L16 Flashcards
what are factors that affect propagation speed
○ Axon diameter
○ Amount of myelination (countinuous vs saltatory)
- Temp.
- nerve fibre type
explain type A nerve fibre
§ Large, fast myelinated
E.g. Sensory + motor neurons
explain type B nerve fibre
§ Small, medium myelinated
§ Visceral sensory
Some autonomic NS
explain type C nerve fibre
§ Smallest, slow unmyelinated
§ Pain, temp. Sensory conduction
§ Some autonomic NS outputs
Heart, bladder
what are 3 places neurons can recieve signals from
○ Axoaxonic
○ Axodendritic
- axosomatic
explain neuroglia
- NOT electrically exitable (only provides support for neurons)
- Make up hald the vol. Of nervous system
Can multiple + divide
- Make up hald the vol. Of nervous system
- 4 types- astrocytes, ependymal, oligodendrocytes, schwann cells
explain astrocyte cells
§ 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
explain ependymal cells
§ Found at base of ventricles
- Have cilia, exchange between blood stream + cerebral spinal fluid
explain oligodendrocyte cells
§ Produce myelin sheath in central nervous system
- On multiple axons at a time
explain schwann cells
§ Make myelin sheath in peripheral nervous system
- Single axon at a time
explain the myelin sheath
○ 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
explain multiple sclerosis and symptoms of it
- 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
compare continuous vs saltatory conduction
- Continous
○ NO myelin
○ Flows through, similar to walking
○ Slow- Saltatory
○ Has myelin
○ Signal jumps along, like skipping
Fast + efficient
- Saltatory
what are synapses and 2 types of them
- 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
what are the steps of signal transmission
- AP arrives at terminal end bulb
- Depolarising wave opens voltage gated Ca2+ channels
- Ca2+ entry causes exocytosis of synpatic vesicles full of neurotransmitters into synaptic cleft
- Diffusion to post synpatic neuron receptors (ligand gated ion channels)
- Ion channel opens + changes post synaptic gap
- Generates AP
- Neurotransmitters rapidly removed by diffusion, enzymes, re-uptake from the synpatic cleft for recycling- important
explain the neuromuscular junction
- Aims to cause contractions of a muscle cell
- Uses acetylcholine
explain myasthenia gravis and its symptoms
- 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
explain post synaptic potentials
- Can be excitatory or inhibitory
- Post synaptic neurons can recieve many signals at once
- Excitatory
○ Depolarising potential - Inhibitory
Hyperpolarising potential
explain neurotransmitter receptors and 2 types
- 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
what are examples of small neurotransmitters
○ Achetyl choline
○ Amines- adrenaline, dopamine
○ Amino acids- glutamate
ATP + purines
what are examples of large neurotransmitters
○ Substance P
○ Endorphins
- Dynorphin
explain summation
- 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)
