Chapter 11 - Muscular and Skeletal Systems Flashcards
Three types of muscle
Skeletal - voluntary muscle
Cardiac - only in the wall of the heart. No conscious control.
Smooth - walls of hollow organs, responsible for GI motility, constriction of blood vessels, uterine contraction. No conscious control
Skeletal Muscle
Voluntary movement in response to somatic motor neurons.
Tendons
Attach muscle to bone.
Strong connective tissue formed primarily of collagen.
Directions of skeletal movement
Flexing - reducing the angle of the joint.
Extending - increasing the angle of the joint.
Abducting - moving away from the midline.
Adduction - move toward the body midline.
And others…
Origin
Point closest to the center of the body where skeletal muscle attaches.
Insertion
Point further away from the body center line where muscle attaches.
Curing contraction, the insertion point is brought closer to the origin.
Antagonistic Muscles
Muscles responsible for movements in opposite directions.
Synergistic Muscles
Muscles that move a join in the same direction.
Fascicles
Bundles of skeletal and connective tissue.
Connective tissue facilitates flexibility in the muscle.
Muscle Fibers
Also known as myofibers.
Refers to a single skeletal muscle.
Has a cell membrane called SARCOLEMMA.
Contain Myofibril.
Multinucleate Syncytia
Result of the fusion of individual cells during development.
Innervated by a single nerve ending.
Stretch the entire length of the muscle.
Sarcolemma
Composed of plasma membrane and an additional layer of polysaccharide and collagen.
Aids fusion with tendons.
Myofibril
Like a specialized organelle.
Causes striated appearance of muscle cell. Generates contractile force of skeletal muscle.
Actin and Myosin in skeletal muscle
polymerized and generate contraction.
Actin - forms thin filaments
Myosin - forms thick filaments
Sarcomeres
Many together form a myofibril.
Create the striated appearance due to the overlap of thin and thick filaments.
Each sarcomere is bounded by two Z-lines.
Thin filaments attach to Z-lines and overlap with thick filaments in the middle.
I bands
Sections of a sarcomere that are only thin filament.
A band
The full-length of the thick filament. (Includes overlapping regions with the thin filaments)
H-Zone
The region with only thick filaments. Only visible in resting sarcomeres.
Sliding Filament Model of Muscle Contraction
Filaments slide over eachother during contraction.
Myosin is an enzyme that uses ATP to create movement (ATP hydrolysis). Each Myosin monomer has a head and tail portion and can be referred to as myosin ATPase as it drives the ATP hydrolytic activity.
Myosin Binding Site
Specific site on thin filament where myosin binds actin.
When connected, they are said to form a CROSS BRIDGE.
Four steps of a contractile cycle
- Cross bridge formation. Myosin is ADP and Pi bound.
- Power Stroke. Myosin head moves to a low energy conformation. ADP is released.
- ATP binds. Release of Myosin head.
- ATP hydrolysis. Cocks the myosin head, putting it in a high energy conformation.
This occurs spontaneously if Myosin, Actin, and ATP in a beaker (with Mg2+)
Does contraction in myofibrils occur spontaneously?
No. Only when cytoplasmic [Ca] increases.
Why?
Because the actin filament also contains a troponin-tropomyosin complex.
Toponin-Tropomyosin Complex
Part of the actin filament and prevents contraction without [Ca] present.
Tropomyosin is long and fiborous. Wraps around actin and blocks all myosin binding sites.
Troponin is a globular protein that binds tropomyosin, but can also bind Ca. Binding of Ca creates a conformational change that results in a freeing of the myosin binding sites.
Neuromuscular Junction (NMJ)
the synapse between an axon terminus and a myofiber.
A long invagination of the cell membrane.
The axon terminus fills the entire cleft.
Allows for depolarization of a large region all at once.
Motor end plate
The long most synaptic region of the myofiber membrane of the NMJ.
Post-synaptic membrane ACh receptors in the NMJ
Are ligand-gated Na+ channels.
End plate potential (EPP)
The depolarization of the post-synaptic cell in the NMJ.
Miniature End Plate Potential (MEPP)
Depolarization resulting from the exocytosis of a single ACh vessicle.
Acetylcholinesterase
ACh degradation in the NMJ. Otherwise it will continue to activate.
An action potential in a myofiber
Only occurs when voltage-gated Na+ channels are activated upon reaching the threshold potential.
It must depolarize the entire myofiber before contraction can occur.
Transverse Tubules
Deep invaginations in the myofibers, that allow AP (which really only occur at the surface of a cell), to depolarize the interior.
Sarcoplasmic Reticulum
A specialized Smooth endoplasmic reticulum that enfolds each myofibril.
Specialized to release and sequester Ca rapidly into the sarcoplasm.
Ca is only realized upon depolarization of the myofiber.
Muscle Twitch
Smallest measurable muscle contraction. Result of one motor unit contracting.
How to increase the force of muscle contraction
(1) Motor unit recruitment - activating more than one motor unit
(2) Frequency summation - if depolarization occurs rapidly enough such that Ca is not re-sequestered by the sarcoplasmic reticulum, the contraction can build in force. Note though, the limiting factor here is the refractory period.
Note though, that overstimulation results in tetanus.
Motor unit
A group of myofibers innervated by the branches of a single motor neuron axon.
Length-tension relationship
Muscle contracts more forcefully at an optimum length.
Corresponds to sarcomere length of 2.2 microns. Result of maximum degree of overlap. Longer, means some don’t bind. shorter, causes obstruction between filaments.
Creatine Phosphate
Glycolysis and TCA cycle are not fast enough to provide sufficient ATP during extended contraction.
Creatine phosphate is an intermediate-term energy storage molecule.
Hydrolysis of creatine phosphate catalyzes ADP + Pi –> ATP.
Myoglobin
Storage of oxygen in muscle cells.
Structure similar to hemoglobin.
Helps to keep muscle contraction aerobic for as long as possible.
Lactic acid
Produced when muscle goes into anaerobic state.
Moved to blood stream, dropping pH.
Liver converts to pyruvate.
Muscle Fiber Types
Type I Slow Twitch
Type II Fast Twitch
Type I Slow Twitch Fibers
Red slow twitch or red oxidative.
High Myoglobin content. Much better oxygen supply due to richer capillary network.
Type II Fast Twitch Fibers
Two subcategories:
Type IIa: Fast twitch oxidative fibers. More mitochondria, so more fatigue resistant. Can maintain contraction for around 30 minutes.
TypeIIb: White fast twitch. Less mitochondria. Contract very quickly, but fatigue quickly as well <1 minute.
Similarities between cardiac and skeletal muscle:
1) Thick and thin filaments are present in same sarcomere structure
2) They have T tubules
3) Tropin-Tropomyosin complex is present
4) Length-tension relationship is present. Even more important for cardiac muscle. Increased exertion can optimize, but over exertion can decrease contractile strength with severe consequences.
Differences between cardiac and skeletal muscle
(1) Ca2+ required in cardiac contraction in part comes from the extracellular environment. All Ca2+ in skeletal muscle is provided by the sarcoplasmic reticulum.
(2) Cardiac contraction does not depend on stimulation by motor neurons.
(3) Cardiac muscles are functional syncitium (only connected via gap junctions), whereas skeletal muscles are structural syncitium.
(4) Cardiac muscles are each connected to several neighbours via intercalated disks.
(5) AP in cardiac muscle also depends on Ca2+, skeletal muscle does not. Plateau in the cardia muscle is important because longer contraction facilitates ventricular emptying and longer refractory period helps prevent disorganized firing.
Similarities of Skeletal and Smooth Muscle
(1) Same 4-step cycle, relying on actin and myosin.
(2) Contraction is stimulated by a increase in Ca
(3) They do not branch.
Differences between Skeletal and Smooth Muscle:
(1) Smooth muscle cells are narrower and shorter.
(2) T-tubules are not present, as they are unnecessary in the much smaller smooth cell size.
(3) Smooth muscles are functional syncytia, not structural syncytia like skeletal muscle.
(4) Thick and thin fillaments are not organized into sarcomeres, but are dispersed in the cytoplasm. ie. no striations
(5) No troponin-Tropomyosin complex. Contraction is mediated by calmodulin and myosin light-chain kinase (MLCK). Calmodulin binds Ca2+ and then activates MLCK, which phosphorylates the myosin molecule activating the enzymatic activity.
(6) SR in smooth muscle is poorly developed and relies in part on extracellular calcium.
(7) Smooth muscle AP, varies depending on location of cell. Most smooth muscles can elicit AP (or spike potentials) similar to skeletal muscles, but they have almost no Na+ fast channels so can take much longer.
(8) Some smooth muscle can sustain prolonged contractions (ex. uterus or vascular smooth muscle), and therefore has APs similar to cardiac muscle but with less of a sharp spike.
(9) Have constantly fluctuating resting potentials called “slow waves”. They are not spike potentials and do not cause contraction, but help coordinate action potentials. Nuerotransmitter binds around local stimuli (ex. bolus), increasing potential closer to threshold and then the fluctuating resting potential allows it to cross threshold. Amplitude is increased by ACh and decreased by NE.
(10) Skeletal muscles are innervated by motor neurons from somatic nervous system, not autonomic. But not as isolated as skeletal muscle, ie. APs propogate entirely through smooth muscle. Skeletal muscle APs only affect a single myofiber.
Summary of depolarization in muscle cells
Table 2 pg. 428
Endoskeleton functions
Made of bone.
Functions:
1. Support the body
2. Form the foundation of movement
3. Protect Vital Organs
4. Store Calcium
5. Hematopoiesis - synthesis of formed elements in the blood
Axial endoskeleton
Skull
Vetebral Column
Rib cage
Appendicular
All other bones not included in the axial endoskeleton
Connective Tissue
All connective tissue is derived from a single progenitor cell, the FIBROBLAST.
Examples of connective tissue:
Collagen (polysaccharide)
Chondrocytes (cartilage cells)
Osteocytes (bone cells)
Bone
Elastin (protein)
Adipocytes
Main difference between connective tissue and other tissue types (epithelial, neural, muscle).
Connective tissue is mainly extracellular material with some cells.
Other tissues are mainly cells with some extracellular material.
Extracellular material of connective tissue
Matrix - composed of fibers like collagen, and elastin
Ground Substance - thick viscous material composed largely of proteoglycans
Proteoglycans
Form major component of ground substance in connective tissue extracellular components.
Has protein core with large carbohydrate chains referred to as glycosaminoglycans (GAGs) and are hydrophilic. This means they are always surrounded by water - which gives the tissue firmness.
Types of Connective Tissue
Loose - Packing tissue. Includes areolar tissue (soft material between most cells in the body) and adipose tissue.
Dense - refers to tissue with large amounts of fibre. Tendons, ligaments, cartilage, bone.
Two types of primary bone shapes
Flat - Location of hematopoiesis and protect organs. Ex. Scapula, ribs, bones of the skull.
Long - bones of the limbs
Diaphysis
Main shaft of a long bone
Epiphysis
The flared end
Bone Structure
Compact - hard and dense bone. the Diaphysis of long bones is always a tube of compact bone.
Spongy - spongy and porous. Always surrounded by a layer of dense bone.
Bone Marrow
Non-bony material found in the shaft of long bones or the pores of spongy bones.
Red marrow
Found in spongy bone of flat bones, and is the site of hematopoiesis.
Yellow Marrow
Found in the shaft of long bones and is filled with fats. It is inactive.
Two ingredients of bone
Collagen and Hydroxyapatite (calcium phosphate crystals)
Collagen forms structure through highly repetitive pattern.
Hydroxyapatite form around the framework of collagen providing the strength.
Spicules or Trabeculae
Spikes of spongy bone that surround marrow containing cavities in spongy bone.
Compact bone structure
Basic unit is the OSTEON (or the Haversian system)
In the Osteon there is a central (Haversian) canal that contains blood, lymph vessels, and nerves.
Concentric rings termed LAMELLAE surround the canal.
CANALICULI branch of the central canal and connect to LACUNAE.
Each Lacuna contains an OSTEOCYTE (or mature bone cell).
Osteocytes have long processes which connect them to other osteocytes via canaliculi. Allows for exchange of nutrients through an impermeable membrane.
Perforating Canals run perpendicular to the central canal and connect osteon.
Chondrocytes
Secrete cartilage - a strong yet flexible extracellular material.
Three types of cartilage
Hyaline - strong and somewhat flexible. Larynx and trachea are reinforced with it. Joints are reinforced with it as well (termed articular cartilage), and creates hyper smooth surface.
Elastic - Outer ear and epiglottis. Because provides support but increased flexibility.
Fibrous - very rigid and in places where strong supports are required. Pubic symphysis (anterior connection of pelvis), intervertebral disks of spinal column.
Cartilage
Not innervated and does not contain blood vessels (avascular).
Nutrition and immune protection are obtained from the surrounding liquid.
Ligaments and Tendons
Composed of dense connective tissue.
Ligaments - connect bones to bones
Tendons - connect bones to muscle
Synarthroses
Immovable joints. Essentially where two bones are fused together ex. skull.
Amphiarthroses
Slightly movable joints. Provide movability but signficant support ex. vertebral joints.
Diarthroses
Freely movable joints. Must be supported by ligaments.
Synovial fluid
Movable joints are lubricated with synovial fluid.
Retained by the synovial capsule.
Epiphyseal plate
In childhood it exists between the diaphysis and the epiphysis.
It is a disk of hyaline cartilage that is actively being produced by cartilage. As Chondrocytes divide it forces the diaphysis and epiphysis apart.
Growth hormone stimulates ossification of the cartilage that is slightly faster than the division of chondrocyte division. At about 18 this results in the diaphysis and the epiphysis being fused and stopping growth.
The fusion is easily noted in X-rays and can be used to inform adolescents when they are no longer growing. It is referred to as the EPIPHYSEAL LINE in adults.
Remodeling
The continual degradation and addition of bone material. Does NOT result in extension.
Osteoblasts
Produce collagen and hydroxyapatite. Once completely surrounded, they are termed OSTEOCYTES.
Osteoclasts
Continually destroy bone by dissolving hydroxyapatite. It is a cousin of the macrophage.
Bone that is dissolved must be replaced by osteoblasts.
Osteoclast osteoblast ratio
A higher amount of osteoclasts increase serum calcium levels and therefore this ratio can be an important regulator of blood calcium.
Parathyroid Hormone, Calcitonin, and Calcitriol all regulate the ratio of osteoclasts and osteoblasts.
Parathyroid Hormone
Stimulates Osteoclast activity.
Increases reabsorption of calcium in the kidneys and stimulates conversion of Vitamin D to Calcitrol.
Via calcitrol, increases Ca absorption in the intestine.
Calcitrol
May stimulate osteoclast activity.
Increase reabsorption of phosphorous in the kidney.
Increases intestinal absorption of calcium.
Calcitonin
Inhibits osteoclast activity.
Decreases reabsorption of calcium in the kidney.
No known effect on the intestine.
