The senses

Information Input

Sensory Adaptation

Sensory receptors are not evenly distributed across the body

• E.g. fingers and lips have more receptors

For many sensory systems, the effect of a stimulus is reduced if it continues at a constant level

• This is called sensory adaptation

• E.g. when getting into bed, you feel the touch and pressure of the sheets. Over time, this feeling goes away

Traditional Senses

There are five traditional

senses

• Vision

• Hearing

• Taste

• Smell

• Touch

Vision

• Vision is the most complex of all senses

• Photoreceptors in the retina detect light at particular wavelengths

  • It converts light stimuli to nerve impulses

• There are two types of photoreceptors

  • Cones: specialized to detect different wavelengths

  • Rods: specialized to detect light at low intensities

Hearing

• The auditory organ for humans is the ear

• The pinna (outer war) focuses on soundwaves

• The soundwaves travel inside the ear, where it hits the ear drum

  • This causes sound vibrations

• These vibrations then hit a chain of tiny bones in the middle ear

  • Malleus (hammer)

  • Incus (anvil)

  • Stapes (stirrup)

Hearing Con’t

• The inner ear contains several fluid-filled compartments

  • Semicircular canals

  • Cochlea

• The vibrations reach the cochlea, which causes hair cells to bend

• In turn, a neurotransmitter is released

Taste

• A tastebud is a receptor that forms a small, pear-shaped capsule with a pore that opens to the exterior at the top

  • They are scattered over the roof of mouth, tongue, and throat

• The tastebuds on the tongue are embedded in outgrowths called papillae

• We can experience 5 basic tastes

  • Sweet, bitter, sour, salty and umami

Taste Con’t

• Signals from taste receptors are sent to the thalamus

• Some signals can trigger emotional responses

  • A pleasant taste can cause salivation

  • An unpleasant taste may produce vomiting and nausea

Smell

• Olfactory receptors are found in the nose

• Each receptor projects into a layer of mucus in the nose

• To be detected, airborne molecules must dissolve into the watery mucus

• Like taste, smell can also trigger emotional responses

Touch

• Mechanoreceptors are embedded in the skin and other surface tissues

• A stimulus can distort proteins in the plasma membrane, which alters the flow of ions

  • In turn, an action potential can occur

• Most touch receptors are located in the fingers, lips, and top of the tongue

  • These areas have the greatest sensitivity to touch

Stress

• Stress is the body’s response to a stimulus that triggers a move away from homeostasis

• Short-term stress is not bad for the body

  • It can cause the body to adapt to changing situations

• Chronic stress, on the other hand, can be dangerous

Symptoms of Stress

• Increase in respiration and heart rate

• Muscle tension

• Frequent urination

• Irritability

• Tiredness

• Trouble sleeping

Hormones Involved in Stress Responses

Pain

• Pain is a protective mechanism that prompts animals to do something to remove or reduce the stimulus immediately

• Pain initiates a reflex response

  • E.g. removing a hand from a hot stove

• Pain receptors (nociceptors) are the most concentrated sensory receptors

  • For every square centimeter of skin, there are around 200 pain receptors

• For protection, pain receptors do not adapt to the environment