The peripheral portion of the central nervous system CNS controls the skeletal muscles. Thus, these muscles are under conscious, or voluntary, control. The basic unit is the muscle fiber with many nuclei. These muscle fibers are striated having transverse streaks and each acts independently of neighboring muscle fibers. Smooth muscle , found in the walls of the hollow internal organs such as blood vessels, the gastrointestinal tract , bladder , and uterus , is under control of the autonomic nervous system.
Home Bones muscles and joints. Actions for this page Listen Print. Summary Read the full fact sheet. On this page. Different types of muscle Make-up of muscle The neuromuscular system Shapes of skeletal muscle Muscle disorders Where to get help Things to remember.
There are about muscles in the human body. Muscles have a range of functions from pumping blood and supporting movement to lifting heavy weights or giving birth. Muscles work by either contracting or relaxing to cause movement.
This movement may be voluntary meaning the movement is made consciously or done without our conscious awareness involuntary. Glucose from carbohydrates in our diet fuels our muscles.
To work properly, muscle tissue also needs particular minerals, electrolytes and other dietary substances such as calcium, magnesium, potassium and sodium.
A range of problems can affect muscles — these are collectively known as myopathy. Muscle disorders may cause weakness, pain or even paralysis. Different types of muscle The three main types of muscle include: Skeletal muscle — the specialised tissue that is attached to bones and allows movement. Together, skeletal muscles and bones are called the musculoskeletal system also known as the locomotor system.
Generally speaking, skeletal muscle is grouped into opposing pairs such as the biceps and triceps on the front and back of the upper arm. Skeletal muscles are under our conscious control, which is why they are also known as voluntary muscles. Another term is striated muscles, since the tissue looks striped when viewed under a microscope. Smooth muscle — located in various internal structures including the digestive tract, uterus and blood vessels such as arteries. Smooth muscle is arranged in layered sheets that contract in waves along the length of the structure.
Another common term is involuntary muscle, since the motion of smooth muscle happens without our conscious awareness. Cardiac muscle — the muscle specific to the heart. The heart contracts and relaxes without our conscious awareness.
Although the currents generated by ions moving through these channel proteins are very small, they form the basis of both neural signaling and muscle contraction. Both neurons and skeletal muscle cells are electrically excitable, meaning that they are able to generate action potentials.
An action potential is a special type of electrical signal that can travel along a cell membrane as a wave. This allows a signal to be transmitted quickly and faithfully over long distances. The myosin then pulls the actin filaments toward the center, shortening the muscle fiber. In skeletal muscle, this sequence begins with signals from the somatic motor division of the nervous system. The motor neurons that tell the skeletal muscle fibers to contract originate in the spinal cord, with a smaller number located in the brainstem for activation of skeletal muscles of the face, head, and neck.
These neurons have long processes, called axons, which are specialized to transmit action potentials long distances— in this case, all the way from the spinal cord to the muscle itself which may be up to three feet away. The axons of multiple neurons bundle together to form nerves, like wires bundled together in a cable.
Signaling begins when a neuronal action potential travels along the axon of a motor neuron, and then along the individual branches to terminate at the NMJ. At the NMJ, the axon terminal releases a chemical messenger, or neurotransmitter , called acetylcholine ACh. The ACh molecules diffuse across a minute space called the synaptic cleft and bind to ACh receptors located within the motor end-plate of the sarcolemma on the other side of the synapse.
Once ACh binds, a channel in the ACh receptor opens and positively charged ions can pass through into the muscle fiber, causing it to depolarize , meaning that the membrane potential of the muscle fiber becomes less negative closer to zero. As the membrane depolarizes, another set of ion channels called voltage-gated sodium channels are triggered to open. Things happen very quickly in the world of excitable membranes just think about how quickly you can snap your fingers as soon as you decide to do it.
Immediately following depolarization of the membrane, it repolarizes, re-establishing the negative membrane potential. Meanwhile, the ACh in the synaptic cleft is degraded by the enzyme acetylcholinesterase AChE so that the ACh cannot rebind to a receptor and reopen its channel, which would cause unwanted extended muscle excitation and contraction.
Propagation of an action potential along the sarcolemma is the excitation portion of excitation-contraction coupling. The arrangement of a T-tubule with the membranes of SR on either side is called a triad Figure 7. The triad surrounds the cylindrical structure called a myofibril , which contains actin and myosin.
Skip to main content. Chapter 7: The Muscular System. Search for:. Skeletal Muscle Learning Objectives Describe the layers of connective tissues packaging skeletal muscle Explain how muscles work with tendons to move the body Identify areas of the skeletal muscle fibers Describe excitation-contraction coupling.
Interactive Link Watch this video to learn more about macro- and microstructures of skeletal muscles. The Neuromuscular Junction.
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