Chapter 9 - Muscular System Flashcards
Connective Tissue around Muscles
- Fascia: thin covering of connective tissue around muscles
- Tendon: cord like mass of connective tissue which connects muscle to bone
- Aponeurosis: sheet like mass of connective tissue which connects a muscle to bone, skin or another muscle
Layers of CT surrounding muscle beneath the Fascia
- Epimysium: surrounds the whole muscle and lies beneath the fascia
- Perimysium: surrounds the fascicles within a muscle
- Endomysium: surrounds the muscle fibers(myofibrils) within a fascicle
- Perimysium: surrounds the fascicles within a muscle
Muscle Structure(least to most complex)
- Got thick and thin filaments; myosin and actin, which interact to cause muscle contractions
- Myofibrils: organelles which cause contractions and are in bundle form of Actin and myosin
- Muscle fibers / Myofibers: many myofibrils covered by the sarcolemma membrane which is then covered by a layer of connective tissue known as the endomysium;
○ which helps electrically insulate the muscle cells from each other and allow for more precise movement - Fasicle: many myofibers bundled together to form a muscle cell which is then covered by perimysium
- Fascicles are bundled together to form the entire muscle and is covered in epimysium,
- The fascia covers all of this
- The fascia, epimysium, endomysium and perimysium then extends past the muscle and connects to the bone to form a tendon
Skeletal Muscle Fiber Components/organelles
- Sarcolemma: cell membrane of muscle fiber
- Sarcoplasm: cytoplasm of muscle fiber
- Myofibrils: organelles in cells containing actin and myosin filaments
- Sarcoplasmic Reticulum: stores calcium and covers each myofibril
- Transverse tubule: relays electrical impulses to the SR
- Triad: unit consisting of 1 T tubule and 2 SR cisternae
Myofibril Structure
- composed of sarcomeres that are composed of Thick and Thin Filaments
Sarcomere Structure
○ I band: lIght band composed of only Actin filaments
○ A Band is the dArk band composed of myosin filaments
○ H Zone: center of A band which has only myosin filaments
○ Z line(disc): the sarcomere boundary where the center of I band anchors actin filaments in place
- M Line: the center of the A Band(H Zone) where myosin filaments are anchored
Thick and thin Filaments
Thick: composed of myosin proteins
- Composed of myosin protein
- Have heads which form cross bridges with thin filaments
Thin: composed of actin proteins
- Have an active binding site for myosin, which are covered when the muscle is not contracting by tropomyosin
○ Troponin removes tropomyosin when muscle contractions are wanted
How muscles Contract
- Muscles contract in response to neurostimulation from a motor neuron
This happens at a myoneural(neuromuscular) junction where the axon of a motor neuron and skeletal muscle fiber interacts
Parts of a Neuromuscular Junction
- Motor neuron
- Motor end plate: specialized folded portion of skeletal muscle fiber where the fiber binds to the neurotransmitter
- Synaptic cleft: space between neuron and muscle fiber which neurotransmitters travel
- Synaptic vessels: membrane bound sacs of neurotransmitters
- Neurotransmitters: chemical messengers (acetylcholine)
Steps in Neuromuscular Stimulation of a muscle
- Nerve impulses reaching the axon terminal open calcium channels, bringing them into the neuron and causing the release of ACh from synaptic vesicles
○ As ACh is released, the calcium is also released from the neuron again - ACh binds to the motor end plate and causes changes in the membrane permeability to sodium and potassium ions,
○ Moves sodium in the muscle, and potassium out, generating a muscle impulse(action potential) - Once the muscle impulse is generated, the ACh that was bound is broken down now by acetylchlolinesterase
- The impulse travels down the T tubule and causes the release of calcium ions from the terminal cisternae, into the cytosol (sarcoplasmic reticulum), causing muscular contractions
Excitation - Connection Coupling
connection between muscle fiber stimulation and muscle contraction
2 stages:
- muscle relaxation
- muscle stimulation
Muscle Relaxation Stage
- Calcium ions are stored in SR
- troponin, tropomyosin complex cover the binding sites on actin filaments
Muscle Stimulation Stage Steps(steps in muscular contractions)
- Muscle impulse travels across the sarcolemma and down the T tubules
- Calcium ions are released from the sarcoplasmic reticulum
- Calcium ions bind to troponin, causing a conformation change
- Tropomyosin is moved off the actin binding sites
- An energized myosin cross bridge binds to the actin molecule
- The power stroke of the myosin cross bridge causes the sliding of the thin filaments
- ATP binds to the cross bridge, causing it to disconnect from actin
- ATP is broken down into ADP which reenergizes and repositions the myosin cross bridge
- Calcium ions are moved back into the SR by active transport
Post Muscle Stimulation - Relaxation
- Acetylcholinesterase decomposes Ach remaining in the synapse, stopping the muscle impulse
- Calcium pump moves Calcium into the SR
- Troponin-tropomyosin complex again covers the actin binding site
Energy Stores for Contractions
ATP reserves:
- Muscle cells only store about 4-6 seconds
Creatine Phosphate:
- Initial source of energy regeneration by storing energy in the phosphate bonds with creatine
- Fuels the cell for approx 10 secs
Cellular Respiration:
- Fuels longer periods of contractions
- Breaks down glucose either stored in the muscle cells(glycogen) or coming from food to produce ATP
Anaerobic Cellular Respiration:
- Small amounts of ATP are produced from glucose when no oxygen is present
- Produces lactic acid as a by product
Muscle Fatigue
the inability to contract muscle due to troponin having less affinity fo calcium
- Causes are:
○ Decreased blood flow
○ Ion imbalances in the Sarcolemma
Accumulation of lactic acid
Muscle Cramps
sustained involuntary contractions due to changes in electrolyte concentration in extracellular fluids in the area
Threshold Stimulus
minimum strength of stimulation of a muscle fiber required to cause a contraction
Twitch: Single Muscle Contraction
Contractile response of a single muscle fiber to a single impulse
- Latent period: delay between stimulation and start of contraction - Period of contraction: fiber pulls at attachments - Period of relaxation: pulling force decreases ○ Takes more time than contraction as there is no force pushing the filaments away, its just the elastic recoil
Summation
What occurs when a muscle fiber is exposed to increasing stimuli frequency, resulting in it being unable to relax before being stimulated again, leading to the twitches combining and the contraction being sustained
- Classified as either partial or complete tetanic contractions depending on the stimulation frequency
Partial Tetany Summation Stimulation
occurs at higher frequencies of stimulation and involves partial relaxation
Complete Tetany Summation Stimulation
occurs at the highest frequencies of stimulation and involves full stimulation with no relaxation
- only achievable in the lab and not in the human body
Motor Unit
a motor neuron and all the muscle fibers it controls
- Coarse movements are composed of large numbers of fibers in a motor unit
- Precise movements are composed of small numbers of fibers in a motor unit
Motor Unit Recruitment
the increase in the number of motor units activated to produce more force
- As intensity increases, more motor units are stimulated until all units are stimulated
- For sustained contractions we start with smaller motor units before recruiting larger motor units as more force is needed
Muscle Tone
the continuous state of partial contraction in resting muscles due to constant small level nerve stimulation
Types of Muscle Contractions
Isotonic: muscle contracts and changes length
- Eccentric: lengthening of the muscle as tension is produced
- Concentric: shortening
Isometric: muscles contract but do not change length
Characteristics of Slow Twitch Muscle Fibers (Type 1)
- Oxidative
- Resistant to fatigue
- Red fibers due to being abundant in myoglobin
- Have many mitochondria
- Slow ATPase activity meaning slow to contract
- E.g. endurance athletes, Triathlons, Marathons,
Fast Twitch Glycolytic Fibers (Type 2b)
- Anaerobic respiration
- White fibers due to less myoglobin
- Fewer mitochondria
- Fast ATPase activity so contract rapidly
- High susceptibility to fatigue
E.g. Sprinting, Box jump, powerlifting
Fast Twitch Intermediate Fibers (Type 2a)
- Intermediate fibers with intermediate oxidative capacity and intermediate glycolytic capacity
- Intermediate amount of myoglobin
- White fibers
- Resistant to fatigue
- Rapid ATPase activity
E.g. sprinters, weight lifters
Use and Disuse of Muscles
Hypertrophy: enlargement of skeletal muscles that are exericsed
Atrophy: decrease in size and strength of skeletal muscles that are unused
Aerobic and Anaerobic Training Effects on muscles
- Aerobic exercise stimulates slow twitch fibers, increasing their capillaries and mitochondria
- Increases fatigue resistance by allowing it to oxidise energy more efficiently
Forceful exercise stimulates mainly fast twitch fibers, producing new actin and myosin filaments and enlarging the muscle
Characteristics of Smooth Muscle
- Shorter fibers
- Single, centrally located nucleus
- Elongated with tapering ends
- Myofilaments are randomly organized(not straited)
- Lack T tubules
Poorly developed SR
2 types
- multiunit
- Visceral
Multiunit Smooth Muscle
- Less organized cells which function as separate units
- Fibers function independently
- E.g. iris of the eye, walls of the blood vessels
Stimulated by neurons and hormones
Visceral Smooth Muscle
- Singe unit muscle cells which respond as a unit
- Sheets of spindle shaped fibers held by Gap junctions
- Contract rhythmically(peristalsis)
Most common type of smooth muscle found in the walls of organs
Characteristics of Smooth Muscle Contractions(differences to skeletal contractions)
- Differs from skeletal muscular contraction as it lacks troponin, and instead uses calmodulin
- Acetylcholine and norepinephrine stimulate contractions
- Stretching of organ walls can stimulate contraction
- They are slower to relax and contract
More resistant to fatigue
Characteristics of Cardiac Muscle
- Branching fibers with a single nucleus
- Striated muscle cells that are joined by intercalated discs
- Network of fibers contracting as a unit(syncytium)
- Self-exciting and rhythmic
- Longer refractory period than skeletal muscles(longer time between contractions)
- No sustained or tetanic contractions
Purpose of Levers
- Levers are designed to multiply force
- This is done by increasing the length of the force arm
Components of Levers
- Rigid bar: bone
- Fulcrum or pivot point: joint
- Force supplying energy: muscles
- Object moved against Resistance: weight)
1st Class Lever
1st Class: fulcrum in the middle with resistance and force on opposite ends
E.g. nodding of the head
2nd Class Lever
resistance in the middle with Fulcrum and force on opposite ends
E.g. Plantarflexion as BW is resistance(coming from midline over foot), fulcrum is the tarsal-metatarsal joint and force is from the calf muscle
3rd Class Lever
force is in the middle, with fulcrum and resistance on opposite ends
- Most common E.g. bicep curl
Interactions of Muscles to Allow for Movement
- Agonists: muscles causing an action
- Prime mover: muscles primarily responsible for an action
- Antagonists: muscles whose contraction causes movement in the opposite direction of the prime mover
Synergists: muscles that assist/stabilize agonists
Temporomandibular Joint Syndrome
an articulation problem between the mandibular condyle and mandibular fossa, affecting the nerves which pass through the region
- Causes clicking jaw, facial pain, ringing in ears, insomnia, tooth sensitivity
- Due to misaligned jaw and grinding/clenching of teeth
- Treatments: physical therapy, oral appliances, injections of botulism toxin
Life Span Changes in Muscles
- myoglobin, ATP and CP decline starting in the 40’s
- Connective tissue and adipose cells begin to replace unused muscle tissue
- By age 80, if nothing is done to prevent it, almost half of their muscle is replaced and atrophied
- Exercise can help maintain muscle mass and function
Anterior Forearm Muscles
medial to lateral:
- brachioradialis
- flexor carpi radialis
- palmaris longus
- flexor carpi ulnaris
- pronator teres (AB)
Posterior Forearm Muscles
Medial to Lateral:
- Brachioradialis
- extensor carpi radialis longus
- extensor carpi radialis brevis
- extensor digitorum
- extensor digit minimi
- extensor carpi ulnaris
- flexor carpi ulnaris
Lateral Head/neck muscles
- temporalis
- occipitalis
- masseter
- buccinator
- Sternocleidomastoid
- scalenes(anterior, middle, posterior)
Anterior head/neck Muscles
- Frontalis
- orbicularis oculi
- zygomatic minor(hidden under eye muscle)
- zygomatic major
- orbicularis oris
- mentalis(cut)
- Platysma
Posterior head/neck muscles
- Occipitalis
- Sternocleidomastoid
- splenius capitis
- Levator Scapulae
- Trapezius
Muscles of the Posterior Upper Body and Upper Limb
- trapezius
- deltoid
- supraspinatus
- infraspinatus
- teres minor
- teres major
- Latissimus Dorsi
- Triceps Brachii
Muscles of the anterior upper body and Upper limb
- Trapezius
- Pectoralis Major
- deltoid
- pec Minor
- coracobrachialis
- Brachialis
- Biceps Brachii
4 Abdominal Muscles(superficial to deep) and their fiber direction
- rectus abdominus(verticle)
- external obliques(lateral top to medial down)
- internal obliques(lateral down to medial top)
- transverse abdominus(lateral fibers)
Muscles of Anterior Hip
- Sartorius(medial band)
- tensor fasciae latae(lateral band)
- rectus femoris
- vastus lateralis
- vastus medialis
- vastus medialis(deep)
- gracilis
Muscles of Posterior Hip
- gluteus medialis
- gluteus maximus
- biceps femoris
- semitendinosus
- semimembranosus
- gracilis
- gluteus minimus(deep)
- piriformis(deep)
Muscles of Posterior Leg:
- gastrocnemius
- soleus
Muscles of Anterior Leg:
- Anterior Tibialis
- Extensor Digitorum Longus(next to long fascia)
