Excitation and Contraction of Smooth Muscle | Contractile Mechanism

Описание: Here again, with an exciting Physiology video stuffed with in-depth knowledge. The topic under discussion is the Excitation and Contraction of Smooth Muscle.

So, bring your pens and paper to note down all the details Smooth muscle Feature, contraction of smooth muscle step, contraction of smooth muscle vs skeletal muscle, and what causes relaxation of smooth muscles?

▬ 📃 Excitation and Contraction of Smooth Muscle
Smooth muscle is composed of small fibers that are usually 1 to 5 micrometers in diameter and only 20 to 500 micrometers in length. Smooth muscle can generally be divided into two major types, which are:
🟡 Multi-unit smooth muscle
🟡 Unitary or single-unit smooth muscle

I know you always end up mixing these types.

You need to watch the video to know this. All the information is just under one click.

▬ 📜 Contractile Mechanism
Smooth muscle does not have the same striated arrangement of actin and myosin filaments as is found in skeletal muscle. Instead, electron micrographic techniques suggest the physical organization, which illustrates:
🟠 Actin Filaments
🟠 Dense Bodies
🟠 Cell membrane
🟠 Myofilament

▬ 📃 Comparison of Smooth Muscle
It is to be expected that both the physical and chemical characteristics of smooth muscle versus skeletal muscle contraction would differ. The main differences are:
🔵 Slow Cycling of the Myosin Cross-Bridges
🔵 Low Energy Requirement to Sustain Smooth Muscle Contraction
🔵 Slowness of Onset of Contraction and Relaxation
🔵 Maximum Force of Contraction
🔵 Latch Mechanism
🔵 Stress-Relaxation of Smooth Muscle

▬ 📜 Regulation of Contraction
👉 Smooth muscle contraction steps:
⚫️ Cytosolic calcium concentration increases.
⚫️ Calcium ions bind reversibly with calmodulin.
⚫️ Calmodulin-calcium complex joins with and activates MLCK.
⚫️ Attachment of the myosin head with the actin filament.
⚫️ Contraction of the smooth muscle.

👉 Smooth muscle relaxation steps:
🟣 Calcium ions must be removed from the intracellular fluids.
🟣 Calcium is then released from calmodulin.
🟣 Myosin phosphatase removes phosphate.
🟣 Detachment of the myosin head from the actin filament.
🟣 Relaxation of the smooth muscle.

▬ 📃 Nervous and Hormonal Control
Physiologic Anatomy of Unitary (visceral) smooth muscle cells:
🟢 Autonomic nerve fibers
🟢 Autonomic nerve varicosities
🟢 Neurotransmitter
🟢 Gap junctions

👉 Physiologic Anatomy of multi-unit smooth muscle:
🔴 Muscle changes length
🔴 Autonomic nerve varicosities

▬ 📜 Membrane and Action Potential
The action potentials of visceral smooth muscle occur in one of two forms:
🟣 Spike potentials
🟣 Action potentials with plateaus

▬ 📃 Depolarization of Multi-Unit Smooth Muscle
Two types of non-nervous and nonaction potential stimulating factors often involved are
🟤 Local tissue chemical factors
🟤 Various hormones

A powerful local feedback control system controls the blood flow to the local tissue area. Some of the specific control factors are as follows:
🟡 Lack of oxygen
🟡 Excess of carbon dioxide
🟡 Increased hydrogen ion concentration

Many circulating hormones in the blood affect smooth muscle contraction to some degree, and some have profound effects. Among the more important of these hormones are:
🔵 Norepinephrine
🔵 Epinephrine
🔵 Angiotensin II
🔵 Endothelin
🔵 Vasopressin
🔵 Oxytocin
🔵 Serotonin
🔵 Histamine

So that was all! The rest can be watched in the video.

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