Senses

Senses: General and Special

• Sensation: Our conscious awareness of incoming sensory information.

  • Filtering: A significant amount of sensory information is filtered out; only a small percentage is relayed to the brain.

Anatomic Regions of the Ear

• External Ear:

  • Auricle: Made of elastic cartilage.

  • External Acoustic Meatus: Channels sound to middle ear.

• Middle Ear:

  • Auditory Ossicles: Tiny bones that amplify sound; includes:

    • Stapes

    • Incus

    • Malleus

  • Tympanic Membrane (Eardrum): Vibrates with sound waves.

  • Auditory (Eustachian) Tube: Equalizes pressure in middle ear.

  • Oval Window: Connects middle ear to inner ear, transmitting vibrations.

  • Round Window: Releases pressure from cochlea.

• Inner Ear:

  • Bony Labyrinth: Contains perilymph, protects inner parts.

  • Membranous Labyrinth: Houses endolymph, critical for sensory functions.

  • Vestibular Branch of CN VIII: Carries balance information.

  • Cochlear Branch of CN VIII: Carries auditory information.

Outer Ear

• Auricle (Pinna):

  • Function: Collects sound; mostly made of elastic cartilage.

• External Auditory Canal:

  • Ceruminous Glands: Produce earwax for protection.

Middle Ear

• Tympanic Membrane: Also known as the eardrum; essential for sound detection.

• Auditory (Eustachian) Tube: Balances pressure in middle ear;

  • Ossicles: Malleus, Incus, Stapes amplify sound.

• Oval Window: Transfers sound to inner ear.

• Round Window: Acts as a pressure outlet.

Inner Ear Anatomy

• Bony Labyrinth: Contains perilymph; structural support.

• Membranous Labyrinth:

  • Cochlea: Converts sound waves to nerve impulses.

  • Vestibular Apparatus: Responsible for balance, detects head position.

Function of Inner Ear Regions

• Cochlea:

  • Contains Spiral Organ (Organ of Corti): Sensory organ for hearing.

• Vestibular Apparatus:

  • Vestibule: Detects head position and linear acceleration.

Detecting Head Position (Vestibule)

• Hair Cells: Located in utricle and saccule.

  • Stereocilia and Kinocilia: Project from hair cells and detect movement.

  • Otolithic Membrane: Contains otoliths (calcium carbonate crystals) for sensing gravity and motion.

Inner Ear: The Ampulla (Semicircular Canals)

• Crista Ampullaris: Contains hair cells for detecting rotational movements.

• Cupula: Gelatinous structure where hair cell projections are embedded.

Motion Sickness

• Caused by conflicting sensory signals between inner ear, eyes, and muscles.

• Most susceptible groups:

  • Children (ages 2 to 12)

  • Pregnant women

  • Young adults (under 60)

Inner Ear: Functionality

• Cochlea: Converts sound waves into action potentials.

  • Spiral Organ houses hair cells: Bending of stereocilia generates nerve impulses.

Sound Waves and Properties

• Loudness: Related to amplitude, measured in decibels.

• Pitch: Related to frequency (higher frequency = higher pitch).

• Sound pathway involves auditory ossicles, tympanic membrane, cochlea.

Hearing Pathway

1. Cochlear nerve axons

2. Cochlear nucleus (medulla)

3. Inferior colliculus

4. Medial geniculate nucleus (thalamus)

5. Primary auditory cortex

Ear Disorders

• Nerve Deafness: Damage to hair cells or CN VIII.

  • Conduction Deafness: Damage to tympanic membrane or ossicles.

  • Otitis Media: Infection/inflammation of the middle ear.

  • Ménière’s Syndrome: Inner ear disorder affecting balance and hearing.

Vestibular Apparatus and Equilibrium

• Works with eyes and brain to maintain balance and orientation.

Disrupted Balance and Vertigo

• Caused by conflicting signals from the vestibular system, leading to involuntary eye movements.

Introduction to the Eye

• Eye Structure:

  • Contains internal and external structures essential for vision.

Eye Structural Overview

• Three Layers/Tunics:

  • Fibrous Tunic: Sclera (white of the eye) and cornea.

  • Vascular Tunic: Iris, ciliary body, and choroid.

  • Neural Tunic: Retina with photoreceptors.

Refraction and Vision Adjustment

• Refraction: Light bending as it passes through lens and cornea.

• Accommodation: Adjusting lens shape for clear vision at various distances.

Vision Disorders

• Myopia (Nearsightedness): Difficulty seeing far objects.

• Hyperopia (Farsightedness): Difficulty seeing close objects.

• Astigmatism: Irregular lens shape causing blurred vision.

Retina Structure and Functionality

• Contains photoreceptors (rods and cones), bipolar cells, ganglion cells.

• Rods: Responsible for dim / peripheral light; no color sensitivity.

• Cones: Responsible for color vision; concentrated in fovea.

Signal Processing in Retina

• Action Potentials: Initiated in ganglion cells while photoreceptors produce graded potentials.

• Phototransduction: Involves rhodopsin in rods and photopsin in cones.

Additional Vision Mechanics

• Dark Adaptation: Adjusting from light to dark involves recovery of photopigments.

• Color Vision: Resultant from cone sensitivity to different wavelengths.

The Visual Pathway

• Light processing involves conversion to nerve impulses, which travel through the optic nerve to the brain.

• Optic Chiasm: Crosses signals from both eyes for unified processing.

Disorders of the Eye

• Cataracts: Opaque lens due to aging/injury.

• Glaucoma: Increased eye pressure affecting vision.

• Age-related Macular Degeneration (AMD): Degeneration in the retina.

LASIK Surgery

• A procedure to correct vision by reshaping the cornea with laser.

Sensory Physiology Review Questions

• Characteristics of sensory receptors.

• The concepts of tonic vs. phasic receptors.

• Understanding receptive fields.

• Photoreception processes for rods and cones.

• Pathway of sound transmission and mechanics for hearing.

Conclusion: Study Recommendations

• Recap the structures and functions somatic senses, visual system, balance, and auditory processing.

• Understand pathways, receptors, adaptations and common disorders.