The Nervous System Flashcards
Describe the anatomy of a neuron.
- Soma, or cell body, containing nucleus, ribosomes, ER
- Dendrites from soma that receive incoming signals
- Axon: long appendage that stretches to target tissue; many are covered in myelin for insulation, prevention of signal loss, and speedy conduction
- Axon hillock: leaves cell body, integrates signals
- Axon terminals: knobs that maximize signal transmission
What are clusters of cell bodies called in the PNS and CNS? What are clusters of axons called in the PNS and CNS?
- Cell bodies - called ganglia in PNS, nuclei in CNS
2. Axons - called nerve in PNS, tracts in CNS
What are the 5 neuroglial cells, and what are their functions?
- Astrocytes: nourish neurons, form blood-brain barrier (controls transmission of solutes)
- Ependymal cells: line brain ventricles and produce CSF (shock absorber)
- Microglia: phagocytes that eat waste and pathogens in the CNS
- Oligodendrocytes (CNS) and Schwann cells (PNS): produce myelin around axons
What is the cell’s resting potential? How is it maintained?
Resting potential = -70mV (inside of neuron is negative relative to outside)
- There is more K in the cell than outside, so potassium leak channels allow it to spill out, establishing a K equilibrium potential of -90mV.
- There is more Na outside than in, so sodium leak channels allow it to come in, establishing an Na equilibrium potential of 60mV.
- Na+/K+ ATPase continuously pumps Na and K back to where they started (out and in) to maintain their gradients
- The cell is slightly more soluble to K, so resting potential is closer to K’s.
What is the threshold for an action potential?
-55 mV
What are the two types of summation?
- Temporal: multiple signals integrated during a short period of time (by 1 neuron)
- Spatial: integration of multiple signals close to each other in space (by multiple neurons)
What occurs during depolarization? Describe inactivation/deinactivation.
Cell interior becomes less negative (about +35mV)
- Voltage-gated Na channels open, so Na moves in
- When the cell reaches +35mV, the Na channels are inactivated. They will have to reach resting potential again to be deinactivated.
When are Na channels closed, open, and inactive?
- Closed: before cell reaches threshold, and after inactivation has been reversed.
- Open: from threshold to about +35mV
- Inactive: from +35mV to threshold
What occurs during repolarization and hyperpolarization?
- Voltage-gated K channels open and cause K+ to exit the cell - inside cell becomes negative again
- Overshoots the resting potential - hyperpolarization - extra negative
- Leads to refractory period, when the neuron can’t have another action potential
What are the two types of refractory periods?
- Absolute refractory period: no amount of stimulation can cause another AP to occur
- Relative refractory period: there must be greater than normal stimulation to cause an AP (because cell membrane is starting from a more negative potential than resting)
How are impulses propagated?
As Na rushes into one segment of the axon, it will cause depolarization in the surrounding regions
- original region will become refractory
- wavelike all the way down to the terminal
- info can therefore only flow one way
Which 3 factors increase the speed of AP propagation?
- Shorter axon
- Greater diameter
- Myelin - membrane is only permeable to ion movement at the nodes of Ranvier (exposed axon), so the signal hops from node to node - saltatory conduction
How do action potentials express stimulus intensity?
By frequency of firing, not greater potential differences
What is an effector?
The muscle or gland a neuron signals to, rather than another neuron
What is the process of neurotransmitter release?
- AP reaches axon terminal
- Voltage-gated Ca2+ channels open, causing Ca2+ to flood in
- This causes fusion of the vesicles holding NT with the cell membrane
- The NT diffuse across the cleft and bind to receptors on the postsynaptic membrane
- NT can be excitatory or inhibitory
