Chapter 34 Nervous System Flashcards
How fast do mammalian neurons transmit signals
20-100 metres per second
What does it mean that neurons are excitable?
They generate and transmit electrical signals called action potentials
In excitable cells, APs generated at one point propagate over the whole membrane
What is a synapse?
cell-to-cell contact point specialized for signal transmission
What are the 4 regions of a neuron?
Dendrite
Cell body
Axon
presynaptic axon terminal
What is a nerve?
Bundle of axons outiside the brain and spinal cord (In brain and spinal cord they are called tracts)
What are the functions of glial cells?
- Help orient neurons towards target cells during embryonic development
- Provide metabolic support for neurons
- Help regulate composition of extracellular fluids and perform immune functions
- Assist signal transmission across sinapses
What cells produce myelin and where
Oligodendrocytes - CNS
Schwann cells - PNS
Define current
flow of electrical charges from place to place; in cells it is based on the flow of ions (e.g. Na+)
What is voltage?
electrical potential difference
- Present if positive charges are concentrated in one place and negative charges concentrated in a different place
Produces currents because opposite charges attract and move towards each other
What is membrane potential?
voltage across a membrane
What is resting potential of a neuron
- 60 to -70 millivolts (mV)
- Negative sign means in side of cell is electrically negative compared to inside
How does ion redistribution occur?
through membrane channel proteins and ion transporters
e.g. sodium-potassium pump
Diffusion is controlled by concentration and electrical effect - when they are equal electrochemical equilibrium is reached
How does the sodium potassium pump work?
Moves:
3 Na outside of cell
2 K inside cell
What does the nernst equation calculate?
equilibrium potential of the ion
Electrochemical equilibrium
Most ion channels are gates. What are the types of gates?
Voltage gated - change in membrane potential
Stretch gated - tension applied to cell membrane
Ligand gated - when ligand binds to channel protein
What is depolarization?
When membrane becomes less negative inside
- Occurs when Na channels open, Na enters cell
What is hyperpolarization?
When charge inside becomes more negative
What types of membrane potential are there?
Graded - changes from resting potential that are less than the threshold of -50mV. Only spread a short distance and disperses
All or None - Depolarization to threshold of -50mV creates AP that does not get smaller and propagates along cell membrane
What does it mean for signals to be integrated and what is a key area for this to occur?
When graded hagnes are added together to make all or none chagnes
Key area is the axon hillock - where APs are most often generated and where axons leave the nerve body
What is an action potentail?
A rapid large change in membrane potential that reverses membrane polarity
What are the steps of an action potential forming?
1) membrane depolarizes from -65mV to + 40mV
2) MP reaches threshold and voltage gated Na channels open, Na enters cell -> more depolarization -> AP
3) Voltage gated Na channels close, Voltage gated K channels open slowly, K moves out
At what point does maximum depolarization occur?
when all Na channels are open
Why do APs only travel in one direction?
Because Na channels have a refractory period wher they cnnot depolarize (or open)
What causes APs to travel faster?
Myelin and larger diameter axons
