lecture 21 test questions

Sensory Systems

• Sensory systems include taste and smell (chemosensory systems), touch, hearing, and balance (mechanoreceptor systems), and sight (electromagnetic receptor systems).

Sensory Receptor Cells

• Rely on membrane receptors embedded in cells that communicate with neurons (taste and sight) or directly in neuron membranes (smell).
• In most multicellular animals, receptor cells are organized into sensory organs.

Sensory Transduction

• Conversion of physical or chemical stimuli into nerve impulse occurs at the sensory receptor.
• Stimulated membrane sensory receptor causes ion channels in the plasma membrane to open.
• Sensory receptors either fire action potentials themselves or synapse with neurons that do.
• Signals are interpreted in the CNS (Perception).

Chemoreceptors

• Provide the sense of smell and taste.
• Respond to molecules in the environment (or our mouth) that bind to receptors in the cell membrane.
• Smell: chemosensitive projections of neurons extend into the mucus that lines the upper part of our nasal passage.
• Taste: taste buds on our tongue are specialized cells that synapse with sensory neurons.

Mechanoreceptors

• Respond to physical deformation of the plasma membrane.
• Open a Na+ ion channel, causing an action potential to fire.
• Responsible for our sense of touch.
• Types of mechanoreceptors:
  • Merkel's disks respond to light touch.
  • Meissner's corpuscles respond to touch and low-frequency vibration.
  • Ruffini endings detect stretch, deformation within joints, and warmth.
  • Pacinian corpuscles detect transient pressure and high-frequency vibration.

Hearing and Balance

• Hair cells are specialized mechanoreceptors that sense mechanical vibration using stereocilia on their surface.
• Do not fire action potentials, but synapse with neurons.
• Stimulation of hair cells alters the rate at which neurons fire.
• Hair cells responsible for hearing are contained in the cochlea.
• Sound vibrations enter outer ear, vibrate the tympanic membrane, and then move the bones in the middle ear (incus, malleus, and stapes).
• Middle ear bones then vibrate the oval window in the cochlea.

Balance

• Hair cells sense balance relative to body orientation to the environment.
• Vestibular system in the inner ear detects gravity, acceleration, and deceleration using 3 semicircular canals.
• Each semicircular canal detects angular momentum in one plane that the head can turn (nodding up-down, turning left or right, or moving side to side).
• When the body moves, fluid in the canals moves hair cells, and the hair cell movement is converted into nerve impulses.

Electromagnetic Receptors

• Respond to electrical, magnetic, and light stimuli.
• Photoreceptors are the most common.
• Opsin: light-sensitive protein that converts light energy into electrical signals.
• Each opsin protein contains a pigment called Retinal.
• When light energy strikes Retinal, it shifts from a cis to trans-isomer configuration.
• This shift in configuration opens Na+ channels to depolarize the cell.
• Animal eye configuration and anatomy vary widely.
• Types of eyes:
  • Eyecups: detect light intensity and direction.
  • Compound Eyes: each lens is called an ommatidium.
  • Single-lens Eyes.