Neurons And The Action Potential

Question 1

What is neurons activity like?

Answer 1

Electrical and chemical

Question 2

Describe briefly how neurons pass signals

Answer 2

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

Question 3

What does a neuron consist of?

Answer 3

Dendrites, cell body, axons and synaptic terminals

Question 4

Explain briefly what do each part of the neuron do?

Answer 4

Dendrite received, cell-body integrates, axons transmit through polarisation

Question 5

How do neurons hold themselves together?

Answer 5

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

Question 6

How to dendrites and axons change?

Answer 6

Dendrites change shapes, sprouting new connections and withdrawing others while axons grow new endings

Question 7

How are neurons manufactured and transported along inside the neuron?

Answer 7

Proteins are mostly manufactured in the cell body and are transported along the cytoskeleton

Question 8

What are tiny protuberances that stick out from dendrites called?

Answer 8

Dendritic spines

Question 9

What happens at dendritic spines?

Answer 9

It is where incoming axons make most of their connections

Question 10

What do end-points of axons respond to?

Answer 10

Molecules called growth factors

Question 11

What do growth factors do?

Answer 11

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

Question 12

What are synapses?

Answer 12

Small gap where dendrites have close contacts with incoming axons of other cells

Question 13

Where are most of the synapse on cells in the cerebral cortex located at?

Answer 13

Dendritic spines

Question 14

What are communication between nerve cells at contact points called?

Answer 14

Synaptic transmission

Question 15

How do synaptic transmission work?

Answer 15

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

Question 16

What is excitation?

Answer 16

Currents that come into the cell

Question 17

What is inhibition?

Answer 17

Currents that move out of the cell

Question 18

How do neuronal signals travel along the axon?

Answer 18

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

Question 19

What happens when an action potential starts at the cell body?

Answer 19

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

Question 20

How are concentration of ions kept in balance?

Answer 20

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

Question 21

How do action potential spread?

Answer 21

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

Question 22

What is a feature of nerve fibre?

Answer 22

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

Question 23

How are electrical voltage measured in neurons in the past?

Answer 23

Placing tiny electrodes inside very large neurons and axons in certain sea creatures to measure changing electrical voltage

Question 24

What is a modern electrical recording technique that enable the study of movement of ions through individual ion-channels through all sorts of neurons?

Answer 24

Patch-clamping

Question 25

What is myelin sheath?

Answer 25

A fatty, insulating blanket made out of stretched out glial cell membrane wrapping around axons

Question 26

How does myelin sheath allow fast electrical impulse?

Answer 26

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

Question 27

How fast can myelinated neurons action potential travel?

Answer 27

100m/s

Question 28

What is the distinctive characteristic of action potentials?

Answer 28

They differ on in how often they occur

Question 29

How are the strength or duration of a stimulus encoded?

Answer 29

By variation of frequency of action potentials

Question 30

What is the frequency of action potential of most efficient axons?

Answer 30

Up to 1000 times/s