Chloe Henry, Delina Tsegay Nerve Impulses Chloe Henry, Delina Tsegay

Resting Membrane Conditions What is the resting state of a neuron? When the nerve cell is not conducting an impulse it is in resting state. This makes the membrane of the axon permeable of K+ and impermeable of Na+ Permeable: to allow things to pass through it Impermeable: not allowing things to pass through it The plasma inside the axon contains high amount of K+ ions and outside the axon contains high amount of Na+ This makes the exchange pump able to exchange 3 Na+ with 2 K+ .

Resting Membrane Conditions Con’t… Soon after the outside of the membrane is positively charged and the inside is negatively charged. The neuron is now in a polarised state This electrical potential difference is called the resting potential.

Resting Membrane Conditions

Generation of Nerve Impulse So how does the nerve impulse start anyway? First the neuron is in resting state, then we apply a stimulus (for example touching something hot) on the polarised membrane. This makes the membrane’s site permeable to Na+ This enables the Na+ ions to move inside the cell. Causing the outside of the membrane to be negatively charged and the inside positive Now the neuron is in the depolarized state.

Generation of a Nerve Impulse What kind of protein channels are in the neuron? Ion channels in the membrane are selective, only allowing certain things to pass through. Only allowing ions of appropriate size and charge to pass through So only Na+ can go through sodium pumps and K+ through potassium pumps. These channels are not continuously open but are gated, which allows them to open and close quickly. Like when depolarization occurs.

Generation of Nerve Impulse

Generation of Nerve Impulse Video: https://www.youtube.com/watch?v=jcZLtH-Uv8M

Conduction of a Nerve Impulse How does the energy go throughout the neuron? When a neuron sends info. Down the axon away from the cell body this is the action potential. This electrical current is created by a depolarization current After depolarization Na+ channels are closed and K+ channels open When permeability is back to its original state K+ channels close. This all happens in a millisecond! Repolarization is when the neuron changes back into its negative state.

Conduction of a Nerve Impulse

Conduction of a Nerve Impulse What is the all or none principle? When depolarization hits threshold (when the impulse reaches the action potential) you cannot stop the current. For any sized neuron the action potential is fired at the same intensity. It either sends the signal completely or not at all.

Conduction of a Nerve Impulse What are the purposes of the myelin sheath? Myelin is a plasma membrane around the nerve axon, this insulates the electrical current. Outgrowth of a glial cell ⅔ of all axons are not myelinated, which these axons only go 2 mph. While myelinated axons go 7 times more faster

Conduction of a Nerve Impulse Video: https://www.youtube.com/watch?v=ifD1YG07fB8

From One Neuron to Another How does the current go from cell to cell? When the action potentials electrical current reaches the end of the axon the axon releases neurotransmitters that go across the synapse unto the next cell. An axon is the long part of the neuron that conduct impulses. It is like an electrical cable, the larger it is the more currency. Neurotransmitters are chemical messengers that enable neurotransmission.

From One Neuron to Another So, how do neurotransmitters work? They are found at the end of axon endings. They are a chemical that stimulates impulses unto the neurons or muscle fibers. Some of these neurotransmitters are acetylcholine (ACH), dopamine, serotonin and endorphin. All these NTs have different effects on the body and brain.

From One Neuron to Another What are the different kinds of synapses? Chemical Synapses: Neuromuscular Junction: Between a motor neuron and muscle cell, most commonly used and allows neurons to form interconnected neural circuits. Electrical Synapses: These are rare, it only occurs when the membranes of two communicating neurons come extremely close at the synapses and linked to a gap junction. Gap Junction: contain aligned channels in the postsynaptic membrane.

From One Neuron to Another

From One Neuron to Another Video: https://www.youtube.com/watch?v=f-88OtK_iUk

Sources https://faculty.washington.edu/chudler/ap.html https://www.khanacademy.org/science/biology/human-biology/neuron- nervous-system/a/the-membrane-potential http://byjus.com/biology/neurons-nerve-impulses/ https://www.ncbi.nlm.nih.gov/books/NBK26910/ https://www.ck12.org/book/CK-12-Life-Science-Concepts-For-Middle- School/section/11.41/