Musculoskeletal System Flashcards
Skeletal muscles cannot move on their own so they are attached to bones by
Tendons
Tendons
Strong connective tissue made of collagen
Connect muscle to bone
By contracting, skeletal muscle draws
The points of attachment on the two bones closer together
Skeletal muscle is not only composed of muscle tissue, but also contains contractile tissue held together in bundles called
Fascicles
Muscle fibers (Myofibers)
Within each fascicles of connective tissue in the muscles
Each myofiber is a
Single skeletal muscle cell
Skeletal muscle cells are multinucleate syncytia formed by
The fusion of individual cells during development
Skeletal muscle cells (myofibers) are innervated by a
Single nerve ending
Skeletal muscle cells (myofibers) stretch the
Entire length of a muscle
The myofiber has a cell membrane called the
Sarcolemma
Made of plasma membrane and an additional layer of polysaccharide and collagen to help muscles fuse with tendons
Within each myofiber are several
Myofibrils
Myofibril is responsible for
Striated appliance of skeletal muscle and generates the contractile force of skeletal muscle
Proteins in the myofibril that generate contraction are polymerized ___ and ____
Actin and Myosin
Actin polymers form ___ while myosin forms ____
Actin: Thin filaments
Myosin: Thick filaments
Striated appearance of the skeletal muscle is due to
Overlapping arrangement of bands of thick and thin filament in sarcomeres
Myofibril has many sarcomeres aligned end-to-end bout by two
Z-lines
Z line
Actin attach to each Z line and overlap with Myosin in the middle of the sarcomere
I bands
Regions of sarcomere with only Actin
A band
Full length of the myosin filament
Includes the overlap regions of myosin and actin and the region with only myosin
H zone
Myosin only (only seen in resting sarcomeres)
Contraction occurs when
Myosin and actin slide over one another, shortening the length of the muscle cell
Filament sliding is powered by
ATP hydrolysis
Myosin is an
Enzyme that uses the energy of ATP to create movement (Myosin ATPase)
Each myosin monomer contains a
Head: attaches to the actin at the myosin binding site
Tail
Contraction occurs when head and tail angle between decreases
Cross bridge
When the myosin is blinded to the actin at the myosin binding site
Steps of the filament sliding during contraction
- Myosin binds to actin forming _______ (Myosin has___ and ___ bound)
- _______ occurs and myosin head moves to low-energy conformation and pulls actin towards _____ of sarcomere (_______)
- ________ needed to release actin from myosin head
- ATP hydrolysis occurs immediately and myosin head is _____ (high energy conformation)
- Myosin binds to actin forming the cross bridge (Myosin has ADP and Pi bound)
- Power stroke occurs and myosin head moves to low-energy conformation and pulls actin towards center of sarcomere (ADP is released)
- Binding new ATP needed to release actin from myosin head
- ATP hydrolysis occurs immediately and myosin head is cocked (high energy conformation)
Myosin actin contraction cycle is spontaneous, but in the body, contraction only occurs when the cytoplasmic Ca2+ increases
Why?
Troponin-tropomyosin complex prevents contraction when Ca2+ is not present
Tropomyosin:
Long fibrous protein winding around the actin polymer, blocking myosin binding sites
Troponin
Globular protein bound to tropomyosin that can bind Ca2+
When Ca2+ is bound, troponin undergoes conformational change that moves tropomyosin out of the way so that myosin heads can attach to actin and filament sliding can occur
What protein is responsible for ATP hydrolysis during muscle contraction
Myosin is responsible for al ATPase activity
Neuromuscular junction
Synapse between myofiber and axon terminus (ACh)
Infolding of the cell membrane
Axon terminus elongated to fill the synaptic cleft
Purpose is to depolarize a large region of the postsynaptic membrane all at once
Motor end plate
Postsynaptic myofiber cell membrane
End plate potential (EPP) vs Miniature EPP (MEPP)
EPP: ACh reaches receptor and invokes a postsynaptic sodium influx which depolarizes the postsynaptic membrane
MEPP: Smallest measurable EPP caused by excitation of a single ACh vesicle
Acetylcholinesterase
Destroy ACh to stop the NMJ firing
Hydrolysis of ACh to choline + acetyl
The AP bus depolarize ___ if the contraction is going to occur
The entire myofiber
Transverse tubules (T-tubules)
Indentations in the cell membrane to allow the AP to reach past the cell membrane and get to the interior of the cell
Sarcoplasmic reticulum
Specialized smooth endoplasmic reticulum which enfolds each myofibril in the cell specialized to sequester and release Ca2+
Active transports in the SR rapidly remove calcium from the sarcoplasm
Upon action potential firing, the sarcoplasmic reticulum releases:
When the cell depolarizes, calcium is
Ca2+ via its VG calcium channels
Actively sequestered by the SR and contraction is ended
Smallest measurable contraction
Twitch
NS can increase the force of contraction via:
Motor unit recruitment: Larger contraction by activating more motor neurons and thus more myofibers
Frequency summation: Rapid firing AP does not allow Ca2+ to leave the cleft and therefore builds on the previous contraction, growing in size
Creatine phosphate role in the cell
Intermediate-term energy storage molecule: Needed because the cells typical measures cannot keep up to provide enough ATP for continuous contraction
Myoglobin
Globular protien similar to one of the four subunits in hemoglobin
Provides oxygen reserve taking O2 from hemoglobin and then releasing as needed during prolonged contraction
During prolonged contraction, the supply of oxygen nevertheless runs low and the cell
Releases lactic acid which moves into the bloodstream and drops pH
When the cell produces lactic acid, the liver
picks up the lactate and converts it to pyruvate which can be used in other pathways
Cramps result from
Exhaustion of energy supplies (temp lack of ATP in cells)
Rigor mortis
Rigidity of skeletal muscles which occurs soon after death
Results from complete ATP exhaustion
Without ATP, myosin heads cannot release actin and the muscle can neither contract nor relax
Skeletal Muscle Type I Slow Twitch Fibers
Red slow twitch/red oxidative fibers
High myoglobin content
Better blood supply due to extensive capillary network
Hence: maintain contraction for extended periods of time without fatigue
Skeletal Muscle Type IIA Fast Twitch Fibers
Fast twitch oxidative, somewhat resistant to fatigue
Intermediate contraction, medium force generation, some mitochondria, medium capillaries, medium fatigue resistance (30 minutes of use)
Skeletal Muscle Type IIB Fast Twitch Fibers
White fast twitch
Lack mitochondria and capillaries
Contract quickly with a lot of force
Fatigue just as quickly, Max out after about 1 minute
Cardiac and skeletal muscle are similar in three ways:
- Actin and myosin organized into sarcomeres (striation)
- T-tubules (transmit AP into the interior of large, thick cell)
- Troponin-tropomyosin (regulates contraction)
Structure of the cardiac muscle compared to skeletal
Cardiac muscle has one nucleus, not broken down like skeletal muscle into smaller components
Muscles of the heart are interconnected by gap junctions known as intercalated disks (allow AP to propagate without sharing cytoplasmic contents)
Heart muscle is called a ____ because it acts like a syncytium but isn’t really one
Functional syncytium
Ca2+ source for skeletal muscle vs cardiac muscle
C: some comes from extracellular environment
S: all comes from SR
Stimulation and contraction differences for skeletal muscle vs cardiac muscle
Cardiac muscle contraction doesn’t depend on motor neurons, but the vagus nerve which is inhibitory to the SA node using ACh to slow the heart rate and prevent continuous contraction
vs. NMJ releasing excitatory ACh
AP depend on which ions? Skeletal vs cardiac muscle
S: depend on Na+ (figure similar to Neuro AP)
C: depend on Na+ and Ca2+ through slow leak channels (caused plateau)
Plateau in the AP of cardiac muscle is important for two reasons:
Longer duration of contraction, better ventricular emptying
Longer refractory period helps prevent disorganized transmission of impulses thought the heart making summation impossible
Smooth muscle length / width vs skeletal muscle
Smooth is much narrower and shorter
T-tubules and smooth muscle
No T-tubules in smooth muscle
Depolarization on surface can depolarize whole cell because the smooth muscle is so small
Smooth muscle cell and structure compared to skeletal
Smooth has only one nucleus and is connected to neighbors by gap junctions like cardiac muscle allowing impulse to speed
Smooth and cardiac are functional syncytia
Smooth muscle vs skeletal:
Sarcomeres
Smooth not organized into sarcomeres
Instead, actin and myosin are dispersed in the cytoplasm giving a smooth appearance
Smooth muscle vs skeletal:
Troponin-tropomyosin
T-T not present in smooth
Contraction is instead regulated by calmodulin and myosin light chain kinase (MLCK)
Contraction is regulated by calmodulin and myosin light chain kinase (MLCK) in smooth muscle which functions:
Calmodium binds Ca2+ and then activates MLCK which phosphorylates a portion of the myosin molecules thus activating its activity
Smooth muscle vs skeletal:
Sarcoplasmic Reticulum
Smooth does not have a well developed SR and instead relies on stored Ca2+ and extracellular stores of Ca2+ for contraction
Smooth muscle vs skeletal:
Action potentials
Smooth AP varies depending on location
Spike potentials are determined by slow channels only, since no Na+ fast channels are present so it takes 10-20x as long to initiate
Some smooth muscle that must maintain prolonged contractions has action potentials similar to cardiac muscle with a less sharp spike
Smooth muscles have a ____ resting potential because
Constantly fluctuating “slow waves”
Ions pass through gap junctions
Slow waves
Changes in RMP of smooth muscle, do not initiate contraction
Help coordinate AP
NT binds to help push RMP closer to threshold in response to stimulus
Slow waves pass through primed cells and reach threshold, undergo spike potential
Amplitude of slow waves is inc by: ___ and dec by: ____
Inc: ACh
Dec: Norepi
Smooth muscle vs skeletal:
Motor neurons
Smooth: autonomic motor neurons instead of somatic meaning no control over them
Individual motor neuron does activate cell but the AP spreads from cell to cell
Skeletal system’s five roles
Support the body Framework for movement Protect vital organs Store calcium Hematopoiesis = synthesize the formed elements of blood (in marrow)
Axial and appendicular components of the endoskeletal system
Axial: skull, vertebral column and rib cage
Appendicular: all other parts
Fibroblast
Makes up all connective tissue (cells and materials they secrete)
Fibroblast excretes fibrous material such as (20
Collagen (strong fibrous protein)
Elastin (ability to stretch tissue and regain shape)
Fibroblast derived cells include (3)
Adipocytes (fat cells)
Chrondocytes (cartilage cells)
Osteocytes (bone cells)
Bone is different in that it is mostly extracellular components with a few cells scattered
The extracellular material is called:
Matrix
Matrix consists of collagen and elastin as well as
Ground substance
Grouns substance
In matrix
Thick, visceral material with protein core and carbohydrate chains (hydrophilic // always surrounded by water giving thickness and firmness)
Loose connective tissue
Areolar tissue (soft material between most cells in body) and adipose tissue (fat)
Dense connective tissue
Large amounts of fibers (specifically collagen) such as tendons, ligaments, cartilage and bone
Two primary bone shapes: flat and long
Flat: Location of hematopoeises (synthesis of blood elements in marrow) and protect organs
-scapula, ribs, skull, etc.
Long: support and movement
-limbs
Diaphysis and ephiphysis
Dia: long shaft
Epi: flared end
Compact or spongy bone
Compact: hard and dense
Spongy: porous, surrounded by compact always
Diaphysis portion of bone is composed only of
Compact bone
Bone marrow
Non-Bony material found in shafts of long bones and pores of spongy bones
Red marrow
Found in spongy bone within flat bones, site of hemapoeitisis
Red marrow activity
increases in response to erythropoietin, kidney hormone
Yellow marrow
Found in shafts of long bone
Filled with fat
Inactive
Bone two principle ingredients
Collagen and hydroxyapatite
During bone synthesis,
collagen is laid down in a highly ordered structure and then hydroxyapatite crystals form around the collagen framework, giving bone its strength and flexibility
Spikes of bone surrounding marrow containing cavities in spongy bone are called
Spicules or trabeculae
Osteon
basic unit of compact bone
Center of the osteon there is a hole called the ___ which contains
Central Canal
Blood, lymph vessels and nerves
Surrounding the osteon’s central canal are the
Concentric rings of bone “lamellae”
____ are tiny channels branching out from the central canal to spaces called lacunae
Canaliculi
In each lacunae is an osteocyte which functions as a
Mature bone cell extending down the canaliculi to contact other osteocytes through gap junctions to exchange nutrients and waste through impermeable membrane
Perforating canals
Channels that run perpendicular to central canals to connect osteons
Cartilage is strong but flexible extracellular tissues secreted by cells called
Chondrocytes
Three types of cartilage:
Hyaline, elastic and fibrous
Hyaline cartilage
Strong and somewhat flexible
Lines joints (articular cartilage) and forms larynx and trachea
Articular cartilage
Lines joints
Type of hyaline cartilage
Elastic cartilage
Found in structures requiring support and more flexibility than hyaline cartilage can provide (outer ear, epiglottis)
Fibrous cartilage
Rigid and found in places where very strong support is needed
(anterior connection of pelvis and spine)
Cartilage is avascular meaning
Does not contain blood vessels and is not innervated
How does cartilage receive nutrients and immune protection?
Surrounding fluid
Ligaments
Connect bones to bones
Synarthoses
Immovable joints
Two bones are fused together (skull)
Amphiarthroses
Slightly movable and much supportive (amphi means both moving and supporting)
Vertebrae
Diarthroses
Freely moving joints
ball and socket, hinge
All movable joints are supported by ___ and lubricated by ____
Ligaments
Synovial fluid
Synovial capsule
Holds synovial fluid
Two surfaces of the bone that are in contact with each other are perfectly smooth because they are
Lined with articular cartilage which lacks blood vessels
Easily damaged by overuse and infection
Inflammation of joints
Arthritis leads to the destruction of articular cartilage causing pain and stiffness
Endochondral ossification
Bone growth (hyaline cartilage Is produced and then replaced by bone)
Epiphyseal plate function
formed in childhood between diaphysis and epiphysis
Actively being produced and forcing the two sections of bone apart
Then the cartilage is replaced by bone
Process of endochondral ossification is stimulated by
Growth hormone and rate of ossification is faster than rate of cell division (cartilage growth) so around age 18 the two halves of bone fuse together and the lengthening can no longer occur
Epiphyseal line
Epiphyseal plate in adults once the bones have fused
Remodling
In adults bone is constantly degraded and remade
Osteoblasts
Cells that make bone
How does the osteoblast shut off
Osteoblast keeps making bone until it is surrounded by bone, space left is called a lacuna and the osteoblast is not called an osteocyte
OsteoClasts
Continually destroy bone by dissolving the crystals to be replaced with osteoblasts
Ratio of osteoclast:osteoblast is important for
Releasing the right amount of calcium and phosphate into the blood stream
Maintains proper blood levels
Parathyroid Hormone (PTH), Calcitonin and Calcitriol role in the cell
Regulate the osteoblast and osteoclast activity and thus blood calcium levels
PTH and Calcitriol: ___ while calcitonin _____
PTH and calcitriol increase blood calcium and calcitonin reduces it
PTH effect on bones
Stimulates osteoclast activity
PTH effect on kidneys
Increases reabsorption of calcium, stimulates conversion of vitamin D into cacitriol
PTH effect on intestines
Indirectly increases intestinal calcium absorption
Calcitriol effect on bones
Stimulates osteoclast activity, minor effect
Calcitriol effect on kidneys
INC reabsorption of phosphorus
Calcitriol effect on intestines
Indirectly increases intestinal absorption of calcium
Calcitronin effect on bones
Inhibits osteoclast activity
Calcitronin effect on kidneys
DEC reabsorption of calcium
