Physiology: muscles Flashcards
describe the physiological functions of skeletal muscles
maintain posture, respiratory movements, heat production, contribute to metabolism, voluntary movement
what are the 3 types of muscle
smooth, cardiac and skeletal
what muscle types are striated
cardiac and skeletal
what muscle type is unstriated
smooth
describe the structure of actin
thin filaments that appear as light bands
describe the structure of myosin
thick filaments that appear as dark bands
what are skeletal nerves innervated by
the somatic nervous system(voluntary)
what are the smooth and cardiac nerves innervated by
the autonomic nervous system(involuntary)
describe the initiation of contraction for skeletal and cardiac muscle
skeletal = neurogenic(motor units) cardiac = myogenic
what junction are involved in skeletal and cardiac muscles
skeletal = neuromuscular junctions cardiac = gap junctions
describe the excitation contraction coupling of skeletal muscle
Ca2+ entirely from sarcoplasmic reticulum
describe the excitation contraction coupling of cardiac muscle
Ca2+ from ECF and sarcoplasmic reitculum
what does the gradation of contraction of cardiac muscle depends on
extent of filling of the heart with blood(preload)- the Frank Starling mechanism
what is the neurotransmitter involved in neuromuscular junctions
Acetylcholine
what are skeletal muscle fibres(cells) organised into
motor units
what is a motor unit
a single alpha motor neuron and all the skeletal muscle fibres it innervates
allow simultaneous contraction of a number of muscle cells
describe how the number of muscle fibres per motor unit varies depending on function
fewer(~10) fibres = finer movements(eg eye)
hundreds to thousands fibres = power over precision(eg thigh)
what is structure contained in a muscle fibre(cell)
myofibril(specialised intracellular structure)
what is the functional unit of muscle cells(fibres)
sarcomeres
what protein molecules are found in myofibril in muscle cells(fibres)
myosin and actin
how long are skeletal muscle cells
usually extend the length of the muscle
describe how muscles are usually attached to the skeleton
by tendons
how are actin and myosin arranged in myofibril and what is this arrangement called
by alternating segments of thin(light) actin bands and dark(thick) myosin bands
called a sarcomere
what is the functional unit of any organ
the smallest component capable of carrying out all the functions of that organ
what are sarcomeres found between, and what separates them
Z-lines, which connect the 2 thin filaments(actin) of adjoining sarcomeres
what are the 4 zones of the sarcomere
H-zone, A-band, I-band, M-line
describe the structure of the A-band of a sarcomere
made up of thick filaments along with portions of thin filaments that overlap in both ends of thick filaments
describe the structure of the H-zone of a sarcomere
lighter area within middle of A-band where thin filaments don’t reach
describe the structure of the M-line of a sarcomere
extends vertically down middle of A-band within the centre of H-zone
describe the structure of I-band of a sarcomere
consists of remaining portion of thin filaments that do not project into A-band
how is muscle tension produced
by actin(thin) molecules sliding on the thick(myosin) filaments
what is force generation of a muscle dependant on
ATP-dependant interaction between the actin(thin) and myosin(thick) filaments
what is ATP required for in muscles
contraction and relaxation
what is CA2+ required for in muscles
to switch on cross bridge formation
what is excitation contraction coupling
process by which surface action potential results in activation of contractile structures of muscle fibres
when is Ca2+ released in skeletal muscle fibres
when the surface action potential travels spreads down the transverse (T)-tubules
where is Ca2+ released from on skeletal muscles
lateral sacs of sarcoplasmic reticulum
describe how Ca2+ allows for cross bridge formation
Ca2+ binds with troponin, which pulls the troponin-tropomyosin complex to the side exposing the cross bridge binding site
what are the 2 primary factors in determining gradation of skeletal muscle tension
number of muscle fibres contracting within the muscle
and the tension developed by each contracting muscle fibre
what is motor unit recruitment
when stronger contraction is achieved by simultaneous contraction of multiple motor units
describe the process that helps to prevent muscle fatigue
asynchronous motor unit recruitment during submaximal contractions
what does the tension developed by each contracting muscle fibre depend on
frequency of stimulation, summation of contractions, length of muscle fibres, thickness of muscle fibres
describe the relative time of an action potential and a muscle twitch, and what this means
action potential much faster than a muscle twitch, therefore multiple action potentials can occur in one twitch
describe what tetanus is
when a muscle fibre is stimulated so rapidly it doesn’t have time to relax in between contractions, results in a sustained contraction
what type of muscle can’t be tetanised
cardiac muscle
how does frequency of stimulation relate to strength of contraction
as frequency increases strength of contraction increase
when is maximal tetanic contraction achieved
at optimal muscle length; at point of optimal overlap of thick filament and thin filament cross bridge binding sites
how is muscle tension transmitted to the bone in skeletal muscle contraction
via stretching and tightening of connective tissue and tendons(elastic component)
describe what an isotonic skeletal muscle contraction is and what its used for
muscle tension remains constant as muscle length changes
used for body movements and moving objects
describe what an isometric skeletal muscle contraction is
when muscle tension develops at constant muscle length
used in supporting objects in fixed positions and maintaining postures
what determines speed of contraction of skeletal muscles
activity of myosin ATPase
what determines skeletal muscles resistance to fatigue
capacity to synthesise ATP
greater capacity = greater resistance to fatigue)
how many types of skeletal muscle are usually found in each motor unit
one type
what different metabolic pathways supply ATP in muscle fibres
oxidative phosphorylation, glycolysis, transfer of high energy phosphate from creatine phosphate to ADP
what are the different types of skeletal muscle fibres
slow oxidative type I(slow twitch)
fast oxidative type IIa(intermediate twitch)
fast oxidative type IIx(fast twitch)
describe function of slow twitch(slow oxidative type I) muscle fibres
used mainly for prolonged relatively low work aerobic activities
describe function of intermediate twitch(fast oxidative type IIa) muscle fibres
use both aerobic and anaerobic metabolism and are useful in prolonged relatively moderate work activities
describe the function of fast twitch(fast oxidative type IIx) muscle fibres
use anaerobic metabolism and are mainly used for short-term high intensity activities
