Membranes and Action Potentials Flashcards
The human nervous system is built out of two types of cells:
Neurons and glia
A neuron is:
The functioning cellular unit of the nervous system specialised to receive, integrate and transmit information through electrical and chemical means.
A glia is:
a non-neuronal cell in the nervous system that maintains homeostasis, forms myelin and provides support and protection for neurons.
Four types of glial cells?
- Myelin sheath- oligodendrocytes (CNS), Schwan cells (PNS)
- Astrocytes- star-shaped cells part of the BBB
- Microglia- take part in the immune system
- Ependymal cells- production of CSF (cerebrospinal fluid) and neuroregeneration
Dendrites are
the short, branching fibres extending from the soma that receive incoming information
soma
cell body, contains nuceli, ribosomes etc
soma
cell body, contains nuclei, ribosomes etc
axon
singular fibre carrying info from soma to axon terminals
Morphological classification of neurons:
- Multipolar (most common)
- Bipolar
- Unipolar
Passive movement of substances across cell membrane:
osmosis and diffusion according to concentration gradient
Active movement of substances across cell membrane:
transporters and pumps move ions against their concentration gradient
The membrane potential is determined by the relative fluxes of __________ through specific ion channels in the cell membrane.
Na+, K+, Cl-
Excitation moves the resting membrane potential towards
0mV; depolarisation
Inhibition makes the resting membrane potential more
negative; hyperpolarisation
At rest, the concentration of K+ is higher or lower inside the cell? (compared to outside the cell)
Higher
At rest, the concentration of Na+ is higher or lower inside the cell? (compared to outside the cell)
Lower
The Na+/K+ pump maintains the electrical gradient. This means that it pumps out _____ and pumps in ______.
3Na+ ; 2K+
The action potential begins with a channel opening for Na+ in the membrane. What happens next?
Driven primarily by the concentration gradient but also by the electrical gradient, Na+ rushes into the cell causing depolarisation.
Na+ rushes into the cell causing depolarisation… and what does the membrane potential reach?
30mV !
Once the membrane potential reaches 30mV, the voltage-gated potassium channels open. What next?
K+ leaves the cell, causing repolarisation. It overshoots a little, but the potassium channels finally close during the hyperpolarisation period.
Absolute refractory period?
Another action potential will not start due to the inactivation gate of the voltage-gated Na+ channel.
Relative refractory period?
A new action potential can be started but only by a stronger stimulus than the one that initiated the current action potential.
An action potential is a
transient reversal of membrane potential due to influx of Na+ during the opening of voltage-gated Na+ channels.
