Section 2 WK6 Reading

• Stimulus-elicited behaviour

  Behaviour produced as an involuntary and relatively immediate consequence of sensory stimulation: the behaviour is an involuntary response to the stimulation
• Stimulus-elicited behaviours examples

  • Jumping or flinching in response to a loud noise
  • Withdrawing foot in response to stepping on a sharp stone
• Eliciting stimulus

  Any stimulus that is effective at evoking a particular behavioural response. Such a stimulus is an eliciting stimulus for that behaviour
• Internally initiated behaviour

  Behaviour initiated and generated by processes entirely within the central nervous system - sensory stimulation does not elicit them and is not required for their production. This kind of behaviour can be either voluntary or involuntary (spontaneous)
• Examples of Internally initiated behaviours

  • Spontaneous eye blinks
  • Voluntary eye blinks
• Proximal stimulation

  Physical energy or force (electromagnetic, mechanical, acoustic, chemical) that impinges upon sensory receptors and evokes a change in their membrane potential. Can also be characteristics or features of this energy, such as its strength, a change in its strength or the rate at which strength is changing
• Distal stimulus

  A perceived/perceptible object, structure, substance, state of affairs or event in the environment/body. These are sources or causes of proximal stimulation (&/or of its features and patterns)
• Reflex

  A stimulus-elicited behaviour in which the eliciting stimulus is proximal. Proximal stimulation of a specific population of receptors elicits the behavioural response
• Examples of Reflexes

  • Acoustic startle eye blink reflex
  • Corneal eye blink reflex
• Modal action pattern

  A stimulus-elicited behaviour that requires identification or recognition of a distal stimulus and/or of features/properties of a distal stimulus
• Examples of Modal action patterns

  • Courtship displays in male birds
  • Egg-retrieval behaviour in ground-nesting birds
• Autonomic reflex

  A reflex mediated by the autonomic nervous system
• Skeletomotor reflex

  A reflex mediated by the somatic nervous system
• Example of an Autonomic reflex

  • Pupillary light reflex
• Pupillary light reflex

  When the intensity of the light entering the eye increases, the pupil gets smaller (constricts); when the intensity decreases, the pupil gets larger (dilates)
• 2 actions that occur in the Pupillary light reflex

  1. Contraction of the iris dilator muscle makes the pupil larger

  2. Contraction of the iris constrictor muscle makes the pupil smaller
• Skeletal muscles

  • Controlled by the somatic nervous system
  • Move body parts
  • Allow us to act voluntarily (to speak, write, walk from place to place, chew, manipulate things and so on)
  • Responsible for producing skeletomotor reflex responses
• Examples of Skeletomotor reflex responses (6)

  • Withdrawal reflexes
  • Scratching and wiping reflexes
  • Orienting reflexes
  • Vestibular-ocular reflexes
  • Eye blink reflexes
  • Startle reflexes
• Stimulus driven response

  The eliciting stimulus evokes neural activity in sensory neurons and this activity is transmitted to the muscles (or glands) responsible for generating the response
• Characteristics of stimulus driven responses

  • Response strength depends upon stimulus strength
  • Response strength variations follow variations in stimulus strength
  • Response duration depends upon stimulus duration
• Stimulus released response

  Neural activity that produces the muscle contractions does not derive directly from the eliciting stimulus. The activity is instead derived from response production circuitry that generates signals to the muscles when activated by the eliciting stimulus
• Characteristics of stimulus released responses

  • Response strength does not depend upon stimulus strength
  • Response strength does not vary with stimulus strength variations
  • Response duration does not depend upon stimulus duration
  • All-or-nothing characteristic: either the response is elicited (all) or it is not (nothing)
• Many stimulus-elicited behaviours involve release of the response by the eliciting stimulus
• Responses that are released by the eliciting stimulus can continue to completion even if the stimulus is removed
• Some stimulus-elicited behaviours have characteristics of both stimulus-driven and stimulus-released responses
• Reflex arc

  The basic neural pathway that links a sensory receptor to a muscle
• Reflex arc characteristics/ components

  • Consists of a sensory neuron, one or more interneurons, and a motorneuron
  • Can be monosynaptic (one interneuron), disynaptic (two interneurons), trisynaptic (three interneurons), or polysynaptic (more than three interneurons)
• Somatosensory receptor

  Receptors found embedded within tissues of the body that respond to the condition of that tissue
• Phasic muscle stretch reflex

  A reflex mediated by a monosynaptic arc, where the eliciting stimulus is stretching of a skeletal muscle and the response is a contraction of that same muscle
• Muscle spindle

  Encapsulated structures within muscles that contain the muscle stretch receptors, formed from the endings of sensory neurons wrapped around tiny muscle fibres
• Muscle spindle receptors

  • Type 1a endings are primarily responsive to how quickly the muscle is being stretched
  • Type II endings are primarily responsive to the degree of muscle stretch
• Intrafusal muscle fibres

  Fibres located within the spindle capsule
• Muscle spindles size/ length

  • Vary in size, smaller in small muscles and larger in larger ones, the smallest are less than 0.5 mm long and the longest may be as much 1 cm long
• Type 1a fibre

  Thicker sensory axon
• Type II fibre

  Thinner sensory axon
• Type 1a endings

  Primary endings, primarily responsive to how quickly the muscle is being stretched
• Type II endings

  Secondary endings, primarily responsive to how much the muscle has been stretched
• Fast adapting receptor

  Responds to how fast a stimulus quantity is changing
• Slow adapting receptor

  Responds to the stimulus quantity itself
• The knee jerk reflex is a manifestation of the phasic stretch reflex