Lecture Outline
Adapted from Martini Human Anatomy7th ed. / Session:
Section:
Days / Time: Instructor: / FALL
52999
MW 5:00 PM – 9:20 PM
RIDDELL
Chapter 9
The Muscular System
Skeletal Muscle Tissue and Muscle Organization
Introduction
Humans rely on muscles for:
Many of our physiological processes
Virtually all our dynamic interactions with the environment
Introduction
There are three types of muscle tissue:
Skeletal muscle
Pulls on skeletal bones
Voluntary contraction
Cardiac muscle
Pushes blood through arteries and veins
Rhythmic contractions
Smooth muscle
Pushes fluids and solids along the digestive tract, for example
Involuntary contraction
Introduction
Muscle tissues share four basic properties:
Excitability
The ability to respond to stimuli
Contractility
The ability to shorten and exert a pull or tension
Extensibility
The ability to continue to contract over a range of resting lengths
Elasticity
The ability to rebound toward its original length
Functions of Skeletal Muscles
Skeletal muscles perform the following functions:
Produce skeletal movement
Pull on tendons to move the bones
Maintain posture and body position
Stabilize the joints to aid in posture
Support soft tissue
Support the weight of the visceral organs
Functions of Skeletal Muscles
Skeletal muscles perform the following
functions (continued):
Regulate entering and exiting of material
Voluntary control over swallowing, defecation, and urination
Maintain body temperature
Some of the energy used for contraction is converted to heat
Anatomy of Skeletal Muscles
Gross anatomy is the study of:
Overall organization of muscles
Connective tissue associated with muscles
Nerves associated with muscles
Blood vessels associated with muscles
Microscopic anatomy is the study of:
Myofibrils
Myofilaments
Sarcomeres
Anatomy of Skeletal Muscles
Gross anatomy
Connective tissue of muscle
Epimysium: dense tissue that surrounds the entire
muscle
Perimysium: dense tissue that divides the muscle into parallel compartments of fascicles
Endomysium: dense tissue that surrounds individual muscle fibers
Anatomy of Skeletal Muscles
Connective Tissue of Muscle
Tendons and Aponeuroses
Epimysium, perimysium, and endomysium
converge to form tendons
Tendons connect a muscle to a bone
Aponeuroses connect a muscle to a muscle
Anatomy of Skeletal Muscles
Gross Anatomy
Nerves and blood vessels
Nerves innervate the muscle
There is a chemical communication between a nerve and a muscle
The nerve is “connected” to the muscle via the
motor end plate
This is the neuromuscular junction
Anatomy of Skeletal Muscles
Nerves and blood vessels (continued)
Blood vessels innervate the endomysium of the muscle
They then branch to form coiled networks to
accommodate flexion and extension of the muscle
Anatomy of Skeletal Muscles
Microanatomy of skeletal muscle fibers
Sarcolemma
Membrane that surrounds the muscle cell
Sarcoplasm
The cytosol of the muscle cell
Muscle fiber (same thing as a muscle cell)
Can be 30–40 cm in length
Multinucleated (each muscle cell has hundreds of nuclei)
Nuclei are located just deep to the sarcolemma
Anatomy of Skeletal Muscles
Myofibrils and Myofilaments
The sarcoplasm contains myofibrils
Myofibrils are responsible for the contraction of muscles
Myofibrils are attached to the sarcolemma at each end of the muscle cell
Surrounding each myofibril is the sarcoplasmic reticulum
Anatomy of Skeletal Muscles
Myofibrils and Myofilaments
Myofibrils are made of myofilaments
Actin
Myosin
Anatomy of Skeletal Muscles
Sarcomere Organization
Myosin (thick filament)
Actin (thin filament)
Both are arranged in repeating units called
sarcomeres
All the myofilaments are arranged parallel to the long axis of the cell
Anatomy of Skeletal Muscles
Sarcomere Organization
Sarcomere
Main functioning unit of muscle fibers
Approximately 10,000 per myofibril
Consists of overlapping actin and myosin
This overlapping creates the striations that give the skeletal muscle its identifiable characteristic
Anatomy of Skeletal Muscles
Sarcomere Organization
Each sarcomere consists of:
Z line (Z disc)
I band
A band (overlapping A bands create striations)
H band
M line
Anatomy of Skeletal Muscles
Levels of Organization
Skeletal muscles consist of muscle fascicles
Muscle fascicles consist of muscle fibers
Muscle fibers consist of myofibrils
Myofibrils consist of sarcomeres
Sarcomeres consist of myofilaments
Myofilaments are made of actin and myosin
Anatomy of Skeletal Muscles
Actin
Twisted filament consisting of G actin molecules
Each G actin molecule has an active site (binding site)
Myosin cross-bridges bind to the active sites on actin
Tropomyosin: A protein that covers the binding
sites when the muscle is relaxed
Troponin: Holds tropomyosin in position
Anatomy of Skeletal Muscles
Myosin
Myosin filaments consist of an elongated tail and a globular head (cross-bridges)
Myosin is a stationary molecule. It is held in place by:
Protein forming the M line
A core of titin connecting to the Z lines
Muscle Contraction
A contracting muscle shortens in length
Contraction is caused by interactions between thick and thin filaments within the sarcomere
Contraction is triggered by the presence of calcium ions
Muscle contraction requires the presence of ATP
When a muscle contracts, actin filaments slide
toward each other
This sliding action is called the sliding filament theory
Muscle Contraction
The sliding filament theory
Upon contraction:
The H band and I band get smaller
The zone of overlap gets larger
The Z lines move closer together
The width of the A band remains constant throughout the contraction
Muscle Contraction
Events leading up to muscle contraction
An impulse travels down the axon of a nerve
Acetylcholine is released from the end of the axon at the motor end plate
This ultimately causes the sarcoplasmic reticulum to release its stored calcium ions
Calcium ions bind to troponin
Muscle Contraction
Events leading up to muscle contraction(continued)
This binding action causes a rotation of the
troponin–tropomyosin complex
This rotation exposes the binding sites on the
actin myofilament
Myosin heads extend and bind to the binding sites on actin
Muscle Contraction
Events leading up to muscle contraction (continued)
The cross-bridges pivot thus sliding the actin
myofilament
As the actin myofilaments are pulled toward each other, the muscle becomes shorter
Motor Units and Muscle Control
Motor Units (motor neurons controlling muscle fibers)
Precise control
A motor neuron controlling two or three muscle
fibers
Example: the control over the eye muscles
Less precise control
A motor neuron controlling perhaps 2000 muscle fibers
Example: the control over the leg muscles
Motor Units and Muscle Control
Muscle Tension
Muscle tension depends on:
The frequency of stimulation
The number of motor units involved
Motor Units and Muscle Control
Muscle Tone
The tension of a muscle when it is relaxed
Stabilizes the position of bones and joints
Muscle Spindles
These are specialized muscle cells that are monitored by sensory nerves
Motor Units and Muscle Control
Muscle Hypertrophy
Exercise causes:
An increase in the number of mitochondria
An increase in the activity of muscle spindles
An increase in the concentration of glycolytic enzymes
An increase in the glycogen reserves
An increase in the number of myofibrils
The net effect is an enlargement of the muscle
(hypertrophy)
Motor Units and Muscle Control
Muscle Atrophy
Discontinued use of a muscle
Disuse causes:
A decrease in muscle size
A decrease in muscle tone
Physical therapy helps to reduce the effects
of atrophy
Types of Skeletal Muscle Fibers
Three major types of skeletal muscle fibers:
Fast fibers (white fibers)
Associated with eye muscles
Intermediate fibers (pink fibers)
Slow fibers (red fibers)
Associated with leg muscles
Types of Skeletal Muscle Fibers
Features of fast fibers:
Large in diameter
Large glycogen reserves
Relatively few mitochondria
Muscles contract using anaerobic metabolism
Fatigue easily
Can contract in 0.01 second or less after stimulation
Produce powerful contractions
Types of Skeletal Muscle Fibers
Features of slow fibers:
Half the diameter of fast fibers
Take three times longer to contract after stimulation
Can contract for extended periods of time
Contain abundant myoglobin (creates the red color)
Muscles contract using aerobic metabolism
Have a large network of capillaries
Types of Skeletal Muscle Fibers
Features of intermediate fibers:
Similar to fast fibers
Have low myoglobin content
Have high glycolytic enzyme concentration
Contract using anaerobic metabolism
Similar to slow fibers
Have lots of mitochondria
Have a greater capillary supply
Resist fatigue
Types of Skeletal Muscle Fibers
Distribution of fast, slow, and intermediate
fibers
Fast fibers
High density associated with eye and hand muscles
Sprinters have a high concentration of fast fibers
Repeated intense workouts increase the fast fibers
Types of Skeletal Muscle Fibers
Distribution of fast, slow, and intermediate
fibers
Slow and intermediate fibers
None are associated with the eyes or hands
Found in high density in the back and leg muscles
Marathon runners have a high amount
Training for long distance running increases the proportion of intermediate fibers
Organization of Skeletal Muscle Fibers
Muscles can be classified based on shape or
by the arrangement of the fibers
Parallel muscle fibers
Convergent muscle fibers
Pennate muscle fibers
Unipennate muscle fibers
Bipennate muscle fibers
Multipennate muscle fibers
Circular muscle fibers
Organization of Skeletal Muscle Fibers
Parallel muscle fibers
Muscle fascicles are parallel to the longitudinal axis
Examples: biceps brachii and rectus abdominis
Organization of Skeletal Muscle Fibers
Convergent muscle fibers
Muscle fibers form a broad area but come together at a common point
Example: pectoralis major
Organization of Skeletal Muscle Fibers
Pennate muscle fibers
Muscle fibers form an oblique angle to the tendon of the muscle
An example is unipennate
All the muscle fibers are on the same side of the tendon
Example: extensor digitorum
Organization of Skeletal Muscle Fibers
Pennate muscle fibers
Muscle fibers form an oblique angle to the tendon of the muscle
An example is bipennate
Muscle fibers are on both sides of the tendon
Example: rectus femoris
Organization of Skeletal Muscle Fibers
Pennate muscle fibers
Muscle fibers form an oblique angle to the tendon of the muscle
An example is multipennate
The tendon branches within the muscle
Example: deltoid muscle
Organization of Skeletal Muscle Fibers
Circular muscle fibers
Muscle fibers form concentric rings
Also known as sphincter muscles
Examples: orbicularis oris and orbicularis oculi
Muscle Terminology
Origin, Insertion, and Action
Origin
Point of muscle attachment that remains stationary
Insertion
Point of muscle attachment that is movable
Action
The function of the muscle upon contraction
Muscle Terminology
There are two methods of describing
muscle actions
The first makes reference to the bone region the muscle is associated with
The biceps brachii muscle causes “flexion of the
forearm”
The second makes reference to a specific joint the muscle is associated with
The biceps brachii muscle causes “flexion at the elbow”
Muscle Terminology
Muscles can be grouped according to
their primary actions into four types:
Prime movers (agonists)
Responsible for producing a particular movement
Antagonists
Actions oppose the action of the agonist
Synergists
Assist the prime mover in performing an action
Fixators
Agonist and antagonist muscles contracting at the same time to stabilize a joint
Muscle Terminology
Prime movers example:
Biceps brachii – flexes the lower arm
Antagonists example:
Triceps brachii – extends the lower arm
Synergists example:
Latissimus dorsi and teres major – contract to move the arm medially over the posterior body
Fixators example:
Flexor and extensor muscles contract at the same time to stabilize an outstretched hand
Organization of Skeletal Muscle Fibers
Most muscle names provide clues to their
identification or location
Muscles can be named for:
Specific body regions or location
Shape of the muscle
Orientation of the muscle fibers
Specific or unusual features
Its origin and insertion points
Primary function
References to occupational or habitual action
Muscle Terminology
Examples of muscle names related to:
Specific body regions or locations
Brachialis: associated with the brachium of the arm
Tibialis anterior: associated with the anterior tibia
Shape of the muscle
Trapezius: trapezoid shape
Deltoid: triangular shape
Muscle Terminology
Examples of muscle names related to:
Orientation of the muscle fibers
Rectus femoris: straight muscle of the leg
External oblique: muscle on outside that is oriented with the fibers at an angle
Specific or unusual features
Biceps brachii: two origins
Teres major: long, big, rounded muscle
Muscle Terminology
Examples of muscle names related to:
Origin and insertion points
Sternocleidomastoid: points of attachment are sternum, clavicle, and mastoid process
Genioglossus: points of attachment are chin and tongue
Primary functions
Flexor carpi radialis: a muscle that is near the radius and flexes the wrist
Adductor longus: a long muscle that adducts the leg
Muscle Terminology
Examples of muscle names related to:
References to occupational or habitual actions
Buccinator (means “trumpet player”): the buccinator area moves when playing a trumpet
Sartorius: derived from the Latin term (sartor), which is in reference to “tailors.” Tailors used to cross their legs to form a table when sewing material
Levers and Pulleys: A Systems Design for Movement
Most of the time, upon contraction, a muscle causes action
This action is applied to a lever (a bone)
This lever moves on a fixed point called the fulcrum (joint)
The action of the lever is opposed by a force acting in the opposite direction
Levers and Pulleys: A Systems Design for Movement
There are three classes of levers:
First class
The fulcrum (joint) lies between the applied force and the resistance force (opposed force)
Example: tilting the head forward and backward
Levers and Pulleys: A Systems Design for Movement
There are three classes of levers:
Second class
The resistance is located between the applied force and the fulcrum (joint)
Example: standing on your tiptoes
Levers and Pulleys: A Systems Design for Movement
There are three classes of levers:
Third class
The force is applied between the resistance and fulcrum (joint)
Example: flexing the lower arm
Levers and Pulleys: A Systems Design for Movement
Sometimes, a tendon may loop around a bony
projection
This bony projection could be called a pulley
Example: lateral malleolus and trochlea of the eye
Aging and the Muscular System
Changes occur in muscles as we age
Skeletal muscle fibers become smaller in diameter
There is a decrease in the number of myofibrils
Contain less glycogen reserves
Contain less myoglobin
All of the above results in a decrease in strength and endurance
Muscles fatigue rapidly
Aging and the Muscular System
Changes occur in muscles as we age (continued)
There is a decrease in myosatellite cells
There is an increase in fibrous connective tissue
Results in fibrosis
The ability to recover from muscular injuries decreases
© 2012 Pearson Education, Inc. Page 1 of 11 BIO 218 F 2012 CH 09 Martini lecture Outlines