ANS 205 Sensory System

Module Overview

• Module 5: Physiology of Sensory System

Learning Objectives (MO 5)

• 5.1: List general and special body senses.

• 5.2: Define, discuss, and identify sensory receptors.

• 5.3: Describe pain and proprioception as general body senses.

• 5.4: Describe five special body senses.

• 5.5: Label the anatomy of the ear diagram.

• 5.6: Describe auditory pathways from outer to inner ear.

• 5.7: Explain structures involved in vestibular sensation.

• 5.8: Label the anatomy of the eye diagram.

• 5.9: Describe eye structure and functions in vision.

Sensory System Overview (MO 5.1)

General Body Senses (Somatosensation)

• Types: Pain, Touch, Temperature, Proprioception.

• Location: Body surfaces and musculoskeletal system.

Special Sense Organs

• Taste: Gustation

• Smell: Olfaction

• Sight: Vision

• Hearing: Audition

• Equilibrium: Vestibular sensation

Sensory Receptors (MO 5.2)

• Definition: Specialized cells or nerve endings that detect environmental changes.

• Transduction: Process converting environmental energy into electrical neural activity.

Five General Types of Sensory Receptors

1. Mechanoreceptors: Respond to stretch and proprioception.

2. Thermoreceptors: Detect hot, cold, and infrared.

3. Nociceptors: Signal dull vs. sharp pain.

4. Photoreceptors: Respond to light.

5. Chemoreceptors: Responsive to taste, smell, CO2, and pH.

Structure of Sensory Receptors

• Unencapsulated Receptors: Lack connective tissue (e.g., free nerve endings).

• Encapsulated Receptors: Have glial or connective tissue wrap (e.g., Meissner's corpuscles, Pacinian corpuscles).

General Body Senses (Somatosensation) (MO 5.3)

Pain

• Definition: Conscious perception of harmful stimuli.

• Types of Noxious Stimuli: Thermal, chemical, mechanical.

• Nociceptors: Receptors for noxious stimuli, are naked nerve endings.

Proprioception

• Definition: Awareness of body position and movement.

• Receptors: Present in musculoskeletal system, including joint receptors, muscle spindles, Golgi tendon organs, and skin mechanoreceptors.

Special Senses (MO 5.4)

Gustation (Taste)

• Nature of Sense: Chemical sense.

• Locations: Specialized receptors on tongue and throat.

• Taste Buds: Structures consisting of taste cells and supporting cells confined in papillae.

Olfaction (Smell)

• Structure: Olfactory epithelium (pseudostratified columnar).

• Process: Odors bind to olfactory cilia, relaying to olfactory nerve and then to brain.

• Vomeronasal Organ: Located in hard palate/nasal cavity with receptors for pheromones.

Hearing Anatomy of Ear (MO 5.4, MO 5.5)

• External Ear: Pinna (Auricle), Auditory Canal.

• Middle Ear: Contains 3 ossicles (Malleus, Incus, Stapes), tympanic cavity, and Eustachian tube.

• Internal Ear: Fluid-filled, includes utricle, sacculus, semi-circular canals, and cochlea.

Hearing Structure (MO 5.4)

• Channels Structure: Three parallel fluid-filled channels - vestibular and tympanic ducts filled with perilymph, cochlear duct filled with endolymph (contains organ of Corti with hair cell receptors).

Auditory Pathway and Physiological Events (MO 5.6)

• Covers pathways and sequence of events as sound waves travel through the ear system to brain interpretation.

Vestibular Sensation (MO 5.7)

• Balance/Equilibrium: Involves utricle, saccule, and semi-circular canals sensing linear and angular acceleration.

Vision (MO 5.8)

Structure of Eye

• Three Tunics of Eyeball:

  • Fibrous: Sclera and Cornea.

  • Vascular: Choroid, Ciliary body, and Iris.

  • Nerve: Retina.

Functioning of Vision (MO 5.9)

1. Light Entry: Light enters the eye and is focused by the lens on the retina.

2. Transduction: Photoreceptors transduce light energy into electrical signals.

3. Processing: Neural pathways process signals into visual images in the brain.

Eye Fluids

• Aqueous Humor: Formed in posterior and anterior chambers, providing nutrition and maintains pressure.

• Vitreous Humor: Jelly-like fluid behind the lens, connects to aqueous humor.

Adaptation to Darkness

• Responses: Changes in cornea-to-sclera ratio, increased rhodopsin concentration, dilation of pupils, and function of tapetum in nocturnal vision.

References

1. Frandson, R.D., Wilke, W.L., Fails, A.D. Anatomy and Physiology of Farm Animals (2009).

2. Silverthorn, D.E. Human Physiology: An Integrated Approach (2019).

3. Akers, R.M., Denbow, D.M. Anatomy and Physiology of Domestic Animals (2008).

4. Aspinall, V., Cappello, M., Phillips, C. Introduction to Veterinary Anatomy and Physiology (2015).