Muscle Structure And Function Flashcards
How many muscles and joints I’m the body
650 muscles and 187 joints
Describe cardiac muscle
Found in heart and circulates blood
Involuntary muscle contraction (ANS)
Small cells and limited ability to repair
Single nucleus in cardiac muscle cells
Many large mitochondria
Cardiac muscle required ATP for constant oxygen supply
Cardiac muscle cells also use lactic acid from skeletal muscle fibres to make ATP
Contraction speed is moderate
Branched cylindrical fibres with central nucleus,
Intercalated discs join neighbouring fibres
Striated muscle cells
Skeletal muscle
Much larger muscle cells- up 30cm long
These cells can partially repair by satellite cells
Multinucleate cells
Under voluntary control (somatic ns)
Attached by tendons to bones
Contraction speed is fast
Long cylindrical fibres with many nuclei at the periphery and striated,
Smooth muscle
Walls of organs like intestines, wall of blood vessels , stomach and oesophagus
Single nucleus in their cells
Fibre thickest in the middle and thinner at periphery - not striated
Can divide and repair itself If damaged- by pericytes
Involuntary muscle contractions (ANS)
Contraction speed is slow
Connective tissue layers
Epimysium- connective tissue around whole muscle
Perimysium- divides muscle into small bundles - the perimysium surrounds fascicles
Endomyisum is connective tissue around individual muscle cell
Myofibril - smallest component makes up muscle fibres
Size order of connective tissue
Largest is epimysium
Perimysium
Endomysium
Skeletal muscle fibre
Functions of muscle tissue
Produce movement of body
Stabilise body positions
Regulate organ volumes eg, sphincter muscles empty bowel or bladder
Move substances through body eg, lymph, blood, air, urine, food or sperm. Also muscle pump in leg for venous return.
Produces heat - involuntary contractions , converts some energy to heat.
Properties of muscle tissue
EEECC
Excitability - responding to a stimulus (chemicals released from nerve cells)
Extensibility - stretched without getting damaged
Elasticity- able to return to original shape after being stretched
Conductivity- ability to propagate electric signals over membrane so muscle fibres contract simultaneously.
Contractility- able to shorten and generate force
Why is skeletal muscle multinucleate
In development, formed by many myoblasts that fuse together. Every myoblast has nucleus so muscle fibre has many nuclei.
Myoblasts that don’t fuse into muscle become satellite cells - muscle stem cells to repair muscle tissue damage.
7 roles of skeletal muscle
Produce skeletal movement
Maintain body position
Support soft and hard tissues - eg, abdominal wall and pelvic floor support abdominal contents.
Guard body openings - sphincter muscles that can contract or close a bodily opening eg, control faeces removal from anus
Maintain body temperature
Store nutrient reserves like glycogen
Role in proprioception
Connective tissue for skeletal muscles has:
Nerves
Blood vessels
Muscle tissue - muscle fibres
EPIMYSIUM
Surrounds entire muscle
Exterior collagen layer - fibrous and irregular
Connects to deep fascia
Separates muscles from surrounding tissue and prevents friction between other muscles and bones
PERIMYSIUM
Surrounds muscle fibres in fascicles
Made of 50% elastic and 50% collagen fibres
ContIns blood vessels and nerve supply to fascicles
ENDOMYSIUM
Surrounds individual muscle cells
Has more elastic fibres
Loosely connects muscle fibres adjacent to each other
Contains capillaries and nerve fibres for muscle cells
Contains satellite cells stem cells
What do the three layers form?
Endo, peri and epimysium combine to form a tendon or an aponeurosis (broad, sheet like fibrous tissue in wide attachment area)
Tendon transfers force from muscle to bone. Musc,e cells shorten and contract to pull on tendon which pulls on the bone to produce movement.
In which layers will you find the nerves and blood vessels?
Perimysium contains blood vessels and nerves for fascicles
Endomysium contains capillaries and nerve fibres for muscle cells
Nerve supply to muscles
Skeletal muscles innervated by peripheral nerves
Fascicles get innervated by a motor neurone
Each muscle cell is supplied by a single branch of the motor neurone
Motor nerve + muscle fibres it supplies = Motor unit
In strength training you get more motor units in the muscle and then processes slow down.
Blood supply
Muscles have extensive vascular systems that:
Supply large amounts of oxygen for strong muscle contractions
Supply nutrients
Carry wastes away eg, lactic acid, oxygen, ADP, water
Each muscle cell is in contact with one or two capillaries
Nerve fibres and capillaries found in endomysium between individual cells.
Development of skeletal muscle cells
Muscle cells develop by fusion of myoblasts.
Some myoblasts don’t fuse and they become satellite cells - stem cells to repair damaged muscle
So summary of skeletal muscle cells:
Long (30cm) and cylindrical
Develop through fusion of myoblasts (mesodermal cells)
Become very large
Multinucleate from fusion of many myoblasts
Nuclei around periphery of the cell
Contain many mitochondria (energy used for muscle contractions)
Sarcolemma
Sarcolemma is muscle cell membrane
Surrounds the sarcoplasm
Sarcolpasm is filled wit tiny threads of myofibrils and myoglobin (red coloured oxygen-binding protein).
T tubules encircle each myofibrils
A change in transmembrane potential causes muscle contraction
T transverse tubules
Invagination of the sarcolemma into the sarcoplasm
T tubule functions :
Filled with extracellular fluid
Carry muscle action potentials down into cell
Allows entire muscle fibre to contract simultaneously.
Mitochondria placed in rows along a muscle fibre. They are near the proteins that use ATP for contraction.
Sarcoplasmic reticulum
Membranous structure around each myofibril
System of tubular sacs similar to a SER
Sarcoplasmic reticulum helps to transmit action potentials to the myofibril
They form terminal cisternae chambers at their ends that attaches to T tubules
Terminal cisternae store calcium ions + release them to start muscle contraction
What is a triad?
A triad is 1 T tubule + 2 terminal cisternae
They concentrate calcium ions by ion pumps
Concentration of calcium in terminal cisternae is 40,000 times as much as the surrounding sarcoplasm.
Terminal cisternae release calcium ions into sarcomeres to begin muscle contractions
Myofibrils and myofilaments
Each muscle cell filled with many threads called myofibrils, separated by sarocplasmic reticulum
Myofibrils made of many myofilaments
Myofilaments are contractile proteins of muscle (actin and myosin)
Largest to smallest component of a muscle
Muscle Fascicles Muscle fibres Myofibrils Myofilaments Sarcomeres
Myofilaments and the sarcomeres
Thick and thin filaments overlap each other in a pattern to form striations. (I bands and A bands).
I band = only actin
A band= myosin and actin
In overlap A band region, 6 actin filaments surround each myosin filament
Sarcomeres are small contractile units of the myofibrils. Ends of sarcomeres marked with a Z-line.
Middle of each sarcomeres has an M line
Around M line is the H zone with only myosin filaments
Summary of sacrcomeres
Contractile units of muscle
Structural units of myofibrils
Form visible striations within myofibril
Transverse T tubules encircle sarcomeres near zones of overlap
Calcium ions released by SR cause thick and thin filaments to interact
What is titin?
Muscle protein may be useful for eccentric contractions
Titin joins myosin to Z line and prevents it overstretchinf
So the muscle can return back to normal size
