Question

Order the events for the detection of somatic sensation. Place a 1 by the first event, a 2 by the second and so on.

The central process transmits the action potential to a second-order sensory neuron in the CNS.
The action potential is transferred to the central process in the posterior root ganglion.
The stimulus triggers an action potential.
The signal is transferred to other (third order) CNS sensory neurons for eventual perception and interpretation.
The action potential is propagated along the peripheral process of the neuron.

Answer 1

1. The stimulus triggers an action potential.

2. The action potential is propogated along the peripheral process of neuron.

3. The action potential is transferred to the central process in posterior root ganglion .

4. The central process transmits the action potential to a second order sensory neuron in CNS.

5. The signal is transferred to other (third order) CNS sensory neuron for perception and interpretation.

Explanation- nervous pathway carry the impulses from the receptors in different parts of body to centres in brain. Each pathway has two or three group of neuron:

1. First order neuron- they receive sensory impulse from the receptors and send them to sensory neuron present in posterior grey horn of spinal cord.

2. Second order neuron- these are present in posterior grey horn. These fibres carry sensory impulses from spinal cord to different brain areas.

3. Third order neuron- present in subcortical areas. Fibres of these carry impulse from subcortical areas to cerebral cortex.