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An Integrated view
Nerve Muscle and
Movement
Exam
 12 SA Q of 5 marks (60)
 4 MCQ Q total 10 marks
 -ve
marks for wrong answers
 Specimen paper
 http://biolpc22.york.ac.uk/404/#exam
 Practical worth 30 marks, deadline 14 Dec
 Submit
1 practical report
To join together…
Nerve conduction
Synaptic physiology
Muscle contraction
Mechanics of Motion
Axon guidance
what could be better than …
…fly jumping?
with a little help from our
genetics friends
Aim
 How a fly is built to get away
 Key reference
 Allen, MJ et al (2006) Making an escape:
Development and function of the Drosophila
giant fibre system Sem Cell & Devel Biol. 17:
31-41
Genetic tools
 EMS-induced
mutations
 Sequenced genome
 UAS GAL4 system
 tissue
specific
knockouts
 tissue specific GFP
 tissue may be a few
cells
How does a fly jump?
Jump using middle leg
Trimarchi & Schneiderman
max distance jumped
(mm) mean ± SE
How far do they go?
30
 Wild type
flies go
30 mm
20
10
0
1
2
3
4
5
6
CS female fly #
7
How much work/force?
 Work
 KE
= ½ m g d = ½ 10-6 x 10 x 0.03 = 150 nJ
 Power output = 40 µW or 300 W / kg
 at the top end of insect muscle output
 Force
 measure
contraction isometrically
 peak force 25 x weight of fly
Which muscles?
 zap head and record muscle potentials
here given one small and one large stimulus
Summary
 thoracic muscles, very energetically
demanding
What’s in a fly?
IFM
TDT
GDN
CNS
mn
foregut
VNC
tc
femur
tibia
tarsus
tc - trochanter
mn - motor neuron
GDN - Giant descending neuron [= GF]
IFM – Indirect flight muscles
TDT – tergal depressor of the trochanter [= TTM]
VNC - ventral nerve cord
What's in the fly CNS ?
brain
thoracic
ganglion
Plan
 start with
 muscle
 motoneuron
 giant
descending interneuron
 sensory input
 development
TDT muscle
Koenig & Ikeda, 2005
this end pulls
• the wing,
• thorax,
• stretching the IFMs
 TDT has a double
whammy
this end pulls
• the leg straight
TDT in section
TDT is…
 Striated muscle
 Tubular muscle
 Fast twitch
Innervation
 innervated by
3 motoneurons
 1 large – very
extensive endings
 2 small
TDT motoneuron
 thoracic
nervous system
 lateral cell
body
 dorsal neuropil
Neuromodulation
 by octopamine –
containing neuron
Summary
 thoracic muscles, very energetically
demanding
 muscle and motoneuron designed for speed
GDN (=GF)
GDN
PSI
TDTmn
GDN → TDTmn synapse
 electrical ↑
 chemical ▼
 ACh
GDN → TDTmn synapse
 shakingB2
 no
electrical synapses
 an innexin mutant
 asymmetry in innexins
 shakingB2 and chats2
 neither
electrical nor
cholinergic synapses
Axonal conduction in GDN
 AP with para Na+ channels and K channels
 identified
shaker potassium channels
 differentiate sh from slo
 sh
– voltage activated K channel
 slo - Ca activated K channel
Excitation of GDN
zap head
 Visual
flash light
+benzaldehyde
Fly eye
Visual input to GDN
 Cobalt fill of GDN in Musca lobular cells
probably electrically
coupled to GDN
Mechanosensory input
antennal endings
GDN (PDB segment)
Habituation of jump response
dunce (phosphodiesterase) & rutabaga (adenyl cyclase)
PSI
 Relay between GDN and ?
 drives
5 DLM
motoneurons
 failure
occurs
separately
 Amplifier ?
Summary
 thoracic muscles, very energetically
demanding
 muscle and motoneuron designed for speed
 GDN circuit designed for speed and
robustness
Development
 GDN & TDTmn
born during
embryogenesis
 Connect during
pupation
Key steps
 GDN neurite outgrowth
 Axon pathfinding (larval stages—24 h APF)
 Target recognition and initial synapse
formation (24–55 h APF)
 meet
TDTmn
 bend
 Synapse stabilization and maintenance (55–
100 h APF)
 So what are the Molecular regulators of
growth
bendless
 Giant axon stops
and does not bend
 Part of
ubiqutination
system for
degrading proteins
 This degrades
signal saying “go”
Semaphorin-1a
 Regulates neurite
outgrowth
 No
sema-1a GDN
axon goes to retina
(50%)
 Regulates bend
 No
sema-1a GDN
axon does not bend
(50%)
 May be the protein
bendless degrades
Target of sema-1a
 Plexins ?
 Which
signal
via Rac, a
GTPase
Too much rac
rac blocked
Summary
 thoracic muscles, very energetically
demanding
 muscle and motoneuron designed for speed
 GDN circuit designed for speed and
robustness
 Identification of signalling molecules
controlling neuronal growth & synapses
Jumping as a test for disease
 Epilepsy
Mutants hyperexcitable followed
by paralysis
eas
+/+
eas
prior
after
bang
Flies as genetic models
 Parkinsonism, Alzheimer, Fragile X…
 Behaviour, anatomy, physiology, cell
biology well known
 Screen for modifiers
Summary
 thoracic muscles, very energetically
demanding
 muscle and motoneuron designed for speed
 GDN circuit designed for speed and
robustness
 Identification of signalling molecules
controlling neuronal growth & synapses
 System for physiological mutant analysis