NSCA Chapter 1: Structure and Function of the Muscular, Nervous, and Skeletal Systems

By: Katie Meredith and Reuben Quero

Introduction to the Muscular System Three types of Muscle tissue: Cardiac Muscle, which composes the walls of

the hear, is involuntary muscle and therefore is not subject to conscious control.

Smooth Muscle, which lines the internal organs such as the intestines and stomach, is also involuntary.

Skeletal Muscle is muscle that attaches to the skeleton via tendons to produce bodily movement.

Muscle System

Introduction to the Skeletal Muscle Agonist: is the muscle that initiates

the desired movement. Antagonist: the opposite muscle that

is being stretched.

For example, when one is doing a biceps curl exercise in an upright position, that biceps are the agonists while the triceps are the antagonists.

Muscle System

Agonist & Antagonist

Three Primary Muscle Actions Concentric Action: When a muscle

overcomes a load and shortens (bicep curl). Eccentric Action: When muscle cannot

develop sufficient tension and is overcome by and external load and progressively lengthens (walking down stairs).

Isometric Action: When muscle generates force against a resistance; it does not shorten, lengthen or cause joint motion (posture muscles).

Isokinetic: is a dynamic muscle action kept at a constant velocity independent of the amount of muscular force generated by the involved muscles.

Muscle System

Gross Muscle Structure and Organization Muscle Fiber: Structural component of skeletal muscle. Cylindrical cell that

contains hundreds of nuclei. Endomysium: Connective tissue that surrounds the individual muscle fiber. Fascicles: Fibers are grouped into different sized bundles that compose the

fasciculus.

Muscle System

Perimysium: Another connective tissue that surrounds each fasciculus.

Fascia: A fibrous tissue that envelops muscles, groups of muscles, and other soft tissue.

Epimysium: The connective tissue encasing the entire muscle body.

Muscle System

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Periosteum: The outer most covering of the bone.

Sarcolemma: A thin plasma membrane beneath the endomysium and surrounding each muscle fiber. Its primary function is to conduct an electrochemical wave of depolarization along the surface of muscle fiber. It also insolates the muscle fibers from one another.

Satellite Cells: Have important regulatory functions for cellular growth.

Muscle System

Microscopic Muscle Structure

Myofibrils: The elements of skeletal muscle that allow the muscle to contract.

Actin: Myofilaments that binds with myosin to cause a muscle action.

Myosin: Myofilaments that lines with actin to cause a muscle action.

Myofilaments: The two primary proteins in a myofibril.

Muscle System

Muscle Fiber Types Fast twitch (Type II): Ability to generate rapid, and

powerful muscle actions. Involved in activities such as a volleyball spike, a tennis serve or a weight training workout.

Slow-twitch (Type I): involved in energy production for prolonged aerobic activities, such as step aerobics, long-distance running, etc. Described as fatigue resistant.

Muscle System

Fast-Twitch (Type 2)Slow-Twitch (Type 1)

Muscle Fiber Types Muscle System

The Sliding-Filament Theory: How Muscle Contracts

Muscle System

The theory suggests that changes in muscle length occur as the myosin and actin myofilaments slide past each other.

The myofilaments do not actually change in length; the sarcomere shortens (concentric action) or lengthening (eccentric action) which results in production of force.

The energy for this molecular motion comes from the splitting of adenosine triphosphate or ATP.

The Sliding-Filament Theory: How Muscle Contracts

Muscle System

Initiation of a Muscle Action Action Potential is a message sent from a motor neuron to a

muscle cell that tells it to act. After the sarcolemma receives the action potential the

electrical impulses travel inward through the muscle. This electrical charge causes quick release of calcium ions.

Once activated, the calcium ions bond with troponin. Troponin initiates tropomyosin which activates myosin cross-

bridges. A power stroke is completed when myosin binds with actin,

thus moving the muscle.

Muscle System

Introduction to the Nervous System

The nervous system is the communication and command system of the body. Its main functions are to sense changes, interpret them and respond.

Two main parts, the central nervous system includes the brain and the spinal cord, while the peripheral nervous system consists of nerves extending from the brain and the spinal cord.

Nervous System

Afferent and Efferent Neurons Afferent Neurons: Gathers

sensory information for the body. Efferent Neurons: Send output

from the central nervous to the body.

The efferent neurons can be further divided into a Somatic and Autonomic Nervous System.

Somatic: Consists of motor neurons, excites skeletal muscle.

Autonomic Nervous System: Excites involuntary muscles such as in the stomach.

Nervous System

Nerve Fibers: Structure and Function The three main divisions of the neuron are:

Cell Body: contains the nucleus, nucleolus, various substances, and other organelles.

Dendrites: are attached to the cell body and transmits sensory messages.

Axon: transmits messages for the cell body to its end organs. A cell body normally has many dendrites but only one axon.

Myelin Sheath: Encircles most of the axons of the peripheral nervous system. Provides insulation and maintenance for the axon.

Nervous System

Mnemonic Device: Remember that all neurons are the SAME: Sensory neurons are Afferent while Motor neurons are Efferent

Nerve Impulses, Depolarization, and Action Potentials

Resting Membrane Potential: The negative charge on the inside of the cell means that the cells outside environment is relatively more positive.

Sodium-Potassium Pump: Regulates the balance of potassium and sodium on the inside and outside of the cell.

Depolarization: Cell membrane charge becomes less negative. Hyperpolarization: Cell membrane charge becomes more negative.

Nervous System

All-or-None Principle: When a cell membrane reaches or exceeds its electrical threshold, the entire message becomes an action potential. The principle involved is called the all-or-none principle.

Repolarization: Immediately following the action potential, the motor nerve restores itself to its resting membrane potential.

Synapse: The junction between two nerves where a neuron transmitter will diffuse from the initial axon to the receiving axon.

Nervous System

The function of the neuromuscular junction is to transmit the electrical impulse from the nerve to the muscle.

Proprioceptors: relay messages to the central nervous system about muscular changes in the body and about limb movement.

Muscle Spindles: Provides sensory feedback concerning the length change and speed of length change of muscle fibers.

Stretch Reflex: can inhibit the stretch in the muscle or cause it to contract.

Golgi Tendon Organs: recognizes changes tension in the muscle.

Nervous System

Axial Skeleton: the central skeleton, consists of the skull vertebral column, sternum and ribs.

Appendicular Skeleton: consist of the shoulder girdles, arms and legs

Skeletal System

Types of Bone Tissue Osseous: an active, living tissue that consists of two types:

Compact Bone: dense bone distinguished by the arrangement of minerals and cells.

Cancellous Bone: porous with branching struts called trabeculae that form a lattice arrangement. This bone tissue allows for marrow and fat storage but also provides a microstructure for bone strength.

Skeletal System

Major Functions, Growth and Remodeling

Ossification: bone growth: the increase in size of bone due to an increase in bone cells. The bone may increase in its thickness or grow longitudinally.

Bone Remodeling: the bone tissues capability to modify its shape size and structure in response to demands and imposed upon it.

Resportion: loss of a substance, specifically bone tissue. The bone matrix consists of three bone cells:

Osteoclasts: bone destroying cells that cause resportion. Osteoblasts: bone forming cells that lead to deposition of bone. Osteocytes: help regulate bone remodeling.

Skeletal System

Connective Tissue

Tendons: Transfer the tension created by the muscle to the bones causing movement.

Collagen: The main constituent of tendon is this protein which is arranged in bundles.

Ground Substance: Contributes to the tensile strength of tendon connective tissue.

Ligaments: bind bone to bone providing support to the joint. Unlike tendons, the ligaments attach to bones at both ends.

Elastin: The concentration of protein found in ligaments. It allows ligaments to have extensibility but also return to their original length.

Fascia: a broad term used to designate all connective tissues that do not have a specific name.

Skeletal System

Question #1 Which of the following is the correct sequence of

components from smallest muscle structure to largest muscle structure?A. Fascia, perimysium, epimysium, endomysium

B. Myofilament, myofibril, fiber, fasciculus

C. Endomysium, epimysium, perimysium, fascia

D. Muscle cell, fasciculus, myofibril, fiber

Study Questions

Explanations B: Myofilament, myofibril, fiber, fasciculus Page 5 – Myofibrils are the elements of skeletal muscle that allow

the muscle to contract. Myofibrils consist of two proteins, actin and myosin which are referred to as myofilaments.

The structural component of the skeletal muscle is the muscle fiber. The fasciculus contains up to 150 muscle fibers.

Study Questions

Question #2 Which of the following describes the properties of Type 1 and

Type 2 muscle fibers?A. High force, slow speed

B. Fast speed, high endurance

C. High endurance, high force

D. Slow speed, low force

Study Questions

Explanations C: High endurance, high force Page 10 – Fast twitch (type 2) and slow twitch (type 1) are

differentiated by their metabolic and contractile properties. Fast twitch fibers generate rapid, powerful muscle actions. These

fibers have a speedy level of calcium ion release, and a high level of myosin.

Slow twitch fibers are involved in energy production for prolonged aerobic activities these fibers have a slower calcium ion handling capability and a lower level of myosin.

Study Questions

Question #3 Which of the following change in muscle length and tension

are associated with a muscle spindle and a Golgi tendon?A. Rapid muscle length change, Increase in muscle tension

B. Decrease in muscle tension, Slow muscle length change

C. Slow muscle length change, Decrease in muscle tension

D. Increase in muscle tension, Fast muscle length change

Study Questions

Explanations A: Rapid muscle length change, Increase in muscle tension Page 14 – Muscle spindles provide sensory feedback

concerning the length change and the speed of length change of muscle fibers.

Golgi tendon organs recognize changes in tension in the muscle.

Study Questions

Question #4 Which of the following is true regarding bone health?

1. Decreased bone mineral density is related to an increased risk of fracture.

2. The most common sites for fracture are the humerus, tibia, and femur.

3. Bone mineral density is promoted by chronic participation in a physically-active lifestyle.

4. Exercise may be beneficial in preventing fractures by decreasing the concentration of osteocytes.

A. 1 and 3 only

B. 2 and 4 only

C. 1,2 and 3 only

D. 2,3 and 4 only

Study Questions

Explanations Answer: C – 1 and 3 only Page 16 – Bone resorption means loss of a substance,

specifically bone tissue. In elderly people, bone resportion is greater that bone formation. Resulting in loss of bone mineral density.

Bone mineral density is highly related to long- term physical activity.

Exercise may be beneficial in preventing fractures by increasing strength.

Study Questions

Applied Knowledge QuestionStructure/Substance Role during a muscle action

Myosin cross-bridges Binds to specific sites on the actin filament, forming the structural and functional link between the two filaments.

ATP The energy for the molecular motion of muscles.

Calcium Released by the sarcoplasmic reticulum and binds with troponin

Troponin Help with actin function in muscle contraction.

Tropomyosin A long, rope-like protein that spirals around the actin double helix, lies in a groove formed by the actin strands, and blocks that binding sites for actin-myosin interaction or coupling.

Acetylcholine The acetylcholine binds with receptors on the muscle membrane which are in close proximity to the neuron. The binding of the acetylcholine to the muscle membrane allows for the initiation of an action potential on the muscle membrane.

Thank You!