review question (!):
explain how a muscle contracts.

 pacemaker cells initiate electrical impulses that spread throughout the heart. 
pacemaker cells have the property of automaticity = they can spontaneously generate electrical impulses 

*cardiac muscle propels blood around the body
*smooth muscle propels food along the alimentary canal and form
         sphincters to regulate entrance/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
         provides nutrition in times of starvation

structure of a skeletal muscle

 what are the different

types of contractions?

enough about skeletal muscle...
what about cardiac and smooth muscle

 Creatine phosphate stores energy in muscle cells. Resting muscles transfer excess ATP energy to creatine forming creatine phosphate.

1. a nerve impulse causes a neurotransmitter (ACh) to be released from the                  end of the nerve.
2. the neurotransmitter travels across the synapse to receptors on the muscle
          fiber's membrane.
3. the muscle fiber is triggered to send this impulse to the sacroplasmic                        reticulum where the calcium is stored.

 motor units

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

what causes the contraction?

 Anaerobic respiration can occurs in the absence of O2. Glucose is broken down into two pyruvates
which generates just a little bit of ATP. 
These pyruvates are then converted to lactic acid which can contribute to muscle fatigue as the lactic acid accumulates. 

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. 

smooth muscle

 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.

and a recap of the muscle
contraction process

this is the unique structure of a muscle fiber

neuromuscular disease:MS:

What is a twitch?
One stimulation/action potential from one motor neuron causes the fibers of its motor unit to contract.
​ Each single contraction is called a twitch, lasting just a few to 100 milliseconds.
Each twitch can be measured by the amount of tension (force of contraction) produced.

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. 

review question:
explain the sliding filament theory of muscle contraction

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.

where does the calcium come from?

muscle fibers are connected by intercalated discs which allow electrical signals to quickly pass from one cell to the next = coordinated contraction 

cardiac muscle

review question:
why is calcium necessary for muscle contraction?

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

review question:
identify parts of the muscle fiber (cell):

sarcomere
sarcoplasmic reticulum
myofibril
thin filament/actin
thick  filament/myosin

*calcium is released from the          sarcoplasmic reticulum and             binds to troponin, a molecule         on the thin filament 
  troponin was blocking a                  binding site on the filament

*this shifts the position of this
   molecule 

*the binding site is now open

​*a piece of the thick filament              called a "head" binds to this            open site forming a
   "cross bridge"

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

*the sarcomere shortens.
  as all of the sarcomere's go              through this same process at          once, the whole muscle                          shortens

the sliding filament theory of muscle contraction

Aerobic respiration produces >90% of the ATP energy required for muscle contraction.

​Glucose is broken down in the presence of O2 to produce CO2, H2O and ATP.

types of muscle fibers

  2. 

review question:
identify:
​epimysium
perimysium
endomysium
​fascicle
muscle fiber

 different people have different proportions of slow-twitch and fast-twitch muscle fibers which can influence their athletic abilities and overall fitness. most people have a mix of both but some individuals are predominantly slow-twitch or fast-twitch.​

     muscle fibers are innervated by only one motor neuron.
    a group of muscle fibers innervated by a single motor neuron is called a motor unit.
            the size of a motor unit is depends on the nature of the muscle. 
​

1. small motor units have a single motor neuron supplying a small number of muscle      fibers with the axon branching into several synaptic end bulbs. this permits very          fine motor control such as the muscles that move eyeballs and the finger control.

2. large motor units have a single motor neuron supplying a large number of muscle         fibers with the axon branching into thousands of synaptic end bulbs. this                         permits gross motor control such as the muscles that flex the arm or leg.

    some large motor units generate tension 50X that of the smallest motor units in            the muscle. think lifting a feather with the same muscles that can lift 10 lb weights.

review question:
what role does the sacrcoplasmic reticulum play in muscle contraction?

muscle strength is proportional to the # of myofibrils and sarcomeres in a muscle fiber not the number of muscle fibers. 

neuromuscular
​ junction

review question:
why does the sarcoplasmic reticulum release its calcium?

sarcoplasmic

reticulum

  3. 

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. 

  1. 

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. 

three types of muscle fiber
slow oxidative = SO
 fast oxidative = FO
  fast glycolytic = FG 

some interesting energy info...

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

rigor mortis 

review question:
how and why are small motor units different from large motor units?

what causes the calcium to be released

in the first place? 

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. 

muscle fatigue

how do muscles get stronger?

1. Isotonic contraction:
the tension in the muscle stays constant as the load moves and the muscle changes length.
   a. concentric contractions occur when
       the muscle shortens.
   b. eccentric contractions occur when the
       muscle lenthens. tension diminishes             and the muscle lengthens. 
2. Isometric contraction:
the muscle produces tension without moving a load even though the muscle shortens. the force produced does not overcome the resistance provided by the load. isometric contractions maintaining posture and joint stability.

most actions are a combination of isotonic and isometric contractions.

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. 

  4. 

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".

slow-twitch muscle fibers have a high concentration of myoglobin.
high myoglobin content gives slow-twitch fibers their reddish appearance and contributes to their ability to efficiently utilize oxygen for energy production, making them ideal for endurance. ​

type of muscle fiber has to do with myoglobin

Myogenesis:
​making muscle

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. 

review question:
describe four functions of the muscular system

pathology