Movement

MOVEMENT

INTRODUCTION

When performing a task related to motion or posture, all motor commands from the central nervous system are expressed through changes in the magnitude of neural excitation of skeletal muscle.

The response of the activated muscle is force generation for the purpose of creating or restraining motion. The magnitude and mode of the resulting muscle force depends on the properties of muscle, the mechanical load experienced by the muscle, the nature of the neural excitation, and feedback from the muscle receptors.

Neural Systems

Hierarchy of motor system : • Spinal cord.• Brain stem and Reticular

formation.• Motor cortex, and the

Premotor cortical areas that include the Basal ganglia.

• Cerebellum.

Each division contains separate neural circuits that are linked to each of the other divisions.

• In the adult human, the spinal cord extends from the foramen magnum to the lower border of the first lumbar vertebra.

• Axons enter and exit the spinal cord via the spinal nerves, each of which consists of a ventral or efferent root and a dorsal or afferent root.

• The ventral roots carry output to the striated muscles from the myelinated nerve fibers of the and γ motoneurons in the gray matter of the ventral horn.

• The dorsal roots carry sensory input from myelinated and unmyelinated nerve fibers that originate from somatic sensory receptors.

• The cell bodies of the afferent fibers are located in the dorsal root ganglia.

• In humans there are 31 pairs of spinal nerves root: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal. In a given species, the spinal nerves grow into the limb bud in a highly stereotyped way, collecting first into plexuses from which major branches emerge.

• In humans, 3 Major Plexuses : Cervical (C-1 to C-4), Brachial (C-5 to T-1), and Lumbosacral (T-12 to S-4)—provide innervation to the muscles of the upper and lower extremities.

• The basic functional unit of a muscle is the motor unit, which consists of an α motoneuron, its motor axon, and all the muscle fibers it innervates.

• A motor unit is stimulated to contract by an electrical impulse, or action potential, which originates from the cell body of the nerve. This potential is propagated down the entire length of the axon from the spinal cord to the peripheral skeletal muscle.

• The nerve forms a synapse with the muscle at a specialized region known as the motor end plate.

• Sensory systems receive information from the environment and within the body through receptors located at the periphery of the body and transmit this information to the spinal cord and brain via 2 pathways: the dorsal column-medial lemniscal tract and the anterolateral tract.

• This information is used for 3 primary functions: sensation, control of movement, and maintaining arousal.

• External stimuli are recognized by specialized neural structures called sensory receptors. Each receptor is sensitive to a specific form of physical energy: mechanical, thermal, chemical, or electromagnetic.

• The somatic sensory system conveys 3 distinct modalities: mechanical (touch) and mechanical displacements of the muscles and joints (proprioception); pain (tissue damaging) stimuli; and thermal sensation stimuli. Within each modality there are submodalities; for example, superficial and deep touch (pressure).

Spinal Mechanisms for Control of Movement

• The spinal cord is engaged in 3 aspects of movement regulation.• In information transmission, the spinal cord relays afferent

information to higher centers in the spinal cord, brain stem, and beyond.

• In the opposite direction, efferent commands are transmitted from higher centers to the motor nuclei within the spinal cord.

• During reflex action, spinal cord neurons and their connections form the substrates for a variety of sensory-motor reflexes.

• A reflex is a stereotypic motor response to a particular sensory input, such as :– Autogenic or homonymous reflexes– Heteronymous reflexes– Synergists reflexes– Reciprocal pattern of activation – Flexor withdrawal reflex– Complex goal-directed reflexes

JOINT STRUCTURE

• Humans belong to the vertebrate portion of the phylum Chordata, and as such possess a bony endoskeleton that includes a vertebral spine and paired extremities.

• Each extremity is composed of articulated skeletal segments linked together by connective tissue elements and surrounded by skeletal muscle.

• Motion between skeletal segments occurs at joints. Most joint motion is minimally translational and primarily rotational.

• Joint stability is created by bony configurations, ligaments, and muscles; combinations of these constructs differ between joints.

• Bone primarily constrains translational motions. Where rotation is needed, there is no bony blockage.

• Because bone is the most rigid anatomic structure, the greater the circumference of the joint enclosed by bone, the greater the amount of inherent translational stability that exists in the joint.

• Ligaments can restrict or constrain rotational or translational motions. By the tension developed in it when it is stretched, a ligament resists motion along the axes in which it lies. Unlike bone, however, ligaments allow some motion to occur, and thus, cannot be considered rigid constraints.

• The position of the ligament is the key to the type of motions it limits. For example, at the knee, the cruciate ligaments limit the anteroposterior (AP) translation of the tibia on the femur.

• Muscle-tendon complexes are also semirigid restraints and complement the action of ligaments to stabilize joints.

• However, because ligaments are only passive stabilizers, muscles, which are active in controlling joint motion, have an obvious advantage. Muscle action, in fact, can protect ligaments from tearing in most instances. Muscle contraction produces compressive force across the joint tending to squeeze the joint together. This compressive force maintains stability against forces that might pivot a joint open.

• Where the compressive forces of a muscle are parallel to those exerted by the tensile forces occurring in the ligament, they provide load sharing. Where their direction of force is opposite, muscles can work in concert with the ligaments and serve to protect the joint when disruption of the ligament occurs.

• An example of this interaction is the protection the hamstrings provide when the anterior cruciate ligament (ACL) is torn. Thus, not only are muscles the force actuators at joints that initiate or prevent a desired movement, but they also can limit motions caused by external body weight or antagonist muscles harmful to joint stability.

• Without joint stability, true functional motion cannot exist because much displacement will occur between the 2 rigid members at the joint surface. The extent to which each of the 3 structures—bone, ligaments, and muscles — contributes to joint stability differs at each joint.

Classification Based on Anatomic Structure

SYNARTHROSIS• A synarthrosis is a junction between bones that is held together by

dense irregular connective tissue. This relatively rigid junction allows little or no movement.

• Examples of synarthrodial joints include the sutures of the skull, the teeth embedded in the mandible and maxillae, the distal tibiofibular joint and the interosseous membranes of the forearm and leg.

• The function of a synarthrosis is to bind bones together and to transmit force from one bone to the next with minimal joint motion. A synarthrodial joint allows forces to be dispersed across a relatively large area of contact, thereby reducing the possibility of injury.

AMPHIARTHROSIS• An amphiarthrosis is a junction between bones that is formed

primarily by fibrocartilage and/or hyaline cartilage. • Example of an amphiarthrosis is the interbody joint of the spine,

pubic symphysis and the manubriosternal joint. • These joints allow relatively restrained movements. They also

transmit and disperse forces between bones.

DIARTHR0SIS (SYN0VIAL J0INT)• A diarthrosis is an articulation that contains a fluid-filled joint cavity

between bony partners. Because of the presence of a synovial membrane, diarthrodial joints are more frequently referred to as synovial joints. Synovial joints are the majority of the joints of the upper and lower extremities

• The joint cavity is filled with (1) synovial fluid. This provides nutrition and lubrication for the (2) articular cartilage that covers the ends of the bones. The joint is enclosed by a peripheral curtain of connective tissue that forms the (3) articular capsule. The articular capsule is composed of two histologically distinct layers.

• The internal layer consists of a thin (4) synovial membrane, which averages three to ten cell layers thick. The external, or fibrous layer of the articular capsule of the synovial joint is composed of dense irregular connective tissue. Certain regions of the fibrous capsule are thicker in order to resist or control specific motions, which represent (5) capsular ligaments. Examples of prominent capsular ligaments are the anterior glenohumeral ligaments and the medial collateral ligament of the knee. The joint capsule is supplied with small (6) blood vessels with capillary beds penetrate as far as the junction of the fibrous capsule synovial membrane. The (7) sensory nerves also supply the fibrous capsule with appropriate receptors for pain and proprioception.

Classification Based on Movement Potential

• A hinge joint is analogous to the hinge of a door, formed by a central pin surrounded by a larger hollow cylinder.

• Angular motion at hinge joints occurs primarily in a plane located at right angles to the hinge, or axis of rotation.

• The humeroulnar joint is a clear example of a hinge joint. As in all synovial joints, slight translation (i.e. sliding) is allowed in addition to the rotation. Although the mechanical similarity is less complete, the interphalangeal joints of the digits are also classified as hinge joints.

• A pivot joint is formed by a central pin surrounded by a larger cylinder.

• Unlike a hinge, the mobile member of a pivot joint is oriented parallel to the axis of rotation. This mechanical orientation produces the primary angular motion of spin, similar to a doorknob's spin around a central axis.

• Two excellent examples of pivot joints are the proximal radioulnar joint, and the atlantoaxial joint between the dens of the second cervical vertebra and the anterior arch of the first cervical vertebra.

• An ellipsoid joint has one partner with a convex elongated surface in one dimension that is mated with a similarly elongated concave surface on the second partner.

• The elliptic mating surfaces severely restrict the spin between the two surfaces but allow biplanar motions, usually defined as flexion-extension and abduction-adduction.

• The radiocarpal joint is an example of an ellipsoid joint. The flattened "ball" of the convex member of the joint (i.e., carpal bones) cannot spin within the elongated trough (i.e., distal radius) without dislocating .

• A ball-and-socket joint has a spherical convex surface that is paired with a cuplike socket.

• This joint provides motion in three planes. Unlike the ellipsoid joint, the symmetry of the curves of the two mating surfaces of the ball-and-socket joint allows spin without dislocation.

• Ball and-socket joints within the body include the glenohumeral joint and the hip joint.

• A plane joint is the pairing of two flat or relatively flat surfaces.

• Movements combine sliding and some rotation of one partner with respect to the other-much like a book can be slid over a tabletop.

• Most of the intercarpal joints are considered to be plane joints. The internal forces that cause or restrict movement between carpal bones are supplied by tension in muscles or ligaments.

• Each partner of a saddle joint has two surfaces: one surface is concave and the other is convex.

• These surfaces are oriented at approximate right angles to one another and are reciprocally curved.

• The carpometacarpal joint of the thumb is the clearest example of a saddle joint. The reciprocal, interlocking nature of this joint allows ample biplanar motion, but limited spin between the trapezium and the first metacarpal.

• A condyloid joint is much like a ball-and-socket joint except that the concave member of the joint is very shallow.

• Condyloid joints usually allow 2 degrees of freedom. Ligaments or bony incongruity restrains the third degree.

• Condyloid joints often occur in pairs, such as the knee, the temporo-mandibular joints, and the atlantooccipital joints, the metacarpophalangeal joint of the finger is also an example of a condyloid joint.

• The root word of the term "condyle" actually means "knuckle."

Standard Terminology

• Flexion and Extension are movements that occur parallel to the sagittal plane.

• Flexion is rotational motion that brings two adjoining long bones closer to each other, such as occurs in the flexion of the leg or the forearm.

• Extension denotes rotation in the opposite direction of flexion; for example, bending the head toward the chest is flexion and so is the motion of bending down to touch the foot. In that case, the spine is said to be flexed.

• If the movement of extension continues past the anatomical position, it is called hyperextension.

• Abduction and adduction are the movements of the limbs in the frontal/coronal plane.

• Abduction is movement away from the longitudinal axis of the body whereas adduction is moving the limb back.

• An another example of angular motion is the movement of the arm in a loop, and this movement is called circumduction.

• The rotation of a body part with respect to the long axis of the body or the body part is called rotation.

• The rotation of the head could be to the left or right. Similarly, the forearm and the hand can be rotated to a degree around the longitudinal axis of these body parts.

RANGE OF MOVEMENT (ROM)

• The range through which a joint can be moved.• Normal movement of a joint depends on:

– Shape of the joint– Restraining effect of the ligament and joint capsule.– Control exerted by the muscle– Nerve that stimulate the muscle

• Range of movement is slightly greater in children, particularly those younger than age 10 years and decreased motion occurs as adult age.

• Limitation of motion may occur on either active or passive movement and usually passive motion is greater and more reliable indication of the actual range of motion.

• Comparing the joint with the other side, can give initial clue for the limitation.

Structure and Function of the Shoulder Joint

• The shoulder joint allows the arm to move with respect to the thorax. This motion normally occurs through a complex interaction of the individual motions of the acromioclavicular, sternoclavicular, and glenohumeral joints as well as the scapulothoracic articulation.

• The shoulder complex allows the greatest range of motion of any “joint” in the body.

• Normal arm elevation in men has been reported as 167° or 168° and in women from 171° to 175°. Average extension or posterior elevation has been shown to be approximately 60° .

Structure and Function of the Elbow Joint

• The elbow is a complex joint that acts as a component link of the lever arm system in placing the hand. As a fulcrum for the forearm lever, its muscles provide the power to perform lifting activities.

• The elbow has 2 degrees of freedom: flexion-extension and axial rotation, or pronation-supination.

• The normal range of motion is between 0° and 140° to 160° of flexion-extension and forearm rotation with about 70° to 80° of pronation and 80° to 85° of supination.

• The functional arc of motion for most activities of daily living is 100° from 30° to 130° of flexion-extension with 50° of pronation and 50° of supination.

Structure and Function of the Wrist Joint

• The wrist or carpus provides a stable support for the hand, allowing for the transmission of grip forces as well as positioning of the hand and digits for fine movements.

• Traditionally, the carpal bones are described as being arranged in 2 anatomic rows. The proximal carpal row consists of the scaphoid, lunate, and triquetrum, and the distal row is formed by the trapezium, trapezoid, capitate, and hamate. The pisiform lies within the flexor carpi ulnaris tendon and, through its articulation with the trapezium, functions as a sesamoid; therefore, it is not included as a functional member of the proximal carpal row.

• The average amount of flexion-extension motion of the wrist is variable with a range of 84° to 169° and an average of 140°. The average range of flexion is 65° to 80° and of extension, 55° to 75°. Flexion usually exceeds extension by approximately 10°.

• The average combined radioulnar deviation is 65°, with a range of 15° to 25° of radial deviation and 30° to 45° of ulnar deviation. At rest, there is physiologic ulnar deviation of the wrist.

• The average arc of pronation-supination is 150° with a pronation range of 60° to 80° and a supination range of 60° to 85°.

• For most activities of daily living, the functional range of motion for the wrist is 5° to 40° of flexion, 30° to 40° of extension, and 10° of radial deviation to 15° to 30° of ulnar deviation.

Structure and Functionof the Hip Joint

• The hip joint is a ball-and-socket joint in which the head of the femur resides in the acetabulum of the pelvis.

• The acetabulum has a hemispheric shape and is composed of portions from all 3 sections of the pelvis (the ilium, ischium, and pubis).

• It faces in an inferior and anterolateral direction.

• The femoral head forms approximately a 125° to 135 ° angle of inclination with the femoral shaft.

• The angle of femoral torsion in the adult measures 12° to15°

• The range of hip flexion-extension averages approximately 135° (knee to chest), and extension averages approximately 30°.

• Internal-external rotation of the hip joint around longitudinal axis about 35° of external rotation and 15° of internal rotation.

• Abduction averages approximately 45° and adduction approximately 25°.

Structure and Functionof the Knee

• The knee actually consists of 2 joints: the femorotibial joint and the patellofemoral joint.

• The femorotibial joint is the largest joint in the body and is considered to be a modified hinged joint containing the articulating ends of the femur and tibia.

• The patellofemoral joint consists of the patella, the largest sesamoid bone, and the trochlea of the femur.

• The bony architecture of the femur, tibia, and patella contributes to joint stability, but the cruciate and collateral ligaments are the major structures limiting motion at the knee.

• Menisci deepen the tibial plateaus slightly, which provides for a somewhat more congruent and constrained surface with the femoral condyles.

TERIMA KASIH