Muscular System The skeleton and muscles function together as the musculoskeletal system. This system plays an important homeostatic role: allowing the individual to move to more favorable external conditions.

Muscular System The muscular system is the biological system of humans that allows to move. Muscle (from Latin musculus “little mouse”). More than 50% of body weight is muscle!!! Muscles convert chemical energy into mechanical energy. Muscles NEVER push, they ONLY pull.

Muscular System Deltoid Pectoralis major Biceps brachi Gluteus maximus Rectus femoris Gastrocnemius

Classification of muscles: Muscular System Classification of muscles: I- Voluntary muscles II- Involuntary muscles

Classification of muscles: Muscular System Classification of muscles: I- Voluntary muscles - Voluntary muscles are controlled by thinking about what you want them to do. - People can run and talk because of voluntary muscles. - e.g., skeletal muscles

Classification of muscles: Muscular System Classification of muscles: II- Involuntary muscles - Involuntary muscles are controlled by the brain without thinking about them. - e.g., Heart and blood vessels. Some muscles are both voluntary and involuntary, the muscles that control breathing are an example.

Functions of the muscles Muscular System Functions of the muscles Movement Warmth Posture

Functions of the muscles Muscular System Functions of the muscles Movement: almost all movements by the human body result from muscle contraction.

Functions of the muscles Muscular System Functions of the muscles 2. Warmth: any activity by muscles generates heat as a byproduct, which is vital in maintaining normal body temperature

Functions of the muscles Muscular System Functions of the muscles 3. Posture: muscle lend support to the body and help it maintain posture against the force of gravity.

Muscular System Muscle Properties Ability to contract Ability to be stretched Ability to respond to a stimulus

Muscular System Muscle is attached to the bone by tendons (tough connective tissue) and other tissues. Tendons attach muscle to bone; the origin is the more stationary bone, the insertion is the more movable bone.

Muscular System

Muscular System Functional Organization of Skeletal Muscle Single Muscle Fibers A muscle fiber is a single, multinucleated muscle cell. A muscle is made up of hundreds or even thousands of muscle fibers, depending on the muscle size.

Muscular System Single Muscle Fibers, cont’d The health of muscle depends on a sufficient nerve and blood supply, each skeletal muscle has a nerve ending that controls its activity (innervation), and an individual system to supply and drain blood (vascularization).

Functional Organization of Skeletal Muscle 2) Bundles of Muscles Muscular System Functional Organization of Skeletal Muscle 2) Bundles of Muscles Muscle fibers consist of bundles of threadlike structures called myofibrils. Each myofibrils is made up of two types of protein filaments, (Thick called myosin, Thin called actin).

Muscular System 2) Bundles of Muscles, cont’d Thin actin filaments are anchored at their midpoints to a structure called the z-line. The region from one z-line to the next is called a sarcomere, which is the functional unit of muscle contractions.

Muscular System All muscle cells produce adenosine triphosphate (ATP) molecules which are used to power the movement of the myosin. Myosin Actin Sarcomere

Muscular System whereas most cells have a single nucleus, muscle fibers have as many as 100 or more nuclei (multinucleated) The other difference is that they can extend the entire length of a muscle.

Muscular System - Each of more than 650 muscles is served by nerves which link the muscle to the brain and spinal cord (Neuromuscular system).

Muscular System - When they receive a signal from the brain, muscle fibers can contract. - The strength of a muscle contraction depends on how many fibers contract at the same time.

Muscular System

Muscular System - In order for a muscle to contract or shorten, muscle fibers must be stimulated by nerve impulses sent through motor neurons or nerves (Neuromuscular junctions). These impulses originate in the brain, then rundown the spine, then they branch out to all parts of the body.

Muscular System In order to create movement, muscles must act in pairs. Muscles are arranged on the skeleton on such a way that the flexing or contracting of one muscle is usually balanced by the lengthening or relaxation of another muscle or group of muscles. In other words, when one muscle or set of muscle contracts, the other relaxes.

Muscular System

Muscular System - When a nerve impulse reaches the end of the motor neuron at the neuromuscular junction, acetylcholine (a chemical neurotransmitter) is released, then it travels across a small gap between the motor neuron and the muscle fiber and attaches to receptors on the membrane of muscle fiber.

Muscular System

Muscular System Muscle Types Skeletal Smooth Cardiac

Muscular System

Muscular System Skeletal muscles or Striated muscles The tissue is made of long fibers, with multiple nuclei. They are attached to bones by tendons. Many of these are voluntary, but some are involuntary. The most abundant tissue in the human body.

Muscular System Skeletal muscles: cont’d They are controlled by the somatic nervous system. An average adult male is made up of 40-50% of skeletal muscle an average adult female is made up of 30-40%.

Muscular System 2. Smooth muscles or Visceral muscles Are involuntary muscles, and found within the walls of organs and structure such as esophagus, stomach, intestines etc… Smooth muscle is NOT under conscious control. They are also found in blood vessels.

Muscular System 2. Smooth muscles: cont’d Smooth muscle occurs at various scales in almost every organ. In the skin (in which it controls erection of body hair) to the blood vessels and digestive tract (in which it controls the caliber of the lumen). Smooth muscle cells are elongated, have only one nucleus.

Muscular System 3. Cardiac muscles These muscles are attached to other muscles instead of bones and tendons. These muscles are involuntary. They are striated with multiple nuclei. Is a specialized kind of muscle found only within the HEART.

Muscular System 3. Cardiac muscles: cont’d Cardiac muscle are typically branched like a tree branch and connect to other cardiac muscle fiber through intercalated discs. Although that they are considered involuntary muscles, they do respond to psychological states such as stress and excitement.

Muscular System All three muscles use the movement of actin against myosin to create contraction. In skeletal muscle, contraction is stimulated by electrical impulses transmitted by the nerves.

Muscular System Cardiac and smooth muscle contractions are stimulated by internal pacemakers cells who regularly contract, and propagate contractions to other muscle cells they are in contact with. All skeletal muscle and many smooth muscle contractions are facilitated by the neurotransmitter acetycholine.

Muscular System Cardiac and skeletal muscles are “striated” and they contain sarcomeres and are packed into highly-regular arrangements of bundles; smooth muscle has neither. Cardiac Smooth Skeletal

Muscular System While skeletal muscles are arranged in regular, parallel bundles, cardiac muscle connects at branching, irregular angels. Cardiac Smooth Skeletal

Muscular System Striated muscles contracts and relaxes in short, intense bursts, whereas smooth muscle sustains longer or even near-permanent contractions. Cardiac Smooth Skeletal

Muscle tone Muscular System Even when the body is at rest, certain muscle fibers in all muscles are contracting. This activity is directed by the brain and cannot be controlled consciously. This state of continuous partial muscle contraction is known as muscle tone.

Muscle tone Muscular System These contractions are not enough to produce movement, but do tense and firm the muscles. In doing so, they keep the muscles firm, healthy and ready for action. Muscle tone is important because it helps individuals maintain an upright posture.

Muscular System Muscle facts: Smallest muscle in the body: (Stapedius) the muscle that activates the stirrup, the small bone that sends vibrations from the eardrum to the inner ear. Largest muscle in the body: (Latissimus dorsi) the large, flat muscle that covers the middle and lower back.

Muscular System Muscle facts: Longest muscle in the body: (Sartorius) the straplike muscle that runs diagonally from the waist down across the front of the thigh to the knee. Strongest muscle in the body: (Glutus maximus) the muscle pair of the hip that form most of the flesh of the buttocks.

Muscular System Muscle facts: Fastest-reacting muscle in the body: (Orbicularis oculi) the muscle that encircles the eye and closes the eyelid. It contracts in less than 0.01 second. Contrary to popular belief, the number of muscle fibers cannot be increased through exercise; instead, the muscle cells simply get bigger (hypertrophy) or split (hyperplasia).