Chapter One
Structure and Function of the Muscular Nervous and
Skeletal System
Three Types of Muscle
 Cardiac- Found only in the heart.
o Involuntary
 Smooth-Lines internal organs. Blood vessels.
o Involuntary
 Skeletal- Attached to bone and used for movement.
o Voluntary
Muscle Characteristics
Muscle accounts for 36-45% of body weight
Gross Muscle Anatomy (Know fig 1.1 page 4)
Microscopic Anatomy of Skeletal Muscle
Muscle Contraction
Sarcomere
 Basic functional unit of a myofibril.
 Contains actin and myosin.
 They run the length of the myofibril stacked end to end and join at the Zdisc.
Myosin
 Thick filament composed of protein.
 Each filament consists of about 200 myosin molecules.
 Each molecule is made up of two protein strands twisted together, which
forms a myosin head.
 Titin- Small filament used to stabilize myosin along its length.
Actin
 The thin filament
 Composed of three different protein molecules.
1. Actin- Backbone of the strand
2. Tropomyosin- Tube shaped and twists around actin backbone.
3. Troponin- Complex protein attached at regular intervals to both actin
and Tropomyosin.
Sliding Filament Theory
 Briefly discuss
Types of Muscle Action
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Concentric- Muscles will shorten during contraction.
Eccentric- Muscles lengthen during contraction.
Dynamic contraction- Joint movement occurs during contraction.
Isometric (static) contraction- Muscle contracts with no change in joint
angle.
 Isokinetic- velocity of movement is kept constant regardless of force
applied.
Delayed-Onset of Muscle Soreness
 Muscular pain/discomfort that occurs 24 to 48 hours after exercise
o Can last one to seven days
 Not caused by lactic acid
 DOMS due to damage to connective and muscle tissue which occurs during
eccentric contraction
 To offset:
o Start slowly
o More likely to occur during heavy eccentric loading
Muscle Fiber Type
 This book states: Type I, Types IIa and Type IIx
 Two basic types of muscle fibers:
o Slow twitch (type I)
 Only one known type of Slow twitch
o Fast twitch (Type II)
 The nomenclature for types of fast twitch are currently
questionable
 Traditional: Type IIa, IIb and IIc
 Wilmore and Costil: Type IIa, IIx and IIc (states IIb is
found in animals.)
 NSCA: Traditional type IIb muscle fibers were thought to
contain the myosin heavy chain protein complex that
resembled the MHC isoform IIb, newer research
demonstrates that the MHC isoform more closely
resembles the MHC IIx isoform.
 McArdle, Katch and Katch: "Recent studies show that
human skeletal muscle contains type I, type IIa, and type
IIx fibers (previously referred to as type IIb) and a new
type IIb subtype."
The Nervous System
 Organization of the Nervous System
o Nervous System divided into:
 Central Nervous System (Brain and Spinal column)
 Peripheral Nervous System (outside the CNS)
 Relays nerve impulses to and from the CNS
o Nervous System also contains
 Somatic function (voluntary)
 Autonomic (involuntary)
 Neurons
o Neuron (nerve cell)- basic unit of the nervous system
o Efferent neuron- conducts impulse from CNS to peripheral
o Afferent neuron- conducts impulse from peripheral to CNS
o Motor neuron- conducts impulse from the muscles (efferent neuron).
 Sensory Neurons
o Muscle Spindle- spindle shaped sensory organ located in the muscle
belly.
 Measures rate and magnitude of muscle lengthening
 Stretch Reflex- stretching muscle contracts in response to rate
and magnitude of lengthening
 Offset by stretching slowly
 Used to increase power during plyometrics
o Golgi Tendon Organ
 Located in the tendon at muscle and tendon junction
 Acts as a strain gauge
 Leads to autogenic inhibition – contacting muscle relaxes when
strain threshold is met
o Motor Unit- motor neuron and all muscle fibers that it inervates
 All motor units contain the same type of muscle fibers
 Gradation of Force
o Two methods for varying muscle force:
o Motor Unit recruitment- Recruit only the number of motor units
required
 Size Principle of motor unit recruitment Start with type I fibers and move up
o Rate Coding- increasing firing rate of already activated muscle
increases force
 If a stimulated muscle is signaled to contract prior to fully
relaxing then force production will increase.
Skeletal System
 Composed of over 200 bones (206 typical)
 Bone Categories- Bones can be split into two major categories:
 Axial Skeleton- Also known as the central skeleton, consist of:
o Skull
o Vertebrae
o Sternum
o Ribs
o Pelvis (sometimes placed with the appendicular skeleton)
 Appendicular Skeleton- Also known as peripheral, consist of:
o Bones in arms, legs, hands and feet.
 Structural organization
o Cortical bone- Relatively nonporous bone
 Provides stiffness
 Handle stress
 Cannot handle strain (deformation)
o Trabecular Bone- Highly porous
 Commonly known as “spongy” bone
 Not as stiff as cortical bone
 Can handle greater amounts of strain before a fracture occurs
 Osteoporosis- (Porous Bone)- loss of bone density leading to brittle bones
o Offset due to weight bearing activity.
 Tendons and Ligaments
o Tendons- Conects muscle to bone
o Ligaments- conects bone to bone
o Fascia- Fiberous tissue that envelops muscle, groups of muscle, and
other soft tissue.