Sensory Receptors/ Endings/ Organs November 23, 2018 sensory receptors

Sensory Receptors Sensory receptors/ endings/ organs Specialized structures Respond to changes in stimuli from the environment (external or internal) Convert stimulus energy into electrical energy: action potential November 23, 2018 sensory receptors

Sensory Receptors The action potential Transmitted to the CNS Information when analyzed may lead to: Conscious sensation: sound, heat, light, pain Regulation of body functions: BP, Osmolarity, blood sugar levels November 23, 2018 sensory receptors

Sensory Receptors Primary receptors Part of the NEURON Forms the peripheral nerve endings or receptor endings November 23, 2018 sensory receptors

Sensory Receptors Secondary receptors Specialized non neural cell that generate action potential in a neuron November 23, 2018 sensory receptors

Classification Based on SOURCE of stimulus Exteroreceptors: Eyes, nose, ears, cutaneous receptors Enteroreceptors: Proprioceptors Visceral receptors November 23, 2018 sensory receptors

Classification Based on anatomical, area, division serving Special sensory receptors Somatic sensory receptors Visceral sensory receptors November 23, 2018 sensory receptors

Classification Based on type of agent stimulating receptors Mechanoreceptors Skin tactile sensibility Free nerve endings, Ruffinis end organs, Merkels discs, Pacinian corpuscles, Meissners corpuscles, hair endorgans November 23, 2018 sensory receptors

Classification Deep tissue sensibility Free nerve endings, pacinian, muscle spindles Hearing: hair cells Equilibrium: hair cells Baroreceptors November 23, 2018 sensory receptors

Classification Thermo-receptors: Cold and warm Nociceptors (pain): Free nerve endings Photoreceptors (electromagnetic) Rods and cones Chemo-receptors.: Taste, smell, PO2, PCO2, osmolarity November 23, 2018 sensory receptors

Specificity Receptors are specially adapted to respond to One type of stimulus At a much lower threshold November 23, 2018 sensory receptors

Specificity Light Adequate stimulus: Particular form of energy to which the receptor is most sensitive Light Rods, cones in the eyes November 23, 2018 sensory receptors

Specificity Temperature Pressure Ruffinis Cold and warm receptor November 23, 2018 sensory receptors

Specificity However, almost all receptors can be activated by different forms of energy Pressure on the eyes – see stars Extreme heat or cold – feel pain November 23, 2018 sensory receptors

Receptor Activation Transduction of sensory stimuli into nerve impulses What process takes place between The application of sensory stimulus The generation of a nerve impulse November 23, 2018 sensory receptors

Receptor Activation Stimulus energy alters membrane potential at receptor to cause Receptor potential This has ability to Generate action potential at sensory axon November 23, 2018 sensory receptors

Receptor Activation Membrane potential depend on receptor type: Mechanisms that alter Membrane potential depend on receptor type: Mechanoreceptors: Have mechanically gated channels Mechanical deformation Stretch the membrane Opens ionic channels November 23, 2018 sensory receptors

Receptor Activation Which changes permeability of membrane to ions Chemoreceptors: Have Ligand gated channels Chemicals opens ionic channels Thermoreceptors: Change in temperature Alter membrane property Which changes permeability of membrane to ions November 23, 2018 sensory receptors

Receptor Activation Photoreceptors Effects of electro magnetic waves Directly or indirectly change membrane characteristics Alter ionic permeability November 23, 2018 sensory receptors

Receptor Activation In general Excitation at afferent nerve endings by different stimuli leads to Local changes in permeability of receptor membrane Leads to flow of ions (K+, Na+,Cl-) along concentration gradients November 23, 2018 sensory receptors

Receptor Activation This leads to change in the trans-membrane potential Leading to a local depolarization (generator/receptor potential) November 23, 2018 sensory receptors

Receptor Activation If the receptor potential is of Adequate magnitude (eg 10 mV for the Pacinian corpuscle) This leads to a conducted action potential November 23, 2018 sensory receptors

Receptor Potential Production of generator potential AP Production of generator potential Example in the Pacinian corpuscle The capsule of the pacinian corpuscle is filled with fluid + + + - - + - November 23, 2018 sensory receptors

Receptor Potential Composition similar to AP Composition similar to That of the extra-cellular fluid Contains collagenous fibers The corpuscle is turgid and scarcely compressible + + + - - + - November 23, 2018 sensory receptors

Receptor Potential Local mechanical stimulus leads to AP Local mechanical stimulus leads to Deformation of lamellar of the corpuscle This causes local change in the permeability of membrane + + + - - + - November 23, 2018 sensory receptors

Receptor Potential Ions flow across the membrane AP Opening ionic channels Ions flow across the membrane Leading to local depolarization Generator potential + + + - - + - November 23, 2018 sensory receptors

Receptor Potential AP If the generator potential is of sufficient magnitude Then action potential is conducted along the sensory nerve + + + - - + - Action potentials Generator potentials November 23, 2018 sensory receptors

Stimulus Strength Effect of stimulus strength As pressure increases The magnitude of receptor (generator, GP) potential increases As the pressure is increased Receptor potential becomes even larger Sensory nerve fires repetitively November 23, 2018 sensory receptors

Stimulus Strength As a result The core continues to Emit receptor potential As long as stimulus is applied As a result As soon as the 1st node of Ranvier repolarizes It discharges once again November 23, 2018 sensory receptors

Stimulus Strength Action potential continues Frequency of AP As long as receptor potential persists Frequency of AP Proportional to amplitude of receptor potential November 23, 2018 sensory receptors

Adaptation of Receptors In most receptors, however, The receptor potential decays during a constant stimulation Receptor adapts to the stimulus Rate of adaptation Vary among receptors November 23, 2018 sensory receptors

Adaptation of Receptors Slowly adapting receptor Stretch receptors Intermediate adaptation Temperature, light Rapid adapting receptor Pacinian corpuscle November 23, 2018 sensory receptors

Adaptation of Receptors Rapidly adapting receptors Suited to record alteration of stimulus With high sensitivity Slowly adapting receptors Serve to detect long term conditions State of muscle stretch November 23, 2018 sensory receptors

Adaptation of Receptors Adaptation of receptors is Reflected in  in frequency of AP During a maintained stimulus November 23, 2018 sensory receptors