PSYC10003 Lecture Notes - Lecture 3: Myasthenia Gravis, Axon Hillock, Axon Terminal
12 Jun 2018
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Lecture 3, Tuesday 8 March 2016
PSYC10003 - MIND, BRAIN & BEHAVIOUR 1
LECTURE 3
MECHANISMS OF COMMUNICATION WITH THE NEURON
•Learning objectives
•Describer the structure of a synapse, the mechanism of neurotransmitter release, and the
activation of post synaptic receptors.
•Understand the ionic movements that underlie postsynaptic potentials, the processes that
terminate them and their integration
•Explain how drugs influence synaptic transmission
•Describe the role of autoreceptors.
•MYASTHENIA GRAVIS
•Myasthenia Gravis is a disorder of synaptic transmission.
•It has many symptoms, including;
‣Extreme fatigability
‣Fluctuation muscle weakness (proximal>distal)
‣Problems chewing (dysphagia) and talking (dysarthria)
‣Leads to respiratory weakness
•Experimental investigations in sufferers of myasthenia gravis have shown that conduction of nerve
messages along the neuron (the action potentials) is normal, and the muscles themselves seem to
function properly, as direct electrical stimulation of them leads to normal contractions.
•It is now clear that myasthenia gravis arises from a problem with the synapses on muscles.
•Neurons are specialised nerve cells that receive, process and/or transmit information to other cells
within the body.
‣They communicate with each other, and muscles and glands.
‣Neurons vary in shape and size depending on where they are located and on their specific
function.
•Dendrites are the thin extensions of a neuron that receive information from other neurons and
transmit it to the soma.
‣Some dendrites have additional little extensions called dendritic spines, each which
represents a point where a neuron can connect with and receive information from a
neighbouring neuron.
•The soma, or cell body, integrates the neural information received from dendrites and sends it to
the axon when action potential begins at the axon hillock, the junction between the cell body and
the axon.
•The axon is a single, tube-like extension that carries neural information away from the soma
towards other neurons.
‣Many axons split into smaller branches called axon collaterals. At the end of the
collaterals are axon terminals. Each axon terminal has a small knob-like swelling at its tip
called a terminal button (sometimes called a synaptic vesicle, synaptic knob or synaptic
button).
‣The terminal button is a small structure like a sac that stores and secretes
neurotransmitters manufactured by the neuron.
•Information travels along the axon as an electrical impulse called an action potential.
‣The myelin sheath around the axon protects and insulates the axon and allows for quicker
transmission. It occurs in segments that are separated by gaps called nodes of Ranvier.
•The synapse consists of three components: the synaptic cleft, the terminal buttons of the
presynaptic neuron and the dendrites of the post synaptic neuron.
Lecture 3, Tuesday 8 March 2016
PSYC10003 - MIND, BRAIN & BEHAVIOUR 1
•Neurons communicate with each other by sending neurotransmitters across the synaptic gap.
‣Synaptic gap is 500 times as thin as a strand of hair.
•Neurotransmitters are a chemical substance produced by a neuron that carries a message to other
neurons or cells in muscles and organs.
‣Neurotransmitters diffuse across the synaptic cleft from the presynaptic terminal button
and attach themselves to receptor sites on dendrites of postsynaptic neurons that are
specialised to receive that specific neurotransmitter.
‣Reuptake is the process by which neurotransmitters that do not bind to receptors are
reabsorbed by the presynaptic neuron to be re used later.
‣Neurotransmission is the process of neurons communicating with one another.
‣Have two effects:
‣Excitatory: depolarizes (stimulates) the post synaptic neuron to make new action
potentials and continue the process.
‣Inhibitory: the post synaptic neuron becomes hyperpolarised, preventing it from
firing.
•Normally, the gates between the inside and outside of a neuron are closed.
•Outside the neuron there is an abundance of Na+ ions, and inside the neuron there is an
abundance of Cl- ions.
•When we open the gates between the inside and outside of a neuron, the Na+ ions and Cl- ions
are able to move due to the force of diffusion and electrostatic pressure.
‣Sodium rushes into the axon as it is attracted to the negative charge inside, and therefore the
neuron becomes less negatively charged and may even become positively charged.
‣Potassium rushes out, attracted to the positive charge outside, making the neuron go back to
zero charge.
•Depolarization - membrane potential moves towards zero.
•Electrical signal (action potential) propagates down the axon, a bit of it is lost and the fluctuation
gets smaller but as long as there is enough fluctuation to get to the next Node of Ranvier, a new
Document Summary
At the end of the collaterals are axon terminals. It occurs in segments that are separated by gaps called nodes of ranvier: the synapse consists of three components: the synaptic cleft, the terminal buttons of the presynaptic neuron and the dendrites of the post synaptic neuron. Psyc10003 - mind, brain & behaviour 1 action potential will be generated there (na in, k out) and it will propagate the signal to the next. Potential (epsp: excitatory postsynaptic potentials (epsps) depolarise the postsynaptic cell membrane, epsps increase the likelihood that an action potential will be triggered in the postsynaptic neuron, amount of nt released differs between synapses, sodium = excitatory ion, potassium = inhibitory ion. Neurotransmitter release: prior to the release of neurotransmitter molecules from the presynaptic terminal button, the membrane potential of the postsynaptic neuron is at its resting level (-70 mv).
