Topic 99 - Axonal transport and synaptic transmission, sensors, types of ion channels

Question 1

Words to include in axonal transport and synaptic transmission

Answer 1

• Axonal transport
  
  • Neuropeptide
  • Vesicles
  • Presynaptic nerve ending
  • Neuro peptides (binding)
  • Modulated peptides (binding)
  • Carrier proteins
• Action potential
• Axon
• Synaptic nerve ending
• Neurotransmitters
  
  • Norepinephrine / noradrenaline
  • Acetylcholine
  • Glicin
  • Larger peptides
• Synthesis
  
  • Peptides
  • Vesicles
  • Soma
  • Neuron
• Motor proteins / transporter
  
  • ATP
  • Microtubular system
• Anterograde transport
  
  • Soma → nerve ending
  • Kinesin
• Retrograde transport
  
  • Nerve ending → soma
  • Dynein
• Synaptic cleft
• Postsynaptic membrane
• Hyperpolarization
  
  • Resting membrane potential ↑
• Depolarization
  
  • Resting membrane potential ↓

Neural network

• Neural network
• Synapse
  
  • Neuron
    
    • Axon
  • Soma
  • dendrite
• CNS
• Neurons
• Electrical synapse
  
  • Presynaptic neurons
  • Postsynaptic neurons
  • Gap junction
  • Fast response
    
    • Defensive reflexes
  • Bidirectional
• Gap junction
  
  • Synapse
  • Free diffusion of charges
  • Connexin
    
    • Hexamer
    • 6 connexin peptide
    • Hydrophilic channel
  • Fast communication
  • Bidirectional
    
    • Rectification
  • CNS
    
    • Fast reflex arches
    • Cardiac cells
• Chemical synapse
  
  • Junctions
  • Non-neuronal cells
  • Vesicles
  • Exocytosis
  • Postsynaptic cell side
  • Threshold action potential
  • Presynaptic terminal
  • Post-synaptic density
  • Voltage gated Ca²⁺ channel
  • Synaptic vesicle
  • Axon terminal
    
    • Neurotransmitters
    • Neurotransmitter re-uptake pump
    • Neurotransmitter receptors
  • Synaptic cleft
  • Dendritic spine
• Metabotropic effect
  
  • Neurotransmitter
  • Receptor
  • Postsynaptic neuron
  • Short term change
  • Long term change
• EPSP (Excitatory Postsynaptic Potential)
  
  • Postsynaptic neuron (↑)
• IPSP (Inhibitory Postsynaptic Potential)
  
  • Postsynaptic neuron (↓)

Question 2

Words to include in sensors, types of ion channels

Answer 2

• Na⁺
• K⁺
• Cl^-
• Leaking Na⁺, K⁺ and Cl^- channels
  
  • Membrane potential
• Voltage dependent Na⁺ and K⁺ channels
  
  • Action potential
• Ligand dependent non-selective Na⁺, K⁺ and Cl^- channels
• Mechanoreceptive
  
  • Mechanical stimuli
• Energy sensor
  
  • K⁺ channe
  • ATP
  • Depolarization
  • ATP concentration
• Voltage dependent Na⁺ channel
  
  • Protein
  • IC part
  • Transmembrane part
  • EC part
  • 6-6 transmembrane segments
  • Tetrodotoxin (TIX)
• Ligand dependent ion channel
  
  • Nicotinic acetylcholine (n-ACh)
    
    • Nicotine
    • Curare
    • Neuro-muscular junction
    • CNS
    • Skeletal muscle
      
      • Pentamer
        
        • 2 α subunit
        • 2 β subunit
        • 1 Δ subunit
          
          • D-tubocurarine
    • Nervous system
      
      • 2 α subunit
      • 3 β subunit
  • Glutamate
    
    • Excitatory system
    • CNS
    • Permable
      
      • Na⁺
      • K⁺
      • Ca²⁺
    • AMPA
    • NMDA
    • Kainate
  • Anion channels
    
    • Hyperpolarization
    • Mediators
      
      • GABA
      • Glycine
  • G-protein mediated
• Mechanoreceptive channels (Ca²⁺-ion channels)
  
  • Ryanodine and DHP
    
    • Voltage sensors
    • T-tubules
    • Triad
    • Dihydropyridine (DPH)
    • Ca²⁺-channels
      
      • Ryanodine
      • Sarcoplasmic reticulum (SR)
  • IP₃-receptor
    
    • IC Ca²⁺ stores
  • Voltage-dependent
    
    • P-type calcium channel
    • T-type calcium channel
    • N-type calcium channel
• Energy sensor ion channel
  
  • ATP
  • Regulator subunit
  • Pore-forming subunit
  • Conformational change
  • K⁺ efflux
    
    • Depolarization
  • Ca²⁺ influx

Question 3

Topics to include in the essay

Answer 3

1. Axonal transport
2. Neural network
   
   • Synapse
     
     • Electrical synapse
     • Gap junction
     • Chemical synapse
     • Metabotropic effect
3. Sensors, types of ion channels
   
   • Voltage dependent Na⁺ channel
   • Ligand-dependent ion channel
     
     • n-ACh
     • Glutamate
     • Anion channels
     • G-protein mediated
   • Mechanoreceptive channels (Ca²⁺ ion channels)
     
     • Ryanodine & DHP
     • IP₃-receptor
     • Voltage-dependent
   • Energy sensor ion channel

Question 4

Axonal transport

Answer 4

• The action potential - conducted through the axon in the synaptic nerve ending produces the release of neurotransmitters​
• The synthesis of peptides and vesicles is only possible in the soma of the neuron
  
  • ​Axonal transport: The produced neuropeptides and vesicles must be transported to the presynaptic nerve ending
• Molecular base of the transport: the binding of the neuro- and modulator peptides to carrier proteins in the soma
  
  • ​These transporter or motor proteins uses ATP on the microtubular system along the axis of the axon
  • Soma → nerve ending: Anterograde transport by kinesin
  • Nerve ending → soma: Retrograde transport by dynein
  • Vesicles stored in nerve endings are released to the synaptic cleft as a result of an action potential
  • The neurotransmitter can bind to their specific receptors on the postsynaptic membrane
  • The result of receptor-binding can be:
    
    • Hyperpolarization: Resting membrane potential ↑
    • Depolarization: Resting membrane potential ↓

Question 5

Axonal transport

What are neurotransmitters composed of?

Answer 5

• Small molecular weight substances, eg.:
  
  • Norepinephrine
  • Acetylcholine
  • Glicin
• Large peptides

Question 6

Neural network

Define synapse

Answer 6

• Synapse:
  
  • Contact between the axon of one neuron and a dendrite or soma of another
  • Allows neurons to from circuits within the CNS
  • Allow the nervous system to connect to and control other systems of the body

Question 7

Neural network

Name the different type of synapse

Answer 7

1. Electrical synapse
2. Gap junction
3. Chemical synapse

Question 8

Neural network

Synapse: Electrical synapse

Answer 8

• A mechanical and electrically conductive link between two neurons that is formed at a narrow gap between the pre- and postsynaptic neurons known as a gap junction
• Compared to chemical synapses:
  
  • Electrical synapses conduct nerve impulses faster
  • Unlike chemical synapses, they lack gain - the signal in the postsynaptic neuron is the same or smaller than that of the originating neuron
• Location: In neural systems that require the fastest possible response
  
  • Eg. defensive reflexes
• Bidirectional (most of the time)

Question 9

Neural network

Synapse: Gap junction

Answer 9

• Allows free diffusion of charges between cells
• Connexin:
  
  • ​Hexamer
  • Built up by six connexin peptide
• The shortest information transduction which allows the fastest communication between cells
• Bidirectional
  
  • ​Rectification: In some junctions one of the directions is dominant
• Location: fast reflex arches in the CNS
  
  • ​Eg. between cardiac cells

Question 10

Neural network

Synapse: Chemical synapse

Answer 10

• Signal between:
  
  • Between neurons
  • Between neuron and non-neuronal cells
• One neuron releases neurotransmitter molecules into the synaptic cleft
  
  • ​Triggered by a nerve impulse/AP
• The neurotransmitters are kept within vesicles and are released into the synaptic cleft by exocytosis. These molecules then bind to receptors on the postsynaptic cell’s side of the synaptic cleft
• In response to a threshold action potential, a neurotransmitter is released at the presynaptic terminal

Question 11

Metabotropic effect

Answer 11

• Metabotropic effect: The binding of neurotransmitters to receptors in the postsynaptic neuron can trigger either short term changes or long term changes
• Long term effects are based on the the fact that neurotransmitters cause intramembrane or IC changes leading to long term depolarization or hyperpolarization
  
  • ​Metabolic changes evokes the alteration of K⁺ and Ca²⁺ conductance, which is the primary reasons of long term depolarization or hyperpolarization
• Gap junction procces leads either to:
  
  • EPSP (Excitatory Postsynaptic Potential)
    
    • ​Man discharge frequency of the postsynaptic neuron ↑
  • IPSP (Inhibitory Postsynaptic Potential)
    
    • ​Man discharge frequency of the postsynaptic neuron ↓
• Transmitters involved: Metabotropic transmitters
  
  • ​Response to them: metabotropic response​

1. Binding of ligand to receptor
2. IC 2^nd messenger
3. IC metabolic (metabotropic) effect
4. Long lasting depolarization or hyperpolarization

Question 12

Types of ion channels

Role

Answer 12

• They are proteins molecules that span across the cell membrane allowing the passage of ions from one side of the membrane to the other side
• They are selective - they only allow certain ions to pass
• They are involved in the transmission of signals in the nervous system

Question 13

Type of ion channels

Name the different types of ion channels

Answer 13

• Leaking sodium, potassium and chloride channels
  
  • Maintenance of the membrane potential
• Voltage-dependent sodium and potassium channels
  
  • Generation of action potential
• Ligand-dependent non-selective sodium, potassium and chloride channels
  
  • Multiple
• Mechanoreceptive
  
  • Uptake of tactile and other mechanical stimuli
• Energy sensor
  
  • Potassium channel sensitive to ATP causes depolarization according to the ATP concentration of cell
• More info about these channels on the next cards:
  
  • Voltage dependent Na⁺ channel
  • Ligand dependent ion channels
    
    • ​Nicotinic acetylcholine dependent non-selective Na⁺/K⁺ channel
    • Glutamate dependent cation channel
    • Anion channels
    • G-protein mediated signal transduction
  • Mechanoreceptive channels (Ca²⁺ ion channels)
    
    • ​Ryanodine and DHP
    • IP₃-receptor
    • Voltage-dependent
  • Energy sensor ion channel

Question 14

Types of ion channels

Voltage dependent Na channel

Answer 14

• This protein contains IC, transmembrane and EC parts
• Four main domains with 6-6 transmembrane segments (1-6) each
• Specific inhibitor: tetrodotoxin (TIX, a poison)

Question 15

Types of ion channels

Name the different types of ligand dependent ion channels

Answer 15

• Nicotinic acetylcholine dependent non-selective Na⁺/K⁺ channel
• Glutamate dependent cation channels
• Anion channels
• G-protein mediated signal transduction

Question 16

Types of ion channels

Ligand dependent ion channels: Nicotinic acetylcholine dependent non-selective Na⁺/K⁺ channel

Answer 16

• Stimulated by nicotine
• Inhibited by curare
• Receptor of the neuro-muscular junction and the CNS
• In skeletal muscle:
  
  • Pentamer containing:
    
    • 2 α-subunits
    • 2 β-subunits
    • 1 Δ-subunit
      
      • Binds d-tubocurarine
• In nervous system:
  
  • Contains:
    
    • 2 α-subunits
    • 3 β-subunits

Question 17

Types of ion channels

Ligand dependent ion channels: Glutamate dependent cation channels

Answer 17

• Important excitatory system of the CNS
• Permeable for Na⁺, K⁺ and Ca²⁺
• Three different types are known:
  
  • AMPA
  • NMDA
  • Kainate

Question 18

Types of ion channels

Ligand dependent ion channels: A__nion channels

Answer 18

• Opening of anion channels causes hyperpolarization
• Two main mediators are known:
  
  • GABA
  • Glycine

Question 19

Types of ion channels

Name the different types of mechanoreceptive channels (Ca²⁺ ion channels)

Answer 19

• Ryanodine and DHP (Dihydropyridine) receptor
• IP₃-receptor
• Voltage dependent

Question 20

Types of ion channels

Mechanoreceptive channels: Ryanodine and DHP (Dihydropyridine) receptor

Answer 20

• Voltage sensors in T-tubules or in triad
  
  • Blocked by dihydropyridine (DPH)
• Mechanically activates the calcium channels (sensitive to ryanodine) located in sarcoplasmic reticulum

Question 21

Types of ion channels

Mechanoreceptive channels: IP₃-receptor

Answer 21

Mobilizes Ca²⁺ from the IC calcium stores

Question 22

Types of ion channels

Mechanoreceptive channels: Voltage-dependent Ca²⁺-channels

Answer 22

• Activated by membrane potential change
• Most well known types:
  
  • P-type calcium channel
  • T-type calcium channel
  • N-type calcium channel

Question 23

Types of ion channels

Energy sensor ion channel

Answer 23

• Low level of ATP: the channel is open
• ATP levels increase:
  
  • Regulator subunit shows conformational change
  • Pore-forming subunit shows conformational change
  • K⁺ efflux terminates, IC + increases, this leads to depolarization
  • Ca²⁺ influx: different metabolic effects