Muscle fibers & tissue Where chemical energy is used to produce force & movement

Types of muscle Identified based on structure, result of contraction, & control. Skeletal – attached to bone & responsible for supporting & moving the skeleton, neurons cause movement & is voluntary Smooth – surround organs & tubes, contraction changes diameter or propels fluids, controlled by ANS, hormones & other chemical messengers Cardiac- heart, contractions propel blood, regulated by ANS

Muscle Bundle of muscle fibers bundled together by connective tissue. Most fibers do not extend the entire length of a muscle

Striated (skeletal) muscle Under a microscope looks like a series of light and dark bands going across the muscle. Looks like it has different bands. Results from thin & thick filaments of the myofibrils

Muscle fiber Single skeletal muscle cell Can be as long as 20 cm nvo.com

Myofibrils Occupies most of the cytoplasm Long “filaments” that stretch the length of a muscle fiber (cell) Bundled together Sarcomere is a single unit inside the myofibril, they are lined up end to end repeating along the length of the myofibril.

Sarcomere Made of alternating thick & thin filaments Thick filament made of myosin Thin filament made of actin During contraction these filaments work to shorten the length of the sarcomere by “sliding” along one another. bodyplusmind.co.uk

Damage to fibers If destroyed cannot be replaced by other muscle fibers, but by undifferentiated cells near the muscle fibers. These do not have the capacity to rebuild severe damage. Most of restoration of strength comes from increasing the size of remaining fibers.

Calcium Calcium in the cytoplasm is important for muscle contraction The electrical stimulation provided to the muscle increases the concentration of Ca in the cytoplasm Increased levels of Ca make muscle contraction possible. Relaxation begins as Ca is pumped out of the cytoplasm hill.com/sites/ /student_view0/chapter10/ hill.com/sites/ /student_view0/chapter10/

Neuromuscular junction Area of muscle fiber under the axon terminal. ACh released into this junction ACh acts to open Ca channels to allow Ca into the cytoplasm. Can be re-stimulated before contraction ends, results in tetany (sustained muscle contraction)

Rigor Mortis The stiffening of skeletal muscles after death Complete by 12 hours post mortem Filaments are stuck in position & cannot slide Rigor mortis starts to disappear about 48 hours after death Disappears due to decomposition of muscle tissue

tendons Connect muscles to bones

Moving bones Analogy people pulling on a rope Each fiber is analogous to a person Rope is analogous to the connective tissue & tendon ex/landing.html ex/landing.html

Smooth muscle Single nucleus Able to divide to produce more cells Under a microscope does not have bands Innervated by autonomic nervous system Still uses actin, myosin and Ca for contractions. Fibers have a smaller diameter than skeletal fibers Has the ability to stretch a great deal w/o affecting function (bladder) class.kmu.edu.tw

Smooth Muscle Contraction Actin & myosin are not organized Can have 2X as much actin as myosin Ca acts on a different molecule that results in contraction Not as much ATP is required to, contraction is slower, but does not fatigue. Can maintain contraction for long period of time. cytochemistry.net

Smooth muscle innervation Axon forms many branches and access many areas along the same muscle fiber Some neurotransmitters excite others relax

Gap junctions Contraction may be stimulated by the contraction/excitation of surrounding fibers Channels between fibers allow flow of ions which conducts the impulse to the next cell Examples: Intestines, blood vessels, uterus

Cardiac muscle Combines properties of skeletal and smooth muscle Cells are striated, short, and have branching Has specialized cells responsible for conducting starting the heart beat and quickly spreading the contraction throughout the heart muscle

Cardiac innervation Receives signals from the sympathetic and parasympathetic system Sympathetic releases norepinephrine (responsible for racing heart) Parasympathetic releases ACh which inhibits contractions

Refractory period Period when a muscle cannot be excited Extremely long in cardiac muscle Cardiac muscle cannot experience tetany

Potassium Potassium also plays a role in muscle contraction Differences exist in the amount of K let back into the cell during contraction