this is a neuromuscular
​ junction

now let's bring in the stimulating neuron

why does the sarcoplasmic reticulum
​release its calcium ions?

Skeletal muscles are formed when many myoblasts (muscle stem cells) fuse forming one ginormous cell with many nuclei. Some of these cells (we call muscle cells muscle "fibers") are almost a foot long!  The many nuclei per cell permit the production of all of the proteins needed by the fiber. 

a bit more about the blocker troponin...

muscle cells are called muscle fibers

Multiple sclerosis (MS) is a chronic, degenerative disease of the central nervous system characterized by demyelination, or the loss of the myelin sheath that protects nerve fibers. This damage disrupts the flow of nerve impulses, leading to a wide range of neurological symptoms. 
MS is an autoimmune disorder:
the body's immune system mistakenly attacks its own myelin sheath. 

and another recap of contraction...

*cardiac muscle propels blood around           the body
*smooth muscle propels food along               the alimentary canal and form
         sphincters to control the                          entrance and exit of the digestive           system
*the partnering of skeletal muscles               and bones via tendons permits               movement, maintains posture               via constant tension on many                 muscle groups, provides                           protection for our internal                       organs and provides nutrition in              times of starvation

structure of a skeletal muscle

sarcolemma sarcoplasm sarcomere...

​see a pattern?

Fibromyalgia is significantly more common in women, with studies showing a female-to-male ratio of approximately 9:1. 

structure of a sarcomere

Muscle Types

the dystrophin protein protects muscle fibers from damage during contraction and relaxation.

what causes the muscle to contract?

ATP (cell energy) fuels these reactions.
If more ATP is added, the contraction lasts longer.
If there's no ATP added, the contraction ends and the filaments slide back to their original positions.
Troponin covers up the binding site again
​and the muscle is at rest. 

calcium binds to troponin, 
    a molecule on the thin filament  
this changes the shape of the
  troponin revealing a binding site

 heat is produced when muscles contract. almost 70% of  body heat is produced by muscles. blood is an essential element in temperature control during exercise, taking heat from the body core and working muscles and redirecting it to the skin when the body is overheating. When the body's internal temperature is too low, thermoreceptors tell the hypothalamus which then stimulates the skeletal muscles to rhythmically contract/relax to produce heat = shivering.

rigor mortis 

relaxation

neuromuscular disease:MS:

the head of the thick filament binds to the open site forming a cross bridge

a power stroke occurs = the head pivots and drags the thin filament along the thick filament.

all of the sacromeres shorten in a row              =
the whole muscle shortens

muscular dystrophies
are a group of 30+ genetic diseases which manifest as  progressive weakness and degeneration of the skeletal muscles that control movement. Duchenne MD is the most common form of MD and primarily affects boys since the allele is found on the X chromosome. A mutated allele prevents the production of 
dystrophin which is a protein that maintains the integrity of muscle. 

Fibromyalgia is a chronic condition characterized by widespread pain, fatigue, and other symptoms. While there's no cure, various treatments can help manage symptoms. The first signs of fibromyalgia often include chronic pain, fatigue, and sleep disturbances. 

the exact cause of fibromyalgia is unknown.
research suggests it's likely due to a combination of factors:
 genetic predisposition
 environmental triggers
 altered pain processing in the brain and central nervous system. 

the carpal tunnel is the passageway in the wrist where the median nerve and flexor tendons pass through a narrow opening.
Carpal tunnel syndrome
occurs when the tendons become inflamed, causing compression of the median nerve. Symptoms include pain, numbness, and eventual weakness in the hand. Carpal tunnel syndrome can occur for a variety of reasons including hereditary predisposition, repetitive movements, diabetes, or thyroid disorders.

contraction

Troponin is a actually protein attached to another protein called tropomyosin.
​When a muscle is relaxed, the troponin/tropomyosin complex sits on the actin covering the binding site for the myosin head. During contraction, calcium channels open in the sarcoplasmic reticulum and calcium is released. Calcium binds to troponin causing it to change shape. The new shape pulls it away from the binding site, exposing the binding site.

Now the myosin head can attach to this site on the actin and "row".

Myogenesis:
​making muscle

A sarcomereis the functional unit of a muscle fiber responsible for the contraction of muscles.
Each sarcomere is  composed of thick and thin filaments.
Sacrcomeres are lined up end to end
parallel ​to the length of a muscle fiber.
As the sarcomeres shorten, the whole muscle shortens.

fibromylagia

The Muscular System

Muscle tissue exhibits:

1. contractibility (muscles can contract/shorten when stimulated)
2.  extensibility (muscles can be stretched without tearing)
​3.  elasticity (muscles return to their resting/normal shape)

Tetanus is an infection caused by the Clostridium tetani bacterium.
The toxin produced by this anaerobic pathogen results in prolonged muscle contractions. Sometimes called “lockjaw”, tetanus can cause  neck and jaw muscles to lock. 

the functional unit of contraction in a muscle is called a scarcomere

pathology

calcium is released from the          sarcoplasmic reticulum. 

the sliding filament theory of muscle contraction

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recap of contraction...