Download Muscles and Muscle Tissue

Muscles and Muscle Tissue
LAB 6
Muscle Overview
• Muscle tissue makes up nearly half the body
mass.
• The most distinguishing functional
characteristic of muscles is their ability to
transform chemical energy ATP into directed
mechanical energy
• The three types of muscle tissue are:
skeletal, cardiac, and smooth
• These types differ in structure, location,
function, and means of activation
MARTINI
PG 133
Muscle Similarities
• Skeletal and smooth muscle cells are
elongated and are called muscle fibers
• Muscle contraction depends on two kinds of
myofilaments – actin and myosin
• Muscle terminology is similar
– Sarcolemma – muscle plasma membrane
– Sarcoplasm – cytoplasm of a muscle cell
– Prefixes – myo, mys, and sarco all refer to
muscle
Functional Characteristics of
Muscle Tissue
• Excitability, or irritability – the ability to
receive and respond to stimuli
• Contractility – the ability to shorten forcibly
• Extensibility – the ability to be stretched or
extended
• Elasticity – the ability to recoil and resume
the original resting length
Muscle Function
• Skeletal muscles are responsible for all
locomotion
• Cardiac muscle is responsible for coursing
the blood through the body
• Smooth muscle helps maintain blood
pressure, and squeezes or propels
substances (i.e., food, feces) through organs
• Muscles also maintain posture, stabilize
joints, and generate heat
Muscle Classification: Functional
Groups
• Prime movers – provide the major force for
producing a specific movement
• Antagonists – oppose or reverse a particular
movement
• Synergists
– Add force to a movement
– Reduce undesirable or unnecessary movement
• Fixators – synergists that immobilize a bone
or muscle’s origin
Naming Skeletal Muscles
• Location of muscle – bone or body region
associated with the muscle
• Shape of muscle – e.g., the deltoid muscle
(deltoid = triangle)
• Relative size – e.g., maximus (largest),
minimus (smallest), longus (long)
• Direction of fibers – e.g., rectus (fibers run
straight), transversus, and oblique (fibers run
at angles to an imaginary defined axis)
Naming Skeletal Muscles
• Number of origins – e.g., biceps (two origins)
and triceps (three origins)
• Location of attachments – named according
to point of origin or insertion
• Action – e.g., flexor or extensor, as in the
names of muscles that flex or extend,
respectively
Bone-Muscle Relationships: Lever
Systems
• Lever – a rigid bar that moves on a fulcrum,
or fixed point
• Effort – force applied to a lever
• Load – resistance moved by the effort
Bone-Muscle Relationships:
Lever Systems
Figure 10.2a
Bone-Muscle Relationships:
Lever Systems
Figure 10.2b
Lever Systems: Classes
• First class – the fulcrum is between the load
and the effort
• Second class – the load is between the
fulcrum and the effort
• Third class – the effort is applied between
the fulcrum and the load
Lever Systems: First Class
Figure 10.3a
Lever Systems: Second Class
Figure 10.3b
Lever Systems: Third Class
Figure 10.3c
Major Skeletal Muscles: Anterior View
The 40 superficial muscles here
are divided into 10 regional
areas of the body:
• 1.- Facial
• 2.- Neck
• 3.-Thorax
• 4.- Shoulder
• 5.- Arm
• 6.- Forearm
• 7.- Abdomen
• 8.- Pelvis
• 9.- Thigh
• 10.- Leg
Figure 10.4b
Major Skeletal Muscles: Posterior View
The 27 superficial
muscles here are divided
into seven regional
areas of the body:
1.- Neck
2.- Shoulder
3.-Arm
4.- Forearm
5.- Hip
6.-Thigh
7.- Leg
Figure 10.5b
Muscles of the Face
• 11 muscles are involved in lifting the
eyebrows, flaring the nostrils, opening and
closing the eyes and mouth, and smiling
• All are innervated by cranial nerve VII (facial
nerve)
• Usually insert in skin (rather than bone), and
adjacent muscles often fuse
Muscles of the Face
Figure 10.6
Muscles of Mastication
• There are four pairs of muscles involved in
mastication
– Prime movers – temporalis and masseter
– Grinding movements – pterygoids and
buccinators
• All are innervated by cranial nerve V
(trigeminal nerve)
Muscles of Mastication
Figure 10.7a
Muscles of Mastication
Figure 10.7b
Extrinsic Tongue Muscles
• Three major muscles that anchor and move
the tongue
• All are innervated by cranial nerve XII
(hypoglossal nerve)
Extrinsic Tongue Muscles
Figure 10.7c
Homeostatic Imbalance
• Many toxins, drugs and diseases interfere
with events at the neuromuscular junction
Ex: Myastenia gravis: Characterize by:
1.- Drooping of the upper eyelids
2.- Difficulty of swallowing and
talking
3.- Muscle weakness
4.- Serum antibodies against
acetilcholine (Ach) receptor
Developmental Aspects: Male
and Female
• There is a biological basis for greater
strength in men than in women
• Women’s skeletal muscle makes up 36% of
their body mass
• Men’s skeletal muscle makes up 42% of
their body mass
Action Potential: Electrical Conditions of a
Polarized Sarcolemma
• The outside
(extracellular)
face is positive,
while the inside
face is negative
• This difference
in charge is the
resting
membrane
potential
Figure 9.8 (a)
Action Potential: Electrical Conditions
of a Polarized Sarcolemma
• The predominant
extracellular ion is
Na+
• The predominant
intracellular ion is
K+
• The sarcolemma
is relatively
impermeable to
both ions
Figure 9.8 (a)
Action Potential: Depolarization and
Generation of the Action Potential
• An axonal terminal
of a motor neuron
releases ACh and
causes a patch of
the sarcolemma to
become permeable
to Na+ (sodium
channels open)
Figure 9.8 (b)
Action Potential: Depolarization and
Generation of the Action Potential
• Na+ enters the cell,
and the resting
potential is
decreased
(depolarization
occurs)
• If the stimulus is
strong enough, an
action potential is
initiated
Figure 9.8 (b)
Action Potential: Propagation of the Action
Potential
• Polarity reversal of the
initial patch of
sarcolemma changes
the permeability of the
adjacent patch
• Voltage-regulated Na+
channels now open in
the adjacent patch
causing it to depolarize
Figure 9.8 (c)
Action Potential: Propagation of the Action
Potential
• Thus, the action
potential travels
rapidly along the
sarcolemma
• Once initiated, the
action potential is
unstoppable, and
ultimately results in
the contraction of a
muscle
Figure 9.8 (c)
Action Potential: Repolarization
• Immediately after the
depolarization wave
passes, the
sarcolemma
permeability changes
• Na+ channels close
and K+ channels
open
• K+ diffuses from the
cell, restoring the
electrical polarity of
the sarcolemma
Figure 9.8 (d)
Action Potential: Repolarization
• Repolarization
occurs in the same
direction as
depolarization, and
must occur before
the muscle can be
stimulated again
(refractory period)
• The ionic
concentration of the
resting state is
restored by the
Na+-K+ pump
Figure 9.8 (d)
Excitation-Contraction Coupling
• Once generated, the action potential:
– Is propagated along the sarcolemma
– Travels down the T tubules
– Triggers Ca2+ release from terminal cisternae
• Ca2+ binds to troponin and causes:
– The blocking action of tropomyosin to cease
– Actin active binding sites to be exposed
Excitation-Contraction Coupling
• Myosin cross bridges alternately attach
and detach
• Thin filaments move toward the center of
the sarcomere
• Hydrolysis of ATP powers this cycling
process
• Ca2+ is removed into the SR, tropomyosin
blockage is restored, and the muscle fiber
relaxes
Excitation-Contraction Coupling
Figure 9.9
Role of Ionic Calcium (Ca2+) in the
Contraction Mechanism
• At low intracellular
Ca2+ concentration:
– Tropomyosin blocks the
binding sites on actin
– Myosin cross bridges
cannot attach to binding
sites on actin
– The relaxed state of the
muscle is enforced
Figure 9.10 (a)
Role of Ionic Calcium (Ca2+) in the
Contraction Mechanism
• At higher intracellular
Ca2+ concentrations:
– Additional calcium
binds to troponin
(inactive troponin
binds two Ca2+)
– Calcium-activated
troponin binds an
additional two Ca2+ at
a separate regulatory
site
Figure 9.10 (b)
Role of Ionic Calcium (Ca2+) in the
Contraction Mechanism
• Calcium-activated
troponin undergoes
a conformational
change
• This change moves
tropomyosin away
from actin’s binding
sites
Figure 9.10 (c)
Role of Ionic Calcium (Ca2+) in the
Contraction Mechanism
• Myosin head
can now bind
and cycle
• This permits
contraction
(sliding of the
thin filaments by
the myosin
cross bridges)
to begin
Figure 9.10 (d)
Sequential Events of Contraction
• Cross bridge formation – myosin cross bridge
attaches to actin filament
• Working (power) stroke – myosin head pivots
and pulls actin filament toward M line
• Cross bridge detachment – ATP attaches to
myosin head and the cross bridge detaches
• “Cocking” of the myosin head – energy from
hydrolysis of ATP cocks the myosin head into
the high-energy state
Sequential Events of Contraction
Myosin head
(high-energy
configuration)
1 Myosin cross bridge attaches to
the actin myofilament
Thin filament
ADP and Pi (inorganic
phosphate) released
Thick
filament
2 Working stroke—the myosin head pivots and
4 As ATP is split into ADP and Pi,
cocking of the myosin head occurs
bends as it pulls on the actin filament, sliding it
toward the M line
Myosin head
(low-energy
configuration)
3 As new ATP attaches to the myosin
head, the cross bridge detaches
Figure 9.11
Motor Unit: The Nerve-Muscle
Functional Unit
• Large weight-bearing muscles (thighs, hips)
have large motor units
• Muscle fibers from a motor unit are spread
throughout the muscle; therefore,
contraction of a single motor unit causes
weak contraction of the entire muscle
Motor Unit: The Nerve-Muscle
Functional Unit
• A motor unit is a motor neuron and all the
muscle fibers it supplies
• The number of muscle fibers per motor
unit can vary from four to several hundred
• Muscles that control fine movements
(fingers, eyes) have small motor units
Motor Unit: The Nerve-Muscle
Functional Unit
Figure 9.12 (a)