W4 - Muscle Tissue Flashcards
LO1: Name the primary germ layer that muscle tissue is derived from
Mesoderm
LO2: Describe the five properties of muscle tissue
Excitability
Muscle cells can respond to a stimulus such as a neurotransmitter released from a neuron, or nerve cell.
Conductivity
Muscle cells have an excitable plasma membrane that can conduct an electrical impulse when the cell is stimulated. The plasma membrane of a muscle cell is known as the sarcolemma.
Contractility
Muscle cells contain contractile proteins that allow them to shorten, thus producing movement.
Extensibility
Muscle cells are not only capable of shortening, but also lengthening.
Elasticity
Muscle cells can return to their original length after either shortening or lengthening.
LO3: Describe and compare the three different types of muscle tissue (cardiac)
Cardiac
Only found in the heart wall.
LO3: Describe and compare the three different types of muscle tissue (skeletal)
Skeletal
Found in the muscles that attach to bones.
LO3: Describe and compare the three different types of muscle tissue (smooth)
Smooth
Found lining the walls of blood vessels and hollow organs, as well as in the eye.
Describe the functions and organisation of skeletal muscle
Voluntary: under our conscious control
Striated: has a striped appearance due to the organisation of the contractile proteins in the muscle cells.
Composition of muscle: structure and composition of skeletal muscle
Skeletal muscle is made of fascicles (bundles of muscle fibers) surrounded by connective tissue layers.
The whole muscle is encased in epimysium (dense irregular connective tissue) and blends with deep fascia.
Each fascicle contains myofibers, which are muscle cells wrapped in endomysium (areolar connective tissue).
Composition of muscle: myofibers and myofilaments
Myofibers are long, cylindrical muscle cells with multiple peripheral nuclei, containing myofibrils. Myofilaments are contractile proteins within the myofibrils: thick filaments made of myosin and thin filaments made of actin, arranged in repeating units called sarcomeres.
Composition of muscle: Sarcomeres
Z discs: Anchor points for thin filaments
I bands: Light regions with only thin filaments, bisected by Z discs
A band: Dark region with thick filaments, partially overlapping thin filaments
H zone: Light area within the A band, containing only thick filaments
M line: Dark line in the center of the H zone, anchoring thick filaments.
Why does muscle appear striated
The regular arrangement of thick and thin filaments within sarcomeres creates alternating light and dark bands, giving skeletal muscle its striated appearance.
What is the role of the somatic nervous system, motor neurons, and neurovascular bundles in skeletal muscle function?
The somatic nervous system innervates skeletal muscles, which are supplied with blood vessels and nerves that travel together in neurovascular bundles. Motor neurons, with long axons, terminate on individual myofibers at the neuromuscular junction, releasing neurotransmitters to transmit electrical impulses that stimulate muscle contraction.
What properties of myofibers allow them to respond to stimuli and enable skeletal muscle contraction?
Myofibers have the properties of excitability (ability to generate an electrical impulse in response to stimulation) and conductivity (ability of the sarcolemma to conduct the electrical impulse), which lead to skeletal muscle contraction.
Describe the functions of the muscular body system
700 voluntary skeletal muscles that produce movements and stabilise bone, joints and other structures
Describe the gross anatomy of a skeletal muscle
Skeletal muscles = considered organs = composed of muscle tissue, epithelial, connective and nervous tissue.
Typical skeletal muscle = muscle belly (contractile portion), tendons (attach it to bone at attachments/insertions/origins)
Rope-like (most common): round/oval cross-section
Tendons
Fibrous connective tissue band that attaches a muscle to a bone (or fascia, cartilage, organs, skin)
Serves as mechanical bridge to transmit muscle strength to bones and joints
Enables muscle contraction to make movement of bone or structure
Stiffer than muscles - greater tensile strength - withstand large loads with minimal deformations
Connective tissue layers surrounding muscle (epimysium, perimysium and endomysium) merge into a single organisation to contact one or more fixed osseous points
Aponeuroses
Fascia
Thin layer of connective tissue outside the epimysium that surrounds individual muscles
Can be superficial or deep
Superficial: found under skin and within superficial adipose layers
Deep: deep to superficial fascia - surrounds and subdivides the muscular compartments
Attaches and stabilises muscles
Transmits mechanical tensiongenerated by muscles and imparts muscle strength
Reduces friction between muscles
Provides support to nerves and blood vessels - contains sensory nerve endings
Separates individual muscles
Also groups muscles together by creating fascial compartments containing muscles that share common functions and nerve/blood supply
Intermuscular Septa: fibrous partitions separating functional groups of muscles . Deep fascia, including intermuscular septa, can be used by muscles as extra attachments sites - efficient function
Patterns of Fascicle Arrangement in Muscles
Define the motor unit
Define the origin and insertion of skeletal muscle
Define the types of muscle contraction and muscle actions (muscle contractions)
2 main types of active muscle contraction:
Isotonic: muscle changes length and produces movement
Concentric: muscle shortens
Eccentric: muscle lengthens
Isometric: no change in length and no movement
Usually, the main muscle producing a particular movement undergoes concentric contraction, while an antagonist muscle simultaneously undergoes coordinated eccentric contraction.
Define the types of muscle contraction and muscle actions (muscle actions)
Prime Mover/agonist: principle muscle involved in a given joint action
Synergist: compliments action of agonist directly or indirectly e.g. biceps brachii assists brachialis in flexing elbow joint
Antagonist: opposes action of agonist e.g. triceps for biceps
Fixator: steadies the proximal parts of a limb through isometric contraction while movements occur in distal parts of limb e.g. rotator cuff steady shoulder joint
