Nervous coordination Flashcards
Structure of a myelinated motor neurones
Dendrites
Nodes of Ranvier
Nucleus
Cell body
Myelin sheath made of Schwann cells
Axon
Sensory neurones
Transmit nerve impulses from a receptor to an intermediate or motor neurone
One dendron that carries the impulse towards the cell body and one axon that carries it away from the cell body
Motor neurones
Transmit nerve impulses from an intermediate or sensory neurone to an effector such as a gland or a tissue
Long axon
Short dendrites
Intermediate neurones
Transmit impulses between neurones
The establishment of a resting potential
The sodium-potassium ion pump actively transports 3 sodium ions out of axon and 2 potassium ions into axon
An electrochemical (concentration) gradient is created e.g. higher concentration of potassium ions inside axon than outside or higher concentration of sodium ions outside axon than inside
Membrane more permeable to potassium ions (open K+ channels) than sodium ions (closed Na+ channels)
Potassium ions move out of axon by facilitated diffusion
The inside of axon negatively charged relative to outside; axon is polarised = resting potential
Changes in membrane permeability lead to depolarisation and the generation of an action potential.
(Stimulus)
Excites the neurone cell membrane
Membrane more permeable to sodium ions as sodium ion channels open
Sodium diffuse into neurone down the sodium ion electrochemical gradient
Makes the inside of the neurone less negative
Changes in membrane permeability lead to depolarisation and the generation of an action potential.
(Depolarisation)
If potential difference reaches threshold, action potential generated because more voltage-gated sodium ion channels open
More sodium ions diffuse rapidly into neurones
Changes in membrane permeability lead to depolarisation and the generation of an action potential.
(Repolarisation)
Sodium ion channels close (membrane less permeable to sodium ions) whilst (voltage-gated) potassium ion channels open so potassium ions diffuse out of neurone down tthe potassium-ion concentration gradient
This starts to get the membrane back to its resting potential
Changes in membrane permeability lead to depolarisation and the generation of an action potential.
(Hyperpolarisation)
Potassium ion channels are too slow to close so there’s a slight overshoot – too many potassium ions diffuse out of neurone
The potential difference becomes more negative than the resting potential
Changes in membrane permeability lead to depolarisation and the generation of an action potential.
(Resting potential restored)
Resting potential is restored by the sodium-potassium pump
Ion channels reset
Maintained until the membrane is excited by another stimulus
The nature and importance of the refractory period
Refractory period is the time to restore axon to resting potential/no further action potential can be generated (time delay)
Produces discrete and discontinuous impulses (action potentials don’t overlap)
Limits frequency of impulse transmission at a certain intensity (limits strength of stimulus
that can be detected); higher intensity stimulus causes higher frequency of action potentials but only up to certain intensity
Unidirectional action potential – can’t be propagated in a region that is refractory
All or nothing nature of action potentials
Once threshold is reached, an action potential will always fire with teh same change in voltage, no matter how big the stimulus is
If the threshold isnt reached, an action potential wont fire (all or nothing)
A bigger stimulus wont cause a bigger action potential but will cause them to fire more frequently
Factors affecting the speed of conductance
(Myelination)
The myelin sheath is an electrical insulator present on some neurones
Depolarisation only occurs at Nodes of Ranvier in myelinated neurone
Saltatory conduction (which is faster) can occur (impulse jumps from node to node)
Impulse doesn’t travel whole axon/no need to depolarise along whole length of axon unlike non-myelinated neurone, where depolarisation happens along the whole length of the membrane
Factors affecting the speed of conductance
(Axon diameter)
Bigger diameter means less leakage of ions/less resistance to flow of ions
So depolarisation reaches other parts of the neurone cell membrane quicker
Factors affecting the speed of conductance
(Temperature)
Increases rate of movement of ions Na+ and K+ as more kinetic energy (active transport/diffusion)
Higher rate of respiration (enzyme activity faster) so ATP produced faster and energy released faster, so active transport also occurs faster
But proteins could denature past a certain temperature and speed will decrease