The synapse Flashcards
Review of the synapse
What is a synapse?
Specialised junction between two neurons
What is a convergent synapse?
Thousands of synapses affecting one postsynaptic cell (complex)
What is a divergent synapse?
Single cell can affect many postsynaptic cells (influential effect of one source)
How much of a delay does a synapse cause?
1-2ms
Can a synapse be both postsynaptic and presynaptic?
Yes, interneurons are both
Outline the process that occurs at a synapse
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
What does the synaptic cleft do?
Prevents direct propagation
How is the membrane potential determined?
Is the sum of all synaptic activity, so depends on number of synapses active and number which are excitatory or inhibitory
What is post-synaptic integration?
Temporal and spatial summation
How might drugs affect synapses?
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
What is the postsynaptic density?
High density of membrane proteins
What is an agonist?
Evokes same response as NT
What is an antagonist?
Blocks response to NT
What are the four main classes of neurotransmitters?
Acetylcholine, biogenic amines, amino acids, neuropeptides
What is ACh?
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
What are the three types of biogenic amines?
Catocholamines, serotonin, histamine
What are three types of catocholamines?
Dopamine, norepinephrine, epinephrine
What roles is dopamine involved in, and the associated disorders?
Voluntary movement and motivation; related disorders are Parkinson’s and ADHD
What roles is norepinephrine involved in, and the associated disorders?
Wakefulness, arousal, flight or fight; related disorders are ADHD, hyperactivity, depression
What roles is epinephrine involved in?
Role in fight or flight
What roles is serotonin involved in, and the associated disorders?
Memory, emotions, wakefulness, sleep and body temperature; related disorders are clinical depression, OCD, migraines, tinnitus, bipolar disorder, anxiety, increased aggressive/angry behaviours
What roles is histamine involved in?
Modulating sleep, vigilance
What are the two types of amino acids and examples?
Excitatory (e.g. glutamate); inhibitory (e.g. GABA)
What roles is glutamate involved in, and the associated disorders?
Most prominent excitatory transmitter; congitive functions, e.g. learning and memory; related disorders are stroke and Alzheimer’s
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
What are three types of neuropeptides?
Endogenous opioids, oxytocin, tachykinins
What roles are endogenous opioids involved in?
Motivation, emotion, response to stress and pain, control of food intake
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
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
What gas is a neurotransmitter?
Nitrous oxide
What roles is NO involved in, and the associated disorders?
Vasodilation and immunity; related disorders are physical weakness and extreme fatigue
What are two purines which act as neurotransmitters?
Adenosine and ATP
What roles is adenosine involved in?
Is an inhibitory NT; promotes sleep and suppresses arousal, anti-inflammatory, action on heart
