6 Responding to Change- Nervous Coordination Flashcards
What are neurones and the 3 main types? (+ description)
Neurones= cells that transmit information from receptors to effectors
Sensory neurones- carry nervous impulses from receptors into CNS
Motor neurones- carry impulses from CNS to effector organs (eg muscle/glands)
Relay neurones- intermediate neurones, receive impulses from sensory neurone & relay them to motor neurones
What is the basic structure of neurones?
-Can be myelinated/non-myelinated
-Dendrites; carry nervous impulse towards cell body
-Axons; carry nervous impulse away from cell body
-Cell body; where nucleus is normally located
What is the structure of myelinated motor neurones?
-Motor neurones in vertebrates= usually myelinated
-Schwann cells= wrapped around axon of neurone, form myelin sheath
-Nodes of Ranvier= gaps between adjacent Schwann cells
What is resting potential?
When a neurone hasn’t been stimulated
Why is there a potential difference at resting state?
-At resting potential—> diff in charge across neurone membrane: inside neurone more negatively charged than outside, as there are more positive ins outside cell than inside
-Diff in charge= potential difference
What is the resting potential maintained by and how?
-Resting potential maintained by sodium-potassium pumps in neurone membrane
-3 Na+ ions are actively transported out of neurone by pumps for every 2 K+ ions transported in
-This leads to build-up of positive ions outside of cell
How do potassium ion channels in the neurone membrane affect the sodium ions?
-Potassium ion channels are in neurone membrane—> it’s permeable to K+ ions
-When K+ ions are transported into neurones, can diffuse back
-Neurone membrane—> also impermeable to Na+ ions so ions can’t diffuse back into cell after they’ve been transported out
What actions establish the resting potential?
-Together, action of sodium-potassium pumps & potassium ion channels lead to potential diff across neurone membrane—> called resting potential (about -70mV)
-Neurone is said to be polarised
When does repolarisation happen?
When a resting neurone is stimulated, its membrane experiences a change in potential difference
What happens when a neurone is stimulated?
-Na+ ions channels in cell membrane open when neurone is stimulated
-Na+ ions flood into neurone
-Potential difference across membrane changes, becomes more positive inside neurone
How does depolarisation occur and what happens as a result?
-If potential diff increases above threshold value (about -55mV) then membrane becomes depolarised
-More sodium channels open and there’s a sharp increase in potential difference to about +30mV
Why is depolarisation called an all-or-nothing response?
-If potential diff reaches threshold, depolarisation always takes place & charge in potential diff will always be the same
-If stimulus= stronger, action potentials will be made frequently but size won’t increase
What is the process of repolarisation?
-After neurone has been depolarised to +30mV, sodium ions channels close & potassium ion channels open
-K+ ions transported back out of neurone, potential diff becomes more negative—> repolarisation
How does hyperpolarisation happen and what is the refractory period?
-Short period after repolarisation of neurone where potential diff becomes slightly more negative than resting potential—> hyperpolarisation
-Hyperpolarisation Prevents neurone from being restimulated instantly—> refractory period
What occurs after the refractory period?
-Potassium ion channels close, membrane returns to resting potential
The process where neurone= depolarised, returns to resting potential—> action potential
