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Due to system maintenance, CK-12 will be unavailable on 8/19/2016 from 6:00p.m to 10:00p.m. PT.

# 5.1: Planning

Difficulty Level: At Grade Created by: CK-12

## Key Ideas

• A reflex is the simplest circuit in the nervous system.
• Once triggered by a stimulus, a reflex goes to completion and causes a response, such as a muscle reaction. Some reflexes are easier to control than others.
• The five parts of a reflex arc are the sensor, sensory neuron, control center, motor neuron, and muscle.

## Overview

In the previous sections students learned about components of the nervous system. In this section they investigate a nerve circuit. They learn that reflexes are simple circuits in the nervous system that result in a response. Students identify reflexes, which are an important part of behavior and serve as protection from harm.

## Objectives

Students:

\begin{align*}\checkmark\end{align*} demonstrate and explain the five-part sequence of a reflex arc.

\begin{align*}\checkmark\end{align*} distinguish between a motor neuron and a sensory neuron.

\begin{align*}\checkmark\end{align*} explain the role of an inhibitory interneuron in a reflex.

reflex, stimulus

## Student Materials

### Activity 4-1: How Fast Is Your Reaction Time?

• Activity Report
• 20 cm metric ruler

## Teacher Materials

### Activity 4-1: How Fast Is Your Reaction Time?

• Activity Report Answer Key

See Activity 4-1 in the Student Edition

### Activity 4-1: How Fast Is Your Reaction Time

• Gather 20 cm\begin{align*}20 \ cm\end{align*} rulers.

## Interdisciplinary Connections

Math Use strings of holiday minilights set to sequence mode to illustrate the nerve impulse traveling down the axon.

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Subjects:
6 , 7 , 8
Date Created:
Sep 08, 2014