Physiology Flashcards
What are the three types of neurons? Where are they most often found (CNS vs PNS)?
Bipolar (PNS)
Multipolar (CNS)
Pseudounipolar (PNS)
What are glial cells?
Non-neuronal cells that maintan homeostasis, form myelin, and provide structural and metabolic support for neurons in the developing and mature nervous system
What do astrocytes do?
they are cells in the CNS that:
- Provide scaffolds for growing axons and migrating neurons during development
- have numerous projections that anchor neurons to their blood supply
- maintain appropriate extracellular ion concentration
- contribute to the formation of the BBB
What do microglia do?
They are specialized cells in the CNS that:
- are capable of phagocytosis
- protect neurons in CNS
What do ependymal cells do?
Line fluid-filled cavities (ventricles) of the brain and spinal cord
- These cells create and secrete CSF and beat their cilia to help circulate CSF
What do oligodendrocytes do?
- Coat axons in the CNS with their cell membrane, forming a specialized membrane differentiation called myelin ==> produces the myelin sheath
What is myelin sheath?
Insulation to the axon that allows electrical signals to propagate more efficienty
What are Schwann cells?
Myelin producing cells of the PNS
- they also play a rone in nerve regeneration following injury
What do satellite cells do?
surround and support nerve cell podies in peripheral ganglia (in PNS)
What is unique about neurons in the CNS vs PNS?
- *CNS:**
- many presynaptic inputs to the postsynptic cell are required to activate a neuron
- Excitatory and inhibitory inputs
- various neurotransmitters (NT)
- Many APs firing sychronously to attain an AP in the target neuron
- *PNS:**
- 1 prensynaptic input to 1 postsynaptic cell
- Excitatory inputs ONLY
- One NT
- 1 AP in a motor neuron fires to attain an AP in target cell
How are CNS synapses mediated?
chemically
Where can neuron-neuron intereaction occur in CNS cells?
- Axon-dendrite interaction
- Axon-soma
- Axon-axon
- Dendrite-dendrite (rare)
- Soma-soma (rare)
What are factors influencing the size of the graded AP in the CNS?
- Amount of neurotransmitter released into synaptic cleft
- Density of receptors on postsynaptic membrane
How does integration of synaptic inputs occur in CNS neurons?
- Graded postsynaptic potentials (both IPSP and EPSP) spread passively through the cell and decay over time and space
- As the PSPs reach the axon hillock, the potentials are integrated and decision is made to trigger (or not trigger) an AP
- PSPs are integrated by summation
What is temporal summation?
Conseutive EPSPs at the same site sum to depolarized the membrane toward the AP threshold
What is spatial summation?
Simultaneous EPSPs at different synapses on the same neuron sum to depolarize the membrane toward the AP threshold
What is it meant by divergence of local synaptic connections?
One neuron is able to influence many postsynaptic neurons
- information is spread out to many cells
What is it meant by convergence of local synaptic connections?
Many presynaptic neurons converge and influence a single postsynaptic neuron
- Increases influence and possibiltiy of postsynaptic cell’s abilty to fire
(increase spatial summation)
What is an Axoaxonic Synapse Type 1?
When the presynaptic neuron influences the voltage at the axon hillock and alters the likelihood of generating an AP on the postsynaptic neuron
What is an Axoaxonic Synapse Type 2?
When the presynaptic neuron influences the voltage at the postsynaptic neuron at the axon terminal and alters the amount of Ca2+ present in the axon terminal of the postsynaptic cell
- This results in altered amount of NT released by the postsynaptic cell (onto its postsynaptic cell)
How can an Axoaxonic Synapse Type 2 lead to presynaptic facilitation?
The “facilitating” neuron’s axon terminal activity results in increased Ca2+ in the axon terminal of the other neuron –> Increased NT release –> Increased EPSP or IPSP size in the final postsynaptic cell
How can Axoaxonic Synapse Type 2 result in presynaptic Inhibition?
The “inhibiting” neuron’s axon terminal activity results in decreased Ca2+ in the axon terminal of the other neuron –> Decreased NT release –> Decreased EPSP or IPSP size in the final postsynaptic cell
What is a feedforward excitation?
A –> B –> C
Neuron A Excites Neuron B –> Neuron B excites Neuron C