The synapse Flashcards

Review of the synapse

1
Q

What is a synapse?

A

Specialised junction between two neurons

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2
Q

What is a convergent synapse?

A

Thousands of synapses affecting one postsynaptic cell (complex)

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3
Q

What is a divergent synapse?

A

Single cell can affect many postsynaptic cells (influential effect of one source)

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4
Q

How much of a delay does a synapse cause?

A

1-2ms

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5
Q

Can a synapse be both postsynaptic and presynaptic?

A

Yes, interneurons are both

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6
Q

Outline the process that occurs at a synapse

A

Action potential arrives at presynaptic knob; depolarisation opens Ca2+ v-gated channels (as depolarisation always open v-gated channels); Ca2+ enter presynaptic knob; Ca2+ causes fusion of docked vesicles with terminal membrane; neurotransmitter leaves vesicles by exocytosis; NTs diffuse across cleft; NT binds to postsynaptic receptors at postsynaptic density; will cause opening or closing of an ion channel (either directly or indirectly via a G-protein); AT AN EXCITATORY MEMBRANE: activated receptor opens small positive charge ion channels on postsynaptic membrane; Na+ in, K+ out, net movement of positive ions is into cell, causing slight depolarisation; graded potential is created as EPSP; if membrane potential is dominated by excitatory synaptic input, will cause depolarisation of membrane, if dominated by inhibitory synaptic membrane, will cause stabilisation or hyperpolarisation; AT AN INHIBITORY MEMBRANE: activated receptors open Cl-/K+ channel; if cell actively regulates intracellular Cl- by active transport, will cause hyperpolarisation as Cl- enters cell, causing IPSP; if cell does not actively regulate Cl-, opening Cl- channel does not change membrane potential but increases influence of Cl- on membrane, so it is difficult for other ions to change membrane potential, causing stabilisation; K+ channels opening allows K+ out of cell, creating an IPSP; NT is removed from synaptic cleft via active transport into presynaptic knob and vesicles or glial cell, enzymatically inactivated, or diffusion away; [NT] decreasing decreases number of occupied receptors; ion channels return to resting state

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7
Q

What does the synaptic cleft do?

A

Prevents direct propagation

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8
Q

How is the membrane potential determined?

A

Is the sum of all synaptic activity, so depends on number of synapses active and number which are excitatory or inhibitory

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9
Q

What is post-synaptic integration?

A

Temporal and spatial summation

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10
Q

How might drugs affect synapses?

A

Release and degradation of NT inside axon terminal; increased NT into cleft; prevention of NT into cleft; inhibition of NT synthesis; reduced or increased reuptake of NT from cleft; reduced degradation of NT in synapse; agonist or antagonist can occupy receptors; reduced biochemical response inside postsynaptic cell

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11
Q

What is the postsynaptic density?

A

High density of membrane proteins

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12
Q

What is an agonist?

A

Evokes same response as NT

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13
Q

What is an antagonist?

A

Blocks response to NT

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14
Q

What are the four main classes of neurotransmitters?

A

Acetylcholine, biogenic amines, amino acids, neuropeptides

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15
Q

What is ACh?

A

Is the major neurotransmitter in PNS and brain; released by cholinergic neurons, and bind to nicotinic and muscarinic; has a variety of excitatory effects in CNS

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16
Q

What are the three types of biogenic amines?

A

Catocholamines, serotonin, histamine

17
Q

What are three types of catocholamines?

A

Dopamine, norepinephrine, epinephrine

18
Q

What roles is dopamine involved in, and the associated disorders?

A

Voluntary movement and motivation; related disorders are Parkinson’s and ADHD

19
Q

What roles is norepinephrine involved in, and the associated disorders?

A

Wakefulness, arousal, flight or fight; related disorders are ADHD, hyperactivity, depression

20
Q

What roles is epinephrine involved in?

A

Role in fight or flight

21
Q

What roles is serotonin involved in, and the associated disorders?

A

Memory, emotions, wakefulness, sleep and body temperature; related disorders are clinical depression, OCD, migraines, tinnitus, bipolar disorder, anxiety, increased aggressive/angry behaviours

22
Q

What roles is histamine involved in?

A

Modulating sleep, vigilance

23
Q

What are the two types of amino acids and examples?

A

Excitatory (e.g. glutamate); inhibitory (e.g. GABA)

24
Q

What roles is glutamate involved in, and the associated disorders?

A

Most prominent excitatory transmitter; congitive functions, e.g. learning and memory; related disorders are stroke and Alzheimer’s

25
What roles is GABA involved in, and the associated disorders?
Chief inhibitory NT in CNS; inhibition of motor neurons; related disorders is abnormal increase in muscle tone caused by reduced GABA absorption in spastic cerebral palsy
26
What are three types of neuropeptides?
Endogenous opioids, oxytocin, tachykinins
27
What roles are endogenous opioids involved in?
Motivation, emotion, response to stress and pain, control of food intake
28
What roles is oxytocin involved in, and the associated disorders?
Social recognition and bonding, trust between people, regulation of body temperature, activity level, wakefulness; associated with autism
29
What roles are tachykinins involved in, and the associated disorders?
Regulation of mood disorders, anxiety, stress, reinforcement, respiratory rhythm, neurotoxicity, nausea and vomiting, pain, vasodilation; associated disorders are fibromyalgia, hypotension
30
What gas is a neurotransmitter?
Nitrous oxide
31
What roles is NO involved in, and the associated disorders?
Vasodilation and immunity; related disorders are physical weakness and extreme fatigue
32
What are two purines which act as neurotransmitters?
Adenosine and ATP
33
What roles is adenosine involved in?
Is an inhibitory NT; promotes sleep and suppresses arousal, anti-inflammatory, action on heart