Ch. 3

Electrical Events Within a Neuron and the Release of Neurotransmitters

Electrical transmissionwithin a neuron must take place before neurotransmissioncan occur

• Generally, the interior of the neuron is negatively charged relative to the exterior of the neuron

  • Electrical potential

    • refers to the difference in electrical charge between the interior and exterior of a neuron

  • Local potential

    • Depolarization(excitatory postsynaptic potential)-describes a reduction in the difference in the positive and negative charges on each side of the neuronal membrane

    • If a local potential is depolarized, we refer to that as an excitatory postsynaptic potential (EPSP)

  • Hyperpolarization (inhibitory postsynaptic potential) - increase in the difference between the positive and negative changes on each side of the neuronal membrane (When the neuron becomes more negative than its resting potential!! so less than -70)

  • a local hyperpolarization is known as an inhibitory postsynaptic potential

Voltage Gated Ion channels

  • opening and closing of these channel can change resting potentials

  • when local potentials are depolarized Na+ channels tend to open

  • if there is a sufficient amount of depolarization then an action potential will occur

Action potential

  • depolarizes, becomes more positive. Then it is hyperpolarized until it goes back to normal

  • all or none-law- once action potential starts it will always trigger a refractory period

Nodes of Ranvier

  • Salutatory Conduction- refers to the jumping of action potentials form one node to the next (speeds up signal)

Receptors

  • ionotropic receptors - are ion channels that open once bound to a neurotransmitter

    • quicker route

    • directly opens and closes an ion channel

  • metabotropic receptors - often associated with G proteins that recruit effector enzymes to activate second messenger systems

    • slower route

  • Presynaptic receptors

    • a messenger for the axon terminal to almost check how much space there is in the synapse

    • auto receptors - activated by transmitter release by its own neuron (usually inhibitory)

    • Heteroreceptors - activated by different transmitter from another neuron

  • Reuptake/Turnover: transporters on the axon terminal moving neurotransmitters back inside the axon terminal and sends a signal to stop neurotransmission

Amino acid neurotransmitters

  • glutamate

    • always excittory

    • 3 ionotropic receptors: NMDA (main one)

    • mGlu is a metabolic receptor

  • GABA

    • always inhibitory

    • A) ionotropic B) metabotropic

  • Gaba and Glutamate are most abundant transmitters in Central nervous system

Monoamine Neurotransmitters

  • dopamine

    • some excitiatory (D1 & D5)

    • Some more inhibitory (D2 & D3 & D4)

    • MAO is enzyme that breaks down dopamine after reuptake

  •  Dopaminergic neurons arise from two brain stem structures (the ventral tegmental area and the substantia nigra) and the hypothalamus

o   Mesolimbic and mesocortical dopamine pathways originate in the ventral tegmental area and terminate in the nucleus accumbens and frontal cortex

o   Nigrostriatal dopamine pathway originates in the substantia nigra and terminates in the basal ganglia

o   Tubero-infundibular dopamine pathway originates in the hypothalamus and terminates in the pituitary gland

Norepinephrine

  • Noradrenergic neurons arise from locus coeruleus

    • Locus coeruleus located in brain stem near dopamine neuron structures

  • A number of metabotropic receptors (alpha 1,2 & beta 1,2,3)

    • Excitatory effects EXCEPT alpha-2 which is inhibitory

  • Catabolic enzymes and reuptake mechanisms are similar to dopamine

Catecholamines: dopamine, Norepinephrine, Epinephrine

Serotonin

  • Indolamine

  • Serotonergic neurons come from the Raphe Nuclei

  • A lot of receptors

    • Mixture on inhibitory, excitatory, and dependent on receptors

  • Catabolism and reuptake are used to terminate neurotransmission

    • MAO enzyme used for destruction

    • Reuptake mechanism is target for anti-depressant meds

Acetylcholine

  • Many structures in the brain contain cholinergic neurons (rest & digest ON)

  • Major neurotransmitter for skeletal muscle (voluntary or we have control over) and parasympathetic NS

  • Nicotinic (ionotropic)and muscarinic (metabotropic) receptors

    • Many subunits of these receptors

    • Nicotinic receptors have excitatory effects

    • Muscarinic have mixture of some excitatory, some inhibitory  

  • Enzymatic catabolism terminates neurotransmission