limbs and back week 3 Flashcards
Describe the ATP pool in skeletal muscle
it is small and capable of supplying only for a very few contractions if not replenisehd
Why are ATP supplies only moderately depleted even as the muscle fatigues?
It is continually replenished
What is the function of creatine phosphate?
It is used to convert ADP to ATP and thus replenish the ATP store during muscle contraction.
Represents the immediate high-energy source for replacing the ATP supply in skeletal muscle, especially during intense exercise
What enzyme catalyses the reaction between ADP and creatine phosphate?
creatine phosphokinase
Where is CPK found?
Mostly in the sarcoplasm but some at the myosin heads too
How big is the creatine phosphate store?
Only 5 times to size of the ATP store and can’t last over 1 minute
How is creatine phosphate replenished?
During recovery from fatigue by using the ATP synthesised by oxidative phosphorylation
Where do muscles get carbohydrates from?
Muscle cells contain glycogen stores which can be metabolised during muscle contraction to provide glucose for oxidative phosphorylation and glycolysis
Muscle cells can also take up glucose from the blood
ATP yields are dependent on an adequate oxygen supply
When are fatty acids important sources of energy for muscle?
During prolonged exercise
Where do muscles get fatty acids from?
Muscle cells contain fatty acids
they can uptake fatty acids from the blood
muscle cells can store triglycerides, which can be hydrolysed to produce fatty acids
How are fatty acids metabolised in muscle?
they are converted into acyl-carnitine in the cytosol then transported into the mitochondria
Then they are converted into acyl-CoA
Within the mitochondria acyl-CoA is then subjected to Beta oxidation and yields acetyl-CoA
This enters the citric acid cycle and ultimately produces ATP.
What is fatigue?
The inability to maintain power output of muscle, reversible by rest
What occurs as a result of fatigue?
reduced force, shortening and relaxation rate
Describe central fatigue
within the nervous system
loss of excitability of the motor cortex, possible reflex inputs from “metabo-receptors” in muscle
can include failure of transition in peripheral nerve and neuromuscular junctions (usually pathological)
Describe peripheral fatigue
within the muscle fibres
failure of excitation - contraction coupling, T-tubule action potential, SR activation, Ca2+ release
How can you determine the type of fatigue?
external stimulation - if direct muscle stimulation delivers smaller forces then fatigue is peripheral. If stimulation delivers “normal” forces, then fatigue is central
Describe excitation failure
most likely in short intensity exercise
High AP firing rates leads to accumulation of K+ ions in tubules
This would make the T-tubule unexcitable and impairs excitation contraction coupling
recovery from this type of fatigue would be rapid
When is central fatigue likely?
Probably likely in occupational work and recreational sport. sensation of fatigue may involve discomfort and lack of motivation.
probably not a factor in elite sport
When does peripheral fatigue occur?
fatigue is not due to decreased ATP
In fatigue concentrations of H+, Pi and ADP all increase
these changes impair calcium fluxes and impair force delivery at cross bridges
Why does the build up of ADP, Pi and H+ inhibit the function of ATP?
An increase in the right and side of the equation will shift the equilibrium to the left and hence slow the break down of ATP
What else do ADP, Pi and H+ all inhibit?
Ca2+ release and reuptake into the sarcoplasmic reticulum. This affects the force and speed of shortening and relaxation.
H+ also competes with Ca2+ for troponin binding
What is the main energy source for long duration exercise?
Carbohydrate and lipid metabolism
What is the main energy source for moderate duration exercise?
aerobic, fuel mix uses more carbohydrates
What is the main energy source for short duration exercise?
aerobic and anaerobic metabolism, carbohydrate dependent, inefficient glycolytic metabolism
Describe the processes of training
requires multiple repetitions of the exercise concerned
for strength - small numbers of high power contractions
for endurance - large numbers of low force contractions
in strength training type 2 fibres enlarge
in true endurance training (e.g. marathon) no demand for increased strength, type 1 fibres may enlarge but type 2 decrease. Usually there is a loss of fat.
Describe the neural phase of strength training
first 4-6 weeks
CNS response, increased recruitment of largest motor units and higher maximum firing rates
Describe the hypertrophy phase of strength training
large motor units grow
significant hormonal changes - after strenuous strength training, GH, local growth hormones and testosterone are all elevated for hours
connective tissues also strengthen
hypertrophy is slow
starts with the development of new filaments attached laterally to existing myofibrils
Later there is fibril splitting - the most enlarged fibrils split longitudinally - thus become more numerous
How can skeletal muscle fibres be classified?
As fast twitch (2a/2b) or slow twitch (1)
How can the different types of muscle fibres be distinguished from one another?
the activities of oxidative and glycolytic pathways.
Describe fast twitch fibres
the activity of the glycolytic enzymes is high and the activity of the oxidative enzymes is low. -
very few mitochondria
more extensive sarcoplasmic reticulum than slow twitch
fatigue quickly
Describe slow twitch fibres
meet metabolic demands by oxidative phosphorylation
fatigue more slowly
What is special about 2a fibres?
They contain both high glycolytic and oxidative capacity - rare in humans
What is spacial summation?
Since fast-twitch muscle fibres are more difficult to excite slow twitch muscle fibre motor units are recruited first.
As more force is required, fast fibres are recruited
What are the advantages of spacial summation?
The first muscle fibres recruited have high resistance to fatigue
the small size of the slow-twitch muscle units allows fine motor control
What are the three bones of the elbow joint?
The humerus, ulna and radius
What are the two articulations of the elbow joint?
Humeri-ulnar = between the trochlea of the humerus and the trochlear notch of the ulna Humero-radial = between the capitulum and upper surface of the radial head
What limits movement at the elbow joint?
fossas
Describe movement at the elbow joint
Flexion and extension - hinge joint, very stable, not likely to dislocate
How can hyperextension occur?
If the olecranon fossa forms a foreman instead, the olecranon of the ulna can pass right through
Describe the proximal radioulnar joint
also contained within the elbow joint capsule
the articulation between the head of the radius and the radial notch of the ulna
annular ligament wraps around the head of the radius and maintains stability of the radius
allows rotation during pronation and supination of the forearm.
Primary supination muscle is the biceps
What are the 3 flexors of the elbow joint?
Brachialis (primary flexor)
Brachioradialis (accesorry) only when forearm is mid-pronated
Biceps bracchi - only if palm is upwards
What is the extensor muscle of the elbow joint?
triceps brachii (long head, lateral head, medial head)
What forms the compartments of the forearm?
The interosseous membrane
What is the function of the interosseous membrane?
Stabilises the radius and ulna
What muscles are contained within the superficial and intermediate layers the anterior compartment of the forearm?
flexor carpi ulnaris
palmaris longus
flexor carpi radialis
pronator teres
What is the nerve supply to the superficial and intermediate layers of the anterior compartment of the forearm?
all musculocutaneous nerve except flexor carpi ulnaris which is supplied by the ulnar nerve
What muscles are contained in the deep layer of the anterior compartment of the forearm?
flexor digitorum profundus
flexor policis longus
pronator quadratus
What is the nerve supply to the deep layer of the anterior compartment of the forearm?
Musculocutaneous expect half of flexor digitorum profundus is supplied by the ulnar nerve - the part that flexes the ring and little fingers
Which muscles are contained within the superficial layer of the posterior compartment of the forearm?
brachioradialis extensor carpi radialis longus extensor carpi radialis brevis aconeus extensor digitorum extensor digiti minimi extensor carpi lunaris extensor retinaculum
What is the nerve supply of the superficial layer of the posterior compartment of the forearm?
Radial nerve
Which muscles are contained within the deep layer of the posterior compartment of the forearm?
Abductor policis longus
extensor policis brevis
extensor indicis
extensor policis longus
What is the nerve supply to the deep layer of the posterior compartment of the forearm?
radial nerve
What is epicondylitis?
Tennis / golfer’s elbow
caused by resisting / limiting wrist movement
pain radiates along affected muscles
What side is tennis elbow?
lateral
What side is golfer’s elbow?
medial
how is epicondylitis treated?
rest or injection of corticosteroids if pain is severe
What is the cubital fossa?
A triangular shaped depression anterior to the elbow
What is the lateral boundary of the cubital fossa?
brachioradialis
What is the medial border of the cubital fossa?
pronator teres
What is the superior border of the cubital fossa?
imaginary line between the medial and lateral epicondyles
What is the floor of the cubital fossa?
brachialis
What is the roof of the cubital fossa?
deep fascia reinforced by bicipital aponeurosis
What is contained in the cubital fossa?
tendon of biceps
brachial artery
median nerve
radial nerve (underneath brachioradialis)
Why is the cubital fossa an important site for venipuncture?
deep fascia protects the underlying brachial artery and median nerve
safe place to take blood sample
Describe the blood supply to the forearm
the brachial artery bifurcates in the cubital fossa into the radial and ulnar arteries.
Where do the radial and ulnar arteries lie?
lateral to the tendons of the flexor carpi ulnas and flexor carpi radialis
Why is the ulnar artery more difficult to palpate?
Mostly covered by the flexor carpi ulnaris
what is gastrulation?
a process of cell division and migration resulting in the formation of 3 germ layers
What are the three germ layers called?
ectoderm, mesoderm, endoderm
What does ectoderm form?
epidermis of skin and its derivatives epithelial lining of mouth and anus cornea and lens of eyes nervous system sensory receptors in the epidermis adrenal medulla tooth enamel epithelium of pineal and pituitary glands
What does mesoderm form?
notochord skeletal system muscular system muscular layer of stomach lining excretory system circulatory and lymphatic systems reproductive systems lining of body cavity adrenal cortex
What does endoderm form?
epithelial lining of digestive tract epithelial lining of respiratory system lining of urethra, urinary bladder and reproductive system liver pancreas thymus thyroid and parathyroid glands
When does mesoderm differentiate?
days 17-21
what does mesoderm differentiate into?
paraxial
intermediate
lateral plate
what does paraxial mesoderm form?
cells moving bilaterally and cranially
forms somites
what does intermediate mesoderm form?
genitourinary systems
what does lateral plate mesoderm form
somatic and splanchnic layers
where does skeletal muscle originate from?
paraxial mesoderm
where does smooth muscle originate from?
visceral layer of the lateral plate mesoderm
where does cardiac muscle originate from?
visceral later of the lateral plate mesoderm
what type of mesoderm gives rise to somites?
paraxial
what stimulates the start of somitogenisis?
NOTCH accumulation on the pre-somatic mesoderm
signal for somite formatoin
once somite is formed NOTCH decreases
What is a somite?
a block of mesoderm which gives rise to skeletal muscle
what do somites split into?
sclerotome and dermatomyotome
What does sclerotome form?
the vertebrae and ribs
what does dermatomyotome split into?
dermatome and myotome
what does dermatome form?
dermis of the back
what does myotome form?
muscles
What are myoblasts?
myotome cells - committed muscle cell precursors
What are the transcription factors involve in skeletal muscle formation?
MYOD and MYF5
Which molecules regulate somite differentiation?
WNT proteins (activating)
BMP (inhibitory)
sonic hedgehog
noggin
describe smooth muscle
orientates from splanchnic mesoderm
serum response factor (SFR) is responsible for smooth muscle cell differentiation
SFR unregulated by kinase phosphorylation pathways
Myocardin / myocardin-related transcription factors enhance SFR activity
Describe skeletal muscle
myoblasts fuse to form long multinucleate fibres
striated , contain many mitochondria
under control of genes sets including MYOD, Mfy5 and myogenic
tendons are derived from the sclerotome under the control of the transcription factor sceraxis
Describe cardiac muscle
splanchnic mesoderm surrounding developing heart tube
striated - different from skeletal
myoblasts adhere to each other via intercalated disks
MYOD not involved in early cardiac muscle development
TInnman - homeobox gene responsible for specification of cardiac muscle
what do sensory neurons do?
relay information centrally to the spinal cord
What do motor neurons do?
responsible for causing muscle contraction - ventral horn of the spinal cord
What are peripheral nerves?
The axons of motor and sensory neurons
Describe the spinal cord in terms of innervation
caudal part of the CNS
continuous with the brain stem
organised segmentally - 8 cervial, 12 thoracic, 5 lumbar and 1 coxygeal
each segment gives rise to a pair of spinal nerves
What nerves form the cervical plexus?
C1-C5
What nerves from the brachial plexus?
C5-T1
What nerves from the lumbosacral plexus?
T12-S5
Describe the difference between myelinated and unmyelinated nerves/
myelinated - large diameter, fast conduction, touch, vibration, motor output
non-myelinated - small diameter, slow conduction, pain, hot, cold
What is a myotome?
each muscle is supplied by a particular level / segment of the spinal cord and its corresponding spinal nerve
What is a dermatome?
An area of skin innervated by a particular level / segment of the spinal cord
What is the ASIA scale used for?
to determine the level and extent of spinal cord injury
What is proprioception?
sensations arising from the deep field as a result of the actions of the organism
What factors contribute to proprioceptive sensations?
passive displacement of the joints (and skin) movement sense (awareness of joint movement) Position sense (awareness of static joint position)
