Download Chapter 8 - s3.amazonaws.com

Chapter 8
Muscular System
Introduction
• Three types of muscles:
–Skeletal
–Smooth
–Cardiac
Structures of Skeletal Muscle
• Tissues present in skeletal muscle
– Muscle, nervous, connective (including
blood)
• Skeletal muscle is held in place by layers of
fibrous connective tissue called fascia
*fascia covers the muscle
Structures of Skeletal Muscle
• Fascia extends beyond the end of a skeletal
muscle to form a cord like tendon (muscle to
bone)
• When connective tissues extend beyond the
muscle to form a sheet-like structure, it is
called an aponeuroses
– Attach to bone or to adjacent muscles
Structures of Skeletal Muscle
• Fascicles are bundles of skeletal muscle fibers
• The connective tissue that covers each muscle
fiber within a fascicle is the endomysium
*the muscles are enclosed and separated into
compartments by epimysium and perimysium
(figure 8.1)
*blood vessels and nerves pass through layers
Analogy Time!
• Pretend you are going to play a joke on someone
and give them 100 pencils. The pencils will
represent muscle fibers. First you wrap each
individual pencil in tissue paper (dense tissue
paper of course!). This would be endomysium.
Then you take about 10 pencils in a bundle (a
fascicle) and wrap them in paper (Perimysium).
Then you take all the bundles and wrap them in
gift wrap (epimysium). But you are going to mail
this joke, so you also have to wrap it in brown
paper representing the fascia.
Skeletal Muscle Fiber
• Single muscle fiber
– Single cell, thin, elongated, contracts
– Sarcoplasm (cytoplasm) contains
–Many nuclei and mitochondria
–Myofibrils (parallel)
Skeletal Muscle Fiber
• Make note of this!
• Myofibrils
– Fundamental role in contraction
– 2 kinds of protein filament
• Thin – actin
• Thick – myosin
Skeletal Muscle Fiber
• What are sarcomeres? (figure 8.3)
– Functional units of muscle contractions
– 1st are light bands of actin filaments which are
attached to Z lines.
– 2nd are A bands which contain myosin filaments overlap actin filaments.
– The segment of a myofibril from one Z line to the
next Z line is known as a sarcomere
– Myofibrils are sarcomeres joined end to end
Skeletal Muscle Fibers
• The network of membranous channels in the
cytoplasm of muscle fibers is the sarcoplasmic
reticulum. A second set of channels is the
tranverse tubules which extend inward from
the fibers membrane.
• These channels activate muscle contraction
when the fiber is stimulated.
Questions to Answer
• What is tendinitis?
• What causes two of the most common forms
of muscular dystrophy?
• What causes muscle strain?
– What is the difference in a mild form and a severe
form?
*Write your answers on a piece of scrap paper
Labeling
• Part D of “Structure of a Skeletal Muscle”
Neuromuscular Junction
• Write these notes below “D” on page 58
• Motor neurons – neurons that control
effectors
• Synapse – functional connection between a
motor neuron and a skeletal muscle fiber
• Muscle fibers and motor neurons not directly
connected – a gap between them called
synaptic cleft
Neuromuscular Junction
• Neurotransmitters – chemicals released by the
neurons to allow communication with the
cells (tell fibers when to move)
• Neuromuscular Junction – connection
between motor neuron and muscle fiber
Neuromuscular Junction
• End of Motor Neuron – rich in mitochondria
and synaptic vesicles (store neurotransmitters)
• Motor end plate – muscle fiber membrane is
folded and contains many nuclei and
mitochondria
• Nerve impulse  end of motor neuron 
release neurotransmitters  motor end plate
 muscle contraction!
Skeletal Muscle Contraction
“Sliding Filament Theory”
• Roles of Actin and Myosin
– Actin - have a binding site for the myosin
cross bridges
– Myosin - have cross bridges that “pull” actin
for contraction
*Part B is answered by notes on page 58
Skeletal Muscle Contraction
“Sliding Filament Theory”
• Use highlighter and Figure 8.8 printout to
highlight key steps
• The sliding filament model gets its name from
the way the sarcomeres shorten
• The filaments do not change, they slide past
one another
– Actin slides toward the center of the sarcomere
from both ends
Skeletal Muscle Contraction
“Sliding Filament Theory”
• Acetylcholine (neurotransmitter) and Calcium
ions (Ca+)
Nerve impulse  motor neuron  releases
acetylcholine  diffuses to muscle fiber  causes
muscle impulse  allows diffusion of Ca+ into
muscle fiber  binding sites open  muscle
contraction begins
Skeletal Muscle Contraction
“Sliding Filament Theory”
• What are cross bridges?
–formed when the projecting parts of
the myosin filament that will occupy a
binding site on the actin filament and
pull
Skeletal Muscle Contraction
“Sliding Filament Theory”
• The action of acetylcholine is halted by the
enzyme acetylcholinesterase
• The enzyme decomposes the
neurotransmitter
Skeletal Muscle Contraction
• Review Handout
– Write on own sheet of paper
– Will finish in class tomorrow
– Worth 20 points
Skeletal Muscle Contraction
• How does ATP supply energy for muscle
contraction?
– ATP = stored energy
– ADP + P = released energy
– What do these equations mean?
Skeletal Muscle Contraction
• How does creatine phosphate supply energy
for muscle contraction?
– Stores energy generated by the
mitochondria much like ATP
– 4 to 6 times more abundant than ATP
– Energy is transferred to ADP molecules,
converting them back to ATP
Skeletal Muscle Contraction
• What happens when creatine phosphate is
exhausted due to heavy work? (think back to
Biology)
• How is commercially produced creatine used?
Skeletal Muscle Contraction
• What substance in muscle seems able to store
oxygen temporarily?
– Myoglobin, a pigment, is synthesized in muscle
cells and imparts the reddish-brown color of
skeletal muscle tissue
– It is able to combine loosely with oxygen, allowing
temporary storage
*hemoglobin in red blood cells acts in the same way
Skeletal Muscle Contraction
• Why is oxygen necessary for muscle
contraction?
– Cellular respiration of glucose, which supplies the
energy needed for a sufficient amount of ATP
– Is this process aerobic or anaerobic?
Skeletal Muscle Contraction
• How does the muscle continue to contract in
the absence of oxygen?
– Anaerobic respiration
– Glucose  pyruvic acid  lactic acid
– Yields a much smaller amount of energy than
aerobic respiration
– Glucose can be synthesized from lactic acid in the
liver
Skeletal Muscle Contraction
• When do you experience oxygen debt?
– Lactic acid accumulation in the liver
– Oxygen debt =
amt. of oxygen liver cells require to convert lactic
acid into glucose + amt. of oxygen muscle cells
require to restore ATP and creatine phosphate
*repayment could take several hours
*training can help increase your bodies ability to
repay its oxygen debt by increasing glycolytic
enzmes, mitochondria, and capillaries
Skeletal Muscle Contractions
• What is meant by muscle fatigue?
– A muscle has lost its ability to contract
• What causes it?
– Interruption in the blood supply
– Accumulation of lactic acid (most likely)
• Lowers pH, fibers no longer respond to stimulation
– Cramps are likely due to a lack of ATP
Skeletal Muscle Contractions
• Less than half the energy released by cellular
respiration is available for metabolic
processes. The rest is lost as heat.
Steroids and Athletes
• Read “Topic of Interest” page 186
• Class discussion on use of steroids and
creatine