Neurons And The Action Potential Flashcards
What is neurons activity like?
Electrical and chemical
Describe briefly how neurons pass signals
Chemical signals received in dendrites from axons that contact them are transformed into electrical signals, which add to or subtract from electrical signals from all other synapses, thus making a decision about whether to pass on the signal somewhere else. Electrical potentials then travel down axons to synapses on the dendrites of the next neuron and the process repeats
What does a neuron consist of?
Dendrites, cell body, axons and synaptic terminals
Explain briefly what do each part of the neuron do?
Dendrite received, cell-body integrates, axons transmit through polarisation
How do neurons hold themselves together?
The outer membrane of neurons which are made of fatty substances are arranged around a cytoskeleton that is built up of rods of tubular and filamentous proteins that extend out into dendrites and axons
How to dendrites and axons change?
Dendrites change shapes, sprouting new connections and withdrawing others while axons grow new endings
How are neurons manufactured and transported along inside the neuron?
Proteins are mostly manufactured in the cell body and are transported along the cytoskeleton
What are tiny protuberances that stick out from dendrites called?
Dendritic spines
What happens at dendritic spines?
It is where incoming axons make most of their connections
What do end-points of axons respond to?
Molecules called growth factors
What do growth factors do?
Growth factors are taken inside the neuron and transported to cell body where they influence the expression of neuronal genes and hence the manufacture of new proteins, these enable neuron to grow longer dendrites or make other dynamic changes to its shape or function
What are synapses?
Small gap where dendrites have close contacts with incoming axons of other cells
Where are most of the synapse on cells in the cerebral cortex located at?
Dendritic spines
What are communication between nerve cells at contact points called?
Synaptic transmission
How do synaptic transmission work?
When dendrite receives one of the chemical messengers that has been fired across the gap separating it from sending axon, miniature electrical currents are set up inside the receiving dendritic spines. All these positive and negative waves of current are accumulated in the dendrites and spread down the cell body. If they don’t add up to much activity, currents soon die and nothing happens. If currents add up to a value that crosses a threshold, the neuron will send a message on to other neurons
What is excitation?
Currents that come into the cell
What is inhibition?
Currents that move out of the cell
How do neuronal signals travel along the axon?
Axons of neurons transmit electrical pulses called action potentials and travel along nerve fibres. Axonal membrane contains ion channels that open and close to let through electrically charged ions. Some channels let through sodium ions (Na+) while others let through potassium ions (K+). When channels open, the Na+ or K+ ions flow down opposing chemical and electrical gradients, in and out of the cell in response to electrical depolarisation of the membrane
What happens when an action potential starts at the cell body?
The Na+ channel opens, and Na+ ions moves into a cell, quickly, the transmembrane voltage switches by about 100mV; it flips from inside membrane voltage that is -70mV to one that is positive +30mV. This switch opens K+ channels, triggering a pulse of K+ to flow out of the cell which causes the membrane potential to swing back to its original negative value on the inside
How are concentration of ions kept in balance?
Concentrations of Na+ and K+ within the cytoplasm do not change significantly during an action potential, however in the long run, they are kept in balance by ion pumps which remove excess Na+ ions
How do action potential spread?
Nerve fibres behave like electrical conductors and action potential generated at one point creates another gradient of voltage between the active and resting membranes adjacent to it, the action potential is actively propelled in a wave of depolarisation that spreads from one end of nerve fibre to the other
What is a feature of nerve fibre?
After a very brief period of silence, the refractory period, the spent membrane recovers its explosive capability, readying the axon membrane for the next action potential
How are electrical voltage measured in neurons in the past?
Placing tiny electrodes inside very large neurons and axons in certain sea creatures to measure changing electrical voltage
What is a modern electrical recording technique that enable the study of movement of ions through individual ion-channels through all sorts of neurons?
Patch-clamping
What is myelin sheath?
A fatty, insulating blanket made out of stretched out glial cell membrane wrapping around axons
How does myelin sheath allow fast electrical impulse?
Usually myelin stealth covers the axons but there are some gaps where the axons is not covered, called the Nodes of Ranvier, where axon concentrates its Na+ and K+ ion channels, these clusters of ion channels function as amplifiers that boost and maintain action potential as it skips along the nerves
How fast can myelinated neurons action potential travel?
100m/s
What is the distinctive characteristic of action potentials?
They differ on in how often they occur
How are the strength or duration of a stimulus encoded?
By variation of frequency of action potentials
What is the frequency of action potential of most efficient axons?
Up to 1000 times/s