Muscles + action potentials Flashcards
What is the peripheral nervous system?
all axons + ganglia outside CNS
Subdivisions of the autonomic nervous system?
parasympathetic
sympathetic
Subdivisions of the somatic nervous system?
efferent motor nerve
afferent sensory nerve
How is resting membrane potential generated + maintained?
cell membrane relatively permeable to potassium ions and relatively impermeable to sodium ions
sodium ATPase pump actively transports 2 potassium ions into cell and 3 sodium ions out of cell
maintains concentration gradient of potassium ions and sodium ions
-70mV
How is an action potential initiated and generated?
- resting potential raised slightly by small ionic change (or other changes)
- threshold voltage for opening of VgNa reached (voltage-gated sodium channels), VgNa channels open
- sodium ions flow into cell down electrochemical gradient, depolarising cell membrane potential from -70mV –> +30mV
- VgK channels open + VgNa channels close
- potassium ions flow out of cell down electrochemical gradient through open VgK channels
- cell becomes repolarised back near resting membrane potential
- following AP (action potential), Vg channels become inactive + refractory
- duration before another AP generated = refractory period
Propagation of an action potential
- unidirectional due to refractory period of VgNa channels
- propagated signal does not vary in amplitude + is a digital signal (all or none)
- largely dependent on frequency of firing rates
What does nerve conduction velocity depend on?
- rate at which membrane ahead can reach threshold
- which depends on longitudinal conductance of cable
- which depends on cable diameter
What is saltatory conduction?
action potential skips from node to node down length of axon
- insulated axons of large diameter
- schwann cells produce myelin
- nodes of ranvier = sodium channels clustered at each node
- reduces losses, speeds conduction + saves energy
Describe what happens at a neuromuscular junction (synapse)
- arriving AP triggers VgCa channels to open at nerve terminal
- calcium ions enter cell + triggers a reaction cascade
- vesicles of acetylcholine integrate with presynaptic membrane
- contained acetylcholine released
- acetylcholine neurotransmitter molecules bind to (nicotinic) acetylcholine receptor (AChR) - ligand-gated ion channel on post-synaptic muscle membrane
- various ions, mainly sodium ions, flow in and depolarise muscle membrane (same way as in axon)
- muscle action potential propagated over muscle cell membrane (sarcolemma) through T (transverse) tubules to inner aspects of muscle fibre (similar to nerve action potential)
Define muscle
bundle of fibrous tissue that can contract to produce movement - voluntary or involuntary
What are the 3 muscle types?
striated (skeletal) muscle - locomotion + posture
smooth muscle - peristalsis
cardiac muscle - heart
Define contraction
Shortening
Define elasticity
Returning to resting state
Define hypertrophy
Increase in size
Define hyperplasia
Increase in number (of muscle cells)
Describe the structure of skeletal muscle
- muscle attached to bone by tendon
- epimysium = surrounds muscle
- epimysium folds inwards to form perimysium which separates muscle chunks into fascicles
- bundles of muscle fibres within fascicles, fibres separated by endomysium
- muscle fibres = multinucleated, multicellular structures
- muscle cells develop from myoblasts (myo = muscle, blast = immature/precursor cell)
Describe a skeletal muscle fibre
filled with myofibrils
sarcolemma analogous to plasma membrane
sarcoplasm analogous to cytoplasm
sarcoplasmic reticulum analogous to smooth endoplasmic reticulum
transverse tubular system (TT) = invaginations of sarcolemma
What are transverse tubular systems?
invaginations of sarcolemma
What is a triad?
2 terminal cisternae of sarcoplasmic reticulum (SR) and transverse tubule (TT) in close proximity
What is a sarcomere?
unit of contraction of myofibril
Define Z-line
either end of sarcomere
thin filaments insertion
Define M-line
origin of thick filaments (middle of sarcomere)
Define A-band
overlap of thick and thin filaments
Define I-band
only thin filaments