Tissues in Action · Lesson 7 of 11
Can we Control Movement in Our Body?
“Some muscles await instructions, while the heart politely ignores your management style.”
• Distinguish voluntary and involuntary movements. • Compare skeletal, smooth and cardiac muscles. • Relate muscle-cell structure to location and function. • Identify the main parts of a neuron. • Explain how nervous and muscular tissues coordinate responses.
Introduction
You can choose to lift a book, walk across a room, or raise your hand. These movements happen because certain muscles work under your conscious control. You can decide when these muscles should contract and when they should relax.
But many important movements inside your body happen automatically. You do not have to think about pushing food through your intestine, controlling the movement of the stomach, or making your heart beat again and again. These actions continue even when you are sleeping.
Because the body needs both voluntary and automatic movements, it has different types of muscular tissue. Some muscles help us perform movements that we control consciously, while others work on their own to keep essential internal processes running continuously.
A voluntary movement is performed under conscious control, such as writing, running or lifting an object.
An involuntary movement occurs automatically without conscious control, such as the movement of food through the intestine or the beating of the heart.
Skeletal muscle is attached to the skeleton and produces movements under conscious control.
Skeletal muscles attach to the skeleton and produce voluntary movement. Their fibres are long, cylindrical, unbranched and multinucleate. Alternating light and dark bands create a striated appearance. When these fibres contract, they pull on attached structures and move the skeleton.
Smooth muscle produces slow, continuous movements inside organs without conscious control.
Smooth muscle occurs in organs such as the stomach and intestine. Its spindle-shaped cells have one nucleus and no visible striations. Smooth muscle produces slow, continuous involuntary movements, including the movement of food through the digestive tract.
Cardiac muscle forms the heart and contracts rhythmically without conscious control.
Cardiac muscle occurs only in the heart. Its fibres are cylindrical and branched, usually with a single nucleus and faint striations. They contract rhythmically throughout life. Continuous action is supported by a rich blood supply and a large number of mitochondria, which provide the energy needed for repeated contraction.
| Feature | Skeletal muscle | Smooth muscle | Cardiac muscle |
|---|---|---|---|
| Control | Voluntary | Involuntary | Involuntary |
| Cell form | Long, cylindrical and unbranched | Spindle-shaped | Cylindrical and branched |
| Nuclei | Many | One | Usually one |
| Striations | Present | Absent | Faintly present |
| Location | Attached to skeleton | Walls of organs such as stomach and intestine | Heart |
| Movement | Body movement | Slow internal movement | Rhythmic heartbeat |
How Does the Body Sense, Communicate and Respond?
Muscles do not decide when to contract. Nervous tissue forms a communication network that receives information, processes it and carries instructions. The brain acts as a control centre for activities, memory and responses. During activity, for example, the brain can signal the heart to beat faster as oxygen demand rises.
A neuron, or nerve cell, is specialised to receive, process and transmit messages.
The cell body contains the nucleus and controls the cell’s activities. Dendrites receive signals from other neurons or receptors. The axon is a long fibre that carries a message away from the cell body. At its far end, axon terminals transmit the message to another cell.
Problem
How can nervous and muscular tissues cooperate when a hand touches something hot?
- 1.Sensory structures detect the harmful temperature.
- 2.Nervous tissue carries information through the communication network.
- 3.A response signal reaches the appropriate skeletal muscles.
- 4.The muscles contract and move the bones of the arm.
- 5.The hand is pulled away through coordinated nervous and muscular action.
Quiz
Which description best matches Voluntary Movement?
Which description best matches Involuntary Movement?
Which term matches this description: A voluntary movement is performed under conscious control, such as writing, running or lifting an object.
Which term matches this description: An involuntary movement occurs automatically without conscious control, such as the movement of food through the intestine or the beating of the heart.
Which statement is a key takeaway from this lesson?
Practice Problems
- Classify writing, heartbeat and movement of food through the intestine as voluntary or involuntary.
- Compare skeletal and smooth muscle cells.
- Which muscle is branched and works rhythmically?
- Arrange these parts in the direction followed by a message: axon terminals, dendrites, axon and cell body.
- Why can muscular tissue not coordinate body activities independently?
- Explain how muscle structure is connected to the function of each muscle type.
Key Takeaways
• Skeletal muscles produce voluntary movement. • Smooth and cardiac muscles work involuntarily. • Nervous tissue controls and coordinates body activities. • Dendrites receive messages, the axon carries them, and axon terminals pass them onward.