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BS2077 - Neuro & Animal Behaviour > Straub > Flashcards

Flashcards in Straub Deck (48)
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1

Describe a reflex with example

Example: Knee jerk reflex
General features:
involuntary, unconscious
triggered by specific stimulus
stereotypic fixed response
polysynaptic reflex
monosynaptic reflex

2

Give an example of specific stimuli and complex behaviour

Example: Egg retrieval in geese and gulls

3

Describe other fixed action patterns (FABs) eg.

- many courtship behaviours
- gaping and pecking responses in young birds

4

Describe FABs

- study of FAPs is particularly linked to work by von Holst, Lorenz and Tinbergen,which can be considered founders of field of neuroethology
- study is based on observation of animal behaviour
- FAPs are innate and species typical
- FAPs are triggered by sign stimulus/releaser – a stimulus that triggers FAP once triggered FAPs are carried out to completion
- today, the term ‘FAP’ has been widely replaced by the term ‘behavioural act’ or ‘behavioural pattern'

5

Who discovered universal FAPs in humans and what were they?

Eibl-Eibesfeldt observed many different cultures – found evidence for universal FAPs in humans:
- ‘eyebrow flash’ – universal greeting
- emotions in deaf-blind children
- coyness behaviour

6

Describe the two hypothesis for control of FAPs

Hypothesis 1: FAPs are generated by a sequence of reflexes --> Reflex chainAlso known as the peripheral control hypothesis
Hypothesis 2:The central control hypothesis –a central pattern generator generates sequence of motor behaviours

7

What arguments exist in central vs peripheral control

Egg retrieval: behaviour carries on after stimulus is removed – suggests that behavioural sequence is generated centrally and not by a reflex chain

FAPs like egg retrieval are too complex for study of neuronal network that controls behaviour

Organisation of basic locomotion is less complex, e.g.
- walking: limbs move forward and backwards
- flying: wings move up and down
- general: locomotion involves rhythmic flexion and extension of muscle groups
--> highly repetitive, good for experimental analysis

8

Describe the pacemaker model for central pattern generators (CPG)

- intrinsic oscillator / pacemaker
- imposes activity (rhythm) on network
- To achieve two opposing phases of activity, neuron(s) that are active whilst pacemaker is inactive require mechanism that drives their activity, e.g.:
- Post-inhibitory rebound (PIR)
- Spontaneously active
- Receives constant excitation

9

Describe the network oscillator model for central pattern generators (CPG)

How to build network oscillator?
Suggestion: Two neurons coupled by excitatory synapse
Problem: Positive feedback – circuit is very unstable!

10

Describe half centre model for central pattern generators (CPG)

- Two neurons coupled by inhibitory synapses – produces stable oscillation (rhythm)
- requires a mechanism that progressively reduces inhibitory effect: ‘fatigue’, adaptation, progressive self-inhibition
- Post-inhibitory rebound (PIR) can sustain oscillation without constant drive

11

Describe the sea angel Clione limacina

- Wings are modified foot of snail
- swimming consists of two alternating phases:
dorsal flexion (D-phase)
ventral flexion (V-phase)
- Clione CNS
few thousand neurons
clustered in a small number of central ganglia

12

Describe the ID of Clione swimming neurons

- backfilling makes it possible to identify neurons with axons in a specific nerve
place cut end of nerve into dye
dye is taken up by axon and migrates to cell body

- mapped neurons can be impaled with intracellular electrodes to record their activity

- ~40 motoneurons in total including
2 large neurons:
1A: innervates dorsal wing side
2A: innervates ventral wing side
smaller motoneurons innervate only certain areas of wing

13

What did experiments tell us about the generation of swim pattern in Clione

- inactivation of individual motoneurons does not affect overall swim rhythm
- in simultaneous recording from two swim motoneurons
hyperpolarisation of D-phase motoneuron (red box) has no effect on V-phase motoneuron
- even photoinactivation of all motoneurons does not interrupt basic rhythm
- m motoneurons are not involved in generation of swim rhythm!

14

Describe swim interneurons

- swim interneurons have no peripheral processes – can not be identified by backfilling
- can only be identified by systematic search using intracellular electrodes – look for neurons that are active in phase with swim motoneurons
- inactivation of swim interneuron by hyperpolarisation (red box) stops swim rhythm

15

Describe how swim interneurons are involved with pattern generation in Clione

- Clione has two groups of swim interneurons called 7 and 8
swim interneurons 7 are active during D-phase
swim interneurons 8 are active during V-phase

- interneurons 7 and 8 are connected by inhibitory synapses

- interneurons in the same group are electrically coupled

- swim interneurons fire on rebound from inhibition ( post-inhibitory rebound)

16

Describe the Clione CPG as a half centre oscillator with a twist

- Clione swim CPG has all the elements of a half-centre oscillator
- rhythm generation can be fully explained by connections between different interneuron types
- Swim interneurons possess intrinsic bursting property!
- Swim rhythm generation is result of the combination of intrinsic cellular properties and network properties

17

SUMMARY FAP, MODELS, CLIONE

- Fixed action patterns are innate behaviours triggered by a sign stimulus/releaser
- Fixed action patterns are centrally controlled
- Various models have been proposed for the central control of rhythmic behaviours including:
pacemaker neurons
half-centre oscillators
closed-loop rhythm generators
- Swim rhythm in the marine snail Clione is generated by a central pattern generator with all the features of a half-centre oscillator
- In addition, the interneurons of the Clione swim pattern generator also have intrinsic bursting properties  so, they have the potential to function as pacemaker neurons

18

Describe the neuroanatomy of the tadpole

- Hatchling tadpole
Spinal cord: ~100 mm diameter

- Eight types of spinal neurons including:
motoneurons:
commissural interneurons
descending interneurons
dorsolateral interneurons
dorsolateral commissural interneurons
Rohon-Beard neurons

- Spinal neurons form longitudinal columns of 100-300 cells on each side of CNS

19

Describe tadpole swim motor neuron

- motoneurons show rhythmic activity in response to brief tail stimulus ---> swim episode
- activity of left and right motoneurons alternates (like pattern of laying bricks)

20

Describe tadpole swim CPG

- Three neuron types are sufficient to generate basic swimming pattern
- All three types show similar activity pattern:
fire single AP during fictive swimming
are tonically excited
receive mid-cycle inhibition
- Neurons form half-centre oscillator

21

Describe what was found in Roberts, Soffe, Perrins (1998) in Neurons, Networks, and Motor Behavior (SUMMARY)

- Commissural interneurons project to opposite site where their axon branches and projects both rostrally and caudally
- Commissural interneurons are responsible for mid-cycle inhibition (Glycine)
- Some have also ipsilateral axons, presumably responsible for recurrent on-cycle inhibition of sensory decussating interneurons (dlc), etc.
- Descending interneurons project caudally on the same side of the cord
- Provide fast AMPA excitation to more caudal neurons and slow NMDA excitation that sustains next cycle
- Motoneurons have peripheral axons, but also descending longitudinal axons that make central synapses (ACh)

- PIR plays a role in pattern generation
- Tonic drive is provided by cycle-by-cycle feedback due to slow NMDA excitation
- Other mechanisms might also play a role

22

Describe the activation of swim CPG

- Rohon-Beard neurons innervate trunk skin
- RB neurons have longidutinal axons in dorsal spinal cord
- Excite dorsolateral (dl) and dorsolateral commissural (dlc) sensory interneurons
- Trigger activity in swim CPG

23

How does motoneuron activity propagate?

- from head to tail
- During swimming, waves of bending pass from the head to the tail
- Progression can also be seen in motoneuron activity in isolated spinal cord

24

What are the two hypothesis for how a wave of activity is propagated

Hypothesis 1:
- single oscillator – variable delays:signal takes longer to reach caudal segments than rostral segments

- Unlikely because:
CPG elements are distributed along the whole length of spinal cord
stretches of spinal cord can be isolated and show rhythmic activity ---> CPG is distributed along the spinal cord


Hypothesis 2:
- tadpole spinal cord represent a chain of unitary oscillators

- leading oscillator hypothesis:
each CPG generates rhythm
CPG with fastest rhythm sets overall frequency and co-ordinates activity in other CPGs

- rostral-caudal wave propagation requires gradient from head to tail that ensures more rostral CPGs oscillate faster than more caudal CPGs

25

How is activity in unitary oscillators coordinators

- spinal cord shows rostral-caudal gradient of excitability:
rostral motoneurons are more depolarised during swimming than caudal motoneurons
rostral motoneurons also receive larger midcycle inhibition
- prediction:changing excitability of caudal segments changes rostral-caudal delay

26

How is excitability manipulated in caudal segments and what does it change

- glutamate is excitatory neurotransmitter involved in swimming
- NMDA application (glutamate receptor agonist) to caudal segments increases excitability in these segments and shortens or even reverses rostral-caudal delay
- AP5 application (glutamate receptor antagonist) to caudal segments decreases excitability and increases rostral-caudal delay

27

Describe longitudinal gradients in exon distribution

- highest number of axons originating from dorsolateral commissural interneurons (dlc), dorsolateral ascending interneurons (dca) and descending interneurons (dIN) are found at rostral end of spinal cord
- could be morphological basis for longitudinal gradient in excitability

28

Describe lamprey swim CPG

- could be morphological basis for longitudinal gradient in excitability

29

What is the leading oscillator hypothesis in lamprey

- as in tadpole, glutamate is excitatory neurotransmitter involved in swimming

- separating the spinal cord into three pools and applying different concentrations of the glutamate agonist NMDA alters wave propagation:
- same concentration in all pools ---> rostral-caudal wave (forward swim)
- high concentration in caudal pool ----> caudal-rostral wave (backward swim)
- high concentration in middle pool ----> two waves propagating rostrally and caudally

30

SUMMARY: TADPOLE AND LAMPREY

- Swimming in tadpole and lamprey consists of undulatory body movements that progress as a rostral-caudal wave
- Rhythms are generated by CPG with characteristics of a half-centre oscillator
- Spinal cord can be considered as a chain of unitary oscillators/CPGs
- Segment with fastest frequency leads wave, other segments follow with a specific phase lag  generation of a propagating wave