Download Unit 7 muscle notes

Muscles:
•
Functions
1. movement
2. Heat production
3. Posture
maintenance
•
Types:
1. Skeletal
2. Cardiac
3. smooth
Functional characteristics
1. Excitability: ability to receive and
respond to stimulus ( neural or hormonal)
2. Contractility: ability to forcibly shorten in
response to stimulus
3. Extensibility: ability to stretch or extend
when pulled
4. Elasticity: ability to return to original
length after being stretched ( contracting)
Skeletal Muscles
• Voluntary, striated, involved in movement
and posture ( multinucleated)
Cardiac Muscle
• Striated, involuntary, single central nucleus
• Fibers are branched, weave together
forming a network
• Individual fibers connected with each other
at the intercalated discs ( these discs
not only tie the fibers together for strength,
but also conduct impulses from one fiber
to another
Smooth Muscle
• Visceral muscle
• Not striated, involuntary, large singel
nucleus
• Found in the walls of organs, iris and
arrector pili muscles
• Does not contract rapidly, but contracts the
longest
Skeletal muscles
• Make up 40% of body weight and consists
of over 600 muscles.
• The difference in strength, endurance, and
coordination is a function of both heredity
and conditioning.
Skeletal muscle
• Are usually long and narrow
• Span a joint
• Are attached to bone at either end by a
tendon
•
Divided into 3 parts:
•
1. origin: stationary part
•
2. insertion: movable end
•
3. belly: middle fat part
Gross Anatomy of skeletal muscles
• Fascia: layers of fibrous C.T. that covers
and separates muscles
• Superficial fascia: joins skin t muscle and
contains much fat ( aereolar c.t.)
• Deep fascia: joins or binds adjacent
muscles and individual muscle fibers
Connective Tissue Wrappings of
skeletal Muscles:
• Endomysium: c.t. that holds muscle fibers
together
• Muscle fiber: same a s a muscle cell
• Tendon: attaches muscle to bone (ligament:
bone to bone)
• Perimysium: c.t that surrounds the groups of
muscle fibers
• Fascicle: group of muscle fibers
• Epimysium: c.t. that holds groups of muslce
fibers together
Microscopic Anatomy
• Fiber: muscle cell
• Sarcolemma: the fibers plasma
membrane
• Sarcoplasm: cytoplasm of muscle cell
• Sarcoplasmic reticulum: a tubular
network inside a cell which surrounds and
connects all the individual myofibrils
Microscopic Anatomy
• Transverse tubules: run transverse
through fibers connecting the
sarcoplasmic reticulum with the
sarcolemma
• Inside the fibers (cells) are many small
myofibrils which are parallel groupings of
2 types of proteins called myofilaments
2 Types of myofilaments found in a
myofibril
• 1. Thin myofilaments made mostly of Actin
(protein)
• 2. Thick myofilaments made mostly of myosin
(protein)
• These 2 myofilaments are arranged into
functional units called sarcomeres
• A myofibril is a chain of sarcomere
• The sarcomeres are separated from each other
by a zone of dense material called a z-line
• The z-line is the boundary of the sarcomere
where actin molecules are attached at each end
Muscle contraction
• During a contraction, the actin
myofilaments are pulled toward the center
of the sarcomere, this pulls the z lines
closer to each other and thus sortens the
sarcomere
• The amount of overlap between the actin
and myosin changes and is seen as
striations on the muscle
Mechanics of a Muscle contraction
skeletal muscles contract by the following steps
1. A motor nerve signals the muscle. Some
of the nuerons in the nerve develop
electrical impulses which signal some
fibers in the muscle. Each axon secretes
a neurotransmitter ( chemical signal)
called acetylchoine at the synapse
(motor end plate) between the neuron
and some muscle fibers. This signal
excites each muscle cell.
Mechanics of a Muscle contraction
skeletal muscles contract by the following steps
2. An electrical signal spreads out along the
sarcolemma ( cell membrane) of each muscle
cell that is signaled.
3. This signal continues transversely int the
sarcoplasm of each muscle cell along the
membranes of the T tubule
4. The T tubule joins the sarcoplasmic reticulum in
the sarcoplasm. The signal spreads from T
tubules to tubular S. R. releasing calcium ion
Mechanics of a Muscle contraction
skeletal muscles contract by the following steps
5. The release of calcium from the S. R. blocks
the action of troponin ( a protein in
myofibriles). Troponin normally inhibits the
interaction of actin and myosin
6. With troponin inhibited, actin and myosin can
interact. Cross bridges on the myosin slide the
actin molecule toward the center of the
sarcomere. As the actin molecules attached to
the z line…. This shortens the sarcomere
Mechanics of a Muscle contraction
skeletal muscles contract by the following steps
7. Hydrolysis of ATP in the cells, into ADP and
phosphate releases energy to drive the sliding
filaments. ATP is rebuilt from an energystorage compound creating phosphate
8. If enough sarcomeres, shorten the myofibriles
shortn. If enough mofibrils shorten, then the
fibers shorten. If enough fibers shorten, then
the muscle contracts
9. Each muscle responds by an all or non law (
with the force of contraction dependent on the
% of cells that are active)
Patterns of muscle contraction
• Tonus : muscle tone
• Tension: force produced by a whole muscle when it
contracts
• Load: resistance. Force exerted on a muscle by a
weight
• Isometic contraction: response in which a muscle does
not contract enough to produce motion ex muscle in
shoulder act isometrically if arm is pushed against an
immovable wall
• Isotonic exercise: better aerobically and produces
endurance
• Isometric exercise builds muscle size and strength
• You should do both
Naming of skeletal muscles
•
1.
2.
3.
4.
5.
6.
7.
8.
Muscles are named according to the following
characteristics:
Location: ex tibialis anterior
Number of attachments: ex biceps brachii
Direction of fibers: ex rectus abdominuis ( rectus =
straight)
Shape/size: ex deltoid ( triangle)
Action: ex extensor muscles
Location of origin and insertion: ex sternohyoid
Number of origins: quadriceps femoris
A muscle name can reveal 2 of these characteristics
Muscle disorders:
• Can be due to infection/damage to the
muscle or to its motor neuron
Muscular dystrophy
• Genetic causation
• Barely understood
• Involves progressive degeneration of
individual skeletal muscle fibers
• Braces and exercise help post-pone
inevitable
• Death occurs due to respiratory failure
Muscular dystrophy
Myasthenia gravis
• Skeletal muscle becomes weak and easily
fatigued due to motor endplate
abnormality
• The receptor for neural impulses are
blocked or destroyed
• Is an autoimmune disease that sometimes
progresses to paralysis or death
Myasthenia gravis
Hernia
• Tear or separation in a muscle wall which
allows part of the organ to protrude
out…usually the abdominal wall or
diaphragm
• Spasm: contractions of a muscle, if very
small are called tics, if painful they are
called cramps
• Usually due to inflammation or water ion
imbalances
Reasons for muscle fatigue
• Strenuous activity with and Cell
respiration going anaerobic, lactic acid
build up
• Poor nutrition
• Poor delivery system: respiratory or
cardiovascular
• Unexplained neural disorder (rare)