Physiology Flashcards
what types of muscles are striated
skeletal and cardiac
what is skeletal muscle contraction initiated by
motor neuron stimulation
what are the physiological functions of skeletal muscles
maintenance of posture
purposeful movement in relation to external environment
respiratory movements
heat production
contribution to whole body metabolism
what innervates skeletal muscles
the somatic nervous system
what innervates cardiac and smooth muscles
the autonomic nervous system
what muscles are involuntarily controlled
cardiac and smooth
what causes the striation of cardiac and skeletal muscles
alternating dark bands (thick myocin filaments)
and light bands (thin actin filaments)
what initiates and propagates contraction of cardiac muscle cells
myogenic (originating within muscle tissue- pacemaker potential)
do cardiac muscles have motor units
no
which type of striated muscle has a neurovascular junction
skeletal
which type of striated muscle has gap junctions
cardiac muscle
where is skeletal muscle Ca++ from
entirely from sarcoplasmic reticulum
where is cardiac muscle Ca++ from
from extra cellular fluid and sarcoplasmic reticulum (Ca++ induced Ca++ release)
what determines the gradation on skeletal muscle contraction
motor unit recruitment
summation of contractions
what determines the gradiation of cardiac muscle contraction
depends on the the extent of the heart filling with blood (pre-load, frank sterling mechanism)
is there continuity of cytoplasm between nerve and skeletal muscle cells
NO need neurotransmitters
what is the neurotransmitter at neurovascular junctions
acetylcholine
what is a motor unit
a single alpha motor neuron and all the skeletal muscle fibres it innervates
where do motor neurons come from
spinal chord
what does the number of muscle fibres per motor unit depend on- explain
the function served by the muscles- fine movement (eye, facial, hand muscles) have fewer fibre per unit (aprox ten). powerful muscles have more units eg thigh muscles (100-1000s)
what makes up muscle fibres (aka muscle cells)
myofibril (contractile intracellular structure) which make up sarcomere (functional unit)
what are the protein molecules contained within myofibril and sacromeres
myocin and actin
how are skeletal muscles usually attached to the bone
by tendons
how are the protein filaments arranged in skeletal myofibrils
alternating actin (light) and myocin (dark) make sarcomeres (functional units)
what is a functional unit
the smallest component capable of performing all the functions of the organ
what is the functional unit of skeletal muscle
sarcomere
what separates sarcomeres
two Z lines (between adjacent sarcomeres)
what are the four zones of the sarcomere
A- band, H-zone, M-line and the I-band (i)
what is the A band of a sarcomere
made of thick filaments along with portions of thin filaments that overlap in both ends of thick filaments
what is the H zone of a sarcomere
lighter area within the middle of the A band where thin filaments dont reach
what is the M line of the sarcomere
extends vertically down middle of the A band within the centre of the H zone
what is the i-band of the sarcomere
the remaining portion of thin filaments that do not project in A band (near to Z line)
what produces muscle tension
the sliding of actin filaments on myocin filaments
what can crossbridges between myosin and actin not form without
ATP and Ca++
why is Ca++ important
required to switch on cross bridge formation
is ATP required for contraction or relaxation
both contraction and relaxation
what is the excitation contraction coupling
the process whereby the surface action potential results in activation of the contractile structures of the muscle fibres
in skeletal muscle fibres when is Ca++ released from lateral sacs of the sacroplasmic reticulum
when the surface action potential spreads down the transverse (T)- tubules
what are T-tubules
extensions of the surface membrane that dip into the muscle fibre
what generates the action potential that travels down T-tubules
acetylcholine released by axon of motor neuron
what do the calcium ions released from the sarcoplasmic reticulum do
bind to troponin on actin filaments, pulling troponin-tropomyosin complex aside to expose cross-bridge binding site (cross bridge binding occurs)
how are cross bridges formed
myosin bind to actin and pulls actin filament toward centre of sarcomere
when does ATP detact from myosin
when bending occurs
when does ATP bind to myosin and what happens to it
after detachment (bending), is dephosphorlyated, energising the myosin for binding (or resting state if no Ca++ present)
what happens to calcium after there is no longer an action potential
is re taken up by sarcoplasmic reticulum
what covers the cross bridging site on actin in the resting state
the troponin-tropomyosin complex
what is the link between excitation and contraction
Ca++
why is ATP needed in relaxation
to release cross bridges
to pump Ca++ back into sarcoplasmic reticulum
what causes rigor mortis
no atp left relax muscles
what influences the tension developed by a skeletal muscle
the number of muscle fibres contracting
and
the tension developed by each contracting muscle fibre
how is a stonger contraction achieved
by stimulation of more muscle units (motor unit recruitment)
what is asynchronous motor unit recruitment
during submaximal contraction, some motor units are recruited, some are not to prevent muscle fatigue
what does the tension developed by each contracting muscle fibre depend on (4)
frequency of stimulation
summation of contractions
length of muscle fibre at the onset of contraction
thickness of muscle fibre
what is longer in skeletal muscle: the duration of the action potential or the duration of the resulting twitch
twitch
what is the latent period
time between action potential starting and muscle twitch starting
what is the summation of twitches
when the repetitive stimulation of skeletal muscles produces a stronger contraction (second twitch added on to first twitch)
what is tetanus
when a muscle fibre is stimulated so rapidly that it does not have an opportunity to relax at all between stimuli creating a maximal sustained contraction
can cardiac muscle be tetanised, explain
no- long refractory period prevents generation of tetanic contraction
what is a twitch
when skeletal muscle is stimulated once
when is maximum tetanic contraction achieved
when the muscle is at its optimum length before the onset of contraction
when is contraction less when muscle fibre are longer or shorter than optimum
as less binding sites are exposed to make cross bridges (the sliding filament mechanism)
what is the optimal skeletal muscle length
length of resting muscle
how is skeletal muscle tension transmitted to the bone
via the stretching and tightening of muscle connective tissue and tendon (elastic component)
what are the two types of skeletal muscle contaction and what makes them different
isotonic= body movements, moving objects. muscle tension remains constant as the muscle length changes
isometric contraction= supporting objects in fixed positions and maintaining body posture. muscle tension develops at constant muscle length
what happens to the velocity of muscle shortening as the load increases
it decreases
what makes skeletal muscles different from one another
their enzymatic pathways for ATP synthesis
describe different types of skeletal muscles resistance to fatigue
muscle fibres with greater capacity to synthesise ATP are more resistant to fatigue
how does the activity of myosin ATPase affect different muscle fibres
determines the speed at which energy is made available for cross bridge cycling (e.i. the speed of contraction)
how many types of muscle fibres does one motor unit contain
one type
what are the three metabolic pathways that supply ATP in muscle fibres
transfer of high energy phosphate from creatine phosphate to ADP- immediate source for ATP
oxidative phosphorylation- main source when O2 is present
glycolysis- main source when O2 is NOT present
what are the three types of skeletal muscle fibres called
slow oxidative (type I)
fast oxidative (type IIa)
fast glycolytic (type IIx)
what are slow oxidative fibres (type I) and what do they do
slow twitch fibres
used mainly for prolonged relatively low work aerobic activities (walking, maintenance of posture)
what are fast oxidative fibres (type IIa) and what are they used for
intermediate twitch fibres
use both aerobic and anaerobic metabolism, useful in prolonged relatively moderate work activities
what are fast glyoclytic (Type IIx) fibres and what do they do
fast twitch fibres
use anaerobic metabolism, mainly used for short term, high intensity activities (jumping)
motor nerves receive inputs from where
the brain and a variety of receptors- can be excitatory or inhibitory input
what is a reflex action
stereotypes response to a specific stimulus
what are the neural pathways for reflexes important in locating
lesions in the motor system
what type of reflex in the stretch reflex
monosynaptic spinal reflex
what is the role of the stretch reflex
serves as a negative feedback that resists passive change in muscle length to maintain optimal resting length of muscle- help maintain posture e.g. while walking
what is activated by muscle stretch and what happens
the sensory receptor is the muscle spindle- stretching the muscle spindle increases firing in the afferent neurons resulting in contraction of stretch muscle
where do the afferent neurons synapse
in the spinal chord, with the alpha motor neurons (efferent limb of the stretch reflex)
what coordinates the stretch reflex
simultaneous relaxation of antagonist muscle
what peripheral nerve (and spinal segment) is target with the knee jerk reflex
femoral nerve (L3,L4)
what peripheral nerve (and spinal segment) is target with the ankle jerk reflex
tibial nerve (S1, S2)
what peripheral nerve (and spinal segment) is target with the biceps jerk reflex
musculocutaneous nerve (C5,C6)
what peripheral nerve (and spinal segment) is target with the brachioradialis reflex
radial nerve (C5, C6)
what peripheral nerve (and spinal segment) is target with the triceps jerk reflex
radial nerve (C6,C7)
what are muscle spindles
sensory receptors for stretch reflex- a collection of specialised muscle fibres called intrafusal fibres
what are extrafusal fibres
normal muscle fibres
where are muscle spindles found
within the belly of muscles and run parrallel to ordinary muscle fibres
what are annulospiral fibres
sensory nerve endings found in muscle spindles
what nerve supply do muscle spindles get
have their own efferent nerve supply called gamma motor neurons
what is the role of gamma motor neurons
adjust the level of tension in the muscle spindles to maintain their sensitivity when the muscle shortens during contraction
what can cause impairment of skeletal muscle function
intrinsic disease of muscle
disease of neuromuscular junction
disease of lower motor neurones
disruption of input to motor nerves
name 7 causes of intrinsic muscle disease
genetically determined myopathies
- congenital
- chronic degeneration of contractile elements (muscular dystrophy)
- abnormalities in membrane ion channels (myotonia)
acquired myopathies
- inflammatory(polymyositis)
- non innflammatory (fibromyalgia)
- endocrine (cushing syndrome, thyroid disease)
- toxic myopathies (alcohol, statins)
what is myotonia
delayed relaxation after voluntary contraction
what is myalgia
muscle pain
what are 5 usefu investigations into neuromuscular disease
electromyography (EMG)
nerve conduction studies
muscle enzymes (CK)
inflammatory markers (CRP, PV)
muscle biopsy
