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1

1. Describe the key cellular properties and processes that lead to the generation of an action potential in a neurone.

An action potential is a change in a short term change in electrical potential that travels along a cell. An action potential is generated by the influx of positive sodium ions causing depolarization of the membrane. Depolarisation results to the membrane to reach threshold potential resulting in the firing of an action potential. An action potential is an all or nothing reaction, if threshold is not reached then an action potential will not be fired. Following depolarization, an action potential undergoes repolarization in which sodium channels close and potassium ions exit the cell to reestablish resting membrane potential. The refractory phase is the final part of an action potential in which sodium channels enter an inactive state, the sodium channels cannot be opened again until the membrane is polarized to resting potential. The sodium potassium pump returns sodium ions to the outside and potassium ions back to the inside. The refractory period is split between the absolute and relative refractory period. In the relative refractory period, some ion channels have recovered and can be stimulated if energy stronger than previous threshold is applied.

2

2. Explain the terms ‘summation’, ‘facilitation’ and ‘depression’ as used in the context of synaptic transmission. Use diagrams if necessary.

These 3 terms refer to the post synaptic potential activity of neurons. Synaptic facilitation and synaptic depression are 2 forms of homosynaptic plasticity. Synaptic depression refers to the phenoma by which a 2nd epsp produces a weaker epsp than that of the original action potential. Synaptic facilitation refers to when an epsp is fired which is stronger than the initial epsp fired. Summation is the addition of post synaptic potentials to eventually reach threshold potential. There is temporal and spatial summation. Temporal summation is successive stimulation on one nerve. Spatial summation refers to addition of simultaneous stimuli from several conducting fibres.

3

Use an annotated diagram to show the patterns of current and voltage surrounding a weakly electric fish during its electrical organ discharge (EOD).

refer to document

4

. List three characteristics that differ in solitarious and gregarious locusts.

- Solitarious are green and Greg are black and yellow or orange
- Solitarious have quick learning abil. Greg don’t have as much, e.g when eat toxic food solitarious don’t eat toxic food whereas greg eat for colouring
- Solirarious are less active and hide more whereas gregs are more active and visible

5

Explain why bats do not use FM calls to determine the relative velocity of their prey

FM calls are frequency modulated calls which transmit a broadband signal and sweep from high to low over a wide range of frequencies. These are short pulses with a duration of 5ms. Although this allows for accuracy in target distance, bats use constant frequency to find target velocity as it has a larger distance and longer duration. As it only fires one constant signal rather than broadband it propagates further. CF have long pulses of 5-30ms

6

Using a diagram, name and explain the three sound elements of birdsong revealed in a sonogram.

note syllables and phrases

7

What 3 features define a fixed action pattern?

A fixed action pattern (FAP) is an instinctive behavioral response triggered by a very specific stimulus. Three key features to define a fixed action pattern are:
- FAP’s are innate and species typical
- FAP’s are triggered by a sign/stimulus releaser, any type of stimulus
- Once triggered FAP’s are carried out to completion

8

A touch to the tail of a lobster triggers an escape response that flips the animal upwards and forwards. In contrast, a touch to the head elicits an escape response that flips the lobster backwards. Briefly explain the neuronal basis for these different responses..

Touching the tail with a probe triggers contraction of the fast flexor muscles which leads to contraction of the tail. The circuitry for this response is located in the abdominal ganglia and the pathway is as follows:
Tail afferents -> Sensory interneurons -> Lateral giant interneurons -> Motor giant neurons -> Fast flexor muscles.
With a head touch, it is the medial giant interneurons that carry the sensory information instead. The LGI synapses with motor neurons in abdominal segments 1-3 so only those muscles contract with a tail touch. In contrast, the medial giant interneurons synapse with all segments.

9

Most of the energy of the Mustached bat's call is present in the second harmonic. Explain what is meant by the term ‘harmonic’ in this context, and describe two major advantages of suppressing the fundamental harmonic.

More energy being in the higher harmonic gives the bat something to compare the fundamental harmonic to. The fact that the lower harmonic only contains 1% of the energy of the higher level is advantageous because it means that only the bat of origin can hear it as it is transferred to the ear via the skull tissue. This means that when the second harmonic comes back as an echo, any bats nearby ignore it because they haven’t heard the first call and the neurons in the auditory cortex only respond to call-echo combinations.

10

Draw an annotated diagram of the neurones and their connections that form the swim central pattern generator (CPG) in the marine snail Clione

See document

11

Name three sensory organs that provide phasic sensory feedback during locust flight

Wing hinge stretch – Active when the wings are elevated
Tegula – During wing downstroke
Campaniform sensilla – At the beginning of wing downstroke until the beginning of upstroke. Signals lift and thrust during depression
COmpound eyes -detect deviation in all 3 exes but they are slow
Ocelli- detect deviation in pitch and roll
-Luminance detectors
-One on either side of midline and third on top of head
-Horizon detectors- signal displacement relative to horizon (light)
Wind-sensitive hairs
detect deviation in pitch and yaw
-Mechanoreceptors like crayfish

-Directionally sensitive
Top of head hairs respond best to wind from the front

-Tonic activation starts and maintains flight
-Phasic bursts cause steering corrections

12

. What three anatomical features make Aplysia ideal for studying the cellular basis of learning and memory?

Large, unmyelinated axons easily accessible
Small number of neurons
Neurons arranged in ganglia making it easier to separate different parts of the brain and determine structure

13

Define long term potentiation (LTP) with reference to pyramidal neurones of the hippocampus.

Long Term potentiation is the process of increasing neuronal synaptic connections mediated by the activity of NMDA and AMPA receptors. In long term potentiation glutamate release allows glutamate ions to flow into the membrane through AMPA receptors. NMDA receptors are blocked by magnesium ions. The influx of positive charge through AMPA receptors causes depolarization and frees the voltage gated NMDA receptor of the magnesium ion allow ca influx. Ca influx causes depolarization resulting in the addition of more AMPA receptors in the membrane. An increase in AMPA receptors allows for this process to occur more frequently and increases strength hence LTP. Hippocampal pyramidal neurons respond to continuous depolarizing current injection with a train of spikes that exhibits spike-frequency-adaptation (accommodation) and some respond with one or more bursts of action potential. This occurs in NMDA depedent LTP.

14

Define the term ‘configural property’ in the context of visual prey recognition in toads, and explain why such properties are important.

Neither the shape or direction of movement alone are sufficient enough to evoke a response in a toad. It is the relationship between the two that matters. 'The whole is greater than the sum of its parts.

15

Describe how population density affects the learned value that desert locusts assign to an unfamiliar odour that is paired with toxic food. Provide an ultimate explanation for the observed differences in learning.

When given the choice between poisonous vanilla and lemon:
Solitary phase locusts begin with vanilla but quickly switch to lemon
Gregarious phase choose lemon for a significant amount of time before switching to lemon. This is because their taste-testing ability is off and instead they use post-ingestive feedback so they don't know to switch until after the food has had a negative effect on the body. Toxic intake is monitored
Newly gregarised stick with vanilla as their taste and post-ingestive feedback are both off because they need to compensate for their lack of warning colours

16

Briefly define the key operating principles that underlie rhythm generation in a 'half-centre oscillator'

Two neurons coupled by inhibitory synapses. An external neuron may drive the network constantly to produce a stable oscillation or this may be replaced by post-inhibition rebound by the neurons. It requires a mechanism that progressively reduces the inhibitory effect and this is achieved by synaptic depression increasing between the active neuron and its interneuron until the depression is enough to remove the inhibition on the other neuron.

17

Explain how serotonin causes short-term spike broadening in the sea slug Aplysia

Short term spike broadening refers to short term sensitization. Sensitization is a type un assosiative learning resulting increases amplitude of response. In Aplysia , serotonin causes s.t.s. through serotogenic interneurons connected to the tail sensory neuron. These interneurons release serotonin resulting in an increased amplitude in the motor neuron. This occurs as serotonin cause PKA phosphorylation of K+ channels resulting in a longer Action potential as repolarization duration is increased, in addition it causes a Ca+ Influx. Serotonin strengthens the sensorimotor synapse.

18

Briefly describe the three key events leading to expression of intermediate early genes following repeated serotonin exposure in the sea slug Aplysia. (Long term sensitization)

Expression of intermediate early genes is due to long term sensitization due to repeated serotonin exposure.
- Serotonin translocates to the nucles
- Phosphrylates CREB1 (cAMP Response Element Binding protein 1)
- CREB1 is a transcription factor for intermediate early genes
-Products of intermediate early genes are TF for late responsive genes
- Late responsive genes expression causes expression of genes that encode proteins required for synapse formation.

19

Briefly describe the key experiment which demonstrated that, in cockroaches, the circadian pacemaker controlling activity rhythms resides in the optic lobe.

Cockroaches of the same species were put under two different conditions; long day (13 hr light, 13 hr dark) and short day (11 hr light, 11 hr dark)
After swapping their optic lobes, they were then put in constant darkness and it was observed that they still maintained the period from the entrainment period which shows that there is a memory system in the optic lobe.