UNIT 8 PART A: MUSCLES Flashcards
Identify the 3 types of muscle tissue.
skeletal, cardiac smooth
Skeletal Muscle
Part of the muscular system that controls
voluntary body movement.
Ø Usually attached to bones by tendons
Ø E.g. muscle tissue found in biceps and triceps
Describe the general properties of skeletal muscle cells
i. Multinucleated cells (many nuclei per cell)
ii. Striated (striped pattern formed from
overlapping proteins).
iii. Long cells, stacked in parallel
Ø A single skeletal muscle cell can run the
length of a whole muscle.
Ø The longest skeletal muscle cells in the human body are found in the sartorius muscle of the leg and can be up to 60 cm long
Which division of the nervous system is skeletal muscle controlled by?
Controlled by somatic nervous system (contraction is
voluntary/under conscious control)
Cardiac Muscle
Muscle tissue that controls the involuntary
contractions of the heart.
Ø Contractions act as a pump to move blood
through the cardiovascular system.
Describe the general properties of cardiac muscle cells
i. Uninucleated cells (one nucleus per cell)
ii. Striated (striped pattern along cells formed
from overlapping proteins).
iii. Shorter cells, stacked end to end.
Ø Cell ends are connected to one another by
intercalated disks that have many gap junctions
Is contraction under voluntray or involuntary control? Which division of the nervous system is cardiac muscle controlled by?
Contraction occurs spontaneously (initiated by specialized cardiac muscle cells within the heart itself).
Rate of contraction is modified by the autonomic nervous system and endocrine
system
Contraction is involuntary/not under conscious control.
Smooth Muscle
a. Muscle tissue that controls the involuntary
contractions of internal organs and tubes
(except for the heart).
Ø For example: walls of the stomach, small and
large intestines, blood vessels, bladder, and
uterus. Also pupillary muscles.
Describe the general properties of smooth muscle cells
i. Uninucleated cells (one nucleus per cell)
ii. NOT striated (gives smooth appearance)
iii. Short spindle shaped cells, organized into sheets or tubes.
Is contraction under voluntary or involuntary control? Which division of the nervous system is smooth muscle controlled by?
Contraction may occur spontaneously (often in response to stretch); but also responds to signals from autonomic nervous system and endocrine system.
Contraction is involuntary/not under conscious control.
Whole Muscles
Usually attached to bones by tendons
tendons
are dense irregular connective tissue that contains a lot of collagen
Origin
attachment of the muscle that is closer to the trunk of the body or that is the more stationary bone during muscle contraction.
E.g. Biceps has origin on the scapula (shoulder blade
Insertion
more distal (further from the trunk) or mobile
bone/attachment.
E.g. Biceps has insertion on the radius
Flexor:
decreases the angle between two bones (bringing them
closer together).
moves bones closer together
E.g. Biceps moves radius towards the humerus
Extensor
Increases the angle between two bones (moving them
apart).
moves bones away from each other
E.g. Triceps moves ulna away from humerus
Antagonistic muscle groups
are pairs or groups of muscles that have opposite actions.
Ø All flexor-extensor pairs that move bones in opposite directions around a joint are antagonists
E.g. the bicep and tricep are an antagonistic muscle group since they have opposite actions (flexion and extension) at the elbow joint.
Ø In order for movement to occur at a joint, one muscle in an antagonistic pair must relax while the other contracts.
fascicles
a group (bundle) of muscle fibers (cells) lying parallel to one another that are also joined to
one another by connective tissue.
whole muscle consists of a group of fascicles
Describe the Structure of Skeletal Muscle Fibers (cells):
- Sarcolemma = muscle cell membrane
- Is electrically excitable (stimulated by lower motor
neuron at the neuromuscular junction (see Unit 7 notes). - Sarcoplasm = cytoplasm of muscle cell
- Sarcoplasmic reticulum = extensive network of smooth endoplasmic reticulum of muscle cell
Sarcoplasmic reticulum
Ø Membranous tubes with enlarged ends called terminal cisternae
Ø Has a very high Ca 2+ concentration
Ø Stores calcium ions (Ca 2+) that can be released into
cytosol to initiate contraction
Why does the Sarcoplasmic reticulum have a very high Ca++ concentration?
a) Ca++ ATPase transporter in SR membrane (uses ATP to pump Ca++ from cytosol into SR)
b) Presence of a Ca++ binding protein called calsquestrin, which binds to Ca++ thereby reducing effective Ca++ concentration so that the Ca++ ATPase can continue to pump Ca++ into SR
Myofibrils
long rods of protein in the cytoplasm of the
muscle fiber that run the length of the cell
are anchored to the cell membrane by the protein dystrophin
What is Duchenne muscular dystrophy?
is an X-linked recessive
inherited disorder in which a mutation in the gene that codes
for the dystrophin protein prevents muscle cells from
producing functional dystrophin. Without a mechanism to
anchor myofibrils (and therefore transmit their contraction) to
the cell membrane, muscles become weak and easily
damaged.
sarcomere
individual units of a myofibril
Transverse tubules (T-tubules)
part of sarcolemma that folds into the inside of the cell at regular intervals (at junction of A and I bands of sarcomeres) and surrounds each of the myofibrils. Lumen of tubule is filled with extracellular fluid.
Ø 1 T-tubule plus the 2 terminal cisternae on either side of it is called a triad.
ØT-tubules carry action potentials from the sarcolemma
deep into the cell. This ensures that the signals for
muscle cell contraction reach all of the sarcomeres in all
of the myofibrils in a cell (even the ones furthest away
from the surface of the cell)
What does the sarcoplasm have a lot of?
Many mitochondria and glycogen granules in
sarcoplasm because muscle contraction requires a lot
of ATP
What are Thick myofilaments composed of?
Myosin – functions in contraction
Ø Protein molecule consists of two identical subunits shaped like a golf club
Ø Tail ends intertwined around each other, globular heads project out at one end
Ø Myosin tails are oriented toward the center of the filament and globular heads protrude at regular intervals
What do myosin heads form?
form crossbridges between thick and thin
filaments by binding to G-actin (a protein of thin filament)
Myosin ATPase
(ATP binding site) - myosin is an ATPase
(similar to Na+/K+ ATPase)
It breaks down ATP
through hydrolysis into ADP and Pi and stores the
released energy to be used to pivot the myosin head
during contraction.
What are thin myofilaments composed of?
G- actin
Tropomyosin
troponin
G-Actin
functions in contraction (G stands for globular, since
the actin protein is in its globular form)
Ø Primary structural protein of thin filaments
Ø G-actin monomers are spherical (globular) but assembled into long chains.
Ø Each actin molecule has special binding site for attachment of the myosin head. Binding (crossbridge formation) and movement of the myosin head results in contraction of the sarcomeres and of the muscle fiber (cell)
Tropomyosin
Regulatory protein (regulates contraction of the sarcomere)
Ø Thread-like proteins that runs the length of the outer surface of the actin chain.
In a relaxed sarcomere what does tropomysoin do?
Ø In a relaxed sarcomere, tropomyosin covers the myosin binding site on actin
So, for contraction to occur, tropomyosin must be moved in order to uncover/reveal the binding sites
Troponin
Ø Also a regulatory protein (regulates contraction of the
sarcomere)
Ø Composed of 3 polypeptide units
i. One binds to tropomyosin (troponin T)
ii. One binds to actin (troponin I)
iii. One can bind with Ca++ (troponin C)
Explain troponins role in contraction
when not bound to Ca2+, troponin stabilizes tropomyosin over actin’s cross-bridge binding sites
This blocks myosin from being able to bind to actin
Ø When Ca2+ binds to troponin, tropomyosin moves away from blocking position
Ø With tropomyosin out of way, the binding sites on actin are revealed, and the myosin head binds to actin forming a crossbridge that will allow contraction to occur
Z-disks
Connect sarcomeres (between two Z-disks = 1 sarcomere).
Point of attachment for thin filaments and titin.
M-line
Made of the protein myomesin
Ø Runs down the middle of the sarcomere
Ø Point of attachment for myosin (thick filaments) and titin
Titin
aligning protein
Ø Large elastic protein.
Ø Joins M-line proteins to Z-disks at opposite ends of the sarcomere
