Properties of reflex arc

PROPERTIES OF REFLEX ARC

One way conduction (Bell and Magendie law)

    

  • The dorsal root fibres of the spinal cord are afferent (sensory), while the ventral root fibres are efferent (motor).
  • The sensory impulses are centripetal (towards the CNS) and motor impulses are centrifugal (away from the CNS).

Slow speed of conduction

  • Slow build up of EPSP to threshold stimulus causes the synaptic delay, thus slows the speed of conduction.
  • Fatigue: Due to exhaustion of the neurotransmitter substance at the synapse.
  • Refractory period: Show both absolute and relative refractory periods.
  • Reinforcement: (Successive induction): By discharging signals from many neurons. It is of two types,
    • Positive successive induction: Irritation at a point of the skin by a tick leads to scratch reflex
    • Negative successive induction: Reciprocal stimulation and inhibition; e.g., biting reflex, reflex flexion and extension of the limbs.
  • Rebound: Increased reflex response following the withdrawal of inhibitory stimulus.
  • After discharge: Continuous impulse discharge from the centre, even after the cessation of the original stimulation.
  • Summation: Subminimal stimuli at rapid succession develop effective EPSP, the temporal summation.
  • Recruitment: Prolonged and altered intensity of stimulus progressively activates more number of motor neurons.
  • Irradiation: Gradual increase in the intensity of stimulus excites the additional neurons, and the effectors.
Last modified: Thursday, 9 June 2011, 6:33 AM