Download Muscle Contraction

Somatic Nervous System
Divisions of the PNS:
Somatic Nervous System
• Controls voluntary actions
• Made up of the cranial and spinal nerves that
go from the central nervous system to your
skeletal muscles
Autonomic Nervous System
• Controls involuntary actions-those not under
conscious control-such as your heart rate,
breathing, digestion, and glandular functions
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
2-3
Skeletal Muscles
Manual of
Structural Kinesiology
Neuromuscular Fundamentals
2-4
Skeletal Muscles
• Over 600 skeletal muscles comprise approximately
40 to 50% of body weight
• 215 pairs of skeletal muscles usually work in
cooperation with each other to perform opposite
actions at the joints which they cross
• Aggregate muscle action - muscles work in groups
rather than independently to achieve a given joint
motion
2-5
Muscle Tissue Properties
Skeletal muscle tissue has 4 properties related to its ability to produce force &
movement about joints
• Irritability or Excitability - property of muscle being sensitive or responsive to chemical,
electrical, or mechanical stimuli
• Contractility - ability of muscle to contract & develop tension or internal force against
resistance when stimulated – unique to muscle
• Extensibility - ability of muscle to be passively stretched beyond it normal resting length
• Elasticity - ability of muscle to return to its original length following stretching
2-6
Muscle Terminology
• Action - specific movement of joint resulting from a concentric
contraction of a muscle which crosses joint
• Ex. biceps brachii has the action of flexion at elbow
• Actions are usually caused by a group of muscles working together
2-7
Muscle Terminology
• Innervation - segment of nervous system defined as being responsible
for providing a stimulus to muscle fibers within a specific muscle or
portion of a muscle
• A muscle may be innervated by more than one nerve & a particular nerve
may innervate more than one muscle or portion of a muscle
2-8
Muscle Terminology
• When a particular muscle contracts
• it tends to pull both ends toward the gaster
• if neither of the bones to which a muscle is attached are stabilized then both
bones move toward each other upon contraction
• more commonly one bone is more stabilized by a variety of factors and the
less stabilized bone usually moves toward the more stabilized bone upon
contraction
• Ex. biceps curl exercise
• biceps brachii muscle in arm has its origin (least movable bone) on scapula
and its insertion (most movable bone) on radius
• In some movements this process can be reversed, Ex. pull-up
• radius is relatively stable & scapula moves up
• biceps brachii is an extrinsic muscle of elbow
• brachialis is intrinsic to the elbow
2-9
Types of muscle contraction
• Contraction - when tension is developed in a muscle as a result
of a stimulus
• Muscle “contraction” – may not necessarily mean shorten
• Muscle contractions also referred to as muscle actions
2-10
Types of muscle contraction
Muscle Contraction
(under tension)
Isometric
Isotonic
Concentric
Eccentric
2-11
Types of muscle contraction
• Isotonic contractions involve muscle developing tension to either
cause or control joint movement
• dynamic contractions
• the varying degrees of tension in muscles result in joint angles changing
• Isotonic contractions are either concentric or eccentric on basis of
whether shortening or lengthening occurs
Types of muscle contraction
• Concentric contraction
• muscle develops tension as it shortens
• occurs when muscle develops enough
force to overcome applied resistance
• causes movement against gravity or
resistance
• described as being a positive contraction
2-13
Types of muscle contraction
• Concentric contraction
• force developed by the muscle is
greater than that of the resistance
• results in joint angle changing in the
direction of the applied muscle force
• causes body part to move against
gravity or external forces
2-14
Types of muscle contraction
• Eccentric contraction (muscle action)
• muscle lengthens under tension
• occurs when muscle gradually lessens in
tension to control the descent of
resistance
• weight or resistance overcomes muscle
contraction but not to the point that
muscle cannot control descending
movement
2-15
Types of muscle contraction
• Eccentric contraction (muscle action)
• controls movement with gravity or
resistance
• described as a negative contraction
• force developed by the muscle is less
than that of the resistance
2-16
Types of muscle contraction
• Eccentric contraction (muscle action)
• results in the joint angle changing in the
direction of the resistance or external
force
• controls body part to allow movement
with gravity or external forces
(resistance)
• used to decelerate body segment
movement
2-17
Types of muscle contraction
• Eccentric contraction (muscle action)
• Some refer to this as a muscle action instead of a contraction since the muscle
is lengthening as opposed to shortening
• Various exercises may use any one or all of these contraction types for
muscle development
2-18
Types of muscle contraction
• Isokinetics (isovelocity) - type of dynamic exercise
using concentric and/or eccentric muscle
contractions
• speed (or velocity) of movement is constant
• muscular contraction (ideally maximum contraction)
occurs throughout movement
• not another type of contraction, as some have described
• Ex. Biodex, Cybex, Lido
2-19
Role of Muscles
• Agonist muscles
• cause joint motion through a specified plane of motion when contracting
concentrically
• known as primary or prime movers, or muscles most involved
2-20
Role of Muscles
• Antagonist muscles
•
•
•
•
located on opposite side of joint from 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
2-21
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
2-22
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
helping synergists & true synergists
2-23
Role of Muscles
• Neutralizers
• counteract or neutralize the action of another muscle
to prevent undesirable movements such as
inappropriate muscle substitutions
• referred to as neutralizing
• contract to resist specific actions of other muscles
• Ex. when only supination action of biceps brachii is
desired, the triceps brachii contracts to neutralize the
flexion action of the biceps brachii
2-24
Throughout the central nervous system, the neurons involved in controlling
skeletal muscles can be thought of as being organized in a hierarchical fashion,
each level of the hierarchy having a certain task in motor control
• Given such a highly interconnected and complicated neuroanatomical basis
for the motor system, it is difficult to use the phrase voluntary movement
with any real precision.
• We will use it, however, to refer to those actions that have the following
characteristics:
• (1)The movement is accompanied by a conscious awareness of what we are doing
and why we are doing it, and
• (2) our attention is directed toward the action or its purpose.
• The term “involuntary,” on the other hand, describes actions that do not
have these characteristics.
• “Unconscious,” “automatic,” and “reflex” are often taken to be synonyms
for “involuntary,” although in the motor system the term “reflex” has a
more precis meaning.
Conceptual Motor Control Hierarchy
I.
The lowest level
(the local level)
a. Function: specifies tension of
particular muscles and angle of
specific joints at specific times
necessary to carry out the
programs and subprograms
transmitted from the middle
control levels.
b. Structures: levels of brainstem
or spinal cord from which motor
neurons exit.
Conceptual Motor Control Hierarchy
II. The middle level
a. Function: converts plans received
from the highest level to a number of
smaller motor programs, which
determine the pattern of neural
activation required to
perform the movement.
These programs are broken down into
subprograms that determine the
movements of individual joints.
The programs and subprograms are
transmitted through descending
pathways to the lowest control level.
b. Structures: sensorimotor cortex,
cerebellum, parts of basal nuclei, some
brainstem nuclei.
Conceptual Motor Control Hierarchy
III. Higher centers
a. Function: forms complex
plans according to individual’s
intention and communicates
with the middle level via
“command neurons.”
b. Structures: areas involved
with memory and emotions,
supplementary motor area, and
association cortex.
All these structures receive and
correlate input from many other
brain structures.
Neurons (nerve cells) - basic functional units of nervous system
responsible for generating & transmitting impulses and consist of
ALL OR NONE PRINCIPLE
• When muscle contracts, contraction occurs at
the muscle fiber level within a particular motor
unit
• Motor unit
• Single motor neuron & all muscle fibers it
innervates
• Function as a single unit
• All or None Principle - regardless of number,
individual muscle fibers within a given motor
unit will either fire & contract maximally or not
at all
2-29
Factors affecting muscle tension development
• 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
2-30
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
2-31
Factors affecting muscle tension development
• Summation
• When successive stimuli are provided before relaxation
phase of first twitch has completed, subsequent
twitches combine with the first to produce a sustained
contraction
• Generates a greater amount of tension than single
contraction would produce individually
• As frequency of stimuli increase, the resultant
summation increases accordingly producing
increasingly greater total muscle tension
2-32
Factors affecting muscle tension development
• Tetanus
• results if the stimuli are provided at a frequency high
enough that no relaxation can occur between
contractions
2-33
Interneurons
• Most of the synaptic input to motor neurons from
the descending pathways and afferent neurons
does not go directly to motor neurons but rather to
interneurons that synapse with the motor neurons.
• Interneurons comprise 90 percent of spinal cord
neurons, and they are of several types.
• The local interneurons are important elements of
the lowest level of the motor control hierarchy,
integrating inputs not only from higher centers and
peripheral receptors but from other interneurons
as well.
• They are crucial in determining which muscles are
activated and when.
• Moreover, interneurons can act as “switches” that
enable a movement to be turned on or off under
the command of higher motor centers.
Proprioception & Kinesthesis
•
Muscle spindles & myotatic or
stretch reflex
1. Rapid muscle stretch occurs
2. Impulse is sent to the CNS
3. CNS activates motor neurons of
muscle and causes it to contract
2-35
Proprioception & Kinesthesis
•
Ex. Knee jerk or patella tendon reflex
•
•
•
•
Reflex hammer strikes patella tendon
Causes a quick stretch to musculotendinis unit of
quadriceps
In response quadriceps fires & the knee extends
More sudden the tap, the more significant the
reflexive contraction
2-36
Proprioception & Kinesthesis
•
Manual of
Structural Kinesiology
Ex. Knee jerk or patella tendon reflex
Neuromuscular Fundamentals
2-37
Proprioception & Kinesthesis
•
Stretch reflex may be utilized to facilitate a greater
response
•
•
Ex. Quick short squat before attempting a jump
Quick stretch placed on muscles in the squat enables the
same muscles to generate more force in subsequently
jumping off the floor
2-38
Proprioception & Kinesthesis
•
Golgi tendon organ
•
•
•
•
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
2-39
Proprioception & Kinesthesis
•
Tension in tendons & GTO increases as muscle contract, which activates
GTO
1. GTO stretch threshold is reached
2. Impulse is sent to CNS
3. CNS causes muscle to relax
4. facilitates activation of antagonists as a protective mechanism
•
GTO protects us from an excessive contraction by causing its muscle to
relax
2-40
Reciprocal Innervation
• Sensory neuron stimulates
motor neuron and interneuron.
• Interneurons inhibit motor
neurons of antagonistic
muscles.
• When limb is flexed,
antagonistic extensor muscles
are passively stretched.
Crossed-Extensor Reflex
• Double reciprocal innervation.
• Affects muscles on the
contralateral side of the cord.
• Step on tack:
• Foot is withdrawn by
contraction of flexors and
relaxation of extensors.
• Contralateral leg extends to
support body.
motor pathways
• Descending motor pathways (i.e.,
those descending from the cerebral
cortex and brain stem) are divided
among the pyramidal tract and the
extrapyramidal tract.
• Pyramidal tracts are corticospinal
and corticobulbar tracts that pass
through the medullary pyramids and
descend directly onto lower
motoneurons in the spinal cord.
• All others are extrapyramidal tracts.
The extrapyramidal tracts originate in the following structures of the brain stem:
• The rubrospinal tract originates in the red nucleus and projects to motoneurons in the lateral
spinal cord.
• Stimulation of the red nucleus produces activation of flexor muscles and inhibition of
extensor muscles.
• The pontine reticulospinal tract originates in nuclei of the pons and projects to the
ventromedial spinal cord.
• Stimulation has a generalized activating effect on both flexor and extensor muscles, with its
predominant effect on extensors.
• The medullary reticulospinal tract originates in the medullary reticular formation and projects
to motoneurons in the spinal cord.
• Stimulation has a generalized inhibitory effect on both flexor and extensor muscles, with
the predominant effect on extensors.
• The lateral vestibulospinal tract originates in the lateral vestibular nucleus (Deiters' nucleus)
and projects to ipsilateral motoneurons in the spinal cord.
• Stimulation produces activation of extensors and inhibition of flexors.
• The tectospinal tract originates in the superior colliculus (tectum or "roof" of the brain stem)
and projects to the cervical spinal cord.
• It is involved in control of neck muscles.
• Both the pontine reticular formation
and the lateral vestibular nucleus have
powerful excitatory effects on extensor
muscles.
• Therefore, lesions of the brain stem
above the pontine reticular formation
and lateral vestibular nucleus, but
below the midbrain, cause a dramatic
increase in extensor tone, called
decerebrate rigidity.
• Lesions above the midbrain do not
cause decerebrate rigidity.
Functional subdivision of
cerebellum
• The cerebellum, or "little brain," regulates movement and
posture and plays a role in certain kinds of motor learning.
• The cerebellum helps control the rate, range, force, and
direction of movements (collectively known as synergy).
• Damage to the cerebellum results in lack of coordination.
I- Archicerebellum
It is concerned with equilibrium.
It represents flocculo-nodular lobe.
It has connections with vestibular &
reticular nuclei of brain stem through
the inferior cerebellar peduncle.
Schematic drawing of cerebellum
showing the relationships between
the anatomical & functional divisions
of cerebellum.
Green =archi-cerebellum,
blue=paleo-cerebellum.
Pink= neo-cerebellum
I- Archicerebellum
It is concerned with equilibrium.
It represents flocculo-nodular lobe.
It has connections with vestibular &
reticular nuclei of brain stem through
the inferior cerebellar peduncle.
Afferent vestibular Fs. Pass from
vestibular nuclei in pons & medulla to the
cortex of ipsilateral flocculo-nodular lobe.
Efferent cortical (purkinje cell) Fs.
Project to fastigial nucleus, which projects to
vestibular nuclei & reticular formation.
Connections of
archicerebellum
It affects the L.M.system bilaterally via
descending vestibulo-spinal & reticulo-spinal
tracts.
2- Paleo-cerebellum=
(spinal part) :
It is concerned with muscle tone &
posture.
Schematic drawing of cerebellum
showing the relationships between the
anatomical & functional divisions of
cerebellum.
Green =archi-cerebellum,
blue=paleo-cerebellum.
Pink= neo-cerebellum
2-Paleo-cerebellum
It is concerned with muscle tone
& posture.
Afferents spinal Fs. consist of
dorsal & ventral spino-cerebellar
tract from muscle, joint &
cutaneous receptors to enter the
cortex of ipsilateral vermis & para
vermis Via inferior & superior
cerebellar peduncles .
Connections of Paleocerebellum.
Efferents cortical fibres pass to
globose & emboliform nuclei, then
Via sup. C. peduncle to contralateral red nucleus of midbrain to
give rise descending rubro-spinal
tract.
3- Neo-cerebellum=
(cerebral part) :
It is concerned with muscular coordination.
controls the planning and initiation of
movements
Schematic drawing of cerebellum
showing the relationships between the
anatomical & functional divisions of
cerebellum.
Green =archi-cerebellum,
blue=paleo-cerebellum.
Pink= neo-cerebellum
3- Neo-cerebellum
It is concerned with muscular coordination.
controls the planning and initiation of movements
It receives afferents from cerebral cortex involved
in planning of movement- to pontine nuclei ,cross to
opposite side Via middle Cerebellar peduncle to end
in lateral parts of cerebellum (cerebro-pontocerebellar tract).
Neo-cerebellar efferents project to dendate
nucleus,which in turn projects to contra-lateral red
nucleus & ventral lateral nucleus of thalamus ,then
to motor cortex of frontal lobe, giving rise
descending cortico-spinal & cortico-bulbar pathways.
Connections of Neo-cerebellum.
Efferents of dentate nucleus form a major part of
superior C. peduncle.
BASAL GANGLIA
The basal ganglia are the deep nuclei of the telencephalon:
• caudate nucleus,
• putamen,
• globus pallidus, and
• amygdala.
There also are associated nuclei, including
• the ventral anterior and ventral lateral nuclei of the thalamus,
• the subthalamic nucleus of the diencephalon, and
• the substantia nigra of the midbrain.
The main function of the basal ganglia is to influence the motor cortex via
pathways through the thalamus.
The role of the basal ganglia is to aid in planning and execution of smooth
movements.
The basal ganglia also contribute to affective and cognitive functions.
Cerebral Cortex
Corticospinal tract and
Corticobulbar projections
Brainstem and
Spinal Cord
Cerebral Cortex
Striatum
Glutamate
Brainstem and
Spinal Cord
Cerebral Cortex
Striatum
Glutamate
D1
D2
Dopamine
Substantai Nigra compacta
Brainstem and
Spinal Cord
Cerebral Cortex
Striatum
Glutamate
Glutamate
D1
GABA-dyn
DA
Direct
Pathway
Thalamus
SNc
GABA
Brainstem and
Spinal Cord
Globus pallidus interna/Substantia Nigra reticulata
Cerebral Cortex
Glutamate
Striatum
D2
GABA-enk
Globus
Pallidus
externa
D1
GABA-dyn
Thalamus
DA
Subthalamic
Nucleus
SNc
Glutamate
Brainstem and
Spinal Cord
Glutamate
GABA
Gpi/SNr
The outputs of the indirect and direct
pathways from the basal ganglia to
the motor cortex are opposite and
carefully balanced:
The indirect path is inhibitory, and
the direct path is excitatory.
Cerebral Cortex
Glutamate
Indirect
Pathway
Striatum
D2
GABA-enk
Globus
Pallidus
externa
Subthala
mic
Nucleus
Brainstem and
Spinal Cord
Gluta
mate
D1
GABAdyn
DA
Direct
Pathway
Thalamus
A disturbance in one of the pathways
SNc
will upset this balance of motor
control, with either an increase or a
decrease in motor activity.
GABA
Glutamate
Such an imbalance is characteristic of
Globus pallidus interna/Substantia Nigra reticulata
diseases of the basal ganglia.
MOTOR CORTEX
• Voluntary movements are directed by the motor cortex, via descending
pathways.
• The motivation and ideas necessary to produce voluntary motor activity are first
organized in multiple associative areas of the cerebral cortex and then
transmitted to the supplementary motor and premotor cortices for the
development of a motor plan.
• The motor plan will identify the specific muscles that need to contract, how
much they need to contract, and in what sequence.
• The plan then is transmitted to upper motoneurons in the primary motor
cortex, which send it through descending pathways to lower motoneurons in
the spinal cord.
• The planning and execution stages of the plan are also influenced by motor
control systems in the cerebellum and basal ganglia.
• The motor cortex consists of three
areas:
• primary motor cortex,
• supplementary motor cortex, and
• premotor cortex.
• Premotor cortex and supplementary
motor cortex (area 6) are the regions
of the motor cortex responsible for
generating a plan of movement,
which then is transferred to the
primary motor cortex for execution.
• The supplementary motor cortex
programs complex motor sequences
and is active during "mental
rehearsal" of a movement, even in
the absence of movement.
• Primary motor cortex (area 4) is the
region of the motor cortex responsible
for execution of a movement.
• Programmed patterns of motoneurons
are activated from the primary motor
cortex.
• As upper motoneurons in the motor
cortex are excited, this activity is
transmitted to the brain stem and spinal
cord, where lower motoneurons are
activated and produce coordinated
contraction of the appropriate muscles
(i.e., the voluntary movement).
• The primary motor cortex is
topographically organized and is
described as the motor homunculus.
• This topographic organization is
dramatically illustrated in jacksonian
seizures, which are epileptic events
originating in the primary motor cortex.
• The epileptic event usually begins in the
fingers of one hand, progresses to the
hand and arms, and eventually spreads
over the entire body (i.e., the
"jacksonian march").