Electrical And Chemical Synapses

Question 1

What is the length between two cell membranes at a neuronal chemical synapse?

Answer 1

30nm

Question 2

What is the gap length at a nerve muscle synapse?

Answer 2

50nm

Question 3

Characteristics of electrical synapses

Answer 3

Bi directional Lack receptors Depolarization of pre synaptic membrane will produce despoliation of the post synaptic membrane Response is usually attenuated due to membrane resistance

Question 4

Functional properties of electrical synapses

Answer 4

Reduced extra cellular space Cytoplasmic and continuity btw pre and post synaptic cells Mediating agent is ionic current Little synaptic delay Signal transmission is rapid

Question 5

Explain Little synaptic delay

Answer 5

Transmission is limited only by the speed of electrotonic transmission across the short distance separating the pre synaptic and post synaptic elements at the synapse

Question 6

What is the structure of gap junctions?

Answer 6

Hexameric complexes consist of subunits of connexonswhich are present in both pre and post synaptic membranes.

Question 7

Classification of synapses

Answer 7

Electrical and chemical

Question 8

Electrical pulse

Answer 8

Membrane of pre and post synaptic neurons come together to form a gap junction or low resistance bridge, direct jumping of electrical currents occur

Question 9

Chemical synapses

Answer 9

Most common , gaps are approx 20nm wide

Question 10

Types of synapses

Answer 10

Axo-axonic, axo- somatic , axo- dendritic

Question 11

What time of synapse is this?

Answer 11

Axo-somatic: axon of pre-synaptic neuron communicates with the cell body of the post-synaptic neuron

Question 12

what type of synaptic is this?

Answer 12

Axo-axonic: axon of pre-synaptic neuron communicates with the axon of the post-synaptic neuron

Question 13

A reciprocal synaptic relationship between two dendrites

Answer 13

A single element is both pre- and postsynaptic to a second element.

Note the accumulations of synaptic vesicles on what is presumed to be the presynaptic side of the synapses

Question 14

Diagram of chemical synapse

Question 15

Synaptic cleft

Answer 15

Synaptic cleft - a gap between the two neurons across which the neurotransmitters migrate.

Question 16

Post synaptic terminal

Answer 16

usually in the dendrites of receiving neurons. This contains receiving sites for the neurotransmitters.

Question 17

Function of chemical synapse

Answer 17

1. Increased extra-cellular space (typically 30 – 50 nm); no cytoplasmic continuity between pre- and postsynaptic elements
2. Mediating agent is a chemical messenger (ACh, NA, peptides, etc.)
3. Significant synaptic delay (at least 0.3 msec, sometimes 1 – 5 msec or longer)
4. Unidirectional

Question 18

Electrical and Chemical Synapses : how do this work?

Answer 18

Electrical and chemical synapses differ fundamentally in their transmission mechanisms. (A) At electrical synapses, gap junctions between pre- and postsynaptic membranes permit current to flow passively through intercellular channels (see blowup). This current flow changes the postsynaptic membrane potential, initiating (or in some instances inhibiting) the generation of postsynaptic action potentials.

(B) At chemical synapses, there is no intercellular continuity, and thus no direct flow of current from pre- to postsynaptic cell. Synaptic current flows across the postsynaptic membrane only in response to the secretion of neurotransmitters which open or close postsynaptic ion channels after binding to receptor molecules (see blowup).

Question 19

What is a neuronal Transmitter?

Answer 19

Small molecules which carry the nerve impulse from the sending neuron to the receiving neuron.

Question 20

Characteristic of transmitter

Answer 20

Occurs naturally in pre-synaptic terminals, and either the precursors and enzymes for its formation or an adequate, specific transport system for its uptake into the terminal must exist

Must be released from the terminals by nerve stimulation

A mechanism must exist for rapid inactivation of the released transmitter substance

A synaptic action must be identified for the substance, and local application must produce effects “exactly” like those of synaptically released transmitter substance

Drugs must produce similar effects upon actions of the substance and natural transmitter substance.

Question 21

Neurotransmitter table

Answer 21

Question 22

function of transmitters

Answer 22

Question 23

two types of chemical synapses?

Answer 23

1. Pre-synaptic transmission process

Determine the release of the chemical messenger

1. Post-synaptic receptive processes-

determine the interaction between transmitter and receptor molecule in the postsynaptic cell

Question 24

depolarising of the membrane signalifies EPSP OR IPSP

Answer 24

If depolarizing, it is an excitatory postsynaptic potential (EPSP); if hyperpolarizing, an inhibitory postsynaptic potential (IPSP).

Question 25

Excitatory Post-synaptic Potentials (EPSPs)

Answer 25

The excitation of a post-synaptic neuron (transient depolarization) by axon endings that release a neurotransmitter that induces a local (sub-threshold) response (EPSPs)

Question 27

Post-synaptic inhibition

Answer 27

The inhibition of a postsynaptic neuron by axon endings that release a neurotransmitter that induces hyperpolarization (inhibitory postsynaptic potentials)

Question 28

Inhibitory Post-synaptic potential

Answer 28

A graded potential in the post-synaptic neuron which makes it more negative and, thus, less likely to fire.

2 mechanisms

K+ gates open up on the postsynaptic membrane and allow K+ ions to leave the neuron.

Chloride ion (Cl-) channels may open up and allow Cl- ions to enter the postsynaptic neuron.

Question 29

Summation

Answer 29

Activity in one synaptic knob is small and occurs in several synaptic knobs. These responses summate to produce depolarization or hyperpolarization

Question 30

Summation is divided into two

Answer 30

1. Temporal

Repeated afferent stimuli cause new EPSPs before previous EPSPs have decayed in the same synaptic knob.

1. Spatial

Activity occurs in more than one synaptic knob at the same time.

Activity on one knob facilitates activity in another to approach the firing level

Question 31

Significance

Answer 31

Significance: excitation of a single pre-synaptic neuron never excites or inhibits the post-synaptic neuron as sufficient NT is not released

Question 32

Facilitation

Answer 32

The process of lowering the threshold for propagation of the action potential by repeated use of a neural pathway or the summation of two or more sub-threshold impulses.

Each succeeding stimulus increased the duration of the AP in the pre-synaptic neuron

Voltage gated Ca2+ channels remain open

Subliminal stimulus primes the post-synaptic neuron so that another such stimulus will evoke discharge of the post-synaptic neuron

1st stimulus facilitates the effect due to prolonged exposure of post-synaptic neuron to the NT

Question 33

Synaptic integration

Answer 33

Synaptic integration – the summation of both EPSP and IPSP at the post synaptic membrane

Determines whether synaptic transmission will occur or not

Question 34

Signal Transduction Cascade

Answer 34

Figure 5.3 Signal-transduction cascade by which an extracellular ligand such as a peptide hormone can bind to its receptor to activate a G protein and, via the cascade, lead to the activation or inactivation of an ion channel, a protein kinase, or a phospholipase. The three shaded boxes to the right contain the major members of the categories to which the boxes are linked by the horizontal dashed lines.

Question 35

Ionotropic and Meta-botropic Acetylcholine Receptors

Answer 35

A, This example illustrates a “nicotinic” acetylcholine receptor, which is a ligand-gated channel on the postsynaptic membrane. In a skeletal muscle, the end result is muscle contraction. B, This example illustrates a “muscarinic” acetylcholine receptor, which is coupled to a heterotrimeric G protein. In a cardiac muscle, the end result is decreased heart rate. Note that the presynaptic release of ACh is very similar here and in A. ACh, acetylcholine; GTP, guanosine triphosphate.