Skeletal Muscle Physiology Flashcards
What types of muscle are smooth muscles
Skeletal and cardiac
What are muscle tissues capable of doing
developing tension and producing movement through contraction
What types of muscles are striated
skeletal and cardiac
What causes striation
Thin actin filaments and thick myosin filaments
What are skeletal muscles innervated by and what are they subject to
the somatic nervous system - subject to voluntary control
What are cardiac and smooth muscles innervated by and what does this result in
Autonomic nervous system - involuntary action
What are the 5 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 are skeletal muscle fibres organised into?
motor units
what is a motor unit
a single alpha motor neuron and all the skeletal muscle fibres it innervates
Muscles which serve fine movements (external eye muscles, muscles of facial expression and intrinsic hand muscles) have fewer fibres per motor unit. True or false
True
When precision is more important than power, how many fibres per motor unit will there be
few
In what case will there be hundreds to thousands of fibres per motor unit
Power more important than precision
Gap junctions are present in skeletal muscle or cardiac muscle
cardiac muscle
What initiates contraction in skeletal muscle
neurogenic initiation
What initiates contraction of cardiac muscle
myogenic initiation
Where is there a neuromusclular junction present - skeletal or cardiac
Skeletal
Where does the Ca++ come from in skeletal muscles
sarcoplasmic reticulum
Where does the Ca++ come from in cardiac muscles
From ECF and sarcoplasmic reticulum
What is excitation contraction coupling
Process whereby the surface action potential results in activation of the contractile mechanism of the muscle fibre
When is Ca2+ released from the lateral sacs of the sarcoplasmic reticulum in Skeletal muscles
When the surface action potential spreads down the transverse tubules (T Tubules)
What are T tubules
Extensions of the surface membrane that dip into the muscle fibre
What is the transmitter at the neuromuscular junction
Acetylcholine
What triggers the release of Ca2+ from lateral sacs of sarcoplasmic reticulum
The spread of action potential down the T tubules
Transverse tubules are surrounded by what
Lateral sacs
Skeletal muscle consists of parallel muscle fibres bundled by what
connective tissue
Skeletal muscle fibres usually extend where
The entire length of the muscle
What usually attaches skeletal muscles to the skeleton
Tendons
What form lever systems
Bones, muscles and joints
What does each muscle fibre contain
Many myofibrils
Myofibrils have alternating segments of what
Thick and thin protein filaments
Actin and mysocin are arranged into what and what are these
Sarcomeres - these are the functional units of muscle
What is the functional unit of any organ
The smallest component capable of performing all the functions of that organ
What is the functional unit of skeletal muscle
Sarcomere
Where is a sarcomere found
Between 2 Z lines - connect the thin filaments of 2 adjoining sarcomeres
What are the 4 zones of the sarcomere
A band
H zone
M line
I band
What is the A band made up of
THick filaments along the portions of thin filaments that overlap in both ends of thick filaments
What is the H zone
the lighter area within the middle of the A band where thin filaments dont reach
Where does the M line extend
Vertically down middle of A band within the centre of H zone
What does the I band consist of
Remaining portion of thin filaments that do not project in A band
What produces muscle tension
Sliding of actin and filaments on myocin filaments
Force generation depends on what
ATP dependent interaction between thick and thin filaments
What is ATP required for
Both contraction and relaxation
What is Ca2+ required for
to switch on cross bridge formation
How does Ca 2+ switch on cross bridge formation
It binds to troponin. This results in repositioning of troponin - tropomyocin complex to uncover the cross bridge binding sites on actin
When a muscle fibre is relaxed, why is there no cross bridge binding
Because the cross bridge binding site on actin is physically covered by the troponin tropomyosin complex
When a muscle fibre is excited, what happens in terms of Ca2+
Released Ca2+ binds with troponin, pulling troponin-tropomyosin complex aside to expose cross-bridge binding site. Cross bridge binding then occurs
What do motor units allow
simultaneous contraction of a number of muscle fibres
How is a stronger contraction achieved?
Stimulation of more motor units - motor unit recruitment
What helps prevent muscle fatigue
Synchronous motor units recruitment during submaximal contraction
Tension developed by each contracting muscle fibre depends on what 3 things?
- Frequency of stimulation and summation of contraction
- Length of muscle fibre at the onset of contraction
- Thickness of muscle fibre
Describe the relationship between action potential and duration of resulting twitch
The duration of the AP is much shorter than that of the resulting twitch
How is it possible to summate twitches to bring about a stronger contraction of skeletal muscle
Through Repetitive fast stimulation of skeletal muscle
Both cardiac and skeletal muscles can be tetanised. True or False
False - cardiac muscle cannot be tetanised
Why can cardiac muscle not be tetanised
The long refractory period prevents generation of tetanic contaction
How does tension in skeletal muscles increase?
With increasing frequency of stimulation
What is an important mechanism for modulating the force of contraction in skeletal muscle
Increasing the frequency of stimulation
When can maximal tetanic contraction be achieved?
When the muscle is at its optimal length before the onset of contraction
What explain the skeletal muscle length tension relationship
The sliding filament mechanism
Skeletal muscle tension is transmitted to bone via what
The stretching and tightening of muscle connective tissue and tendon
What are the 2 types of skeletal muscle contraction
Isotonic conraction and Isometric contraction
Isotonic contraction is used for what?
body movements and for moving objects - muscle tension remains constant as the muscle length changes
Isometric contraction is used fo what?
Supporting objects in foxed positions and for maintaining body posture
Muscle tension develops at constant muscle lenght
How are isotonic and isometric contractions transmitted to bone
Via the elastic components of muscle
Describe the relationship between velocity of muscle and load
As the load increases, the velocity of muscle shortening decreases
What produces purposeful skeletal muscle activity
Input from a variety of sources influence the activity of motor unit to produce purposeful skeletal muscle activity
Input to motor nerves could be excitatory or inhibitory. True or False
True
What 4 things can cause impairment of skeletal muscle function
Intrinsic disease of muscle
Disease of NMJ
Disease of lower motor neurons which supply the muscle
Disruption of inputs to motor unit
What are 3 types of genetically determined myopathies
Congenital
Degeneration (muscular Dystrophy)
Membraine ion channels (myotonia)
What are 3 types of acquired myopatihes
Inflammatory (polymyosytis)
Endocrine (Cushing syndrome, thyroid disease)
Toxic (alcohol, statins)
What is a reflex action
A stereotyped response to a specific stimulus
Reflex actions are the simplest form of what?
coordinated movement
What are important for localising lesions in the motor system
The neural pathaways for reflexes
Where are pathways responsible fore reflex action located at?
Various levels of the motor system
The stretch reflex is the simplest what?
Monosynaptic spinal reflex
What does the stretch reflex serve as
A negative feedback that resists passive change in muscle lenghth to maintain optimal resting length of muscle
What is the muscle spindle? and when is it activated?
The sensory receptor and By the muscle stretch
By stretching the muscle spindle, what does this do to the afferent neurons
It increases firing in the afferent neurons
Where do the afferent neurons synapse
In the spinal cord with the alpha motor neurons
The stretch reflex is coordinated by what?
simultaneous relaxation of antagonist muscle
How cant he stretch reflex be elicited
By tapping the muscle tendon with a rubber hammer
What muscle is stretch in the patella tendon reflex (knee jerk)
Quadriceps fermoris
Name 5 examples of reflexes that can be elicited by the rubber hammer
Knee, Ankle, Biceps, Triceps Jerk and the brachioradialis
What spinal segment is effected in the biceps jerk and brachioradialis
C5-6
What peripheral nerve is affected by the brachioradialis and triceps jerk
Radial nerve
what spinal segment is affected by the
a) knee jerk
b) ankle jerk
a) L3,4
b) S1,2
What spinal segment is affected in the triceps jerk
C6-7
What peripheral nerve is affected by the knee jerk
Femoral nerve
What peripheral nerve is affected in the ankle jerk
Tibial nerve
What peripheral nerve is affected in the biceps jerk
Musculocutaneous Nerve
What are the sensory receptors for the stretch reflex?
Muscle spindles
What are muscle spindles
A collection of specialised muscle fibres
What are muscle spindles also known as
intrafusal fibres
What are ordinary muscle fibres referred to as?
extrafusal fibres
Where are muscle spindles found and where do they run
Within the belly of muscles and they run parallel to ordinary muscle fibres
Muscle spindles have sensory nerve endings. What are these known as?
Annulospiral fibres
What are the efferent neurons that supply muscle spindles called
gamma motor neurons
what do gamma motor neurons do?
adjust the level of tension in the muscle spindles to maintain their sensitivity when the muscle shortens during muscle contraction
The contraction of intrafusal fibres contributes to the overal strength of the muscle contraction
False - it does not contribute
What does the discharge from the muscle spindles sensory ending do?
increases as the muscle is stretched
What are the 3 main differences between different types of skeletal muscle fibres
The enzymatic pathways for ATP synthesis
The resistance to fatigue - muscle fibres with greater capacity to synthesise ATP are more resistant to fatigue
The activity of myosin ATPase - ths determines the speed at which energy is made available for cross bridge cycling ie. the speed of contraction
What are 3 metabolic pathways that supply ATP in muscle fibres
Transfer of high energy phosphate from creatine Phosphate to ADP
Oxidative phosphorylation (main source when O2 is present)
Glycolysis (main source when O2 is not present)
What are type 1 fibres used for
prolonged relatively low work aerobic activities - maintenance of posture, walking
What are type 2a fibres used for
prolonged relatively moderate work activities - jogging
What are type 2x fibres used for
short term high intensity activities - jumping
What are 3 useful investigations in neuromuscular disease
Electromyography (EMG)
Nerve conduction studies
Muscle enzymes
