Lec 5: Membrane Potential Flashcards
- Functional Units of Nervous System
- receive, process and transmit information to other cells
Neurons
Three main parts of neuron
- Soma
- dendrites
- Axon
metabolic maintenance
Soma
receptive surface that brings signals from other neurons toward the cell body
Dendrites
- conduct signals away from the cell
- carry information for long distances with high fidelity and without loss
Axons (nerve fibers)
Types of neurons
- sensory or afferent neuron
- motor or efferent neuron
- interneuron
carry signals from sensory receptors
sensory or afferent neuron
transmit signals from the CNS to muscles or glands, leading to an action or response
Motor or efferent neuron
act as connectors or intermediaries between sensory and motor neurons.
Interneurons
Transmission of signals in a single neuron
- surface membrane innervated
- action potential initiation
- AP carried from spike-initation zone to axon terminal
integrates input to initiate an action potential
Soma
surface membrane of motor-neuron dendrites & soma are ____
Innervated
Where is the spike-initiating zone of a motor neuron located
near axon hillock to the axon terminal
Potential target of AP when it reach axon terminal
Skeletal muscle cell or glands
- Localized electrical gradient
- electrical potential differences across the cell membrane caused by different concentration of K+, Na+ and Cl- ions
Membrane potential
Membrane potential of neurons is usally between ___ and ___ mV
-60 to -80 mV
Excitable cells use changes in membrane potential as
communication signals
location of excess of negative charges
Plasma membrane side
location of excess positive charges
on the other side
Every cell has what?
- Voltage or membrane potential across its plasma membrane
is a localized electrical gradient across membrane
Membrane potential
are more concentrated within a cell
Anions (negative)
are more concentrated in the extracellular fluid
Cations (positive)
Factors affecting membrane potential
- Concentration gradient for an ion
- Membrane that is permable to that ion
measures membrane potential
Voltmeter
Resting pontential of an unstimulated cell
-70 mV
equal numbers of anion and cations
Electroneutral
Channel that potassium ions move out of the cell along concentration gradient
Potassium channel
Results when potassium moves out
- Electronegativity
draw positive charges into the cell
Excess negative charge inside
How a cell maintain a membrane potential
- Cations
- Anions
the principal intracellular cation
K+
is the principal extracellular cation
Na+
is principal extracellular anion
Cl–
principal intracellular anions
- Proteins
- Amino acids
- Sulfate
- Phosphate
Cations
- K+
- Na+
Anions
- Proteins
- Amino acids
- Sulfate
- Phosphate
- Cl-
at resting potential, concentration of ___ is greater inside the cell, while ___ is greater outside the cell
K+ greater inside the cell, Na+ is greater outside the cell
use the energy of ATP to maintain these K+ and Na+ gradients across the plasma membrane
Sodium-potassium pumps
converts chemical potential to electrical potential
opening of ion channels
a neuron at resting potential
- many open K+ channels
- fewer open Na+ channels
- K+ diffuses out of the cell
allow ions to diffuse across the plasma membrane
- always open
Non-gated ion channels
can generate large changes in their
membrane potential
Excitable cells
open or close in response to stimuli
Gated ion channels
Types of gated ion channels
- Chemically-gated ion channels (ligand-gated ion channels)
- voltage-gated channels
open or close in response to a chemical stimulus
Chemically-gated ion channels (ligand-gated ion channels)
open or close in response to a change in membrane potential
voltage-gated ion channels
are changes in membrane potential
Graded potentials
Types of graded potentials
- Hyperpolarization
- Depolarization
- Gated K+ channels open
- K+diffuses OUT of the
cell - the membrane
potential becomes
more negative
Hyperpolarization
Gated Na+ channels open
- Na+diffuses INTO the cell
- the membrane potential becomes less
negative
Depolarization
All or Nothing
Depolarization
The Action Potential
What happens when graded potentials sum to approximately -55 mV?
Threshold potential is achieved
What happens when threshold potential is reaches?
Action potential is triggered
In resting state, what happens to K+ channels
- Closed voltage-gated K+ channels open slowly, in response to depolarization
Two gates of Voltage-gated Na+ channels
- Closed activation
- Open inactivation
open rapidly in response to depolarization
Closed activation gates
close slowly in response to depolarization
Open inactivation
Phases of action potential
- Depolarization
- Overshoot
- Repolarization
a result of a temporary
inactivation of the Na+ channels.
Refractory period
What happens to action potential after the refractory period
Cannot be initiated
a state of recovery that occurs after a neuron has fired an action potential
Refractory period
Where does nerve impulses propagate?
Along the axon
the rapid method by which nerve impulses move down a myelinated axon
Saltatory conduction
Site of excitation
Nodes of Ranvier
Classes of Synapses
- Electrical synapses
- Chemical synapses
action potential travels directly from the presynaptic to the postsynaptic cells via gap junctions
Electricl synapses
more common than electrical synapses
- chemical synapses
is a region where
neurons nearly touch and where nerve impulse is transferred
Synapse
is the small gap between neurons
Synaptic cleft
Carried out transmission across synapse
Neurotransmitters
Primary factors influencing impulse transmission
- Axon diameter
- Myelination
- Temperature
Typical diamter of axon
around 1 micrometer
formation of the myelin sheath around a nerve
Myelination
the lower the temperature, the
____ the impulses move.
slower
varies as a function of axon diameter and myelination
Velocity of impulse propagation
how fast the membrane
ahead of the active region is brought to threshold by the local-circuit current
Conduction velocity of AP
Evolutionary adaption to increase length constant
Invertibrates - increase axonal diameter
Vertebrates - myelination
