Muscles Flashcards
- Motion
Movement of skeletal muscles. I.e. Walking.
Breathing and movement of body fluids.
Cardiac muscle and digestion.
Functions of muscles:
- Motion
- Heat production
- Posture and body support
- Heat production
40% of body weight is muscle and produces friction and heat with contraction.
- Posture and body support
The skeleton gives shape, muscles support joints and give posture.
3 muscle types:
Cardiac, skeletal, smooth
Properties of muscle:
- Irritability
- Contractility
- Extensibility
- Elasticity
- Irritability
Muscle tissue receives and responds to nerve stimulus
- Contractility
Muscle contracts due to stimulus
- Extensibility
Muscle contracts with stimulus. After stimulus an opposing muscle contracts and stretches the 1st muscle to it’s original length.
- Elasticity
Muscle can stretch and return to it’s original length
Muscle development:
- 4 weeks after conception blocks of mesoderm (myotomes) in the trunk begin rapid mitotic division. New cells are called myoblasts.
- Syncytial myotubule.
- At 9 weeks primitive myofilaments appear.
- Growth continues by adding myoblasts.
- Quickening - fetal movement. Occurs at the 17th week or 5th month.
- Just before birth myoblast production stops. You are born with all the muscle cells you will have. Conditioning, weight training increases size, but not the # of muscle cells.
Syncytial myotubule –
A multi nucleated mass from the union of many myoblasts
Connective tissues:
1. Origin -
The fixed end of a muscle. Usually proximal to the trunk.
Connective tissues:
2. Insertion -
The moveable end of a muscle. Usually distal to the trunk.
Connection tissues:
3. Belly or gastor -
Thickened center portion of a muscle.
Connective tissues:
4. Tendon -
Dense fibrous connective tissue which spans a joint and joins muscle to bone.
Connects to the periosteum of bone. Transfers contraction force from the muscle to the bone and causes movement.
Connective tissues:
5. Aponeuroses -
A flat sheet like tendon over broad areas. I.e. Connects frontalis to occipitalis over the top of the head.
Connective tissues:
6. Retinaculum -
Connective tissue that houses a group tendons
Associated Connective Tissue:
Arranged in muscle to protect, strengthen, and bind muscle fibers into bundles.
Associated Connective Tissue:
1. Endomysium -
Binds adjacent fibers into groups & supports nerves and capillaries
Associated Connective Tissue:
2. Perimysium -
Binds groups into bundles called fascicle
Associated Connective Tissue:
3. Epimysium -
Covers entire muscle and is continuous with a tendon
Associated Connective Tissue:
4. Fascia -
Binds separate muscles together
Muscle groups:
- Synergistic -
Muscles that work together for one function.
I.e. Biceps brachii and the brachialis muscle that work together to flex the forearm.
Muscle groups:
- Antagonistic -
Muscles perform different functions.
I.e. Triceps brachii which functions to extend the forearm, is antagonistic to the biceps brachii and brachialis.
Muscles classified by…?
Fiber arrangement.
- Parallel or fusiform -
Contract over a long distance, good endurance, not necessarily strong.
I.e. Sartorius - a strap like muscle over the thigh.
- Convergent -
Fibers converge at the insertion to maximize contraction force. Fan shape.
I.e. Deltoid or pectoralis major.
- Pennate -
Many fibers per unit. Fibers arranged around one or more central tendons like the barbs of a feather. Pennate muscles shorten only to a limited extent, but they can produce very powerful actions. Strong, provides dexterity, short length, and tire quickly.
I.e. Pinnate muscles in forearm, calf, or thigh.
- Circular -
Surround body openings.
I.e. Orbicularis oris (mouth), oculi (eye)
Blood and nerve supply
Muscle has a high metabolic rate and needs food blood supply to provide O2 and remove waste & CO2.
Small muscles have their own artery.
Large muscles have many veins & arteries. Capillaries are in the endomysium surrounding each fiber.
Muscle cell -
Multi nucleated, contains the usual cell organelles & is a cylinder up to 30 cm long.
Called a muscle fiber and striated (striped).
Sacolemma -
Cell membrane
Sarcoplasm -
Cytoplast
Sarcoplasmic reticulum -
Endoplasmic reticulum. Modified to pump Ca+ to muscle fibers.
Transverse tubules (T tubules)
Formed by sacrolemma. Open to the extra cellular fluid. Brings in Ca+ to the sacroplasmic reticulum.
Actin -
The thin filament in the muscle composed of actin monomers.
Myosin cross bridge
Myosin -
The thick filament of muscle composed of myosin. (Resembles golf clubs)
Sacromere -
Unit of contraction in muscle
Rigor Mortis -
All ATP binding sites are attached. No fresh supply of ATP, so myosin doesn’t detach.
Isotonic contraction -
Force of contraction remains constant throughout the contraction.
Isometric contraction
Muscle length is constant. The opposing force = muscle contraction force.
Sliding filament theory of muscle contraction:
Myosin -
Looks like a golf club. The head of myosin will bond to 1 of 3 active sites on actin.
ATP acts as the “glue” between actin and myosin.
Sliding filament theory of muscle contraction:
Actin -
Looks like a string of pearls. Each “pearl” monomer has has 3 active sites.
Sliding filament theory of muscle contraction:
Tropomyosin -
A long chain protein molecule that covers the active sites of actin and prevents contraction.
Sliding filament theory of muscle contraction:
Troponin -
A control protein that hold tropomyosin in place on the active sites of actin. Ca+ causes tropomyosin and troponin to roll off the active sites of actin.
Sliding filament theory of muscle contraction: some steps
- Nervous stimulation releases Ca+ from the T tubules into the sarcoplasmic reticulum.
- Ca+ bonds to troponin and rolls tropomyosin and troponin off the active site.
- Myosin forms a cross bridge with ATP to actin.
- ATP –> ADP + P The bond energy is used to bend the myosin head, pulling actin (a bit of contraction takes place).
- New ATP is added. The cross bridge breaks and a new bond forms. This cycle continues until the muscle is contracted.
Neuromuscular junction:
Synaptic knob -
The expanded tip of the axon branch, on the sarcolemma called the motor end plate. Acetylcholine or neurotransmitter is released here & triggers Ca+ release and muscle contraction.
Neuromuscular junction:
Synaptic cleft -
The space that separates the synaptic knob and motor end plate.
Neuromuscular junction:
Motor end plate -
The end of the muscle that received the signal to contract. It also releases acetylcholinesterase to decompose acetylcholine in the cleft after the initial impulse.
Steps in contraction:
1.
- Release of ACH from synaptic knob into the synaptic cleft.
ADH diffuses to motor end plate.
Steps in contraction:
2.
- Depolarization of the motor end plate.
- Increases Na+ permeability. Na+ rushes in, depolarizers the membrane, and causes a (+) charge inside the muscle cell membrane.
- Depolarization lasts 2-20 microseconds.
- Acetylcholinesterase degrades ACH
- The Sodium Potassium pump returns Na+ to the outside and the membrane is repolarized.
Steps in contraction:
3.
- Generation of action potential.
Depolarization at the end plate spreads across the sarcolemma.
-Excitability
-Action potential
Excitability -
Ability to conduct electrical impulse.
-Only muscle and nerve are excitable.
Action potential -
Depolarization sweeps across the sarcolemma.
Energy usage:
- ATP –> ADP + P
- Creatine Phosphate is a high energy storage compound in muscles
- ATP + CP –> Creatine Phosphate + ADP –> ATP + Creatine
Glycogen -
A polysaccharide chain of glucose stored in muscle between myofibrils
- Glycogen –> Glucose + ATP
Types of stimulus and contraction
Myograms
Steps in muscle contraction
Action potential, Ca+ release, Ca+ binds, tropomyosin shifts and unblocks the active site on actin, actin is reattached across myosin
