a neuron may terminate on one of what three structures
- another neuron (synapse)
- a muscle (neuromuscular junction)
- a gland
motorneurons
nerves that innervate muscle fibers
In what tissues does electrical synaptic transmission occur
- heart
- smooth muscle
- liver
name the three location of synapses
- axo-dendritic
- axo-somatic
- axo-axonic
In electrical synapses, the cytoplasms of membranes are physically connected by what
gap junctions
- usually for fast transmission
what is the distance between two cells who have electrical synaptic transmission
short, about 3 nm
where does current flow in electrical synaptic transmission
either direction
gap junctions link electrically coupled cells and consist of what?
connexons
** low resistance pathways
what type of synaptic transmission is characterized by no synaptic delay and conduction in both directions
electrical synapses
why do cardiac and smooth muscles consist of gap junctions
- gap junctions are important for synchronizing electrical and contractile activity
- tissues with gap junctions act as a functional syncytium
name the synaptic transmission described below
- more common
- either excitatory or inhibitory
- no physical continuity between pre and post synaptic neurons
- has synaptic delay (1-5 ms)
chemical synapses
in what way is neurotransmitter released in chemical synaptic transmission
released in individual packets or “quanta”
- one vesicle released one quantum of neurotransmitter
postsynaptic potentials are graded. What does this mean
they depend on the number of quanta released
the number of quanta released per action potential varies with what
the type of tissue
- ex: motor neurons innervating skeletal muscle release 150 quanta while CNS axon terminals release 1-10 quanta
what is the role of Ca2+ in chemical synaptic transmission
ca2+ is required for the mobilization and fusion of the vesicles (contained neurotransmitter) to the membrane
List the process of excitation-secretion coupling in chemical synapses
- action potential depolarizes the axon terminal
- depolarization opens voltage-gated Ca2+ channels
- Ca2+ enters cell
- calcium entry triggers exocytosis of synaptic vesicle contents
- neurotransmitter diffuses across the synaptic cleft and binds with receptors on the postsynaptic cell
- neurotransmitter binds initiates a response in the post-synaptic cell
what happens to neurotransmitter released into synaptic cleft
- diffusion
- reuptake
- enzymatic degradation
what is the direct way neurotransmitters can affect ion channels
receptor is an integral part of an ion channel (ex: nicotinic Ach)
what is the indirect way that neurotransmitters can affect ion channels
receptor is linked to the ion channel via G-protein modulation (ex: muscarinic acetylcholine, amines, peptides)
action (+ and/or -) of acetylcholine and receptor used
- +/-
- receptor: cholinergic (nicotinic and muscarinic)
action (+ and/or -) of norepinephrine and receptor used
- +/-
- adrenergic (alpha or beta)
action (+ and/or -) of GABA and receptor used
- -
- GABAergic (GABA a(Cl-) GABA b(K+))
action (+ and/or -) of dopamine
+/-
action (+ and/or -) of serotonin (5-HT)
+/-
