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100 Cards in this Set

  • Front
  • Back
From where does the energy come to shorten muscles?
Muscle cells convert the chemical energy of ATP into mechanical energy.
Three types of Muscle Tissue
- Skeletal
- Cardiac
- Smooth
Two Visual Categories of Muscle Tissue
- Striated: Skeletal & Cardiac
- Unstriated: Smooth
Two Functional Categories of Muscle Tissue
- Voluntary: Skeletal
- Involuntary: Cardiac & Smooth
Four Functions of Muscle Tissue
- Movement of body parts & organ contents
- Control of passageways & openings
- Prevent movement - Communication
- Body heat production
Universal Characteristics of Muscle
- Excitability: responds to chem, stretch, elec. signals
- Conductivity: electrical change triggers excitation wave
- Contractility: Shortens when stimulated
- Extensibility - Elasticity
Describe Skeletal Muscle
- Voluntary striated muscle attached to bones
- Alternating light and dark transverse bands
What are those Alternating light and dark transverse bands in Skeletal Muscle?
- Overlapping arrangement of internal contractile proteins
Three Parts of Skeletal Muscle
- Origin: Attachment to stationary end of muscle
- Body: thicker middle region of muscle
- Insertion: attachment to mobile end of muscle
Connective Tissue Elements of Muscle
- Endomysium, Perimysium, epimysium, fascia, tendon
- Not excitable or contractile
- Somewhat extensible & elastic
- Called Series-elastic components
What Do Series-Elastic Components Do?
- Are connected to each other in linear series
- Help return muscles to their resting lengths
- Add Significantly to muscle power output and efficiency
Describe Epimysium
- Covers whole body of muscle
- Blends into connective tissue that separates muscles
Describe Perimysium
- Slightly thicker layer of CT than Epimysium
- Surrounds a bundle of muscle cells called a fascicle
Describe Endomysium
- Thin layer of areolar tissue surrounding each cell
- Allows room for capillaries and nerve fibers
Location of Fascia: a fibrous connective tissue
- Deep Fascia between adjacent muscles
- Superficial fascia (= hypodermis) found between skin and muscles. Contains adipose tissue
Four Muscle Attachments
- Direct (fleshy) attachment to bone
- Indirect bone attachment: epimysium - tendon - bone
- Attachment to dermis
- Attachment to other muscles
Three Coordinated Muscle Actions
- Prime Mover (antagonist): produces most force
- Synergist: aids PM, stabilizes joint, modifies direction
- Antagonist: Opposes PM, prevents excess movement & injury
Describe Intrinsic & Extrinsic Muscles
- Intrinsic: contained within region of movement
-- muscles of hand moving fingers
- Extrinsic: found outside region of movement
-- muscles of forearm moving fingers
Skeletal Muscle Anatomy (8 major parts)
- Muscle Belly - Fascicle
- Muscle Fiber/Cell - Myofibril
- Thick Filaments - Thin Filaments
- Actin - Myosin
Sliding Muscle Theory
- Muscle contraction is the result of thin filaments sliding past thick filaments.
- Pull on Z lines & shorten the sarcomere & the cell as a whole.
Skeletal Muscle Fiber Anatomy
- A band - H band - I band - M band - Z band - Z disc
- Nucleus - Mitochondria - Myofibrils
-Sarcoplasm - Sarcoplasmic reticulum - Sarcolemma
- Triad: - 2 Terminal cisternae - 1 Transverse tubule
Muscle Fiber
- Single skeletal muscle cell (up to 2.5 feet long)
- Multiple Mitochondria for ATP production
- Made of multiple myofibrils and nuclei from fused cells
Parts of Muscle Fiber
- Sarcoplasm: may contain glycogen & myoglobin
- Sarcolemma: Plasma membrane
- T (Transverse) -tubules: infoldings of sarcolemma
- 2 terminal cisternae & 1 Transverse Tubule
- Connects electrical signal on sarcolemma to release Ca from Sarcoplasmic reticulum
- Specialized contractile element
-- 80% of muscle cell
-- 100s lie in parallel in a muscle cell
- Appears banded (striated) by thick & thin filaments
- Thick filaments made of myosin with titin core
- Thin filaments made of Actin, Tropomyosin & Troponin
Thick Filaments
- 200 to 500 myosin molecules
-- 2 entwined polypeptides
- Core of titin recoils after stretching
- Arranged in bundle w/ heads out and bare zone
Myosin Protein Making Thick Filament
- 2 subunits with tails intertwined
- Globular head (paddle) has actin binding site and myosin ATPase site
Thin Filaments
- "String" of Balls of actin each with active site
- Double bands of tropomyosin (blocking protein)
- Troponin: Regulating protein of 3 subunits: Ca Binding, Actin binding, Tropomyosin binding
3-D Actin-Myosin Interaction
- Cross bridging: 16B thick & 32B thin filaments/fiber
- Geometric relationship: 1 thick surrounded by 6 thin
Neuromuscular Junction
- Where nerve fiber makes functional connection with a target muscle cell
- Acetylcholine (Ach) opens ligand-gated channels on muscle cells
Motor End Plate
- Specialized muscle cell membrane under terminal button
- Has ACh receptors, ligand-gated channels, ion channels
- Electrical change = end plate potential
Nerve-Muscle Relationships
- Cell bodies of somatic (alpha) motor neurons in brainstem or ventral horn of spinal cord
- Axons of SMN are called somatic nerve fibers
- Each branches to supply 200 fibers (motor units)
Motor Unit
- One motor neuron & innervated fiber
- Weak contraction over wide area
- Motor units take turns (asynchronous recruitment)
- Small and Large motor units
Small Motor Unit for Fine Control
- Contains as few as 20 muscle fibers per nerve fiber
- Small, controlled movements - e.g. eye muscles
Large Motor Unit for Strength
- Large contractions - e.g. posture
-- gastrocnemius has 1000 fibers per nerve fiber
Acetylcholinesterase: The OFF Signal for the Neuromuscular Junction
- Enzyme inactivates ACh by degrading it
- Always present in synaptic cleft
- Stops end plate potential (& muscle contraction)
- Keeps contraction proportional to nerve stimulation
Toxins and Paralysis: Cholinesterase Inhibitors
- Bind to AChesterase to prevent Ach degradation
-- Spastic paralysis, possible suffocation
-- Contracted muscles unable to relax
-- Used in some pesticides
Toxins and Paralysis: Tetanus or Lockjaw
- Spastic Paralysis caused by Clostridium bacteria toxin
- Blocks glycine release in the spinal cord
Toxins and Paralysis: Curare
- Competes w/ ACh: Binds to ACh receptors
- Prevents contraction, causing flaccid paralysis
- Can lead to respiratory arrest
4 Actions Involved in Muscle Contraction and Relaxation
- Excitation: APs in Nerve lead to APs in muscle fiber
- Excitation-contraction coupling link AP to myofilament activation (via Ca) -Contraction of muscle fibers
- Relaxation of muscle fiber to resting length
Excitation of Muscle Fiber: Steps 1 & 2
- Nerve signal (AP) stimulates voltage-gated calcium channels
- Causes exocytosis of synaptic vesicles containing ACh
- ACh released into synaptic cleft
Excitation of Muscle Fiber: Steps 3 & 4
- ACh binds to ligand-gated channels on muscle cell
-- Allows Na and K to diffuse
-- Results in an end-plate potential (EPP)
--- local/graded potential
Excitation of Muscle Fiber: Step 5
- Voltage change in end plate region (EPP) opens nearby voltage-gated channels in plasma membrane
--Produces AP on muscle cell (sarcolemma
- Whole sarcolemma gets action potential
Excitation-Contraction Coupling
- Links muscle APs and contraction
- ACh stimulates APs over the surface of whole fiber
- Transverse (T-) tubule: sarcolemma extention conducts AP along SR deeply into cell (triad) between A & I bands
Sarcoplasmic Reticulum
- Modified ER
-- Stores Ca++
-- Terminal cisternae sacks sit at junction of A & I bands
Excitation-Contraction Coupling: Steps 6 & 7
- 10,000x more Ca++ in SR than in sarcoplasm
- AP spreads over sarcolemma
- Enters T-tubules where Voltage-gated channels open
- Opens Ca gates in SR & Ca released to sarcoplasm
Excitation-Contraction Coupling: Steps 8 & 9
- Ca release by SR into sarcoplasm
- Ca binds to Troponin
- Troponin-tropomyosin complex changes shape and exposes active sites on actin - regulates contraction
Contraction: Steps 10 & 11
- Myosin ATPase in Myosin head hydrolyses ATP
-- Activates head and cocks it in extended position
-- Energy is now stored in myosin head
- Myosin binds to active site on actin
Contraction: Steps 12 & 13
- Power Stroke: head releases ADP and P as it flexes and pulls thin filament
- Binds more ATP, releases thin filament & attaches to new active site further down thin filament
Power Stroke
- Ca++ binds Troponin, which slides tropomyosin over, allowing Myosin to bind actin
- Binding causes conformational change: myosin bends inward, new ATP causes release, returns to original form
Role of ATP
- Myosin ATPase splits ATP, Energy stored (cocking)
- Ca allows power stroke: release of ADP & P from myosin
- New ATP binds to myosin/Mg complex for release (or else rigor mortis)
Single Contraction
- Shortens muscle by 1%
- Each head 5 strokes per second = 5 ATP
- Skeletal muscle can shorten up to 40%
Relaxation: Steps 14 & 15
- Nerve stimulation ceases
- AChesterase removes ACh from receptors
-- Ends stimulation of the muscle cell
Relaxation: Step 16
- Ca moved to Sr from sarcoplasm via active transport pumps
- ATP needed for relaxation as well as contraction
- Ca binds to calsequestrin in SR
Relaxation: Steps 17 & 18
- Loss of Ca from Carcoplasm results in troponin-tropomyosin complex moving back over the active sites
- Muscle fiber returns to resting length by stretching series-elastic components & antagonistic contractions
Rigor Mortis
- Begins in 3-4 hrs. Peak at 12 hrs. Next 48 to 60 hours
- Deteriorating SR releases Ca, activating contraction
- Relaxation needs ATP
- Fiber contraction continues until myofilaments decay
Sarcomere: The Functional Unit of Skeletal Muscle
- Z-line to Z-line
- Smallest component of muscle that can contract
Striations: Organization of Filaments
- Dark anisotropic (A) bands / Light isotropic (I) bands
- A band of thick filaments end to end
- H band: lighter central area without thin filaments
- I band: light region, thin filaments w/ Z-line & connectin
A Band (Dark Band)
- Thick filaments
- Part of thin filaments
- H zone where thin filaments do not reach
- Support Proteins of M-line anchoring thick Filaments
I Band (Light Band)
- Contains only thin filaments, but not their whole length
- Space between thick filaments
- Z-line: Cytoskeletal structure, protein called connectin, anchoring elastic & thin filaments
Elastic Filaments
- Titin: Huge springy protein runs through core of each thick filament, connects thick filament to Z disc structure
- Functions: keep thick & thin aligned, resist overstretching, help cell recoil to resting length
Sarcomere Contraction: Muscle Cells Shorten Because Their Individual Sarcomeres Shorten
- Sliding filaments: thin slide closer together
-- I band shorter, A band unchanged, H zone shorter
- Filaments don't change length, only overlap increases
- contraction produced by one action potential on one muscle fiber
- amount of contraction per fiber
-- number of muscle fibers contracting
- turning on more and more motor units
-- to increase tension in whole muscles
Length-Tension Relationship
- Amount of tension generated depends on length of muscle before it was stimulated
- Central Nervous System maintains optimal length
-- muscle tone
Phases of a Twitch Contraction
- Latent period: between stimulus and contraction start
-- only elastic components, so no shortening
- Contraction: external tension develops/muscle shortens
- Relaxation: tension loss, returns to resting length
Twitch Summation
- incomplete tetnus
- next signal to contract comes before muscle has fully relaxed
- Each stimulus creates identical response 10/sec max
Complete Tentus
- Sustained maximal contraction
-- increased cytosolic Ca++
- twitchs fuse into smooth prolonged contraction; no relaxation; 40-50 stimuli per second
- Each twitch has time to recover but develops more tension than the one before; 10-20 stimuli per sec
- Ca++ not completely back into SR
- Heat of tissue increases myosin ATPase efficiency
Incomplete Tetnus
- sustained fluttering contractions generates gradually more strength of contraction
- higher frequency 20-40/sec
-- each stimulus arrives before recovery of the previous
Recruitment & Stimulus Intensity
- stimulating the whole nerve with higher and higher voltage produces stronger contractions of motor units
- multiple motor unit summation: more motor units are being recruited as more work is done
Isometric & Isotonic Muscle Contractions
- Isometric: develops tension without changing length
- Isotonic:
-- Equal tension while shortening: Concentric
-- Equal tension while lengthening: Eccentric
Muscle Sensors: Muscle Spindles
- monitor change in muscle length
- has own efferent and afferent nerve supply (gamma motor neurons) to keep spindles taut
- annulospiral and flowerspray sensory nerve endings
Muscle Spindle Nerve Endings: Annulospiral
- Wrapped around intrafusal fiber
- Sense length and rate of stretch
Muscle Spindle Nerve Endings: Flowerspray
- at end of intrafusal fiber
- senses length
Muscle Sensors: Proprioception
- Sense of body position and movement
Stretch Reflex
- Stretch sensed by muscle spindles
-- activate alpha motor neurons
-- cause contraction
--- e.g. patellar tendon reflex
Golgi Tendon Organs
- Located in tendons
- Sense muscle tension; tension stretches receptors
- Reaches conscious level: proprioception
-- ability to weight objects
Muscle Metabolism
- Need ATP for power stroke, release of actin/myosin cross bridge, active transport of Ca into SR
- 3 major sources: Phosphagens (1-20 seconds), Glycolysis (10-120 secs), Aerobic Respiration (2+ min)
Phosphagen System
- Provide energy for immediate needs
- Transfer phosphate groups to ATP
- Myokinase system: P from ADP to ADP = ATP + AMP
- Creatine kinase sys: P from creatineP = ATP + creatine
- Anaerobic: makes 3 ATP net
- Pyruvic acid converted to lactic acid
Aerobic Respiration
- Citric Acid Cycle in mitochondria
- Aerobic
- 36 to 38 ATP net
- limits: glycogen depletion and fluid/electrolyte loss
- Progressive weakness and loss of contractility from prolonged use
- Ability to maintain-intensity exercise
- Depends on the supply of organic nutrients
Slow & Fast Twitch Fibers
- Slow oxidative fibers: more mitochondria, myoglobin & capillaries
- Fast glycolytic fibers: phosphagen enzymes & glycogen lactic acid systems SR releases Ca quickly
Oxygen Supply
- Slow Red Fibers rich in Myoglobin
- Fast White Fibers poor in Myoglobin
Oxygen Debt
- Excess Post Exercise Oxygen Consumption
- Replaces Oxygen reserves
- replenishes phosphagen system
- reconverts lactic acid to glucose
Muscle Efficiency
- At rest: 58% of energy lost to body heat
- Active skeletal muscle: 85% loss to body heat
Smooth Muscle
- Around tube and hollows
- Sheets of spindle-shaped cells; no Z-lines or banding
- No troponin or tropomyosin; little SR; No T-tubules
- Very slow cycles; uses 10 to 300x less ATP
Smooth Muscle
- Dense Bodies: Same protein as Z-lines
- 10 - 15 thin per thick filaments
- Huge contractility
Smooth Muscle Contraction
- Ca++ from ECF binds to calmodulin
- complex binds to myosin light chain kinase
- MLCK uses an ATP to phosphorylate cross-bridge
- Cross-bridges bind to actin
Smooth Muscle Response to Stretch
- Opens mechanically gated calcium channels
- Tissues briefly contract then relax
Types of Smooth Muscle
- Multiunit: Nerves to individual myocytes in motor unit
- Single Unit
Multi Unit Smooth Muscle
- Neurogenic contraction
Cardiac Muscle
- Combination of features from skeletal and single unit smooth muscle
- Involuntary & striated
Single Unit Smooth Muscle
- Electrically linked via gap junctions
- self excitable
- Autonomic Nervous System
Cardiac Muscle
- Cells are shorter, thicker, have anastamoses
- linked at intercalated discs
- Autorhythmic due to pacemaker cell
- Use Aerobic Respiration
Spontaneous Depolarization
- Pacemaker Potentials
- Slow wave potentials: in digestive tract