A&P CH. 6

Question Answer
Contractility Ability of skeletal muscle to shorten with force
excitability capacity of skeletal muscle to respond to a stimulus
extensibility the ability to be stretched
elasticity ability to recoil to original resting length after being stretched
each skeletal muscle is surrounded by a connective tissue sheath which is called epimysium
Fascia another connective tissue located outside the epimysium. Surrounds and separates muscles.
a muscle composed of numerous visible bundles called muscle fasciculi, which are surrounded by loose connective tissue called perimysium
the fasciculi are composed of single muscle cells called fibers
Each fiber is surrounded by a connective tissue sheath called endomysium
the cytoplasm of each fiber is filled with a threadlike structure that extends from one end to the other and it is called myofibrils
actin myofilaments thin. resemble 2 mini strands of pearls twisted together
myosin myofilaments thick. resemble bundles of mini golf clubs.
actin and myosin myofilaments form highly ordered units called sarcomeres
the outside of most cell membranes is positively charged compared to the inside of the cell membrane, which is negatively charged. Charge difference is called resting membrane potential
when a muscle cell is stimulated the membrane characteristics change briefly. the brief reversal back of the charge is called action potential
motor neurons are nerve cells that carry action potentials to skeletal muscle fibers
axons enter the muscles and branch. each branch that connects to the muscle forms a neuro musclular junction, synapse
a single neuron and all the skeletal muscle fibers it innervates are called a motor unit
the enlarged nerve terminal is called presynaptic terminal
muscle fiber postsynaptic terminal
space between the presynaptic terminal and the musce cell is the snaptic cleft
each presynaptic terminal contains synaptic vesicles
Occipitofrontalis raises eyebrows
Orbicularis oculi closes the eyelids and causes “crows feet” wrinkles in the skin at the lateral corners of the eye
Orbicularis oris puckers the lips
Buccinator flattens the cheeks
Orbicularis oris and buccinator the kissing muscles.
Zygomaticus smiling muscle
Levator labii superioris sneering
Depressor anguli oris frowning
mastication chewing
Sternocleidomastoid lateral neck muscle and prime mover. Rotates and abducts the head
Erector spinae group of muscles on each side of the back. Responsible for keeping the backstraight and the body erect.
thoracic muscles muscles that move the thorax
External intercostals elevate the ribs during inspiration
Internal intercostals contract during forced expiration.
dome shaped muscle. Aids in breathing.
Diaphragm accomplishes quiet breathing
Trapezius rotates scapula
Serratus anterior pulls scapula anteriorly
Pectoralis major adducts and flexes the arm
Latissimus dorsi medially rotates, adducts, and powerfully extends the arm. “Swimmermuscles”
Deltoid attaches the humerus to the scapula and clavicle, and is the major abductor of theupper limb.
Triceps brachii extends the forearm. Occupies the posterior compartment of the arm
Biceps brachii flexes the forearm. Occupies the anterior compartment of the arm.
Brachialis flexes forearm
Brachioradialis flexes and supinates the forearm.
Retinaculum (bracelet) strong band of fibrous connective tissue that covers the flexor and extensor tendons and holds them in place around the wrist so that they do not “bowstring” duringmuscle contraction.
Flexor carpi flexes the wrist.
Extensor carpi extends the wrist
Flexor digitorum flexes the fingers.
Extensor digitorum extends the fingers.
Gluteus maximus buttocks. Contributes most of the mass of the buttocks
Gluteus medius, hip muscle and common injection site.
Quadriceps femoris extends the leg; anterior thigh muscles
Sartorius “tailors muscle”; flexes the thigh
Hamstring muscles posterior thigh muscles; flexes the leg and extends the thigh.
peroneus The lateral muscles of the leg,
intrinsic foot 20 muscles located within the foot
recruitment. The increase in number of motor units being activated
Tetany where the muscle remains contracted without relaxing.
relaxation phase. The time during which the muscle relaxes
contraction phase. The time of contraction
lag phase. The time between application of a stimulus to a motor neuron and the beginning of a contraction
This phenomenon is called the all-or-none response.
A muscle fiber will not respond to stimulus until that stimulus reaches a level called threshold
Muscle twitch is a contraction of an entire muscle in response to a stimulus that causes the action potential in one or more muscle fibers.
sliding filament mechanism The sliding of actin myofilaments past myosin myofilaments during contraction
acetylcholinesterase The acetylcholine released into the synaptic cleft between the neuron and muscle cell is rapidly broken down by an enzymes
acetylcholine. secrete a neurotransmitter called
Each presynaptic terminal contains synaptic vesicles
insertion is the end of the muscle undergoing the greatest movement.
belly. The portion of the muscle between the origin and the insertion
synergists. Muscles that work together to accomplish specific movements
antagonists 7. Muscles that work in opposition to one another

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