the nervous system

Question 1

two major parts of the nervous system

Answer 1

Central Nervous System: brain and spinal cord

Peripheral nervous system:
cranial + spinal nerves
connects CNS to muscles/glands/sensory receptors

Question 2

name and describe the two principle types of cells in nervous tissue

Answer 2

neurons / nerve cells: cell body, dendrites and axon
neuroglia: do not generate or conduct nerve impulses

Question 3

function of neurons

Answer 3

receive, integrate, conduct and transmit signals

Question 4

multipolar neuron structure

Answer 4

cell body with dendrites
myelinated axon
axon terminal

Question 5

how is an action potential triggered?

Answer 5

by depolarisation of a neuron’s plasma membrane

RMP about -60 mV
stimulus depolarises to -40mV, threshold potential opens voltage-gated Na+ channels –> +40mV

Question 6

the flow of any ion through a membrane channel protein is driven by…

Answer 6

the electrochemical gradient for that ion, influenced by the voltage gradient and the conc gradient

Question 7

the Nerst equation is used to find…

Answer 7

find the equilibrium potential (V) for an ion given the internal and external ion concentrations

Question 8

Nernst Equation

Answer 8

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

Question 9

how does an action potential propagate along the length of an axon?

Answer 9

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

Question 10

what do Schwann cells do?

Answer 10

myelinate axons in the PNS

Question 11

purpose of myelination

Answer 11

increases speed and efficiency of action potential propagation in nerve cells

Question 12

purpose of nodes of ranvier

Answer 12

facilitates saltatory conduction: where action potential propagates by jumping from node to node
travels much faster while conserving metabolic energy

Question 13

how to monitor ion channel activity

Answer 13

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

Question 14

synapse

Answer 14

site of transmission of signal from neuron to terminal (muscle cell or another neuron)

Question 15

how is a signal carried across the synaptic cleft? + mechanism

Answer 15

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)

Question 16

two types of neurotransmitters + examples

Answer 16

excitatory - acetylcholine, glutamate
inhibitory - GABA, glycine

Question 17

main receptors for excitatory neurotransmitters

Answer 17

ligand-gated cation channels (for acetylcholine / glutamate)

Question 18

main receptors for inhibitory neurotransmitters

Answer 18

ligand-gated Cl- channels

Question 19

how is a chemical signal converted back to an electrical signal at the post-synaptic terminal?

Answer 19

NT diffuses rapidly across sun cleft and binds to PM of target cell, causing a CHANGE IN MEMBRANE POTENTIAL –> fires action potential

Question 20

neuromuscular junction

Answer 20

synapse between motor neuron and muscle

Question 21

what NT is released at a neuromuscular junction?

Answer 21

acetylcholine - excitatory, causes muscle fibres to contract
(still triggered by opening of Ca2+ channels)

Question 22

structure of ACh receptor in PM

Answer 22

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

Question 23

what conformational change does an ACh receptor undergo?

Answer 23

“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

Question 24

what does a motor neuron in the spinal cord look like?

Answer 24

thousands of synapses form on the cell body and dendrites of the motor neuron