Lab 4-The Muscular System7-11 Muscle cells are involved in every movement that our bodies perform. When muscles are stimulated they can shorten to produce movement relax to allow the body part to return to its original length Muscles must be pulled back to their original length either by gravity or by opposing muscles, called “antagonistic muscles”

Lab 4-The Muscular System There are 3 types of muscles: Skeletal muscles Cardiac muscles Smooth muscles

Lab 4-The Muscular System Skeletal muscles attach to the bones of our skeleton and provide strength and mobility for our body Cardiac muscle found in the heart; this muscle pumps blood throughout the body Smooth muscles found in most internal organs

Lab 4-The Muscular System Muscles may also be classified as voluntary (muscles over which we have conscious control) involuntary (muscles over which we have no conscious control)

Skeletal Muscle Is also called Striated or Voluntary muscle they have striations (or stripes) which are caused by alternating dark and light “bands” bands are composed of tightly packed contractile proteins called myofilaments Myofilaments composed of actin and myosin are multinucleated cells are arranged in a parallel fashion are responsible for all locomotion and manipulation they enable us to respond quickly to changes in the external environment

Skeletal Muscle Summary Key words to remember are striated, and voluntary Muscle fibers are long, cylindrical and multinucleated Fibers are structurally and functionally independent of each other Muscle can contract rapidly but tires easily and requires rest after short periods of activity

Cardiac Muscle Cells are striated BUT, (unlike skeletal muscle), the cells are short, fat, branched and interconnected Have specialized areas called intercalated disks where the cells connect with each other These connections allow cardiac muscle to work as a single, coordinated unit usually contracts at a steady rate set by the heart’s pacemaker, but neural controls allow for a faster beat for brief periods (i.e. when you perform intense activities)

Cardiac Muscle Summary Key words to remember are involuntary and intercalated disks Muscle is highly resistant to fatigue

Smooth Muscle Cells are shorter than skeletal and cardiac muscle cells Cells do not have striations (thus they are called smooth muscle) Cells have fewer contractile proteins (thus no striations) Cells are spindle shaped (thicker in the middle and tapered at each end); each cell has a centrally located nucleus Are found in the walls of hollow visceral organs (i.e. stomach, intestines, bladder, blood vessels) role is to force fluids and other substances through body channels

Smooth Muscle Summary Key words to remember are visceral, nonstriated, and involuntary Cells are short and spindle shaped muscle contractions are slow and sustained,

Skeletal Muscle Contraction Contractile proteins or myofilaments, called actin and myosin, slide past each other using energy from ATP molecules. These myofilaments produce alternating light and dark areas called striations The Z-line is a thin, dark line where sets of actin myofilaments are woven together The space between 2 Z-lines is called a sarcomere; a sarcomere is the smallest contractile unit of a muscle fiber

The Z-line is a thin, dark line where sets of actin myofilaments are woven together The space between 2 Z-lines is called a sarcomere A sarcomere is the smallest contractile unit of a muscle fiber

Muscle Contraction In order for a muscle to contract, its cells must be stimulated by a nerve The motor neuron secretes acetylcholine (ACh) at the neuromuscular junction (the space where the motor neuron and muscle cell meet). ACh is a neurotransmitter--a chemical which can either stimulate or inhibit another “excitable” cell (either a nerve cell or a muscle cell)

Muscle Contraction The ACh diffuses across the space between the neuron and the muscle cell (called the synaptic cleft) and binds to receptor sites on the muscle cell membrane. The ACh binding causes the muscle cell membrane to generate an electrical impulse which travels along the cell membrane and along the T-tubules (cylindrical extensions of the cell membrane which travel into the interior parts of the cell) the function of the T-tubules is to allow the electrical impulse to quickly travel to all cell parts

The T-tubules are in close contact with the sarcoplasmic reticulum. Muscle Contraction The T-tubules are in close contact with the sarcoplasmic reticulum. The sarcoplasmic reticulum stores calcium. The electrical impulse triggers the release of calcium from the sarcoplasmic reticulum so the muscle can contract. Relaxation of a muscle cell occurs when nerve cell stimulation stops.

Energy Use by Muscle Cells Muscle contraction requires energy ATP is the muscle’s energy source Typically muscle cells store enough ATP for only 30-40 seconds of heavy activity. After this, muscles must rely on stored glycogen. Glycogen is broken down (a process called glycolysis).

Energy Use by Muscle Cells Glucose molecules are removed from the glycogen and the cell uses the glucose to synthesize more ATP. Part of the glucose breakdown process can be done anaerobically. This is a fast process but only yields 2 ATP molecules per glucose molecule. It also produces lactic acid as a waste product which can make muscles sore.

Energy Use by Muscle Cells The most efficient, but much slower, process for energy production is aerobic metabolism. This yields 36 ATP molecules from 1 molecule of glucose. Carbon dioxide is produced as a waste product.

Gross Anatomy of Skeletal Muscle Individual muscle fibers are wrapped and held together by several different layers of connective tissue The outermost layer is called the epimysium and surrounds the whole muscle. The fibers within the muscle are grouped into fascicles or bundles and resemble a bunch of sticks. The perimysium surrounds each fascicle. The individual muscle fibers are surrounded by the endomysium.

Gross Anatomy of Skeletal Muscle Each of the connective tissue coverings are continuous with the other ones and also with the tendons located at the end of the muscle. Tendons attach muscle to bone.

Movememt If the muscle spans a joint, one bone moves while the other one remains stationary the muscle’s origin is on the bone which does not move the insertion is on the bone which moves Terms used to describe movement are on page 48 of your lab manual. You need to know the bulleted terms.

REMINDER 1. There are 4 slides to look at: Learn muscle tissues using the slides. Learn the motor nerve ending slide. 2. Learn the microstructure of muscles using models and the diagrams. 3. Learn the location and function of selected muscles in tables 7.1, 7.2 and 7.3. 4. Perform the muscle physiology experiments on page 58. 5. Complete the chart on page 59.