Page 11 - LN-NEURAL CONTROL & COORDINATION

(v) Spinal cord conducts impulses to and from the brain and controls most of

the reflex activities and provides a means of communication between spinal
nerves and the brain.
Reflex Action and Reflex Arc
The entire process of response to a peripheral nervous stimulation, that occurs
involuntarily, i.e., without conscious effort or thought and requires the
involvement of a part of the central nervous system is called a reflex action.
The nervous pathway taken by nerve impulses in a reflex action is called reflex
arc.

Types of Reflexes
Reflexes are categorised into two
(i) Unconditioned (inborn reflexes and transmitted through heredity) breast
feeding and swallowing.
(ii) Conditioned (acquired after birth, i.e., adopted during the course of life
time.) e.g., Withdrawl of a body part (like limb) which comes in contact with
objects that are extremly hot, cold, pointed or animals that are scary or

poisonous.
Mechanism of Reflex Action
(i) The reflex pathway comprises atleast, one afferent (receptor) neuron and
one efferent (effector) neuron arranged in a series.
(ii) The afferent neuron receives signal from a sensory organ and transmits the
impulse via a dorsal nerve root into the CNS (at the level of spinal cord).

(iii) The efferent neuron then carries signals from CNS to the effector. The
stimulus and response in this way forms a reflex arc, e.g., Knee jerk reflex as
shown above in the diagram.
Peripheral Nervous System (PNS)

The peripheral nervous system consists of
1. Somatic Neural System (SNS)
2. Autonomic Neural System (SNS)