sensory physi
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jturner916 on March 2, 2012
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52 terms
Terms | Definitions |
|---|---|
 Sensory Function | specialized cells that monitor internal and external conditions |
| Two types of senses | ... |
| General | receptors are distributed throughout the body 1. Afferent impulses are sent to the somatosensory cortex |
| Special | receptors are concentrated in sense organs 1. Afferent impulses are sent to special sense cortexes |
| Afferent (sensory) division | carries sensory info from receptors to the CNS |
| i. Somatic afferent fibers | carries impulses from skin, skeletal muscles and joints |
| ii. Visceral afferent fibers | carries impulses from organs within ventral body cavities |
| iii. Special sense afferent fibers | eyes, ears, taste, smell |
| Pseudounipolar neuron(sensory neuron) except special sensory | 1. Cell body lies in the dorsal root ganglia 2. Action potential is initiated at the peripheral end of the neuron |
| Sensory Receptors | -found on the peripheral end of sensory neurons. -Act as transducers to change an incoming stimulus of one type into an electrical impulse |
| Adequate stimulus | receptors are specific for the type of stimulus it is sensitive to an can transducer, ie cants shine light in ear and hear something. |
| ...exception | Receptors can respond to other types of stimuli if strong enough. ie press on eye (mechainal stress) you will see flashes of light. |
| "Law of Specific Nerve Energies | regardless of the type of stimulus the sensation is perceived as what the receptor is specific for |
| Sensory Transduction | i. A stimulus alters the membrane permeability of the receptor. This leads to the production of a graded receptor potential |
| Sensory Transduction | ii. Receptors that are modified endings of the afferent neuron produce generator potentials |
| Sensory Transduction | iii. Receptors that are separate cells from the afferent neuron produce receptor potentials |
| Sensory Transduction | iv. Release chemicals that open ligand gated channels on the afferent neuron |
| i. Free nerve endings | 1. Nociceptors 2. Themoreceptors |
| 1. Nociceptors | activation causes the sensation of pain a. Free nerve endings found in the skin, joints, bones, and blood vessels b. Sensitive to chemicals, tissue damage, and extreme temperatures |
| 2. Themoreceptors | react to changes in temperature a. Free nerve endings in the dermis, hypothalamus, and liver b. You have 3X more cold receptors than warm receptors, cold vs colder= more action potiental high fequency, 10 degree or less you feel pain /45 then pain |
| Mechanoreceptors | stimulated by physical change such as pressure or movement |
| Merkel cells | cells in the stratum basale associated with free nerve endings, detect fine touch |
| Hair root plexus | free nerve endings associated with hair follicles, detect movement of hair |
| Meissner's corpuscles | -detect touch, found in dermal papillae |
| Ruffini corpuscles | sensitive to stretch and distortion, found in the dermis |
| Pacinian corpuscles | deep pressure receptors found in the dermis |
| Baroreceptors | sensitive to internal pressures. Monitors blood pressure in vessels (carotid sinus and aorta), lungs, bladder, intestines |
| Proprioceptors | monitors position and stretch of muscles, tendons, ligaments, and joint capsules. Helps maintain posture and sense of body position |
| Chemoreceptors | detect chemicals dissolved in solution. Olfactory, taste, osmolarity, pH, CO2, O2 alot of special senses |
| Ascending tracts | a bundle of axons transmitting impulses towards the brain. Usually involves three successive neurons (three levels of processing) tend to be on dorsal and lateral sides of your spinal cord |
| i. Receptor level | Primary neuron running from the receptor to the posterior horn of the spinal cord or medullary nuclei |
| ii. Circuit level | Secondary neuron synapses with the first and transmit impulses to the thalamus (all sensors go to thalamus but olfactory) |
| iii. Perception level | Tertiary neuron running from the thalamus to the primary somatosensory cortex or a special senses cortex. The cerebral cortex is responsible for |
| cerebral cortex is responsible for | 1. Sensation - the awareness of the stimuli 2. Perception - the interpretation of the stimuli |
| Each sensory fiber is a "labeled line | the type, location, strength, and the intensity of the stimuli is encoded in the area of the cortex it travels to and the frequency of the impulse |
| Determining type of stimulus or receptor activated | 1. Depends on the pathway it takes and the area of the cerebral cortex it travels to |
| Determining type of stimulus or receptor activated | 2. The area of the cortex devoted to each region is related to the regions sensitivity (# of receptors |
| Referred pain | many primary neruons sinape with the same secondary neruon, usually defalt to the most frequently stimulated ie skin not heart |
| Phantom pain | remodeling of the cortex, or a secondary neuron is irritated |
| Localization of the stimulus | Accuracy of localization depends on the size of the receptor field. The smaller the receptor field the more accurate. |
| Localization of the stimulus | Accuracy also depends on lateral inhibition. Only the most intensely stimulated pathway is excited. Less excited pathways surrounding the stimulated area are inhibited |
| Number of receptors stimulated - stronger stimuli usually affect larger areas | Number of receptors stimulated - stronger stimuli usually affect larger areas |
| usually affect larger areas | Frequency of action potentials - stronger stimuli generate larger receptor potential, therefore a greater frequency of action potentials |
| Duration of the stimulus | Adaptation - receptors change their sensitivity in the presence of constant stimulus ie a watch on your wrist |
| Phasic receptors | fast adapting i. Report changes in the environment ii. Burst of firing at the beginning and end of stimulus iii. Examples: temperature, smell, touch |
| Tonic receptors | slow adapting or not at all i. Constant firing rate ii. For situations were continuous information about a stimulus is valuable iii. Examples: proprioceptors pain, muscle stretch |
| pain | is subjective , influenced by past adn present experiences, and is coupled with emotional responses |
| fast pain pathways | sharp pain, easy to localize, myleineated |
| slow pain pahtways | unmyleined, dull aching pain, persists long and hard to locialize |
| what stimulates the pain pathway | nociceptors are sensite to chemcials released by damaged tissues. prostaglandins, bradykinins, histamine, capsaicin |
| pain pathway | nocicieptors stimulated and primary neurion relases suspstance P- secondary neuron then thalamus and to the reticular formation(brain stem- level of alertness) and hypothamlus( emotinal response) |
| analgesic pathway | endorphins bind to opiate recepotros on the axon termainal and block the release of susbstance P(example of presnapic inhibition) |
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