Case 9 - Yaffas Flashcards
what are the two types of lower motor neurones
alpha and gamma
what do the alpha LMNs innervate and what are they involved in
extrafusal muscle fibres, and so are involved with the strength and power of a muscle
what do the gamma LMNs innervate and that are they involved in
innervate intrafusal muscle fibres, and so are involved with muscle tone and muscle tension
where do individual motor neurone axons branch
within muscles to synapse on many different fibres that are typically distributed over a relatively wide area within the muscle
what comes together to constitute the smallest unit of force that can be activated to produce movement
a single alpha motor neurone and its associated muscle fibres
what do small alpha motor neurones innervate
few muscle fibres and form motor units that generate small forces
what do large motor forces innervate
larger, more powerful motor units
what are examples of slow twitch muscle fibres
type I, red muscle - ‘slow oxidative fibres’
what are slow twitch muscle fibres innervated by
small alpha motor neurones and so form part of small motor units
do slow twitch muscle fibres have a rich blood supply
yes - rich capillary beds
why do the muscles appear red
rich myoglobin
two more features of slow twitch muscle fibres
greatly increased number of mitochondria
resistant to fatigue
what are slow twitch muscle fibres especially important for
activités that require sustained muscular contraction, such as the maintenance of an upright posture
examples of intermediate muscle fibres
type IIA - fast oxidative glycolytic fibres
features of intermediate muscle fibres
they are fast fatigue resistant motor inits and of intermediate size so not quite as fast as FF units
they generate more force than a slow motor unit and, are substantially more resistant to fatigue than an FF unit
they can generate ATP by substrate level phosphorylation (glucose > lactic acid)
what are examples of fast twitch muscle fibres
type IIB, white muscle - fast glycolic fibres
what are fast twitch muscle fibres innervated y
large alpha motor neurones and so form part of gait fatigueable motor units
what are the large fibres important for
great strength of contraction
features of fast twitch muscle fibres that allows for rapid release of calcium ions to initiate contraction
extensive sarcoplasmic reticulum
what is found in large amounts in fast twitch muscle fibres that allows for rapid release of energy by the glycolic process
large amounts of glycolytic enzymes
other features of fast twitch muscle fibres
less extensive blood supply
fewer mitochondria
easily fatigued
what are the principle energy storage molecules utilised by type IIb (fast twitch muscle fibres)
creatine phosphate and glycogen
motor unit types summary diagram
what is a basic rod-like unit of muscle called
myofibril
what are myofibrils composed of
actin, myosin, and titin and other proteins that hold them together
how are these proteins organised?
into thin filaments and thick filaments, which repeat along the length of the myofibril in sections called sacromeres
what are the thin filaments
actin
what are the thick filaments
myosin
why do the myofibrils have alternate light and dark bands
the myosin and actin filaments partially interdigrate
what do the light bands contain
only actin filaments and are called I bands
what do the dark bands contain
myosin filaments and actin filaments and are called A bands
where are the ends of the actin filaments attached to
a Z disc
features of the Z discs
from the Z disc, these filaments extend in both directions to interdigitate with the myosin filaments.
the Z disc passes crosswise across the myofibril and also crosswise from myofibril to myofibril, attaching the myofibrils to one another all the way across the muscle fibres. therefore, the entire muscle fibres has light and dark bands, as do the individual myofibrils. these bands give skeletal and cardiac muscle their striated appearance.
what is the portion of the myofibril that lies between two successive Z discs called
the sacromere
digram of muscle fibres
what is the sarcoplasm
the cytoplasm of muscles
what are the spaces between myofibrils filled with
this intracellular fluid
what is this fluid composed of
significant amounts of myoglobin, an oxygen binding molecule.
potassium, magnesium and phosphate ions
sarcoplasmic reticulum
protez enzymes
what lie parallel to myofibrils
mitochondria
feature of one end of a titin molecule
one end is elastic and is attached to the Z disc, acting as a spring and changing length as the sacroemere contrast and relaxes
what is the feature of the other part of the titin
tethers it to the myosin thick filament
what is the backbone of the actin filament
is the double stranded F actin protein molecule
what is each strand composed of
G actin molecules
what is attached to each G actin molecule and what is this thing
is one molecule of ADP and this is the active site
what is wrapped spirally around the sides of the F actin helix
tropomyosin
what happens in the resting state
the tropomyosin molecules lie on top of the active sites of the actin so that attraction cannot occur between the actin and myosin filaments to cause contraction
what is attached intermittently along the sides of the tropomyosin molecules
troponin
what does troponin I have a strong affinity for
actin
what does troponin T have a strong affinity for
tropomyosin
what does troponin C have a strong affinity for
calcium ions
what is believed to initiate the contraction process
the strong affinity of the troponin for calcium ions
what is a myosin molecule composed of
head, neck and tail
what does the myosin head bind to
the actin filament
what does the myosin head function as
an ATPase enzyme
what does the myosin neck act as
a linker and as a lever arm for transfusing force generated by the motor domain.
the myosin neck can also serve as a binding site for myosin light chains, which have regulatory functions
what does the myosin tail connect to
the myosin head to the body of the myosin molecule
what are the protruding tails and heads together called
cross bridges
neuromuscular junction, sequence of events.
Impulse (action potential) arrives at axon terminal.
Ca2+ ions rush in (as action potential activated Ca2+ gates); Ca2+ reacts with synaptic vesicles.
Synaptic vesicles fuse with cell membrane of axon terminal.
“ACh (acetylcholine) released through a process known as exocytosis.
ACh is synthesised in the axon terminal through the use of ATP. “
“ACh binds with motor end plate receptors: depolarization occurs as Na+ rushes into the
muscle cell, causing an end plate potential (EPP).
ACh is destroyed by acetylcholinesterase.”
Impulse travels through T-tubules which excite the sarcoplasmic reticulum (SR).
Ca2+ ions released from the SR.
Ca2+ binds with troponin.
Shift of tropomyosin, which makes the binding sites available for myosin S1 units to bind.
ATPase splits (hyrolysis) ATP = ADP + Pi + Energy
Myosin can now bind to active sites on actin.
Sliding action of actin over myosin called the Power Stroke.
Impulse stops to muscle; calcium ions pumped back into SR by Ca2+ (active transport) pumps.
Tropomyosin returns over the active sites on actin and muscle action ceases.
what destroys ACh and what does this do
acetylcholinesterase.
this rapid removal of the acetylcholine prevents continued muscle re-excitation after the muscle fibre has recovered from its initial action potential
what does each impulse that arrives at the neuromuscular junction cause
about three times as much end plate potential as that required to stimulate the muscle fibres
therefore the normal neuromuscular junction is said to have a high safety factor
however, continuous stimulation of the nerve fibre at great rates diminishes the number of acetylcholine vesicles so much that impulses fail to pass into the muscle fibre. this is called fatigue of the neuromuscular junction
what is the resting membrane potential in skeletal fibres
about -80 to -90 millivolts
what is the motor end point
a motor nerve fibre forms a complex of branding nerve terminals that invaginate into the surface of the muscle fibre but lie outside the ,muscle fibre plasma membrane
what is the motor end plate covered by
Schwann cells that insulate it
what happens when the T tubule action potentials act on the membranes of the longitudinal sarcoplasmic tubules
causes a release of calcium ions into the muscle sarcoplasm from the sarcoplasmic reticulum, resulting in contraction
calcium induced calcium release
The T tubule action potentials also open voltage-gated calcium channels in the membranes of the T Tubules themselves, which causes calcium ions to diffuse directly into the sarcoplasm.
The diffusion of calcium ions activates calcium release channels, also called ryanodine receptor channels, in the sarcoplasmic reticulum membrane of the longitudinal sarcoplasmic tubules.
This triggers the release of calcium ions from the sarcoplasmic reticulum into the sarcoplasm.
Calcium ions in the sarcoplasm then interact with troponin to initiate cross-bridge formation and contraction.
This is called calcium-induced calcium release.
what would happen without the extra calcium from the T tubules
the strength of muscle contraction would be reduced considerably
what does the strength of contraction of muscle depend on
the concentration of calcium ions in the extracellular fluids
what happens at the action potential
influx of calcium ions to the interior of the muscle fibre is suddenly cut off, and the calcium ions in the sarcoplasm are rapidly pumped back out of the muscle fibres (via the Na+/Ca2+ exchanger) into both the sarcoplasmic reticulum (SERCA Ca2+ pumps) and the T tubule–extracellular fluid space through the plasma membrane (PMCA Ca2+ pumps), stopping contraction or it is stored in the sarcoplasmic reticulum.
what are the four steps of muscular contraction
- ATP is hydrolysed when myosin head is unattached. the hydrolisation of ATP into ADP and inorganic phosphate allows the myosin head to return to the resting position
- ADP+ P are bound to myosin as myosin head attaches to actin
- ADP+P release causes head to change position and actin filament to move
- binding of ATP causes myosin head to return to resting position. binding of ATP causes myosin head to detach from the actin filament.
how does the contraction force increase
the greater number of cross bridges in contact with the actin filament at any given time
what happens in contraction
H and I bands shorten
A ands stay the same size
what are the two ways that summation occurs in skeletal muscle contraction
by increasing the number of motor units contracting simultaneously, which is called multiple fibre summation
bu increasing the frequency of contraction, which is called frequency summation and can lead to tetanisation
what are the 4 different types of muscle contraction
isometric
isotonic
concentric
eccentric
what is isometric muscle contraction
when the muscle does not shorten during contraction. the length of the muscle remains unchanged. e.g pushing against a wall
what is isotonic muscle contraction
when length of the muscle shortens but the tension on the muscle remains constant throughout the contraction
what is concentric muscle contraction
in the direction of contraction of a muscle
what is eccentric muscle contraction
in the opposite direction of contraction of a muscle
what is creatine phosphokinase
phosphocreatine contains high energy phosphate bonds which can be used to phosphorylate ADP to ATP by the enzyme creatine kinase
it is located in the Z line
what is myokinase
catalyses the transfer of a phosphate group from one ADP molecule to another to form ATP and the by product adenosine monophsophate
this is known as the last gap of short term energy stores
what happens in the metabolism with muscle contraction
In normal muscular contraction, glucose is covered into pyruvate and then CO2. this requires ATP via oxidative phosphorylation.
there is plentiful ATP but the process is slow
metabolism in intense muscular contraction
glycogen is converted into glucose and then lactate. this requires ATP via substrate level phosphorylation. there is limited ATP but the process is fast. oxygen and nutrient supply is rate limiting
what is the Cori cycle
oxygen is used by the liver to produce glucose from lactate
what does muscle hypertrophy result from
an increase in the number of actin and myosin filaments in each muscle fibre
what is fibre aplasia
the rate of synthesis of muscle contractile proteins is far greater when hypertrophy is developing in turn, some of the myofibrils themsevles have been observed to split within hypertrophying muscle to form new myofibrils
what happens when a muscle remains unused for many weeks
the rate of degeneration of the contractile proteins is more rapid than the rate of replacement
therefore, muscle atrophy occurs
the pathway that appears to account for much of the proteind graduation in a muscle undergoing atrophy id the ATP dependent ubiquitin proteasome pathway
what does loss of innervation to a muscle result in
atrophy
what happens after about 2 months
proteasome degradation, causing further muscle wastage
if the muscle is innervated again, when is full recovery made
within 3 months
what are the muscle fibres replaced with in the final stage of denervation atrophy
fibrous and fatty tissue
what does the fibrous tissue have a tendency to continue doing
shortening for many months which is called contracture
what can exercise lead to an increase in
muscle mitochondrial biogenesis
how does this happen
This is probably via Ca2+ signalling pathways in the cell as well as via a chronic imbalance of ATP demand versus ATP production by mitochondria which causes activation of signalling protein kinases.
what is AMPK
adenosine monophosphate-activated protein kinase:
This enzyme plays a role in cellular energy homeostasis.
This is the ‘fuel gauge of the cell’.
During a bout of exercise, AMPK activity increases while the muscle cell experiences metabolicstressbrought about by an extreme cellular demand for ATP.
Upon activation, AMPK increases cellular energy levels by inhibitinganabolic energy consuming pathways (fatty acidsynthesis,protein synthesis, etc.) and stimulating energy producing,catabolic pathways (fatty acid oxidation, glucose transport, etc.).
what does lack of exercise lead too
atrophy in muscles
Skeletal muscle atrophy causes a drop in:
Protein levels, fibre diameter, force production, and fatigue resistance.
A reduction in protein synthesis coupled with increased protein degradation pathways contribute to muscle loss due to disuse.
Proteolytic pathways (ubiquitin-proteasome, lysosomal, and calpain) are involved in muscle atrophy.
Transcription factor NF-κB and myostatin are important cell signallers for muscle cell atrophy. Lack of exercise leads to increase in these factors in muscle.
what does the gait cycle consist of
one cycle of swing and stance by one limb
what does the stance phase begin with
heel strike, when the heel strikes the ground and begins to assume the bodys full weight and ends with a push off by the forefoot - a result of plantarflexion
what are the four phases of the stance phase and what are the muscles used in each
Heel strike (initial contact) – Gluteus maximus and Tibialis anterior
Loading response (foot flat) – Quadriceps femoris
Midstance – Soleus and gastrocnemius (together known as Triceps surae)
Terminal stance (heel off) – Soleus and gastrocnemius (Triceps surae)
when does the swing phase start
begins after push off when the toes leave the ground and ends when the heel strikes the ground
what are the 3 phases of the swing phase and what are the muscles used
Preswing (toe off) – Rectus femoris
Initial and Midswing – Iliopsoas and rectus femoris
Terminal swing – Hamstrings, Tibialis anterior and Ankle dorsiflexers
how much of the walking cycle does each phase take up
the swing phase takes up 40% and the stance phase takes up 60%
why is the stance phase longer
because it features a period of double support as the weight is being transferred from one leg to the other
in running, there is no period of double support
what are local circuits in the spinal cord called
central pattern generators
what are these central pattern generators fully capable of controlling
the timing and coordination of complex patterns of movement, and of adjusting them in response to altered circumstances
what is the Romberg’s test
With the eyes open, three sensory systems provide input into the cerebellum to maintain truncal stability.
These are vision, proprioception, and vestibular sense.
Ask the subject to stand with their feet together without support, first with their eyes open and then with their eyes closed.
Closing the eyes eliminates vision.
If the proprioception and vestibular pathways are intact the subject will not sway.
If patient sways - Romberg positive.
If the subject sways with their eyes closed this indicted a defect in their proprioception pathways.
If the patient starts to sway with their eyes open or closed, this indicates a cerebellar lesion.
what is a stress fracture
a fracture occurring in normal bone that has been subject to excessive and repeated trauma resulting in cumulative microscopic fractures.
over time these micro-fractures exceed the capacity of normal healing resulting in the development of a macro fracture
how is stress fracture diagnosed
initially X rays are normal. but a bone scan or MRI will usually allow diagnosis to be made
what is the treatment for a stress fracture
protected weight bearing, rest, cross training and surgery
what is an osteophyte
these are bony projections that occur at the sites of cartilage degeneration or destruction near joints and intervertebral discs.
They are usually shaped like a rose-thorn.
why do osteophytes form
because of the increase in damaged joint’s surface area.
This is most common from the onset of arthritis.
Osteophytes limit joint movement and typically cause pain.
Osteophyte formation is related to sequential and consequential changes in bone formation that is due to aging, degeneration, mechanical instability, and disease.
why do more men than women get ACL injuries
Physical conditioning
Muscular strength
Neuromuscular control
Pelvis size – females have wider hips and so working their legs will cause the vastus lateralis to develop more than the vastus medialis, thus pulling the patella laterally and causing the tear in the ligament.
Lower extremity (leg) alignment
Increased looseness in ligaments
Effects of oestrogen on ligament properties
what are the three bones that meet to form the knee joint
the femur, tibia and patella
what are the 4 primary ligaments of your knee
medial and lateral collateral
cruciate ligament
posterior
what type of imaging shows an ACL injury
MRI
how are ACL tears surgically repaired
the ligament must be reconstructed
replaces the torn ligament with a tissue graft th
this graft acts as a scaffolding for a new ligament to grow on
may take up to 6 months recovery
what is the female athlete triad syndrome
syndrome of 3 interrelated conditions which include
- eating disorder
- menstrual dysfunction
- decreased bone mineral density
what is the two types of amenorrhoea
Primary amenorrhoea, which is the absence of menstruation by the age of 16.
Secondary amenorrhoea, which is the absence of menstruation for 3 months in a woman who has previously had cycles.
can hyperprolactinamyia cause amenhorrhoea
yes
what is shin splints
This is described as pain along the inner edge of the shinbone (tibia).
They are a common injury affecting athletes who engage in running sports or other forms of physical activity.
Most prevalent lower leg injury.
It ischaracterised by general pain in the lower region of the leg between thekneeand ankle.
They are caused by repeated trauma to theconnectivemuscle tissuesurrounding thetibia.
what Is pain associated with shin splints caused from
disruption of Sharpey’s fibres that connect the medial soleus fascia through the periosteum of the tibia where it inserts into the bone
when is the impact worsened
by running uphill, downhill on uneven terrain or on hard surfaces
what is patient/agent driven decision making
physician presents all options and the patient makes his or her own choice physician provides no recommendations
what is physician recommendation decision making
the physician explains all the options and also makes a recommendation
what is shared decision making
the patient and the physician work together to reach a mutual decision
what is the link between osteophytes and amenhorrhea
loss of oestrogen can damage bone health - low bone density
