Smooth muscle and Related Topics

Muscle contraction

Activation of tension-generating sites within muscle cells.

In vertebrate animals, there are three types of muscle tissues: 1) skeletal, 2) smooth, and 3) cardiac

Sliding filament theory: A sarcomere in relaxed (above) and contracted (below) positions

Force–velocity relationship: right of the vertical axis concentric contractions (the muscle is shortening), left of the axis eccentric contractions (the muscle is lengthened under load); power developed by the muscle in red. Since power is equal to force times velocity, the muscle generates no power at either isometric force (due to zero velocity) or maximal velocity (due to zero force). The optimal shortening velocity for power generation is approximately one-third of maximum shortening velocity.

Swellings called varicosities belonging to an autonomic neuron innervate the smooth muscle cells.

Key proteins involved in cardiac calcium cycling and excitation-contraction coupling

A simplified image showing earthworm movement via peristalsis

Asynchronous muscles power flight in most insect species. a: Wings b: Wing joint c: Dorsoventral muscles power the upstroke d: Dorsolongitudinal muscles (DLM) power the downstroke. The DLMs are oriented out of the page.

Electrodes touch a frog, and the legs twitch into the upward position

Unlike skeletal muscle, the contractions of smooth and cardiac muscles are myogenic (meaning that they are initiated by the smooth or heart muscle cells themselves instead of being stimulated by an outside event such as nerve stimulation), although they can be modulated by stimuli from the autonomic nervous system.

Muscle cell

Diagram of skeletal muscle fiber structure

A muscle cell is also known as a myocyte when referring to either a cardiac muscle cell (cardiomyocyte), or a smooth muscle cell as these are both small cells.

The iris in humans is the colored (typically brown, blue, or green) area, with the pupil (the circular black spot) in its center, and surrounded by the white sclera.

Iris (anatomy)

Thin, annular structure in the eye, responsible for controlling the diameter and size of the pupil, thus the amount of light reaching the retina.

Light micrograph of the iris near to the pupil. M. sph. sphincter muscle, L lens

Anterior chamber cross-section imaged by an SD-OCT.

Among human phenotypes, blue-green-gray eyes are a relatively rare eye color and the exact color is often perceived to vary according to its surroundings.

Adult male with amber-colored eyes: This color is extremely rare and occurs when an unusually stronger presence of the yellow pigment (lipochrome) exists in the iris, with a rather small amount of pigment (melanin). This gives the eye an orange copper/gold hue.

Example of a blue iris featuring a yellow iris nevus (eye freckle)

Example of heterochromia - one eye of the subject is brown, the other hazel.

Fluorescein angiograpy of the iris reveals a radial layout of blood vessels.

The muscle cells of the iris are smooth muscle in mammals and amphibians, but are striated muscle in reptiles (including birds).

Cardiac muscle

3D rendering showing thick myocardium within the heart wall.

The swirling musculature of the heart ensures effective pumping of blood.

Intercalated discs are part of the cardiac muscle cell sarcolemma and they contain gap junctions and desmosomes.

Cardiac muscle (also called heart muscle or myocardium) is one of three types of vertebrate muscle tissue, with the other two being skeletal muscle and smooth muscle.

Urinary bladder

Hollow organ in humans and other vertebrates that stores urine from the kidneys before disposal by urination.

Male and female urinary bladders in lateral cross-section

Bladder location and associated structures in the male

Calcifications on bladder wall caused by urinary schistosomiasis

Cross-section of the bladder showing a cancer within it. When a cancer occurs it is most likely to be a transitional cell carcinoma.

Urinary bladder (black butterfly-like shape) and hyperplastic prostate (BPH) visualized by medical ultrasound

Layers of the urinary bladder wall and cross-section of the detrusor muscle

Anatomy of the male bladder, showing transitional epithelium and part of the wall in a histological cut-out

The trigone is an area of smooth muscle that forms the floor of the bladder above the urethra.

Diagram of stomach, intestines and rectum in the average human

Gastrointestinal tract

Tract or passageway of the digestive system that leads from the mouth to the anus.

It is considerably shorter in the living body because the intestines, which are tubes of smooth muscle tissue, maintain constant muscle tone in a halfway-tense state but can relax in spots to allow for local distention and peristalsis.

Skeletal muscle

Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system that are mostly attached by tendons to bones of the skeleton.

Types of pennate muscle. A – unipennate; B – bipennate;
C – multipennate

ATPase staining of a muscle cross section. Type II fibers are dark, due to the alkaline pH of the preparation. In this example, the size of the type II fibers is considerably less than the type I fibers due to denervation atrophy.

Structure of muscle fibre showing a sarcomere under electron microscope with schematic explanation.

Diagram of sarcoplasmic reticulum with terminal cisternae and T-tubules.

Human embryo showing somites labelled as primitive segments.

When a sarcomere contracts, the Z lines move closer together, and the I band becomes smaller. The A band stays the same width. At full contraction, the thin and thick filaments overlap.

(a) Some ATP is stored in a resting muscle. As contraction starts, it is used up in seconds. More ATP is generated from creatine phosphate for about 15 seconds. (b) Each glucose molecule produces two ATP and two molecules of pyruvic acid, which can be used in aerobic respiration or converted to lactic acid. If oxygen is not available, pyruvic acid is converted to lactic acid, which may contribute to muscle fatigue. This occurs during strenuous exercise when high amounts of energy are needed but oxygen cannot be sufficiently delivered to muscle. (c) Aerobic respiration is the breakdown of glucose in the presence of oxygen (O2) to produce carbon dioxide, water, and ATP. Approximately 95 percent of the ATP required for resting or moderately active muscles is provided by aerobic respiration, which takes place in mitochondria.

Exercise-induced signaling pathways in skeletal muscle that determine specialized characteristics of slow- and fast-twitch muscle fibers

Jogging is one form of aerobic exercise.

In muscular dystrophy, the affected tissues become disorganized and the concentration of dystrophin (green) is greatly reduced.

Prisoner of war exhibiting muscle loss as a result of malnutrition.

The other types of muscle are cardiac muscle which is also striated and smooth muscle which is non-striated; both of these types of muscle tissue are classified as involuntary, or, under the control of the autonomic nervous system.

Myosin

Myosins are a superfamily of motor proteins best known for their roles in muscle contraction and in a wide range of other motility processes in eukaryotes.