Synapses

Question 1

types of synpases

Answer 1

1. electrical
   - pre and postsynaptic membranes are bound together by channels
   - APs always propagated
   - rare : in some vestibular nuclei, eye
2. chemical
   - pre and postsynaptic cells are not bound and require the use of neurotransmitters to communicate
   - APs not always propagated (why not??)
   - very common

Question 2

synapse

Answer 2

site of communication between a neuron (pre-synaptic cell )and other cell (post-synaptic cell)

Question 3

Types of Neurotransmitter

Answer 3

excitatory neurotransmitters cause depolarisation,
inhibitory neurotransmitters cause hyperpolarisation

but for the Structural classes:
acetylcholine, amines (e.g. Dopamine, norepinephrine, epinephrine, serotonin), amino acids (e.g. GABA), neuropeptides (e.g. endorphines), purines, gases, lipids

Question 4

Neurotransmitter storage and synthesis

Answer 4

Storage
* neurotransmitters are stored in the pre-synaptic terminals
* these terminals also contain mitochondria to fuel metabolism and transport

Synthesis
Synthesis depends on the nature of the neurotransmitter

Small neurotransmitters (e.g. ACh, amines) are synthesised and packaged in the synaptic terminals

Peptide neurotransmitters are synthesised and package in the cell body and transported to synaptic terminals

Question 5

Describe the steps involved in neurotransmitter release from the axon terminal into the synaptic cleft.

Answer 5

1. action potentail depolarises the axon terminal
2. depolarisation opens voltage-gated Ca2+ channels and Ca2+ enters the cell
3. calcium entry triggers exoctyosis of synaptic vesicle contents
4. neurotransmitter diffuses across the synpatic cleft and binds with receptors on the post synpatic cleft
5. neurotransmitter binding initiates a response in the postsynpatic cell

Question 6

Relationship between Frequency and Stimulus Strength/Duration:

Answer 6

The frequency of action potentials is directly related to the strength and duration of a stimulus.

A stronger or more prolonged stimulus is associated with a higher frequency of action potentials.

weak stimulus = fire action potentials at a lower frequency, strong or prolonged stimulus = a higher frequency of action potentials.

Question 7

Neurotransmitter Receptors types

Answer 7

Two main receptor types:
* Ligand-gated ion channels (ionotropic): fast response,
ion channels open and ions immediately flood into
(or out of) cell
* G protein-coupled receptors (metabotropic):
slow response, ion channel opening relies on an
intermediary ‘second messenger’

Question 8

neurotransmitter receptors and their mechanisms of post-synaptic signalling

Answer 8

1. Ionotropic Receptors:
   ligand-gated ion channels.
   When a neurotransmitter binds to the ionotropic receptor, the receptor undergoes a conformational change, allowing ions to flow through the channel.
   The flow of ions directly affects the membrane potential of the postsynaptic neuron, leading to rapid changes in electrical signaling.
2. Metabotropic Receptors + ion channel:
   GPCR : g protein coupled receptors
   When a neurotransmitter binds to the metabotropic receptor, the receptor activates G protein to activate ion channel and let ions in cell
3. Metabotropic Receptors + signalling cascade:
   GPCR : g protein coupled receptors
   G proteins activated to create signalling cascade, leading to the modulation of intracellular enzymes or ion channels.
   The signaling cascades initiated by metabotropic receptors are slower and can have more prolonged effects compared to ionotropic receptors.

Question 9

Describe the different ways in which neurotransmission is terminated

Answer 9

1. Reuptake
   * neurotransmitter can be returned to the axon terminals for resuse or transported into glial cells
   * neurotransmitters can be repacakged into vescicles or broken down by enzymes
2. Enzyme degradation
   * enzymes inactivate neurotransmitters
   * break down into smaller inactive molecules to be recycled or cleared away
3. Diffusion
   * diffuse away from the synpatic cleft
   * move away from synpase and into surrounding ECF (extracellular fluid)

Question 10

Outline the sequence of events that occur during neurotransmission at the neuromuscular junction at the presynapse

Answer 10

Consists of neuromuscular junction (NMJ) and motor end plate
NMJ : axon terminals, schwann cell sheaths
motor end plate : muscle membrane and ACh receptors

1. arriving AP depokarises synaptic knob
2. Ca2+ ions enter the cytoplasm and ACh is released through exocytosis of vesicles
3. ACh binds to Na channel receptors on post membrane and poduces graded depolarisation
4. depolarsation ends as ACh is broken down = ACH –> acetate + choline by AChE
5. synpatic knob reabsorbs choline from synpatic cleft to synthesis new ACh molecules

Question 11

Outline the sequence of events that occur during neurotransmission at the neuromuscular junction at the postsynapse

Answer 11

Consists of neuromuscular junction (NMJ) and motor end plate
NMJ : axon terminals, schwann cell sheaths
motor end plate : muscle membrane and ACh receptors

1. Na+ entry and efflux of K+ through ACh receptor/channel initiates muscle action potential
2. Action potential in T-tuble causes a change in the conformation of the DHP receptor
3. DHP receptor ACTIVATES ryanodine receptors (RyR) on SR
4. RyR activated and calcium channels open for and Ca2+ enters cytoplasm
5. Ca2+ binds to troponin, allowing actin-myosin binding
6. myosin heads execute power stroke
7. actin filament slides forward toward centromere

Question 12

common neurotransmitter : Noradrenaline

Answer 12

Location: Found in the brain and the Autonomic Nervous System (ANS).
Receptor Type: Acts through G Protein-Coupled Receptors (GPCRs).
Function: Typically has excitatory effects on target cells.

Question 13

common neurotransmitter : Dopamine

Answer 13

Location: Primarily found in the Central Nervous System (CNS).
Receptor Type: Acts through GPCRs.
Function: Can have both excitatory and inhibitory effects depending on the specific receptor subtype and the location in the brain.

Question 14

common neurotransmitter : Serotonin

Answer 14

Location: Mainly in the CNS.
Receptor Types:
Acts through GPCRs.
Some serotonin receptors function as ligand-gated ion channels.
Function: Exhibits a variety of effects, including both excitatory and inhibitory actions, depending on the specific receptor subtype.

Question 15

common neurotransmitter : Glutamate

Answer 15

Location: Acts as the primary excitatory neurotransmitter in the Central Nervous System (CNS).
Receptor Types: Acts on ionotropic receptors, including NMDA and AMPA receptors, which are ligand-gated ion channels.
Function: Excites target cells by inducing the influx of ions such as sodium and calcium.

Question 16

common neurotransmitter : GABA (Gamma-Aminobutyric Acid)

Answer 16

Location: Acts as the primary inhibitory neurotransmitter in the brain.
Receptor Types: Acts on GABA-A and GABA-B receptors, which are ligand-gated ion channels and GPCRs, respectively.
Function: Inhibits target cells by inducing the influx of chloride ions through GABA-A receptors or modulating intracellular signaling pathways through GABA-B receptors

Question 17

EPSP

Answer 17

excitatory postsynpatic potential
–> changes in membrane potential of postsynaptic membrane to make it more likely to fire action potential

Question 18

IPSP

Answer 18

inhibitory postsynpatic potential
–> changes in membrane potential of postsynaptic membrane to make it less likely to fire action potential

Question 19

EPSP/IPSP and summation

Answer 19

EPSPs and IPSPs represent the excitatory and inhibitory influences on a post-synaptic neuron, respectively.

Spatial and temporal summation involve the integration of these signals to determine whether the neuron will generate an action potential.

If the combined effects of EPSPs and IPSPs are net depolarizing, the neuron is more likely to fire an action potential.

If the net effect is more EPSPs, the post-synaptic neuron is more likely to fire an action potential.

If the net effect is more IPSPs, the likelihood of an action potential decreases.