Muscle Types and Functions

Lecture 7

Muscular System

Types of Muscle
______muscle – voluntary striated muscle that is usually attached to one or more bones
Long, thin, cylindrical fibers
Packed with ______microfilaments that overlap each other producing light and dark bands (striations)
More than one ______per cell
Cardiac muscle – heart muscle, involuntarily controlled
______, but involuntary
One nucleus per cell
______muscle – involuntarily controlled
No striations
One nucleus per cell
Functions of Muscle
______– Allow body to move from place to place and movement of individual body parts
Also moves body contents in course of respiration, circulation, digestion, urination, and childbirth
Stability – Muscles maintain posture for resisting the pull of ______
Communication – Muscles are used for facial expression, ______language, writing and speech
Control of body openings and passages – Sphincter muscles around eyelids, pupils, and ______control admission of light, food, and drink into the body; other sphincter muscles control movements out of the body
______production- The skeletal muscles produce 85% of body heat
Properties of Muscle
Excitability – When stimulated, muscle cells respond with ______changes across the plasma membrane
Conductivity – When the muscle is stimulated, electrical excitation is conducted throughout the entire plasma membrane
Contractility- Muscle fibers shorten ______when stimulated, which allows them to create movement
Extensibility – Muscle cells can be stretched as much as ______times their contracted length.
Elasticity – If a muscle is stretched, and then the tension is released, it can ______to its original resting length

General Anatomy of Muscles

Connective Tissues and Fascicles
Endomysium – a thin sleeve of connective tissue that surrounds each muscle ______(muscle cell)
Fascicles – bundles of muscle fibers, visible to the naked eye as parallel strands
Perimysium – connective tissue that surrounds ______
Epimysium – a fibrous sheath that surrounds and entire skeletal muscle
Fascia – connective tissue that separates muscles from one another (deep fascia) or that separates muscles from the overlying ______
Fascicles and Muscle Shapes
Fusiform muscles – muscles that are thick in the middle and tapered at each end
Moderately strong contractions
Parallel muscles – muscles that are of uniform width and that have parallel fascicles
Span ______distances, weaker than fusiform
Convergent muscles – muscles that are fan shaped, with fibers meeting at a single point
Relatively strong because of the relatively ______insertion
Pennate muscles- feather shaped, with fascicles inserting obliquely on a tendon that runs the length of the muscle (fibers meet at a ______, rather than a single point)
Strong muscles such as rectus femoris
______muscles (Circular muscles) – form rings around body openings
Muscle Attachments
______– relatively stationary (and proximal) point of muscle attachment
Insertion – more mobile (and distal) point of muscle attachment
Belly – middle region between the origin and the insertion
Functional Groups of Muscles
Prime mover (agonist) – muscle that produces most of the ______during a particular contraction
Example: biceps brachii for flexion of the elbow
______– Muscle that aids the prime mover to produce more power than a single muscle could
Example: brachialis muscle assists the biceps brachii
Antagonist – Muscle that ______the prime mover
It relaxes to give the prime mover almost complete control over an action
It may maintain some tension on a joint, limiting the speed or range of the prime mover, preventing excessive movement and joint injury
Example: triceps brachii opposes the biceps brachii
______– Muscle that prevents a bone from moving
Example: The fixator muscles of the scapula hold the scapula firmly in place during flexion of the elbow
Intrinsic and Extrinsic Muscles
Intrinsic muscles are entirely contained within a particular region, having both its origin and ______there
Extrinsic muscles act on a particular region, but has its origin elsewhere
Some movements of the fingers are produced by extrinsic muscles in the ______
Muscles, Bones, and Levers
______- any elongated, rigid object that rotates around a fixed point
Fulcrum – fixed point around which a lever rotates
Effort- ______applied against inertia; something done through exertion
Resistance- force that tends to oppose motion
Effort arm- part from the fulcrum to the point of ______
Resistance arm- part from the ______to the point of resistance
Functions of a lever?
Exert more ______against a resisting object than the force applied to the lever
OR move the resisting object farther or ______than the effort arm is moved
There is a trade-off between force and speed or distance
Mechanical advantage-Ratio of its output force to its input force
Lever classes
First-class lever – ______is between the effort and the resistance
Second-class lever – ______is between the effort and the fulcrum
Third-class lever – ______is between the fulcrum and the resistance

Microscopic Anatomy

Ultrastructure of Muscle Fibers
Sarcolemma – plasma membrane of a muscle cell
Transverse tubules – tunnel-like infoldings of the sarcolemma that penetrate through the cell membrane and carry an electrical current from the surface of the cell to the interior when the cell is stimulated
______- cytoplasm of a muscle cell
Myofibrils – long protein bundles about 1 micrometer in diameter
Glycogen – provides stored ______for the muscle during exercise
Myoglobin – binds oxygen until it is needed for muscular activity
Sarcoplasmic reticulum – reservoir for ______ions which are needed to activate the muscle contraction process
Myofilaments – parallel protein microfilaments that make up myofibrils
2main kinds
Myosin myofilaments – thick – about ____ nm in diameter
Actin myofilaments – thin – about 7 nm in diameter
Striations and Sarcomeres
Actin myofilaments run ______to each other and are anchored at one end to a Z line (or Z disc)
Mysosin myofilaments run parallel to each other and fit ______actin myofilaments
A sarcomere is the term for the segment that spans from one Z line to the next Z line
Because the sarcomere contains areas where there are only thin filaments, areas where there are only thick filaments, and areas with overlapping thick and thin filaments, there are ______areas and light areas
I bands are light (lIght) and contain only ______filaments
A bands are dark (dArk) and contain thick filaments (overlapping with thin filaments at the ends)
H bands are found in the middle of the _____ band
They are found where actin and myosin filaments do no overlap (containing only thick filaments)
Shortening
The sarcomere shortens during muscle contraction, but the ______do not
As the Z lines get closer together, actin and myosin filaments overlap more and more.
Because I bands are the areas consisting of areas where thin filaments are not overlapped by thick filaments, the I bands ______during muscle contraction
Because the H bands are the areas consisting of areas where thick filaments are not overlapped by thin filaments, the H bands ______during muscle contraction
Because the A bands extend from one end of the thick filaments to the other end (overlapping with thin, or not), and because the filaments themselves do not shorten, A bands remain the same length
The Nerve-Muscle Relationship
Skeletal muscles only contract when stimulated by neurons
Motor neurons are nerve cells that lead from the central nervous system to muscles (or glands)
Each motor nerve fiber branches about 200 times at its distal end, leading to different muscle fibers
Each muscle fiber is innervated by only ______motor neuron
Synapse – a ______at the end of an axon where it stimulates another cell
Neuromuscular junction – a synapse between a nerve fiber and a muscle cell
Synaptic ______– The swollen tip at the distal end of an axon; the site of synaptic vesicles and neurotransmitter release
Synaptic vesicles – A spheroid organelle in a ______knob; contains neurotransmitter
Neurotransmitter – A chemical released at the distal end of an axon that stimulates an adjacent cell
Motor ______plate – A depression in a muscle fiber where it has synaptic contact with a nerve fiber and has a high density of neurotransmitter receptors
Synaptic cleft – a narrow ______between the synaptic knob of an axon and the adjacent cell
A neurotransmitter has to diffuse across this space

Motor Unit – a motor neuron and all the skeletal ______innervated by it
Small motor units – where fine control is needed
Very few muscle fibers per nerve fiber
Provide fine degree of control needed for subtle movements
Small neurons that are ______stimulated
Large motor units
Many muscle fibers per nerve fiber
Much stronger, but lacking ______control
Large neurons that are harder to stimulate

Functional Perspectives

Muscle Growth and Atrophy
Growth - Exercise stimulates muscle fibers to produce more protein myofilaments
Myofibrils, as a result, grow ______
At a certain point, a large myofibril splits longitudinally, so a well- conditioned muscle cell has more ______
Some scientists think that entire muscle cells may split, leading to increased numbers of muscle ______(not just myofibrils)
Atrophy – muscle shrinks if it is not used
Disuse atrophy – typically seen when a limb is kept in a cast for weeks
Denervation atrophy – seen in cases where the spinal cord or ______connections to a muscle are damaged
Senescence atrophy – occurs due to aging, regardless of exercise
Physiological Classes of Muscle Fibers
Slow-twitch
Well adapted to ______respiration
Fibers do not generate lactic acid or fatigue easily
Fast-twitch
Rich in enzymes for ______fermentation
Fibers do produce lactic acid and fatigue more easily
Well adapted for quick responses but not for endurance

Cardiac and Smooth Muscle

Cardiac Muscle
Makes up most of the ______
Striated like skeletal muscle
Short, stumpy, slightly branched cells
Have intercalated discs where the cells meet
Each cell has one centrally-placed nucleus
Smooth Muscle
Found in blood vessels, ______passages, the iris of the eye, and digestive, respiratory, urinary and reproductive tracts
Fusiform in shape
Each cell has a single nucleus