Senses

Senses

General Sense Organs

  • Individual receptor cells widely distributed

  • Different from special sense organs

Special Sense Organs

  • Large, complex organs with specialized receptors

Sensory Receptor Types

  • By covering:

    • Encapsulated

    • Unencapsulated (free or naked)

  • By stimulus type:

    • Photoreceptors (light)

    • Chemoreceptors (chemicals)

    • Pain receptors (injury)

    • Thermoreceptors (temperature)

    • Mechanoreceptors (movement)

    • Proprioceptors (body position)

Sensory Pathways

  • All sense organs can detect stimuli

  • Stimulus converted to nerve impulse, perceived as sensation in CNS

General Sense Receptors

  • Widespread distribution in skin

  • Types:

    • Free nerve endings (pain, touch, temperature)

    • Tactile (Meissner) corpuscle (fine touch)

    • Bulbous (Ruffini) corpuscle (pressure)

    • Lamellar (Pacini) corpuscle (pressure/vibration)

    • Bulboid (Krause) corpuscle (touch)

Disorders of General Senses

  • Third-degree burns destroy receptors

  • Temporary impairment with reduced blood flow

The Eye

  • Layers of the eyeball:

    • Sclera (outer coat)

    • Choroid (vascular layer)

    • Retina (innermost layer with rods and cones)

  • Pupil: hole in the iris controlled by muscle contraction

Visual Pathway

  • Signal travels from rods/cones to bipolar/ganglion cells

  • Leaves through the optic nerve, blind spot at exit

  • Visual processing in cerebrum visual cortex

Eye Fluids

  • Aqueous humor (anterior cavity)

  • Vitreous humor (posterior cavity)

The Ear

  • Divisions: External, middle, inner ear

  • Responsible for hearing and balance

External Ear

  • Auricle (pinna) and external acoustic canal

Middle Ear

  • Contains ossicles (malleus, incus, stapes)

  • Eustachian tube connects to throat

  • Inflammation (otitis media) possible

Inner Ear

  • Bony labyrinth with perilymph, membranous labyrinth with endolymph

  • Receptors for balance (vestibule, semicircular canals)

  • Organ of Corti for sound

Equilibrium

  • Mechanoreceptors located in the vestibule and semicircular canals

Taste

  • Chemoreceptors (taste buds)

  • Cranial nerves VII and IX transmit gustatory signals

  • Basic tastes: Sweet, sour, bitter, salty

Smell

  • Olfactory receptors in nasal mucosa

  • Sensitive and can fatigue easily

Integration of Senses

  • Brain integrates signals for perception

  • Nasal congestion can impair taste

  • Aging may reduce sensory function