Chapter 1 Flashcards
How do motor unit recruitment patterns affect force production? Describe how
muscle force is graded and explain the different methods for improving force
production in athletes
Muscle force output varies depending on the task at hand, which is crucial for performing
smoothly coordinated movement patterns.
Muscle force is graded in two ways:
1. Frequency of motor unit activation (twitch)
2. Increase in the total number of activated motor units
Increasing the twitch frequency increases muscular force. Each twitch only produces a small
amount of force. Twitches that occur one after the other are additive, meaning that movement
is accomplished by multiple twitches one after the other.
Tetanus is a state of muscle activation where the twitches are so frequent they merge together.
Large muscles can activate at near tetanic frequency when called upon.
Adaptations to resistance training that improve force production include both increased twitch
frequency and increased numbers of activated motor units.
Muscle force production in athletes can be improved through the following:
• Incorporating phases of training with heavier loads
• Increasing the muscle cross-section area through resistance training
• Focusing on explosive, multi-muscle, multi-joint exercises
Describe the location and function of muscle spindles and Golgi tendon organs.
Muscle spindles and Golgi tendon organs (GTOs) are specialized sensory receptors known as
proprioceptors.
These receptors provide the central nervous system with information regarding the position of
body parts with respect to gravity.
Proprioceptive information is largely processed at the subconscious level, allowing the nervous
system to maintain muscle tone and perform complex coordinated movements.
Muscle Spindles
• Modified muscle fibers enclosed in a sheath of connective tissue
• Known intrafusal fibers and run parallel to normal muscle fibers (extrafusal fibers)
• Provide information concerning the muscle length and rate of change in length.
• Muscle spindles cause their corresponding muscle fibers to contract when stretched
• Spindles indicate the degree of muscle activation needed to overcome resistance
• Increased spindle activation results in increased motor unit activation
Golgi Tendon Organs
• Located in the tendons near the myotendinous junction
• Attached end-to-end in series with the extrafusal muscle fibers
• Activate when the tendon attached to an active muscle is stretched
• Discharge of the GTOs increases as the level of tension in the muscle increases
• GTO discharge stimulates inhibitory neurons in the spinal cord, reducing tension in
the muscle
• GTO response though to protect against excessive muscle tension
• Motor cortex signals can override GTO response
➢ Possibly an adaptation to heavy resistance training that increases muscle
force development
Overall, activation of muscle spindles increases activation in the respective motor unit.
GTO activation decreases activation in the respective motor unit.
Describe the structure of the heart.
The heart is a muscular organ that consists of two separate but interconnected pumps.
The right side of the heart pumps blood through the lungs for oxygenation, and the left side of
the heart pumps the oxygenated blood throughout the body.
The heart consists of the following chambers:
• Right atrium - receives non-oxygenated blood from the body
• Right ventricle - pumps blood through the pulmonary circulation
• Left atrium - receives oxygenated blood from pulmonary circulation
• Left ventricle - pumps oxygenated blood through the body
The heart contains a system of valves that passively ensure proper blood flow direction:
• Tricuspid valve and mitral valve (Atrioventricular valves) - prevent backflow of blood
from ventricles into atria during contraction (Systole)
• Aortic and pulmonary valves (Semilunar valves) - prevent bloodflow from aorta and
pulmonary arteries during ventricular relaxation (Diastole)
A specialized conduction system of bundles and nodes controls the contraction of the heart:
• Sinoatrial node - Pacemaker of the heart, source of the rhythmic electrical impulses
• Atrioventricular node - Delays impulse from the SA node to allow blood into the
ventricles
• Atrioventricular bundle - Conducts impulse to ventricles via the left and right bundle
branches - further branching into Purkinje fibers. AV bundle transmits signals nearly
simultaneously to the left and right ventricles
Describe the nervous system’s involvement in heart activity and the standard
variation in resting heart rates.
The rhythm of the heart muscles (Myocardium) is controlled by the medulla in the brain. The
signals from the medulla are transmitted through the sympathetic and parasympathetic
nervous systems.
Sympathetic Nervous System
• Accelerates depolarization of SA node, increasing heart rate
Parasympathetic Nervous System
• Decreases the rate of depolarization, decreasing heart rate
Typical resting heart rate ranges from 60 BPM to 100 BPM.
Fewer than 60 bpm is known as bradycardia, while a bpm of over 100 is known as tachycardia.
Describe the electrical activity of the heart as represented on an ECG that
results in mechanical contraction.
The electrical activity of the heart can be recorded at the surface of the body and graphically
represented by an electrocardiogram (ECG).
A normal ECG contains a P-wave, QRS complex, and a T-wave, represented by the spikes on the
ECG monitor.
• P-Wave - graphically represents the electrical depolarization of the atria, which
results in mechanical contraction
• QRS Complex - represents depolarization of the ventricles
• T-Wave - represents ventricular repolarization, resetting the heart between each
beat
Atrial repolarization occurs as well but is masked on a typical ECG by the QRS Complex.
Describe blood and the system of vessels that carries it throughout the body.
Blood includes the following substances:
• Hemoglobin - an iron-protein molecule that transports oxygen and buffers blood pH
• Red blood cells - contain hemoglobin and facilitate CO2 removal
The arterial system transports blood throughout the body through the following structures:
• Arteries - large tubes that rapidly transport blood from the heart
• Arterioles - small tubes that branch off the arteries and control the blood before
entering the capillaries
• Capillaries - smallest tubes that facilitate exchange of O2, CO2, and nutrients
between blood and tissues
The venous system returns blood to the heart through the following structures
• Venules - collect blood from capillaries and transport it to veins
• Veins - larger tubes that return blood to the heart
Arteries have stiff walls to contain the high pressure of blood from the heart.
Veins have thinner, dilatable walls that constrict or expand depending on the current needs of
the body
Describe the respiratory system and the process of air exchange and respiration.
The respiratory system consists of a series of passages that ultimately bring oxygen into the
body and return carbon dioxide:
• Nasal cavities - warm, purify, and humidify air entering the body
• Trachea - first-generation respiratory passage
• Right and left bronchi - second-generation passages that split from the trachea
towards the right and left lungs
• Bronchioles - additional 23 generations of passageways that deliver air to the alveoli
• Alveoli - location in lunges where gas exchange (diffusion) occurs nearly
instantaneously
During normal inspiration, the diaphragm contracts, creating negative pressure in the lungs that
pulls in air.
In normal expiration, the diaphragm relaxes and elastic recoil in the lungs and chest cavity
expels the air.
During heavy breathing, inspiration is increased through elevation of the rib cage by the
following muscles:
• Intercostals
• Sternocleidomastoids
• Anterior serrati
• Scaleni
The lungs are surrounded by pleural membranes that normal contain negative pleural pressure
that increases during inspiration and decreases during expiration.
Alveolar pressure is the pressure inside the lung alveoli when the glottis is fully open and no
airflow in or out of the lungs is occurring. Alveolar pressure falls during inspiration and
increases during expiration.
Describe the relative muscle fiber composition in different muscle groups and
their involvement in activities.
Specific muscles will vary in their fiber types based on the primary use of the muscle.
Postural Muscles
• Large composition of Type I fibers
• Needed throughout the day so endurance is required
• Example: Soleus
Prime Mover Muscles
• Include Type I and Type II fibers due to varying needs
• The intensity of the activity will determine the relative involvement of fiber types
• Example: Quadriceps group (involved in both low and high power activities)
Describe the muscle fiber types and characteristics.
Muscle fibers are primarily grouped into two categories: fast twitch and slow twitch.
Each motor unit is made up of fibers of the same type and are classified based on the type of
muscle fibers in that motor unit.
Slow-twitch fibers are known as Type I fibers.
Fast-twitch fibers are known as type II fibers and are further classified as Type IIa and Type IIx.
Type I Fibers
• Efficient
• Resistant to fatigue
• High capillary density
• High density of mitochondria
• High capacity for using aerobic energy.
• Low recruitment threshold, meaning they will be activated at a lower demand than
required for type II fiber activation.
• Limited potential for rapid force development and anaerobic power.
• Type I fibers have a much greater capacity for endurance and fatigue resistance than
type IIa and Type IIx.
Type II Fibers
• Includes Type IIa and Type IIx
• Inefficient and rapidly fatigue
• Capable of rapidly producing force for short periods of time
• Significant anaerobic power
• Type IIa fibers have a greater capacity for aerobic metabolism and more capillaries
than Type IIx making them more resistant to fatigue.
Describe the Phases of Muscle Contraction According to the Sliding Filament
Theory.
Resting Phase
• Majority of the calcium is stored in the sarcoplasmic reticulum
• Few myosin crossbridges are bound to actin
Excitation-contraction Coupling Phase
• Nervous system signals the motor unit to contract
• Action potential discharges across the neuromuscular junction
• Calcium is released from the sarcoplasmic reticulum
• Calcium released binds with troponin situated along the actin filament
• H-Zone and I-band shrink
• Z-lines pull together as sarcomere shrinks
Contraction Phase
• ATP on the myosin crossbridge breaks down via hydrolysis, catalyzed by an enzyme
called myosin ATPase
• The breakdown of ATP into ADP and phosphate delivers the energy for the pulling
action, known as the power stroke.
Recharge Phase
• New ATP replaces the ADP on the myosin crossbridge
• If calcium, ATP, and ATPase available, the contractions repeat
Relaxation Phase
• Calcium is pumped back into the sarcoplasmic reticulum
• Actin and myosin return to unbound state
• Muscle relaxes
Describe motor units
Motor units consist of the motor neuron and the muscle fibers they innervate.
Motor neurons are the nerve cells responsible for innervating muscle fibers.
The junction between the muscle fiber and motor neuron is known as the neuromuscular
junction.
Each muscle fiber only has one neuron responsible for innervation.
A single motor neuron can innervate up to hundreds, and even thousands, of individual muscle
fibers.
When the motor unit delivers the signal to contract by the discharge of an action potential, all
fibers innervated by the motor neuron in that motor unit contract simultaneously. This is
known as the ‘all-or-nothing principle.’
Motor Unit Components
• Motor neuron
• Neuromuscular Junction
• Corresponding muscle fibers
Describe the organization of sarcomeres.
The sarcomere is the smallest contractile unit in a muscle.
Sarcomeres are organized based on the areas that contain myosin or actin.
The A-band corresponds to the alignment of myosin filaments
The I-band corresponds with the area between two adjacent sarcomeres containing only actin.
The Z-line runs perpendicular to the I-band separating each sarcomere.
The H-zone in the middle of the sarcomere contains only myosin filaments.
Sarcomere Organization
• A-Band -alignment of myosin filaments
• I-Band - contains actin filaments
• Z-Line - splits the I-band and separates sarcomeres
• H-Zone - the center of sarcomeres that contains myosin filaments
Describe the microstructure of individual muscle fibers.
Muscles are composed of individual muscle cells, called muscle fibers.
Muscle fibers are cylindrical cells of about 50-100 micrometers in diameter.
Each fiber contains contractile components floating around in sarcoplasm.
Muscle fibers are grouped into bundles known as fasciculi that consist of up to 150 fibers.
Muscle Fiber Contents
• Sarcolemma (Muscle fiber membrane)
• Protein myofibrils
• Additional protein
• Stored glycogen
• Fat particles
• Enzymes
• Mitochondria
• Sarcoplasmic reticulum
Myofibrils are composed of actin and myosin protein myofilaments.
The actin and myosin myofilaments are organized longitudinally in the sarcomere, which is the
smallest contractile unit in a muscle.
Pairs of myosin filaments form crossbridges with one another, and the interactions between
actin fibers and myosin crossbridges are responsible for muscle contraction.
An intricate system of tubules called the sarcoplasmic reticulum surrounds each myofibril and
contains calcium ions that regulate muscle contraction.
T-tubules run perpendicular to the sarcoplasmic reticulum and terminate near the Z-line
between two sarcomeres. The T-tubules are contiguous with the sarcolemma and deliver the
signal from the motor neuron simultaneously to all depths of the muscle fiber.
Describe the macrostructure of skeletal muscles. Include the different layers of
connective tissue within the muscles.
Skeletal muscles are organs that contain muscle tissue, connective tissue, nerves, and blood
vessels.
Tendons attach the muscles at multiple points to the bone periosteum, a specialized
connective tissue that covers all bones.
Fibrous connective tissue called epimysium covers every muscle in the human body and is
contiguous with the tendons at the end of each muscle.
Individual muscle cells, called muscle fibers, are long cylindrical muscle cells of about 50-100
micrometers in diameter. The fibers are grouped into bundles known as fasciculi that consist of
up to 150 fibers.
Each bundle is wrapped in a connective tissue layer called perimysium.
Within the fasciculi, individual fibers are surrounded by connective tissue called endomysium,
which is contiguous with the muscle fiber’s membrane, or sarcolemma.
All connective tissue in the muscle tissue is contiguous with the tendon, allowing the tension
developed in the muscle to be transmitted to the tendons and bone attachments.
Macrostructure of Muscle Connective Tissue Layers
• Tendon - attaches to bone periosteum
• Epimysium - outer connective tissue layer surrounding the muscle
• Perimysium - middle connective tissue surrounding fasciculi
• Endomysium - inner connective tissue that surrounds each muscle fiber
• Sarcolemma - muscle fiber membrane contiguous with endomysium
Describe the categories of muscle attachments to bones.
The points where muscles connect to bones are categorized based on the location of the
attachment.
Limb muscle attachments are categorized based on their relative location to the body’s midline.
Trunk muscles are categorized based on their position relative to the head.
Attachment Categories
• Proximal Attachment - limb muscle attachment closer to the midline
• Distal Attachment - limb muscle attachment further from the midline
• Superior attachment - trunk muscle attachment closer to the head
• Inferior attachment - trunk muscle attachment closer to the feet
