Sensory Nervous System Week 10 Dr. Walid Daoud A. Professor

Sensory Receptors Sensory receptors are specialized structures at the end of sensory neurons. - Detectors for energy changes in the environment. environment. - Transducers as they transform energy changes to action potentials. changes to action potentials.

Classification of Receptors According to specific type of energy needed to stimulate them: 1- Mechanoreceptors:. Touch receptors.. Touch receptors.. Pressure receptors.. Pressure receptors.. Proprioceptors.. Proprioceptors.. Vibration receptors.. Vibration receptors.. Vestibular receptors.. Vestibular receptors.

Classification of Receptors 2- Thermoreceptors. 3- Photoreceptors: Rods and cones in retina. 4- Nociceptors: Free nerve ending in skin &mm 5- Chemoreceptors:. Chemosensitive cells in olfactory mm.. Chemosensitive cells in olfactory mm.. Taste buds.. Taste buds.. Osmoreceptors in hypothalamus.. Osmoreceptors in hypothalamus.. Glucoreceptors in hypothalamus.. Glucoreceptors in hypothalamus.

Mechanism of Stimulation of Receptors 1- Receptor potential. 2- Spread of receptor potential. 3- Action potential. 4- Frequency of action potential is directly proportional to logarithm intensity of the proportional to logarithm intensity of the stimulus. stimulus.

Properties of receptor potential 1- Local state of partial depolarization which propagate passively. which propagate passively. 2- Increasing intensity of stimulus increases its amplitude. increases its amplitude. 3- Does not obey all or none rule. 4- Can be summated. 5- Its duration is 5-10 sec.

Adaptation of Receptors It is the decrease in receptor potential and the frequency of action potentials conducted in sensory nerve despite application of stimulus of constant energy to the receptor. Causes: 1- Remodeling in structure of receptor. 2- Inactivation of Na channels in nerve fiber membrane leading to accomodation of the nerve. membrane leading to accomodation of the nerve.

Adaptation of Receptors 1- Slowly adapting receptors: Pain receptors, muscle spindle, mechano- receptors in carotid sinus and alveolar Pain receptors, muscle spindle, mechano- receptors in carotid sinus and alveolar stretch receptors. stretch receptors. 2- Moderately adapting receptors: Temperature, smell and taste receptors. Temperature, smell and taste receptors. 3- Rapidly adapting receptors: Touch receptors. Touch receptors.

Somatic Sensations 1- Mechano-receptive sensation: A- Tactile sensation: A- Tactile sensation: 1- Light touch. 1- Light touch.. Crude touch.. Crude touch.. Fine touch.. Fine touch. 2- Deep touch (pressure). 2- Deep touch (pressure). 3- Vibration. 3- Vibration. 4- Tickling and itching. 4- Tickling and itching. B- Position senses (proprioceptive senses) B- Position senses (proprioceptive senses)

Pathway of Crude Touch 1- Receptors: Free nerve ending & hair end organ Free nerve ending & hair end organ 2- Transmission: A delta fibewrs st order neuron nd order neuron: Ventral spinothalamic tract. Ventral spinothalamic tract rd order neuron: From thalamus to sensory area of cerebral cortex. From thalamus to sensory area of cerebral cortex.

Pathway of Fine Touch 1- Receptors: Meissner,s corpuscles and Merkel,s discs. Merkel,s discs. 2- Transmission in A beta fibers:. 1 st order neuron: Gracile & cuneate tract. 1 st order neuron: Gracile & cuneate tract. 2 nd order neuron: dorsal column.. 2 nd order neuron: dorsal column.. 3 rd order neuron: from thalamus to. 3 rd order neuron: from thalamus to sensory area of cerebral cortex. sensory area of cerebral cortex.

Pathway of vibration sense 1- Receptors: Paccinian coruscles and Meissner,s corpuscles. Meissner,s corpuscles. 2- Pathway as fine touch.

Pathway of Position Sense 1- Receptors: proprioceptors. 2- Pathway as fine touch.

Thermal Sensation Types of thermal receptors: 1- Cold receptors: Free nerve endings & specialized receptors attached to C fibers and A gama fibers Free nerve endings & specialized receptors attached to C fibers and A gama fibers 2- Warn receptors: Free nerve ending attached to C fibers. Free nerve ending attached to C fibers. 3- Cold pain receptors & heat pain receptors These receptors are stimulated by change in concentration of metabolites due to affection of metabolic rate by temperature.

Pathway of Thermal Sensation. 1 st order neuron: To posterior horn cells of spinal cord. To posterior horn cells of spinal cord.. 2 nd order neuron: Along lateral spinothalamic tract of opposite side. Along lateral spinothalamic tract of opposite side.. 3 rd order neuron: Arise from thalamus to sensory area of Arise from thalamus to sensory area of cerebral cortex. cerebral cortex.