Download 7 - Muscle_Structure

Properties of Muscle Fibers
The Neuromuscular System
▪Irritability
▪Contractibility
▪Elasticity
▪Extensibility
▪Conductivity
The Neuromuscular System
The Motor Unit
▪a complex linkage of muscles and nerves
▸signals sent and received by:
–CNS Central Nervous System
– brain and spinal cord
–PNS Peripheral Nervous System
– Motor and Sensory nerves
– Autonomic and Somatic Systems
– Proprioreceptors
– ex. Golgi Tendon Organs
– ex. Muscle Spindle
▪ definition - a
nerve (neuron)
and the muscles
fibres it activates
spinal
cord
▪ a single nerve impulse
resulting in contraction is
called a muscular
spinal
twitch
cord
▪ muscles with fine motor
control fire less fibers
per neuron
- ex. eye has 1 neuron for 3
fibers vs leg muscles at 1
nerve for 300-800 fibers
▪The All or None
Principle:
▸when a nerve fires,
all fibres are
activated or none
–ie whether it is 10 or
800 fibres per 1
motor unit
▪ a motor nerve ends at
the neuromuscular
junction
▪ a chemical signal sends
neuron
transmitters across
the synaptic cleft
which is then detected
by receptors
Types of Muscle
spinal
cord
Smooth Muscle
Types of Muscle Tissue
Smooth
▪
▪
▪
▪
▪
Cardiac Muscle
cells are spindle shaped
no striation, single nucleus
cells are bound together to form large sheets
controlled by autonomic nervous system
e.g. intestinal wall , middle layer of blood vessels
Types of Muscle Tissue
Cardiac
▪ shorter cells, branch frequently
▪ striation, single nucleus
▪ structure allow for a rapid spreading of electrical
signal
▪ produces powerful contraction to push blood
▪ autonomic control
▪ e.g. only found in the heart
Skeletal Muscle
Types of Muscle Tissue
Skeletal
▪
▪
▪
▪
cells (called fibres) are long cylindrical
striation, multi-nucleated
surrounded by a membrane called sarcolemma
conscious control
Skeletal Fibre Types
Type I
▪“red” or slow twitch
▪usually found in postural
muscles
▪myoglobin - protein that helps
transport oxygen in cell
▪e.g. soleus (deep muscle in calf)
pg.90
Skeletal Fibre Types
Skeletal Fibre Types
Type II
▪“white” or fast twitch
▪explosive movement
▪e.g. gastrocnemius (superficial
muscle of calf)
▪another way of naming fiber types:
‣SO - slow oxidative
‣FOG - fast oxidative/glycolytic
‣FG - fast glycolytic
Structure of a Skeletal Muscle
Myosin cross
bridges
Z bands
Actin
- thin filament
Myosin
- thick filament
Myofibril
Column of
Myofibrils
Sarcolemma
Muslce Fibre
(endomysium)
Fasciculi
- abundle of fibres
(perimysium)
Skeletal Muscle
(epimysium)
1 Straw = 1 Myofbril
3 Straws = 1 Muscle Fibre Clear tape = sarcolema
Scotch tape = endomysium
9 Straws = 1 Fascicle
Athletic tape = Perimysium
27 Straws = 1 Muscle
Paper Towel = Epimysium
Myosin
Actin
Sliding Filament Theory
▪ Step 1 - message from brain
▪ Step 2 - which travels down
spinal cord and PNS
The Nervous System
Sliding Filament Theory
▪ Step 3 - to axon of
motor neuron to the
synaptic terminal
▪ Step 4 - across the
terminal via
acetylcholine to
sarcolemma by the ttubules
Skeletal Muscle and Sarcoplasmic Reticulum
▪ Step 5 - calcium is
then released from
terminal cisterna of
sarcoplasmic reticulum
The Troponin Complex and Tropomyosin
Sliding Filament Theory (con’t)
▪Step 6 - calcium attaches to binding sites on
troponin complex
▪Step 7 - tropomyosin moves to expose binding
sites for myosin on actin filaments
▪Step 8 - myosin attaches themselves to actin
Sliding Filament Theory (con’t)
▪Step 9 - ATP broken down by ATPase, causing the
power stroke - a change in the shape of myosin
cross-bridge pull the actin filaments together
▪Step 10 - when signal stops, calcium is put back in
S.R. , troponin and tropomyosin, again cover binding
sites of actin
3. Cross bridge
release when new
ATP attaches
4. ATP splits into
ADP and P, and
myosin changes
shape
A review
of the
process
from the
moment
the signal
gets to
terminal
1. Crossbridge
attach to actin
2. Power Stroke ADP and P are
released, and
myosin moves
Sliding
The Strength
FilamentCurve
Theory
YouTube - ‪‫‏‬sliding filament theory‬
- the relationship between
the length of the muscle and
the force that it can produce
- there is an optimal range of
myosin and actin connection