L16

Question 1

what are factors that affect propagation speed

Answer 1

○ Axon diameter
○ Amount of myelination (countinuous vs saltatory)
- Temp.
- nerve fibre type

Question 2

explain type A nerve fibre

Answer 2

§ Large, fast myelinated
E.g. Sensory + motor neurons

Question 3

explain type B nerve fibre

Answer 3

§ Small, medium myelinated
§ Visceral sensory
Some autonomic NS

Question 4

explain type C nerve fibre

Answer 4

§ Smallest, slow unmyelinated
§ Pain, temp. Sensory conduction
§ Some autonomic NS outputs
Heart, bladder

Question 5

what are 3 places neurons can recieve signals from

Answer 5

○ Axoaxonic
○ Axodendritic
- axosomatic

Question 6

explain neuroglia

Answer 6

• NOT electrically exitable (only provides support for neurons)
  
  • Make up hald the vol. Of nervous system
    Can multiple + divide
• 4 types- astrocytes, ependymal, oligodendrocytes, schwann cells

Question 7

explain astrocyte cells

Answer 7

§ Able to pick up oxygen + glucose + convert it into glycolytic metabolite called lactate
- Releases, neurons pick up, convert to pyruvate for oxidative phosphorylation, produces ATP

Question 8

explain ependymal cells

Answer 8

§ Found at base of ventricles
- Have cilia, exchange between blood stream + cerebral spinal fluid

Question 9

explain oligodendrocyte cells

Answer 9

§ Produce myelin sheath in central nervous system
- On multiple axons at a time

Question 10

explain schwann cells

Answer 10

§ Make myelin sheath in peripheral nervous system
- Single axon at a time

Question 11

explain the myelin sheath

Answer 11

○ Produced over time by schwann cells + oligodendrocytes
○ Surrounds axons of most neurons
○ Made of proteins + lipids
- Acts as insulator- provides protection, + allows signals to travel faster

Question 12

explain multiple sclerosis and symptoms of it

Answer 12

• Disease resulting from when myelin sheath doesnt form properly, or cant regenerate due to damage due to inflammation + scarring
  
  • Affects the signal propagation around the body
  • Genetic, autoimmune disorder
  • Symptoms
    ○ Losing ability to walk/move
    ○ Weakness
    ○ Loss of coordination
    ○ Tiredness
    ○ Eyesight
    - Memory

Question 13

compare continuous vs saltatory conduction

Answer 13

• Continous
  ○ NO myelin
  ○ Flows through, similar to walking
  ○ Slow
  • Saltatory
    ○ Has myelin
    ○ Signal jumps along, like skipping
    Fast + efficient

Question 14

what are synapses and 2 types of them

Answer 14

• Is a junction between cells
  
  • Important site for pharmaceutical drug interventions and toxins
  • 2 types
    ○ Chemical
    § 1 way
    § Transfer of info from presynaptic to postsynaptic
    ○ Electrical
    § Gap junctions connect cells
    § Synchronises the acitivty of a group of cells very fast
    § E.g. Heart
    - Does NOT require a particular chemical substrate to transfer from pre to post, instead has the gap junctions

Question 15

what are the steps of signal transmission

Answer 15

1. AP arrives at terminal end bulb
   
   2. Depolarising wave opens voltage gated Ca2+ channels
   3. Ca2+ entry causes exocytosis of synpatic vesicles full of neurotransmitters into synaptic cleft
   4. Diffusion to post synpatic neuron receptors (ligand gated ion channels)
   5. Ion channel opens + changes post synaptic gap
   6. Generates AP
2. Neurotransmitters rapidly removed by diffusion, enzymes, re-uptake from the synpatic cleft for recycling- important

Question 16

explain the neuromuscular junction

Answer 16

• Aims to cause contractions of a muscle cell
  - Uses acetylcholine

Question 17

explain myasthenia gravis and its symptoms

Answer 17

• Muscle weakness disease
  
  • Treated by not cured by Ach esterase inhibitors
  • Results from immune system producing antibodies that block/destroy receptors sites for acetylcholine (so muscle receives less nerve signals, resulting in weakness) so uses Ach esterase inhibitors to stop the enzyme that breaks down the Ach
  • Symptoms
    ○ Weakness
    - Difficulty breathing + swallowing

Question 18

explain post synaptic potentials

Answer 18

• Can be excitatory or inhibitory
  
  • Post synaptic neurons can recieve many signals at once
  • Excitatory
    ○ Depolarising potential
  • Inhibitory
    Hyperpolarising potential

Question 19

explain neurotransmitter receptors and 2 types

Answer 19

• Ionotropic- ligand gated ion channels
  
  • Metabotropic- not direct, GPCR

Same neurotransmitters can be exitatory OR inhibitory, at different synapses, depending on receptor it binds to

Question 20

what are examples of small neurotransmitters

Answer 20

○ Achetyl choline
○ Amines- adrenaline, dopamine
○ Amino acids- glutamate
ATP + purines

Question 21

what are examples of large neurotransmitters

Answer 21

○ Substance P
○ Endorphins
- Dynorphin

Question 22

explain summation

Answer 22

• If several presynaptic end bulbs release their neurotransmitters at same time, the combined effect may generate a nerve impulse due to summation
  
  • AP generated when sump of exitatory and inhibitory post synaptic potential = threshold at trigger zone
• Can be spatial (multiple released at same time) or temporal (released from one over time)