HUBS1403 Lecture Notes - Lecture 26: Acetylcholine, Conformational Change, Microtubule

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grayhippopotamus876

8 Jun 2018

School

University of Newcastle

Department

Human Biosciences

Course

HUBS1403

Professor

karen mate

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Synaptic Transmission

A synapse is the junction between neurons or between a neuron and an effector

• Electrical synapse: gap junctions connect cells and allow the transfer of information to

synchronise the activity of a group of cells

• Chemical synapse: one-way transfer of information from a presynaptic neuron to a

postsynaptic neuron

We will focus on chemical synapses

Information transfer to and from the brain

• Specific brain pathways are activated

o Eg, dorsal column pathway, corticospinal pathway

• These pathways are composed of a series of neurons

• Neurons communicate via specialised called synapses

• Communicate and modulate each other with NS

• LOTS of different placed on axon that synapses can occur

o Eg axo-dendric synapse - axon to dendrite

o Axo-somatic synapse

o Axo-axon-synapse

• Communication between neurons is referred to as synaptic transmission

• Synaptic transmission may be either by:

o Electrical - via connexons

o Chemicals - mediated by neurotransmitter

Electrical Synapse

• Function: synchrionise activity of interconnected neurons

o Eg respiratory system for synchronised movement of repirtory organs

o Eg peacemaking capacity I heart

• Advantage: very very fast

• Disadvantage: not able to be regulated in the same way as a chemical synapse, not modulated

Chemical Synapse

• Function: transmit signals from 1 neuron to another using neurotransmitter

Events at the Chemical Synapse: Synaptic Transmission

1. AP arrives at the synaptic bouton (= synaptic terminal)

2. Depolarises synaptic bouton

3. Depolarisation opens gated Ca2+ channels (ICF/ECF Ca concentration gradient means Ca2+

moves into terminal)

4. Ca2+ influx, triggers synaptic vesicle (SV) fusion (Ca2+ sensing proteins activated on SV

membrane and pre synaptic neuron membrane resulting in fusion)

5. Neurotransmitter released from synaptic vesicles

6. Activates receptors on postsynaptic cell

7. Neurotransmitter diffuses or is cleared from synaptic cleft

• Neurotransmitter diffuses across and activates receptors, if receptors are direct gates channels

open and ions flow into or out of th cell causing depolarisation (+ve charges) or

hyperpolarisation (-ve charges) of the post synaptic cell membrane

• Neurotransmitter then released and cleared either diffuses away to transporter proteins, re-

uptake by transporter proteins into pre-synaptic terminal, or enzymatically inactivated

o Eg Acetile choline then acetile choline esterase breaks down Ach

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Document Summary

Specific brain pathways are activated: eg, dorsal column pathway, corticospinal pathway, these pathways are composed of a series of neurons, neurons communicate via specialised called synapses, communicate and modulate each other with ns. Lots of different placed on axon that synapses can occur: eg axo-dendric synapse - axon to dendrite, axo-somatic synapse, axo-axon-synapse, communication between neurons is referred to as synaptic transmission. Synaptic transmission may be either by: electrical - via connexons, chemicals - mediated by neurotransmitter. Function: transmit signals from 1 neuron to another using neurotransmitter. Space between presynaptic terminal and postsynaptic cell - synaptic cleft. Neurotransmitters regulate ion channels directly or indirectly: directly - ligand gated ion channel receptors, receptor is part of the ion channel complex, neurotransmitter binding changes permeability of ion channel, allows fast postsynaptic potentials (10-100ms duration) Receptors on post synaptic membrane: ligand (neurotransmitter) unbound channel closed. Ligands binds and receptor complex undergoes a conformational change and opes ion channel.

Related Questions

a) Which of the following statements about the autonomic nervous system is INCORRECT?

A The preganglionic fibres in the parasympathetic division are usually long compared to the postganglionic fibres

B The sympathetic division mediates responses that allow the body to respond to âflight and frightâ situations

C The ganglia of the sympathetic division are usually close to the spinal cord

b) Glutamate is an example of an excitatory amino acid neurotransmitter that acts via direct synaptic transmission when it is released from presynaptic neurons in the brain

Based on the background information, which of the following is a CORRECT statement regarding events at the synaptic cleft after glutamate is released?

A Glutamate acts by stimulation of receptors on the presynaptic neuron

B The postsynaptic glutamate receptors are in the family of tyrosine-kinase linked receptors

C On the postsynaptic membrane, glutamate activates ligand-gated sodium channels, which are an example of ion-channel linked receptors

D The events at this synapse are an example of electrical transmission

E The pathway of receptor activation includes activation of a signal transduction pathway and production of second messengers

D The adrenal medulla is a sympathetic ganglion

E The parasympathetic nerves arise from the brain stem and the sacral region of the spinal cord

fuchsiafish404

The junction specialized for the transmission between a neuron and another cell is called a (1) _____ ______. Usually, the signal being sent to the receiving cell is carried by chemical messengers called (2) _____. (3) _____ is an example of this type of chemical messenger, which diffuses across the synaptic cleft, combines with protein receptor molecules on the muscle cell membrane, and soon thereafter is rapidly broken down by enzymes. At an (4) ____ synapse, the membrane potential is driven toward the threshold value and increases the likelihood that depolarization and an action potential will occur. At an (5) ____ synapse, the membrane potential is driven away form the threshold value, and the receiving neuron becomes hyperpolarized and is less likely to achieve an action potential. A specific transmitter substance can have either excitatory or inhibitory effects depending on which type of protein channel it opens up in the (6) ____ membrane. (7) ____ are neuromodulators that inhibit perceptions of pain and may have roles in memory and learning, emotional states, temperature regulation, and sexual behavior. (8) ____ ________ at the cellular level is the moment-by-moment tallying of all excitatory and inhibitory signals acting on a neuron. Incoming information is (9) ____ by the cell bodies, and the charge differences across the membranes are either enhanced or inhibited. Some narrow-diameter neurons are wrapped in lipid-rich (10) _______ produced by specialized neuroglial called Schwann cells; each of these is separated from the next by a(n) (11) ________ ________ - a small gap where the axon is exposed to extracellular fluid. A (12) ____ is an involuntary sequence of events elicited by a stimulus. During a (13) _______ ________, a muscle contracts involuntary whenever conditions cause a stretch in length; many of these help you maintain an upright posture despite small shifts in balance. Imbalances can occur at chemical synapses; a neurotoxin produced by Clostridium tetani blocks the release of GABA and glycine, thus freeing the motor neurons from (14) _____ control, which may cause tetanus â a prolonged, spastic paralysis that can lead to death. A. Excitatory H. Stretch reflex B. Inhibitory I. Summed C. Myelin J. Neurotransmitters D. Chemical synapse K. Postsynaptic E. Synaptic integration L. Endorphins F. Exposed node M. Acetylcholine (ACh)

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HUBS1403 Lecture Notes - Lecture 26: Acetylcholine, Conformational Change, Microtubule

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