HHP:1100 Human Anatomy - Vision, Equilibrium, and Hearing

Lecture Overview

  • Vision
    • Structures
    • Humors
    • Pathways
  • Equilibrium and Hearing
    • Hearing, static and rotational equilibrium structures
    • Pathways

Vision

  • Eyes utilize photoreceptors to create visual images.
  • Accessory structures:
    • Extrinsic muscles
    • Eyelids
    • Medial & lateral canthus
    • Lacrimal caruncle

Conjunctiva

  • A lining covering the eyelids and the anterior surface of the eye,
  • Doesn't cover cornea.

Lacrimal Apparatus

  • Produces, collects, and drains lacrimal fluid (tears):
    • Lacrimal gland
    • Lacrimal canaliculi
    • Lacrimal sac
    • Nasolacrimal duct

Eye Structure

  • Anterior Cavity: Front of lens; contains circulating aqueous humor.
  • Posterior Cavity: Behind lens; contains vitreous humor.
  • Eye Wall: Composed of three layers:
    • Fibrous Tunic
    • Vascular Tunic
    • Retina

Aqueous Humor - Secretion & Reabsorption

  • Glaucoma results from blockage of trabecular meshwork, causing pressure buildup.
    • Flow: Secreted by ciliary processes into posterior chamber, moves through pupil to anterior chamber, excess resorbed via scleral venous sinus.

Fibrous Tunic

  • Composed of two regions:
    1. Cornea
    2. Sclera

Vascular Tunic

  • Contains three regions:
    1. Choroid: Supplies nutrients/oxygen to retina.
    2. Ciliary body: Changes lens shape.
    3. Iris: Controls light entry, contains sphincter and dilator muscles.

Retina

  • Inner layer of the eye with:
    • Neural layer: Contains photoreceptors, converts light into nerve impulses.

Organization of Neural Layer

  • Composed of:
    1. Photoreceptor cells (rods and cones)
    • Rods: Dim light & low acuity.
    • Cones: Daylight, high acuity, and color vision.
    1. Bipolar cells: Synapse between photoreceptors and ganglion cells.
    2. Ganglion cells: Axons form optic nerve (CN II).

Visual Pathways

  • Conversion Process: Retinal photoreceptors convert light to neural signals.
  • Pathway:
    1. Axons cross at optic chiasm.
    2. Optic tracts extend laterally, posteriorly.
    3. Optic radiation from thalamus to occipital lobe.

Visual Acuity

  • Definition: Ability to distinguish fine detail.
  • 20/20 vision: Normal vision.
  • 20/<20: Better than normal.
  • 20/>20: Worse than normal.
  • Common Visual Conditions:
    • Nearsightedness (myopia)
    • Farsightedness (hyperopia)
    • Presbyopia
    • Astigmatism

Common Eye Disorders

  • Conjunctivitis: Inflammation of conjunctiva.
  • Cataracts: Clouding of the lens; often resolved with surgery (IOL).
  • Glaucoma: Increased intraocular pressure.
  • Diabetic Retinopathy: Damage to retina due to diabetes.
  • Strabismus: Misalignment of the eyes.

Equilibrium and Hearing

  • Ear anatomy: Divided into three regions:
    1. External Ear: Auricle, external acoustic meatus, tympanic membrane (eardrum).
    2. Middle Ear: Contains auditory tubes and ossicles (Malleus, Incus, Stapes).
    3. Inner Ear: Contains organs of equilibrium (utricle, saccule, semicircular canals) and hearing (cochlea).

Equilibrium

  • Refers to head position awareness.
  • Vestibular apparatus:
    • Detects static equilibrium (utricle and saccule) and linear acceleration.
    • Semicircular ducts detect angular acceleration.

Dynamic Equilibrium

  • Mechanism: Crista ampullaris within semicircular canals detects head rotation via hair cells embedded in the cupula.

Hearing

  • Cochlea is the organ for hearing.
    • Filled with endolymph; contains the spiral organ/Organ of Corti.

Pathway of Sound Waves

  • Flow:
    1. Oval window
    2. Perilymph (scala vestibuli)
    3. Endolymph (cochlear duct)
    4. Spiral organ stimulation, resulting in sensory impulse transmission via cochlear nerve.

Pitch and Loudness Discrimination

  • Pitch: Varies based on sound frequency affecting basilar membrane response.
  • Loudness: Depends on amplitude; greater vibration results in increased hair cell activity.

Learning Outcomes

  • Identify accessory structures of the eye and evaluate their functions.
  • Describe the three tunics of the eye and major components.
  • Trace light path to retina and nerve impulses from retina to cortex.
  • Identify structures of external, middle, and inner ear, explaining their functions.