The Nervous System, Sensory Receptors; Neuronal Circuits for Processing Information

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SENSORY RECEPTORS

  1. Five basic types of Sensory Receptors
    1. Mechanoreceptors
    2. Thermoreceptors
    3. Nocioreceptors
    4. Photoreceptors
    5. Chemoreceptors
  2. Sensory Receptors are highly sensitive to one particular type of stimulus - "the labeled line" priciple.
    1. sensory modality
    2. anteriolateral system (spinothalamic tract) - pain
  3. Receptors transduce a physico-chemical stimulus into a Nerve Impulse
  4. The Sensory fiber linked to each receptor exhibits "threshold phenomena"
  5. The receptor potential is proportional to stimulus intensity
    1. frequency
  6. Sensory receptors adapt their stimuli either partially or completely over time
    1. accomodation
  7. Receptors are classified as slowly adapting or rapidly adapting
    1. Slowly adapting receptors
      1. Tonic receptors
    2. Rapidly adapting receptors
      1. rate receptors or movement receptors
  8. Physiological Classification of receptors
    1. Two different schemes have been devised to classify the entire range of peripheral nerve fibers
      1. Types A and C 
      2. Fiber diameter and conduction velocity
  9. Intensity of a Stimulus
    1. Intensity is represented in sensory fibers using the features of spacial and temporal summation
      1. receptive field
  10. Transmission and Processing of Signals in neuronal Pools
    1. neuronal pool
    2. receptive field
  11. Afferent systems can provide either threshold or subtreshold stimulation to the neuronal pool
    1. facilitated 
  12. In some neuronal pools, divergence of incoming signals is a common feature
    1. amplification
  13. The processing in neuronal pools might utilise mechanism of convergence
  14. On the afferent side, a single neuron or pool of neurons can give rise to both excitatory and inhibitory output signals
    1. feedforward inhibition
  15. Signal Processing in neuronal pools can involve reveberating circuit or oscillating circuits
    1. excitory neurons located within the pool 
    2. self propogating sequence of signals
    3. a continuous train of efferent signals
    4. a rhythmic output signal
  16. Extensive and Diverse Connectivity in the Nervous System
    1. These factors can produce functional instability in the brain when operations go awry.
      1. epileptic seizure
      2. functional inhibition 
        1. Inhibitory interneurons
        2. synaptic fatigue
In the nervous system, the anterolateral system is an ascending pathway that conveys pain,[1]temperature (protopathic sensation), and crude touch from the periphery to the brain. It comprises three main pathways:
NameDestinationFunction
spinothalamic tract (lateral and anterior)thalamusimportant in the localization of painful or thermal stimuli
spinoreticular tractreticular formationcauses alertness and arousal in response to painful stimuli
spinotectal tracttectumorients the eyes and head towards the stimuli

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