* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download SBI 4U Homeostasis 2
Neuroregeneration wikipedia , lookup
Development of the nervous system wikipedia , lookup
Neuroanatomy wikipedia , lookup
Clinical neurochemistry wikipedia , lookup
Activity-dependent plasticity wikipedia , lookup
SNARE (protein) wikipedia , lookup
Signal transduction wikipedia , lookup
Patch clamp wikipedia , lookup
Nonsynaptic plasticity wikipedia , lookup
Node of Ranvier wikipedia , lookup
Action potential wikipedia , lookup
Synaptic gating wikipedia , lookup
Neuropsychopharmacology wikipedia , lookup
Membrane potential wikipedia , lookup
Single-unit recording wikipedia , lookup
Synaptogenesis wikipedia , lookup
Nervous system network models wikipedia , lookup
Electrophysiology wikipedia , lookup
Neuromuscular junction wikipedia , lookup
Biological neuron model wikipedia , lookup
Neurotransmitter wikipedia , lookup
Resting potential wikipedia , lookup
Stimulus (physiology) wikipedia , lookup
Molecular neuroscience wikipedia , lookup
Homeostasis 2: The Electrical Nature of Nerves Electrical Nature of Nerves • Neurons use electrical signals to communicate with other neurons, muscles and glands. • When microelectrodes are placed on either side of the membrane of an inactive neuron, measurements from a voltmeter indicate an electrical potential difference of -70mV (millivolts) • The charge of the inside of the neuron cell is negative in relation to the outside • This charge separation across the membrane is known as the membrane potential. Electrical Nature of Nerves Sodium Potassium Pump • A system that uses ATP in order to keep the electrical potential difference across the membrane. • For every three sodium ions transported out of the cell, two potassium ions are transported into the cell. • An overall positive charge is going to accumulate on the outside of the cell membrane and a negative charge on the inside. • This ensures the resting potential of the neuron is at -70mV so that the cell is ready for an impulse to happen. The Sodium Potassium Pump Action Potential • A nerve cell is polarized because it has a negative charge. • It will depolarize during an action potential because the inside becomes less negative. • An action potential is the movement of an electrical impulse along the membrane of a nerve cell’s axon. • Action potentials are an all-or-none phenomenon where the strength of the action potential is always the same as long as there is enough depolarization to trigger the potential. (usually around -50mV and is called the threshold potential). Action Potential Across the Membrane Steps of an Action Potential • Action potential triggered when threshold potential is met. • Voltage gated sodium channels open and make membrane more permeable to sodium ions and they rush into the cell, making it depolarize. Now the membrane potential is +40mV • Sodium channels close, potassium channels open, potassium moves down the concentration gradient out of the cell, which makes the membrane repolarize and actually becomes even hyperpolarized to about -90mV. • Potassium channels close and the sodium-potassium pump continues to work so that the resting potential is restored. • The next few milliseconds the membrane cannot be stimulated again as the membrane goes through a refractory period. Myelinated Nerve Impulse • At regular intervals along the axon, the nerve has nodes of Ranvier that are parts of exposed nerves between glial cells of the myelin sheath. • These nodes contain many voltage-gated sodium channels. • When the sodium ions move into the cell, the charge travels through the cell to the next node. • This occurs at each node along the axon until it reaches the end of the neuron. • Because the action potentials are forced to jump from one node to the next due to the myelin sheath, the conduction of an impulse along a myelinated neuron is called saltatory conduction (saltatory means to jump in latin) • Saltatory conduction: 120 m/s, unmyelinated: 0.5m/s Myelinated Propagation Synapse • A synapse is a junction between two neurons or between a neuron and an effector (muscle or gland) • A neuromuscular junction is a synapse between a motor neuron and a muscle cell. • Neurons are not directly connected. They have a small gap between them called the synaptic cleft. Signal Transmission Across a Synapse • When an impulse reaches the far end (called the synaptic terminal), the impulse must travel from the presynaptic neuron to the postsynaptic neuron. • Chemical messengers called neurotransmitters carry the neural signal from one neuron to the next neuron or effector. • Neurotransmitters are found in the presynaptic terminal inside synaptic vesicles. • Once the impulse reaches the synaptic terminal the synaptic vesicles move towards and fuse with the presynaptic membrane. • Neurotransmitters are released into the synaptic cleft. • Neurotransmitters bind to receptor proteins and affect the postsynaptic neuron. • An enzyme comes in and breaks up the neurotransmitter and its components will be reabsorbed by the presynaptic neuron. Synapse Neurotransmitters • Can have either an excitatory or an inhibitory effect on the postsynaptic membrane. • If the effect is excitatory, the receptor proteins will allow positive ions, such as sodium to flow into the postsynaptic neuron and the membrane will depolarize. • If the neurotransmitter is inhibitory, the receptor will trigger potassium ions to open, allowing potassium ions to flow out, hyperpolarizing the membrane. Examples of Neurotransmitters • Acetylcholine: crosses a neuromuscular junction and excites the muscle causing depolarization and contraction of the muscle. • Dopamine: affects brain synapses in control of body movements, linked to sensations of pleasure (eating) • Serotonin: regulates sensory and temperature perception, involved in mood control • Endorphins: act as natural pain killers, emotional areas of the brain. • Norepinephrine: complements the actions of the hormone epinephrine that ready the body to respond to danger or stress. Practice: • P. 362 # 6, 7, 9, 10, 11.