Chapter 50 - Sensory & Motor Mechanisms

Question 1

Describe types of sensory receptors.

Answer 1

• Mechanoreceptors:
  Sense physical deformation (pressure, touch, stretch, motion)
• Chemoreceptors:
  
  • General:
    Respond to total solute of solution
  • Specific:
    Respond to indvidual types of molecules
• Electromagnetic Receptors:
  Detect light, electricity, magnetism
• Thermoreceptors:
  Respond to heat or cold (internally & externally)
• Pain Receptors (Nociceptors):
  Naked dendrites in epidermis (from extreme temps., pressure, chemicals from damaged or inflamed tissues)
  Stimulus leads to defensive reaction (very important receptors!)

Question 2

Describe hearing & equilibrium in terms of mechanoreceptors in different animals.

Answer 2

• Invertebrates:
  
  • Equilibrium:
    Statocysts detect movement of statoliths (dense particle that settles in response to gravity)
  • Hearing:
    Body hairs that vibrate
    Some have tympanic membrane over internal air chamber
• Mammals:
  
  • Hearing & equilibrium closely related via ear
  • Sound waves travel down membrane to chochlea and then transmitted to brain
• Fish & aquatic amphibians:
  
  • Inner ears without cochlea, eardrums, orifices
  • Swim bladder vibrates
  • Lateral line system (series of pores, receptor units along sides of body; detects water movements)
• Reptiles & terrestiral amphibians:
  
  • Develoepd inner ear
  • Single middle ear bone & eardrum
  • Birds & reptiles have cochlea

Question 3

Describe taste vs. smell in terms of chemoreceptors in different animals.

Answer 3

• Taste = gustation
  
  • ​detects tastants in solution
• Smell = olfaction
  
  • ​detects odorants in air
• Terrestrial animals:
  
  • separate taste & smell
  • Flehmen response from Jacob’s organ
  • Taste buds on tongue & in mouth
  • Olfactory receptor cells line upper part of nasal cavity
• Aquatic animals:
  
  • No distinction between taste & smell
• Insects:
  
  • Taste with sensilla (hairs) on feet & mouthparts
  • Smell with olfactory hairs on antennae

Question 4

Describe types of photoreceptors found in different animals.

Answer 4

• Invertebrates:
  
  • Ocellus (eyespot):
    Light intesnity & direction, no images
    ex: flatworm
  • Compound eye:
    Many ommatidia with light-focusing lens
    Excellent movement & colour detection
    ex: insects
  • Single-lens eye:
    Camera-like: iris changes pupil diameter
    Lens moves back & forwards to focus
    ex: spiders, molluscs
• Vertebrates:
  
  • Camera-like: focus by changing shape of lens
  • Aqueous & vitreous humors are “liquid lenses” which help focus light
  • Rods responsible for light sensitivty
  • Cones responsible for distinguishing color
    
    • (ex: nocturnal animals have more rods than cones for night-vision)

Question 5

Descirbe the role of actin, myosin, calcium ions, and action potentials in muscle contraction.

Answer 5

• Myofibrils (longitudinal budnle in a muscle cell) are composed of:
  
  • Thin actin filaments
  • Thick myosin filaments
• In a muscle contraction: myosin head binds ot actin, froms “cross-bridge” and pulls actin toward center of sarcomere (repeating unit of striated muscle)
• Calcium cations bind to troponin complex unlblocking byosin binding sites to allow sliding & contraction to occur
• Action potential in motor neuron stimulates for contaction acetylcholine (ACh) is released at synapse and depolarizes muscle fibers generated an action potential; this also releases calcium cations.

Question 6

Describe types of skeletons.

Answer 6

• Hydrostatic:
  
  • ex: cnidarians, worms.
  • Muscles change shape of fluid filled compartments.
• Exoskeletons:
  
  • ex: most molluscs, arthropods.
  • Composed of hard outer coverings.
• Endoskeletons:
  
  • ex: sponges, echinoderms, chordates.
  • Hard internal support embedded in soft tissue.
• Mammalian skeleton:
  
  • Bones and cartilage
  • Some bones fused, other shave ligaments

Question 7

Describe pros & cons of modes of locomotion.

Answer 7

• Swimming:
  
  • Buoyancy decreases need for gravity resistance.
  • Increased friction (drag) because water is denser than air.
• Locomotion on Land:
  
  • Gravity is stronger than friction.
  • Crawlers have increased friction to deal with.
• Flying:
  
  • Wings must have enough lift to overcome gravity.
  • Streamlined shapes decrease drag.
  • “Most expensive.”