Function of Muscle Tissue
• Movement
– Contraction (shortening) causes movement
– Of the body as a whole when connected to skeleton
– Of materials through the body (blood, food, etc.)
• Maintenance of posture
– Continual maintenance of posture via muscle
contractions to either keep body standing or sitting
• Joint stabilization
– Muscle tone stabilizes and strengthens joints
• Heat generation
– Muscles produce heat as a by product of contraction
Characteristics of Muscle
• Contractility
– Forceful contraction, fibers in cells shorten
• Excitability
– Excited by nerve cell electrical impulse to
contract
• Extensibility
– Ability of muscle to stretch by the contraction
of opposing muscles
• Elasticity
– After stretching, muscles can recoil passively
Classification of Muscle Tissue
• Skeletal
• Smooth
• Cardiac
• Each of these muscle types is an organ
composed of mostly muscle tissue with blood
and vessels, C.T. and nerves.
• Largest amount of tissue of body ≈ 40% of body
weight
Skeletal Muscle
• Voluntary Muscle:
– Skeleton
• Movement and posture
– Diaphragm
• breathing
– Sphincters
• Circle of skeletal muscle important in voluntary
release of urinary and fecal waste
Skeletal Muscle
• Regulation of contraction –
voluntary control
• Thick and thin filaments of
myofibrils (contractile
proteins)
• Long muscle fibers =
muscle cell
• Multinucleated w/ nuclei
near surface
• Mitochondria
prominent to
supply energy
for contraction
• C.T. layer
(endomysium)
between each
fiber
Cardiac Muscle
•
•
•
Occurs only in the heart
Heart wall = myocardium
Single nucleus, many
mitochondria (a lot of ATP)
• Pump blood through heart
chambers and into general
circulation
• Involuntary control
– Can even continue to function
w/out central nervous
stimulation…. “autorhythmicity”
Cardiac Muscle
• Joined end to end creating
intercalated discs
– Junction where plasma
membranes interlock
• Hold cells together and
allow ions to pass,
transmission of electrical
impulse
• Branched and
interconnected which allow
impulses to travel cell to cell
Smooth Muscle
• Lacks striations
• Found surrounding hollow
tubes
• Involuntary control
– Contraction slow and
sustained (blood vessels
and visceral organs)
– Resistant to fatigue
• Peristalsis
– Wave-like contractions that
move foodstuffs through
the alimentary canal
Connective Tissue and Fascicles
• Fascia – fibrous C.T. that surrounds
muscles and holds it in position
• Epimysium
– Dense irregular C.T. that surrounds skeletal muscle
and may blend with deep fascia between neighboring
muscles.
• Perimysium
– Fibrous C.T. that extends inwards from epimysium to
separate muscle tissue into sections (fascicles)
– Surrounds groups of fibers
• Endomysium
– Thin sheet of reticular fibers around each muscle fiber
Motor Unit
• Muscle cell = muscle fiber
• Motor neuron and all of the muscle cells it stimulates
• Actions depend largely
upon the kind of joint
and the manner of
attachment on either
side of that joint.
• Skeletal muscle is
fastened to a relatively
immovable part and
the other end
connected to a
movable part on the
other side of a joint.
• Aponeuroses
– C.T. associated with muscle
that forms a broad fibrous
sheet of attachment.
• E.g. abdominal aponeuroses
Lever Systems
Lever Systems
• Bone = lever
• Joint = fulcrum or pivot point
• Muscle = force applied to
lever
• Law of Levers
– When the effort is farther from
the fulcrum than is the load =
mechanical advantage
– When the effort is nearer the
fulcrum than the load =
mechanical disadvantage
Lever
Systems
1st Class Lever
Force
Effort
Force
Resistance
Fe
Fr
Fulcrum
e.g. triceps pulls on ulna
Lever Systems
Law of Levers
– When the effort is farther
from the fulcrum than is
the load = mechanical
advantage
– When the effort is nearer
the fulcrum than the load
= mechanical
disadvantage
2nd Class Lever
Force
Resistance
Force Effort
Fr
Fulcrum
e.g. gastronemius pulls on calcaneus with fulcrum at ball of foot
Fe
3rd Class Lever
Force Effort
Fe
Fulcrum
Force
Resistance
Fr
Interactions of Skeletal Muscles
• Prime movers – Agonists
– Muscle that bears the major responsibility for a particular
movement
– e.g. biceps brachii flexes forearm at elbow
• Antagonist muscle
– Muscle that reverses, or opposes, the action of another muscle
– e.g. triceps brachii returns arm to straight position
• Muscles cannot push, so muscles usually lie on opposite
side of a joint.
• Synergist muscle
– Muscle that aids the action of a prime mover by contributing to
the same movement or by stabilizing joints to prevent
undesirable movements.
– e.g. fingers move while wrist is stable
Naming of Skeletal Muscles
• Location - e.g., tibialis anterior (tibia), biceps femorus (thigh)
• Shape - e.g., deltoid (triangle), rhomboid, serratus (saw tooth)
• Relative Size - e.g. adductor longus, vastus lateralis, peroneus brevis
• Direction of cell fibers - e.g., transversus abdominus (right angle to
midline), external oblique (oblique to midline), rectus abdominus (rectus =
straight, parallel to midline)
• Origin and insertion - location of attachments- origin always named
first. e.g., sternocleidomastoid.
• Number of divisions or origins - quadriceps (4 heads), tricep (3
heads), bicep (2 heads)
• Action - e.g., adductor longus, extensors and flexors of hand, foot, digits,
e.g. extensor digitorum
Actions Performed by Muscles
• Flexor (F) - bend limb at joint
• Lateral flexion (LF) - bending the trunk away from the body midline.
• Extensor (E) - straighten limb at joint
• Abductor (AB) - move limb away from midline
• Adductor (AD) - move limb toward midline
• Rotator (Ro) - medial or lateral rotation, moves bone around its
longitudinal axis
– Medial rotation (MR) - rotation of the anterior surface toward the
medial plane
– Lateral rotation (LR) - rotation of the anterior surface toward the
lateral plane
Actions Performed by Muscles
• Pronator (PR) - turns palm downward (posterior)
• Supinator (SUP) - turns palm upward (anterior)
• Elevator (EL) - raise or elevate part of body
• Depressor (DEP) - lower part of body
• Dorsiflexor (DF) - turn foot upward
• Plantarflexor (PF) - point foot or toes downward
• Inversion (IN) - turn the ankle to point the sole medially
• Eversion (EV) - turn the ankle to point the sole laterally
Suggestions on Learning
• If you know the origin and insertion you can often figure out
action of a joint.
• Use a rubber band to stretch between origin and insertion
points. Rubber band can only pull, not push, similar to a
muscle.
• Use your own body to test for the action of certain muscles.
• Remember, some muscles can cross more than one joint, e.g.
gastrocnemius (femur to calcaneous), sartorius (iliac crest to
tibial condyle)
• Muscles only act at the joint(s) between the origin and
insertion.
Be able to:
1.
Identify the assigned human muscles on any chart or
model and give the action of each.
2.
Locate the superficial muscles on yourself.
3.
Give the actions and approximate origins and insertions of
the assigned human muscles noted with a *.
4.
Be able to cite the dangers of anabolic steroid use.
5.
Know the following muscle related clinical terms:
myalgia, myopathy, RICE, spasm, cramp, strain