Introduction to the neurone - L2

Question 1

do retinal receptors hyperpolarise in ight?

Answer 1

yeop

Question 2

2 main categories of sen sory receptors?

Answer 2

short and long

Question 3

describe long receptors

Answer 3

“long” receptors which send afferent axons to the CNS and fire action potentials,

Question 4

describe short receptors

Answer 4

“short” receptors without an axon, which immediately synapse with a second-order cell for conduction to the CNS.

“Short” receptors often generate a graded potential instead of firing spikes, leading to graded changes in transmitter release at the synapse, and a graded generator potential in the second order cell, which modulates the rate of spike firing.

Question 5

long vs short receptors$

Answer 5

Question 6

In long receptors the magnitude of the stimulus is normally encoded as,,,,

Answer 6

In long receptors the magnitude of the stimulus is normally encoded as the frequency of action potential firing, as in this cutaneous sensory receptor.

Question 7

describe sensory receptor adaptation

Answer 7

Sensory receptors normally adapt, leading to a diminution of firing frequency with time; this adaptation can take place over either a slow or a rapid time scale.

Question 8

Cutaneous mechanoreceptors are the quintessential “___” receptors.

Answer 8

Cutaneous mechanoreceptors are the quintessential “long” receptors.

Question 9

Special senses are mostly supplied with “____” receptors

Answer 9

short

The exception is the olfactory receptor, which sends axons directly to the olfactory bulb.

Question 10

observe

Answer 10

noiocw

Question 11

describe how mechano-receptors work

Answer 11

the transduction process is direct, involving the opening of stretch- sensitive channels coupled to the cytoskeleton or, for hearing, to more specialised structures.

Question 12

direct vs indirect

Answer 12

Question 13

Monosynaptic stretch reflex

Answer 13

Question 14

If you inject a steady current into a spinal motor neuron to perturb its membrane potential and then stimulate the Group IA afferents, the EPSP changes sign at a potential of around zeromV. This implies that the excitatory post-synaptic current must reverse at this potential. This value does not correspond to the reversal potential of any single ion,

what does this imply

Answer 14

implying that this glutamate- gated channel must allow more than one ion to pass. In fact it is permeant to both Na+ and K+ ions, so the current reverses when the inward Na+ flux balances the outward flux of K+. In some cases, glutamate-gated channels in the CNS also allow Ca2+ to enter, with important implications for synaptic plasticity.

Question 15

If, instead, you excite Group IA afferents from the antagonist muscle, then they inhibit the -motor neurons of the agonist, via inhibitory interneurons which release ____.

Answer 15

If, instead, you excite Group IA afferents from the antagonist muscle, then they inhibit the -motor neurons of the agonist, via inhibitory interneurons which release glycine.

Question 16

The inhibitory post-synaptic potential in an alpha motor neuron reverses at –80mV. This reversal potential is made less negative by injecting __ ions from the recording electrode, indicating that it is due to an elevation in __ conductance.

Elsewhere in the CNS, inhibition may be achieved by either elevated ______ conductance via the central inhibitory transmitter GABA.

Answer 16

The inhibitory post-synaptic potential in an alpha motor neuron reverses at –80mV. This reversal potential is made less negative by injecting Cl- ions from the recording electrode, indicating that it is due to an elevation in Cl- conductance. Elsewhere in the CNS, inhibition may be achieved by either elevated Cl- or K+ conductance via the central inhibitory transmitter GABA.

Question 17

you understadn that many IPSPs and EPSPs summate at the axon hilock right?

Answer 17

yep. good. they combine to produce a net effect

Question 18

3 places synapses can be located

Answer 18

Question 19

For example, a cortical pyramidal cell receives synapses …. where?

Answer 19

or example, a cortical pyramidal cell receives synapses on the soma, on the dendritic shaft and on dendritic spines.

Question 20

Type 1 and 2 synapses

Answer 20

Question 21

how do action potentials spread along nerves?

Answer 21

The action potential spreads along a nerve fibre by means of local circuit currents, which raise the nerve membrane to threshold ahead of the present location of the action potential.

Question 22

what is the space constant

Answer 22

at steady state the potential decays away exponentially with a space constant, , governed by the relative magnitudes of the membrane and longitudinal resistances.

Question 23

current decay in neurones

Answer 23

Question 24

splitting teh dendritic tree into many cables - and moddling EPSP decay is a start.

but are there booster mechanisms?

Answer 24

however recent evidence suggests that voltage-gated conductances (both to Na+ and Ca2+) are present in the dendrites of many neurons, serving to boost the decaying passively conducted dendritic signal.

Question 25

where is the AP initiated?

Answer 25

axon hillock

Question 26

what are the 2 main cable parameterS>?

Answer 26

Question 27

what are APS initiated at the axon hillock?

Answer 27

lowest threshold

Question 28

how do we know the AP is started at the axon hillock

Answer 28

Question 29

do APs spread back up the dentrits?

Answer 29

yep

Question 30

The extent to which a given synapse can influence the potential at the axon hillock depends on….

Answer 30

how far away from the cell body it is located along the dendritic tree.

Question 31

describe how the size (diameter) of the dentrite affects the influence of an supstream synapse?

Answer 31

Large = less impedance for potential

small = big impedance for potential

Question 32

The space constant of an unmyelinated nerve varies with the ……

Answer 32

The space constant of an unmyelinated nerve varies with the square root of its diameter.

Question 33

effect of dendritic diameter

Answer 33

Question 34

read and absorb

Answer 34

Question 35

Answer 35

Question 36

describe shunting inhibition

Answer 36

if the inhibitory synapse is located closer to the cell body on the same dendrite, then much of the excitatory current leaves before it can ever influence the cell body. Arithmetically, this is equivalent to division, and is called shunting inhibition

Question 37

The effectiveness of shunting inhibition explains ……

Answer 37

The effectiveness of shunting inhibition explains why most excitatory inputs are located further out on the dendrites, while inhibitory inputs are mostly close to the soma.

Question 38

what are Axo-axonic synapses

Answer 38

Axo-axonic synapses mediating presynaptic inhibition offer powerful control over synaptic transmitter release

often inhibition

Question 39

pre-synaptic inhibition

Answer 39

Question 40

describe pre-synaptic inhibtion

Answer 40

• opening Cl- or K+ reduces the height of the action potential in the presynaptic terminal.
• leading to a slight primary afferent depolarization, which partially inactivates Na+ channels.
• This reduction in action potential height leads to reduced opening of voltage-gated Ca2+ channels.
• Ca2+ channels can also be modulated directly by second messenger systems within the presynaptic terminal. The reduced Ca2+ influx leads to a reduction in transmitter release: since vesicle fusion depends steeply on Ca2+, a subtle change can result in a substantial decrease in release.

Question 41

how important in timing in pre-synaptic transmission?

Answer 41

The timing of inhibition needs to be precise, since it must arrive at virtually the same time as the action potential. This constraint is relaxed somewhat with peptide transmitters, which have slower neuromodulatory actions than ionotropic transmitters.

Question 42

fat

Answer 42

mamba