Physiology Flashcards
what are the 3 types of muscles
skeletal
cardiac
smooth
which type of muscles are striated
skeletal
cardiac
striation can be visualised under a microscope as alternating dark and light bands - what causes the colour
dark - myosin
light - actin
what nervous system supplies each type of muscle
skeletal - somatic (voluntary control)
smooth and cardiac - autonomic (involuntary)
what are the physiological functions of skeletal muscles
maintenance of posture movement respiratory movements heat production whole body metabolism
skeletal muscle fibres are organised into motor units - what is a motor unit
single alpha motor neuron and all the skeletal muscle fibres it innervates
muscles which serve fine movements have more fibres per motor unit - true or false
false
they have fewer fibres per motor unit
why is there fewer fibres per motor unit in muscles involved in fine movements
precision more important than power
when power is more important than precision, how many fibres are in a muscle per motor unit
hundreds to thousands
e.g. thigh muscles
what is the functional unit of skeletal muscles
sarcomere
which type of muscles has gap junctions - cardiac or skeletal
cardiac
where does the skeletal muscle get calcium from
entirely from sarcoplasmic reticulum
where does cardiac muscle get calcium from
ECF and sarcoplasmic reticulum
what is excitation contraction coupling
process whereby the surface action potential results in activation of the contractile mechanisms of the muscle fibre
in skeletal muscle, when is calcium released from the lateral sacs of the SR
when the surface action potential spreads down the transverse (T)-tubules
steps to contraction of muscle
1 - ACh released by axon of motor neurone and binds to receptor
2- AP generated in response and moves down T tubules of muscle cell
3 - AP in T tubule triggers calcium release from SR
4 - calcium ions released from lateral sacs bind to troponin on actin filaments
5 - tropomyosin moved aside to uncover cross-bridge binding sites on actin
6 - myosin cross bridges attach to actin filaments toward centre of sacromere (powered by ATP)
7 - calcium taken up by SR when there is no longer a AP
8 - when calcium no longer bound to troponin, tropomyosin moves to block actin binding site again.
Contraction ends
there is continuity of cytoplasm between nerve and skeletal muscle cells - true or false
false
there is NO continuity
what is the transmitter at neuromuscular junctions
ACh
what triggers the release of Ca2+ from lateral sacs of SR
spread of AP down the T-tubules
what does muscle fibre contain
myofibrils
what are myofibrils composed of
thin and thick protein
thin - actin (lighter)
thick - myocin (darker)
what are actin and myocin arranged as
sacromeres
where is the sarcomere found
between two Z lines
what are the 4 zones of sarcomere
A-band
H-zone
M-line
I-band
what is the A band
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
remaining portion of thin filaments that do not project in A-band
how is muscle tension produced
sliding of actin filaments on myosin filaments
what is required for muscle movement
ATP - for contraction and relaxation
Ca2+ - to switch on cross bridge formation
how does calcium 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
when is the actin binding site covered by the troponin-tropomyosin complex
when muscle fibres are relaxed
what is required for a stronger contraction
stimulation of more motor units
- motor unit recruitment
what helps prevent muscle fatigue
a synchronous motor unit recruitment during sub maximal contractions
what factors are responsible for tension developed by each contracting muscle fibre
- freq of stimulation and summation of contractions
- length of muscle fibres at the onset of contraction
- thickness of muscle fibre
what is the basic physiological rule in skeletal muscles
the duration of AP is much shorter than the duration of resulting twitch
therefore possible to summate stronger contractions through repetitive fast stimulation
what is tetanus
muscle fibre is stimulated so rapidly that it does not have time to relax at all between stimuli it reaches a maximal sustained contraction
why can cardiac muscle not be tentanised
due to a long refractory period
what is it called when a skeletal muscle is stimulated once and why is it useless
single contraction is called twitch
produces little tension which is not useful for meaningful skeletal muscle activity
how can the response be amplified
second stimulation before it has had time to completely relax
how can tension developed by skeletal muscle increase
increasing frequency of stimulation
how is a sustained and much stronger contraction produced
skeletal muscle is stimulated very rapidly with no opportunity to relax between stimuli
when can maximal tetanic contraction be achieved
when muscle is at optimal length before onset of contraction
what does developed tension depend on
initial length of skeletal muscle fibre
the resting length of a skeletal muscle is NOT its optimal length - true or false
false
it is
what are the two types of skeletal muscle contraction
isotonic
isometric
what is isotonic contraction
used for body movements and for moving objects
muscle tension remains constant as the muscle length changes
what is isometric contraction
used for supporting objects in fixed position and for maintaining body posture
muscle tension develops at constant muscle length
what is the rule for the velocity of muscle shortening
The velocity of muscle shortening decreases as the load increases
what is the stretch reflex
the simplest monosynaptic spinal reflex
negative feedback that resists passive change in muscle length to maintain optimal resting length of muscle
what is the pathway of the stretch reflex
sensory receptor i.e. muscle spindle activated by muscle stretch.
Increase firing in the afferent neurones
Synapse in the spinal cord with the alpha motor neurones (efferent limb)
Innervate the stretched muscle
what needs to happen for the stretch reflex to happen
the antagonist muscle must relax
what spinal segment and peripheral nerve are responsible for the knee, ankle, biceps, brachioradialis and triceps jerk
Knee - L3,L4 - Femoral Nerve Ankle - S1,S2 - Tibial nerve Biceps - C5-C6- Musculocutaneous nerve Brachioradialis - C5-C6- Radial nerve Triceps - C6,C7 - Radial nerve
what are muscle spindles and where are they found
collection of specialised muscle fibres that have sensory nerve endings
found within belly of muscles are run parallel to ordinary muscle fibres
when does the discharge from the muscle spindles increases
when the muscle is stretched
what supplies the muscle spindles
gamma motor neurones
adjust level of tension in the muscle spindles to maintain their sensitivity when the muscle shorten during muscle contraction
what are the main differences between different types of skeletal muscles
the enzymatic pathways for ATP synthesis
resistance to fatigue (muscles with greater capacity to synthesis ATP are more resistant to fatigue)
activity of myosin ATPase
what are the metabolic pathways suppling ATP in muscle fibres
Glycolysis
Oxidative phosphorylation
Transfer of high energy phosphate from creatine phosphate to ADP
what are the 3 types of muscle fibres
Type I - slow oxidative
Type IIa - fast oxidative
Type IIx - fast glycolytic
what are Type I muscle fibres used for
a.k.a slow-twitch fibres
prolonged relatively low work aerobic activities e.g. maintenance of posture, walking
what are Type IIa muscle fibres used for
a.k.a intermediate-twitch fibres
used for both aerobic and anaerobic metabolism in prolonged relatively moderate work
e.g. jogging
what are Type IIx fibres used for
a.k.a fast twitch fibres
anaerobic metabolism and used for short term high intensity activities
e.g. jumping
what is the pathway of innovation for skeletal muscles
Myelinated motor neurone»_space;> unmyelinated branches»_space;> each branch innervates an individual skeletal muscle cell within a muscle (neurone + no. of fibres = motor unit) »_space;> multiple fine branches
what do the multiple fine branches end with
terminal bouton that forms a chemical synapse with the neuromuscular junction
what are the 3 types of joint
synovial
fibrous
cartilaginous
what are fibrous joints
bones united by fibrous tissue
doesn’t allow movement
e.g. skull
what are cartilaginous joints
bones united by cartilage
allow limited movement
e.g. intervertebral discs, pubic symphasis
what are synovial joints
bones separated by a cavity and united by a fibrous capsule lined by synovial membrane
what does the synovial membrane contain
synovial cells (fibroblasts) which produce synovial fluid
what is the difference between simple and compound synovial joints
simple - one pair of articular surfaces
compound - more than one pair of articular surfaces
functions of synovial fluid
lubricates joint facilitates joint movements minimise wear and tear of joints aids nutrition of articular cartilage supplies the chondrocytes with oxygen and nutrients and removes CO2 and waste product
why does synovial fluid have a high viscosity
due to presence of hyaluronic acid produced by synovial cells
what is rapid movement associated with in reference to synovial fluid
decreased viscosity
increased elasticity
these properties become defecting in diseased joints e.g. OA
when would synovial fluid be red instead of colourless
hemorrhagic arthritis
when would the WBC count increase in synovial fluid
inflammatory and septic arthritis
what is hyaline cartilage composed off
ECM predominantly of water, type II collagen and proteoglycans
where is proteoglycan found in cartilage and what is it composed of
highest conc in middle and deep zone
composed of glycosaminoglycan
what synthesis and degrades ECM
Chondrocytes
articular cartilage has a rich blood supply - true or false
false
is avascular; receives nutrients and O2 from synovial fluid
when would joint disease occur
rate of ECM degradation exceeds the rate of its synthesis
what are the catabolic and anabolic factors of cartilage matrix turnover
catabolic - Stimulate proteolytic enzymes and inhibit proteoglycan synthesis. e.g. Tumour necrosis factor (TNF)-α and Interleukin (IL)-1
Anabolic - Stimulate proteoglycan synthesis and counteract effects of IL-1 e.g. Tumour growth factor (TGF)-β and Insulin-like growth factor (IGF)-1
what are markers of cartilage degradation
type II collagen in synovial fluid
serum and synovial keratin sulphate
where do the terminal (bouton) synapse
the endplate region of skeletal muscle fibres
what is the pre-synaptic process of skeletal muscle
- choline transported into terminal by choline transporter
- ACh synthesised in cytosol from choline and acetyl CoA by enzyme CAT
- stored in vesicle
what happens in cell once AP arrives
depolarisation and opening of voltage-activated calcium channels
thus allowing entry of calcium to the terminal causing vesicles to fuse with presynaptic membrane
what happens after vesicles fuse with presynaptic membrane
ACh diffuses into the synaptic cleft to activate post synaptic nicotinic ACh receptors in the endplate region
what is the post-synaptic process
opens central gate with two molecules of ACh - allows Na to enter (influx) and potassium to exit (efflux)
influx of sodium greater than efflux of potassium
what does the greater influx of sodium cause
depolarisation known as the end plate potential
what is a miniature endplate potential (m.e.p.p)
electrical response to one quantum of transmitter, due to activation of nicotinic ACh receptors at the end plate
in what fashion does the e.p.p. elicit a response
all or none propagated AP
what does the e.p.p trigger
opening of voltage activated sodium channels causing a muscle action potential
how does the muscle AP cause contraction
by the release of Calcium from intracellular stores
how is the action of ACh terminated
by AChE
hydrolyses ACh to choline (picked up by choline transporter) and acetate (diffuses from synaptic cleft)
what are the 3 types of pain
nociceptive, inflammatory, pathological
nociceptive pain caused by nociceptive receptors has a low threshold - true or false
false
has high threshold provoked only by intense stimuli
what does a trigger of the nociceptive receptors/pain cause
withdrawal reflex (moving hand away from something hot)
why do we have inflammatory pain
caused by immune system
discourages physical contact
discourages movement
promotes repair
how is pathological pain differ form inflammatory pain
no protective function
results from abnormal nervous system function
what are the subtypes of nociceptor
Aδ-fibres are mechanical/thermal nociceptors that are thinly myelinated
C-fibres are nociceptors that are unmyelinated
which type of fibre response to fast and ‘first’ pain
Aδ-fibres
3 types of stimuli
mechanical, thermal or chemical
how is the amplitude of generator potential graded in pain
proportional to stimulus intensity
outline of neurogenic inflammation
1 - peptides (SP and CGRP) released from free nerve endings due to damage/trauma
2 - SP causes vasodilation, release of histamine from mast cells
3 - CGRP induces vasodilation
4 - primary + secondary hyperalgesia and allodynia
