Overview
This lecture covers the lesser-studied senses beyond vision and hearing, including the chemical senses (taste, smell) and various body senses related to touch, pain, temperature, balance, and body position.
The Chemical Senses
- Taste (gustation) and smell (olfaction) respond to molecules and are called chemical senses.
- Flavor perception results from combined gustatory and olfactory input.
- Six basic taste groupings: sweet, salty, sour, bitter, umami (savory), and possibly fat.
- Taste buds with receptor cells detect dissolved molecules, sending signals to the gustatory cortex.
- Olfactory receptor cells in the nasal cavity detect odor molecules, sending signals to the olfactory bulb and cortex.
- Dogs have more olfactory receptor genes, making them more sensitive to smells than humans.
- Pheromones are chemical messengers influencing behaviors, especially in reproduction.
Somatosensory, Thermoceptive, and Nociceptive Senses
- Skin contains various touch receptors: Meissner’s (light pressure, low vibrations), Pacinian (deep pressure, high vibrations), Merkel’s (light pressure), and Ruffini (stretch).
- Free nerve endings in skin detect temperature (thermoception) and pain (nociception).
- Touch, temperature, and pain signals travel via the spinal cord to the somatosensory cortex.
- Pain can be inflammatory (tissue damage) or neuropathic (nerve damage).
- Congenital insensitivity to pain is a rare genetic disorder preventing pain perception, leading to injury.
Vestibular, Proprioceptive, and Kinesthetic Senses
- Vestibular sense (inner ear) maintains balance and posture; organs include the utricle, saccule, and semicircular canals.
- Vestibular hair cells detect head movement and gravity, signaling the brain about balance.
- Proprioception is the sense of body position; kinesthesia is the sense of body movement.
- Proprioceptive and kinesthetic information comes from muscle, joint, and skin receptors and travels to the brain via the spinal column.
- Both systems work with the vestibular sense to control movement and reflexes.
Key Terms & Definitions
- Gustation — the sense of taste.
- Olfaction — the sense of smell.
- Umami — the fifth taste, associated with savory flavors and monosodium glutamate.
- Pheromones — chemical signals used for communication between individuals.
- Thermoception — the sense of temperature.
- Nociception — the sense of pain or harmful stimuli.
- Congenital analgesia — genetic condition causing insensitivity to pain.
- Vestibular sense — sense of balance and spatial orientation.
- Proprioception — sense of body position.
- Kinesthesia — sense of movement of body parts.
Action Items / Next Steps
- Review the structure and function of each sensory system.
- Complete any associated readings or exercises on the chemical and body senses.