Week 9

• Sensory receptors transduce stimulus energy and

  transmit signals to the central nervous system.
• Sensory receptors convert environmental stimuli into stimulus energy

  that propagates through the central nervous system (CNS) and results

  in the perception of the stimulus a.k.a sensation
• 5 types of receptors: respond to different energy types: mechanoreceptors, pain receptors (nociceptors), thermoreceptors,

  chemoreceptors and electromagnetic receptors
• sensory receptors are activated by specific stimuli
• sensory inputs are sent to and integrated by CNS
• specific pathways will be activated and lead to motor responses
• multiple simultaneous stimuli require complex decision making

  processes
• Sensory cells are either a specialised

  neurons or a non neuronal cell that

  regulates afferent neurons
• exteroreceptors: stimuli from outside

  the body e.g. heat, light, chemicals
• interoceptors: stimuli inside the body

  e.g. position, blood pressure
• Sensory information travels through the nervous system as action potentials (AP)
• stimulus intensity is coded by AP frequency
• greater stimulus increases AP frequency only
• in many cases, stronger stimuli recruit additional sensory receptors
• allows CNS to sense increased stimulus

  strength
• Action potentials from the diverse range

  of sensory receptors are essentially the

  same
• Multiple neurons from the same sensory

  body are grouped together
• These nerve bundles connect to different

  regions within the CNS
• The differentiation of the stimuli into the

  perception of touch, smell, light etc occurs

  within the brain.
• Key Concept: In hearing and equilibrium, mechanoreceptors detect moving fluid or settling particles
• Mechanoreceptors sense physical deformation which can be caused by a diverse array of mechanical energies
• Mechanoreceptors are central to the perception of

  • Pressure

  • Touch

  • Stretch

  • Motion

  • Sound
• Typically mechanoreceptors link to Ion channels that change permeability in response to the physical stimulus
• The basilar membrane reduces in thickness along the length

  of the tympanic canal
• The membrane resonates differentially down its length in

  response to different frequencies
• Hair cells along the length of the Tympanic canal convert this

  discrete spatial vibration into AP that are perceived as

  different sounds in the CNS.
• The same apparatus that detects

  sound can also sense gravity and

  motion
• The semi-circular canals of the inner ear are arranged in three spatial

  planes to detect angular movement
• Hair cells at the base of the canals detect the direction of fluid motion

  in each direction
• The Utricle and Saccule inform on linear acceleration and position
• Fish have a number of systems to help them detect sound/movement/vibrations
• Low frequency vibrations/movements are detected by the lateral line system.
• • Hair cell clusters capped by a cupula sense water movements within the lateral line canal
• The water movement is translated into action potentials to relay direction and velocity of the water movement
• Fish can also sense vibrations using their

  inner ears.
• Otolith bones covered in hair cells react to a

  higher range of frequencies than the lateral

  line
• As with mammals sound can be “too loud”

  for fish, loud noise can damage the hair cells,

  this can be stressful and lead to loss of

  “hearing”.
• While fish don’t have the ear drum, cochlea

  or opening to the outside, some species

  connect their inner ear to their swim bladder
• Key Concept: The diverse visual receptors of animals depend on light-absorbing pigments
• ability to detect light is important in many animals