Chapter 2
Neuromuscular
Fundamentals
2-1
Manual of
Structural Kinesiology
Skeletal Muscles
 Responsible for movement of body and all of its
joints
 Muscle contraction produces force that causes
joint movement
 Muscles also provide
 protection
 posture and support
 produce a major portion of total body heat
2-2
Muscle Nomenclature
 Muscles are usually named due to
 visual appearance
 anatomical location
 function
 Shape – deltoid, rhomboid
 Size – gluteus maximus, teres minor
 Number of divisions – triceps brachii
 Direction of its fibers – external abdominal
oblique
2-3
Shape of Muscles & Fiber
Arrangement
 Cross section diameter
 factor in muscle’s ability to exert force
 greater cross section diameter = greater force
exertion
 Muscle’s ability to shorten
 longer muscles can shorten through a greater
range
 more effective in moving joints through large
ranges of motion
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Muscle Terminology
 Origin
 Structurally, the proximal attachment of a muscle or the
part that attaches closest to the midline or center of the
body
 Functionally & historically, the least movable part or
attachment of the muscle
 Insertion
 Structurally, the distal attachment or the part that
attaches farthest from the midline or center of the
body
 Functionally & historically, the most movable part is
generally considered the insertion
2-5
Types of muscle contraction
 Muscle contractions can be used to cause,
control, or prevent joint movement or
 to initiate or accelerate movement of a body
segment
 to slow down or decelerate movement of a body
segment
 to prevent movement of a body segment by
external forces
 All muscle contractions are either isometric or
isotonic
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Structural Kinesiology
Types of muscle contraction
Muscle Contraction
(under tension)
Isometric
Isotonic
Preventing
Motion
Concentric
Causing
Neuromuscular Fundamentals
Motion
2-7
Eccentric
Controlling
Motion
Manual of
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Types of muscle contraction
 Isometric contraction
 active tension is developed
within muscle but joint angles
remain constant
 static contractions
 significant amount of tension
may be developed in muscle
to maintain joint angle in
relatively static or stable
position
 may be used to prevent a
body segment from being
moved by external forces
 preventing motion
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Structural Kinesiology
Types of muscle contraction
 Concentric contractions
involve muscle developing
active tension as it shortens
 Causing motion
 Eccentric
contractions involve
the muscle
lengthening under
active tension
 Controlling motion
2-9
Role of Muscles
 Agonist muscles
 cause joint motion through a specified plane of motion when
contracting concentrically
 known as primary or prime movers

Some agonist muscles, because of their relative location,
size, length, or force generation capacity, are able to
contribute significantly more to the joint movement than
other agonists
 Assisters or assistant movers

Agonist muscles that contribute significantly less to the joint
motion
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Role of Muscles
 Antagonist muscles
 located on opposite side of a joint from the
agonist
 have the opposite concentric action
 known as contralateral muscles
 work in cooperation with agonist muscles by
relaxing & allowing movement
 when contracting concentrically perform the
opposite joint motion of agonist
 Ex. quadriceps muscles are antagonists to
hamstrings in knee flexion
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Role of Muscles
 Stabilizers
 surround joint or body part
 contract to fixate or stabilize the area to enable another
limb or body segment to exert force & move
 known as fixators
 essential in establishing a relatively firm base for the
more distal joints to work from when carrying out
movements
 Ex. biceps curl


muscles of scapula & glenohumeral joint must contract in
order to maintain shoulder complex & humerus in a relatively
static position so that the biceps brachii can more effectively
perform curls
Proximal stability is needed for distal mobility.
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Role of Muscles
 Synergist
 assist in action of agonists
 not necessarily prime movers for the action
 known as guiding muscles
 assist in refined movement & rule out undesired
motions
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Role of Muscles
 Force Couples
 Force couples occur
when two or more forces
are pulling in different
directions on an object,
causing the object to
rotate about its axis
 Coupling of muscular
forces together in the
body can result in a more
efficient movement
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Lines of Pull
Consider the following
1. Exact locations of bony landmarks to which muscles attach
proximally & distally and their relationship to joints
2. Planes of motion through which a joint is capable of moving
3. Muscle’s relationship or line of pull relative to the joint’s
axes of rotation
4. As a joint moves the line of pull may change & result in
muscle having a different or opposite action than in the
original position
5. Effect of a muscle’s relative length on its ability to generate
force
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Factors affecting muscle tension
development
 All or None Principle - regardless of number, individual
muscle fibers within a given motor unit will either fire &
contract maximally or not at all
 Difference between lifting a minimal vs. maximal
resistance is the number of muscle fibers recruited
 The number of muscle fibers recruited may be increased
by
 activating those motor units containing a greater
number of muscle fibers
 activating more motor units
 increasing the frequency of motor unit activation
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Motor Control
 A motor neuron and the muscle
fibers it innervates.
 Fine control
 small motor units contain as few
as
20 muscle fibers per nerve fiber
 eye muscles

Allow for greater dexterity
because of a lower neuron to
muscle fiber ratio.
 Gross control
 gastrocnemius muscle has 1000
fibers per nerve fiber

One motor neuron controls many
muscle fibers which allows for
strength production.
Recruitment and Stimulus
Intensity
 Strength of muscle
contraction is dependant of
# of motor units recruited
 Multiple motor unit
summation

The harder the activity is the
more motor units will be
recruited.


Lifting 1 lb vs. 100 lbs
How do you explain the
rapid strength gains when
you first start training?
All or None Principle
 Typical muscle contraction
 The number of motor units
responding (and number of
muscle fibers contracting)
within the muscle may vary
significantly from relatively
few to virtually all
 depending on the number
of muscle fibers within each
activated motor unit & the
number of motor units
activated
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Metabolism and Skeletal Muscle Fibers Types
 There are 3 different types skeletal muscle fibers based
histological differences, duration of a twitch and the method of
ATP production
 slow oxidative fibers
 fast oxidative fibers
 fast glycolytic fibers
 Proportions genetically determined
Fast Glycolytic, Fast-Twitch
Fibers
 Fast glycolytic, fast-twitch fibers:
 rich in enzymes for phosphagen and glycogen-lactic
acid systems
 Limited # of mitochondria and high concentration of
glycogen stores makes it adapted for anaerobic
metabolism

a lack of myoglobin in glycolytic fibers results in a white color
 sarcoplasmic reticulum releases calcium quickly so
contractions are quicker which are required for
movements that produce speed and power.

extraocular eye muscles, gastrocnemius and biceps brachii
Slow- Twitch Fibers
 Slow oxidative, slow-twitch fibers
 Oxidative fibers contain greater amounts of mitochondria
and myoglobin which binds oxygen.
 Rich blood supply and high concentration of myoglobin
these fibers appear red in color.
 adapted for endurance (resistant to fatigue)
 Soleus and postural muscles of the back are predominantly
this type.
Fast Oxidative Fibers
 Fast oxidative fibers:
 characteristics of both fast and slow fibers.
 have a fast twitch (use ATP quickly)
 Increased mitochondria make it moderately resistant
to fatigue
 Usually make up 10% of fibers.
 Training will make these fibers adapt to
become functionally more fast or slow.
Cellular Adaptations to Physical
Demands
 Strength training: high intensity training stresses
anaerobic pathways.
 Increased # and size of glycolytic associated enzymes
and substrates

ATP, creatine phosphate and glycogen
 Endurance training: Enhance the aerobic pathways.
 increased # and size of mitochondrial membranes and
associated enzymes.
 This will increase O2 uptake ( VO2
the formation of lactic acid.
max)
which will delay
Factors affecting muscle tension
development
 Number of muscle fibers per motor unit varies
significantly
 From less than 10 in muscles requiring precise and
detailed such as muscles of the eye
 To as many as a few thousand in large muscles that
perform less complex activities such as the
quadriceps
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Muscle Length - Tension
Relationship
 Generally, depending upon muscle involved
 Greatest amount of tension can be developed when a
muscle is stretched between 100% to 130% of its
resting length

Stretch beyond 100% to 130% of resting length
significantly decreases the amount of force production
 A proportional decrease in ability to develop tension
occurs as a muscle is shortened

When shortened to around 50% to 60% of resting
length ability to develop contractile tension is essentially
reduced to zero
Muscle Length - Tension
Relationship
 Maximal ability of a muscle
to develop tension & exert
force varies depending upon
the length of the muscle
during contraction
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Muscle Length - Tension
Relationship
 Ex. 1 Increasing ability to
exert force
 squat slightly to stretch the
gastroc, hamstrings, &
quadriceps before
contracting same muscles
concentrically to jump
 Ex. 2. Reducing ability to
exert force
 isolate the gluteus maximus
by maximally shortening the
hamstrings with knee flexion
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Reciprocal Inhibition or
Innervation
 Antagonist muscles groups must relax & lengthen
when the agonist muscle group contracts
 This reciprocal innervation effect occurs through
reciprocal inhibition of the antagonists
 Activation of the motor units of the agonists causes a
reciprocal neural inhibition of the motor units of the
antagonists
 This reduction in neural activity of the antagonists allows
them to subsequently lengthen under less tension

Biceps contracts triceps must relax
Active & Passive
Insufficiency
 As muscle shortens its ability to exert force
diminishes
 Active insufficiency is reached when the muscle
becomes shortened to the point that it can not
generate or maintain active tension
 Passively insufficiency is reached when the opposing
muscle becomes stretched to the point where it can
no longer lengthen & allow movement
Active Insufficiency
 When a multi-joint muscle contracts
simultaneously over 2 joints the muscle is
unable to generate a maximum muscle
contraction.
 Ex. Rectus femorus contracts concentrically to
both flex the hip & extend the knee
 Hamstrings: contracts both knee flexion and hip
extension
 Gastrocnemius: Knee flexion and plantar
flexion
 Biceps brachii: shoulder flexion and elbow flexion
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Passive Insufficiency
 Agonist muscle unable to reach full
range of motion because of
inadequate length of antagonistic two
joint muscle.

Hamstrings can’t stretch enough to
allow both maximal hip flexion &
maximal knee extension.

Knee flexion cannot be fully achieved
if the hip is fully extended. Rectus
femoris length limits motion.

Finger flexion is limited if wrist flexion
occurs simultaneously.
Proprioception
 Subconscious mechanism by which body is able to
regulate posture & movement by responding to stimuli
originating in proprioceptors of the joints, tendons,
muscles, & inner ear
 Proprioceptors - internal receptors located in skin,
joints, muscles, & tendons which provide feedback
relative to:
 tension, length, & contraction state of muscle.

position of body & limbs.

movements of joints.
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Proprioception
 Proprioceptors specific to muscles
 Muscles spindles

concentrated primarily in muscle belly between the fibers

sensitive to stretch & rate of stretch

Insert into connective tissue within muscle & run parallel with
muscle fibers
 Golgi tendon organs (GTO)

found serially in the tendon close to muscle tendon junction

sensitive to both muscle tension & active contraction

much less sensitive to stretch than muscle spindles

require a greater stretch to be activated
Muscle spindle
 Muscle spindles & myotatic
or stretch reflex
1. Rapid muscle stretch occurs
2. Afferent Impulse is sent to the
CNS
3. CNS activates motor neurons
of agonist muscle while
inhibiting the antagonist
muscle.
4. Stretched or agonistic muscle
contracts
Monosynaptic Reflex

Ex. Knee jerk or patella tendon reflex
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Golgi Tendon Organ
 Golgi tendon organ

Tension in tendons & GTO increases
as muscle contract, which activates
GTO
1.
2.
3.
4.

GTO stretch threshold is reached
Impulse is sent to CNS
CNS causes muscle to relax
facilitates activation of antagonists as
a protective mechanism
GTO protects us from an excessive
contraction by causing its muscle to
relax
Manual of
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Chapter 3
Basic Biomechanical
Factors & Concepts
Basic Biomechanical Factors &
Concepts
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Structural Kinesiology
Biomechanics
 Biomechanics - study of the mechanics as it relates to the
functional and anatomical analysis of biological systems
 Necessary to study the body’s mechanical characteristics
& principles to understand its movements
 Mechanics - study of physical actions of forces
 Musculoskeletal system may be thought of as a series of
simple machines
 Machines - used to increase mechanical advantage
 Consider mechanical aspect of each component in analysis
with respect to components’ machine-like function
Levers

Humans moves through a system of levers

Levers cannot be changed, but they can be utilized more
efficiently


lever - a rigid bar that turns about an axis of rotation or a
fulcrum
axis - point of rotation about which lever moves

Levers rotate about an axis as a result of force (effort, E) being
applied to cause its movement against a resistance or weight

In the body



bones represent the bars
joints are the axes
muscles contract to apply force
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Levers
 Three points determine type of lever & for which
kind of motion it is best suited
 Axis (A)- fulcrum - the point of rotation
 Point (F) of force application (usually muscle
insertion) - effort
 Point (R) of resistance application (center of
gravity of lever) or (location of an external
resistance)
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Concepts
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Levers Systems
 1st class lever – axis (A) somewhere
between force (F) & resistance (R)
 2nd class lever – resistance (R) somewhere
between axis (A) & force (F)
 3rd class lever – force (F) somewhere
between axis (A) & resistance (R)
Manual of
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Levers
• FAR
1st
Force Arm
|
||
Resistance Arm
F
|
R
A
• ARF
2nd
| Resistance Arm |
|
Force Arm
R
|
F
A
• AFR
3rd
|
|
Force Arm
|
Resistance Arm
F
A
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Concepts
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|
R
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First-class Levers
 Produce balanced movements
when axis is midway between
force & resistance (e.g., seesaw
or scissors)
 Produce speed & range of
motion when axis is close to
force, (triceps in elbow
extension)
 Produce force motion when axis
is close to resistance (crowbar)
Manual of
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First-class Levers
 Head balanced on neck in flexing/extending
 Elbow extension in triceps applying force to
olecranon (F) in extending the nonsupported forearm (R) at the elbow (A)
 Agonist & antagonist muscle groups are
contracting simultaneously on either side of
a joint axis

agonist produces force while antagonist
supplies resistance
First-class Levers
 Force is applied where muscle inserts
in bone, not in belly of muscle
 Ex. in elbow extension with shoulder
fully flexed & arm beside the ear, the
triceps applies force to the olecranon
of ulna behind the axis of elbow joint
 As the applied force exceeds the
amount of forearm resistance, the
elbow extends
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Structural Kinesiology
Levers
 The mechanical advantage of levers may be
determined using the following equations:
Mechanical advantage =
Resistance
Force
or
Mechanical advantage =
Length of force arm
Length of resistance arm
Torque and length of lever arms
First class levers
A, If the force arm & resistance arm
are equal in length, a force equal to
the resistance is required to balance it;
B, As the force arm becomes longer, a
decreasing amount of force is required
to move a relatively larger resistance;
C, As the force arm becomes shorter,
an increasing amount of force is
required to move a relatively smaller
resistance
Second-class Levers
 Produces force movements,
since a large resistance can be
moved by a relatively small
force
 Wheelbarrow
 Nutcracker
 Loosening a lug nut
 Raising the body up on the toes
Second-class Levers
 Plantar flexion of foot to raise the
body up on the toes where ball (A)
of the foot serves as the axis as
ankle plantar flexors apply force to
the calcaneus (F) to lift the
resistance of the body at the tibial
articulation (R) with the foot
 Relatively few 2nd class levers in
body
Torque and length of lever arms
Second class levers
A, Placing the resistance halfway
between the axis & the point of force
application provides a MA of 2;
B, Moving the resistance closer to
the axis increases the MA, but
decreases the distance that the
resistance is moved;
C, the closer the resistance is
positioned to the point of force
application the less of a MA, but the
greater the distance it is moved
Third-class Levers
 Produce speed & range-of-motion
movements
 Most common in human body
 Requires a great deal of force to move
even a small resistance

Paddling a boat

Shoveling - application of lifting force to a
shovel handle with lower hand while upper
hand on shovel handle serves as axis of
rotation
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Concepts
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Third-class Levers
 Biceps brachii in elbow flexion
Using the elbow joint (A) as the axis,
the biceps brachii applies force at its
insertion on radial tuberosity (F) to
rotate forearm up, with its center of
gravity (R) serving as the point of
resistance application
Torque and length of lever arms
Third class levers
A, a force greater than the resistance,
regardless of the point of force
application, is required due to the
resistance arm always being longer;
B, Moving the point of force application
closer to the axis increases the range
of motion & speed;
C, Moving the point of force application
closer to the resistance decreases the
force needed
Torque and length of lever
arms
 Long levers produce more
linear force and thus better
performance in some sports
such as baseball, hockey, golf,
field hockey, etc.
 For quickness, it is desirable
to have a short lever arm
3-55
Pulleys
 Single pulleys function to
change effective direction of
force application
 Mechanical advantage = 1
 Pulleys may be combined to
form compound pulleys to
increase mechanical
advantage
 Each additional rope increases
mechanical advantage by 1
Pulleys
 Ex. lateral malleolus acting as a pulley
around which tendon of peroneus longus
runs
 As peroneus longus contracts, it pulls toward
it belly (toward the knee)
 Using the lateral malleolus as a pulley, force
is transmitted to plantar aspect of foot
resulting in eversion/plantarflexion
Force
 Muscles are the main source of force that produces or
changes movement of a body segment, the entire
body, or some object thrown, struck, or stopped
 Strong muscles are able to produce more force than
weak muscles
 both maximum and sustained exertion over a period of
time
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Force
 Forces either push or pull on an object in an attempt
to affect motion or shape
 Without forces acting on an object there would be no
motion
 Force - product of mass times acceleration
 Mass - amount of matter in a body
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Force
 The weight of a body segment or the entire body X the
speed of acceleration determines the force
 Important in football
 Also important in activities using only a part of the body
 In throwing a ball, the force applied to the ball is equal
to the weight of the arm times the speed of acceleration
of the arm
 Leverage factors are also important
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Concepts
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Mechanical loading basics
 Significant mechanical loads are generated &
absorbed by the tissues of the body
 Internal or external forces may cause these loads
 Only muscles can actively generate internal force, but
tension in tendons, connective tissues, ligaments and
joints capsules may generate passive internal forces
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Web Sites
Biomechanics: The Magazine of Body Movement and Medicine
www.biomech.com/
Biomechanics World Wide
www.uni-essen.de/~qpd800/WSITECOPY.html
 This site enables the reader to search the biomechanics
journals for recent information regarding mechanism of injury.
Kinesiology Biomechanics Classes
www.uoregon.edu/~karduna/biomechanics/kinesiology.htm
 A listing of numerous biomechanics and kinesiology class site
on the web with many downloadable presentations and notes
The Physics Classroom
www.physicsclassroom.com/
 Numerous topics including the laws of motion and other physics
principles
Basic Biomechanical Factors &
Concepts
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Manual of
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Web Sites
Edquest
www.edquest.ca/pdf/sia84notes.pdf
 Text, pictures, and illustrations on simple and complex
machines
COSI Hands-on science centers
www.cosi.org/files/Flash/simpMach/sm1.swf
 A Flash site demonstrating simple machine explanations
EuclideanSpace - building a 3D world
www.euclideanspace.com
 Information on how to simulate physical objects with
computer programs
Physics Homework Help
http://tutor4physics.com/index.htm
 Physics formulas, principles, tutorials
Basic Biomechanical Factors &
Concepts
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Web Sites
GRD Training Corporation
www.physchem.co.za
 Explanations of physics principles for in motion with quizzes
International Society of Biomechanics
www.isbweb.org/
 Software, data, information, resources, yellow pages, conferences
Sports Coach—Levers
www.brianmac.demon.co.uk/levers.htm

A basic review of levers with excellent links to the study of muscle
training & function.
Integrated Publishing
www.tpub.com/content/engine/14037/index.htm

Engine mechanics
Basic Biomechanical Factors &
Concepts
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Web Sites
Human Anatomy Online
http://innerbody.com/image/musfov.html
 An interactive site with details on the muscular and nervous
systems.
BBC Science & Nature
http://bbc.co.uk/science/humanbody/body/interactives/3djigs
aw_02/index.shtml
 An interactive site allowing you to select the innervation for
the muscles.
Functions of the Muscular System
http://training.seer.cancer.gov/anatomy/muscular
 Several pages with information on skeletal muscle structure,
types, and groups, along with unit review and quizzes.
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Web Sites
U.S. National Library of Medicine’s Visible Human Project AnatQuest
Anatomic Images Online
http://anatline.nlm.nih.gov/AnatQuest/AwtCsViewer/aq-cutaway.html

A great resource using a cut-away viewer to see cadaver images
throughout the body to identify the relevant anatomy.
The Physician and Sportsmedicine
www.physsportsmed.com/index.php?article=1476

Refining rehabilitation with proprioception training: expediting return
to play.
Get Body Smart
www.getbodysmart.com/index.htm

An online interactive tutorial on the muscular and nervous systems.
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Web Sites
Neurologic Exam: An anatomical approach
http://medlib.med.utah.edu/neurologicexam/home_exam.html
 A very thorough site on neurological exams, including numerous
movies with both normal and pathological results.
Cranial Nerves: Review info
www.gwc.maricopa.edu/class/bio201/cn/cranial.htm
 A good resource on the cranial nerves.
University of Arkansas for Medical Sciences Nerve tables
http://anatomy.uams.edu/anatomyhtml/nerves.html
 Numerous tables of all nerves throughout the body.
Dermatomes
www.meddean.luc.edu/lumen/MedEd/GrossAnatomy/learnem/dermat/m
ain_der.htm
 An interactive review of the body’s dermatomes.
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Web Sites
Loyola University Medical Education Network Master Muscle List
www.meddean.luc.edu/lumen/MedEd/GrossAnatomy/dissector/mml

An interactive and graphical review of the muscles indexed alphabetically and by region.
Proprioception Exercises Can Improve Balance
http://sportsmedicine.about.com/library/weekly/aa062200.htm

Proprioception.
Muscular System
www.bio.psu.edu/faculty/strauss/anatomy/musc/muscular.htm

Cadavaric photos of the cat muscular system.
Functions of the Nervous System
http://training.seer.cancer.gov/anatomy/nervous

Several pages with information on the nervous system organization, nerve structure, unit
review, and quizzes.
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Web Sites
Training for Proprioception & Function
www.coachr.org/proprio.htm

Information on improving body awareness movement efficiency.
Neuromuscular Fundamentals
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Manual of
Structural Kinesiology