Other Sensory Mechanisms (College Board AP® Psychology): Revision Note

Gustation is the sense of taste

• It is called a chemical sense because taste receptors respond to chemicals in food and drink rather than to physical energy like light or sound

Taste begins on the tongue:

• The tongue is covered in small bumps called papillae

• Inside the papillae are taste buds — clusters of taste receptor cells that detect dissolved chemicals from food and drink

• When chemicals from food dissolve in saliva and contact the taste buds, transduction occurs

  • The chemical signal is converted into a neural signal sent to the cerebral cortex for processing

There are six basic tastes:

• Sweet, e.g. sugar, ripe fruit

• Sour, e.g. lemon juice, vinegar

• Salty, e.g, potato chips, pretzels

• Bitter, e.g. coffee, dark chocolate

• Umami, a savory, meaty taste; e.g. broth, soy sauce, mushrooms

• Oleogustus, the taste of fat; e.g. the distinct taste of fatty foods like butter or cream

The number and density of taste buds varies between individuals, which is why people differ in how intensely they experience taste:

Olfaction is the sense of smell

• Lke taste, it is a chemical sense because smell receptors respond to airborne chemical molecules rather than physical energy

When you breathe in, airborne molecules travel into the nose and contact olfactory receptor cells in the nasal epithelium (the lining of the nasal cavity)

• These receptor cells transduce the chemical signal into a neural signal

• Signals travel to the olfactory bulb

  • This is the brain structure that first receives and processes smell information

Olfaction is the only sense that bypasses the thalamus:

• Rather than routing through the thalamus first, olfactory signals travel directly to the amygdala (involved in emotion) and the hippocampus (involved in memory) in the limbic system

• This direct connection to the limbic system explains why smells can instantly trigger vivid emotional memories

  • E.g. the smell of sunscreen may immediately bring back memories of a childhood vacation

Pheromones are chemical signals produced by animals that trigger specific behavioral or physiological responses in others of the same species

• They are detected via the olfactory system

  • E.g. many animals use pheromones to signal readiness to mate or to mark territory

The chemical senses interact - without smell, taste is greatly reduced

• E.g. when you have a blocked nose, food tastes bland because flavor is largely a combination of taste and smell

Touch is detected by receptor cells in the skin that respond to different types of stimulation:

• Pressure, e.g. feeling the weight of a book in your hand

• Vibration, e.g. feeling a phone buzz in your pocket

• Texture, e.g. distinguishing between rough sandpaper and smooth glass

• Temperature is detected by separate warm receptors and cold receptors

  • The sensation of "hot" is produced when both warm and cold receptors are activated simultaneously — this is why very cold water can feel like it is burning

Touch information is detected by skin receptors and travels to the spinal cord, then to the medulla oblongata, then to the thalamus, and finally to the somatosensory cortex for processing.

The somatosensory cortex (located in the parietal lobe) processes all tactile information

• Different body parts are represented here in proportion to their receptor density, not their physical size

• E.g. your fingertips and lips have very high receptor density and a large representation in the somatosensory cortex

Receptor density varies across the body:

• High density (high sensitivity): fingertips, lips, tongue

• Low density (lower sensitivity): back, thighs

Pain is processed both in the body and in the brain

• The amount of pain a person feels does not always directly match the extent of physical injury

  • E.g. a person may experience intense chronic pain with no detectable tissue damage at all

Gate control theory proposes that the spinal cord contains a neurological "gate" that can open or close to allow or block pain signals from reaching the brain

• Non-painful stimuli can close the gate and reduce pain perception

  • E.g. rubbing or pressing near an injury sends fast tactile signals that close the gate, reducing the pain signal - this is why rubbing a bruise instinctively helps

  • E.g., becoming absorbed in an activity (distraction) or feeling strong positive emotions can also close the gate - explaining why athletes sometimes do not notice injuries until after a game

Phantom limb sensation is the experience of sensation or pain in a limb that has been amputated

• It occurs because the brain's somatosensory cortex retains a representation of the missing limb and continues to generate signals even in its absence

  • E.g. a person who has lost an arm may feel an intense itch or burning pain in a hand that no longer exists - this is a neurological phenomenon, not a psychological one

Endorphins are naturally produced chemicals in the brain that bind to pain receptors and reduce pain perception

• E.g. the "runner's high" experienced during intense exercise is partly caused by endorphin release

• Opioid drugs such as morphine and codeine work by mimicking endorphins, which is why they are effective painkillers

The body has two senses dedicated to tracking its own position and movement:

• Vestibular sense

• Kinesthesis

Vestibular sense detects the body's overall orientation and balance in space

• The primary receptor structures are the three semicircular canals in the inner ear

  • These are three fluid-filled loops oriented in different planes (horizontal, frontal, and sagittal)

• When your head moves, fluid inside the canals shifts and bends hair cells, which generate neural signals indicating the direction and speed of the movement

  • E.g., when you spin around and then stop, the fluid in your semicircular canals continues moving briefly - this is why you feel dizzy, as your brain is receiving conflicting signals about whether you are still moving

• Disruption of the vestibular sense causes dizziness and nausea

  • E.g., motion sickness occurs when visual information (your eyes say you are still) conflicts with vestibular information (your canals say you are moving)

Kinesthesis is the sense of the position and movement of individual body parts

• It is detected by receptors in muscles, tendons, and joints throughout the body

• It allows coordinated movement without needing to watch each body part

  • E.g. you can type on a keyboard or play a musical instrument without looking at your fingers because kinesthetic receptors continuously feed information about finger and hand position to the brain