MUSCULAR CONTRACTION

-
The process of muscular contraction occurs over a number of key steps, including:
  • Depolarisation and calcium ion release
  • Actin and myosin cross-bridge formation 
  • Sliding mechanism of actin and myosin filaments
  • Sarcomere shortening (muscle contraction)



1.  Depolarisation and Calcium Ion Release
  • An action potential from a motor neuron triggers the release of acetylcholine into the motor end plate
  • Acetylcholine initiates depolarisation within the sarcolemma, which is spread through the muscle fibre via T tubules 
  • Depolarisation causes the sarcoplasmic reticulum to release stores of calcium ions (Ca2+)
  • Calcium ions play a pivotal role in initiating muscular contractions
Imagen relacionada

2.  Actin and Myosin Cross-Bridge Formation
  • On actin, the binding sites for the myosin heads are covered by a blocking complex (troponin and tropomyosin)
  • Calcium ions bind to troponin and reconfigure the complex, exposing the binding sites for the myosin heads
  • The myosin heads then form a cross-bridge with the actin filaments
Resultado de imagen de Actin and Myosin Cross-Bridge Formation

3.  Sliding Mechanism of Actin and Myosin
  • ATP binds to the myosin head, breaking the cross-bridge between actin and myosin
  • ATP hydrolysis causes the myosin heads to change position and swivel, moving them towards the next actin binding site
  • The myosin heads bind to the new actin sites and return to their original conformation
  • This reorientation drags the actin along the myosin in a sliding mechanism
  • The myosin heads move the actin filaments in a similar fashion to the way in which an oar propels a row boat

Imagen relacionada
4.  Sarcomere Shortening
  • The repeated reorientation of the myosin heads drags the actin filaments along the length of the myosin
  • As actin filaments are anchored to Z lines, the dragging of actin pulls the Z lines closer together, shortening the sarcomere
  • As the individual sarcomeres become shorter in length, the muscle fibres as a whole contracts
Resultado de imagen de process of sarcomere shortening

Comentarios

Publicar un comentario

Entradas populares de este blog

HUMAN EMBRYOGENESIS (STEP 1-4)

-
Imagen
Embryogenesis, the first eight weeks of development after fertilization, is an incredibly complicated process. It’s amazing that in eight weeks we’re transforming from a single cell to an organism with a multi-level body plan. The circulatory, excretory, and neurologic systems all begin to develop during this stage. Luckily, like with many complex biological concepts, fertilization can be broken down into smaller, simpler ideas. The big idea of embryogenesis is going from a single cell to a ball of cells to a set of tubes.  Starting from the very beginning Step 1 : a  zygote  is the single cell formed when an egg and a sperm cell fuse; the fusion is known as fertilization Step 2 : the first 12-to 24-hours after a zygote is formed are spent in  cleavage  – very rapid cell division The zygote’s first priority is dividing to make lots of new cells, so it’s first few days are spent in rapid mitotic division. With each round of division, it doubles in cell number. This divisio
Leer más

CENTRAL NERVOUS SYSTEM

-
Imagen
The Central Nervous System (CNS) The central nervous system is divided into two major parts: the brain and the spinal cord.   Firstly,we are going to talk about the brain. Parts of the Human Brain and their Subdivisions Human encephalon resembles, in structure and function, with that of the other vertebrates. The scientists reveal that parts of the human brain are Forebrain, Midbrain & Hindbrain and the related structures that collectively act as a single highly specialized unit. These parts work in coordination and perform  different functions of brain . More specifically, it is divided into five major regions, namely, telencephalon, diencephalon or inter-brain, myelencephalon (hindbrain/medulla oblongata), metencephalon and mesencephalon (midbrain). Here follows a precise but comprehensive description of each of the above given divisions. Telencephalon/Cerebrum—Anterior Part Of Forebrain Further composed of cerebral cortex, limbic and basal ganglia, it is th
Leer más

SKELETAL SYSTEM (PHYSIOLOGY)

-
Imagen
Support and Protection The skeletal system’s primary function is to form a solid framework that supports and protects the body’s organs and anchors the skeletal muscles. The bones of the axial skeleton act as a hard shell to protect the internal organs— from damage caused by external forces. The bones of the appendicular skeleton provide support and flexibility at the joints and anchor the muscles that move the limbs. Movement The bones of the skeletal system act as attachment points for the skeletal muscles of the body. Almost every skeletal muscle works by pulling two or more bones either closer together or further apart. Joints act as pivot points for the movement of the bones.  Hematopoiesis Red bone marrow produces red and white blood cells in a process known as hematopoiesis. Red bone marrow is found in the hollow space inside of bones known as the   medullary cavity .  The amount of red bone marrow drops off at the end of puberty, replaced by yellow bone marrow.
Leer más