VII Glossary

Acetylcholine (ACh): Neurotransmitter that plays a key role in muscle contraction and communication between neurons in the nervous system. (Chapter 7.3)

Actin: A protein that forms thin filaments in muscle fibers and essential for muscle contraction through its interaction with myosin. (Chapter 7.3)

Action potentials: Rapid electrical signals. (Chapter 7.3)

Agonist: A muscle that contracts to produce a specific movement. Also known as the “prime mover.” (Chapter 7.3)

Amyotrophic lateral sclerosis (ALS):  A disease that causes the nerve cells in both the upper and lower parts of the body to stop working and die; also called Lou Gehrig’s disease. (Chapter 7.6)

Antagonist: Muscle with the opposite action of the prime mover. (Chapter 7.3)

Aortic hiatus: Opening in the diaphragm that allows the aorta, the body’s main artery, to pass from the thoracic cavity into the abdominal cavity. (Chapter 7.3)

Aponeurosis: A flat, broad connective tissue that connects muscles to each other or to bones. (Chapter 7.3)

Atrophy: Decrease in the size and strength (but not the number) of muscle fibers. (Chapter 7.3)

Belly: The central, fleshy part of a muscle, which typically contains the bulk of muscle fibers. (Chapter 7.3)

Biceps brachii: A muscle located in the upper arm. It has two main parts (or “heads”) and is responsible for bending the elbow and rotating the forearm. (Chapter 7.3)

Biceps femoris: Muscle located on the lateral side of the posterior thigh. (Chapter 7.3)

Bipennate: Fascicles on both sides of the tendon. (Chapter 7.3)

Brachialis: Provides additional power in flexing the forearm at the elbow; found deep to the biceps brachii. (Chapter 7.3)

Brachioradialis: A muscle of the forearm that helps flex the elbow. (Chapter 7.3)

Brevis: Muscles that are short in length. (Chapter 7.3)

Buccinator: Muscle found in the cheeks that allows you to whistle, blow, and suck. (Chapter 7.3)

Calcaneal tendon: A strong tendon that inserts on the calcaneal bone; also referred to as the Achilles tendon. (Chapter 7.3)

Cardiac muscle: Involuntary, striated muscle tissue found only in the heart. (Chapter 7.2, Chapter 7.4)

Caval opening: Opening in the diaphragm that allows the inferior vena cava (a large vein) to pass from the abdomen into the chest cavity. (Chapter 7.3)

Cerebral palsy: A group of conditions that affects movement and posture caused by damage to the developing brain, most often before or right after birth. (Chapter 7.6)

Circular muscles: Muscles that are arranged in a circular pattern around an opening or a surface. (Chapter 7.3)

Concentric contraction: Type of muscle contraction where the muscle shortens while generating tension, typically occurring during the lifting phase of a movement. (Chapter 7.3)

Contractility: The ability of muscle tissue to shorten with force and pull on its attachment points. (Chapter 7.2)

Convergent muscle: Muscles that have a broad origin and converge to a single tendon or point of insertion. (Chapter 7.3)

Deltoid: Thick muscle that creates the rounded lines of the shoulder and is the major abductor of the arm, but it also facilitates flexing and medial rotation, as well as extension and lateral rotation. (Chapter 7.3)

Depolarize: The process by which the membrane potential of a cell becomes less negative. (Chapter 7.3)

Desmosome: A cell structure that anchors the ends of cardiac muscle fibers together, so the cells do not pull apart during the stress of individual fibers contracting. (Chapter 7.4)

Diaphragm: Separates the thoracic and abdominal cavities and is dome-shaped at rest. (Chapter 7.3)

Duchenne muscular dystrophy (DMD): Progressive weakening of the skeletal muscles. It is one of several diseases collectively referred to as “muscular dystrophy.” (Chapter 7.6)

Eccentric contraction: Type of muscle contraction where the muscle lengthens while generating tension, typically occurring during the lowering phase of a movement. (Chapter 7.3)

Elasticity: The ability of muscle tissue to return to its original length after being stretched, due to the presence of elastic fibers. (Chapter 7.2)

Endomysium: Thin connective tissue that surrounds individual muscle fibers within a fascicle. (Chapter 7.3)

Epicranial aponeurosis: Muscle on the back of the head. (Chapter 7.3)

Epimysium: A connective tissue layer that surrounds and protects skeletal muscles. (Chapter 7.3)

Esophageal hiatus: Opening in the diaphragm through which the esophagus passes from the thoracic cavity into the abdominal cavity. (Chapter 7.3)

Excitable: Able to respond to stimulation from the nervous system by generating an electrical signal. (Chapter 7.2)

Excitation-contraction coupling: Links electrical signals to muscle contraction. (Chapter 7.3)

Extensibility: The ability of muscle tissue to stretch or extend without being damaged and still contract. (Chapter 7.2)

External oblique(s): Flat superficial skeletal muscle in the antero-lateral wall of the abdomen. (Chapter 7.3)

Extrinsic eye muscles: Control the movement of the eyeball. (Chapter 7.3)

Fascia: A fibrous tissue that encloses muscles and organs. (Chapter 7.3)

Fascicles: Bundles of muscle fibers grouped together within a muscle. (Chapter 7.3)

Fibromyalgia: Disorder characterized by widespread musculoskeletal pain accompanied by fatigue, sleep, memory, and mood issues. (Chapter 7.6)

Fixator: Stabilizes a joint or body part, allowing the agonist to perform its action more effectively. (Chapter 7.3)

Frontalis: Muscle on the forehead. (Chapter 7.3)

Fusiform: A type of muscle shape characterized by a tapered end and a wider belly, resembling a spindle. (Chapter 7.3)

Gap junction: Channels between cardiac muscle fibers to allow the depolarizing current to flow from one cardiac muscle cell to the next. (Chapter 7.4)

Gastrocnemius: The most superficial and visible muscle of the calf. (Chapter 7.3)

Gluteus maximus: The largest of the gluteus muscles that extends the femur and laterally rotates the thigh. (Chapter 7.3)

Gluteus medius: The muscle deep to the gluteus maximus that abducts the femur at the hip and medially rotates the thigh. (Chapter 7.3)

Gluteus minimus: Smallest of the gluteal muscles and deep to the gluteus medius. (Chapter 7.3)

Gracilis: Adducts the thigh, in addition to flexing the leg at the knee. (Chapter 7.3)

Hamstring group: Group of three muscles that flex the knee, extend the hip, and rotate the thigh. (Chapter 7.3)

Hypertonia: Excessive muscle tone. (Chapter 7.3)

Hypertrophy: Increased mass and bulk in a skeletal muscle. (Chapter 7.3)

Hypotonia: Absence of the low-level contractions that lead to muscle tone. (Chapter 7.3)

Iliopsoas: Muscle group consisting of the iliacus and psoas major muscles. They flex the thigh at the hip, rotate it laterally, and flex the trunk of the body onto the hip when sitting up from a supine position. (Chapter 7.3)

Infraspinatus: Inferior to the spine of the scapula and laterally rotates the arm. (Chapter 7.3)

Insertion: The moveable end of a muscle that attaches to the bone being pulled. (Chapter 7.3)

Intercalated disc: Allows the cardiac muscle cells to coordinate contraction so that the heart can work as a pump. (Chapter 7.4)

Intercostal muscles: A group of muscles located between the ribs. (Chapter 7.3)

Internal oblique(s): Perpendicular to the external oblique and extending superiorly and medially, the direction the thumbs usually go when the other fingers are in the pants pocket. (Chapter 7.3)

Involuntary: Describes muscle movement that occurs without conscious control. (Chapter 7.2)

Isometric contraction: Type of muscle contraction where the muscle generates tension without changing length, maintaining a static position. (Chapter 7.3)

Isotonic contractions: Muscle contractions that involve a change in muscle length while maintaining a constant tension. (Chapter 7.3)

Lateralis: Muscles located away from the midline of the body. (Chapter 7.3)

Latissimus dorsi: A broad, triangular muscle located on the inferior part of the back where it inserts into a thick connective tissue sheath called an aponeurosis. (Chapter 7.3)

Linea alba: Fibrous strip in the middle of the abdomen where the abdominal muscles meet. (Chapter 7.3)

Longus: Muscles that are elongated or long in shape. (Chapter 7.3)

Masseter: Main muscle used for chewing. (Chapter 7.3)

Mastication: Anatomical term for chewing. (Chapter 7.3)

Maximus: Muscles that are large or the largest in a group. (Chapter 7.3)

Medialis: Muscles located toward the midline of the body. (Chapter 7.3)

Medius: Muscles that are moderate or medium-sized. (Chapter 7.3)

Minimus: Muscles that are small in size. (Chapter 7.3)

Motor end plate: Specialized region of the sarcolemma at the neuromuscular junction where ACh receptors are concentrated. (Chapter 7.3)

Motor unit: Responsible for muscle contraction, with the number of fibers influenced by the precision of movement required. (Chapter 7.3)

Multipennate: Multiple tendons with muscle fibers branching out from each side. (Chapter 7.3)

Muscle fibers: Elongated cells that make up muscle tissue and responsible for contraction and movement. (Chapter 7.3)

Muscle tension: Force generated by the contraction of the muscle (or shortening of the sarcomeres). (Chapter 7.3)

Muscle tone: Constant, low-level contraction of muscles that maintains posture and stability and regulated by the nervous system. (Chapter 7.3)

Myasthenia gravis: A chronic neuromuscular disease that causes weakness in the skeletal muscles; it is an autoimmune disease. (Chapter 7.6)

Myofibrils: Long, thread-like structures within muscle fibers that contain the contractile proteins actin and myosin and responsible for muscle contraction. They are arranged in a repeating pattern, forming sarcomeres, the functional units of muscle. (Chapter 7.3)

Myosin: A motor protein that forms thick filaments in muscle fibers and responsible for muscle contraction by interacting with actin to generate force. (Chapter 7.3)

Neuromuscular junction (NMJ): The synapse or connection point between a motor neuron and a muscle fiber where the transmission of signals occurs to initiate muscle contraction. (Chapter 7.3)

Neurotransmitter: Chemical messengers. (Chapter 7.3)

Oblique: Muscles that are at an angle in the abdomen. (Chapter 7.3)

Occipitofrontalis: Muscle that raises the eyebrows and wrinkles the forehead. (Chapter 7.3)

Orbicularis oculi: Circular muscle around each eye that closes the eye(s). (Chapter 7.3)

Orbicularis oris: Circular muscle around the mouth that compresses and puckers the lips. (Chapter 7.3)

Origin: The end of the muscle attached to a fixed (stabilized) bone. (Chapter 7.3)

Parallel muscles: Type of muscle architecture where the muscle fibers run parallel to the long axis of the muscle. (Chapter 7.3)

Patellar ligament: Connects the patella (kneecap) to the tibia (shinbone). (Chapter 7.3)

Pectoralis major: A large, fan-shaped muscle in the chest that aids in shoulder movement. (Chapter 7.3)

Pectoralis minor: Rotates shoulder anteriorly (throwing motion). (Chapter 7.3)

Pelvic or hip girdle: Serves as a foundation for the lower limbs. (Chapter 7.3)

Pennate muscles: Muscles characterized by a feather-like arrangement of fibers. (Chapter 7.3)

Perimysium: Connective tissue that surrounds individual muscle fascicles within a muscle. (Chapter 7.3)

Polio: A highly infectious disease caused by a virus that invades the nervous system and can cause total paralysis in a matter of hours. (Chapter 7.6)

Popliteal fossa: Diamond-shaped space at the back of the knee. (Chapter 7.3)

Prime mover: A muscle that plays the primary role in producing a specific movement. Also known as an “agonist. (Chapter 7.3)

Quadriceps femoris group: Consists of four muscles that extend and stabilize the knee; often referred to as the “quads.” (Chapter 7.3)

Quadriceps tendon: Connects the quadriceps muscle group (located in the front of the thigh) to the patella (kneecap). (Chapter 7.3)

Raphe: Very slender tendon. (Chapter 7.3)

Recruitment: Process by which an increase in the number of active motor units enhances muscle contraction strength. (Chapter 7.3)

Rectus: Muscles characterized by their straight alignment. (Chapter 7.3)

Rectus abdominis: The straight muscle in the anterior wall of the abdomen; commonly called the “sit-up” muscle. (Chapter 7.3)

Rectus femoris: On the anterior aspect of the thigh. (Chapter 7.3)

Rectus sheaths: Fibrous coverings that enclose the rectus abdominis muscles. (Chapter 7.3)

Repolarizes: The process by which a cell’s membrane potential returns to its resting state after depolarization, typically involving the efflux of potassium ions from the cell. (Chapter 7.3)

Rhomboid major: Attaches the vertebral border of the scapula to the spinous process of the thoracic vertebrae. (Chapter 7.3)

Rhomboid minor: Attaches the vertebral border of the scapula to the spinous process of the thoracic vertebrae. (Chapter 7.3)

Rotator cuff: Circle of tendons around the shoulder joint. (Chapter 7.3)

Sarcolemma: Cell membrane that surrounds a muscle fiber, playing a crucial role in conducting electrical impulses and maintaining the fiber’s structural integrity. (Chapter 7.3)

Sarcomere: The basic functional unit of a muscle fiber; the segment between two Z discs. They contain overlapping thin (actin) and thick (myosin) filaments, which interact to produce muscle contraction. (Chapter 7.3)

Sarcoplasm: The cytoplasm of a muscle fiber, containing various organelles, myofibrils, and energy stores, such as glycogen and myoglobin, essential for muscle function. (Chapter 7.3)

Sarcoplasmic reticulum: A specialized form of the endoplasmic reticulum in muscle cells that stores and regulates calcium ions that are crucial for muscle contraction and relaxation. (Chapter 7.3)

Sartorius: A band-like muscle that extends from the anterior superior iliac spine of the pelvis to the medial side of the proximal tibia. (Chapter 7.3)

Semimembranosus: Most medial muscle of the three from mid-thigh to medial knee. Part of it is deep to the semitendinosus. (Chapter 7.3)

Semitendinosus: Muscle located medially next to the biceps femoris. (Chapter 7.3)

Serratus anterior: Moves arm from side of body to front of body. (Chapter 7.3)

Skeletal muscle: Voluntary, striated muscle tissue attached to bones and around entrance points to body. (Chapter 7.2, Chapter 7.3)

Sliding filament model of muscle contraction: Actin and myosin filaments slide past each other to shorten the sarcomere, resulting in muscle fiber shortening and contraction. (Chapter 7.3)

Smooth muscle: Involuntary, non-striated muscle tissue found in the walls of organs. (Chapter 7.2, Chapter 7.5)

Soleus: A wide and flat muscle found deep to the gastrocnemius. (Chapter 7.3)

Spasticity: An increase in muscle tone and stiffness. (Chapter 7.3)

Sphincters: Circular muscles that encircle and control the opening of various passages in the body. (Chapter 7.3)

Sternocleidomastoid: Major muscle that laterally flexes and rotates the head. (Chapter 7.3)

Striations: Stripes in muscle tissue created by the regular arrangement of proteins within the cells. (Chapter 7.2)

Subscapularis: A large muscle located on the anterior surface of the scapula and responsible for internal rotation and adduction of the shoulder. (Chapter 7.3)

Supraspinatus: A shoulder muscle located above the scapula that initiates arm abduction and stabilizes the shoulder joint. (Chapter 7.3)

Synaptic cleft: Small gap between a motor neuron and the muscle fiber’s sarcolemma. (Chapter 7.3)

Synergist: A muscle that assists the agonist (prime mover) in performing a specific movement. (Chapter 7.3)

Temporalis: Muscle that lifts and pulls back the mandible. (Chapter 7.3)

Tendinitis: Inflammation of a tendon, the thick band of fibrous connective tissue that attaches a muscle to a bone. (Chapter 7.6)

Tendinous intersections: Fibrous bands that divide the rectus abdominis muscle into segments, creating the “six-pack” appearance. (Chapter 7.3)

Tendons: A fibrous connective tissue that attaches muscle to bone. (Chapter 7.3)

Teres major: Thick and flat; inferior to the teres minor and extends the arm and assists in adduction and medial rotation. (Chapter 7.3)

Teres minor: Laterally rotates, adducts, and extends the arm. (Chapter 7.3)

Tetanus: A serious disease of the nervous system caused by a toxin-producing bacterium that affects the neuromuscular junction and causes muscle contractions, particularly of the jaw and neck muscles. (Chapter 7.6)

Thick filaments: Composed primarily of myosin, these filaments are thicker than actin and are responsible for generating force during muscle contraction by interacting with thin filaments in the sarcomere. (Chapter 7.3)

Thin filaments: Composed primarily of actin, these filaments are thinner than myosin and are referred to as thin filaments in the sarcomere. They play a key role in muscle contraction by interacting with thick filaments (myosin). (Chapter 7.3)

Tibialis anterior: Long and thick muscle on the anterolateral surface of the tibia. (Chapter 7.3)

Transverse abdominis: The deep muscle is the transversus abdominis. (Chapter 7.3)

Trapezius: Muscle that elevates shoulders (shrugging), pulls shoulder blades together, and tilts head backwards. (Chapter 7.3)

Triceps brachii: A muscle located at the back of the upper arm. It has three heads (points of origin) and is responsible for straightening the elbow. (Chapter 7.3)

Unipennate: Fascicles located on one side of the tendon. (Chapter 7.3)

Vastus intermedius: Between vastus lateralis and vastus medialis and deep to the rectus femoris. (Chapter 7.3)

Vastus lateralis: On the lateral aspect of the thigh. (Chapter 7.3)

Vastus medialis: On the medial aspect of the thigh. (Chapter 7.3)

Voltage-gated sodium channels: Membrane proteins that open in response to changes in electrical potential. (Chapter 7.3)

Voluntary: Muscle movement that is under conscious control. (Chapter 7.2)

Zygomaticus: Muscle from the zygomatic bone to the mouth; the “smiling’ muscle. (Chapter 7.3)