Question

Rearrange the parts of a reflex arc given below in the order in which the nerve impulse travels from the sense organ to the muscle. sense organ | relay neuron | motor neuron | sensory neuron | muscle fibres

Short answer

The correctly arranged order is: sense organ, sensory neuron, relay neuron, motor neuron, muscle fibres.

Step-by-step solution

Identify the Start and End Points

The nerve impulse starts at the sense organ and ends at the muscle fibres. So, these two items form the start and end points respectively of the arrangement.

Place the Sensory Neuron

The sensory neuron is the first to receive the impulse from the sense organ. So, it comes immediately after the sense organ in the order.

Place the Relay Neuron next

After the sensory neuron, the relay neuron comes next in the order. It passes on the impulse received from the sensory neuron to the next neuron in the sequence.

Place the Motor Neuron

The motor neuron receives the impulse from the relay neuron and send it to the muscle fibres, so it comes right before muscle fibres in the order.

Key concepts

Sense Organ

The human body is equipped with specialized structures known as sense organs which serve as the initial starting point for a reflex action. These organs are adept at detecting changes in the environment, a process referred to as sensory input. For instance, your hand touching a scalding surface will activate the sensory receptors in your skin.

When receptors in a sense organ are stimulated, they convert this environmental stimulus into an electrical signal, which is then relayed to the nervous system. To understand this in the context of the reflex arc exercise, the nerve impulse begins its journey at the sense organ, much like the baton in a relay race being passed from the starting runner. The sensory neurons, serving as the next runners, are standing ready to receive the baton and continue the race towards responding to the stimulus.

Neural Pathway

Imagine a complex highway of biological 'wires' transmitting signals at light speed. This is the essence of a neural pathway. It's the route taken by nerve impulses as they navigate through the body’s nervous system. Initiated at the sense organ, the signal travels along the sensory neuron, passes through the relay neuron in the spinal cord, and eventually reaches the motor neuron. This intricate series of connections is essential for the body to process information and respond accordingly.

• The sensory neuron acts as the messenger that carries the impulse from the sense organ to the spinal cord.
• The relay neuron, also known as an interneuron, serves as an intermediary within the spinal cord, refining and directing the signal.
• Motor neurons are the final leg of the journey, delivering the command to the muscles.

Each component plays a crucial role in ensuring the signal travels along the correct pathway to elicit an immediate and appropriate response, such as pulling your hand back from a hot stove.

Motor Neuron

Finally, we come to the motor neuron. This is the last relay in the sequence before the baton – the nerve impulse – crosses the finish line at the muscle fibres. Motor neurons have a critical role; they are responsible for transforming neurological signals into mechanical action. Upon receiving the signal from the relay neuron, the motor neuron fires an impulse directly to the muscle fibres, causing them to contract.

How Motor Neuron Works

When the motor neuron activates, it prompts the muscle fibres to engage in a coordinated response. This could be any muscular action, from the simple reflex of jerking your knee upon a tap to the complex movement of your fingers as you type. The efficiency of this process is vital for both voluntary movements and reflexes, enabling the organism to react swiftly to stimuli, thereby protecting the body from harm.