Lecture 26 Flashcards
Nervous system =
CNS + PNS
Dendrites are:
a short branched extension of a nerve cell, along which impulses received from other cells at synapses are transmitted to the cell body. There can be multiple dendrites but only one axon.
Axon is:
the long thread-like part of a nerve cell along which impulses are conducted from the cell body to other cells.
Soma is:
Cell body
Synaptic inputs are:
Input from other neurons recieved on the dendritic tree and the soma.
Action potentials are:
Axon conducted messages away from the soma to the axon terminals (synaptic boutons)
Electric signals:
Dendrites, cell body, axon
Chemical signals:
synapses
Resting Membrane Potential of the cytoplasm compared to the extracellular space:
50 to 70 mV lower (i.e. more negative)
RMP is:
the electrical potential difference across the cell membrane which results from seperation of charge. There is more negative charges inside the cell than outside.
The potential outside the cell is defined as:
zero.
The RMP is a result of: (x3)
- Unequal concnetrations of Na+ and K+ inside and outside of the cell.
- Unequal permeability of the cell membrane to these ions.
- Electrogenic action of the Na-K pump - only a small contribution.
How are concentration gradients for K+ and Na+ maintained?
-By the Na/K pump
How is unequal permability of the cell membrane to diff ions explained?
- By the two types of ion channeks in neurons:
1. Non-gated leak channels (open at rest)
2. Gated channels (closed at rest) - In cell membrane of neurons, there are many leak K+ channels, but very few leak Na+ channels. At rest: Pk+/PNa+ = 40/1
In cell membrane of neurons, there are many leak ___ channels, but very few leak __ channels
many K+, few Na+
How does unequal concnetration and unequal cell membrane permeability to Na+ and K+ result in a negative RMP?
-At intracellular potential at which the net flow of ions is zero, in spite of a conc gradient and permeability
Nernst equation:
Eion = 61.5 mV x log [ion]o / [ion]i
-Only applies to a situation when a cell membrane is permeable to only one ion. eg. Glia cells
Rule: The higher the permeability of the cell membrane to a particular ion, ___
the greater the ability of this ion to shift the RMP towards its equilibrium potential
At rest, in neuron the permeability is much higher to ___
K+ than Na+. Thus the RMP is closer to the eq potential for K+ than Na+
