muscular system notes

Skeletal Muscle

Muscles attached to the bones that are striated and voluntary.

Cardiac Muscle

Muscle located in the heart that is striated and involuntary.

Smooth Muscle

Muscle found in blood vessels and hollow organs that is nonstriated and involuntary.

Movement of the body

Contraction of skeletal muscles responsible for overall body movements.

Maintenance of posture

Skeletal muscles constantly maintain tone to keep us sitting or standing erect.

Respiration

Muscles of the thorax carry out breathing movements.

Production of body heat

Skeletal muscle contraction releases heat as a by-product, critical for maintaining body temperature.

Communication

Skeletal muscles are involved in speaking, writing, typing, gesturing, and facial expressions.

Constriction of organs and vessels

Contraction of smooth muscle in internal organs and vessels causes constriction.

Contraction of the heart

Contraction of cardiac muscle causes the heart to beat and propel blood throughout the body.

Excitability

The capacity of muscle to respond to a stimulus.

Extensibility

The ability of a muscle to be stretched beyond its normal resting length and still contract.

Elasticity

The ability of muscle to recoil to its original resting length after being stretched.

Epimysium

Connective tissue sheath surrounding each skeletal muscle.

Fascicles

Groups of muscle cells within a skeletal muscle.

Perimysium

Connective tissue covering surrounding each fascicle.

Endomysium

Connective tissue covering surrounding each skeletal muscle fiber.

Sarcolemma

Cell membrane of a muscle fiber.

T tubules

Tubelike inward folds of the sarcolemma that connect to the sarcoplasmic reticulum.

Sarcoplasm

The cytoplasm of a muscle fiber.

Myofibrils

Bundles of protein filaments within a muscle fiber.

Sarcomere

The basic structural and functional unit of a skeletal muscle.

Actin myofilament

Thin filament within a sarcomere.

Myosin myofilament

Thick filament within a sarcomere.

Z disk

Boundaries of a muscle sarcomere.

H zone

Center of the A band where there is no overlap between thick and thin myofilaments.

M line

Attachment site for the thick myofilaments in the center of the A band and sarcomere.

Troponin

Complex of three regulatory proteins integral to muscular contraction.

Tropomyosin

Two-stranded alpha-helical coiled coil protein found in the cell cytoskeletons.

Excitability of muscle fibers

The ability of muscle fibers to generate and conduct electrical impulses.

Resting membrane potential

The electrical charge difference across the cell membrane of an unstimulated cell.

Action potentials

Rapid changes in the membrane potential that allow muscle cells to perform contractions.

Resting membrane potential

The electrical potential difference across the cell membrane of a resting cell.

Action potential

A rapid change in charge across the cell membrane that allows for the transmission of electrical signals.

Depolarization

The process in which the inside of the cell membrane becomes more positively charged than the outside.

Repolarization

The process in which the cell membrane returns to its resting membrane potential after depolarization.

Motor neurons

Specialized nerve cells that stimulate muscles to contract.

Neuromuscular junction

The synapse where the fiber of a nerve connects to a muscle fiber.

Synapse

The junction between a nerve cell and either another nerve cell or an effector cell, such as a muscle or gland.

Motor unit

A group of muscle fibers that a motor neuron stimulates.

Presynaptic terminal

The end of a neuron cell axon fiber.

Synaptic cleft

The space between the presynaptic terminal and the postsynaptic membrane.

Post synaptic membrane

The muscle fiber membrane or sarcolemma.

Synaptic vesicles

Vesicles in the presynaptic terminal that store and release neurotransmitter chemicals.

Neurotransmitter

Chemicals that stimulate or inhibit the postsynaptic cells.

Acetylcholine (ACh)

A neurotransmitter that stimulates skeletal muscles.

Muscle contraction

The result of an action potential in a muscle fiber, leading to the shortening of the muscle.

ATP

Adenosine triphosphate, the energy currency of cells.

Cross-bridge

The attachment between myosin and actin during muscle contraction.

Krebs Cycle

A series of chemical reactions that occur in the mitochondria to produce ATP aerobically.

Glycolysis

The breakdown of glucose to produce ATP anaerobically.

Creatine phosphate

A molecule that stores energy in muscle cells and can be used to resynthesize ATP.

Muscle twitch

A single contraction of a muscle fiber in response to a stimulus.

Lag phase or latent phase

The time between the application of a stimulus and the beginning of contraction.

Contraction phase

The time during which the muscle contracts.

Relaxation Phase

The time during which the muscle relaxes.

Slow Twitch Fibers

Muscle fibers that contract slowly, fatigue slowly, have a considerable amount of myoglobulin, and use aerobic respiration. They are darker in color and are used by long-distance runners.

Fast Twitch Fibers

Muscle fibers that contract quickly, fatigue quickly, use anaerobic respiration, and get energy from glycogen. They are lighter in color and are used by sprinters.

Muscle Fatigue

A temporary state of reduced work capacity in muscles, caused by factors such as acidosis, ATP depletion, and oxidative stress.

Isometric Contractions

Muscle contractions that increase tension in the muscle without changing its length.

Isotonic Contractions

Muscle contractions that have a constant amount of tension while decreasing the length of the muscle.

Concentric Contractions

Isotonic contractions in which muscle tension increases as the muscle shortens.

Eccentric Contractions

Isotonic contractions in which tension is maintained in a muscle, but the opposing resistance causes the muscle to lengthen.

Tendon

Connects skeletal muscle to bone.

Aponeuroses

Broad, sheetlike tendons.

Origin

The attachment of a skeletal muscle at the least mobile location.

Insertion

The end of the muscle attached to the bone undergoing the greatest movement.

Belly

The part of the muscle between the origin and the insertion.

Action

The specific body movement a muscle contraction causes.

Agonists

A group of muscles working together.

Antagonists

A muscle or group of muscles that oppose muscle actions.

Synergist

A group of muscles working together to produce a movement.

Prime Mover

A muscle that plays a major role in accomplishing the desired movement.

Fixators

Muscles that hold one bone in place relative to the body while a usually more distal bone is moved.

Muscle Attachment

The point where a muscle is attached to a bone.

Nomenclature

The naming of muscles based on factors such as location, size, shape, orientation of fascicles, origin and insertion, number of heads, and function.

Muscles of Mastication

Muscles involved in the movement of the jaw.

Temporalis

• A muscle that elevates and draws the mandible posteriorly, closing the jaw.
  

• Insertion: Anterior portion of the Mandibular Ramus and Coronoid Process

• Origin: Temporal fossa

Masseter

• Origin: Zygomatic arch

• Insertion: Lateral side of mandibular ramus

• Action: Elevates and pushes mandible anteriorly; closes jaw

Lateral Pterygoid

• Origin: Lateral pterygoid plate and greater wing of sphenoid

• Insertion: Condylar process of mandible and articular disk

• Action: Pushes mandible anteriorly and depresses mandible; closes jaw

Medial Pterygoid

• • Origin: Lateral pterygoid plate of sphenoid and tuberosity of maxilla

• • Insertion: Medial surface of mandible

• • Action: Pushes mandible anteriorly and elevates mandible; closes jaw

Muscles of Facial Expression

Muscles involved in facial expressions.

Buccinator

• Origin: Maxilla and mandible

• Insertion: Orbicularis oris at corner of mouth

• Action: Draws corner of mouth posteriorly; compresses cheek to hold food between teeth

Depressor Anguli Oris

• • Origin: Lower border of mandible

• • Insertion: Skin of lip near corner of mouth

• • Action: Lowers corner of mouth; “frown”

Levator Labii Superioris

• Origin: Maxilla

• Insertion: Skin and orbicularis oris of upper lip

• Action: Raises upper lip; sneer

Occipitofrontalis

• Origin: Occipital bone

• Insertion: Skin of eyebrow and nose

• Action: Moves scalp; raises eyebrows

Orbicularis Oculi

• • Origin: Maxilla and frontal bones

• • Insertion: Circles orbit and inserts onto SKIN around eyelids

• Action: Closes eyes; blinking, winking, squinting

Orbicularis Oris

• Origin: Nasal septum, maxilla, and mandible

• • Insertion: Fascia and other muscles of lips

• Action: Closes and purses lips; “kissing”

Zygomaticus Major

• • Origin: Zygomatic bone

• • Insertion: Angle of mouth

• • Action: Elevates and abducts upper lip and corner of mouth; “smile”

Zygomaticus Minor

• • Origin: Zygomatic bone

• • Insertion: Orbicularis oris of upper lip

• • Action: Elevates and abducts upper lip; “smile”

Flexors (Muscles of the Neck)

• • Origin: Anterior side of vertebrae

• • Insertion: Base of skull

• • Action: Flex head and neck

Extensors (Muscles of the Neck)

Originates from the posterior side of vertebrae and inserts into the base of the skull. They extend the head and neck.

Sternocleidomastoid

• Origin: Manubrium of sternum and medial part of clavicle

• Insertion: Mastoid process and nuchal line of skull

• Action: Individually rotate head; together flex neck

Trapezius

Originates from the posterior surface of the skull and upper vertebral column (C7-T12), and inserts into the clavicle, acromion process, and scapular spine. It extends and laterally flexes the neck.

INTRINSIC

• • Origin: Inside tongue

• • Insertion: Inside tongue

• • Action: Changes shape of tongue

• EXTRINSIC

• Origin: Bones around oral cavity or soft palate

• •Insertion: Onto tongue

• Action: Moves tongue

Suprahyoid muscles (geniohyoid, stylohyoid, and hyoglossus)

• • Origin: Base of skull, mandible

• • Insertion: Hyoid bone

• • Action: Elevates or stabilizes hyoid

INFRAHYOID

• • Origin: Sternum, larynx

• • Insertion: Hyoid bone

• • Action: Depresses or stabilizes hyoid

ELEVATORS

• Origin: Soft palate and auditory tube

• Insertion: Pharynx

• Action: Elevate pharynx

CONSTRICTORS

• Origin: Larynx and hyoid

• Insertion: Pharynx

• Action: Constrict pharynx