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Chapter 6: Muscles

contractility the ability of skeletal muscle to shorten with force
excitability the capacity of skeletal muscle to respond to a stimulus.
extensibility the ability to be stretched
elasticity ability to recoil to their original resting length after they have been stretched
epimysium connective tissue sheath that surrounds skeletal muscle
fascia connective tissue located outside the epimysium; surrounds and separates muscles
muscle fasciculi numerous visible bundles that compose muscles
perimysium loose connective tissue that surrounds muscle fasciculi
fibers single muscle cells that make up the fasiculi
endomysium connective tissue sheath that surrounds each fiber
myofibrils a threadlike structure that extends from one end of the fiber to another
actin myofilaments thin myofilaments. They resemble two minute strands of pearls twisted together
myosin myofilaments thick myofilaments. They resemble bundles of minute golf clubs
actin and myosin myofilaments form? sacromeres
sacromeres: joined end to end to form the myofibril; basic structural and functional unity of muscle
Where does each sacromere extend to? one z line to another z line
Z line an attachment site for actin
I band consists of actin and is on each side of z line (light area)
A band extends the length of myosin, darker central region in each sacromere
H zone consists of only mysoin and is in the center of each sacromere. (light area)
M line dark staining band in the middle of sacromere where mysoin myofilaments are anchored
charge of most outside cell membranes positive
charge of most inside cell membrane negative
resting membrane potential the charge difference across the membrane
action potential brief reversal back of the charge
motor neurons nerve cells that carry action potentials to skeletal fibers
axons enter where? muscles and branches
neuromuscular junction/synapse each branch that connects to the muscle
motor unit single motor neuron and all the skeletal muscle fibers it innervates; form a single muscle
neuromuscular junction formed by? an enlarged nerve terminal resting in an indentation of the muscle cell membrane
presynaptic terminal enlarged nerve terminal
synaptic cleft the space between the presynaptic terminal and muscle cell
postsynaptic terminal the muscle fiber
synaptic vesicles secrete a neurotransmitter; inside presynaptic terminal
acetylocholine neurotransmitter; diffuses across the synaptic cleft and binds to the postsynaptic terminal causing a change in the postsynaptic cell
when action potential reaches the nerve terminal causes the synaptic vesicles to releases acetylcholine into the synaptic cleft by exocytosis
the combination of acetylcholine with its receptor causes an influx of sodium ions into the muscle fiber
influx causes an action potential in the muscle cell, which causes it to contract
acetylcholinesterase enzymes that break down the acetylcholine released into the synaptic cleft between the neuron and muscle cell
what does the enzymatic breakdown ensure? that one action potential in the neuron yields only one action potential in the skeletal muscle, and only one contraction of the muscle cell.
muscle contraction occurs as actin and myosin myofilaments slide past one another causing sacromeres to shorten
sliding filament mechanism sliding of actin myofilaments past mysoin myofilaments during contraction
in sliding filament mechanism what happens? the H and I bands shorten, but the A bands do not change in length
muscle twitch a contraction of an entire muscle in response to a stimulus that causes the action potential in one or more muscle fibers
threshold at which point the muscle fiber will contract maximally (aka all-or-none response)
lag phase the time between application of a stimulus to a motor neuron and the beginning of a contraction
contraction phase time of contraction
relaxation phase time during muscle relaxes
tetany where the muscle remains contracted without relaxing
recruitment the increase in number of motor units being activated
ATP needed for energy for muscle contraction; produced in mitochondria ; short lived and unstable
ADP plus phosphate
creatine phosphate high-energy molecule that can be stored when atp cant be stockpiled
anaerobic respiration without oxygen
aerobic respiration with oxygen
after intense exercise.. the respiration rate remains elevated for a period of time even though the muscles are no longer actively contracting.
oxygen debt the amount of oxygen needed in chemical reactions to convert lactic acid to glucose and to replenish the muscle cells
muscle fatigue results when ATP is used during muscle contraction faster than it can be produced in the muscle cells
two types of muscle contractions isometric and isotonic
isometric equal distance; the length of the muscle does not change, but the amount of tension increases during the contraction process
isotonic equal tension; the amount of tension produced by the muscle is constant during contraction, but the length of the muscle changes
muscle tone refers to constant tension produced by muscles of the body for long periods of time. keeps head up and back straight.
fast-twitch fibers contract quickly and fatigue quickly. Well adapted to perform anaerobic metabolism
slow-twitch fibers contract more slowly and are more resistant to fatigue. They are better suited for aerobic metabolism
origin (head) ; the most stationary end of the muscle.
insertion the end of the muscle undergoing the greatest movement.
belly portion of the muscle between the origin and the insertion
synergists muscles that work together to accomplish specific movements
anatagonists muscles that work in opposition to one another
prime mover one muscle plays the major role in accomplishing the desired movement
occipitofrontalis raises the eyebrows
orbicularis oculi closes eyelids; causes "crows feet"
orbicularis oris puckers the lips
buccinator flattens the cheeks
zygomaticus smiling muscle
levator labii superioris snerering
depressor anguli oris frowning
mastication chewing
4 pairs of mastication muscles 2 pair of pterygoids, temporalis, masseter
intrinsic tongue muscles change shape of tongue
extrinsic tongue muscles move the tongue
neck muscle sternodeidomastoid: lateral neck muscle and prime mover
trunk muscles erector spinae: group of muscles on each side of back
thoracic muscles muscles that move the thorax
muscles most involved in breathing external intercostals and internal intercostals
external intercostals elevate the ribs during inspiration
internal intercostals contract during forced expiration
diaphragm accomplishes quiet breathing; dome-shaped muscle; aids in breathing
abdominal wall muscles flex and rotate the vertebral column, compress the abdominal cavity, and hold the abdominal viscera
linea alba tendinous area of the abdominal wall that consists of white connective tissue rather than muscle
rectus abdominis on each side of the linea alba
tendinous inscriptions cross the rectus abdominis at three or more locations, causing the abdominal wall of a well-muscled person to appear segmented
lateral to the rectus abdominis are layers of muscles called... external abdominal oblique, internal abdominal oblique, and transverses abdominis muscles
trapezius rotates scapula
serratus anterior pulls the scapula anteriorly
pectoralis major and latissimus dorsi muscles attach arm to thorax
pectoralis major adducts and flexes arm
latissimus dorsi medially rotates, adducts, and powerfully extends the arm.
deltoid attaches the humerus to the scapula and clavicle, and is the major abductor of the upper 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 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” during muscle contraction
Flexor carpi flexes the wrist
Extensor carpi extends the wrist
Flexor digitorum flexes the fingers
Extensor digitorum extends the fingers
intrinsic hand muscles 19 hand muscles that are located within the hand
Interossi muscles located between the metacarpals, are responsible for abduction and adduction of 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
Gastrocnemius and soleus forms the calf muscle; They join to form the calcaneal tendon
calcaneal tendon (Achilles tendon) flex the foot and toe
peroneus muscles the lateral muscles of the leg; primarily everters (turning the lateral side of the foot outward) of the foot, but they also aid in plantar flexion
intrinsic foot muscles 20 muscles; flex extend, abduct, and adduct the toes
Created by: fnkelle1



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