Physiology Flashcards
what are the 3 types of muscle in the human body?
skeletal
cardiac
smooth
what are the 3 types of muscle capable of?
developing tension & producing movement through contraction
which types of muscle are striated?
skeletal & cardiac
what do striations look like?
dark bands & light bands
what are the light bands in striations caused by?
actin (thin)
what are the dark bands in striations caused by?
myocin (thick)
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 are skeletal muscle fibres organised into?
motor units
what is one motor unit?
a single alpha motor neurone and all the skeletal muscle fibres it innervates
what does the number of muscle fibres per motor unit depend on?
the functions served by the muscle
- strength - lots of muscle fibres
- precision - fewer muscle fibres
how long is a muscle fibre?
the length of the muscle it’s in
what is the mechanism of the initiation of contraction in skeletal muscle?
neurogenic
what is the mechanism of the initiation of contraction in cardiac muscle?
myogenic
what two things are present in muscles that allow the propagation go contraction in skeletal muscle?
motor units & neuromuscular junctions present.
what one thing is present in muscles that allow the propagation go contraction in cardiac muscle?
gap junctions
where does the Ca++ from from to cause excitation coupling contraction in skeletal muscle?
Ca++ entirely from sarcoplasmic reticulum
where does the Ca++ from from to cause excitation coupling contraction in cardiac muscle?
Ca++ from ECF & sarcoplasmic reticulum
what does the gradation of contraction depend on in skeletal muscle?
1) motor unit recruitment
2) summation of contractions
what does the gradation of contraction depend on in cardiac muscle?
depends on the extent of heart filling with blood
what is excitation contraction coupling?
the process whereby the surface action potential results in activation of the contractile mechanism of the muscle fibre
where is Ca++ released from in skeletal muscle fibres & when?
released from the lateral sacs of the sarcoplasmic reticule when the surface action potential spreads down the transverse tubules (T-tubules)
what are the muscle fibres in skeletal muscle bundled by?
connective tissue
how are skeletal muscles usually attached to the skeleton?
by tendons
what intracellular structure does each muscle fibre contain lots of?
myofibrils
what do myofibrils have alternating segments of?
thick (myocin) & thin (acctin) protein filaments
how are actin & myosin arranged within each myofibril?
arranged not sacromeres
what are sarcomeres?
functional units of skeletal muscle
what is the functional unit of any organ?
the smallest component capable of performing all the functions of that organ
where is the sarcomere found?
between two z-lines which connect the thin filaments of 2 adjoining sacromeres
what are the four zones of a sarcomere?
the A-band, the H-zone, the M-line & the I-band
what is the A-band?
Made up of thick filaments along with portions of thin filaments that overlap in both ends of thick filaments
what is the H-zone?
Lighter area within middle of A-band where thin filaments don’t reach
what is the M-line?
Extends vertically down middle of A-band within the centre of H-zone
what is the I-band?
Consists of remaining portion of thin filaments that do not project in A-band
how is muscle tension produced?
by the sliding of actin filaments on myocin filaments
what does force generation depend on?
ATP-dependent interaction between thick (myocin) & thin (actin) filaments
what is required in both contraction & relaxation?
ATP
how does Ca++ switch on cross bridge formation?
Ca2+ binds to troponin. This results in repositioning of troponin- tropomyocin complex to uncover the cross bridge binding sites on actin.
what two primary factors does gradation (strength of contraction) of skeletal muscle depend on?
number of muscle fibres contracting within the muscle & tension developed by each contracting muscle fire
what is motor recruitment?
a stronger contraction can be achieved by stimulation of more motor units
what kind of motor unit recruitment can help prevent muscle fatigue?
a synchronous motore units recruitment during sub maximal contraction
what does tension developed by each contracting muscle fibre depend on?
- frequency of stimulation & summation of contraction
- length of muscle fibre at the onset of contraction
- thickness of muscle fibre
in skeletal muscle is the AP or the muscle twitch shorter?
the AP
how can you bring about a stronger contraction?
summate twitches to bring about a stronger contraction through repetitive fast stimulation of skeletal muscle
what happen if a muscle fibre is restimulated after it has completely relaxed?
the magnitude of the second twitch will be the same as the first twitch
what happens if a muscle fibre is restimulated before it has completely relaxed?
the second twitch is added onto the first twitch resulting in summaion
what happens if a muscle fibre is stimulated so rapidly that it does not have an opportunity to relax at all?
a maximal sustained contraction known as tetanus occurs
what prevents cardiac muscle from being tetanised?
the ling refractory period
what does a single twitch produce?
little tension & is not useful in bringing about meaningful skeletal muscle activity
if the frequency of stimulation is increased what happens to the tension developed by skeletal muscle?
increases
when can maximal tetanic contraction be achieved?
when the muscle is at its optimal length before the onset of contracion
what is the optimal length of muscle?
the point of optimal overlap of thick filament cross bridges & thin filaments cross bridge binding sites.
when does the percentage of maximal titanic contraction that can be achieved decrease?
when the muscle fibres is longer or shorter than optimum length before contraction
why does the muscle fibre being longer decrease the percentage of maximal titanic contraction that can be achieved?
When it is longer, fewer thin-filament binding sites are accessible for binding with thick-filament cross bridges, because the thin filaments are pulled out from between the thick filaments
why does the muscle fibre being shorter decrease the percentage of maximal titanic contraction that can be achieved?
When the fiber is shorter, fewer thin-filament binding sites are exposed to thick-filament cross bridges because the thin filaments overlap & further shortening and tension development are impeded as the thick filaments become forced against the Z lines
what is resting muscle length in the body?
optimal length
how much can muscles cary beyond their optimal length?
30% due to skeletal attachments
how is skeletal muscle tension transmitted to bone?
as a result of cross bridge cycling (contractile component) it is transmitted via the stretching & tightening of muscle connective tissue & tendon (elastic component)
what is isotonic contractions used for?
body movements & moving objects
what happens in isotonic contraction?
muscle tension remains constant as the muscle length changes
what is isometric contraction used for?
supporting objects in fixed positions & maintaining body posture
what happens in isometric contraction?
muscle tension develops at constant muscle length
how is muscle tension transmitted to the bone in the two types of contraction?
via elastic components of muscle
what 4 things can impairment of skeletal muscle function be caused by?
(1)Intrinsic disease of muscle (in the muscle itself)
(2) Disease of neuromuscular junction
(3) Disease of lower motor neurons
which supply the muscle
(4) Disruption of inputs to motor
unit
what main two types of myopathies are there?
genetic or acquired
what types of genetic myopathies can you get?
- congenital
- chronic degeneration of contractile elements
- abnormalities in muscle membrane ion channels
what happens in congenital myopathies?
characteristic microscopic changes lead to reduced contractile ability of muscles
give an example of a disease which involves the chronic degeneration of contractile elements
muscular dystrophy
give an example of a disease which involves abnormalities in muscle membrane ion channels
myotonia
what 3 types of acquired myopathies are there?
- inflammatory
- endocrine
- toxic
name an inflammatory myopathy
polymyosytis
name an endocrine myopathy
Cushing syndrome or thyroid disease
name a toxic myopathy
alcohol or statins
what is a reflex action?
a stereotyped response to a specific stimulus i.e. the simplest form of coordinated movement
what is the stretch reflex?
the simplest monosynaptic spinal reflex
what type of feedback is the stretch reflex?
negative feedback
what does the stretch reflex resist?
passive Chang ein muscle length to maintain optimal resting length of muscle
what does the stretch reflex help to maintain?
posture e.g. while walking
what is the sensory receptor in the stretch reflex?
the muscle spindle found in the muscle belly running parallel to ordinary muscle fibres
what does stretching the muscle spindle do?
increase firing in the afferent neurones
where do afferent neurones synapse?ion of the stretch reflex cause?
in the spinal cord with the alpha motor neurone (efferent limb of the stretch reflex) that innervate the stretched muscle
what does activation of the stretch reflex cause?
contraction of the stretched muscle
what is the stretch reflex coordinated by?
simultaneous relaxation of the antagonist muscle
how can the stretch reflex be elicited?
by tapping the muscle tendon with a rubber hammer
which spinal nerves are involved in the knee jerk?
L3 & L4
which peripheral nerve is involved in the knee jerk?
femoral nerve
which spinal nerves are involved in the ankle jerk?
S1 & S2
which peripheral nerve is involved in the ankle jerk?
tibial nerve
which spinal nerves are involved in the biceps jerk?
C5 & C6
which peripheral nerve is involved in the biceps jerk?
musculocutaneous nerve
which spinal nerves are involved in the brachioradialis?
C5 & C6
which peripheral nerve is involved in the brachioradialis?
radial nerve
which spinal nerves are involved in the triceps jerk?
C6 & C7
which peripheral nerve is involved in the triceps jerk?
radial nerve
what are muscle spindles?
collection of specialised muscle fibres
what are muscle spindles also known as?
intrafusal fibres
what are ordinary muscle fibres known as?
extrafusal fibres
what are the muscle spindles sensory nerve endings known as?
annulospiral fibres
what happens to the discharge from the muscle spindle endings as the muscle is stretched?
increases
what nerves supply the muscle spindle?y
have their own efferent (motor) nerve supple (gamma motor neurone)
what do gamma motor neurones adjust to keep muscle spindles’ sensitivity during contraction?
adjust the level of tension in the muscle spindles
does the contraction of intrafusal fibres contribute to the overall strength of muscle contraction?
no
what are the main differences between different types of skeletal muscle fibres?
- enzymatic pathways for ATP synthesis
- resistance to fatigue
- activity of myosin ATPase
which muscle fibres are more resistant to fatigue?
muscle fibres with a greater capacity to synthesise ATP
what does the activity of myosin ATPase determine?
the spread at which energy is made available for cross bridge cycling i.e. speed of contraction
what 3 metabolic pathways can supply muscle fibres with ATP?
- 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 slo oxidative type 1 fibres used for?
used mainly for prolonged relatively low work aerobic activities e.g. maintenance of posture, walking
what are fast oxidative type 2a fibres used for?
use both aerobic and anaerobic metabolism and are useful in prolonged relatively moderate work activities e.g. jogging
what are fast glycolytic type 2b fibres used for?
use anaerobic metabolism and are mainly used for short-term high intensity activities e.g. jumping
name 3 investigations useful for neuromuscular diseases
- electromyography (useful to differentiate between primary muscle disease or neurological disease)
- nerve conduction studies (determine functional integrity of peripheral nerves)
- muscle enzymes
what is skeletal muscle innervated by?
motor neurones with myelinated axons & cell bodies in the spinal cord or brain stem
what does the motor neurone axon divide into unmyelinated branches?
near to the muscle fibre
what does each unmyelinated branch of the motor neurone axon innervate?
an individual muscle cell
what do the unmyelinated branches of the motor neurone axon further divide into
multiple fine branches ending in a terminal bouton
what does each terminal bouton form a chemical synapse with?
the muscle membrane at the neuromuscular junction
what are action potential arising in the cell body conducted via?
the axon to the boutons causing the release of the transmitter acetylcholine
what are the key features of the skeletal neuromuscular junction?
- terminal bouton & surrounding schwann cell
- synaptic vesicles
- synaptic cleft
- end plate region of muscle cell membrane
where do synaptic vesicles awaiting release cluster?
active zones
where are the nicotinic acetylcholine receptors located?
regions of the junctional folds that face the active zones
what is acetylcholine synthesised from?
choline & acetyl coenzyme A
what do nicotinic ACh receptors assemble as?
pentamer of glycoprotein subunits that surround a central cation selective pore
the gate in the nicotinic ACh receptor opens when what?
2 molecules of ACh bid to the exterior of the receptor
what enters the muscle cell when the gat of the nicotinic ACh receptor is open?
sodium
what leaves the muscle cell when the gate of the nicotinic ACh receptor is open?
potassium
is influx of sodium or efflux of potassium greater at resting membrane potential?
influx of sodium is greater
what is the e.p.p?
end plate potential
caused by the activation of nicotinic ACh receptors at the endplate & is a graded response
If large enough, what does the e.p.p trigger?
the opening of voltage-activated Na+ channels around the end plate causing an action potential
what does one action potential in the motor nerve normally trigger?
one action potential in the muscle and a subsequent twitch
where does the action potential need to arrive at to trigger the release of calcium from the sarcoplasmic reticulum?
T-tubule triggers
what does the release of calcium from the sarcoplasmic reticulum cause?
contraction by interacting with troponin associated with the myofibrils
what is the rapid termination of neuromuscular transmission the result of?
hydrolysis of ACh by acetylcholinesterase (AChE)
what does AChE hydrolyse ACh to?
choline and acetate
what happens to the viscosity and elasticity of synovial fluid during rapid movement?
decreased viscosity
increased elasticity
what does normal synovial fluid look like?
clear & colourless
how do the zones of articular cartilage differ?
in organisation of collagen fibres & relative content of cartilage components
name the 4 zones of articular cartilage
superficial zone
middle zone
deep zone
calcified zone
what is the function of water in cartilage?
maintains the resilience of the tissue & contributes to the nutrition & lubrication system (705)
what is the function of collagen in cartilage?
maintain cartilage architecture and provides tensile stiffness & strength (20%)
what is the function of proteoglycan in cartilage?
responsible for the compressive properties associated with load bearing (10%)
which cells synthesise, organise, degrade & maintain the ECM>
chondrocytes
what do catabolic factors do to the cartilage matrix?
stimulate proteolytic enzymes & inhibit proteoglycan synthesis
name two catabolic factors
tumour necrosis factor-alpha
interleukin-1
what do anabolic factors do to the cartilage matrix?
stimulate proteoglycan synthesis & counteract effects of IL-1
name two anabolic factors
tumour growth factor-beta
insulin-like growth factor-1
what happens to serum & synovial keratin sulphate levels during cartilage breakdown?
increase
other than cartilage breakdown, when do serum & synovial keratin sulphate levels rise?
with age & in OA
what happens to type 2 collagen in synovial fluid during cartilage breakdown?
increase
when is type 2 collagen in synovial fluid particularly useful?
in evaluating cartilage erosion
what are the 3 types of pain?
nociceptive pain
inflammatory pain
pathological pain
which type of pain is maladaptive?
pathological pain
what are nociceptors?
specific peripheral primary sensory afferent neurones
when are nociceptors activated?
preferentially by intense stimuli that are noxious (e.g. thermal, mechanical, chemical)
what type of neurones are nociceptors?
first order neurones that relay information to second order in the CNS by chemical synaptic transmission
what causes inflammatory pain?
activation of the immune system in injury or infection
what does inflammatory pain cause?
pain hypersensitivity and allodynia
what does inflammatory pain assist with?
healing of a damaged body part by discouraging physical contact and movement
what does pathological pain result from?
abnormal nervous system function
what are the two types of pathological pain?
neuropathic or dysfunctional
what two fibre types compromise nociceptors?
Aδ-fibres
C-fibres
what are Aδ-fibres?
mechanical/thermal nocicepetors that are thinly myelinated
what do Aδ-fibres do?
respond to noxious mechanical and thermal stimuli, mediated “first” or fast pain
what are C-fibres?
unmyelinated
what do C-fibres do?
collectively respond to all noxious stimuli, mediate “second” or slow pain
which receptors are stimulated by thermal stimuli?
members of the transient receptor potential (TRP) family, particularly TRPV1
which receptors are stimulated by H+?
acid sensing ion channels (ASICs)
which receptors are stimulated by ATP?
P2X and P2Y
which receptors are stimulated by bradykinin?
B2 receptors
