QUIZ FOR PHYSIOLOGY FOR LEC

• Forms of energy converted by the receptors

  • Mechanical (touch, pressure)
  • Thermal (degrees of warmth)
  • Electromagnetic (light)
  • Chemical (odor, taste, oxygen content of blood)
  • Sound
• Adequate stimulus


  The particular form of energy to which a receptor is most sensitive to
• Sensory receptors


  • Receptors responsible for feeding the CNS information about the internal and external environment of the body
  • They are called transducers for they convert various forms of energy in the environment into action potentials in the neurons and they form part of the sense organs
• Classification of sense organs

  • Special senses (smell, vision, hearing, rotational and linear acceleration, taste)
  • Cutaneous senses (receptors in the skin)
  • Visceral senses
• Other classification of sense organs

  • Teleceptors (receptors concerned with events at a distance)
  • Exteroceptors (those concerned with the external environment near at hand)
  • Interceptors (those concerned with the internal environment)
  • Proprioceptors (those which provide information about the position of the body in space at any given instance)
  • Nociceptors (pain receptors)
  • Chemoreceptors (those receptors which are stimulated by a change in the chemical composition of the environment in which they are located)
  • Mechanoreceptors (those which are stimulated by mechanical types of stimulus)
• Cutaneous senses


  • Touch-pressure
  • Cold
  • Warmth
  • Pain
• Cutaneous sense organs


  • Naked nerve endings
  • Expanded tips on sensory nerve terminals (Merkel's disks, Ruffini endings)
  • Encapsulated endings (Pacinian corpuscles, Meissener's corpuscles, Krause's end-bulbs)
• Cutaneous sense organs


  They respond to tactile stimuli
• Principal sensory modalities


  • Vision (Rods/Cones, Eye)
  • Hearing (Hair cells, Ear)
  • Smell (Olfactory neurons, Olfactory mucous membrane)
  • Taste (Taste receptor cells, Taste buds)
  • Rotational acceleration (Hair cells, Ear (semicircular canals))
  • Linear acceleration (Hair cells, Ear (utricle and saccule))
  • Touch pressure (Nerve endings, Various nerve endings)
  • Warmth (Nerve endings, Various)
  • Cold (Nerve endings, Various)
  • Pain (Naked nerve endings, Various)
  • Joint position and movement (Nerve ending, Various)
  • Muscle length (Nerve ending, Muscle spindle)
  • Muscle tension (Nerve ending, Golgi tendon organ)
  • Arterial BP (Nerve ending, Stretch receptors in carotid sinus and aortic arch)
  • Central venous pressure (Nerve endings, Stretch receptors in the wall of great veins and atria)
  • Inflation of lungs (Nerve endings, Stretch receptors in lung parenchyma)
  • Temperature of blood in head (Neurons, Hypothalamus)
  • Arterial oxygen pressure (Nerve endings, Carotid and aortic bodies)
  • pH of CSF (Receptors, Ventral surface of medulla oblongata)
  • Osmotic pressure of plasma (Cells, Anterior hypothalamus)
  • A/V blood glucose difference (Cells, Hypothalamus)
• Adaptation


  • When a maintained stimulus of constant strength is applied to a receptor, the frequency of the action potentials in its sensory nerve declines over a period of time
  • The degree to which adaptation occurs varies with the type of sense organ. Touch adapts rapidly. Organs for cold and pain adapt very slowly and incompletely
• Projection


  No matter where a particular sensory pathway is stimulated along its course to the cortex, the conscious sensation produced is referred to the location of the receptor
• Doctrine of Specific Nerve Energies

  • The specific sensory pathways are discrete from the sense organ to the cortex
  • When the nerve pathways from a particular sense organ are stimulated, the sensation evoked is that for which the receptor is specialized no matter how and where along the pathway the activity is initiated
• Recruitment of Sensory Unit


  • Single sensory axon and all its sensory branches
  • As the strength of the stimulus is increased, it tends to spread over a large area and generally not only activates the sense organs immediately in contact with it but recruits those in the surrounding area as well
  • Receptors of other units are also stimulated and consequently units fire