types of mucles Flashcards
How many types of muscles are there?
Skeletal:- attaches to the bone
-Is innervated by alpha motor neurons
- referred to as extrafusal fibers
- not influenced by hormonal signals
- Striated, multinucleated,responsable for
volontary movements
Smooth: - small, single nucleus,not striated
- part of the autonomic system
- have gap junctions to allow cell-cell
comunication
- located near internal organs
Cardac: -rescticted to the heart
- striated
-pumps blood around
- doesn’t require volontary control but can be
influenced by emotions
What are similarities in the types of muscles?
Intracellular Ca++ signals initiate muscle contraction
Movement = the protein myosin uses energy from ATP to change its conformation
Why are muscles found in pairs?
Muscles only contrant so to perform opposite actions one need to be responsable for the primary movement (agonist) and the other for the opposite (antagonist)
Tendon vs ligament?
tendon is muscle to bone
Ligamnet is boe to bone
What is a muscle cell called? and what are its specifci components
cell=muscle fiber
Endoplasmic reticulum= sarcoplasmic reticulum (stores
Ca2+)
cell membrane= sarcolemma
t-tubules= invaginations allowing for better transmission of action potential as it doesn’t have to travell in the cytoplasm
Nucleus= found on teh surface for more efficient surface distribuition of contractile fibers
types of protein found in skeletal muscles?
Actin= makes up thin filaments, g-actin globular, f-actin filament, has a binding site to myosin
Myosin= thick filaments, has 2 heads, light chains(4 these are the ones calmodulin-Ca+ binds to) heavy chains(2 mkae up the tai). It is also called myosin ATPase cause it hydrolyses ATP), binds to actin
Troponin= found as C when it binds to Ca+(bodyguard)
T when it binds to tropomyosin
I when it binds to actin
Tropomyosin= sits in the bonding site for actin and myosin and only moves when tropoin binds to Ca+
Nebulin= non elastic stabilises actin ( from Z to nearly M)
Titin= elastic fiber spans from Z to next M line, keeps myosin in place
What moves musces?
Somatic motor neurons ( alpha if innerving extrafusal gamma if intrafusal)
Events of contraction
- Action potentail from motor neuron releases AcH at neuromuscular junctions
- Ach binds to Ach receptor- channes allowing Na+ and K+ to get in the cell causing depolarisation more positive inside and down the T-Tubule
- causes a EPP
- Hydropyridine voltage sensitive receptors connected to Ryanodine and these, found on SR release Ca+
- Ca+ binds to troponin C causing a conformational change that pulls tropomyosin from the binding site of actin
- corked myosin ( bound to ADP and Pi) can now fully bind actin causing the slining filament model
- once myosin is done it changes conformationand is now able to bind ATP and repeat
Events of relaxation
-Action potential stops
- SR starts actively pumping Ca+ back in with Ca2+-ATPase
-< [Ca2+] causes tropinin to release Ca2+
-tropomyosin goes back cockblocking myosin
Twitch is complete
Prefered energy source of skeletal muscles?
Phosphocreatine, shit ton of enzymes found in skeletal muscles to break it down
Structure of muscles (smallest to biggerst )
- Myofibil
- Muscle fiber
- Muscle fascicle
What are the other components of muscles?
Connective tissue
Blood vessels
Adipose
Nerve
what is a sarcomere?
.A sarcomere is the basic unit of a muscle. Muscle cells are composed of tubular myofibrils. Myofibrils are composed of repeating sections of sarcomeres, which appear under the microscope as dark and light bands. Sarcomeres are composed of long, fibrous proteins that slide past each other when the muscles contract and relax.
Do muscle fibers shorten during contraction?
No they slide according to the sliding model mechanism which says actin and myosin pull on each other causing an overall shorteing not due to the fibers getting shorter but fibers sliding ( H zone getting shorter)
what is an Action potential?
(electrical impulses that send signals around your body) = a temporary shift (from negative to positive) in membrane potential caused by ions suddenly flowing in and out of the cell.
Define tension twitch sarcomere
- Tension: force generated by contraction
- Twitch: contraction relaxation cycle
- sarcomere: Z line to Z line
What is motor unit?
Somatic motor neurons innervating several muscle fibers. These differ in number of fibers attached to them creating a gradient of force produced
What are the different fiber types?
- Slow twitch: develops tension slower but is able to maintain for longer ( posture standing and walking)difference is creadted by having different isoforms of Myosing ATPase as well as slower uptake od CA2+
- Fast twitch/oxidative-glycolytic: intermedite speed, relys on aerobic respiration, contraction duration is short , fatigue resistant
- Fast twitch glycolitic: fastest large diameter short duartion of contraction, eye movement, easily fatigued
Factors defining muscle tension
maximum tension depends on sarcomeres and frequency of action potential
duration: resistance to fatigue and Ca2+ pump speed
Speed tension depemds on isoform of myosin ATPase
What is fatigue?
Fatigue is defines as muscle not being able to generatet or maintaing tension. It depends on:
- Intensity and duration of contraction
- aerobic or anaerobic
- muscle composition
- fitness of individual
Types of fatigue
CNS: protective reflexes( increase of pH) and feeling of tiredness
PNS: occurs cause of defects between neurotransmitter and contractile elements
How does moduation of contraction occur?
Force can be modulated by either activating specific units ( same motor neuron secretes GF so all the fibers are the same type) or by increasing the n of units.
1) slow twith
2) fast twitch oxidative/ glycolitic
3) fats oxidative
isometric vs isotonic
Isometric generates tension without resulting in significant contraction lenth or movement
isotonic meets the load and is able to contract and move
Proprioception
awarness of the body in space
3 types: muscle spindles
Golgi tendon organs
joint capsules
These 3 provide constat input of the space occupied by the bodykinesthesia
behavioral actions
Muscle spindles
Found parallel to extrafusal fibers( sleletal muscles ) these innervate alpha motor neuron.
They respond to stretch and allow to respond to a load that can be supported.
They are innervated by gamma motor neurons
they have an elastic part( intrafusal) and in the middle no myofibrils this is what is maintained at a constant tension
If a muscle contracts gamma neurons will sense this and firts cause the alpha neurins to contract extrafusal then in response intrafuals will contact and stetch the middle to matain a constant firing rate
Golgi body
these are found between muscles and tendons and respond to tenstion. respond to isometric tension and send a signal this will result in it inhibiting the alpha neurons and tension will cese
Joint capsules
allow you to know where your joints are positioned in space
How many types of movements are there?
3 main types: -reflex
- volontary
- rhythmic
Descibe a reflex movement
- require no input from the cortex
-proprioceptor provide constant info to the spinal cord, brain stem (posture and hand eye movement) and cerebellum ( fine movements)
Signal-> sensory receptor-> SP-> muscle contraction-> negative feedback.
Describe volontary movemnts
- require coordination from cerebral cortex cerebellum and basal ganglia
1) planning is carrie dout by basal ganglia( posture), cortical associatiation areas( constant sesory input) and cerebellum ( fine movements)
2) initiating movement coordinated by motor cortex( including negative feedback to basal andcerebellum)
3) Executing movemnt involves the cerebellum again as well as negative feedback to contantly adjust
Describe rhythmic movements
Initiated and terminated in the cortex but are carried out by special interneurons called control pattern generators. They are thought to be potential treatment for paralysis
What is a feedfoward reflex?
It is what allows the body to prepare for volontar movements, the feedback from these movements helps create smooth movements.
How are smooth muscles categorised?
Location:-vascular
-ocular
-gastrointestinal
-urinary
-respiratory
-reproductive
Contraction pattern: -contraction-relaxation ( phasic like
oesophagus , it contracts when
needed and relaxes when needed)
-Always contracted like sphinctres
Cell-cell comunication:- unitary contraction contract as a
unit
- multi-unit each one fuctions independently
12 things smooth muscles can do
- Operate over a range of lenths
- they run in several directions allowing for change in shape of the organ for specific need
- Duration of muscle twitch is x5 times longer
- uses less energy to generate and maintain force
- Sustains a contration for longer without fatiguing
- small spinde shape mononucleated
- no sarcomeres
- initiated by chemical or electrical
- controlled by the autonomic
- lacks receptor region like end plate potential it has receptors all over
- Ca2+ comes mainly from extracellular space
- Ca2+ initiates a cascade not the mail thing
- no troponin
How much more actin is there in smooth compared to skeletal?
x5
a feature that allows smooth muscles to maintain a contration
the large amount of actin + myosin filament covered in heads as well as a head will attach every 12 actins allows smooth to strecth but maintain overlap= longer contraction
What is a dense body?
part of the cytoskeleton of smooth muscles connected via intermediate filaments.
What does actin attach to in smooth muscles?
dense bodies and these are attached to the membrane allowing the cell to steady actin in place
Descibe the mechanism of smooth muscle contraction
- Ca2+ enters from ECF+ SR
- Ca2+ binds calmodulin
- This complex activates Myosin light chain kinase (MLCK)
- MLCK phosphorilates light chains and oncreases myosin ATPase activity
- Contration occurs as crosbridges slide along actin
Mechanism of smooth muscles relaxation
- Ca2+ is actively pumped (Ca2+ ATPase and Na+Ca+ exchanger) out of cytosol either back out of in the SR
- This causes Calmodulin to unbind from Ca2+=> MLCK activity decreases
- Myosin Phosphates removes Phosphate from iight chains
- Decrease of Myosin ATPase activity
- This results in decrease muscle tension
What alters myosin respinse to Ca2+?
low phosphatase activity= myosin sensitised to Ca
high phosphatase activity= desensitised yo Ca
What is a contraction that has initiated whitout a significant change in membrane potential?
pharmacomechanical coupling
