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Lecture 4

KINE 1P90 Lecture Notes - Lecture 4: Muscle Tone, Protein Isoform, Muscle Spindle

Physical Education and Kinesiology
Course Code
Klentrou Panagiota

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Muscle activation and motor control
For a muscle to contract, it needs a neural impulse (an electrical event)
oNeural impulses are electrical currents that pass along nerve fibres
How does the nerve activate the muscle?
The anatomy of the nerve
oNeurons connected through synopses (helps communication from neurons
to muscles)
oMyelin insulated the axon and allows for faster nerve conduction
oNot all neurons are myelinated
oNerve impulse has to jump because 'nodes of ranvier' are spaces that
makes is so that the connection cant travel in a continuous line
oThe electrical signal that travels along the nerve is an action potential
oWhat is meant by 'potential'?
Membrane Potential
oPlasma membranes have a membrane potential
oIn other words, the electric charge inside the cell is different than the
electric charge outside of the cell (electrically polarized)
This is caused by a difference in the relative number of cations (+)
and anions (-) in the intracellular fluid (ICF) and the extracellular fluid
oThe ions responsible for producing the membrane potential are
Sodium (Na+) - move across membrane
Potassium (K+) - move across membrane
Anions (A-) - large intracellular proteins
oExcitable cells (nerves and muscles) have the ability to produce rapid
transient changes in their membrane potential
oThese brief changes serve as electrical signals
oThe membrane potential inside a nerve cell is -70mV (resting potential)
oThe inside of the cell is -70mV compared to the outside of the cell
oDepolarization: the membrane becomes less polarized compared to the
resting potential (-60mV)
oRepolarization: the membrane returns to resting potential after being
depolarized (back to -70mV)
oHyperpolarization: the membrane becomes more polarized than at resting
potential (-80mV)
Resting membrane Potential
oHow is it created?
Passive diffusion of Na+ and K+ across the plasma membrane
Active transport of Na+ and K+ across the plasma membrane via
the Na+-K+ ATPase (Na+-K+ pump) (20%)
oDepends on the concentration gradients of ions across the plasma
membrane and the presence of ion channels in the plasma membrane

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oChemical driving force pushing ions across the plasma membrane
oPermeability of the plasma membrane to these two ions is different; helps
establish the RMP - more permeable to K+ ions
oWith more positive charge leaving the cell, a negative membrane potential
Electrical Signals and Ion Movement
oChanges in membrane potential are brought about by changes in ion
movement across the membrane
Action potentials
oGoing from excited state to resting state
oAction potential: brief, rapid, large (100mV) changes in membrane
potential during which potential actually reverses
oAction potential = cell to cell communication
Depolarization proceeds slowly at first until it reaches a critical
level known as threshold potential
Once threshold is reached the result is an action potential
oOnce a triggering event initiated an action potential (at the axon hillock)
the action potential is conducted (propagated) along the entire axon in a
nondecremental fashion
oAction potential propagation
As the action potential develops at one point in the plasma
membrane, it regenerates an action potential at the next point in the
Therefore it travels along the plasma membrane
When action potential reaches axon…
Chemicals known as neurotransmitters are released
These either excite or inhibit (depending on the
neurotransmitter) an action potential at the next target (nerve, muscle,
Common Neurotransmitters
oDopamine (parkinsons)
oSerotonin (feelings)
oHistamine (allergies)
oGamma-amino butyric acid (GABA)
Muscle Contractions
oContractions of whole muscle can be of varying strength
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