Lecture 14 - Musculoskeletal system 4: muscles Flashcards
What is the function of pectoralis major
Flexes the arm
-adducts the arm anteriorly and draws it across the chest
What is the function of the latissimus dorsi
Extends the arm
-adducts the arm posteriorly
What is the function of the deltoid
Abducts the arm
-assist in flexion and extension of the arm
What is the function of supraspinatus
Assists in abducting the arm
What is the function of Teres minor
Rotates the arm outward
What is the function of Teres major
Assists in extension, adduction, and medial rotation of the arm
What is the function of Infraspinatus
Rotates the arm outward
What is the function of Subscapularis
Medial rotation
What is the function of biceps brachii
Flexes the supinated forearm
-supinates forearm and hand
What is the function of brachialis
Flexes the forearm
What is the function of brachioradialis
Flexes the semi pronated or semi supinated forearm
What is the function of triceps brachii
Extends the lower arm
What is the function of pronator teres
Pronates and flexes the forearm
What is the function of pronator quadratus
Pronates the forearm
What is the function of supinator
supinates the forearm
What are 3 main functions of muscle
- movement
- heat production
- posture
What are 4 characteristics of muscle
- excitability
- contractility
- extensibility
- elasticity
what’s are 3 unique characteristics of myocytes
- sarcolemma: plasma membrane
- Sarcoplasma: cytoplasm (fluid matrix)
- Nucleus: many poly nucleated cells and is close to sarcolemma
What is in Sarcoplasma
ATP,
Glycogen(reserve)
Myoglobin (analogue hemoglobin)(binds to oxygen)
-basically protein that helps carry O2
What is T-tubule
Transverse tubule :
- perpendicular extensions of the sarcolemma
- Penetrates into cell
What is sarcoplasmic reticulum (S.R.)
- contains lots of Ca2+
- membrane has a Ca2+ pump to help accumulate it
What are myofibrils
Bundles of cytoskeleton filaments
- 1000+ per cell
- made of myofilaments (actin = thin or myosin = thick filament)
- each one is surrounded by sarcoplasmic reticulum (responsible for the contraction)
Describe microfilament actin
- thin filament that consists of actin molecules (kidney shaped) twisted into a helix (rope like)
- has sites that interact with myosin HEADS
- at rest this site is hidden by the tropomyosin protein that is held by troponin protein
Describe microfilament myosin
- thick filament
- interwoven into sarcomere (Z-line)
- 200 myosin molecules per myofilament
- loos like 2 interwoven golf clubs
- has bilobed head that is exposed and a tail which is parallel to the cells
What is sarcomere
The basic contractile unit for striated muscle cells
- about 15000 per myofibril
They are organization of the myofilaments actin and myosin
What is movement of sarcomere and myofilaments during a contraction
Sarcomere shortens during contraction and myofilaments (actin and myosin) slide on top of one another
what makes visible bands/ striations on skeletal muscle when we look in microscope
The way the filaments are organized
What is the Z-disk
Anchor for thin myofilaments
-elastic filament (Titin) attaches myosin and actin to the Z disk thus ensures the structural stability of the sarcomere
What is M-line
Line of M-proteins that hold the myosin filaments
What is A-band
Runs the entire length of myosin filaments
What is I-band
Includes Z-disk and ends of actin filaments
What is H-band
Region of myosin filament with no overlapping actin filaments
What do myosin heads have
- a site to link actin
- a site to link ATP
What is initiation of sliding filament theory of contraction
Ca is released from the sarcoplasmic reticulum to the sarcoplasm (membrane)
What is the sliding filament theory of contraction
- myosin head stores ADP+ and P+
- Ca2+ from S.R. binds to troponin
- tropomyosin shifts from blocking active site on actin
- myosin head binds to active site then releases ADP+ and P+
- release of those molecules gives myosin head energy to pull actin molecule
- ATP binds to myosin and myosin is released from the active site
during contraction, each actin is bound to:
millions of cross bridges of myosin
do all the bonded actin-myosin groups detach at the same time
no they need to keep tension on the actin myofilament
what happens during relaxation in sliding filament theory of contraction
- Ca2+ reabsorbed
- tropomyosin hides the link site on actin
when does rigor mortis usually set in
3-4 hrs after death (max 12 hrs)
-this is because Ca2+ is slowly realeased in the sarcoplasm which causes the contraction
Why is rigor mortis a continuous contratioc
because ATP is no longer available (cells are no longer active)
-the myosin heads stay bonded to actin filaments and contraction is maintained
what causes relaxation after rigor mortis
after 48-60 hrs the muscles relax again due to the degradation of the contractile proteins
What are the energy sources for contractions
ATP
Glucose & Oxygen
Catabolic Pathways
Heat production
how many seconds of contraction can muscle get with resynthesized ATP
2-4s so constantly resynthesizing
What is a secondary source for resynthesizing ATP and how many seconds of contraction can the muscle achieve
Creatine phosphate and can get 20s of contraction
How is ATP resupplied
through cellular respiration
What happens if there is no more ATP going to muscles
End of contractions
What is glucose and oxygen role in energy source for contractions
- release of energy from glucose in cellular respiration produces ATP
- Muscle fibers store glucose as glycogen
- Oxygen is stored in muscle as myoglobin
What are the catabolic pathways used to produce ATP
Aerobic: -max energy, requires a lot of oxygen
Anaerobic:-no immediate need of oxygen
-rapid
-results in fermentation of lactic acid
-when oxygen available, lactic acid can be converted back to glucose in liver
-excess post exercise oxygen consumption
What is heat production role in energy source for contraction
- as catabolic processes not 100% efficient; thermogenesis
- important for homeostasis
- shivering thermogenesis
What is a motor unit of muscle
combination of:
- Motor neurons
- Grps of myocytes they innervate
What is the motor nerve that each muscle receives one of
- contains hundreds of myelinated axons
- branches into many axon terminals
- each terminal forms a neuromuscular junction with 1 myocyte
How are cells of a motor unit dispersed
-interconnected by gap junctions so they can contract together
The # of myocytes in a motor unit depends on:
the muscle itself
- ex. 2000 cells in 1 motor unit = very strong muscle like arm, thigh
- ex. a few cells in motor unit = precision muscle like larynx
What is a muscle twitch
aka - muscle fasciculation
- depolarization of small muscles leading to transient muscle contraction
- contraction that follows only 1 nervous stimulation
- intensity depends on the # of motor units involved
What are 3 phases of muscle twitch
- latent period
- period of contraction
- period of relaxation
What is latent period of muscle twitch
- myocyte does not shorten at this point
- myosin heads start to pullon actin & titin stretchs
- time needed for excitation- contraction = few ms
What is period of contraction of a muscle twitch
- The force genrated is greater than the resistance and so the muscle shortens
- duration up to 100ms
What is the period of relaxation in muscle twitch
- Ca2+ is reabsorbed in the sarcoplasmic reticulum (S.R.) and contraction stops
- duration more than 100ms
What dictates the speed at which a muscle will contract
Depending on their function, myocytes of different muscles will contract faster or slower due to many variations in the cells proteins
-The bigger the muscle, the longer it takes for the contraction and relaxation
What needs to be done in order to affect the force of contraction
- increase the frequency of stimulation (temporal summation and tetanus)
- increase the intensity of stimulation (multiple motor unit summation)
What is temporal summation (T.S.) or wave summation
- When a skeletal muscle is stimulated twice in a short interval of time
- The magnitude of the 2nd contraction will overlap with the 1st because the Ca2+ released by 1st hasn’t been completely reabsorbed, making 2nd contraction a bit stronger
What is tetanus
- Rapid stimulation of a skeletal muscle
- Results in a continuous or prolonged type of contraction
- Normal state: the nerve impulses rapidly arrive to the motor units & provoke a tetanus instead of an isolated twitch
- complete tetanus = contractions are all fused
What is muscle tone or tonus
- Tension of skeletal muscles at rest
- when you stimulate a muscle, it is voluntary (ATP & Ca2+ essential for contraction)
- Healthy & resting skeletal muscles are always slightly contracted but without producing any movement(involuntary)
- spinal reflexes activate a grp of motor units activating the muscles and tendons governing stretch
Function of tonus
- stabilize articulations
- maintain posture
Myocytes are often metabolically minimally active, when are they intensely active
when they contract
What is the quantity of ATP present in myocytes
small only 4-6 sec. of contraction
-ATP is the energy source used for contraction
What 3 pathways to obtain ATP
- Direct phosphorylation(~15 sec)
- release of energy from ATP bond breaking - Anaerobic glycolysis & lactic acid production(30-60s)
- ATP formed from breaking glucose down in pyruvate - Aerobic respiration(for many hrs)
- Kreb’s cycle, ETC
- Oxygen required
- myoglobin and hemoglobin transport
What are the smooth muscles
- small, fusiform,
- not striated as myofilaments not organized with sarcomere
- sarcolemma has no T tubules
- central nucleus due to network arrangment of myofilaments
- contains least S.R.
- Endomysium = CT w/ blood vessels & neural fibers
- found in viscera / walls of hollow organs
Events that differ in smooth muscle contraction
Calcium attaches to calmodulin (on myosin) and is activated
-Calmodulin functions slowly, so slows calcium effect on contraction
What are 2 types of smooth muscle
- Single unit smooth muscle (visceral)
2. multiunit smooth muscle
What is single unit smooth muscle(visceral)
- has important gap junctions that link networks
- has pacemaker cells
- neurons of the autonomic nervous system innervate a few smooth myocytes & the action potentials spread to other networks
- hormones influence complete networks
- ex. bladder, uterus, digestive sys.
What is multiunit smooth muscle
- not many gap junctions
- each myocyte has synapses (neuromuscular junctions) btw neuron & myocyte w/ the ANS
- React to hormonal regulation
- ex. large arteries, large airways, arrector pili muscles
What is myalgia
Pain in the muscle bcs of a myopathy (muscular disease)
What is myositis
muscle inflammation
What is tetanus
- infectious disease
- acute: fast acting, not lengthy in time, can die suddenly
- Chronic: slow acting, over prolonged period of time
- caused by a toxin frm Clostridium tetani (bacteria)
- =painful spasms & contractures (jaw, cervical, trunk, limbs)
- w/o vaccination can die of respiratory failure
What is poliomyelitis
- viral inf. of body frm polio virus
- sometimes asymptomatic
- infection travels along motor neuron pathway
- leads to paralysis and death
- no tx once infected
What is Duchenne progressive muscular distrophy
- hereditary disease, recessive, linked to sex (almost always in men
- muscle hypertrophy (fat & CT deposits)
- myocytes degenerate & atrophy
- missing dystrophin: maintain integrity of the sarcolemma
What is myasthenia gravis
- Chronic weakness, especially in face & throat
- begin w/ mild weakness progress to longer periods & more muscles involved
- resp fail possible
- caused by autoimmune malfunction, ACh receptors in sarcolemma are targeted
- leads to impulses that are unable to produce full contractions
