the nervous system Flashcards
two major parts of the nervous system
Central Nervous System: brain and spinal cord
Peripheral nervous system:
cranial + spinal nerves
connects CNS to muscles/glands/sensory receptors
name and describe the two principle types of cells in nervous tissue
neurons / nerve cells: cell body, dendrites and axon
neuroglia: do not generate or conduct nerve impulses
function of neurons
receive, integrate, conduct and transmit signals
multipolar neuron structure
cell body with dendrites
myelinated axon
axon terminal
how is an action potential triggered?
by depolarisation of a neuron’s plasma membrane
RMP about -60 mV
stimulus depolarises to -40mV, threshold potential opens voltage-gated Na+ channels –> +40mV
the flow of any ion through a membrane channel protein is driven by…
the electrochemical gradient for that ion, influenced by the voltage gradient and the conc gradient
the Nerst equation is used to find…
find the equilibrium potential (V) for an ion given the internal and external ion concentrations
Nernst Equation
V = RF/zF ln(Co/Ci)
z = valence / charge of the ion
Co = conc outside, Ci = conc inside
at room temp (25˚C), RT/F = 25.693mV
how does an action potential propagate along the length of an axon?
opening of Na+ channels and flow of Na+ into axon alters membrane potential –> travelling action potential
shortly after, voltage-gated K+ channels open and K+ flows out of the axon –> return to RMP
what do Schwann cells do?
myelinate axons in the PNS
purpose of myelination
increases speed and efficiency of action potential propagation in nerve cells
purpose of nodes of ranvier
facilitates saltatory conduction: where action potential propagates by jumping from node to node
travels much faster while conserving metabolic energy
how to monitor ion channel activity
using a patch-clamp recording
micro electrode tip forms seal – current can leave/enter micro electrode only by passing through channels in the patch of membrane at the tip
synapse
site of transmission of signal from neuron to terminal (muscle cell or another neuron)
how is a signal carried across the synaptic cleft? + mechanism
by neurotransmitters - electrical signal is converted into a secreted chemical signal
AP reaches nerve terminal, opens v-gated Ca2+ channels, Ca2+ flows in and causes synaptic vesicles to fuse with the PM, releasing NT
(DIFFUSES from presynaptic to postsynaptic cell, across synaptic cleft)
two types of neurotransmitters + examples
excitatory - acetylcholine, glutamate
inhibitory - GABA, glycine
main receptors for excitatory neurotransmitters
ligand-gated cation channels (for acetylcholine / glutamate)
main receptors for inhibitory neurotransmitters
ligand-gated Cl- channels
how is a chemical signal converted back to an electrical signal at the post-synaptic terminal?
NT diffuses rapidly across sun cleft and binds to PM of target cell, causing a CHANGE IN MEMBRANE POTENTIAL –> fires action potential
neuromuscular junction
synapse between motor neuron and muscle
what NT is released at a neuromuscular junction?
acetylcholine - excitatory, causes muscle fibres to contract
(still triggered by opening of Ca2+ channels)
structure of ACh receptor in PM
gate consists of five transmembrane subunits forming a pore
two ACh binding sites
negatively charged amino acid side chains inside pore ensure only positively charged Na+ and K+ can pass
what conformational change does an ACh receptor undergo?
“closed” conformation: ACh is NOT bound
Pore is occluded by hydrophobic amino acid side chains at the gate region
open: ACh bound
hydrophobic side chains move apart and gate opens, allowing Na+ to flow
what does a motor neuron in the spinal cord look like?
thousands of synapses form on the cell body and dendrites of the motor neuron
