Chapter 1 structure and function of the muscular, neuromuscular, cardiovascular, and respiratory syste
Structure and and Respiratory
Cardiovascular,Function of the
Structure and Function
of the Muscular,
Gary R. Hunter, PhD, CSCS, FACSM
Robert T. Harris, PhD
• Describe the macrostructure and microstructure of muscle.
• Describe the sliding-filament theory.
• Describe the characteristics of different
muscle fiber types.
• Describe the characteristics of the cardiovascular and respiratory systems.
• We will focus on the muscular and
neuromuscular systems, review pages 1319 on your own (heart and lungs)
The Muscular System
• ....DesktopESS 2600 VideosHuman Body
Pushing The Limits E1 part 2.mp4
• Macrostructure and Microstructure
– Each skeletal muscle is an organ that contains
muscle tissue, connective tissue, nerves, and blood
– Fibrous connective tissue, or epimysium, covers the
body's more than 430 skeletal muscles.
• The epimysium encases the muscle
• All of the various layers of CT
(endomysium, perimysium and the
epimysium blend and are contiguous with
• Tendon: Attaches the muscle to the bone (it
is much stronger than muscle tissue)
• Each fasiculi may consist of up to 150
• Each muscle fiber is surrounded by a
connective tissue known as endomysium.
• The fasiculi themselves are surrounded by
connective tissue known as perimysium.
– Think of this as the connective tissue within the
• Muscle fibers (also known as cells) are
about the same diameter as a strand of
human hair and can reach lengths as long
as the muscle itself
• Muscle fibers are made up of many
myofibrils bundled together
• Again, what myofilaments do we find in the
• Strategically arranged actin and myosin
• What is the smallest “contractile unit” of
– The sarcomere
• Sarcomeres are lined up in series along the
length of the myofibril
– (remember: myofibrils make up each muscle fiber,
so simultaneous contraction of the sarcomeres
within all of the myofibrils leads to muscle cell
• What is the Sliding-Filament Theory of
– The sliding-filament theory states that the actin
filaments at each end of the sarcomere slide inward
on myosin filaments, pulling the Z-lines toward the
center of the sarcomere and thus shortening the
– Sliding Filament Theory
Contraction of a Myofibril
– (a) In stretched muscle the I-bands and H-zone are
elongated, and there is low force potential due to
reduced cross-bridge–actin alignment.
– (b) When muscle contracts (here partially), the
I-bands and H-zone are shortened.
– (c) With completely contracted muscle, there is low
force potential due to reduced cross-bridge–actin
• The nervous system works via electrical
impulses (action potentials), it signals the
muscle to contract by sending action
potentials to the muscle
• What is a motor unit?
– A motor unit consists of a motor neuron and the
muscle fibers it innervates.
– There are typically several hundred muscle fibers in
a single motor unit.
• The discharge of an action potential from a
motor nerve signals the release of calcium
from the sarcoplasmic reticulum into the
myofibril, this allows the “cross bridges” of
the myosin to attach to actin.
• Using the energy from ATP, tension can
now be developed in muscle.
• Neuromuscular System
Activation of Muscles
Muscle Fiber Types
Motor Unit Recruitment Patterns During Exercise
• Muscle Spindles
• Golgi Tendon Organs
Activation of Muscles
What chemical is released following an action potential?
– Arrival of the action potential at the nerve terminal causes the release
of acetylcholine. Once a sufficient amount of acetylcholine is
released, an action potential is generated across the sarcolemma, and
the fiber contracts.
– What determines the level of muscular control.
– Hand vs. Thigh
• Muscles that function with great precision may have as
few as one muscle fiber per motor neuron.
• Muscles that require less precision may have several
hundred fibers served by one motor neuron.
ACTIVATION OF MUSCLES
Once enough acetylcholine
crosses the neuromuscular
junction, the action potential
is transmitted and the
This occurs because the
sarcolemma (muscle cell
membrane), then T-tubule
depolarizes and the
• All of the muscle fibers in the motor unit
contract and develop force at the same time.
There is no such thing as a motor neuron
stimulus that causes only some of the fibers to
contract. Similarly, a stronger action potential
cannot produce a stronger contraction.
Stimulated Motor Unit
• Twitch, twitch
tetanus of a motor
– a = single twitch
– b = force resulting
from summation of
– c = unfused tetanus
– d = fused tetanus
• Muscle Fiber Types
– Type I (slow-twitch)
– Type IIa (fast-twitch)
• Type IIab (fast-twitch); now named as Type IIax
• Type IIb (fast-twitch); now named as Type IIx
– Type IIx are “true” fast-twitch fibers and are highly if not
100% glycolytic in nature
– All other Type II fibers are oxidate and glycolytic
MUSCLE FIBER TYPES
• Postural muscles
composed of a
of type 1 fibers
• Whereas larger
(quadriceps) have a
• Motor units are composed of muscle fibers
with specific morphological and physiological characteristics that determine their
• Motor neurons, motor units and/or muscle
fibers can be characterized as type .. Motor
units are always the same type (you won’t
find a motor neuron innervating both type I
and type II fibers)
• Motor Unit Recruitment Patterns During
– The force output of a muscle can be varied through
change in the frequency of activation of individual
motor units or change in the number of activated
– Occurs when a load is lifted,
since sufficient force must be
developed to overcome the
inertia of the load
– Information concerning
kinesthetic sense, or conscious
appreciation of the position of
body parts with respect to
– Processed at subconscious
• How Can Athletes Improve Force
– Recruit large muscles or muscle groups during an
– Increase the cross-sectional area of muscles
involved in the desired activity.
– Preload a muscle just before a concentric action to
enhance force production during the subsequent
– Use preloading during training to develop strength
early in the range of motion.
• Proprioceptors are specialized sensory
receptors that provide the central nervous
system with information needed to maintain
muscle tone and perform complex coordinated movements.
– Muscle Spindles
• Also known as intrafusal fibers
• Muscle spindles are proprioceptors that consist of several
modified muscle fibers enclosed in a sheath of connective
• Figure 1.7
– When a muscle is stretched, deformation of the
muscle spindle activates the sensory neuron, which
sends an impulse to the spinal cord, where it
synapses with a motor neuron, causing the muscle
• Example: If you are being stretched by your trainer and they
push the muscle a little too far/fast .. What is your natural
– Golgi Tendon Organs (GTO)
– Where are GTOs located?
• Golgi tendon organs are proprioceptors located in tendons
near the myotendinous junction.
• They occur in series (i.e., attached end to end) with
extrafusal muscle fibers.
Golgi Tendon Organ
• What happens when you lift something that
is far too heavy?
– When an extremely heavy load is placed on the
muscle, discharge of the GTO occurs.
– The sensory neuron of the GTO activates an
inhibitory interneuron in the spinal cord, which in
turn synapses with and inhibits a motor neuron
serving the same muscle.
• Older Muscle
– Muscle function is reduced in older adults.
– Reductions in muscle size and strength are
amplified in weight-bearing extensor muscles.
– Muscle atrophy with aging results from losses in
both number and size of muscle fibers, especially
Type II muscle fibers.
– Inactivity plays a major role but cannot account for
all of the age-related loss of muscle and function.
– The heart is a muscular organ made up of two
interconnected but separate pumps.
• The right ventricle pumps blood to the lungs.
• The left ventricle pumps blood to the rest of the body.
Heart and Blood Flow
• Figure 1.9 (next slide)
– Structure of the human heart and course of blood
flow through its chambers
• Tricuspid valve and mitral (bicuspid) valve
• Aortic valve and pulmonary valve
• Valves open and close passively, depending on the
– Conduction System
• Controls the mechanical contraction of the heart
Electrical Conduction System
• Figure 1.10 (next slide)
– The electrical conduction system of the heart
• Figure 1.11 (next slide)
– Transmission of the cardiac impulse through the
heart, showing the time of appearance (in fractions
of a second) of the impulse in different parts of the
• Recorded at the surface of the body
• A graphic representation of the electrical activity of the
• Figure 1.12 (next slide)
– Normal electrocardiogram
to atrial contraction
• Blood Vessels
– Blood vessels operate in a closed-circuit system.
– The arterial system carries blood away from the
– The venous system returns blood toward the heart.
Distribution of Blood
• Figure 1.13 (next slide)
– The slide shows the arterial (right) and venous (left)
components of the circulatory system.
– The percent values indicate the distribution of blood
volume throughout the circulatory system at rest.
– Hemoglobin transports oxygen and serves as an
– Red blood cells facilitate carbon dioxide removal.
• The cardiovascular system transports
nutrients and removes waste products while
helping to maintain the environment for all
the body’s functions. The blood transports
oxygen from the lungs to the tissues for use
in cellular metabolism, and it transports
carbon dioxide from the tissues to the
lungs, where it is removed from the body.
• Respiratory System
– Exchange of Air
– Exchange of Respiratory Gases
• Figure 1.14 (next slide)
– Gross anatomy of the human respiratory system
• Exchange of Air
– The amount and movement of air and expired gases
in and out of the lungs are controlled by expansion
and recoil of the lungs.
Expiration and Inspiration
• Figure 1.15 (next slide)
– The slide shows contraction and expansion of the
thoracic cage during expiration and inspiration,
illustrating diaphragmatic contraction, elevation of
the rib cage, and function of the intercostals.
– The vertical and anteroposterior diameters increase