Problem 11 - Biology: How Life Works

Question

Diagram a simple circuit that includes a sensory neuron that synapses with a motor neuron to produce a reflex Indicate where in the nervous system this synapse is found.

Step-by-Step Solution

Answer

The synapse is located in the spinal cord.

Step 1: Understand the Components

To diagram the circuit, we need to identify the basic components: a sensory neuron and a motor neuron. The sensory neuron detects stimuli and sends signals to the motor neuron, which then produces a response. A synapse is the junction where these neurons communicate.

Step 2: Define the Pathway

In a simple reflex circuit, the sensory neuron receives a signal (like a touch or heat) and then transmits an electrical impulse. This impulse travels through an axon to reach the synapse with a motor neuron.

Step 3: Identify the Synapse Location

In humans, simple reflex arcs like the knee-jerk reflex involve the synapse between the sensory and motor neurons located in the spinal cord. This is part of the central nervous system (CNS).

Step 4: Draw the Circuit

Draw a diagram starting with a receptor (e.g., skin) connected to a sensory neuron. This neuron leads to the spinal cord where it connects at a synapse to a motor neuron. From there, the motor neuron extends to an effector (e.g., muscle). Clearly label each part.

Key Concepts

Sensory Neuron

The sensory neuron plays a critical role in the reflex arc as it is responsible for detecting external stimuli. These stimuli could be things like heat, cold, pressure, or pain. Once a sensory neuron detects such a stimulus, it converts it into an electrical signal.
This process is known as transduction. After this conversion, the signal travels along the sensory neuron's axon towards the central nervous system (CNS).
In the context of a reflex, the sensory neuron has the important task of initiating the reflex response quickly and efficiently without directly involving the brain.

Motor Neuron

Motor neurons are nerve cells that carry signals from the central nervous system to effector muscles or glands. They are critical in executing a response after receiving a signal from a sensory neuron.
After the sensory neuron detects a stimulus and relays this via a synapse in the spinal cord, the motor neuron receives this signal.
The motor neuron's role is to then convert this signal into an action, such as contracting a muscle or triggering a gland. This is why motor neurons are essential for creating a rapid and immediate response, such as pulling your hand away from a hot surface.

Synapse

A synapse is the junction where two neurons communicate. It serves as the site for chemical or electrical signaling between neurons.
Within a reflex arc, the synapse places a sensory neuron in contact with a motor neuron. This is a crucial step because it ensures the proper relay of the signal.
At a chemical synapse, neurotransmitters are released from the sensory neuron and bind to receptors on the motor neuron, allowing the signal to pass through.
In a reflex arc like the knee-jerk reflex, the synapse is located within the spinal cord area of the central nervous system, helping in quick signal transmission.

Spinal Cord

The spinal cord is a critical component of the central nervous system, serving as a conduit for messages between the brain and the rest of the body. For reflex actions, the spinal cord acts as the primary processing center, promptly responding to signals.
In a reflex arc, the spinal cord is where the sensory neuron and motor neuron meet and synapse.
This location allows the reflex actions to occur rapidly by bypassing the brain, which would delay response time. Such efficiency is vital for survival as it enables a quick reaction to potentially harmful stimuli.

Central Nervous System

The central nervous system (CNS) is composed of the brain and spinal cord. It processes external information and coordinates activity throughout the body.
In the context of a reflex arc, the CNS, specifically the spinal cord, facilitates the relay of information between sensory and motor neurons. This system prioritizes speed and efficiency to ensure a quick response.
Despite the brain's usual role in processing complex information, reflex arcs demonstrate how the CNS can delegate processing power to the spinal cord for rapid involuntary responses, displaying the adaptive nature of this vital system.