Exam 3 Review:  Chapter 11:  Neuron-to-Neuron Transmission

axodendritic - A term pertaining to an excitatory or inhibitory synaptic connection between the presynaptic axon of a transmitting neuron and the postsynaptic dendrite(s) of a receiving neuron in a nerve impulse pathway.

axosomatic - A term pertaining to an excitatory or inhibitory synaptic connection between the presynaptic axon of a transmitting neuron and the postsynaptic cell body/soma of a receiving neuron in a nerve impulse pathway.

axoaxonic - A term pertaining to an excitatory or inhibitory synaptic connection between the presynaptic axon of a transmitting neuron and the postsynaptic axon hillock or axon of a receiving neuron in a nerve impulse pathway.

electrical synapse - The specialized type of synapse between two excitable cells, e.g., cardiac muscle cells, some smooth muscle cells, and some neurons, in which the impulse is transmitted from one cell to the next by the depolarization of the sending cell creating a local ionic current flow which destabilizes the voltage gated Na+ channels in the adjacent cell so that it also depolarizes; such cells are usually connected by gap junctions; no neurotransmitter is required.

gap junction - A type of communicating intercellular junction; an bridging network of integral protein channels present in both cell's outer membrane which facilitates the cell-to-cell passage of ions, hormones, and neurotransmitters; these junctions are often found in autorythmic cells such as cardiac and smooth muscle cells.

connexon - The functional unit of gap junctions; an assembly of six membrane spanning proteins, connexins, having a water filled gap in the centre; two connexons in juxtaposed membranes link to form a continuous pore through both membranes.

chemical synapse - The general type of synapse between two excitable cells, e.g., a neuron connected to a muscle cell, a glandular cell, or another neurons, in which the impulse is transmitted from one cell to the next by the release of neurotransmitter molecules from the sending neuron's axon end bulbs which bind to the receptors on gated Na+, K+, or Cl- channels in the synaptic cleft of the adjacent cell causing a local ionic current flow which destabilizes the receiving cell so that it either depolarizes or hyperpolarizes to some degree, creating a local graded potential.

synaptic cleft - The crevice or indentation in the cell membrane of an excitable cell (neuron, muscle cell, or gland cell) which is immediately adjacent to the axon end bulb of the neuron which can transmit a nerve impulse to the excitable cell; the two cell membranes are very close to each other but do not actually come into contact.

postsynaptic potential - The short-distance local membrane surface signaling events, induced by the arrival of neurotransmitters, which alter membrane permeability and affect the threshold for firing, producing graded responses in proportion to the amount and kinds of neurotransmitters, excitatory and inhibitory, that are arriving at the dendrites and axon-hillock at any specific point in time.

synaptic delay - The time lag in impulse transmission which occurs when an impulse must cross a chemical synapse, due to the relatively slow rate of neurotransmitter release and diffusion and interaction with postsynaptic receptors, compared to the more rapid time of transmission of an impulse along the length of a neuron membrane; the actual time of delay, approximately 0.3-0.5 msec, is the rate limiting step in neural transmission.

excitatory postsynaptic potential (EPSP) - The local graded depolarization events which occur at excitatory postsynaptic membranes in response to the arrival of excitatory neurotransmitter molecules which bind with and open membrane gated Na+ channels; EPSPs help to trigger an action potential at the axon hillock of the postsynaptic neuron.

inhibitory postsynaptic potential (IPSP) - The local graded hyperpolarization events which occur at excitatory postsynaptic membranes in response to the arrival of inhibitory neurotransmitter molecules which bind with and open membrane gated K+ channels or Cl- channels; IPSPs help to raise the threshold for firing and thus inhibit an action potential at the axon hillock of the postsynaptic neuron.

diffusion - The spontaneous movement of molecules or other particles in solution, owing to their random thermal motion, to reach a uniform concentration throughout the solvent, a process requiring no addition of energy to the system.

uptake (into cells) - The process of transferring molecules from the external environment across the cell membrane and into cells, usually referring to a process that is controlled by some form of specialized regulated transport protein in the cell membrane; e.g., the ability of neurons to reabsorb the breakdown products of their neurotransmitter from the synapse for resynthesis and storage in the axon end bulbs.

enzymatic degradation -The enzyme-catalyzed decomposition of a compound/molecule by stages, exhibiting well-defined intermediate products; e.g., when a neurotransmitter is broken down in the synapse.

presynaptic facilitation - The response which occurs when the release of excitatory neurotransmitter by one neuron is assisted by the activity of another neuron via an axoaxonic synapse; the end result is that more neurotransmitter is released and bound, and larger excitatory postsynaptic potentials  (EPSPs) are formed.

presynaptic inhibition - The response which occurs when the release of excitatory neurotransmitter by one neuron is inhibited by the activity of another neuron via an axoaxonic synapse; the end result is that less neurotransmitter is released and bound, and smaller excitatory postsynaptic potentials  (EPSPs) are formed.

spatial summation (of PSP's) - The response which occurs when the postsynaptic neuron is stimulated at the same time by a large number of axon terminals from the same or, more commonly, different neurons; huge numbers of its receptors bind neurotransmitter and simultaneously initiate excitatory postsynatptic potentials (EPSPs), which summate and dramatically enhance depolarization.

temporal summation (of PSP's) - The response which occurs when one or more presynaptic neurons transmit impulses in rapid-fire order and bursts of neurotransmitter are released in quick succession; the first impulse produces a slight excitatory postsynaptic potential (EPSP), and before it dissipates, successive impulses trigger more excitatory postsynatptic potentials (EPSPs); these summate, producing a much greater depolarization of the postsynaptic membrane than would result from a single excitatory postsynatptic potential (EPSP).

List:

12. Two types of synapses, in terms of molecular mode of stimulus transmission, the structures unique to each, and where in the body they can be found.
electrical synapse pre- and post-synaptic cells have gap junctions to permit direct transmission of action potential = depolarization event from one cell to the next cardiac muscle, some smooth muscle, very few neurons in adult humans
chemical synapse pre-synaptic cells have mitochondria for local ATP production, endoplasmic reticulum and Golgi apparatus and its vesicles for synthesis and storage of neurotransmitter molecules, cytoskeletal elements responsive to Ca++ ion influx to move neurotransmitter vesicles to axon end bulb membrane when nerve impulse = action potential arrives; post-synaptic cells have specific chemically gated ion channels which will bind the neurotransmitter molecules to achieve either depolarization (excitatory transmission) or hyperpolarization (inhibitory transmission). widely distributed in the peripheral (PNS) and central (CNS) nervous systems


13. Two types of postsynaptic potentials.

               excitatory postsynaptic potential (EPSP) and inhibitory postsynaptic potential (IPSP)

Sketch and Label:

4. The parts of a chemical synapse. What are the differences, if any, in a chemical synapse between two neurons and a neuromuscular junction?

[Note:  In the figure above, the mitochondria, endoplasmic reticulum, Golgi apparatus, vesicles for neurotransmitter storage, and cytoskeletal elements involved in vesicle movement have been omitted.]

The only significant differences between a chemical synapse between two neurons and a neuromuscular junction are (1) the location, and (2) the fact that a variety of neurotransmitters are used in communication between neurons while only acetyl choline is used at the neuromuscular junction.