Slide 1
Lecture 2 — Outline
Excitable Tissues
Stanfield & Germann 1.2
• Muscle — structure,
innervation & function
– Smooth
– Cardiac
– Skeletal
• Motor endplate
• Motor unit
• Muscle-fibre types
• Nervous Tissue
– Cells
– Fibres.
Dr Alan Tuffery
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Slide 2
Muscle
• Contraction
• Force generation
– Movement, posture
• NB generates heat.
From G&S Fig. 1.2. (Not to scale)
G&S Fig.
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Slide 3
Muscle —three types
a) Skeletal muscle
Fibres,
striations,
peripheral
nuclei
b) Cardiac muscle
______
Fibres
(branching),
striations,
central
nuclei
______
c) Smooth muscle
Dr Alan Tuffery
Passmore & Robson (1968). Fig.15.1
Cells,
central
nuclei
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Slide 4
Smooth muscle
• Small cells, little force
• Graded contraction
• Contraction spreads
via gap junctions
• ‘Incomplete’ innervation
• Slow contractions
• ‘tone’
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Slide 5
Smooth muscle — innervation
• Multi-unit
– Each cell innervated
– Variable force
– e.g. airways, large
arteries
• Single-unit
– Greater diffusion
distance
– Cells coupled
– Synchronous contraction
– e.g. gut, uterus.
Germann & Stanfield Fig. 1.29
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Slide 6
Smooth muscle (TS Duodenum)
Outer
Plane of section of fibres:TS
Orientation wrt gut: longitudinal
Inner
Plane of section of fibres:
longitudinal
Orientation wrt gut: circular
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Slide 7
Cardiac muscle
• Function
– All-or-none (‘twitch’)
– Highly resistant to
fatigue
SA Node
AV Node
• Innervation
– Pacemaker cells
– Electrical conduction
(purkinje fibres).
Dr Alan Tuffery
Purkinje fibres
Germann & Stanfield Fig. 14.9
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Slide 8
Cardiac Muscle
G&S Fig. 14.27
• Continuous, rhythmic
activity
• Electrical signal
propagated throughout
heart — via
– gap junctions
– specialised muscle cells
• Purkinje fibres.
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Slide 9
Skeletal Muscle
G&S Fig. 14.27
G&S Fig. 13.2
• The most contractile
apparatus (actin and myosin)
– Striations
– Most powerful
contraction
• Single innervation
– i.e. one nerve ending
per fibre
• All-or-none contraction.
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Slide 10
Skeletal muscle — striations
Striations due to
alignment of filaments
of myofibrils
G&S Fig. 13.3
Review sliding filament
theory.
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Slide 11
Motor endplate (a synapse)
Synaptic
vesicles
• Muscle surface specialised
– Junctional folds.
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Slide 12
Generalised synapse
Key features
• Presynaptic side
separated by a gap from
post-synaptic side
• Signalling by chemical
neurotransmitter
• Most synapses are
nerve-nerve.
Junqueira & Carneiro (2003)
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Slide 13
Motor Unit
• All the muscle fibres
innervated by a single
neurone
• All the fibres are of the
same type
• All fibres of a motor unit will
contract together.
G&S Fig. 12.14
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Slide 14
Muscle-fibre types (SDH)
SDH — mitochondrial
enzyme (activity)
G&S Fig. 13.25
Dark: Type I
Light: Type II
Mosaic arrangement
What determines the
properties of the
muscle fibres?
Neurone.
Note higher density of dark-stained capillaries around Type I fibres
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Slide 15
mATPase activity staining
Type II Fibres
• High mATPase activity
• Fuel source:
endogenous highenergy phosphates
• Rapid contraction
• Fatigue easily.
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Slide 16
Muscle-fibre types (properties)
Type I
Type II
mATPase activity
(anaerobic)
low
high
Oxidative capacity
(aerobic)
high
low
Speed of contraction
slow
fast
Resistance to fatigue
high
low
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Slide 17
Muscle-fibre type-grouping
Type I grouping
Mechanism:
Denervation of
Type II fibres and
re-innervation by
adjacent ‘Type I’
axons.
‘Collateral reinnervation’
Normal mosaic replaced by group
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Slide 18
Muscle-fibre type-grouping
Consequences?
• Fibre-type composition of the
muscle?
• Type I dominate
• Motor units?
• Increased size…
• Loss of fine control.
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Slide 19
Neurone/Nerve fibre
• Cells — neurones
 Cell body
 Processes
Axons — outgoing
Dendrites — incoming
• Distinguish:
 anatomical nerve
(named)
 nerve
branches/bundles
 nerve axon
Sherwood Fig. 4.14
Dr Alan Tuffery
 nerve fibre
(myelinated).
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Slide 20
Neurone
Integrating Function
• Many inputs
• From neurones/receptors
• Many outputs (dendrites)
• to neurones
• Larger process — axon
• with myelin sheath
• to effectors
(muscle, glands etc).
Sherwood Fig. 4-17
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Slide 21
Dorsal root ganglion (H&E)
H&E (left)
Nerve cells
Large, pale nuclei,
dark nucleoli,
blue granules
Glia/satellite cells
Neurone (Methylene Blue)
Nerve fibres
Pale (lipid)
Axon stained
pink/purple
Dr Alan Tuffery
Large, pale nucleus,
prominent nucleolus,
granules (ribosomes),
processes.
Small nuclei — glial cells.
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Slide 22
Nerve fibres (H&E vs OsO4)
H&E (no lipid)
Stained: axon,
endoneurium
OsO4 (lipid only)
Stained: myelin sheath.
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