A&P 1.12 Flashcards
Sternocleidomastoid
SCM
A, I, O
Named for it’s attachment. Sterno- sternum Clavicular- clavical mastoid - mastoid process
I: mastoid process of the temporal bone and lateral portion of the superior nuchal line of occiput
O: sternal head: top of the manubrium
Clavicular head: medial one third of the clavicle
Unilaterally: contralateral rotation of the head, ipsilateral flexion of the head/neck
Bilaterally: flexion of the neck, extension of the head
Sutures in the skull
All adjacent to Parential Bone
Coronal - Frontal bone
Lambdoid - Occipital bone
Squamous - Temporal Bone
Sternum parts
3 main parts
Manubrium
Body
Xiphoid
Function of muscles
3
Movement
Heat production
Posture
Layers of muscles
3
Muscle - organ —- epimysium
Fascicles- bunches of muscle —– perimysium
Fibers- muscle cells — endomysium
Connective tissue covering muscles
3
Epimysium
Perimysium
Endomysium
Muscle action
4
Electrically excitable- respond to nervous system
Contractility - ability to get small
Extensibility - ability to stretch
Elasticity - ability to return to neutral state after contraction or stretch
Muscle fiber
Muscle cell
Generally run the length of muscle
Have threadlike shape
Sarcolemma
Define
Sarco - flesh, lemma - sheath
Plasma membrane of the muscle fiber
Transverse (T) tubules
Defined
Extensions of the scacolemma that “tunnel” into the center (or core) of the muscle fibers.
They allow the electrical signals or impulses to move deeper into the cell
Wrap around the organelles or myofibril
Sarcoplasmic reticulum
Network of tubules and sacs ( not T tubules)
Wrapped around T Tubules and store calcium
Sarcoplasm
The cytoplasm of the muscle fiber
Nuclei
Unlike other cells skeletal muscle fibers have several nuclei
Myofibrils
Described
Bundles of fine fibers 1000 or more in each muscle fiber
Extend lengthwise along skeletal muscle fibers and almost fill their sarcoplasm
Lying side by side (but not the whole length of the muscle fiber) are thousands of finer fibers called thick and thin myofilaments, which in turn are made up of proteins. Myofilaments are arranged in compartments called sarcomeres.
Organelles*
Thick filaments
Described
Made up of protein myosin
Shaped like tubes of golf clubs coming off of them (long shaft bundle together and heads stick out)
Chemically attracted to actin
Thin filaments
Described
Made up of three proteins: actin, tropomysin, and troponin
Actin molecules are strung together like beads to form 2 fibrous strands
Sarcomere
Described
The basic contractile unit of the muscle fiber
Segment of the myofibril between Z disks (dense plate where thin filaments attach)
Sarco- flesh, comere-measure
Unit of measure
Function of the skeletal muscle
3
Motor unit
Tetanus
Muscle tone
Motor unit
Description
A single motor neuron and the muscle fibers it innervates (attaches to)
Functional unit
Variable numbers of branches
Few muscle fibers = more precise (fingers, eyes)
Many muscle fibers= less precise (leg/arm)
Tetanus
Described
Smooth, sustained contractions (multiple twitch waves) resulting from coordinated contractions of different motto units within the muscle.
This is what we see exhibited by normal skeletal muscle most of the time (raising arm is controlled not “jerky”)
Muscle tone
Described
A tonic contraction is a continual, partial contraction of a muscle.
It is a low level continuous contraction characteristic of the muscles of normal individuals when they Are awake. The amount of tension even when the muscle is relaxed.
Normal posture
Defined
Normal posture in the presence of gravity is achieved by tonus. Exercising increases the tonus of muscles used. (Relay race when each is tired it’s someone else’s turn to run.
Muscle contraction = sliding filament mechanism
5 parts
Motor neurons Neurotransmitter Excitation Contraction Relaxation
Motor neuron
Special nerve cell that connects to the sarcolemma at the neuromuscular junction
Neurotransmitter
Chemical that uses nerves to communicate with the neurotransmitter of the neuromuscular junction is Ach (acetylcholine )
Excitation
When the electrical impulse going to next cell
Contraction
When the impulse is conducted over sarcolemma inward to the T tubules.
Calcium released the sarcoplasmic reticulum and the “protective” covering (tropomysin ) is moved from the thin filament. With covering removed, the myosin (thick filaments) heads grab thin filaments (actin) and pull towards center of sarcomeres. Thin filaments slide inward, Z disks come together, and the sarcomere shortens, causing shortening of the whole muscle fiber causing shortening of the whole muscle.
Relaxation
Sarcoplasmic reticulum pumps calcium back into sacs again shutting down contraction process
Action of a muscle
Muscle belly contraction
As the combined contraction of multiple muscle fibers (recruiting) to create a motion
Motor units take turns to maintain action without fatigue
What percentage of muscle fibers need to be used to contract a muscle?
In general you will never use 100% of muscle fiber unless you are a power lifter
