Lecture 7 - Muscle Physiology Flashcards
Skeletal muscle functions?
Producing body movements
Generating heat
Stabilizing body positions
Cardiac muscle functions?
Involuntary movement of the heart
Smooth muscle functions?
Involuntary movement of organs and blood vessels.
Control of blood vessels, airways, digestive tract, urinary tract.
Four properties of muscular tissue that enable muscle to function and contribute to homeostasis?
Excitability
Contractility
Extensibility
Elasticity
Excitability
Ability to respond to stimuli
Contractility
Ability to contract forcefully when stimulated
Extensibility
Ability to stretch without being damaged
Elasticity
Ability to return to an original length
Three types of muscle tissues?
Skeletal, cardiac, and smooth muscle.
Skeletal muscle
Inserted onto bone via connective tissue; tendons and ligaments.
Long cylindrical cells
Many nuclei per cell
Striated
Voluntary
Rapid contractions
Cardiac muscle
Found in walls of the heart, specifically the myocardium.
Branching cells, branched fibers
1-2 nuclei per cell
Striated
Involuntary
Medium speed contractions
Smooth muscle
Lines hallow organs.
Fusiform cells
1 nuclei per cell
Non-striated
Involuntary
Slow, wave-like contractions
Muscles can only do two things: ________ and _______.
contract and relax
Fascia
Dense sheet or broad band of irregular connective tissue that surrounds muscles.
Epimysium
A sheath of fibrous elastic tissue surrounding a muscle, outmost layer.
Separates 10-100 muscle fibers into fascicles.
Perimysium
Surrounds numerous bundles of fascicles.
Endomysium
Separates individual muscle fibers from one another.
Tendon
Cord that attaches a muscle to a bone.
Aponeurosis
Broad, flattened tendon.
Neurons that stimulate skeletal muscle to contract are ________.
somatic motor neurons
The ____ of a somatic motor neuron typically branches _______. Each branch extending to a _______ skeletal muscle fiber.
- axon
- many times
- different
The __________ fibers is set before birth. Most of these cells last a lifetime.
number of skeletal muscle
Skeletal muscle structure from largest to smallest unit.
- muscle bellies
- muscle fibers
- myofibrils
- myofilaments
- sarcomeres
- actin & myosin
Muscle belly is covered by connective tissue called _________.
epimysium (outer layer)
Bundles of muscle fibers called fascicles are surrounded by ________.
perimysium (middle layer)
Within fasciculi are individual muscle fibers surrounded by _________.
endomysium (inner layer)
Sarcolemma
Plasma membrane of a muscle cell
Transverse (T-tubules)
Tunnel in from the plasma membrane. Muscle action potentials travel through the T-tubules.
Sarcoplasm
Cytoplasm of a muscle fiber.
Includes glycogen used for synthesis of ATP and myoglobin which binds O2 molecules.
(Myoglobin releases O2 which is needed for ATP production)
Myofibrils
Thread-like structures which have a contractile function.
Sarcoplasmic Reticulum (SR)
Membranous sacs that encircle each myofibril.
Stores calcium ions (Ca++).
Release of Ca++ triggers muscle contraction.
Filaments
Function in the contractile process.
2 types - thick and thin filaments.
2 thin filaments for every thick filament.
Sarcomeres
Compartments of arranged filaments.
Basic functional unit of a myofibril.
Segment between two neighboring Z-lines. Each sarcomere is made up of actin and myosin myofilaments.
Myosin forms the thick filament.
Actin forms the thin filament.
Z line/discs
Separate one sarcomere from the next
A band
Darker middle part of the sarcomere.
Contains both actin and myosin myofilaments (they overlap).
I band
Lighter in color and contains only the thin actin myofilaments. Z discs pass through the center of each I band.
H zone
Center of each A band which contains thick (myosin) but no thin (actin) filaments. Appears to shorten when muscle contracts.
M line
Supporting proteins that hold the thick filaments together in the H zone.
What are the two regulatory proteins on actin?
Troponin and tropomyosin
Actin
Thin filaments.
Actin molecules provide a site where myosin head can attach.
Tropomyosin and troponin are also part of the thin filament.
Myosin
Thick filaments.
Functions as a motor protein which can achieve motion.
Convert ATP to energy of motion.
Projections of each myosin molecule protrude outward (myosin head).
Myofibrils are built from what three types of proteins?
Contractile proteins, Regulatory proteins, and Structural proteins.
Contractile proteins
Actin and myosin
Generate force during contraction
Regulatory proteins
Switch contraction process on and off
Structural proteins
Titin - Stabilize the position of myosin. Accounts for much of the elasticity and extensibility of myofibrils.
Dystrophin - Links thin filaments to the sarcolemma.
Excitation-Contraction Coupling
For voluntary muscle contraction to occur, action potentials must arrive from the motor neuron. This stimulates the release of a neurotransmitter, in most cases of skeletal muscle it is ACh. ACh diffuses across the synaptic cleft, and binds to nicotinic receptors on the post-synaptic muscle cell. If the stimulus is strong enough, action potentials are produced, and the muscle is stimulated to contract.
Events leading to muscle fiber contraction (4 steps)
- A motor neuron releases acetylcholine (ACh).
- ACh binds to receptors on the sarcolemma.
- The action potential triggers release of Ca2.
- The Ca2 binds to troponin on the actin filament, and the troponin pulls tropomyosin off the active sites, allowing myosin heads to attach to the actin filament.
Sarcomere _________ is the basis for muscle __________.
- shortening
- contractions
Shortening happens by __________ the degree of overlap of thick and thin myofilaments in each sarcomere.
increasing
The sliding filament mechanism
Myosin heads attach to and walk along thin filaments at both ends of sarcomere.
Progressively pulling the thin filaments toward the center of the sarcomere.
Z discs come closer together and the sarcomere shortens.
Leading to shortening of the entire muscle.
Skeletal muscle can contract ______ but ______ easily and must be rested.
- rapidly
- tire
Skeletal muscle contractions _________ depending on use.
vary in force
Cardiac muscle contracts at a ________ rate but can _______ to cope with demand.
- steady
- accelerate
Smooth muscle contracts in ________, ________ contractions and continues _________.
- steady, sustained
- tirelessly
