Neuron Function

1
Neuron Function

• By Jasmine Fukuda, Stevie Haut,
• Danica Ozaki, Shane Mclin

2
The Membrane Potential

• A characteristic feature of a living cell is a
  polarized cell membrane.
• An undisturbed cell has a cell membrane that is
  polarized because it separates an excess of
  positive charges where negative charges in the
  inside.
• Since the charges are separated by cell membrane
  this potential difference is called a membrane
  potential.
• The measurement of potential difference is the
  volt V.
• Potential difference is the act of positive and
  negative charges held apart.
• The membrane potential of a undisturbed cell is
  known as resting potential.

3
Factors of Membrane Potential

• Intercellular and extracellular fluid differ in
  ionic composition.
• Differences between intercellular and
  extracellular are proteins that are too large to
  cross in the cytoplasm.
• Also ions can enter and leave a cell only with
  the aid of membrane channel or carrier proteins.
• Some channels are always open ( leak channels)
  whereas others open and close under specific
  circumstances ( gated channels).
• Passive and active processes act across the cell
  membrane to determine the membrane potential.
• The passives forces are chemical and electrical.

4
Changes in Membrane Potential

• Any stimulus that alters membrane permeability to
  sodium or potassium or alters the activity of
  the exchange pump disturbs the resting potential
  of a cell.
• Any change in the resting potential can have an
  immediate effect on the cell.
• A stimulus opens gated ion channels that are
  closed when the cell membrane is at its resting
  potential.
• Depolarization is the shift in a direction.
• As a number of positively charged ions on the
  inner surface of a cell membrane increases.
• Membrane potential shifts toward 0 mV.

5
Generation of an action potential

• An action potential begins with the cell membrane
  at the axon hillock depolarizes to threshold.
• There are four steps to an Action potential.
• Step 1 is Depolarization to threshold.
• Step 2 is Activation of voltage regulated sodium
  channels and rapid depolarization.
• Step 3 is Inactivation of sodium channels and
  activation of voltage regulated potassium
  channels.
• Step 4 is The return to normal permeability and
  resting state.

6
Neural Communication

• In the nervous system, info. Moved from one
  location to another in the form of action
  potentials along axons.
• The electrical events are known as nerve
  impulses.
• When one neuron communicates with another, the
  synapse may occur on a dendrite.
• Synapse between a neuron an another cell type is
  called neuroeffector junctions.
• A neuron communicates with a muscle cell at a
  neuroncellular.
• At a neuroglandular junction, a neuron controls
  pr regulates the activity of a secretory cell.

7
Structure of a Synapse

• Communication between neurons and other cells
  occurs in only one direction across a synapse.
• At a synapse between two neurons, the impulse
  pass through from the synaptic knob of the
  presynaptic neuron to the postsynaptic neuron.
• The opposing cell membranes are seperated by a
  narrow space called the synaptic cleft.
• Each synaptic terminal contains mitochondria,
  synaptic vesicles, and endoplasmic reticulum.
• Each synaptic vesicle contains thousands of
  molecules of a specific neuron transmitter.
• The neuron transmitter the diffuses across the
  synaptic cleft and binds to receptors on the
  postsynaptic membrane.

8
Synaptic Function in Neuron Transmitters

• There are many different neuron transmitters.
• Acetylcholine is released at cholinergic
  synapses.
• Cholinergic synapses are widespread inside and
  outside of the CNS.
• Step 1 is the arrival of an action potential at
  the synaptic knob.
• Step 2 is the release of the neurotransmitter
  Ach.
• The release of Ach stops because the calcium ions
  are rapidly removed from the cytoplasm by active
  transport mechanisms.

9
Membrane Potential

• To maintain a potential difference across the
  cell membrane, active processes are needed both
  to counter the combined chemical and electrical
  forces.
• The resting potential stays stable because the
  actions of the exchange pump.
• This ion pump exchanges three intracellular
  sodium ions for two extracellular potassium ions.
• A cell at -70mV is ejected as fast as it enter
  the cell.
• Then making the cell go through a net loss of
  positive charges.
• Resulting in exsess of negative charges, from
  negatively charged proteins.

10
Membrane Potential

• An action potential is a propagated change in the
  membrane potential of the entire cell membrane.
• Only skeletal muscle fibers and the axons of
  neurons have excitable membranes that conduct
  action potentials.
• In the skeletal muscle membranes the action
  potential begins at the neuromuscular junction
  and continues through the entire membrane.
• This results in ion movements that trigger a
  contraction.
• Action potential is generated by the opening and
  closing of gated sodium and potassium channels.
• A given stimulus gives a typical action
  potential, or it does not produce one at all.

11
Definitions

• Refractory period- limits the rate at witch
  action potentials can be generated in an
  excitable membrane.
• Threshold- a potential that depolarizes to this
  level.
• All-or-none-principle- A given stimulus either
  triggers a typical action potential.
• Saltatory propagation- this word means to leap,
  this nerve impulses along an axon at speeds
  ranging from 18-140 meters per second.
• Neurotransmitters- The information transfer
  occurs through the release of chemicals.
• Graded potentials- are changes in the membrane
  potential that cannot spread far from the site of
  stimulation.

12
Quiz

• 1 Threshold is the ___________depolarization
  lowest level?
• 2 What is Refractory period limit?
• 3 What is all-or-none principal?
• 4 An action potential is a propagated change in
  the membrane potential of the entire cell
  membrane? T or F
• 5 A Refractory period limits the rate at witch
  action potentials can be generated in an
  excitable membrane? T or F
• 6 A all-or-none principal is a given stimulus
  either triggers a typical action potential? T or
  F

13
Answers

1. Potential
2. limits the rate at witch action potentials can be
   generated in an excitable membrane.
3. A given stimulus either triggers a typical
   action potential.
4. True
5. True

14
Thank You

• By Jasmine Fukuda, Stevie Haut
• Shane Mclin, Danica Ozaki