Convergence of input
presynaptic inputs to postsynaptic neuron
divergence of output
presynaptic outputs to postsynaptic neurons
three different types of synapses
- •When a motor neuron reaches a skeletal muscle, it divides into many terminal branches, each of which forms a neuromuscular junction with a single muscle cell;
- •The presynaptic neuron releases a neurotransmitter that binds to receptors located in a muscle cell
- -made up of a motor neuron and the skeletal muscle fibers innervated by that axon.
- - Groups of motor units often work together to coordinate the contractions of a single muscle
Two types of presynaptic input
Excitatory-Brings membrane closer to threshold(EPSP)
inhibitory -Takes membrane farther from threshold potential (usually hyperpolarizes)(IPSP)
when does a synaptic signal end?
when neurotransmitter broken down by enzymes or taken back into presynaptic cell for reuse.
–Integration of multiple inputs on multiple dendrites
- -When two or more EPSPs or IPSPs are generated at one time along different regions of the dendrites and cell body
- -does not cross threshold
- –Two or more EPSPs arrive at same location in quick succession.
- -Crosses threshold
simultaneous activation of both inputs resulting in no potential change due to cancellation
- -Endogenous chemicals that transmit signals from a neuron to a target cell across a synapse
- -Categorized by size, structure and function–All nervous systems operate with combined excitatory and inhibitory actions of neurotransmitters
What causes release of neurotransmitters
Release of neurotransmitters usually follows an action potential, but may also follow graded electrical potentials
How to neurotransmitters act in the absence of electrical stimulation?
Neurotransmitters are secreted at a low level baseline
How a Kinesin Molecule Walks
•The feet end has reactive groups that “walk” along a microtubule or microfilament by making an attachment, forcefully swiveling a short distance, and then releasing
A molecular motor used to carry debris from synapse back to cell across a microtubule for degradation in lysosome
three aminos that convert to neurotransmitters
tryptophan to serotonin
Histidine to Histamine
tyrosine to dopamine to norepinephrine to Epinephrine
-Small protein-like molecules (peptides) secreted by neurons as signaling molecules that influence the NS
involved in: analgesia, reward, food intake, metabolism, reproduction,social behaviors, learning and memory
Neuropeptides vs Peptide Hormones
- •In some cases peptides function in the periphery as hormones also have neuronal functions as neuropeptides
- •The distinction between neuropeptide and peptide hormone has to do with the cell types that release and respond to the molecule
- –Neuropeptides are secreted from neuronal cells
- –peptide hormones are secreted from neuroendocrine cells
Enzymes that synthesize neuropeptides and peptide hormones
- –Prohormone convertases
- –Carboxypeptidases that selectively cleave the peptide precursor at specific processing sites to generate the bioactive peptides.
Combined effect of electrical and chemical gradients.