2 functions of neurons/nerve cells
1. building blocks of the nervous system 2. instruments of communication
monitor environment and internal events
process and store information
responses to sensory input or commands
human brain composed of
100 billion neurons
Inputs from other neurons (______ inputs) are received at the ________. The signal spreads _______ to the _____ _____. The ____ conducts ______ ______ away from the _____ (cell body), to the tips of the axon, where their synaptic ______ also called axon _______ communicate with other neurons.
Inputs from other neurons (_sensory_ inputs) are received at the _dendrites_. The signal spreads _passively_ to the _trigger_ _zone_. The _axon_ conducts _action_ _potentials_ away from the _soma_ (cell body), to the tips of the axon, where their synaptic _boutons_ also called axon _terminals_ communicate with other neurons.
2 types of signals used in communication and where they are used
electrical signals (dendrites, cell body, axon) + chemical signals (synapses)
is the resting potential of most cells in the body positive or negative
excitable tissue =
suddenly respond to stimuli with a transient change in the resting potential (i.e action potential)
excitable tissues include
muscle fibres, neurons, some endocrine cells
2 methods for measuring intracellular potentials
- patch clamp technique - microelectrode
resting membrane potential (RMP)
electrical potential difference of 50-70mV across the membrane which results from the seperation of charge.
more positive inside the cell than out. TRUE/FALSE
FALSE. By definition outside the cell is zero. Because the potential inside the cell is less, it is considered negative.
electrons and ions are responsible for the potential difference across the membrane. Yeah or no.
NO! electrons are not. ONLY ions are responsible for the difference in charge.
potential outside the cell is defined as being equal to _, meaning that the absolute intracellular potential is usually ________.
potential outside the cell is defined as being equal to _0_, meaning that the absolute intracellular potential is usually _NEGATIVE_. ~-65mV
3 things RMP is due too
1. unequal Na+/K+ concentrations inside/outside the cell 2. unequal permeability of the cell membrane to Na+/K+ [3. electrogenic action of NaKATPase] - very small contribution
[K+] outside vs. inside cell
HIGHER INSIDE - inside = 100mM - outside = 5mM
[Na+] outside vs. inside cell
HIGHER OUTSIDE - inside = 15mM - outside = 150mM
[Cl-] outside vs. inside cell
HIGHER OUTSIDE - inside = 13mM - outside = 150mM
[Ca2+] outside vs. inside cell
WAY HIGHER OUTSIDE - inside = 0.0002mM - outside = 2mM
does calcium affect the RMP?
no it doesn't because the membrane is not permeable to them at rest
does chlorine affect the RMP?
no because Cl- is distributed passively - there are no active Cl- pumps in neurons. This is why it has the same equilibrium potential as RMP (-65mV)
What affect to the numerous, negatively charged proteins in the cytosol have?
they DO NOT AFFECT RMP because the membrane is totally impermeable to them
how are Na+/K+ concentration gradients maintained?
by the Na+/K+ pumps. 3Na+ out, 2K+ in
2 ion channels present in neurons (open/ closed at rest?)
1. non-gated "LEAK" channels - OPEN at rest 2. gated channels (VOLTAGE, LIGAND, MECHANICALLY) - usually CLOSED at rest
number of K+ leak channels vs. number of Na+ leak channels at rest. PK+/PNa = ?
PK+/PNa+ = 40/1
nervous system =
cns + pns
net flow of ions is zero, in spite of concentration gradient and permeability. Electrical gradient and concentration gradient are opposing each other. e.g. as each K+ moves out, a negative charge replaces it
calculate the equilibrium potential for each ion Eion = 61.5mV (at 37 degrees c) x log [ion]o / [ion]i
what are the equilibrium potentials for 1. K+ 2. Na+ 3. Cl- 4. Ca2+
1. K+ = -80mV 2. Na+ = +60mV 3. Cl- = -65mV 4. Ca2+ = +120mV
interpretate the value of Eion of 120mV for Ca2+
you would require an opposing potential of 120mV inside the cell, to prevent entry of Ca2+, if the membrane was fully permeable to it.
what are Cl- and Ca2+ important in
fault in Nernst equation
only applies to a situation where the membrane is permeable to only one type of ion (leak channels for just one ion)
leak channels only for K+. therefore, RMP = -80mV
the higher the permeability of a membrane to a particular ion, the...?
the greater the ability for this ion to shift the RMP towards its equilibrium position. e.g. small permeability to Na+ is why RMP is much closer to the E of K+.
a way of calculating the RMP by taking into account both the concentration gradients and permeability ratio between Na+/K+
what's this and where would you find it?
multipolar neuron - motor neurons - carry signal from the CNS out to an effector
What's this and where would you find it?
unipolar neuron - sensory neuron (e.g. in the PNS)