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35 Cards in this Set
- Front
- Back
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Define "sensation"
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-conscious or unconscious awareness of external or internal stimuli
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Give examples of "internal stimuli"
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-Determination of body temperature, bolood glucose, blood osmotic strength
-unconscious |
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Give examples of "external stimuli"
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-taste, touch, temperature and tympanic input (sound)
-usually consicious |
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What is perception?
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Perception = conscious awareness and interpretation (usually w localization) of a sensation
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Define sensory modalities.
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Sensory modalities = modes of sensation
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Why is it ill-informed to say we only have 5 senses?
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-touch alone has @ least 7 unique sensations (warm, hot, cold, texture, pressure, sharp pain, diffuse burning pain)
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Define "transduction"
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-Conversion of an environmental physical property (stimulus) into a neuronal electrochemical property
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What are the 4 general steps involved in sensation?
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1. Stimulation
2. Transduction 3. Impulsion generation (conduction) 4. cortical integration |
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With what does the process of transduction begin?
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-Process of transduction begins w stimulus acting on the sensory receptor
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How are sensory receptors specialized?
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-Sensory receptors are specialised to act on one type of stimuli and not to others (selective)
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Specialized sensory receptors are found in how many grades of complexity? What are these grades?
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3 grades
1. free nerve endings 2.encapsulated ending 3. seperate receptor cell |
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How do nerve endings work as sensory receptors?
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-uncovered distal end of sensory axon w membrane proteins generate voltage potential in response to stimulus
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How do encapsulated endings work as sensory receptors?
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-specialized covering of the distal end of the axon modifies properties of the stimulus to better activate a membrane voltage change
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How do seperate cells work as sensory receptors? Give an example.
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-Specialized sensory receptor cell carries out function
-Hair cell in the ears = seperate cell |
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How does stimuli affect a sensory receptor?
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-Stimuli causes changed in ion channels @ sensory receptor
-Results in graded potentials = receptor potentials = generator potentials |
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How can a stimulus cause a generator potential?
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-If stimulus is intense enough or lasts long enough (temperal summation) it will cause a large enough GP
-GP will depolarize the 1st node of Ranvier to threshold and initiate an AP |
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What is a primary sensory neuron?
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-First sensory neuron w periphearl ending in skin or muscle
-has axon in peripheral nerve -has cell body in dorsal root ganglion -has nerve terminals that end in either spinal cord or medulla |
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What kind of primary sensory neurons have nerve terminals that end in spinal cord? What about in medulla?
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-Sensory neurons that have nerve terminals that end in spinal cord = pain and temp
-that end in medulla = fine touch and pressure |
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Define dorsal root ganglion.
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-Dorsal root ganglion is found at distal end of the dorsal root
-It contains neuron cell bodies of the nerve fibres conveyed by the root. |
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Name and explain 4 characteristics of sensation.
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1. Modality (determined by receptor and concerved by separate axon bundles to cortex)
2. Intensity (encoded by frequency of APs) 3. Acuity (determined by size of receptive field, 2 pt discrimination 4. localization (determined by topography of skin, pathway, cortical representation, somatotopic organization) |
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Define the term "somatotopic"
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-Somatotopic = correspondence of receptors in regions of the body via respective nerve fibers to specific functional areas of the cerebral cortex
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Name 5 different sensations that each have a separate receptor mechanism in the skin.
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1. Heat
2. Cold 3. Sharp Pain 4. Dull Pain 5. Fine Touch |
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How is it that different sensations can have seperate receptor mechanisms?
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- Peripheral endings are of separate primary sensory axons
- These have seperate connections (axons) - Reach different/separate regions in cortex |
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Explain what happens when the stimulus is strong.
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-Strong stimulus causes stronger GP and thus probability of have AP is greater
-APs occur more frequently in axon of 1° sensory neuron -more NT is released -Causes greater synaptic potential @ central synapses and leads to higher frequency of AP through the cortex |
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On what does the detection of a stimulus on an area of skin surface depend?
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-On the branching of peripheral ending = the peripheral field
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What has higher acuity, skin of the chest or skin of the hands? Why?
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-Hands
-Primary endings in skin of hands have narrow branches and tactile acuity is high -Primary endings in skin of chest branch widely, tactile acuity is low |
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From what does the ability to localize sensation arise?
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-Ability to localize sensation arises from fact that body surface maps onto the cerebral cortex
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Explain why onset of a touch stimulus is more significant than the continuation of a touch stimulus.
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-Receptors get used to (adapt to) stimuli and no longer generate same level or receptor potential
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What is adaptation in relation to receptors to a stimulus?
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-Receptor potential decreases in amplitude during a sustained constant stimulus
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Give an example of a receptor that adapts quickly to stimuli.
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Phasic receptors adapt quickly to stimuli.
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Give an example of a receptor that adapts slowly to stimuli.
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Tonic receptors adapt slowly to stimuli.
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Where do pain and temperature afferent neurons synapse?
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-Pain and temperature afferent neurons synapse in the spinal cord onto spinothalamic neurons
-These neurons cross the midline and ascend to the thalamus |
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Where do touch and pressure afferent neurons synapse?
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-Touch and pressure afferent neurons ascend the dorsal column and synapse in the dorsal column nuclei in the medulla
-Synapse onto neurons that cross the midline and ascend to the thalamus as the medial lemniscus |
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Give and explain an example of descending control of sensory input.
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-Repression of pain stimulus by descending projections from the periaquaductal grey to the dorsal horn.
-NT for this pathway =enkephalin |
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What artificial NT has the same effect as enkaphalin?
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morphine
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