Download Muscular System

Muscular System
Functions
Voluntary Movement
Maintain Posture
Maintains normal body temperature
Generates 85% of body heat
Compensates for cold by
shivering
1
2
Skeletal
Skeletal
4
3
Cardiac
Smooth
Muscle Cell Characteristics
Skeletal
Voluntary
Attached to bones
Cylindrical
Striated
Multi-nucleated
Nuclei near
membrane
Tight Junctions
Form Motor Units
Cardiac
Involuntary
Heart
Cylindrical/Branched
Striated
Single Nucleus
Central Nucleus
Gap Junctions –
intercalated discs
Figure 8 shaped
Pacemaker
Muscle Cell Characteristics
Smooth Muscle
Involuntary
Surrounding walls
of hollow organs
and glands
Spindle shaped
Not striated
Single nucleus
Central nucleus
Gap Junctions
Single and Multiunit
Muscle Cell Anatomy
Myofiber – muscle cell
Sarcolemma – specialized cell
membrane of muscle cell (actively
transports Na+ and K+
Sarcoplasm – cytoplasm of muscle –
has most mitochondria of any cell
Sarcoplasmic Reticulum – specialized
SER for storing and releasing and
actively transporting Ca++
Muscle Cell Anatomy Cont.
Transverse Tubules – special
passages for Na+ that pass over SR
Myofibrils – cylindrical organelles
that contain the myofilaments
needed for muscle contraction
Myofilaments – protein fibers
Thick filaments – myosin
Thin filaments – actin
Sarcomere – functional unit of
contraction – part of a myofibril
Sarcomere Anatomy
Z Line – membrane that marks the end of
the sarcomere – actin is attached here
A Band – Dark part of sarcomere –
contain myosin (some parts have
overlapping actin)
H zone – very center of A band – a little
lighter than rest of A band since only
contain myosin – no overlapping actin
M line – membrane in the center of the
sarcomere
I band – at edges of sarcomere – light
band – contains only actin
I band disappears during contraction and
so does the H zone as actin is pulled in
over myosin
Muscle Anatomy
Fiber – cell
Endomysium – fibrous sheath around
each muscle cell or fiber
Fasicle – bundle of muscle cells surround
by the perimysium fibrous sheath
Muscle – bundle of fasicles covered in the
epimysium
Tendon – fibrous proteins attaching the
muscle to the bone
MUSCLE INNERVATION
Motor Unit – One nerve and all of the
muscle cells or fibers that it innervates
All of None Principle – when you contract a
motor unit, ever fiber or cell in the motor
unit contracts and each contracts to the
fullest extent
How can you get different strengths of
contraction in the same muscle???
# OF MOTOR UNIT ACTIVATE!
Neuromuscular Junction
Sarcolemma – cell membrane
Motor end plate – specialized part of
sarcolemma with neurotransmitter
receptors – part where muscle membrane
meets the nerve
Axon – cytoplasmic extension of the nerve
cell that meets the muscle
Acetylcholine (Ach) – neurotransmitter
that sets off contraction
Synaptic Cleft – space in between axon
and motor end plate where Ach is dumped
T-Tubule – when Ach binds to receptors on
motor end plate – opens T-tubule channels
and allows Na+ to flow in
Components of Muscle Contraction
Myosin – thick filament that pulls actin in
to cause contraction
Actin – thin filament/has binding sites for
myosin
Tropomyosin – a rope like protein that
wraps around actin covering the active
sites on actin so that myosin can’t bind to
the actin
Troponin – small proteins that attach to
the tropomyosin– has a Ca++ binding site
– when Ca++ binds it changes shape and
in turn causes the tropomyosin to swivel
off of the active sites on actin
Contraction
Ach is released from the axon into
the synaptic cleft
Ach binds to receptors on the motor
end plate
This opens the T tubules – Na+ flow
in through the T-tubules
Steps of Contraction
Na+ flowing in through the T-tubules
causes channels in SR to open
releasing Ca++
Ca++ attaches to troponin causing it
to change shape
The troponin shape change causes
the tropomyosin to swivel off of the
actin active sites
Activated myosin heads pop up and
grab on to actin and swivel forward
(power stroke) dragging the actin
inward
Contraction
Many myosin heads are popping up
and grabbing on all at once – they
are staggered so that some are
always attached
This continues as long as there is
Calcium present and ATP to power
the process (usually don’t run out of
the ATP)
How to Stop a Normal Contraction
This is not exhaustion – just normal
stopping
Destroy the Ach
Pump out the Na+
Pump all of the Ca++ back into the
SR
Motions Muscles Make
Flexion – decreasing angle in the
joint – bringing bones closer together
Extension – increasing the angle in
the joint – straightening the joint
Hyperextension – straightening more
than 1800
Abduction – movement of a limb
away from the midline of the body
Adduction – movement of a limb
toward the midline
Motions Continued
Rotation – movement of a bone
around its axis without medial or
lateral displacement
Circumduction – movement of distal
portion around stationary proximal
portion of the bone
Pronation – turning the palms down
(special kind of rotation)
Supination – turning the palms up
(also rotation)
Motions Continued
Inversion – turning the sole of the
foot in
Eversion – turning the sole of the
foot out
Dorsiflexion – pulling the toes up
toward the tibia
Plantar Flexion – pointing toes –
pushing them downward
Muscle Twitch
A single muscle contraction
Latent period – Ach is released, Na+
rushes in, Ca++ is released, active sites
are uncovered on actin, myosin binds to
actin
Contraction period – myosin is pulling
actin inward
Relaxation period – Ca++ is being sucked
up by the SR, tropomyosin is recovering
active sites on actin, myosin can no longer
bind to actin, Na+ is also pumped out and
Ach is destroyed in the synaptic cleft
Energy Usage
Creatine phosphate – enzyme
transfers phosphate from creatine to
ADP – make ATP quickly for a few
seconds
Glycolysis/Fermentation – only make
2 ATP/glucose – ineffective but don’t
need oxygen
Aerobic Cellular Respiration – make
38 ATP/glucose – only efficient way
to make enough ATP for sustained
muscle contraction
Aerobic Respiration
Needs a lot of oxygen to burn glucose this
way and make ATP
Myoglobin – red protein in muscle that
binds oxygen and stores it
Why need oxygen?
– Make ATP aerobically
– Replenish creatine phosphate
– Reload myoglobin
Oxygen debt – can’t get enough , can’t
make enough ATP – feel fatigued,
breathe heavily
Fast vs. Slow Twitch Muscles
Fast Twitch Muscles
– Contract faster
– White/Little myoglobin
– Bigger SR/Faster Ca++ release
Slow Twitch Muscles
– Take longer to contract but can sustain
the contraction
– Red/Lots of myoglobin
– More mitochondria
Isotonic Muscle Contractions – muscle shortens –
force of muscle is greater than the load
Isometric – muscle doesn’t shorten – force of
load > force of muscle
Muscle Tone – some motor units are contracted
but not enough to move the muscle
Hypertrophy – muscle cells increase in size by
increasing the amount of actin and myosin, SR,
and mitochondria due to stress on muscle
Atrophy – shrinkage of a muscle because each
muscle cell gets smaller – loses actin and myosin
due to disuse
Rigor Mortis – after death, calcium leaks out of
SR and the troponin/tropomyosin complex is
moved from actin active sites – myosin binds but
not ATP is being produced to unattach it so
muscle becomes rigid – as tissue starts to break
down after a day, it goes away
Cardiac Muscle
No neurons innervating cells, no motor units –
one pacemaker and then conductive protein
fibers to carry the impulse to other cardiac cells
Gap junctions (intercalated discs) cause ions to
flow from cell to cell to get a coordinated
contraction
Impulse starts in atria and then travels through
ventricles so atria contract and then ventricles
The cardiac muscle cells have the same
arrangement of actin and myosin (striations) but
only have one nucleus and have bigger
mitochondria and only 1 T-Tubule
Contracts slower – takes more time for calcium to
diffuse
Contracts about 70 times/min.
Long Refractory period so there is no tetanus
even when the hear is beating fast
Smooth Muscle
Contracts slower and longer (takes longer
for Ca++ to diffuse and to be pumped
back into the SR)
Actin and myosin different from cardiac
and skeletal – actin is attached to dense
bodies and membrane but myosin still
pulls it in – just pulls in in every direction
No motor units – instead most are single
unit junctions – a nerve synapses with one
smooth muscle cell and the impulse
spreads thru gap junctions so it all
contracts in a wave
In pupil – multi-unit – each smooth
muscle cell has its own nerve