Muscle Function, Properties, Classification, Skeletal Muscle Structure

FUNCTIONS OF MUSCLE TISSUE

Functions of muscle tissue

Movement: Our body's skeleton gives enough rigidity to our body that skeletal muscles can yank and pull on it, resulting in body movements such as walking, chewing, running, lifting, manipulating objects with our hands, and picking our noses.
Maintenance of posture: Without much conscious control, our muscles generate a constant contractile force that allows us to maintain an erect or seated position, or posture.
Respiration: Our muscular system automatically drives movement of air into and out of our body.
Heat generation: Contraction of muscle tissue generates heat, which is essential for maintenance of temperature homeostasis. For instance, if our core body temperature falls, we shiver to generate more heat.
Communication: Muscle tissue allows us to talk, gesture, write, and convey our emotional state by doing such things as smiling or frowning.
Constriction of organs and blood vessels: Nutrients move through our digestive tract, urine is passed out of the body, and secretions are propelled out of glands by contraction of smooth muscle. Constriction or relaxation of blood vessels regulates blood pressure and blood distribution throughout the body.
Pumping blood: Blood moves through the blood vessels because our heart tirelessly receives blood and delivers it to all body tissues and organs.

PROPERTIES OF MUSCLE TISSUE

All muscle cells share several properties: contractility, excitability, extensibility, and elasticity:

Contractility is the ability of muscle cells to forcefully shorten. For instance, in order to flex (decrease the angle of a joint) your elbow you need to contract (shorten) the biceps brachii and other elbow flexor muscles in the anterior arm. Notice that in order to extend your elbow, the posterior arm extensor muscles need to contract. Thus, muscles can only pull, never push.
Excitability is the ability to respond to a stimulus, which may be delivered from a motor neuron or a hormone.
Extensibility is the ability of a muscle to be stretched. For instance, let's reconsider our elbow flexing motion we discussed earlier. In order to be able to flex the elbow, the elbow extensor muscles must extend in order to allow flexion to occur. Lack of extensibility is known as spasticity.
Elasticity is the ability to recoil or bounce back to the muscle's original length after being stretched.

THREE TYPES OF MUSCLE

Cardiac Muscle

Cardiac muscle is only found in the heart.

It is striated

It is involuntarily. (AUTOMATIC)

Skeletal Muscle

Skeletal muscle is also known as voluntary muscle because we can consciously, or voluntarily, control it in response to input by nerve cells.

It is striated ("striped") because it has a microscopically streaked or striped appearance.

Skeletal muscle and its associated connective tissue comprise about 40% of our weight.

Smooth Muscle

Smooth muscle is widely distributed throughout the body, being found in the walls of hollow organs such as our digestive, reproductive, and urinary tracts, tubes such as blood vessels and airways, and in other locations, such as the inside of the eye.

It is not striated

It is involuntarily. (AUTOMATIC)

Smooth muscle is sometimes known as visceral muscle because it is a major component of many internal (visceral) organs.

Hierarchy of Skeletal Muscle

Fibrous Connective Tissue (FCT)Fibres.

Endomysium: The endomysium is a meshwork of FCT that surrounds each striated muscle fibre individually.

Perimysium: A group of these striated muscle fibre is bound together in a bundle (fascicle) by an FCT envelope known as the perimysium.

Epimysium: The entire muscle is bound within an FCT sheath called the epimysium.

Muscle Cell/Fibre

👍Sarcoplasm is the cytoplasm of a muscle fibre.

It is a water solution containing ATP and phosphagens, as well as the enzymes and intermediate and product molecules involved in many metabolic reactions.

Muscles are composed of long bundles of cells called muscle fibres or myofibres or myocytes
Muscle fibres primarily consist of myofibrils, mitochondria, and a specialized structure known as the sarcoplasmic reticulum. There are hundreds of thousands of myofibrils in one muscle fibre
Myofibrils are made up of repeating subunits called sarcomeres
Sarcomere are made up of two types of filaments: thin filaments (Actin) and thick filaments (Myosin) referred to as myofilaments
When a muscle contracts, the sarcomeres shorten in length due to the myosin and actin filaments sliding over each other. This results in an overlap between the filaments and shortens the H-zone and the I band.