Download Muscular System

Muscular System
3 Types of Muscle Tissue
Location
Cell shape
&
appearance
SKELETAL
Attached to bones via
tendons
CARDIAC
Forms walls of heart
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Single, long cylindrical
cells arranged in
bundles
Multinucleated cells
Striated due to
arrangement of protein
filaments
Regulation
of
contraction
Voluntary – subject to
conscious control via
nervous system
Function(s)
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Produces movement
Maintains posture and
provides support
Stabilizes joints
Body heat production
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Branching chains of
cylindrical cells
Uninucleated cells
Striated
Fibers arranged in
spiral bundles joined
by intercalated discs
Involuntary – controlled by
heart ‘pacemaker’,
nervous and endocrine
system
 Changes size & shape
of organ space to
TRANSPORT
MATERIALS through
the body – pushing
blood through vessels
SMOOTH
In walls of hollow visceral
organs – stomach,
bladder, respiratory
passages, etc
 Spindle shaped cells
 muscle arranged in
longitudinal and
circular layers
 Uninucleated cells
 No striations
Involuntary – controlled by
nervous and endocrine
system

Changes size & shape
of organ space to
TRANSPORT
MATERIALS through
the body
PROPERTIES of muscular tissue:
 Irritability – muscle responds to electrical stimulation from nerve impulses (electrical excitability)
 Contractility – muscle responds to stimuli by contracting or shortening
 Extensibility – during relaxation, fibers stretch beyond its resting length
 Elasticity – fibers recoil to their original resting length
Microscopic Anatomy of Skeletal Muscle
Connective tissue that covers fascicle
Epimysium blends
into tendons or
into aponeuroses
which attach
muscles indirectly
to bones, cartilage
or c.t. membranes
muscle cell
bundle of fibers
Connective tissue
that covers entire
muscle
Muscle Fiber -
Connective tissue that
covers muscle fiber
Cell Membrane

Myofibril – organelle that
contains contracting units
called sarcomeres

Sarcomeres are made up of
an A band and I band which
contain myofilaments (actin
& myosin).

Myosin – thick protein
myofilament that contains
ATPase enzyme to generate
power for muscle activity

Actin – thin protein
myofilament that is anchored
to the Z disc
Sliding Filament Theory –
As the myofilaments slide, the
Z lines are brought closer
together. The A bands remain
the same during contraction,
but the H and I bands narrow
progressively and eventually
disappear.
Muscle Contraction
A nerve serving a muscle fiber has both motor and sensory neurons. Each motor neuron has an
axon that extends from the Central Nervous System (CNS) to a group of muscle fibers. At the end of
the nerves axon are axon terminals containing vesicles filled with neurotransmitters such as Ach
(acetylcholine).
A neuromuscular junction is
composed of the axon terminals
forming a junction with the
sarcolemma of the muscle fiber.
1. The nerve impulse reaches the axon terminal causing the release of ACh into the synaptic cleft.
2. ACh diffuses across the synaptic cleft and binds to receptors on the sarcolemma.
3. The sarcolemma becomes temporarily permeable to sodium ions (Na+) & potassium ions (K+).
4. Na+ rush in the cell (depolarization) and K+ rushes out of the cell (repolarization). This influx of
positive ions generates an electric current called action potential which travels along the
sarcolemma.
o Once started, muscle cell contraction cannot be stopped. That is why this is often
called the “All-or-None” law of muscle contraction.
5. Action potential stimulates the Ca+ to be released from the Sarcoplasmic Reticulum.
6. Calcium attaches to binding sites on the Actin.
o Myosin heads form cross bridges (binds) to the
Actin and pull actin inward towards the H-Zone.
Energized by ATP, each cross
bridge attaches and detaches
several times during a contraction.
o As this process continues the Actin is completely
pulled into the H-Zone on both sides.
o The result is that the muscle is shortened/”contracted”
Sliding filament
theory
7. Action Potential ends & Calcium is reabsorbed by the Sarcoplasmic Reticulumn
8. Sodium Potassium Pump:
o moves Na/K back to their original location
o Active Transport b/c it requires energy
9. The muscle cell relaxes and lengthens.
All these steps occur in
thousandths of a second!
Contraction “Rules”
 “All-or-nothing” law muscle physiology applies to
the muscle cell and not the whole muscle. Muscles
cells must contract to its fullest extent when it is
Motor unit – one neuron and all the skeletal
muscle cells it stimulates. One nerve cell may
stimulate 100-150 muscle fibers. When a
nerve impulse travels through a motor unit all
the fibers will contract simultaneously to their
maximum.
stimulated adequately; it never partially contracts.
 The whole muscle reacts to stimuli with a graded response or different degrees of shortening.
Graded muscle contractions can be produced two ways: by changing the frequency of muscle
stimulation or the number of muscle cells being stimulated at one time.
Response to Rapid Stimulation
Tetanus (normal)
o When the muscle is stimulated so rapidly that no evidence of relaxation is seen and the
contractions are completely smooth and sustained.
Muscle twitch (abnormal)
o Single, brief, jerky contraction; can indicate nervous system problems
Providing Energy for Muscle Contractions
As a muscle contracts, the bonds of ATP molecules are hydrolyzed to release the needed energy.
Muscles store very limited supplies of ATP – only 4-6 seconds’ worth. Because ATP is the only
energy source that can be used directly to power muscles, ATP must be regenerated continuously.
 Working muscles use three primary pathways for ATP regeneration.
1. Direct phosphorylation of ADP by creatine phosphate – using creatine to form ATP - supply is
only good for 15 seconds.
2. Aerobic respiration – series of pathways that use oxygen to break down glucose to form ATP
– 95% of energy comes from aerobic respiration.
3. Anaerobic respiration and lactic acid fermentation – breakdown of glucose w/o oxygen –
occurs when muscle activity is intense resulting in low oxygen and glucose levels.
Muscle Fatigue
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If we exercise our muscles strenuously for a
long period, muscle fatigue occurs. The
inability of muscle to contract even though it
is stimulated.
Causes:
o Oxygen debt – low O2 levels
o Lactic acid buildup
o Lack of ATP
Contraction Types
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Isotonic contractions: muscle shortens
and movement occurs
o
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Stimulation + contraction = movement
Isometric contractions: myofilaments
produce tension in muscles
o
Stimulation + no contraction = no
movement
Effects of Exercise on Muscles
Muscle Tone – a continuous partial contraction
 Muscle remains firm, healthy and constantly ready for action
 If nerve supply is destroyed, the muscle is no longer stimulated, it loses tone and becomes
paralyzed. The muscle becomes flaccid (soft/flabby) and begins to atrophy (waste away).
Types of exercise – regular exercise increases muscle size,
Muscle inactivity (due to a loss of nerve
supply, immobilization or whatever the
strength, and endurance.
cause) always leads to muscle weakness
1. Aerobic or endurance - results in stronger, more flexible
and atrophy. “Use it or lose it!”
muscles with greater resistance to fatigue
 does NOT cause muscle to increase in size
 overall metabolism is more efficient, improves digestion, enhances coordination
2. Resistance or Isometric - increase muscle size & strength due to enlargement of muscle fibers
Types of Body Movements – occurs when muscles contract across joints
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Flexion - movement that decrease angle of
joint and brings 2 bones closer together
Extension – movement that increases
angle of joint; Hyperextension – extension
>180o
Abduction – moving a limb away from the
midline of the body
Adduction – moving a limb toward the
midline of the body
Rotation – movement of a bone around its
longitudinal axis
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Circumduction – combination of flexion,
extension, abduction, adduction
Dorsiflexion – standing on your heels
Plantar flexion – standing on your toes
Inversion – turning sole medially
Eversion – turning the sole laterally
Supination – forearm rotates laterally so
that the palm faces anterior
Pronation - forearm rotates medially so the
palm faces posterior
Muscle Attachment
origin- attached to immovable or less movable bone
insertion- attached to movable bones
 during contraction the insertion moves toward the origin
Muscles can’t push – they can
only pull as they contract – so
most often body movements
are results of two or more
muscles acting together or
against each other.
Types of Muscles
Prime Mover- has major responsibility for causing a particular movement
Antagonist- opposes or reverses a movement
 When a prime mover is active, it antagonist is stretched and relaxed.
Synergist- helps primer movers by producing the same movement or by reducing undesirable
movements; stabilizes joint so movement is smooth
Fixators- specialized synergist that hold a bone still or stabilize the origin of a prime mover
Naming SKELETAL muscles
1. Direction of muscle fibers – rectus (straight) or
oblique (slant)
2. Relative size of muscle – maximus, minimus,
longus
3. Location of muscle – named for bone with which
they are associated
4. Number of origins – bicep (2 origins)
5. Location of muscles origin and insertion –
sternocleidomastoid muscle (sternum & clavicle)
6. Shape of muscle – deltoid (triangular)
7. Action of the muscle – flexor, extensor
Muscular Problems
Muscular Dystrophy – inherited muscle-destroying
disease that affects specific muscle groups. The
muscles enlarge due to fat and connective tissue
deposits, but the muscle fiber degenerate and atrophy.
Myasthenia gravis – disease involves a shortage of
acetylcholine receptors at the neuromuscular junction.
Autoimmune disease - antibodies destroy receptors.
The muscle cells are not stimulated properly and get
progressively weaker.
Gross Anatomy of Skeletal Muscles
Muscles
Masseter
Frontalis
Orbicularis oculi
Orbicularis oris
Sternocleidomastoid
Pectoralis Major
Intercostal muscles
Rectus abdominus
External obliques
Latissimus dorsi
Trapezius
Biceps brachi
Brachialis
Triceps brachi
Deltoid
Brachioradialis
Gluteus maximus
Gluteus minimus
Iliopsoas
Rectus femoris
Vastus Lateralis
Vastus medialis
Sartorius
Adductor longus
Gracilis
Hamstrings
Tibialis anterior
Soleus
Gastrocnemius
Fibularis longus
Head and
Neck
muscles
Trunk
muscles
Muscles
of the
upper limb
Muscles
of the
lower limb
Action
closes jaw
raises eyebrows
blinks and closes eye
closes and protrudes lips
flexes neck and rotates head
adducts and flexes the arm
raise and lower rib cage during respiration
flex the vertebral column
flex vertebral column and rotate/bend the truck
Extends and adducts the humerus
extends head and moves scapula
flexes forearm
lifts ulna as bicep lifts radius
extends elbow
abducts arm
synergist in flexion of forearm
extends hip
hip abductor and steadies pelvis during walking
flexes hip
extend knee
“Quads”
flexes thigh on hip
adducts thigh
adducts thigh
flex knee and extend hip
Dorsiflexes and inverts foot
Plantar flex foot
Plantar flexes foot and flexes knee
Plantar flex and evert foot