Sensory System

Sensory System Notes

Functions of the Sensory System

• Allows experience of the world through various senses (sight, sound, touch, taste, smell).
• Acts as a warning system in threatening environments (e.g., pain from a hot surface).
• Monitors internal conditions of the body (e.g., fullness of the stomach prompts digestion).

Types of Sensory Receptors

Five Types of Sensory Receptors:

1. Chemoreceptors

• Detect changes in chemical concentrations.
• Example: Taste and smell.

1. Nociceptors (Pain Receptors)

• Respond to tissue damage.
• Example: Pain from injuries.

1. Thermoreceptors

• React to temperature changes.
• Examples: Stimulated by heat and cold.

1. Mechanoreceptors

• Respond to pressure/movement of fluids.
• Examples: Hearing and equilibrium.

1. Photoreceptors

• React to light.

Sensation and Perception

• Sensation: Awareness of sensory information (can be conscious/unconscious).
• Perception: Conscious interpretation of sensations.

Four Components of Sensation:

1. Stimulus: The energy involved (e.g., light for sight).
2. Receptor: Specialized neurons that detect the stimulus.
3. Sensory Nerve: Transmits impulses to the CNS (e.g., optic nerve).
4. Area of the Brain: Interprets the sensory information (e.g., occipital lobe for sight).

Characteristics of Sensation:

• Projection: The brain associates sensation with its source, explaining why the brain perceives pain in an extremity (like phantom limb pain).
• Adaptation: The decrease in sensitivity to constant stimuli (e.g., becoming accustomed to a strong smell).

General and Special Senses

General Senses:

• Includes pain, touch, temperature, pressure, and proprioception.
• Receptors are widely distributed throughout the body (skin, muscles, joints).

Special Senses:

• Taste (Gustation), Smell (Olfaction), Sight (Vision), Hearing (Audition), and Equilibrium (Balance).

Sense of Smell (Olfaction)

• Olfactory receptors in the nasal mucosa detect chemical changes.
• Sent through cranial nerve I to temporal and frontal lobes for processing.

Sense of Taste (Gustation)

• Taste buds on the tongue detect chemicals in food.
• Four basic taste sensations: sweet, salty, sour, and bitter.
• Information travels via cranial nerves VII, IX, and X to the gustatory cortex in the parietal lobe.

Sense of Sight (Vision)

Structure of the Eye:

• Eyeball Layers: Sclera, choroid (vascular), retina (contains photoreceptors).
• Visual Accessory Organs: Eyebrows, eyelids, eyelashes, lacrimal apparatus.

Pathway of Light:

• Light enters the eye, passing through the cornea, aqueous humor, pupil, lens, and vitreous humor before reaching the retina.

Sense of Hearing (Audition)

Structure of the Ear:

• External Ear: Auricle and external auditory canal.
• Middle Ear: Contains the tympanic membrane and ossicles (malleus, incus, stapes).
• Inner Ear: Cochlea (hearing), vestibule, semicircular canals (balance).

Pathway of Sound:

1. Sound waves hit the tympanic membrane, causing vibrations.
2. Vibrations transmitted through ossicles to the oval window.
3. Fluid movement in cochlea bends hairs in the organ of Corti, generating nerve impulses sent via CN VIII to the brain.

Sense of Balance (Equilibrium)

Types of Equilibrium:

• Static Equilibrium: Maintains posture; detected by maculae in the vestibule.
• Dynamic Equilibrium: Responds to movement; detected by cristae in semicircular canals.
• Information is sent to the cerebellum via CN VIII.

Disorders of the Senses

• Glaucoma: Increased intraocular pressure leading to optic nerve damage.
• Cataracts: Clouding of the lens affecting vision.
• Conjunctivitis: Inflammation of the conjunctiva.
• Otitis Media: Middle ear infection.

Aging and the Sensory System

• Diminished sensitivity of receptors leads to lower detection of pain, touch, and temperature.
• Loss of taste and smell begins around age 50, and hearing loss can occur after age 60 due to hair cell damage.
• Vision diminishes by age 70 due to various factors affecting light input and focusing.

Conclusion

• The sensory system plays a vital role in how we interact with our environment. Understanding its components helps us appreciate the complexity of sensation and perception.