Senses_final

Human Anatomy and Physiology: Senses

Overview

  • Instructor: Prof. Maribel O. Losito, RMT, MPH

Learning Outcomes

By the end of the lesson, students should be able to:

  1. Identify the various types of general sensory receptors.

  2. List the stimuli that activate general sensory receptors.

  3. Describe the five special senses: olfaction, taste, sight, hearing, and balance/equilibrium.

Sensory Processing

Steps of Sensory Perception:

  1. Detection: A sensory receptor detects a stimulus from the environment.

  2. Transmission: Sensory neurons conduct nerve impulses to the spinal cord or directly to the brain.

  3. Interpretation: The brain interprets the information from sensory receptors.

  4. Perception: The brain's understanding of the stimulus is termed perception.

Key Definitions

  • Stimuli: Anything that induces a response from an organism's system.

  • Senses: Ways in which the brain receives information about the environment and the body.

  • Sensation: The process initiated by stimulating sensory receptors.

  • Perception: The conscious awareness of stimuli.

Types of Senses

General Senses:

  • Receptors distributed all over the body:

    • Somatic (touch, temperature, pain, proprioception)

    • Visceral (located in internal organs)

Special Senses:

  • More specific and localized:

    1. Smell (olfaction)

    2. Taste

    3. Vision

    4. Hearing

    5. Balance

General Senses: Receptors

Types of Receptors:

  • Mechanoreceptors: Respond to mechanical stimuli (bending/stretching).

  • Photoreceptors: Respond to light.

  • Chemoreceptors: Respond to chemicals.

  • Thermoreceptors: Respond to temperature changes.

  • Nociceptors: Respond to potential pain-inducing stimuli.

Touch and Other General Senses:

  1. Touch - Receptors in skin, muscles, joints.

  2. Pressure - Detected by specialized receptors.

  3. Proprioception - Awareness of body position and movement.

  4. Temperature - Sensed by thermoreceptors.

  5. Pain - Localized by nociceptors.

  6. Itch - Stimulated in response to certain irritants.

Special Senses: Olfaction and Taste

Olfactory Perception:

  • Mechanism: Airborne odorants dissolve in mucus, bind to receptor molecules leading to action potentials.

  • Neuronal Pathway:

    • Olfactory neurons (bipolar) in epithelium form olfactory nerves.

    • Relay information through olfactory bulb to brain.

  • Connection to Emotions: Olfactory information connects directly to limbic system, affecting emotions and memory.

Taste Perception:

  1. Mechanism: Taste buds with cells detect dissolved substances.

  2. Taste Sensations: Five basic types - sour, salty, bitter, sweet, umami.

  3. Neuronal Pathway: Taste sensations transmitted via facial (anterior tongue), glossopharyngeal (posterior tongue), and vagus nerves (root of tongue).

Sensory Receptors for Taste and Smell

  • Chemical Receptors: Chemoreceptors are responsible for both taste and smell, detecting chemicals in respective mediums.

Vision

Anatomy of the Eye:

  • Structures:

    • Fibrous Tunic: Sclera, Cornea

    • Vascular Tunic: Choroid, Ciliary Body, Iris

    • Nervous Tunic: Retina (includes rods and cones for low/bright light perception).

  • Function: Light is focused onto the retina where photoreceptors generate signals transmitted to the brain.

Visual Disorders:

  1. Myopia: Nearsightedness, difficulty seeing distant objects.

  2. Hyperopia: Farsightedness, difficulty seeing close objects.

  3. Astigmatism: Distorted vision due to uneven lens curvature.

Retinal Conditions:

  • Cataracts: Opacification of the lens; common in aging.

  • Diabetic Retinopathy: Caused by blood vessel damage in the retina.

Hearing and Balance

Anatomy of the Ear:

  1. External Ear: Collects sound waves.

  2. Middle Ear: Transmits vibrations via auditory ossicles (Malleus, Incus, Stapes).

  3. Inner Ear: Contains cochlea (hearing) and vestibular system (balance).

Hearing Mechanism:

  1. Sound waves vibrate the tympanic membrane.

  2. Ossicles amplify and transmit vibrations to the oval window.

  3. Fluid movement in the cochlea stimulates hair cells to generate action potentials sent to the brain.

Balance Mechanism:

  1. Static Equilibrium: Evaluates head position relative to gravity.

  2. Dynamic Equilibrium: Evaluates changes in head movement.

Senses and Aging

  • General Sensory Decline: Decrease in Meissner and Pacinian corpuscles, affecting touch and proprioception.

  • Presbyopia: Loss of lens flexibility affects accommodation.

  • Presbycusis: Age-related hearing loss from hair cell degeneration.

Conclusion

  • Understanding sensory anatomy and physiology is crucial for recognizing how we interact with our environment and the implications of sensory decline with aging.