Activity 4.2.1: Muscle Rules
Introduction
All movement in the human body, from wiggling a toe or swimming a mile to eating
and digesting a sandwich, is the result of muscle action. In previous lessons, you
have learned about connective and nervous tissue. In this unit, you will explore the
structure and function of another incredible tissue -- the muscle.
When we think of muscles, we usually focus on the muscles that move our bones
and allow us to move about the Earth; the tissues we see from the outside. But
inside the amazing human, you will find other types of muscle tissue that work
silently to move substances around the body. Your heart keeps beating and your
food continues to digest even when you fall fast asleep and close your conscious
mind for the day. Without muscle moving blood or distributing nutrients from food,
the human machine would power down.
There are 206 bones in the human body, but over 600 skeletal muscles allow our
bodies to move in different directions. Over sixty of these muscles are found in your
face alone. You use forty of these muscles every time you frown, but only twenty
muscles when you smile. The human body is even built to make it easier to be
happy than to be sad.
Skeletal muscles are attached to bones with tough cords or sheets called
tendons
and these bones meet other bones at junctions called
joints
. The contraction or
shortening of muscles pulls on bone and moves the body.
In this activity, you will observe and compare the structure and function of the three
types of muscle tissue. You will explore the structure of skeletal muscle both by
looking at slides and by creating a model of a muscle unit. Before you move on to
building actual muscle groups, a series of demonstrations will help you see that the
placement of muscles on bones follows specific patterns and rules. These rules will
