Test 3 July 22 2025 Electrophysiology Action potential Excitable tissue a wave of electrical tissue The wave travels from its origin to propagate to its final destination Cells nerves or neurons muscle cells o Need to create action potentials to function Voltage pos neg end o Charge separation with voltage o Voltage pressure water o Functions as a pressure through one end electrons are negative o The higher the voltage the stronger the electrical current Muscle cells have a voltage of 85 millivolts across the cell membrane One electron is out on the inner cell and the voltage is relative outside 0 to act as the baseline to measure the inside An action potential happens in half a millisecond Where the wave sky rockets because the excited cells have 2 types of membrane channels When the cell is at rest the channel is closed but with a depolarized membrane the voltage gated Na channel opens 1 Voltage gated Sodium channels 2 Voltage gated potassium channels Potential voltage Resting membrane voltage potential Sodium moves from higher to lower concentration out to in The net flow of Na inside the cell takes 5 milliseconds Charged particles cancel out negative inside of the cell and raise depolarize the inside of the cell The membrane becomes rapidly less polar When it is it goes to reverse polarity positive voltage o Typically stops at 20 MV Na opens at 55 mV to activate the channel and after 5 ms the Na channel closes P has a delay of about 5 ms later than when the Na closes right as the P channel opens The potassium concentration gradient is opposite to sodium There is more P on the inside of the cell than there is outside P is a monovalent cation that repolarizes the cell Once initiated it propagates the wave of de repolarization A rolling wave that travels down the membrane Self propagation and self regulation are as long as the membrane goes and the other follows Ex Dominos NMJ Sarcolemma Sarcomere based on the axon connects to the cell body which is the connection between the motor neuron muscle Most are chemical synapses that move past the voltage gated calcium channels as they experience the wave that induces the gate to open which is densely packed at the end of the axon Acetylcholine is a neurotransmitter A chemical that transmits to a target cell Travels through exocytosis Sarcolemma muscle Diffuse from the neuron to interact with proteins embedded in the axon The gap between the axon is called a synaptic cleft Ligand channel is closed unless a specific chemical binds to a site outside the channel Acetal choline binds in a specific keyhole When it opens the sodium moves from outside lower to the inside Neuromuscular junctions action potentials on either side that move higher through the sarcolemma Muscle cells action contract o The contravention is based on the electrical activity excitation contraction coupling o Muscle cells will have fundamental units sarcomere is the smallest unit for contraction When looking at the picture 2 types of filaments o Actin thin composed of protein o Myosin thick o Myo muscle Sarcomeres shorten by various globular heads that reach out to grip thin and pull those closer together Cross bridge cycling muscle stimulates to release of calcium which increases the calcium Calcium interacts with thin filaments The globular heads pull thin The ATP binds to the myosin head and forces to detach from the thin filaments Hydrolysis of ATP is to liberate enough energy to recock the head Neuron makes chemical synapses These synapses have action potentials that release the neurotransmitter Which then brings the info from the neuron to the muscle cell synaptic cleft and binds to the ligand gated ion channels An organic small molecule that interacts with big transmembrane proteins causing the shape to change The key acetylcholine 2 and a neurotransmitter This then depolarizes the synapse leading to an action potential and moving down the sarcolemma Ligand gated ion channels acetylcholine gated sodium ion channels Acetylcholine binding isn t permanent because of hydrogen bonds The key opens the lock at the same time to prevent the key from going back in it is broken down It is important that the green triangle is inserted into the membrane Uncontrolled maximal contraction acetylcholine not controlled This would lead to full body convulsions which is fatal wouldn t be able to breathe However this doesn t happen because the enzyme Acetylcholinesterase destroys the acetylcholine though it catalyzes hydrolyzes it into acetate and choline cuts the ester bonds The nervous system regulates its control of the muscles Nervous and endocrine systems need to turn off in a controlled way and when they aren t is when you get cancer Cancer is when mitosis has no off switch Ex Cooking analogy turn a stove on must be able to turn it off When the acetylcholine is cut the acetate is diffused into the interstitial fluid and the choline is used in secondary active transport where it is transported back into the axon It is recycled in the axon to rebind to acetate revascularized A motor unit a motor neuron and all its fibers it controls Found in the spinal cord base of the brain Relationship with muscle cells it controls Makes neuromuscular junctions synapses Muscle fiber muscle cell Fascicles are the strings we see One Neuron controls a certain number of muscle cells fibers 1 motor neuron the fibers it controls When the neuron fires the action potential it comes down the trunk of Stimulates the fibers however many you have to contract the axon simultaneously The Axon launches the action potential at the base to go to the target This then branches into sub axons The neuromuscular junction is with its muscle fiber Types of motor units 3 types 1 Small neurons are always 1 but the size is controlled by how many fibers it control 5 10 fibers 2 Intermediate dozens of fibers 20 80 which leads to a stronger response in the muscle 3 Larger one neuron forms over a thousand connections The average muscle has all three types of motor units However your quads are going to have a higher proportion of larger motor units Whereas in your eyelids you will have a high proportion of small motor units Dexterity smaller motor units Power strength larger motor units The zone of reserve cartilage has a cartilaginous plate that acts as a seed bed Think grow cartilage kill then replace with bone Early on it is endochondral cartilage then the cartilage becomes apoptotic where the dead cells are replaced