Skeletal muscle Flashcards
What are the different roles of skeletal muscles?
Force generation for movement (of the skeleton)
Force generation for breathing (diaphragm)
Heat movement ( shivering- homeostasis)
Metabolism - a reservoir for amino acids
forms of glucose storage-glucose can be released upon demand
What are the types of muscles found in the human body
Cardiac
Smooth muscles
Skeletal
Describe the structure of skeletal muscle
Striated skeletal muscle Voluntary Controlled by somatic nervous system no branching MULTI NUCLEATED
Describe the structure of cardiac muscle
Striated cardiac muscle Involuntary Controlled by autonomic nervous system branching cells joined by interrelated disk
Describe the structure of smooth muscle
Non-striated cardiac muscle Involuntary Controlled by autonomic nervous system single cells spindle shaped
Describe some of the properties of skeletal muscles
Human muscles fibre= muscle cell
40-100 um in diameter and several cm long
Myonuclei located in the periphery - controls the COMMON cytoplasm- packed with myofibrils and mitochondria.
Describe the role of tendons in muscle contraction
Muscles attach to the skeleton via tendons- which transmits muscles force to the bone- these cause the skeleton to move at the joint.
Tendons are stiff and strong as they are made up of collagen
How do muscles work?
They work by pulling
they work in antagonistic pairs which allows for a range of movements- skeleton can return to original position
Flexor muscle- decreases the angle anteriorly-the muscle that bend the joint
Extensor muscle- increases the angle anteriorly- the muscle that extends the joint
Different movements possible depending on the type of joint and the muscle arrangement
What are the types of muscle contraction?
Isotonic- dynamic
Isometric
Concentric
the muscles shortens when it contracts
Eccentric
the muscle lengthens during force production eg slowly extending muscle after flexion
Isometric
the muscle exerts the force without changing the length
eg moving an immovable object
Prime mover
Agonist- muscle contraction is concentric (bicep)
eg Gravity
Antagonist-
It apposes the action of the prime mover (tricep)
Fixator-
steadies and holds position through isometric contraction
Synergist-
Compliments the action of the prime mover either with single movement by acting as a fixator or an intervening joints
Describe the general structure of skeletal muscle and connective tissue
Epimysium- a piece of connective tissue (deep fascia) tough outermost layer surrounding the entire muscle
ensures that each muscle is separated and that there is a bit of fluid in that system- FRICTION FREE MOVEMENT- due to the lubrication
Perimysium -a piece of connective tissue which groups muscle fibres into fascicles. The space between fascicles allows for the vessels and nerves to supply muscle fibres
Endomysium- connective tissue seperating the muscle fibres- each one is electrically isolated as each one has a separate nerve supply- ensures that the structural integrity to remain
Blood vessels are embedded into the connective tissue
Tendons connect the bone to be continuous with muscle
How does the number of branching of nerve supply affect the function of muscles
POWER- branches are greater than 2000
CONTROLLED- branches few than 16
Describe the structure of the muscle fibres
Many myofibrils- Many contractile elements (sarcomeres)
Satellite cells
Sarcolemna-
Satellite cells are embedded into basal lamina
nuclei
T tubles-
terminal cisternae of sarcoplasmic reticulum- repeating series of networks around the myofibrils extending from one junction to another- meeting at terminal cisternae. Acts reservoirs for Ca 2+ and also contain many mitochondria
They contain voltage sensor proteins which activated when the membrane is depolarised- inducing sarcoplasmic reticulum to release Ca
What are the advantages and disadvantages to having a longer muscle fibre
good because the longer fibres will result in greater contraction potential
But it does mean that it is not possible to move material up and down the cell
THIS IS WHY THE CELL IS MULTI NUCLEATED
How are skeletal muscles formed
Myoblasts (single cell with single nuclei) encouraged to divide , expand and poliferate by responding to growth factor containing medium
To form muscle fibres, place in a medium of low growth factor which allows for differentiation
This will allow cells to fuse together to from a multinucleate myotube- immature muscle fibres
What satellite cells?
Satellite cells are undifferentiated- specialised muscle stem cells
They are mitotically quiescent- normally
but they can be activated to enter the cell cycle into myoblast when applied the right trigger.
These can provide more myonucelei- existing or new
What are the functions of satellite cells?
They can self renew to maintain stem cell population: Muscle growth after birth Muscle Maintainance Muscle hypertrophy Muscle Repair and generation
Describe the structure of the sacromere
2 major protein filaments-
thick filaments- myosin
thin filametns- actin
Titin molecule- holds the myosin filament from z- line to m line
In the relaxed form it curls up- providing the tension even though muscle is relaxed
In the contracted phase- titan molecule curls up even more
When one muscle contracts the other muscle on other side of the joint will stretch- muscle elongates- titin coils allowing myosin and actin to slide past with each other with minimal damage
Nebulin- extends from the z band along the length of one thin actin filament - TEMPLATE- ensures actin is regulated
Describe the muscle innervation
a myofibril receives innervation from one motor neurone
Each motor neurone makes contact with multiple muscle fibres- ONE MOTOR UNIT.
The size of the motor unit dictates the degree of muscle control - small end plates in the muscle of hand and eye - finer degree of control. larger ones in the leg muscle
Describe the innervation and initiation of contraction
1) ACH released from motor end plate to synaptical junction
These diffuse across and bind to voltage grated Na+ channels
2) The Na+ channels open and diffuse into the cell
3) This depolarises the plasma membrane spreading via the T tubule
(GIVEN THAT: depolarisation is sufficient enough to trigger AP)
4) This causes Ca 2+ to be released into the sarcoplasm
They bind to the troponin complex which causes tropomyosin to change shape- this allows myosin head to attach- contraction is initiated
Describe the Contraction Cycle
1) Attachment- the myosin head is tightly bound to the actin molecule on the think filament
2) Release- ATP binds to the myosin head which induces the release of the myosin head from the actin filament- this relaxes the muscle
3) Bending- The ATP causes further changes to the myosin head allowing it to bend .
The bending initiates hydrolysis of ATP-ADP +Pi.
Both remain on the head
4) The myosin head binds to the new molecule and Pi is released.
This increases the binding affinity of the myosin for the actin
The myosin head creates a force to straighten up which forces the thin filament along the thick filament-
ADP released
5) This shortens the sarcomere because the z lines move closer together, the same amount at which h zone decreases in length
A band stays the same length
Describe muscle relaxation
Ca 2+ removed from the cytosol
They are pumped back into the sarcoplasmic reticulum by ATP synthase
As [Ca 2+] decreases, Ca 2+ released from troponin, removes tropomyosin binding sites- cross bridged released- no filament sliding
Comment on duration of action potential vs Twitch
AP time is much less than Twitch time
When a number of action potential occur before the initial is complete- they superimpose each other - the action potentials add up to reach the threshold
This is due to the fact that the frequency of twitch occurs at a faster rate than Ca 2+ is removed-continuing the AP
Name the three types of Muscle fibres
Slow Twitch oxidative Type 1
Fast Twitch Oxidative glycolytic Type 2A
Fast Twitch Glycolytic Type 2B
Slow Twitch oxidative Type 1
sustained contraction
slow speed of development of max tension and myosin ATP activity
small diameter of fibre
oxidative:aerobic
High capillary density and many mitochondria
fatigue resistant
Supplied by myoglobin
Fast twitch oxidative Type 2A
phasic movements- walking
intermediate speed of development of max tension fast myosin ATP activity
medium diameter of fibre
glycolytic but can become more oxidative:aerobic with training
Medium capillary density and moderate number of mitochondria
fatigue resistant
Fast twitch oxidative Type 2B
phasic movements- explosive
fastest speed of development of max tension fast myosin ATP activity
large diameter of fibre
glycolytic- anaerobic
Low capillary density and Low number of mitochondria
fatigued easily
Describe the pathway of activating groups
the greater the load- the more groups are activated over time- max Type II B
when one group fatigues another group takes over
What is Duchenne Muscular Dystrophy
Symptomatic- less than 1 year to 5 years
Leads to death between 20-30- due to respiratory and cardiac causes
This is due to dystrophin function- x chromosome- it helps link contractile apparatus to the ECM
Stabilises sarcolemma, transmitting forces laterally across sarcolemma to ECM
People with dystrophy- the re[air for torn muscle fibres is constant- necrosis and fibrosis of muscle tissue occurs not by alike tissue.
ie. non contractile
How is muscle formed embryonically
All the trunk/limbs derived from embryonic structures called somites- turn into progenitors of skeletal and muscle cells- when they go into certain environments- the myoblasts differentiate accordingly dependant on the environment due to cell signalling
Describe the length tension relationship
Tension in a muscle can generate related to the number of the cross bridges formed between thick and thin filaments
In elongated fibres there will be few cross bridges - therefore little power generated
As sarcomere shortens- increase in number of cross bridges- the force increases until fully overlapped- hence the tension decreases rapidly since there are no new binding sites
