Muscular system Flashcards
What are the components of a basic motor unit?
Central motor control area Primary neurone to synapse Spinal chord Motor neuron Neuro-muscular junction Muscle
Brain control of movement
Lateral pathways = voluntary muscle movements from direct cortical control
Ventromedial pathways = posture and locomotion from brain stem control
Why is white matter in the spinal chord so important?
White matter = information highway
Ascending tracts: sensory inputs
Descending tracts: motor inputs (autonomic and somatic)
Cell bodies of motor neurons lie within the ventral horn of the spinal chord (grey matter)
Neurotransmission at the neuromuscular junction
A neuron is activated when the membrane potential reaches a threshold level, triggering an action potential. This triggers an action potential. 1. Action Potential 2. Ca2+ entry 3. Vesicle fusion 4. ACh release 5. ACh receptor activation 6. Current Propogation 7. ACh removal
Excitation-contraction coupling
Excitation of a muscle cell causes its contraction nearly simultaneously
Made possible by:
- close proximity between sarcolemma/T tubule, sarcoplasmic reticulum and myofibrils
Myofibrils surrounded by sarcoplasmic reticulum
T tubules continuous with extracellular fluid
Depolarisation of t-tubule membrane = big release of Ca+ into cystol from different sources
Describe a myofibril
Sarcoplasm contains many long, protein-rich structures called myofribrils
Made up of:
- actin (thin strands)
-myosin (thick strands)
which are organised into sarcomeres = basic contractile unit of a muscle fibre
Sliding filament hypothesis
AT REST: troponin (protein) covers actin filament
- when calcium is released from SR due to action potential, calcium binds to troponin exposing the actin
- myosin head binds to exposed sites and pivots, shortening myosin filaments = contraction
- ATP is needed to disengage the myosin head = muscle relaxation
What are the two components needed for muscle contraction and their importance?
ATP
- obtained from creatinine phosphate, aerobic and anaerobic metabolism
- allows for detachment of myosin head from actin binding sites
- rigor mortis if no ATP
CALCIUM
- at rest is stored in sarcoplasmic reticulum
- action potential triggers release from SR, binding to actin to expose actin binding sites, myosin head attaches = contraction
- active re-uptake by SR
- myopathies, statins-induced myotoxicity
The importance of acetylcholine at the neuromuscular junction
Is the neurotransmitter released at the synapse to propagate action potential
Broken down by ACETYLCHOLINESTERASE
into choline and acetic acid which is reabsorbed (choline transporter)
What is neuropathy?
Disease or dysfunction of peripheral nerves
What is myopathy?
Disease of muscle tissue
Which part of the brain is responsible for Parkinson’s disease?
Basal ganglia - facilitates wanted movements, suppresses unwanted movements
Parkinson’s = degeneration of dopaminergic neurones
Which part of the brain is responsible for MS?
Cerebellum - coordination action in posture, movement pathways may be affected
How does botox work?
Disrupts SNARE complex formation - synaptic vesicles can’t release acetylcholine into the NMJ = muscles do not get signal to contract
Therapeutic application for cerebral palsy
Myasthenia gravis
Autoimmune disease
Antibodies against acetylcholine receptors are produced
- inefficient detection of acetylcholine leads to muscle weakness and fatigue
Motor neurone disease
Progressive muscle weakness and atrophy
Degeneration of large alpha motor neurons and neurons od the motor cortex that synapse onto these
Causes: excitotoxicity, build up of harmful free radicals
Sciatica
Compression of spinal roots by herniated intervertebral discs
- weakness of leg muscles
- pain in back of thigh
Describe cardiac muscle
- Small, branched cells interconnected to other
cardio myocytes, centrally located nucleus, striated - rely on cardiac self-contractile pacemaker cells for contractions
- functions are blood circulation and to maintain hydrostatic BP
Describe smooth muscle
- Small, spindle-shaped cells with tapered ends, centrally located nucleus, non-striated
- located in walls of blood vessels, hollow organs, respiratory, digestive, CV and reproductive tracts
- can be self-contractile/ require innervation from autonomic nerves
- functions are movement of food, urine and reproductive tract secretions, regulation of diameter of airways/ blood vessels
Describe skeletal muscle
- Very long, striated cells, multinucleated
- located throughout the body, associated with bones and connective tissue
- innervated by somatic and voluntary motor nerves
- functions are movement of skeleton, guards entrances to respiratory/digestive/urinary tracts, protects internal organs, nutrient store
Definition of synergist muscles
Muscles that work together/in the same direction
Definition of an antagonist muscles
Works in the opposite direction to a given muscle eg. triceps, quadriceps, extensor digitorum
Definition of agonist muscles/prime mover
Muscle whose contraction is responsible for producing a particular movement eg. biceps, hamstrings, flexor digitorum superficialis and flexor digitorum profundus
Name the 3 layers surrounding a muscle
Epimysium: (outer layer) dense collagen layer surrounding the muscle, separating it from the nearby tissue
Perimysium: (middle layer) divides muscles into fascicles, contains collagen, elastic fibres, nerves and blood vessels
Endomysium: (inner layer) flexible layer inside fascicles, contains fine capillaries and nerve supply
