L3: Synaptic Transmission Flashcards
What causes difference of membrane potential?
Uneven distribution of ions
What are the main ions responsible for membrane potential?
K+, Na+, Cl-, Ca2+
What causes depolarisation? How does the potential change?
Rush of positively charged Na+ ions by opening sodium channels into the neurone, moving down the concentration gradient. Membrane becomes less -ve. ‘All or nothing’ when a threshold is reached no way back.
What is the rising phase?
Rapid and sudden change in membrane permeability to Na+ ions during depolarization, causes the rising phase of the action potential
What causes repolarisation?
The subsequent return to resting potential, repolarization, is mediated by the opening of potassium ion channels. To reestablish the appropriate balance of ions, an ATP-driven pump (Na/K-ATPase) induces movement of sodium ions out of the cell and potassium ions into the cell
What causes hyperpolarisation? How does the potential change?
Caused by the closing of sodium ion channels and the opening of potassium ion channels. Hyperpolarization occurs due to an excess of open potassium channels and potassium efflux from the cell. Membrane becomes more -ve
What is absolute refractory period? What causes it?
Inactivation of Na+ channels accounts for the absolute refractory period. Period following an AP when a second AP cannot be inititated.
What is relative refractory period?
When AP can be generated but with increased current injection required
What is equilibrium potential?
The electrical potential difference across the cell membrane that exactly balances the concentration gradient for an ion. OR the potential at equilibrium where there is no current and co concentration gradient to cause irreversibilities.
What does the equilibrium potential depend upon?
- concentration of the ion inside and outside of the cell
- temperature
- valency of the ion
- energy needed to separate a quantity of charge
How can equilibrium potential be determined?
By Nernst equation
What is the function of myelin?
electrical insulation which speeds conductance along the axon
Where are voltage-gated Na+ channels present along the axon?
In the little gaps between myelin sheaths called ‘Nodes of Ranvier’.
What is saltatory conduction?
When action potentials ‘leap’ from one Node of Ranvier to another
What are the classes of neurotransmitters?
- Amino Acids (Glutamate; GABA)
- Biogenic Amines
i) Acetylcholine;
ii) Monoamines
a) serotonin;
b) catecholamines (dopamine; noradrenaline; adrenaline))) - Peptides (Substance P)
- others (ATP; Nitric Oxide)
SEE L3, slide 16
What does Peripheral Nervous System consist of?
afferent (sensory) nerves
What are the classes of Peripheral Nervous System?
- somatic (skeletal muscle (voluntary))
-
autonomic (smooth, cardiac muscle, exocrine glands (involuntary))
i) sympathetic (fight/flight)
ii) parasympathetic (rest/repose)
Describe somatic efferent system (its transmitter and receptors)
One somatic efferent nerve between the CNS and skeletal muscle, transmitter - acetylcholine, receptors - nicotinic
Describe parasympathetic system (its transmitter and receptors)
In the autonomic nervous stem there are two efferent nerves between the CNS and the effector tissue. First synapse: transmitter - acetylcholine, receptor - nicotinic; second synapse: transmitter - acetylcholine, receptor - muscarinic
What are the classes of Autonomic Nervous System? Give examples of organs belonging to each of them
- sympathetic (eye, blood vessels, salivary glands, heart, lungs, adrenal medulla, liver, GI tract, bladder, genitalia, sweat glands)
- parasympathetic (eye, lacrimal gland, salivary glands, heart, lung, upper GI tract, lower GI tract, bladder, genitalia)
Describe Autonomic Nervous System
- autonomic neurones have their cell body in the spinal cord
- parasympathetic pre-ganglionic axon is long
- parasympathetic ganglia are not always well defined
- GP ileum
What is the lifecycle of a neurotransmitter?
1) synthesis (inside the neurone)
2) storage (inside the neurone)
3) release (inside the neurone)
4) activation (outside the neurone)
5) termination (outside the neurone)
How is acetylcholine synthesized?
Acetyl-CoA + choline –> acetylcholine
enzyme: choline acetyltransferase
How is acetylcholine released?
- Neurotransmitter is released from pre-synaptic nerve terminals following the entry of calcium via voltage gated ion channels
- synaptic cleft has a very small volume, so high concentrations of ACh achieved
