Axonal Transmission Flashcards
Describe the basic components of a neuron
-Cell body = contains Nucleus, ribosomes, cytoplasm, mitochondria
-Dendrites
-Axon
-Presynaptic terminals
(aprox 10^9 neurons in the brain)
Name 3 types of neuron
- Interneuron
- Motor neuron
- Sensory neuron
What is axonal transmission?
Transmission of info from location A to location B
What is synaptic transmission?
Integration/Processing of infomation
What occurs in multiple sclerosis?
Axonal transmission failure due to auto immune disease causing myelination degeneration
Name some symptoms of MS? Why are they so varied?
- Eye movements, uncontrolled, double vision
- Speech, slurred
- Paralysis, partial/complete
- Temor
- Lack of concentration
- Weakness, tired
- Sensory, numbness, prickling pain
Different axons are attacked (by autoimmune, trigger by virus?) this causes varied symptoms
Why is MS hard to diagnose? Who does it usually affect?
- Early symptoms are slight
- Other disease have similar symptoms
- No current lab test
- MS usually affects people aged 20-40
- Affects more women than men
- Often temperate zones
- Areas of high sanitation
Describe neronal action potential
- Final resting potential is -70mv, Na+/K+ pump means than 3 Na+ are pumped out for 2 K+ pumped in
- K+ and Cl- can move in and out according to diffusion and electrostatic pressures
- Na+ channels open, causing Na+ influx = depolarisation to +30mv
- K+ channels open causing K+ outflux = repolarisation
- Na+ channels begin to close (return to normal, some sodium leaks in at resting potential)
- K+ channels begin to close (return to normal)
What is relative refractory period?
A period of time shortly after action potential when greater than normal stimulation can cause a second action potential to occur
What is absolute refractory period?
A period of time straight after action potential when a second action potential cannot occur
How does myelination affect speed of transmission? What is this conduction called?
Saltatory conduction
myelination = speed
Describe the mechanism of saltatory conduction?
Action potential jumps along unmyelinated nodes of Ranvier
How do excitatory neurotransmitters affect the resting potential?
- Neurotransmitters activate receptors on dendrites
- Opens ion channeles
- Causes depolarisation
- Increases chance of action potential (chance of reaching threshold of excitation)
- This action potential is called an EXCITATORY POST SYNAPTIC POTENTIAL
How do inhibitory neurotransmitters affect the resting potential?
- Neurotransmitters activate receptors on dendrites
- Opens ion channeles
- Causes hyperpolarisation
- decreases chance of action potential (chance of reaching threshold)
- This is called an INHIBITORY POST SYNAPTIC POTENTIAL
What is temporal summation?
When there is a high frequency of action potentials and so they overlap and summate with each other
What is spatial summation?
When there is input from multiple presynaptic cells
Which of the cranial nerves have parasymp innervation?
CNX, IX, VII, III (1973)
What are some signs of ANS (autonomic system) dysfunction?
- Postural hypotension -baroreceptor pathway (also called Orthostatic hypotension -the tendency for blood pressure to decrease on standing due to gravity.)
- Tachycardia/bradycardia (rapid HR/slow HR)
- Impotence
- Bladder/bowel dysfunction
- Anhydrosis (failure of sweat glands)
What is the difference between unipolar, bipolar and multipolar cells
The number of neutrites, they all have one long axon
unipolar - has one dendrite
bipolar - has two
multipolar - multiple
Name the 3 main groups of neurotransmitters
- Amino acids (glutamate, aspartate, GABA, glycine)
- Amines (acetylcholine, dopamine, noradrenaline, adrenaline, serotonin (5-HT))
- Peptides (endorphins, enkephalins, substance P)
(nitric oxide)
What neurotransmitter is used at all skeletal neuromuscular junctions?
Acetylcholine
What neurotransmitter is used at autonomic junctions?
a. Symp
b. Parasymp
Symp = noradrenaline and adrenaline Parasym = acetylcholine
What is the main excitatory neurotransmitter in the CNS?
Glutamate
What is the main inhibitory neurotransmitter in the CNS?
GABA, glycine
What are the main modulatory neurotransmitters in the CNS?
5-HT
dopamine etc
these work in a slower manner and modulate fast transmission
Name types of glia cells, what are their functions?
Glia cells are supporting cells, they have a protective and structural role
- Astrocytes
- Oligodendrocytes
- Ependymal cells
- Microglia
- NG2+ glia
Describe astrocytes
Multipolar cells
Help control neuronal environment, influencing local neurotransmitter and electrolyte concentrations
Regulate blood-brain barrier by foot processes closely applied around capillaries
Radial glia crucial in guiding developing neurons
Eg: Bergmann glia – cerebellum
Muller cells – retina
(star like)
Describe oligodendrocytes
Most numerous cell in CNS
Produce myelin sheaths that insulate CNS axons
In white matter (and also in grey matter)
Demyelinating disease – eg. Multiple sclerosis
(fried egg appearance)
Describe ependymal cells
Lines most of the ventricular system and the central canal (in spinal cord)
Have cilia, microvilli and desmosomes
Provide barrier between CSF and brain
Secretion, absorption, transport and receptor function - speculative
Describe microglia
Resident macrophages of CNS
Seen in meninges, brain parenchyma and vasculature
Contribute to CNS homeostasis and outcome of brain injury and disease
Describe the action of neurotransmitter release
- Ca2+ channels open when action potential reaches pre-synaptic terminal
- Ca2+ ions causes vesicles to move to release sites - they fuse with cell membranes and discharge contents
- Transmitter substance diffuses across the synaptic cleft
- It attaches to receptor sites on post synaptic membrane
Name the 5 fundamental processes of synaptic transmission
- Manufacture - intracellular biochemical processes
- Storage - vesicles
- Release - via action potentials
- Diffusion across membrane and receptor activation
- Inactivation - reuptake or breakdown
Name the 5 fundamental processes of synaptic transmission in the context of Ach
- Manufacture - in neuron
- Storage - in vesicles in the neuron
- Release - via vesicles
- Diffusion and receptor activation - diffuses to Ach receptor
- Reuptake or breakdown - broken down into Ch and A and taken back into the neuron
Name 3 fast neurotransmitters (released quickly, have short term affects)
- Ach
- GLU
- GABA
Name 3 neuromodulators (slow affect, last a long time)
- Serotonin 5-HT
- Dopamine DA
- Noradrenaline
What are endorphins?
Peptides with opiate-like effects
-endorphins and opiates inhibit substance P (which is released by pain receptors)
runners high = endorphins released due to pain
How do local anaesthetics work? - Procaine and lignocaine
-Blocks Na+ channels
-Well absorbed through mucous membranes
-Blocks progression of action potential
used alot in medicine and dentristry
What affects ACh?
- Cigerettes (nitotine agonist = mimics the action of Ach at receptors)
- Posion arrows (curare is an antagonist = binds to receptor but does not activate it )
Name some effects of autonomic flight/fight response?
Can stimulate and inhibit
- Pupils dilate
- Mouth dries
- Muscle tense
- Chest pain
- Sweating
- Adrenaline release
- Increase BP and HR
- liver releases glucose so more energy is available
- digestion slows
- sphincters close and then relax
- cortisol is release (this depresses the immune system)
What nerves are in the parasympathetic system?
- Cranial outflow - CNX, CNIX, CNVII, CNIII (1973) = head, neck, thorax and abdomen
Oculomotor, facial nerve, glossopharyngeal, vagus - Sacral outflow 2S, S3, S4 = abdominal and pelvic organs
What nerves are in the sympathetic system?
- Sympathetic chain
T1-L2 = supplies visceral organs and structures of superficial body regions - Adrenal gland
chromaffin cells - release norepinephrine and epinephrine into blood (fight/flight response, increases HR and BP etc)
