Nerve Impulses Flashcards
State the function of sensory neurons
Carriers nerve impulses from receptor towards intermediate neurons within CNS
State the function of motor neurons
Connect sensory to motor neurons
Describe the structure and function of the axon
Single long fiber that carriers nerve impulses
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 neuron’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
-Sodium-potassium pump uses active transport to move 3 Na+ out of neurone for every 2 K+ ions moved in
-ATP needed to do this
-Membrane isn’t permeable to Na+ = can’t diffuse back
-Creates sodium ion electrochemical gradient
∵ more Na+ outside cell than inside
-Membrane is permeable to K+ = diffuse back out though K+ channels, down their concentration gradient
facilitated diffusion
-Makes outside of cell positively charged compared to inside
Neurone cell membranes become ________ when they’re stimulated
Depolarised
If a stimulus is big enough, it triggers rapid change in ___
p.d.
Name the 5 stages of how an action potential occurs i.e. how neurone cell membranes become depolarised when they’re stimulated
-Stimulus
-Depolarisation
-Repolarisation
-Hyperpolarisation
-Resting potential
Action Potentials
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
Describe the stage depolarisation
Once threshold has been met (around -55mv), more Na+ channels open = more Na+ to diffuse in rapidly
Action Potentials
Describe the stage repolarisation
-(At around +30mV) Na+ channels close and the K+ channels open
-(Na+ channels have to close or membrane will remain depolarised)
-Membrane is now more permeable to K+
= K+ diffuse out of neurone down K+ conc. gradient
-Gets membrane back to its resting potential
Action Potentials
Describe the stage hyperpolarisation
-K+ channels are slow to close so there’s a slight overshoot where too many K+ diffuse out of neurone
-Causes p.d. to become more negative than resting potential
Action Potentials
Describe the stage resting potential
-Ion channels are reset
-Sodium-potassium pump returns membrane to its resting potential
& 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
