B15 Nervous Coordination And Muscles Flashcards
Describe the general general structure of a motor neurone
Cell body : contains organelles & high proportion of RER (rough endoplasmic reticulum)
Dendrons : branch into dendrites which carry impulses towards cell body
Axon : long, unbranched fibre carries nerve impulses away from cell body
Describe the additional features of a myelinated motor neurone
Schwann cells : wrap around axon many times
Myelin sheath : made from myelin-rich membranes of Schwann cells
Nodes of Ranvier : very short gaps between neighbouring Schwann cells where theres no myelin sheath
Name 3 processes Schwann cells are involved in
Electrical insulation
Phagocytosis
Nerve regeneration
How does an action potential pass along an unmyelinated neurone
1- stimulus leads to influx of Na+, first section of membrane depolarises
2 - local electrical currents cause Na+ voltage-gated channels further along membrane to open. Meanwhile, the section behind begins to repolarise
3 - sequential wave of depolarisation
Explain why myelinated axons conduct impulses faster than unmyelinated axons
Saltatory condition: impulse ‘jumps’ from one node of ranvier to another. Depolarisation cannot occur when myelin sheath acts as electrical insulator
So impulse doesn’t travel along whole axon length
What is resting potential
Potential difference (voltage) across neurons membrane when not stimulated (-50 to -90 mV, usually about -70 mV in humans).
How’s resting potential established
Membrane is more permeable to K+ than Na+
Sodium-potassium pump actively transports 3Na+ out of cell & 2K+ into cell
Establishes electrochemical gradient: cell contents more negative than extracellular environment
Name the stages in generating an action potential
Depolarisation
Repolarisation
Hyper polarisation
Return to resting potential
How might drugs decrease synaptic transmission
Inhibit release of neurotransmitter
Decrease permeability of postsynaptic membrane to ions
Hyper polarise postsynaptic membrane
