Muscular System
List of muscles to know is posted in canvas.
Muscle Facts The average human heart will beat 3,000 million times in its lifetime and pump 48 million gallons of blood. Muscle is about 15% more dense than fat. The tongue consists of 8 different muscles. The masseter is the strongest muscle in the human body. It can exert as much as 975lb of force. The human heart creates enough pressure when it pumps blood, that it could squirt blood 30 feet. The smallest muscle in the body is the stapedius attached to the stapes in the ear. It takes the interaction of 72 different muscles to produce human speech.
Function of Muscles to pull against bones to produce movement. to maintain posture to stabilize joints to generate heat (mitochondria) to pump blood through the body (heart muscle).
Types of Muscle Skeletal – striated & voluntary Smooth – involuntary Cardiac – heart & involuntary The word “striated” means striped. Skeletal muscle appears striped under a microscope.
Origin and Insertion The origin of a muscle is a fixed bone for attachment. The insertion is the bone that the muscle moves when it contracts. The biceps and triceps are antagonistic muscles.
Gross Anatomy of a Muscle: Bundles 1. Actin & myosin myofilaments are bundled into myofibrils 2. Individual myofibrils (muscle cells) are bundled together into fibers. 3. Muscle fibers are bundled into fasicles 4. Fasicles are bundled into the whole muscle.
Linear view of muscle bundling… Whole Muscle myofibril Fasicle myofilaments Muscle Fiber
Gross Anatomy Skeletal Muscle
Muscle Layers
Myofibrils are made of myofilaments ACTIN = thin filaments (light bands) MYOSIN = thick filaments (dark bands)
How Muscles Work with the Nervous System NEUROMUSCULAR JUNCTION - where a motor nerve and muscle fiber come together
There are rules to muscle contractions… Threshold stimulus: motor neuron releases enough acetylcholine into synaptic cleft to reach threshold All-or-None Response: individual muscle fibers (and all the myofibrils within) will contract when stimulated. Recruitment: more and more fibers contract as the intensity of the stimulus increases. (stimulus is acetylcholine) more stim=heavier object
Actin & myosin contractile units are called sarcomeres. Contraction of sarcomeres contracts muscle as a whole.
When a muscle contracts the Z-line (sarcomere) shortens When a muscle contracts the Z-line (sarcomere) shortens. This is called the Sliding filament theory
Actin & Myosin Contraction Animation
As is the case with any body system… Issues can arise! -hypertrophy -atrophy -tetanus -muscle cramp -muscle fatigue -oxygen debt
Hypertrophy - muscles enlarge (working out or certain disorders) Atrophy - muscles become small and weak due to disuse
What is tetanus? Tetanus causes cholinosterase to not break down the acetylcholine in the synapse. This results in a person's muscles contracting and not relaxing. A tetanus shot must be administered shortly after exposure to the bacteria. Once you develop tetanus, there is no cure.
Muscle Fatigue - muscle loses ability to contract after prolonged exercise or strain Muscle Cramp - a sustained involuntary contraction Oxygen Debt - oxygen is used to create ATP, -- not have enough oxygen causes Lactic Acid to accumulate in the muscles → Soreness
What is rigor mortis? A few hours after a person or animal dies, the joints of the body stiffen and become locked in place. This stiffening is called rigor mortis. Depending on temperature and other conditions, rigor mortis lasts approximately 72 hours. The phenomenon is caused by the skeletal muscles partially contracting. The muscles are unable to relax, so the joints become fixed in place.
Body Worlds
Body Worlds
Body Worlds
Body Worlds
Body Worlds
Body Worlds