muscular system Flashcards
what are muscles
a type of tissue that produces movement and heat in the body. there are 3 types of muscle tissue- skeletal, smooth and cardiac
characteristics of muscles
excitability- muscle cells stimulated into action
elasticity- after being extended it can go back to original length
extensibility- can extend in length
contractility- can shorten in length
functions of the muscle
maintain posture and body position, stabilising joints, movement, heat production
what is the skeletal muscle composed of
skeletal muscle cells, CT wrapping and tendons, blood vessels, nerve supply
structure of muscle tissue
it is composed of numerous elongated muscle cells (or fibers). the muscle cells are bunched together into fascicles which collectively make up the muscle belly of individual skeletal muscles. a nerve, artery and vein enter and exit a skeletal muscle belly near its central point then branch throughout the muscle. connective tissue wrappings surround the muscle belly, seperate fascicles and surround individual muscle cells.
what 2 ways does skeletal muscles attach to the bone via connective tissue
direct attachment- epimysium of muscle is fused to the periosteum of the bone
indirect attachment- connective tissue tendons extend beyond the muscle belly to attach to bone
each muscle attaches to at least 2 bones and crosses the joint between them to generate movement and stabilise the joint. the attachment site for a particular muscle is identified as..
origin- attachment site on a bone that does not move when the muscle contracts
insertion- attachment site on a bone that moves when the muscle contracts
what extra cellular organelles does muscle cells contain as-well as the usual ones
glycosomes- granules of glycogen (long chains of glucose stored in the cell)
myoglobin- red pigment that stores oxygen
myofibrils- rod like structure that contain the contractile components of the cell and make up the bulk of muscle cells
what do myofibrils have in them
the smallest contractile units of muscle called sarcomeres
what do sarcomeres contain
they are stacked end to end along the length of the myofibril and contain two types of myofilaments
thick filaments- composed of contractile protein myosin
thin filaments- composed of the contractile protiens actin, tropomyosin and troponin
how do muscles contract (skeletal muscles)
they are stimulated to contract by the neurotransmitter (acetylcholine) released from the somatic lower motor neurons and neuromuscular junctions. it binds to the excitatory receptors on the sarcolemma, generating an electrical impulse that is transmitted through the muscle cell by the t tubules. the action potential stimulates the sarcoplasmic reticulum to release calcium ions, which then bind to the troponin on the thin filament, exposing myosin binding sites on the actin protein.
axial muscle groups
these muscles stabilise, position and support structures of the head, neck and trunk.
appendicular muscles
stabilise, support and move the limbs
what connective tissue wraps around the muscle belly
epimysium
what connective tissue separates and surrounds the fascicle
perimysium
what connective tissue surrounds the individual fascicle muscle cells
endomysium
do muscle cells have multiple nuclei to make proteins in all areas of the cells in the muscle
yes. myofibrils are in the muscle cells and run the whole length of it, which are make of sarcomeres
what are z discs
they are at the end of each sarcomere
the process of myosin grabbing the actin (skeletal muscle contracting)
the cell has calcium in it that is stored away and then a nerve signal from the brains somatic nervous system (acetylcholine) goes to the muscle and excites it (excitability) and the cell releases the calcium which bind to the thin filament exposing binding sites for the myosin heads to reach and grab the actin. as the myosin heads flex, they pull the actin closer towards the centre of the sarcomere and the z discs get pulled closer to each other which makes the muscle shorten. this happens over and over again very fast so that the muscle fully contracts otherwise if the signal is too slow to excite the muscle cells then the muscle will fully extend back before the next contraction which causes a twitching motion
what is a motor unit
one lower motor neuron and all of the muscle cells it stimulates. a nerve cell can stimulate multiple cells to make it move. there are lots of motor units in a cell.
what does muscle strength depend on
how many motor units are activated at once
where is smooth muscle found/ functions
it forms one layer within organ walls. in all hollow organs apart from the heart and helps to move a lot of things- air, food, semen etc found in blood vessels, respiratory tract, digestive tract, renal tract
what is the shape of smooth muscle
they are short with tapered ends and are in layers.
what are the 2 layers of smooth muscle
circular layer is when it wraps around the circumference of the muscle and constrict the diameter
longitudinal layer is when they lay along the length of the muscle so they shorten the length of the muscles
how do smooth muscles contract
there are no sarcomeres of myofibrils but they have actin and myosin. they are arranged in a spiral from end to end of the muscle cell. this means that when the muscle contracts the cell gets shorter and squeezes and gets fatter in the middle. the cells are connected via gap junctions- the protein channels are open and connected so electrical signals are passed through so all the cells in the area contract together. these signals come from the autonomic nervous system
what is the autonomic nervous system
when it happens involuntary and unconsciously
what is the somatic nervous system
when it happens voluntary and consciously
what does cardiac muscle do
it is used to pump blood and is located in the heart.
what is the shape of cardiac muscles
the ends of the cells are split. the cells are connected by intercalated discs which have gap junctions in them (allows the signal to go from one cell to the other so they don’t all need to be stimulated)
how does cardiac muscles contract
they have myofibrils and sarcomeres. the contractions work the same as the skeletal muscles. the main stimulus is pacemaker cells which set the pace of contraction. - they self stimulate
factors of smooth muscle
- contains only a single nucleus
- cells are connected by gap junction
- found within the intestinal wall
- found lining the walls of blood vessels
- found in hollow organs apart from the heart
- controlled by unconscious nerve signals or hormones or pacemaker cells
factors of skeletal muscle
- attach to bones via tendons
- controlled by conscious nerve signals
- cells contain multiple nuclei
- cells are not connected, but wrapped in bundles
factors of cardiac muscle
- cells are connected by intercalated discs
- forms muscle tissue of the heart
- controlled by pacemaker cells or unconscious nerve signals
- cells have one or two nuclei
what is the sarcoplasmic reticulum (smooth endoplasmic reticulum)
it forms a tubular network around each myofibril and stores calcium ions necessary for muscle contraction
what is the sarcolemma (plasma membrane)
it has narrow tubes called T-tubules that extend through the muscle cell, surrounding individual myofibrils and allowing the transmission of action potentials throughout the entire muscle cell
what are the myofilaments anchored to
the thin filaments are anchored to the z line at the ends and the thick filaments are anchored to the m line at the centre
2 factors are required to generate enough tension in a muscle to cause movement or sustain a particular body position which are
recruitment- the number of motor units simulated (the more motor units working, the stringer the contraction)
frequency- the rate of action potential simulation/ firing within a motor unit (the greater the frequency the stronger the contraction)
describe the myosin- actin coupling/ cross bridge mechanism of skeletal contraction
when an action potential is triggered in a skeletal muscle it stimulates the release of calcium
calcium binds to troponin on actin leading to the exposure of myosin binding sites on the actin filaments
myosin heads then bind to the exposed binding sites on actin, making a cross bridge. myosin heads ‘flex’ (bend) pulling the actin towards the M line (center of the sarcomere)
this brings the z lines (ends of sarcomere) close together, shortening the sarcomere
ATP is required to release myosin heads from the actin binding sites, allowing further contraction to occur (in the presence of calcium) or relaxation (lengthening of the sarcomere)
how is smooth muscle different from skeletal muscle
the cells are shorter, with tapered ends
cells contain only one nucleus
there are no T-tubules
myofilaments are not arranged into sarcomeres, but instead the thick and thin filaments criss-cross each other diagonally in a spiral arrangement down the length of the cell
the thin filaments contain calmodulin instead of troponin for binding calcium (Ca2+)
the thick filaments contain myosin heads along their entire length
