8 - Neurotransmission in the Nervous System Flashcards
Stare the 3 neurotransmitters and their function?
Glutamate (excitatory) = active in areas of brain involved in learning, thought and emotions (F+M)
GABA (inhibitory) - major in brain (neural inhibition in CNS) (F+M)
Glycine (inhibitory) - major in spinal cord (F)
What is the function of ACh?
ACh (excitatory) = affects movement, learning, memory, REM sleep (F+M)
State the 3 biogenic Amines neurotransmitters
Noradrenaline (M), 5-HT (F+M), Dopamine = affects movement, attention, learning, reinforcement, pleasure (m) Also epinephrine (Adrenaline)
What does the norepinephrine, epinephrine, serotonin, endorphins affect?
Norepinephrine = affects eating, alertness, wakefulness Epinephrine = affects metabolism of glucose, energy release during exercise Serotonin = affects mood, sleep, appetite, impulsivity, aggression Endorphins = provide relief from pain and feelings of pleasure and well-being
What are the differences between neuromodulator and neurotransmitters?
Neurotransmitter =
Speed - Fast - milliseconds
Mediated by - Pentameric and tetrameric receptor that incorporate ion channels → ligand gated ion channels
Examples - Glutamate, ACh, GABA, Glycine, 5-HT
Neuromodulator =
Speed - Slower - seconds to minutes
Mediated by - G protein coupled receptors
Examples - Same 5 neurotransmitters and Noradrenaline
Dopamine
What does EPSP and IPSP mean?
EPSP = an excitatory postsynaptic potential = a postsynaptic potential that makes the postsynaptic neuron more likely to fire an action potential. This temporary depolarization of postsynaptic membrane potential, caused by the flow of positively charged ions into the postsynaptic cell, is a result of opening ligand-gated ion channels.
IPSP = inhibitory postsynaptic potentials = which usually result from the flow of negative ions into the cell or positive ions out of the cell. EPSPs can also result from a decrease in outgoing positive charges, while IPSPs are sometimes caused by an increase in positive charge outflow. The flow of ions that causes an EPSP is an excitatory postsynaptic current (EPSC).
EPSPs, like IPSPs, are graded (i.e. they have an additive effect). When multiple EPSPs occur on a single patch of postsynaptic membrane, their combined effect is the sum of the individual EPSPs. Larger EPSPs result in greater membrane depolarization and thus increase the likelihood that the postsynaptic cell reaches the threshold for firing an action potential.
State the concentration of K+ and Na+ on the inside and outside and what maintains the gradient?
High K+ on the inside and low on the inside
Low Na+ on the inside and high on the outside
Gradients maintained by Na/K ATPase
State the resting potential
Resting potential of -60mV
Describe the 4 steps of EPP (End Plate Potentials) with ACh
- Nicotinic acetylcholine activated by two molecules of ACh
- Opens the channel and becomes permeable to the Na+ and K+ ions
- Na+ and K+ flow into the cell
- Lead to depolarisation
State the 4 steps of IPSP with GABA
- Binding of GABA to channel open the channel
- Becomes permeable to Cl- ions
- Cl- ions move inward
- Hyperpolarises the cell making depolarisation less likely
Also makes the membrane leakier to current
What are the 2 mechanisms involved in the termination of transmitter action?
- Termination of transmitter action
Transmitter breakdown - Reuptake using selective transport mechanisms
What are 3 scenarios where the transmitter action is terminated?
- diffusion away from synaptic cleft
- enzymatic degradation
- reuptake of transmitter into presynaptic ending
Describe the process of acetylcholine breakdown/enzymatic degradation
ACh broken down by acetylcholinesterase found in the synaptic cleft
Can be inhibited by organophosphate nerve agents such as sarin (nerve gas) and insecticides
Medicinally inhibited by neostigmine and physostigmine for treatment of conditions such as myasthenia gravis
BUT Ach is unusual
Describe the process of reuptake
Glutamate transporters in both neurons and glia
GABA reuptake into presynaptic terminals and astrocytes by GATs
Biogenic amine reuptake into presynaptic terminals
All amine and amino acid transporters utilise the energy stored in the Na+ gradient
neurotransmitters broken down by deactivating enzymes
i.e. Achase-breaks down Ach into choline and recycles the choline
Define nerve conduction studies
Nerve conduction studies involve activating nerves using small electrical shocks over several points on the body limbs and measuring the obtained responses. They are used to gather data about the peripheral nervous system and often used, in conjunction with electromyograms to distinguish between neuropathy and myopathy.
What parameters do nerve conduction studies analyse?
latency(s)- interval between stimulus and response
distance (m)- distance between two electrodes response
amplitude- tells how much of nerve tissue is active
What are the 2 main types of nerve conduction study?
Sensory nerve study
Motor nerve study
What does demyelination show?
Demyelination results in slow conduction velocity. This is because myelinated nerves transmit signals faster than unmyelinated ones because of saltatory conduction (action potentials jumping node to node)
Axonal disease manifests as a smaller amplitude of CMAP/SNAP because axons have the same conduction but there are fewer axons present.
State the 3 different wavves and muscle action potentials recorded by electrical stimulation of peripheral nerve
M-wave = direct activation of motor units by electrical stimulation
H-reflex = electrical equivalent to stretch-reflex
Elicited by submaximal stimuli. Electrical equivalent of the tendon reflex. Involves sensory axon stimulation to produce delayed motor responses.
F-wave = antidromic motor nerve action potentials bouncing off the a-motoneurons
Recording activated muscle cell backfiring when stimulus applied. In Andromic direction (towards spinal cord) and has a longer latency
What sort of abnormalities might you detect from sensory nerve tests?
Record evoked muscle action potentials Peripheral demyelination Look for giant motor units (MND/ALS) Lambert-Eaton myasthenic syndrome Myasthenia Gravis Carpal tunnel entrapment Record sensory nerve volley by recording in the digits Peripheral demyelination
