Overview
This lecture covers the homunculus as a model of sensory mapping, and explains how we sense and perceive sound, taste, smell, touch, and balance.
The Homunculus and Sensory Mapping
- The homunculus is a visual representation of how much sensory input different body parts provide to the brain.
- Body parts with more sensory receptors, like hands and mouth, appear disproportionately large in the homunculus.
Sensation vs. Perception
- Sensation is receiving sensory information from the environment through receptors.
- Perception is the brain's process of organizing and interpreting sensory information to create meaning.
Hearing: Sound and the Ear
- Sound waves travel through air, causing vibrations detected by the ear.
- High frequency = high pitch; low frequency = low pitch; amplitude = loudness (in decibels).
- The outer ear funnels sound to the eardrum, which vibrates ossicle bones (stirrup, hammer, anvil).
- Vibrations reach the cochlea, where hair cells trigger nerve signals to the auditory cortex for interpretation.
- Two ears allow stereophonic (3D) hearing.
Taste and Sensory Interaction
- Taste buds contain receptor cells that detect molecules and identify five tastes: sweet, salty, sour, bitter, and umami (savory).
- The old "taste map" dividing the tongue into regions is inaccurate.
- Sensory interaction means one sense can affect another (e.g., smell influences taste).
Smell (Olfaction)
- Smell is a chemical sense; airborne molecules activate millions of nose receptor cells.
- Information reaches the olfactory bulb and parts of the limbic system tied to emotion and memory.
- Odor is identified by combinations of receptor activation, allowing us to recognize thousands of smells.
- Emotional responses to smells are linked to personal experiences.
Synesthesia
- Synesthesia is a condition where senses mix involuntarily, like tasting colors or seeing sounds.
- Theories include abnormal neural connections, delayed sense differentiation in childhood, or altered neurochemistry.
Touch and Kinesthesis
- Touch combines four skin sensations: pressure, warmth, cold, and pain.
- Tickling, itching, and wetness are variations of these sensations.
- Kinesthesis is the body's ability to sense movement and position, involving sensors in muscles and joints.
- Vestibular sense, located in the inner ear, detects balance and head position using semicircular canals and fluid-filled sacs.
Key Terms & Definitions
- Homunculus — Sensory map showing body parts sized by sensory input.
- Sensation — Receiving physical energy from the environment.
- Perception — Interpreting sensory information.
- Ossicle bones — Tiny middle-ear bones: hammer, anvil, stirrup.
- Cochlea — Inner ear structure converting vibrations to neural signals.
- Umami — The fifth basic taste, savory or meaty.
- Sensory interaction — When one sense affects another.
- Synesthesia — Neurological condition mixing senses.
- Kinesthesis — Sensing body movement and position.
- Vestibular sense — Sensing balance and head position.
Action Items / Next Steps
- Review the difference between sensation and perception.
- Prepare for next lecture on how sensory perception can be fooled.