Types, structure and functions of muscles

Up to 40–50% of the adult body weight is made up of elongated cells, which make up muscle tissue and change length in response to stimulation. A muscle cell changes its length by converting the mechanical energy of contraction from the chemical energy of ATP. Muscle contraction and relaxation alternate to produce motion. Muscle tissues also stabilize body position, control organ volume, produce heat, propel fluids, and move food via different bodily systems.

Functions of Muscle

• Movement
  • The skeletal muscles enable whole-body movement, including head nodding, walking, running, and locomotion, as well as movement of specific body parts like the finger or hand.
• Stabilization
  • Contraction of skeletal muscles stabilizes joints and aids in preserving body posture, such as standing or sitting straight.
• Generating Heat (Thermogenesis)
  • Heat is produced when skeletal muscles contract.
• Storage
  • Some smooth muscles serve as temporary storage. For instance, the stomach temporarily stores food, while the bladder temporarily stores pee.

Physiological Characteristics of Muscle Tissue

Four unique qualities of muscular tissue make it possible for it to function and preserve homeostasis.

•  Contractility
  • Muscular tissue must possess contractility in order to contract vigorously in response to an action potential. The length or tension of the muscle fibers changes as a result of internal muscle events.
• Extensibility
  • Muscle tissue's extensibility refers to its capacity for stretching without suffering harm. Even when a muscle is already stretched, it still enables strong contractions.
• Elasticity
  • The capacity of muscle tissue to regain its initial length and shape following contraction or extension is known as elasticity.
•  Electrical Excitability (Irritability)
  • It is a characteristic of both nerve and muscle cells. Excitability is the capacity to generate electrical signals known as action potentials in response to specific stimuli.

Types of Muscular Movement

A coordinated effort of various skeletal muscle groups causes each movement at a joint. These muscle groups are categorized and given names based on their intended use: -

• Prime Movers (Agonists)
  • These muscles are the ones that contract to create a specific movement, such as the biceps producing forearm flexion and the hamstrings creating knee flexion.
• Antagonists (Opponents)
  • They are opposed to the main forces. They cause the limbs to expand, for example, the quadriceps femoris muscle in the thigh causes the knee joint to extend, and so on.
• Fixators
  • ​​​​​​​In order for the desired movement to occur at the distal joint on a fixed base, these muscle groups stabilize the proximal joint of an limb.
• Synergists
  • Synergists are the prime movers that pass through multiple joints. A few muscles stop the unwanted movements at the proximal joints.

Types of Muscle

Muscle tissues are divided into three groups based on their locations

• Skeletal
• Cardiac
• Smooth

Smooth Muscles

A non-striated, involuntary muscle is the smooth muscle. They go by the name visceral muscles as well. They are made up of cells with a single, centralized nucleus and a narrow spindle form. The walls of hollow visceral organs like the blood arteries, stomach, urine bladder, and respiratory passageways are covered in smooth muscles. Contrary to skeletal muscle, smooth muscle tissue contracts gradually and automatically. Smooth muscles' primary job is to move substances along a predetermined tract or passage within the body.

Characteristics of Smooth Muscles

• Spindle-shaped.
• Possess a solitary nucleus.
• without striations
• Located on the walls of hollow visceral organs, such as the bladder and stomach.
• Control that is forced.
• Inside the body, propels substances along a defined tract.
• Stacked or laid out in sheets. The two layers are typically arranged in two circular layers and one longitudinal layer.
• These muscles slowly and steadily contract.

Cardiac Muscle

The myocardial, in particular, comprises the cardiac muscle, which is an involuntary, striated muscle. The cardiac muscle tissue also contains intercalated discs, which are peculiar microscopic structures that link the ends of the cardiac muscle fibers to one another. The presence of cardiac muscle allows the heart to perform its pumping action, delivering blood to all body tissues and into blood arteries. This muscle resembles skeletal muscles because it is striated and smooth muscles since it is uncontrollable and involuntary.

Characteristics of Cardiac Muscle

• Only the heart contains this kind of muscle.
• It has ridges.
• Its actions cannot be intentionally controlled.
• Small amounts of delicate connective tissue cushion it.
• The bundles of this muscle are organized in a spiral or figure 8 pattern.
• The pacemaker cells in the heart regulate its regular rate of contraction.
• The heart muscle contains intercalated discs.