The synapse

Question 1

What is a synapse?

Answer 1

Specialised junction between two neurons

Question 2

What is a convergent synapse?

Answer 2

Thousands of synapses affecting one postsynaptic cell (complex)

Question 3

What is a divergent synapse?

Answer 3

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

Question 4

How much of a delay does a synapse cause?

Answer 4

1-2ms

Question 5

Can a synapse be both postsynaptic and presynaptic?

Answer 5

Yes, interneurons are both

Question 6

Outline the process that occurs at a synapse

Answer 6

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

Question 7

What does the synaptic cleft do?

Answer 7

Prevents direct propagation

Question 8

How is the membrane potential determined?

Answer 8

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

Question 9

What is post-synaptic integration?

Answer 9

Temporal and spatial summation

Question 10

How might drugs affect synapses?

Answer 10

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

Question 11

What is the postsynaptic density?

Answer 11

High density of membrane proteins

Question 12

What is an agonist?

Answer 12

Evokes same response as NT

Question 13

What is an antagonist?

Answer 13

Blocks response to NT

Question 14

What are the four main classes of neurotransmitters?

Answer 14

Acetylcholine, biogenic amines, amino acids, neuropeptides

Question 15

What is ACh?

Answer 15

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

Question 16

What are the three types of biogenic amines?

Answer 16

Catocholamines, serotonin, histamine

Question 17

What are three types of catocholamines?

Answer 17

Dopamine, norepinephrine, epinephrine

Question 18

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

Answer 18

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

Question 19

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

Answer 19

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

Question 20

What roles is epinephrine involved in?

Answer 20

Role in fight or flight

Question 21

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

Answer 21

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

Question 22

What roles is histamine involved in?

Answer 22

Modulating sleep, vigilance

Question 23

What are the two types of amino acids and examples?

Answer 23

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

Question 24

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

Answer 24

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

Question 25

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

Answer 25

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

Question 26

What are three types of neuropeptides?

Answer 26

Endogenous opioids, oxytocin, tachykinins

Question 27

What roles are endogenous opioids involved in?

Answer 27

Motivation, emotion, response to stress and pain, control of food intake

Question 28

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

Answer 28

Social recognition and bonding, trust between people, regulation of body temperature, activity level, wakefulness; associated with autism

Question 29

What roles are tachykinins involved in, and the associated disorders?

Answer 29

Regulation of mood disorders, anxiety, stress, reinforcement, respiratory rhythm, neurotoxicity, nausea and vomiting, pain, vasodilation; associated disorders are fibromyalgia, hypotension

Question 30

What gas is a neurotransmitter?

Answer 30

Nitrous oxide

Question 31

What roles is NO involved in, and the associated disorders?

Answer 31

Vasodilation and immunity; related disorders are physical weakness and extreme fatigue

Question 32

What are two purines which act as neurotransmitters?

Answer 32

Adenosine and ATP

Question 33

What roles is adenosine involved in?

Answer 33

Is an inhibitory NT; promotes sleep and suppresses arousal, anti-inflammatory, action on heart