Anatomy
Chapter 6 – The Muscular System
Overview of Muscle Tissues
Connective tissue wrappings
of skeletal muscle
Muscle Functions:
1.
2.
3.
4.
Producing movement
Maintaining posture
Stabilizing joints
Generating heat
Microscopic Anatomy of a skeletal muscle
fiber (cell)
The major role of this elaborate system is to store
calcium and to release it on demand when the
muscle fiber is stimulated to contract.
Motor Units consist of a motor neuron and all the muscle fibers it
activates.
Photomicrograph
of a portion of a
motor unit.
Neuromuscular junction
(synaptic cleft)
Axon hillock
Schwann cell
Typical Nerve Cell - Neuron
Muscle cells have two special functions:
1) irritability – the ability to receive and respond to a stimulus
2) contractility – the ability to shorten (forcibly) when an adequate stimulus is received
The neuromuscular junction:
Acetylcholine –
neurotransmitter
that stimulates
skeletal muscle cells
Contraction of a Skeletal Muscle as a Whole
• Graded response - different degrees of shortening; involves cells with an “all-or-none”
response; (1) changing frequency of muscle stimulation, (2) changing the number of
muscle cells being stimulated.
• Muscle twitch – single, brief, jerky contraction; not normal operation
• Complete tetanus – fused muscle contraction; stimulation so rapid, no evidence of
relaxation, contractions are smooth and sustained
• Incomplete tetanus – unfused; muscle motion not completely smooth
• How forcefully a muscle contracts depends on how many cells are being stimulated; the
hand that caresses, can also deliver a stinging slap
Providing Energy for Muscle Contraction:
ATP molecules are hydrolyzed to release the needed energy. Muscles store very limited
supplies of ATP – 4 to 6 seconds worth. ATP is the only energy source that can be used
directly to power muscle activity.
Direct Phosphorylation
Aerobic Respiration
Anaerobic Respiration
Muscle fatigue and oxygen debt – exercising for prolonged times depletes ATP
in the muscle; cannot be contracted even with stimulation; true muscle
fatigue results in the muscle quitting, rarely occurs because most of us stop
long before it happens – marathon runners.
Types of Muscle Contractions:
 Isotonic – “same tone” or tension; muscle shortens, movement
occurs (knee bend, smiling).
 Isometric – muscles do not shorten; “skidding you heels”,
pushing against the wall, wall sits.
Muscle tone – muscle remains firm, healthy, ready for action; continuous partial
contractions.
Resistance – isometric exercises, muscles pitted against immovable object.
Exercise – “Use it or lose it”; strength, stamina,
endurance.
Types of Muscle movements:
Every one of the 600 muscles in the body is attached to a bone or
connective tissue structure, at no less than two points.
• Origin – attached to the immovable or less movable bone
• Insertion – attached to the movable bone, moves toward the origin
Body movement occurs
when muscles contract
across joints.
Muscle attachments – when a skeletal
muscle contracts, its insertion moves
toward its origin.
Types of Body Movements:
Sagittal Plane
Opposite of flexion
Greater than 180*
Rotation is movement of a bone around its
longitudinal axis. Common in ball-andsocket joints. (Atlas and dens of axis)
Abduction is moving limb away from the midline of the body.
Adduction is moving limb toward midline of body.
Circumduction – combination of
flexion, extension, abduction,
adduction.
Interactions of Skeletal Muscles in the Body:
 Muscles cannot push – they only pull as they contract.
 Movement is most often the result of the activity of two or more
muscles acting together or against each other.
o Prime mover – the muscle with the major responsibility for
causing a particular movement (biceps)
o Antagonist – muscle that oppose or reverse a movement
(triceps)
o Synergist – help prime movers by producing the same movement
or reducing undesirable movements (stabilizers)
o Fixators – specialized synergists – stabilize the origin of prime
movers so all tension can be used to move the insertion bone
Naming Skeletal Muscles:
 Direction of muscles – reference to imaginary line; rectus – straight, oblique –
running at an angle
 Relative size – gluteus maximus – Large; gluteus minimus – small, longus – long
 Location of muscle – bone associated with, frontalis, temporalis, occipitalis
 Number of origins – biceps, triceps, quadriceps
 location of the muscles origin and insertion – sternocleidomastoid
 Shape of muscle – deltoid is triangular, trapezius
 Action of muscle – adductor magus
Arrangement of the fascicles:
• Circular – concentric circles, external
body openings that close by contracting;
sphincters; orbicularis oris
• Convergent - fascicles converge toward
single insertion tendon; fan-shaped;
pectoralis major
• Parallel – length of fascicles run parallel
to the long axis; strap-like; sartorius
• Fusiform - spindle-shaped with
expanded midsection; biceps brachii
• Pinnate - feather pattern; unipennate ,
bipennate, multipennate
Gross Anatomy of skeletal muscles: Head and Neck
Facial muscles –
inserted into soft
tissues; facial
expressions.
Chewing muscles –
mastication of
food, elevating the
mandible
Neck muscles –
move the head and
shoulder girdle
Trunk muscles: move vertebral column; anterior thorax muscles;
abdominal walls
Anterior muscles:
Muscles of
the upper
limb:
Posterior muscles:
Muscles of the lower limb: cause
movement of the hip, knee, and foot
Muscles causing
movement at
the hip:
Muscles causing
movement at
the knee joint:
Muscles causing movement at
the ankle and foot:
Several large, bulky, muscles are chosen as injection
sites, when relatively small amounts of medicine must
be given intramuscularly.
Major superficial muscle of the anterior surface of the body:
Major superficial muscles of the posterior surface of the body: