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.