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35 Cards in this Set

  • Front
  • Back
Define "sensation"
-conscious or unconscious awareness of external or internal stimuli
Give examples of "internal stimuli"
-Determination of body temperature, bolood glucose, blood osmotic strength
Give examples of "external stimuli"
-taste, touch, temperature and tympanic input (sound)
-usually consicious
What is perception?
Perception = conscious awareness and interpretation (usually w localization) of a sensation
Define sensory modalities.
Sensory modalities = modes of sensation
Why is it ill-informed to say we only have 5 senses?
-touch alone has @ least 7 unique sensations (warm, hot, cold, texture, pressure, sharp pain, diffuse burning pain)
Define "transduction"
-Conversion of an environmental physical property (stimulus) into a neuronal electrochemical property
What are the 4 general steps involved in sensation?
1. Stimulation
2. Transduction
3. Impulsion generation (conduction)
4. cortical integration
With what does the process of transduction begin?
-Process of transduction begins w stimulus acting on the sensory receptor
How are sensory receptors specialized?
-Sensory receptors are specialised to act on one type of stimuli and not to others (selective)
Specialized sensory receptors are found in how many grades of complexity? What are these grades?
3 grades
1. free nerve endings
2.encapsulated ending
3. seperate receptor cell
How do nerve endings work as sensory receptors?
-uncovered distal end of sensory axon w membrane proteins generate voltage potential in response to stimulus
How do encapsulated endings work as sensory receptors?
-specialized covering of the distal end of the axon modifies properties of the stimulus to better activate a membrane voltage change
How do seperate cells work as sensory receptors? Give an example.
-Specialized sensory receptor cell carries out function
-Hair cell in the ears = seperate cell
How does stimuli affect a sensory receptor?
-Stimuli causes changed in ion channels @ sensory receptor
-Results in graded potentials = receptor potentials = generator potentials
How can a stimulus cause a generator potential?
-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
What is a primary sensory neuron?
-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
What kind of primary sensory neurons have nerve terminals that end in spinal cord? What about in medulla?
-Sensory neurons that have nerve terminals that end in spinal cord = pain and temp
-that end in medulla = fine touch and pressure
Define dorsal root ganglion.
-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.
Name and explain 4 characteristics of sensation.
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)
Define the term "somatotopic"
-Somatotopic = correspondence of receptors in regions of the body via respective nerve fibers to specific functional areas of the cerebral cortex
Name 5 different sensations that each have a separate receptor mechanism in the skin.
1. Heat
2. Cold
3. Sharp Pain
4. Dull Pain
5. Fine Touch
How is it that different sensations can have seperate receptor mechanisms?
- Peripheral endings are of separate primary sensory axons
- These have seperate connections (axons)
- Reach different/separate regions in cortex
Explain what happens when the stimulus is strong.
-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
On what does the detection of a stimulus on an area of skin surface depend?
-On the branching of peripheral ending = the peripheral field
What has higher acuity, skin of the chest or skin of the hands? Why?
-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
From what does the ability to localize sensation arise?
-Ability to localize sensation arises from fact that body surface maps onto the cerebral cortex
Explain why onset of a touch stimulus is more significant than the continuation of a touch stimulus.
-Receptors get used to (adapt to) stimuli and no longer generate same level or receptor potential
What is adaptation in relation to receptors to a stimulus?
-Receptor potential decreases in amplitude during a sustained constant stimulus
Give an example of a receptor that adapts quickly to stimuli.
Phasic receptors adapt quickly to stimuli.
Give an example of a receptor that adapts slowly to stimuli.
Tonic receptors adapt slowly to stimuli.
Where do pain and temperature afferent neurons synapse?
-Pain and temperature afferent neurons synapse in the spinal cord onto spinothalamic neurons
-These neurons cross the midline and ascend to the thalamus
Where do touch and pressure afferent neurons synapse?
-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
Give and explain an example of descending control of sensory input.
-Repression of pain stimulus by descending projections from the periaquaductal grey to the dorsal horn.
-NT for this pathway =enkephalin
What artificial NT has the same effect as enkaphalin?