3.4.3 Nerve Impulses and Synaptic Transmission Flashcards Preview

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Flashcards in 3.4.3 Nerve Impulses and Synaptic Transmission Deck (71)
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State the function of sensory neurones

Carriers nerve impulses from receptor towards intermediate neurones within CNS


State the function of motor neurones

Carries nerve impulses away from the CNS towards an effector


State the function of intermediate neurones

Connect sensory to motor neurones


Where are intermediate neurones found?

Within spinal cord

(have numerous short dendrites)


Describe the structure and function of the axon

Single long fibre that carriers nerve impulses


Describe the structure and function of dendrites 

Small extensions of cell body which carry impulses toward cell body


Describe the structure and function of the cell body 

  • Contains a nucleus and large number of endoplasmic reticulum
  • Produces neurotransmitters


Describe the structure of the myelin sheath

  • Covers the axon
  • Made up of membranes of Schwann cells
  • Membranes are rich in the lipid myelin


Describe the structure and function of Schwann cells

Surround and wrap around axon, providing protection and electrical insulation


Describe the structure of Nodes of Ranvier 

  • Small gaps between adjacent Schwann cell
  • Sodium ion channels are concentrated at the nodes


When is the sympathetic system activated?

In times of stress


What is the sympathetic system responsible for?

For increasing heart rate and ventilation and pupil dilation


When is the parasympathetic system active?

Most active in relaxed states


What is the parasympathetic system responsible for?

Responsible for decreasing heart rate and ventilation rate and pupil constriction


What does the parasympathetic system enable?

Enables everyday tasks to be completed (digest food, fight infections, etc.)


Describe and explain the charge of a neurone's resting state

  • In neurone's resting state, outside of membrane is positively charged compared to inside
    • ∵ more positive ions outside cell than inside
    • (resting potential = about -70 mv)​
  • ∴ membrane = polarised 
    • Difference in charge across it


State how resting potential is created and maintained

By sodium-potassium pumps & potassium ion channels


Describe how the resting potential is created and maintained by sodium-potassium pumps and potassium ion channels

  1. Sodium-potassium pump uses active transport to move 3 Na+ out of neurone for every 2 K+ ions moved in 
    1. ATP needed to do this
  2. Membrane isn't permeable to Na+ = can't diffuse back
  3. Creates sodium ion electrochemical gradient
    1. ∵ more Na+ outside cell than inside
  4. Membrane is permeable to K+ = diffuse back out though K+ channels, down their concentration gradient
    1. facilitated diffusion
  5. Makes outside of cell positively charged compared to inside


Neurone cell membranes become ________ when they're stimulated



If a stimulus is big enough, it triggers rapid change in ___



Name the 5 stages of how an action potential occurs i.e. how neurone cell membranes become depolarised when they're stimulated

  1. Stimulus
  2. Depolarisation
  3. Repolarisation
  4. Hyperpolarisation
  5. Resting potential 


Action Potentials 

1. Describe the stage stimulus

  • Stimulus excites neurones cell membrane = Na+ channels to open, making membrane more permeable to Na+
  • Na+ then diffuse (down electrochemical gradient) into neurone, making it less negative


Action Potentials 

2. Describe the stage depolarisation

Once threshold has been met (around -55mv), more Na+ channels open = more Na+ to diffuse in rapidly


Action Potentials 

3. Describe the stage repolarisation

  1. (At around +30mV) Na+ channels close and the K+ channels open
    • (Na+ channels have to close or membrane will remain depolarised)
  2. Membrane is now more permeable to K+
  3. = K+ diffuse out of neurone down K+ conc. gradient
  4. Gets membrane back to its resting potential


Action Potentials 

4. Describe the stage hyperpolarisation

  1. K+ channels are slow to close so there’s a slight overshoot where too many K+ diffuse out of neurone
  2. Causes p.d. to become more negative than resting potential


Action Potentials 

5. Describe the stage resting potential 

  1. Ion channels are reset 
  2. Sodium-potassium pump returns membrane to its resting potential
  3. & maintains until membrane's excited by another stimulus


Explain why after an action potential, the neurone cell membrane can't be excited again straight away

  • ∵ ion channels are recovering & can't be made to open
  • Na+ channels are closed during repolarisation and K+ are closed during hyperpolarisation


Describe how an action potential moves along a neurone

  1. When action potential occurs, some Na+ that enter neurone diffuse sideways
  2. Causes Na+ channels in next region of neurone to open and Naions diffuse into that part
  3. Causes wave of depolarisation to travel along neurone
  4. Wave move away from parts of membrane in refractory period ∵ these parts can't fire an action potential


What is the refractory period?

When ion channels are recovering and can't be opened


What does the refractory period act as?

Acts as a time delay between 1 action potential and the next

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