyeball with blink reflex along w eyelashes (from foreign bodies)

• Spread tears/prevent drying of cornea

Conjunctiva:

Highly vascularized thin transparent mucous membrane

covering the inner eyelids and anterior sclera

Composed of: non-keratinizing stratified squamous epithelium with goblet cells + stratified columnar epithelium 

Functions:

• Lubrication 

• Protection 

• Immune defense

Lacrimal apparatus:

Network of structures of the eye that secrete tears on surface of eye and drain them from the surface of the eyeball (tear production and drainage)

Includes:

• Lacrimal glands → secrete tears

• Lacrimal canals, lacrimal ducts, lacrimal sacs, and nasolacrimal ducts by which the fluid is conveyed in the cavity of nose.

71. Acoustic and vestibular organ – general characteristics, ontogenesis. External ear.

The ear is responsible for:

1. Hearing (acoustic function)

• Detect sound waves

• Convert them into nerve impulses

2. Balance/equilibrium (vestibular function)

• Maintain posture

• Detect head movement and position

Because it performs both functions, its called the acoustic vestibular organ 

The ear is divided into 3 parts:

• External ear: collects sound

• Middle ear: transmits and amplifies sound

• Internal ear: Hearing+equilibrium receptors

Hearing mechanism 

Sound waves:

Auricle → external acoustic meatus → tympanic membrane → ossicles → cochlea → brain

Ontogenesis: ectoderm, endoderm and mesenchyme

External ear

Part of the ear that collects and conducts sound waves to the tympanic membrane

Consists of:

1. Auricle (pinna)

2. External acoustic meatus

3. Tympanic membrane 

Auricle:

Funnel like structure, captures and transmits sound to external acoustic meatus

External acoustic meatus:

Lies within the temporal bone, connects auricle to tympanic membrane

Curved tube that extends inward from the floor of the auricle

• Contains ceruminous glands that secretes ear wax to discourage insects and foreign particles from entering ear

Tympanic membrane:

Made of epithelial and simple cuboidal tissue 

Changes acoustic energy to mechanical energy– vibrates in response to sound waves

72. Middle ear

Air-filled cavity located inside of the petrous part of temporal bone

Function: 

• Transmit + amplify sound vibrations from tympanic membrane to internal ear

Consists of the following parts:

1. Tympanic membrane

2. Tympanic cavity

3. Ossicles

4. Mastoid

5. Eustasian tube

6. Middle ear muscles

Tympanic membrane:

Thin membrane, closes the cavity of the middle ear

Changes acoustic energy to mechanical energy– vibrates in response to sound waves

Tympanic cavity:

Air-filled, membrane lined space 

Located between ear canal and eustachian tube

Tympanic membrane separates it from the ear canal

Auditory ossicles:

Middle ear contains the smallest bones in the body– malleus, incus, stapes

Function: transmit vibration and amplify sound, connects to the oval window

Middle ear muscles:

Tensor tympani → tenses tympanic membrane (mandibular nerve)

Stapedius → stabilizes stapes + dampens loud sounds (facial nerve)

Auditory (eustachian) tube:

Connects middle ear and nasopharynx 

Consists of– bony part + cartilaginous part 

Functions: 

• Pressure equalization (on both sides of tympanic membrane)

• Ventilation (allows air entry into middle ear)

• Drainage (removes secretions)

Mastoid antrum and air cells:

Air-filled spaces in mastoid processes

Functions:

• Air reservoir

• Pressure regulation

Functions of the middle ear:

• Conduction: sound from outer to inner ear

• Protection: creates barrier to protect middle and inner ear from foreign particles

• Transducer: acoustic energy → mechanical energy → hydraulic energy

• Amplifier: amplifies sound

73. Internal ear. The bony labyrinth.

Deepest part of the ear. 

Located in– Petrosal part of temporal bone

Contains:

• Receptors for hearing + equilibrium

Divisions:

1. Bony labyrinth

2. Membranous labyrinth

Bony Labyrinth

System of interconnected cavities within temporal bone

Surrounds membranous labyrinth

• Filled with perilymph

Parts of bony labyrinth:

1. Vestibule (static balance)

2. Semicircular canals (dynamic balance// rotational movement)

3. Cochlea (hearing)

Vestibule:

• Central part of bony labyrinth

• Located between cochlea and semicircular canals

Contains: Utricle and saccula (vestibular apparatus) → responsible for static equilibrium 

Semicircular canals

3 curved bony interconnected canals located posterior to the vestibule, positioned approx @ right angles to each other

each canal has large end called ampulla → contain receptors for equilibrium

Lined with cilia and filled with endolymph

• The endolymph moves the cilia when the head moves, thus acting as a motion sensor

Function: Detect rotation/angular movements of head 

Cochlea 

Spiral-shaped bony canal forming ‘hearing organ’

Composed of sensory hair cells which convert vibrations into neural messages

Neural messages → auditory nerve → brain

74. Internal ear. The membranous labyrinth - cochlear part. Organ of Corti. Cochlear nerve.

Pathway of hearing.

System of membranous sacs and ducts located inside the bony labyrinth 

• Filled with endolymph

Consists of:

1. Cochlea duct

2. Endolympthatic duct

3. Utricle and saccule

4. Semicircular ducts

Cochlea duct

Located in the bony scaffolding of the cochlea

Held in place by spiral lamina

Triangular shaped: 

• Roof: membrane that separates cochlea duct from scala vestibuli known as RESSINERS MEMBRANE

• Floor: membrane that separates cochlea duct from scala tympani known as 

• BASILAR MEMBRANE

• Lateral wall: formed by thickened periosteum known as SPIRAL LIGAMENT

Organ of corti

Located in cochlea, rests on basilar membrane of fluid-filled cochlear duct

Body’s primary receptor for hearing

Contains sensory hair cells and stereocillia

Acts as a biological TRANSDUCER— converting mechanical sound into electrical nerve impulses, which the brain interprets as sound

• Transduction occurs through vibrations of structures in the inner ear, causing displacement of cochlea fluid and movement of hair cells @ the organ of cort, to then produce electrochemical signals.

Pathway of hearing/ how hearing works

Vibration, movement, deflection, impulse

Sound waves vibrate tympanic membrane → ossicles transmit vibration → stapes moves oval window → perilymph moves → basilar membrane vibrates/organ of corti moves along with it → hair cells/ stereocilia bend → electrical impulse generated then auditory nerve to brain

**the bending opens ion channels in the hair cells and generates electrical signals

Cochlear nerve: part of CN VIII (vestibulocochlear) 

Carries hearing impulses from the cochlea 

Path

Hair cells 

spiral ganglion → auditory/ cochlear nerve → brainstem

Fibers ascend thru:

• Sup olivary complex

• Lateral lemniscus

• Inf colliculus

• Medial geniculate body (thalamus)

Final destination: Auditory complex (temporal lobe)

75. Internal ear. The membranous labyrinth - vestibular part. Organ of equilibrium.

Vestibular nerve. Pathway of equilibrium.

Responsible for balance, posture, detection of head movements

Located inside– vestibule and semicircular canals

Filled w/ endolymph

Components of vestibular part 

1. Utricle

2. Saccule

3. Semicircular ducts

These structures contain receptors called organ of equilibrium 

Utricle:

Larger sac

Located in vestibule

Receives opening of semicircular ducts

Contains specialized organ for equilibrium → macula utriculi 

Saccule:

Smaller sac, globular shape

Receives cochlear duct

Carries sensory organ for equilibrium → macula saccula 

Endolymph drains from saccule and utricle to endolympathic duct

Utricle → Horizontal acceleration (like moving forward in a car)

Saccule → vertical acceleration (like going up/down an elevator)

Semicircular ducts

Located in semicircular canals

Allows processing of balance by sending signals of change in speed or direction of the flow of endolymph upon movement of head

Pathway of equilibrium

Hair cells
→ Vestibular ganglion
→ Vestibular nerve (vestibular branch of vestibulocochlear)
→ Vestibular nuclei (combine info from both ears)
→ Cerebellum / ocular nuclei / spinal cord / cortex (parietal lobe and insular cortex)