Lecture 4 - Synapse

Question 1

Synapse

Answer 1

Specialized junction where an axon terminal contacts another neuron or cell type.

Mediate information/impulse.

Question 2

Axodendritic

Answer 2

Axon to dendrite

Question 3

Axosomatic

Answer 3

Axon to cell body

Question 4

Axoaxonic

Answer 4

Axon to axon

Question 5

Dendrodendritic

Answer 5

Dendrite to dendrite

Question 6

The Neuromuscular Junction (NMJ)

Answer 6

Synapse between neuron and muscle

Question 7

How many synapses are in one neuron?

Answer 7

1,000 to 10,000

Question 8

What are the two types of synapses?

Answer 8

Electrical (less common) and Chemical synapses

Question 9

Electrical synapses

Answer 9

Allows the direct transfer of ionic current from one cell to the next.

Gap junction is composed of 6 connexins that make up a connexon.

Ions can flow bidirectionally.

Cells are electronically coupled. Conduction speed is very fast.

Found in neuronal pathways associated with escape reflexes or in neurons that need to be synchronized.

Common in non-neuronal cells.

Important in development.

Question 10

Chemical synapses

Answer 10

Can occur between neurons, and between neurons and muscle cells.

Question 11

Synaptic cleft

Answer 11

20-50nm wide. Held together by a fibrous extracellular matrix.

Question 12

Synaptic bouton (presynaptic element)

Answer 12

Contains synaptic vesicles and secretory granules called large, dense core vesicles.

Question 13

Membrane differentiations

Answer 13

Accumulations of proteins on either side of the synaptic cleft.

Question 14

Active zones

Answer 14

Presynaptic site of neurotransmitter release

Question 15

Postsynaptic density

Answer 15

Contains receptors to translate INTERcellular signal (neurotransmitter) into an INTRAcellular signal (chemical change or membrane potential change).

Question 16

Release of neurotransmitter (10 steps)

Answer 16

1. Neurotransmitter is synthesized and then stored in vesicles.
2. Action potential enters the axon terminal (presynaptic terminal).
3. Depolarization of presynaptic terminal causes opening of voltage gated Ca++ channels.
4. Influx of Ca++ through channels.
5. Ca++ activates proteins in the vesicle and active zone. Activated proteins cause synaptic vesicles to fuse with the membrane.
6. Neurotransmitter is released via exocytosis.
7. Transmitter binds to the receptor molecules in postsynaptic membrane.
8. Opening or closing of postsynaptic channels.
9. Postsynaptic causes excitatory or inhibitory postsynaptic potential that changes the excitability of the postsynaptic cells.
10. Retrieval of vesicular membrane from plasma membrane.

Question 17

Neurotransmitter

Answer 17

A substance that transmits nerve impulses across synapse.

Question 18

Criteria to be considered as a neurotransmitter (6 total)

Answer 18

1. Must be present at presynaptic terminal.
2. Must be released by depolarization (Ca+++ dependent).
3. Specific receptors must be present.
4. When added to extracellular fluid, it must mimic the effects of presynaptic stimulation.
5. A mechanism for removal should exist (enzymatic inactivation or re-uptake into cells).
6. Effects of drugs must block/mimic the neurotransmitter physiological effect.

Question 19

What are the 6 types of neurotransmitters?

Answer 19

Amino acids
Amines
Opioids
Peptides
Catecholamines
Gases

Question 20

What are the two functional classifications of neurotransmitters?

Answer 20

Excitatory neurotransmitters - cause depolarization (ex. glutamate)

Inhibitory neurotransmitters - cause hyperpolarization (ex. GABA and glycine)

Some have both excitatory and inhibitory effects. Determined by the receptor type of the postsynaptic neuron.

Question 21

Acetylcholine

Answer 21

Stimulates muscle contraction, hormone release, in CNS wakefulness, attentiveness, anger, aggression, thirst.

Question 22

Glutamate

Answer 22

Excitatory neurotransmitter associated with learning and memory.

Question 23

Dopamine

Answer 23

Inhibitory neurotransmitter, controlling movement, posture, in CNS, positive reinforcement and dependency.

Question 24

GABA

Answer 24

Inhibitory neurotransmitter, in CNS, motor control, vision, other cortical functions, regulates anxiety.

Question 25

Norepinephrine

Answer 25

Attentiveness, emotion, sleeping, dreaming, learning, also controls fight or flight reactions, heart stimulator, vasoconstrictor.

Question 26

Serotonin

Answer 26

Regulate body temperature, mood, sleep, appetite, pain, depression, impulsive behavior.

Question 27

What are the 2 major categories of neurotransmitter receptors?

Answer 27

1. Transmitter (ligand) gated ion channels.
2. G-protein coupled receptors.

Question 28

EPSP

Answer 28

Excitatory Post Synaptic Potentials

Open up ligand-gated Na+ channels.
Moves resting membrane potential TOWARD threshold (depolarization).

Question 29

IPSP

Answer 29

Inhibitory Post Synaptic Potentials

Open up ligand-gated Cl- channels.
Moves resting membrane potential AWAY from the threshold (hyperpolarization).

Question 30

What are the two types of Summation?

Answer 30

Temporal and Spatial summation.

Question 31

Temporal summation

Answer 31

If EPSP in pre-synaptic knob are successfully repeated without significant delay so the effect of the previous stimulus is summated to the next.

Question 32

Spatial summation

Answer 32

When EPSP is in more than one synaptic knob at the same time.

Question 33

Clostridium tetani (tetanus toxin)

Answer 33

Prevents vesicle fusion with the membrane, inhibiting neurotransmitter release and causes increased muscle contraction.

Question 34

Clostridium botulinum bacilli toxin (botulism)

Answer 34

Interferes with actions of SNARE proteins at excitatory synapses that activates muscles. Botulism is characterized by muscle paralysis.

Question 35

The generation of action potentials is prevented by local anesthetics because they block _______.

Answer 35

Voltage-gated Na+ channels.

Question 36

What else can change neurons and their connections?

Answer 36

Accidents, diseases, and drugs & alcohol.