Chapter 15

🌟 STUDY GUIDE: The Senses Made Simple 🌟

🧠 Sensory Receptors – How We Detect the World

• Job: Detect stimuli (things like light, sound, touch) and turn them into signals your brain can understand.

  • This process is called sensory transduction (think: translation for your brain!)

🧭 Location Types:

• Exteroceptors: Feel the outside world (like a breeze or a loud sound)

• Interoceptors: Monitor the inside of your body (like when you're hungry or your heart beats fast)

🧪 By What They Detect:

• Chemoreceptors – Detect chemicals (taste & smell)

• Photoreceptors – Detect light (vision)

• Mechanoreceptors – Detect touch, pressure, motion

• Thermoreceptors – Detect temperature

• Nociceptors – Detect pain (ow!)

🧠 Memory Trick:
"C-PMT N" → "Cool People Make The News!"

💤 Sensory Adaptation

• If a stimulus stays the same, you notice it less over time.

  • Ex: You smell your shampoo at first, but then don’t notice it later.

• Fast adapting = smell

• Slow adapting = pain

🧠 Memory Trick:
“Fast fades (smell), Slow stays (pain).”

💪 15.2 SOMATIC SENSES – Body Awareness

These help you feel things in muscles, joints, skin, and organs.

Types of Receptors:

• Proprioceptors – Tell you where your body is and how it moves

  • Muscle spindle: Senses stretch → makes muscles contract

  • Golgi tendon organ: Senses tension → makes muscles relax

🧠 Think: "Proprio = position"

• Cutaneous Receptors – In the skin

  • Sense touch, temperature, pain, pressure

  • Types:

    • Free nerve endings – pain, hot, cold

    • Merkel disks, Meissner corpuscles – touch

    • Pacinian corpuscles, Ruffini endings – pressure

• Pain Receptors – Signal tissue damage

  • Can also cause referred pain (ex: heart attack → pain in left arm)

👅👃 15.3 CHEMICAL SENSES – Taste & Smell

👅 Taste

• Taste buds on tongue contain taste cells

• Detect tastants:

  • Sweet (sugar), Sour (acid), Salty (salt), Bitter (toxins), Umami (meaty taste)

🧠 Memory Trick: "SSSBU" = Some Super Sweet Burgers, Umami!"

• Signal path:
  Taste cell → neuron → gustatory cortex (parietal lobe)

👃 Smell

• Olfactory cells in the top of your nose detect odorants

• More sensitive than taste!

• Path:
  Olfactory cell → olfactory bulb → olfactory cortex (temporal lobe)

• Linked to memory through the limbic system

  • (That’s why smells can remind you of people or places!)

🧠 Memory Trick: "Odors = Old Memories!"

👁 15.4 VISION – How We See

Layers of the Eye:

1. Outer – Sclera, Cornea (clear part)

2. Middle – Choroid, Ciliary body, Iris (controls pupil size)

3. Inner – Retina (has photoreceptors)

Inside the Eye:

• Lens – Focuses light

• Humors – Fluids (aqueous = front, vitreous = back)

Photoreceptors:

• Rods – See in dim light

• Cones – See color & detail

• Rhodopsin = Light-sensitive pigment in rods

🧠 Memory Trick:
"Rods = Really dark", "Cones = Colorful"

Special Areas:

• Fovea centralis – Sharpest vision (all cones!)

• Blind spot – No photoreceptors

Vision Pathway:

Retina → optic nerve → optic chiasma → thalamus → visual cortex (occipital lobe)

Vision Problems:

• Color blindness – Genetic, red-green is most common (more in males)

• Nearsighted/Farsighted – Trouble focusing

• LASIK – Laser eye surgery to fix vision

👂 15.5 HEARING & BALANCE

Ear Parts:

1. Outer Ear: Pinna, Auditory canal

2. Middle Ear: Eardrum, Ossicles (Malleus, Incus, Stapes), Eustachian tube

3. Inner Ear: Cochlea, Semicircular canals, Vestibule

Path of Sound:

Pinna → eardrum → ossicles → cochlea → brain

• Hair cells in the cochlea detect vibrations

  • High pitch = beginning of cochlea

  • Low pitch = end of cochlea

🧠 Memory Trick:
"Tiny hairs hear!"

Balance

• Rotational Equilibrium (spinning)

  • Semicircular canals → cupula + endolymph

• Gravitational Equilibrium (head position)

  • Vestibule → utricle + saccule

  • Use otoliths (tiny crystals) to detect head tilt

🧠 Memory Trick:
"Spinning = semicircular"
"Tilting = vestibule"