Somatic nervous system and muscle contraction Flashcards
Cardiac muscles
- Striated
- Lines walls of the heart
- Under involuntary control
Smooth muscle
- Lines the visceral organs
- Have a spiral like structure
- Under involuntary control
Skeletal muscle
- Allows us to move
- Striated
- Under voluntary control
How many muscle fibres are present in fasciculi?
Consist of 150 muscle fibres in bundles known as fasciculi
What is sarcolemma?
Muscle fibre membrane
What are present within the sarcoplasm?
- Glycogen
- Fat
- Enzymes
- Mitochondria
What is the sarcoplasmic reticulum?
SR is where Ca2+ is stored and released from
What are the thick filaments known as?
Known as myosin
What are the thin filaments known as?
Known as actin
Steps involved in calcium stimulated muscle contraction
- Myosin head hydrolyses ATP into ADP and inorganic phosphate. The energy released
- Ca2+ binds to troponin, which causes the tropomyosin to shift and exposes the myosin head binding site
- Myosin head binds into the myosin head binding site forming a cross bridge
What is required in order to break actin-myosin bonds?
ATP is required to break actin-myosin bonds
What does the somatic nervous system provide?
Provides voluntary control over skeletal muscle
What are efferent neurons?
Efferent neurons are that which innervate muscle i.e motor neurons
What is a motor unit?
A motor unit is a single motor neuron and all the muscle fibres it controls
What do single fibres do?
They contract completely or not at all
How can motor units regulate strength of muscle contraction?
Can regulate strength of muscle contraction by varying how many activated motor units there are
Action potentials along neuromuscular junctions
- Action potential arrives along motor neuron
- This causes depolarisation and moves along the membrane and move down T-tubules which enter the muscle
- This causes depolarisation of the sarcoplasmic reticulum and this causes Ca2+ to be released
- The Ca2+ is released to the cytosol and causes contraction of the muscle
What are the 2 types of cholinergic receptors?
- Muscarinic(Primarily in CNS, GCPR and are slow)
- Nicotinic(In neurons/NMJs, and are fast)
What happens when Ach binds to a nAchR?
- 2 molecules of Ach bind to nicotinic AchR causing a conformational change
- Opens ion pore
- Opening of ion pore results in rapid increase in Na+/Ca2+ and membrane depolarisation leading to muscle contraction
What is a tetanus contraction?
Its when the rate of action potential is so high that muscle doesn’t release between stimuli.
Why does duchenne muscular dystrophy occur?
Occurs due to mutated gene dystrophin
What does dystrophin do?
Dystrophin connects actin filaments to the sarcolemma, required for mechanical stability
What does a lack of dystrophin do and what does this cause?
Lack of dystrophin causes dysfunction of sarcolemma stretch
-This causes ion pores to open and there’s increased
intracellular Ca2+
What happens in Duchenne muscular dystrophy?
Degradation of structural proteins and CK is lost from cell into blood. CK is required for ATP
What is ALS?
Its a neuron disease affecting motor neurons
What is myasthenia gravis?
Chronic autoimmune NMD
What does myasthenia gravis cause?
Causes skeletal muscle weakness and fatigue
What happens in myasthenia gravis?
- Body makes antibodies against AchR’s at NMJ’s
- Blocks AchR’s, increasing AchR degradation and causes impaired signal transduction
What treatment is there for myasthenia gravis?
Treatment with acetyl cholinesterase inhibitors or immunosuppressants
