Additional Material (Testable on Midterm) Flashcards
What is muscle tissue?
Specialized cells that use ATP in the generation of force
3 Types of Muscle Tissue
- Skeletal
- Smooth
- Cardiac
Muscle Tissue (Functions)
Body movement, Substance Movement, Control of Substance Movement, Thermogenesis
What are the characteristics of muscle tissue?
- Electrical Excitability
- Contractility
- Extensibility
- Elasticity
Electrical Excitability
-The ability to respond to certain stimuli by producing electrical signals
-Electrical signals produced are called action potentials
Contractility
-Ability of muscle tissue to generate tension (force) when stimulated by an action potential
Extensibility
-Ability of muscle to stretch (lengthen) without being damaged
-Muscle can still contract when stretched
Elasticity
-Ability of muscle tissue to return to it’s original shape after contraction or stretch
Skeletal Muscle
-a.k.a. striated muscle
-Striations are alternating light and dark bands that are characteristic of this muscle type
-Voluntary/Conscious control (also subject to involuntary control)
Hierarchy of Skeletal Muscle Organization
- Muscle
- Fascicle
- Muscle Fibre (Muscle Cell)
- Myofibril
Muscle
-Size: cm
-Named
-Subdivided into bundles of fascicles
Fascicles
-Size: mm
-Each fascicle is made up of many muscle fibres
Muscle fibres
-a.k.a. the muscle cell
-Size: Small
-Cylindrical in shape
-Multinucleated
-Filled with myofibrils
-Within muscle fibres: Sarcolemma, Transverse Tubules (T-tubules), Sarcoplasm, Myoglobin, Mitochondria
Sarcolemma
The cell (plasma) membrane of the muscle cell
Transverse Tubules
-a.k.a. T-tubules
-Tiny invaginations tunnel in from the sarcolemma towards the centre of the muscle fibre
Sarcoplasm
The cytoplasm of the muscle fibres - contains lots of glycogen
Myoglobin
A protein that binds oxygen that has diffused into the muscle fibre and delivers it to the mitochondria
Mitochondria
Lots of them
Myofibrils
-Specialized contractile organelles of the muscle cell
-Size: extend the length of the muscle cell
-Held in place by cytoskeleton proteins
-Composed of a number of sarcomeres arranged in series (end to end)
-Within Myofibrils: sarcoplasmic reticulum
Sarcoplasmic Reticulum
Fluid filled tubes an sacs running along and surrounding each myofibril - they store and release calcium into the cell (when it’s needed)
Sarcomere
-Functional unit of a myofibril (of contraction)
Contain 2 contractile proteins: actin and myosin (a.k.a. myofilaments)
-Thick and thin filaments overlap and their interaction is what generates force/contraction
-Their overlap also creates light and dark strips which gives skeletal muscle it’s striated appearance
Actin
Makes up thin fillaments
Myosin
Makes up thick fillaments
Motor Neuron
Neuron/nerve cell that conducts action potentials to muscle cells
Neurological Control
- To generate tension, skeletal muscle cells must be stimulated by a nerve signal from a motor neuron
- Axon connects with muscle - when it reaches the muscle, it branches out into a number of axon terminals
- Each axon terminal forms a junction called neuromuscular junction (NMJ) with the sarcolemma of a number off different muscle cells
- Axon terminal and the sarcolemma never actually touch - there is a gap between them called the synaptic cleft
- When the signal arrives, it releases a neurotransmitter (acetylcholine (ACh)) which crosses the synaptic cleft
Sliding Filament Mechanism
- When signal crosses the synaptic cleft it stimulates the sarcolemma (cell membrane)
- Signal is continued by the muscle fibres and spreads out across the sarcolemma
- Signal travels down the transverse tubules and stimulates the sarcoplasmic reticulum to release calcium
- Calcium allows myosin (of thick filament) to connect with the actin (of the thin filament)
- Myosin pulls actin/thin filaments together
- Disengages and starts cycle again
- This reattaching of filaments used ATP
- With repetition, it shortens the sarcomere, myofibril, and the muscle
- When APs stops, sarcoplasmic reticulum pumps calcium back inside (uses ATP)
- Without sufficient calcium, thick filaments cannot continue their reattaching of thin filaments
- Tension generation stops
Production of ATP in Muscle Fibres
-Skeletal muscle fibres need to vary the levels at which they consume ATP
-Muscle fibres store enough ATP to last for ~3sec of activity
What are the 3 energy pathways through which more ATP can be generated?
- Creatine phosphate
- Anaerobic glycolysis
- Aerobic cellular respiration
Creatine Phosphate
- Is a molecule that stores high amounts of energy in its chemical bonds
- Pcr is split by an enzyme, the energy released is used to reform ATP
- Happens very fast therefore PCr is the first source of energy used when muscle contraction begins
- Provides energy for ~3-15 sec of maximal contraction
- No oxygen needed
- No lactic acid produced (hence anaerobic alactic)
Anaerobic Glycolysis
- In context of muscles: when muscle activity continues and PCr is depleted, glucose is used to make ATP
- Cell breakdown glycogen stored in their cytoplasm/sarcoplasm or glucose from the blood and the energy release in breaking them down is used to reform ADP + PI
- Process of making ATP from glucose occurs in the cell cytoplasm and is called glycolysis
- Through glycolysis, a molecule of glucose is broken into 2 molecules of pyruvic acid and 2-3 ATP
- Normally, pyruvic acid enters mitochondria where it undergoes a series of reactions (that requires oxygen) called aerobic cellular respiration.
- During heavy excercise/demand, not enough oxygen is available (hence anaerobic)
- In absense of oxygen, pyruvic acid does not go through mitochondria - is converted into lactic acid/lactate
- Lactic acid diffuses out of the cell into the blood
- No oxygen required and producing lactic acid = anaerobic acid
- Capable of supplying energy for 30-40 sec
Lactic Acid/Lactate
- Metabolic by-product of anaerobic glycolysis
- At lower levels of activity, any lactate produced is consumed by other muscle fibres, less active nearby muscles, and heart so lactate does not accumulate
- Is converted back into glucose/glycogen in the liver
- Lactic acid has a 1/2 life of 15-25 minutes and is cleared in a matter of hours
Aerobic Cellular Respiration
- Pathway is actie when you are able to get oxygen into the cells (e.g. at rest or low-moderate intensity exercise)
- Oxygen is delivered by myoglobin or from oxygen diffusing from the blood
- In presence of oxygen, pyruvic acid enters the mitochondria and in a series of reactions (that uses oxygen), produces much more ATP (much more than glycolysis)
- Carbs, fats, and proteins can be used in this process to make ATP
- Carbohydrates yield relatively little APT
- Fats yield a lot of ATP
- Proteins aren’t used readily (often not even included)
- At rest, cells of the body use aerobic metabolism to generate their ATP
- In activities that last longer than 10min, most (90%) of the ATP generated comes from the aerobic system
Skeletal Muscle Fibres
-Not all skeletal muscle fibres are the same - differences include:
-The speed at which they generate tension
-How they use different energy substrates
-How they fatigue
What are the 3 main types of skeletal muscle fibres?
- Slow Oxidative (a.k.a. type I)
- Fast Oxidative-Glycolytic (a.k.a. type IIa)
- Fast glycolytic (a.k.a. type IIx)
Slow Oxidative
-a.k.a. type I, slow-twitch fibres
-Recruited 1st (i.e. before type II fibres)
-Fatigue resistant
-Used in endurance-type functions (e.g. maintaining posture, running a marathon)
-Lots of mitochondria, myoglobin, capillaries
-Generate ATP via aerobic cellular respiration (i.e. oxygen is available)
-With immobilization, they atrophy faster (than type II fibres)
Fast Oxidative-Glycolytic (FOG) Fibres
-a.k.a. type IIa fibres
-Recruited 2nd
-Moderately high resistance to fatigue
-Used in endurance (e.g. walking) and shorter-duration functions (e.g. sprinting)
-Intermediate amounts of mitochondria, myoglobin, capillaries
-Generate ATP via aerobic and anaerobic energy pathways
Fast glycolytic (FG) Fibres
-a.k.a. type IIx fibres
-Recruited 3rd
-Low resistance fatigue
-Used in high intensity, short duration activities (e.g. weight lifting, slap shot) and shorter-duration functions (e.g. sprinting)
-Relatively low amounts of mitochondria, myoglobin, capillaries
-Generate ATP via anaerobic energy pathways (i.e. glycolysis)
Distribution of Muscle Fibres
-Most muscles are a mix of SO, FOG, FG fibres
-Within a given motor unit, all fibre types are the same
Muscle Fibre and Motor Unit Recruitment
- When AP travels down motor neuron to the muscle fibres (i.e. the motor unit), all fibres in that motor unit will generate force
- Not all motor units are recruited with every contraction
- All motor units recruited for a given action do not contract at the same time
- Smallest/Weakest motor units (i.e. SO) are recruited first
- Precise movements require small changes in muscle contraction
- Muscles that perform fine movements will be made up of small motor units (few m. fibres/motor unit)
- Large (imprecise) movements dont require small changes in muscle contraction - they typically require large amounts of tension
- Muscles that perform gross movements will be made up of large motor units (many m. fibres/motor unit)
To increase the amount of force generated?
- Increase number of motor units recruited
- Increase the frequency of neuronal AP firing (wave summation)
*Length Tension Relationship
-The forcefulness of contraction (the ability to generate force) depends on length of the sarcomeres within a muscle before the contraction begins
-Optimal Overlap (~resting length) = greatest ability to generate tension
-Minimal Overlap (Lengthened) = decreased ability to generate tension
-Excessive overlap = decreased ability to generate tension
Isotonic
Muscle contraction through a range against a resistance that is not changing
Concentric
Shortening Contraction
Eccentric
Lengthening Contraction
Isometric
Muscle contraction in which the length of a muscle does not visibly change
Variable Resistance
Muscle contraction through a range in which the equipment varies the resistance to match the strength curve
Isokenetic
Muscle contraction through a range in which the equipment varies the resistance to match the strength curve keeps the velocity of movement constant
Muscle tone
-Resting tone: small amount of tension being generated in the muscle
-Not strong enough to produce movement
Resting tone
small amount of tension being generated in the muscle
Twitch Contraction
Brief contraction of all the muscle fibres in a motor unit in response to a single AP in it’s motor neuron
Flaccidity
Lack of tone from the nerve being damaged or cut
Hypertrophy
Increase in muscle size
Atrophy
Decrease in muscle size
Fatigue
-Inability of a muscle to function at the required level
-Energy substrate depletion
-Metabolic by-products
-Neurological fatigue
-Central nervous system fatigue (Motivation)
Epimysium
Surrounds the entire muscle
Perimysium
Surrounds the fascicles
Endomysium
Surrounds the muscle fibres
Tendon
-epimysium, perimysium, and endomysium are all interconnected
-extend beyond the muscle fibres to connect the muscle to the periosteum
Musculotendinous Junction
Transition from muscle tissue to tendon
Tendoperiosteal Junction
Transition from tendon to periosteum
Aponeurosis
Broad, flat, tendon
Tendon Sheath
Tube that surrounds a tendon to protect it
Satellite Cells
*Stem cells of muscles
-Undifferentiated muscle cells
-Actively involved in muscle repair and regeneration
-Capacity is limited
Cardiac Muscle
-Same actin/myosin arrangement as skeletal muscle
-Fibres are branched - Ends are fit tightly together with neighbouring fibres at junctions called intercalated discs
-Anchoring junctions hold them together and gap junctions allow for cells to communicate quickly
-Involuntary control
Autorhythmicity
-Specialized cells within the heart can generate their own electrical signals
-Act as a pacemaker
Smooth muscle
*If you stretch smooth muscle it will contract
-Found in walls of hollow tubes
-Spindle shaped
-Have gap junctions
-Involuntary
-Contractions start slowly and last longer
Aging and Muscle Tissue
-Capacity for skeletal strength progressively decreases after approx. age 25
-Greater proportion is lost after approx. age 50
-Exercise is beneficial at any age
-Adaptation to exercise is slower
-Balance can become an issue later in life
Respiration
Exchange of gases between the atmosphere, blood and body cells
Atmosphere <-> Blood <-> Body Cells
Pulmonary Ventilation
Inhalation (a.k.a. Inspiration): Flow of air into the lungs
Exhalation (a.k.a. Expiration): Flow of air out of the lungs
Inhalation
-a.k.a. Inspiration
-Flow of air into the lungs
Exhalation
-a.k.a. Expiration
-Flow of air out of the lungs
Pulmonary Respiration
Exchange of gases across the respiratory membrane
Tissue Respiration
Exchange of gases between blood and tissue cells
Cellular Respiration
Metabolic reactions that consume oxygen and release carbon dioxide in the production of ATP
Structural Divisions
nose, pharynx, larynx, trachea, bronchi, lungs
Upper Respiratory System
nose, pharynx
Lower Respiratory System
larynx, trachea, bronchi, lungs
Functional Divisions
-Conducting zone
-Respiratory zone
Conducting Zone (Structures)
nose, pharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles
Conducting Zone (Functions)
-To filter, warm, and moisten the air and to conduct it into the lungs
-To receive olfactory (smell) stimuli
-Sound generation for speech
Respiratory Zone (Structures)
Respiratory bronchioles, alveolar ducts, alveolar sacs, alveoli
Respiratory Zone (Function)
Gas Exchange
Nose
-Houses olfactory receptors
-Rich blood supply
-Sticky mucous traps particulate
-ciliated cells move the mucous to the throat (pharynx) where it is swallowed and digested
Pharynx
-a.k.a. throat
-Funnel shaped tube just begind the nasal cavity and above the larynx
-Passageway for air and food, as a resonating chamber for sounds and as a housing for the tonsils
-At inferior end, it opens into the esophagus (posteriorly) and larynx (anteriorly)
Larynx
-a.k.a. voice box
-Inferior to where pharynx divides
-Epiglottis protects the top of the larynx
-Voice production (vocal folds)
-Connects the trachea (inferiorly)
Trachea
-a.k.a. windpipe
-anterior to the esophagus
-fairly rigid - C-shaped rings of hyaline cartilage reinforce and support it’s shape
-Lined with mucous membrane to filter particulate
-Cilia sweep particulate out of the trachea to the throat for expectoration or digestion
*Mucocilary Elevator
Bronchi
-At 5th thoracic vertebrae divides into the right and left primary bronchi which travel to the right and left lungs
-Carina: Internal ridge where trachea divides - is one of the most sensitive areas of the trachea and larynx for triggering a cough reflex
Carina
Internal ridge where trachea divides - is one of the most sensitive areas of the trachea and larynx for triggering a cough reflex
Mucociliary Elevator
A region of goblet & ciliated cells that is the primary area for trapping particulate and sweeping it back up towards the throat to be either coughed up or digested
Mediastinum
Region in the thoracic cavity between the lungs - It extends from the sternum to the vertebrae and from the 1st rib to the diaphragm
Alveoli
A cup-shaped outpouching lined with simple squamous epithelium supported by a thin elastic basement membrane
Alveolar Sac
2 or more alveoli that share a common opening
Lungs
-2 organs separated by the heart and other structures in the mediastinum
-Top is the apex
-Bottom is the base
-Within the lungs, each bronchus subdivides into smaller and smaller units: secondary bronchi (3 on the right, 2 on the left), tertiary bronchi, bronchioles, terminal bronchioles
-Smooth muscle increases, cartilage decreases
-Terminal bronchioles divide further and further until you get to alveoli
Pulmonary respiration happens at the level of the ________________.
Alveoli
Alveolar Cells
-Cells for gas exchange (simple squamous epithelium)
-Cells for fluid secretion (to keep the cells moist) - fluid contains surfactant which reduces the surface tension of the fluid which reduces the tendency of alveoli to colapse
-Alveolar Macrophages remove dust
-Fibroblasts make reticular and elastic fibres
Fibroblasts
Make reticular and elastic fibres
Alveolar Macrophages
Remove dust
Cells for fluid secretion (to keep the cells moist) - fluid contains ____________ which reduces the ________________ of the fluid which reduces the tendency of alveoli to colapse
surfactant, surface tension
Blood Supply to the Lungs
-Alveoli are surrounded by capillaries
-Gas exchanges happen through simple diffusion across the alveolar and capillary walls, which together form the respiratory membrane (alveolar epithelium, basement membrane underlying alveolar epithelium, endothelium)
-Oxygen from the air into the blood
-Carbon dioxide from the blood into the air
Alveoli are surrounded by ____________.
Capillaries
Gas exchanges happen through _________________ across the alveolar and capillary walls, which together form the __________________________ (alveolar epithelium, basement membrane underlying alveolar epithelium, endothelium)
simple diffusion, respiratory membrane
Gas Transport
Oxygen and Carbon Dioxide
Oxygen
-Most of the oxygen is carried from the lungs to the body tissues bound to hemoglobin (Hb)
-A little is dissolved in the blood
-Oxygen goes to the body tissues and is used
Carbon Dioxide
-Most is carried in the blood in the form of bicarbonate (HCO2)
-Some is carried attached to Hb (carboxyhemoglobin)
-A little is dissolved in the blood
-It is released at the lungs and exhaled
The Pleural Membrane
-Each lung is enclosed in, and protected by a double layered serous membrane called the pleural membrane
Visceral Pleura
Layer of the pleural membrane that covers the lungs
Parietal Pleura
Layer of the pleural membrane that covers the inside of the thoracic cavity
Pleural Cavity
Space between the visceral and parietal pleura which contains lubricating fluid
Ventilation
Inhalation and Exhalation
Inhalation
-M. contraction expands the lungs and the thoracic cage
-Thoracic volume increases
-Thoracic volume decreases
-Air rushes in to normalize the pressure
Exhalation
-A passive process (when at rest)
-Muscles relax, elastic recoil of the thoracic cage
-Thoracic volume decreases
-Thoracic pressure increases
-Air rushes out to normalize the pressure
Forced Vital Capacity (FVC)
Largest volume of air that can be brought into the lungs
Forced Expiratory Volume (FEV1)
Volume of air that can be exhaled in 1 sec (after maximal inhalation)
Tidal Volume (VT)
Volume of air in one regular breath
Control of the Respiratory System
Central control and peripheral chemoreceptors
Central Control
-Respiratory control centre (in brain stem) controls the rhythm and rate of breathing
-Central chemoreceptors detect rising concentrations of CO2 and H+ and respond by increasing ventilation
Peripheral Chemoreceptors
-Located in the carotid arteries and the arch of the aorta
-They respond to rising CO2 and H+ concentrations and/or dropping O2 concentrations and respond by increasing ventilation
Aging and the Respiratory System
-Airways and tissues become less elastic
-Chest wall becomes more rigid
-This decreases lung capacity
-Alveolar macrophages are less functional/active
-Cilia are less functional
-This increases the risk of certain respiratory infections (e.g., pneumonia, bronchitis)
