Stanbridge - T1 - Physiology - W3 - Bones, Joints, and Muscular System

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Questions and Answers

What is a characteristic of smooth muscle?

Multinucleated and striated

Controlled by conscious thought

Non-striated with no sarcomeres (correct)

Striated and voluntary

Which of the following statements about muscle fibers is true?

Cardiac muscle fibers are non-striated.

Smooth muscle fibers contain sarcomeres.

Skeletal muscle fibers are striated and can be voluntarily controlled. (correct)

Skeletal muscle fibers are always shorter than smooth muscle fibers.

What primarily determines the contractile strength of muscle fibers at rest?

The amount of stored glycogen

The level of muscle fiber acidity

The amount of calcium ions available

The length of the muscle fibers (correct)

Which of the following describes the structure of smooth muscle?

It is non-striated and lacks organized sarcomeres. Signup and view all the answers

Which statement accurately reflects the dynamics of isometric contractions?

There is no net change in muscle length while generating force. Signup and view all the answers

What occurs during muscle fiber depolarization?

More Na+ flows into the muscle cell than K+ flows out. Signup and view all the answers

What initiates the release of Ca2+ from the sarcoplasmic reticulum?

Triggering of action potential in the motor neuron. Signup and view all the answers

What is the role of ATP in the cross-bridge cycle during muscle contraction?

It helps release myosin from actin. Signup and view all the answers

In which type of muscle contraction does the muscle neither shorten nor lengthen?

Isometric contraction. Signup and view all the answers

What happens during the repolarization phase of a muscle action potential?

K+ ions flow out of the cell. Signup and view all the answers

The size principle of recruitment relates to which of the following concepts?

Motor units with the smallest muscle fibers are activated first. Signup and view all the answers

What mechanism prevents continuous contraction of muscle fibers after the stimulus has ended?

Pumping Ca2+ back into the sarcoplasmic reticulum. Signup and view all the answers

What is the result of maximizing stimulus intensity in relation to muscle tension?

All motor units are recruited. Signup and view all the answers

What is the main role of tendons in stabilizing synovial joints?

Muscle tone keeps tendons taut, providing reinforcement. Signup and view all the answers

Which type of synovial joint allows for movement in all three planes?

Multiaxial joint Signup and view all the answers

What defines the movements allowed at a synovial joint?

Shapes of joint surfaces Signup and view all the answers

Which of the following is NOT one of the six structural types of synovial joints?

Spiral joints Signup and view all the answers

What movement occurs in a plane joint?

Gliding movement only Signup and view all the answers

Which factor has the most significant impact on the stabilization of joints?

Tendons crossing the joint Signup and view all the answers

What type of movement is characteristic of uniaxial joints?

Movement limited to one plane Signup and view all the answers

What is a primary function of bursae in synovial joints?

Reduces friction between structures Signup and view all the answers

What is a key characteristic of a condylar joint?

Permits movement in two planes Signup and view all the answers

What role do the shapes of articular surfaces play in synovial joints?

They determine the range of joint movement. Signup and view all the answers

What range of muscle fiber length allows for maximal force generation?

80-120% of optimal resting length Signup and view all the answers

Which muscle fiber type primarily uses anaerobic glycolysis for ATP production?

Fast glycolytic fibers Signup and view all the answers

Which factor influences the speed of contraction in muscle fibers?

Speed of myosin ATPases splitting ATP Signup and view all the answers

What is the primary energy source for muscle fibers under aerobic conditions?

Cellular respiration Signup and view all the answers

What byproduct is primarily produced during anaerobic exercise?

Lactic Acid Signup and view all the answers

Which characteristic is NOT associated with smooth muscle fibers?

Multiple nuclei Signup and view all the answers

How does smooth muscle maintain contraction tension compared to skeletal muscle?

With less than 1% of the energy of skeletal muscle Signup and view all the answers

What is the role of myoglobin in muscle cells?

Stores extra oxygen Signup and view all the answers

What differentiates isometric contraction from other types of muscle contractions?

Maintains constant muscle length while producing tension Signup and view all the answers

What structural feature of smooth muscle aids in the rapid influx of calcium during contraction?

Caveolae Signup and view all the answers

Which type of muscle contraction occurs when a muscle generates force as it lengthens?

Eccentric contraction Signup and view all the answers

What is a notable characteristic of eccentric contractions compared to concentric contractions?

They can generate about 50% more force at the same load. Signup and view all the answers

What does isotonic refer to in the context of muscle contractions?

Muscle tension remains constant while muscle length changes. Signup and view all the answers

What is the main factor that causes skeletal muscles to have a slight contraction even when relaxed?

Spinal reflexes activating motor units Signup and view all the answers

Which of the following statements about muscle tone is accurate?

Muscle tone is a result of activated stretch receptors in muscles. Signup and view all the answers

What is a potential consequence of eccentric contractions?

Delayed onset muscle soreness Signup and view all the answers

In an isotonic contraction, which aspect is typically inconsistent?

Muscle tension Signup and view all the answers

Which type of contraction is characterized by the muscle remaining at a fixed length?

Isometric contraction Signup and view all the answers

What primarily activates the motor units responsible for maintaining muscle tone?

Activated stretch receptors in the muscles Signup and view all the answers

Which type of contraction would most often be associated with lowering a weight under the influence of gravity?

Eccentric contraction Signup and view all the answers

Study Notes

Bones

Primary text: Fox, S. (2019). Human physiology (15th ed.).
Tissue Structure Chapter 1, section 3 Fox
Bone cell function, Chapter 19, section 6

Objectives

List the functions of bone
Describe the structure of a flat bone and a long bone, naming all parts.
Describe the structure of compact and spongy bone
List the locations and purpose of red and yellow bone marrow
Describe how a long bone grows in length and width
Describe bone remodeling
Understand Wolff's Law and provide examples of it
List the various types of bone cells and describe their functions

Functions of Bones

Support (e.g., skull, spinal vertebrae, rib cage)
Protection
Movement
Mineral and growth factor storage
Blood cell formation (in red bone marrow of some bones)
Triglyceride storage (in bone cavities)
Hormone production (osteocalcin): helps regulate bone formation, protects against obesity, glucose intolerance and diabetes mellitus

Bone Structure

Compact: external layer, appears smooth and solid. Also called lamellar bone or cortical bone
Spongy or Trabecular: internal layer; filled with red bone marrow (produces RBCs, WBCs, thrombocytes) or yellow bone marrow (stores fat) in living tissue

Bone Structure (continued)

Organic components (bone cells and osteoid): Made of soft components which allow bone to resist tension (stretch) and twisting
Cells: osteoblasts, osteocytes, osteoclasts, bone lining cells
Osteoid: 1/3 of the matrix, includes ground substance and collagen fibers (both made by osteoblasts)
Inorganic components (mineral salts): 65% of bone mass. Consists of hard components which allow bone to resist compression. Hydroxyapatites (mineral salts, mainly calcium and phosphate). Located in and around the collagen-fiber matrix

Structure of Short, Irregular, and Flat Bones

Thin plates of spongy bone covered by compact bone
Compact bone covered by connective tissue membranes
Periosteum covers outside of compact bone
Endosteum covers inside of compact bone
No shaft or epiphyses
Bone marrow between trabeculae, but no well-defined marrow cavity
Where these bones form movable joints, hyaline cartilage covers surface

Structure of Long Bones

Most long bones have the same structure
Shaft (diaphysis)
Bone ends (epiphysis)
Membranes (periosteum and endosteum)

Long Bone Structure: Epiphysis

Outside: compact bone; periosteum lines the outside
Inside: spongy bone; endosteum lines the inside
Thin layer of hyaline cartilage covers joint surface, to cushion during movement and absorb stress

Long Bone Structure: Diaphysis

Thick compact bone surrounds medullary cavity or marrow cavity
In adults, cavity contains yellow marrow (fat)

Metaphysis or Epiphyseal Line

Where diaphysis and epiphysis meet
In adults, remnant of epiphyseal plate (disc of hyaline cartilage that grows during childhood to lengthen bone)

Red Marrow Cavities

Meaning: Contain red marrow or hematopoietic tissue (makes red blood cells)
Usually in trabecular cavities of spongy bone of long bones
In newborn infants: located in the medullary cavity of the diaphysis and all areas of spongy bone
In most adults: located in the femoral heads and humeral heads and in some flat bones (some skull bones, sternum, ribs, scapulae), clavicles, and irregular bones (coxal bones and vertebrae)

Yellow Marrow Cavities

Meaning: Contains fat
Most of the marrow cavities of long bones in adults has become yellow marrow cavities
It goes from the diaphysis into a lot of the epiphysis of long bones in adults
Can change back into red marrow cavities due to demand for more red blood cells, like in significant anemia

Membranes

Periosteum: Double layered membrane, covers external surface of entire bone except joint surfaces
- Outer (fibrous) layer: dense irregular connective tissue
- Inner (osteogenic) layer: mainly osteogenic stem cells - makes all bony cells except osteoclasts
- Some collagen fibers secure periosteum to bone
- Periosteum also anchors tendons and ligaments with dense tissue
Endosteum: Covers internal bone surfaces, lines trabeculae of spongy bone and canals that pass through compact bone
- Contains the same cell types as in the inner (osteogenic) periosteal layer

Bone Cell Types

Osteogenic cells: stem cell, only cells that divide
Osteoblasts: bone forming cells
Osteocytes: mature osteoblasts
Osteoclasts: bone destroying cells. Reabsorption

Compact (Lamellar) Bone

Osteon or Haversian System: structural unit of compact bone
Elongated cylinder parallel to bone axis
An osteon is a group of hollow matrix tubes, wrapping around each other like the rings in a tree trunk
Lamella (each matrix tube)
Cannaliculi connect lacunae (small spaces between lamella) together
Central canal runs through the core of the osteon AKA Haversian canal
Perforating (Volkmann's canals) connect blood and nerve supply of medullary cavity to the central canal.

Compact (Lamellar) Bone: Osteon

Neighboring lamella have fibers that run in a different direction (for torsional stress)
Central canal: small blood vessels and nerve fibers
Volkmann's canals: at right angles to long bone axis; connect blood and nerve supply from periosteum to central canals and medullary cavity.

Spongy Bone

Trabeculae align along stress lines
Trabeculae are only a few cells thick with irregular lamellae arrangement
Nutrients diffuse through canaliculi from surrounding capillaries in endosteum

Growth in length of bones

Epiphyseal plates (growth plates)
Chondrocytes (cartilage cells) multiply
Outer margin of growth plates "ossify"
Bone grows longer
Growth stops when cartilage is all ossified

Growth in thickness of bones

"Appositional growth" (bone growth in diameter)
Osteoblasts in the periosteum lay down new bone matrix on the outer surface of the bone
Osteoclasts remove bone from under the inner layer (endosteum) of the diaphysis
Normally there is slightly more building up than breaking down which creates a thicker, stronger bone but not too heavy.

Wolff's law

Bone grows or remodels in response to the demands placed on it
Compact bone is thickest where there is the most bending stress, usually midway down the diaphysis
Trabeculae of spongy bone lay down struts in response to compression
Where active muscles pull on bone, there are large bony projections
The dominant arm has thicker bones
Bones atrophy in people that are bedridden
A fetus has bones without features on it (no stresses placed on it yet)

Joints (Articulations)

Site where two or more bones meet
Give skeleton mobility
Hold skeleton together Functional Classification
Synarthroses-immovable joints
Amphiarthroses-slightly movable joints
Diarthroses-freely movable joints Structural Classification
Fibrous joints
Cartilaginous joints
Synovial joints

Functional Classification of Joints: Synarthroses

"syn" = together; "arthro" = joint
Ex: Sutures of the skull

Functional Classification of Joints: Amphiarthroses

“amphi” = both sides
Ex: Pubic symphysis and intervertebral joints

Functional Classification of Joints: Diarthroses

“Dia” = throughout or completely
Exs.: hip, knee, shoulder

Structural Classification of Joints: Fibrous Joints

Connected by fibrous tissue
"Fixed" or "immovable" (do not move)
No joint cavity
Most are synarthrotic functionally
Sutures: Between bones of skull
Syndesmoses: (slightly moveable) Between long bones (radius, ulna)
Gomphosis: Between root of tooth and socket

Fibrous Joints- Sutures

Rigid, interlocking joints
Immovable joints for protection of brain
Contain short connective tissue fibers

Fibrous Joints- Syndesmoses

Bones connected by ligaments (bands of fibrous tissue)
Fiber length varies so movement varies, i.e.:
Little to no movement at distal tibiofibular joint
Large amount of movement at interosseous membrane connecting radius and ulna

Fibrous Joints- Gomphoses

Peg-in-socket joints of teeth in alveolar sockets
Fibrous connection is the periodontal ligament

Structural Classification: Cartilaginous Joints

Connected by cartilage
Slightly moveable
Form growth regions (epiphyseal line)
Synchondroses: Epiphyseal lines on long bones
Symphyses: Fibrocartilage with hyaline cover
Intervertebral discs

Cartilaginous Joints- Synchondroses

Bar/plate of hyaline cartilage unites bones
Bones united by hyaline cartilage
Epiphyseal plate (temporary hyaline cartilage joint)
Joint between first rib and sternum (immovable)

Cartilageinous Joints- Symphyses

Fibrocartilage unites bone
All are amphiarthrotic functionally
Body of vertebra
Fibrocartilaginous intervertebral disc (sandwiched between hyaline cartilage).
Pubic symphysis

Structural Classification of Joints: Synovial Joints

All are diarthrotic functionally
Six distinguishing features
- Articular cartilage: hyaline cartilage
- Cushions, supports, reinforces, and resists compressive stress Primarily found covering the ends of long bones
- Joint (synovial) cavity
  - Small, fluid-filled "potential" space
  - Normally almost nonexistent space, but can expand if fluid accumulates with inflammation
- Articular (joint) capsule: two layers
  - External Fibrous layer: Dense irregular connective tissue.
  - Inner Synovial membrane: Loose connective tissue
  - Makes synovial fluid
- Synovial fluid: Viscous, slippery filtrate of plasma and hyaluronic acid. Lubricates and nourishes articular cartilage. Contains phagocytic cells to remove microbes and debris
- Reinforcing ligaments
  - Capsular: Thickened part of fibrous layer
  - Extracapsular: Outside the capsule
  - Intracapsular: Deep to capsule, covered by synovial membrane
- Nerves and blood vessels: Nerve fibers detect pain, monitor joint position and stretch, capillary beds supply filtrate for synovial fluid

Other Features of Some Synovial Joints

Fatty pads: Cushioning between fibrous layer and synovial membrane or bone
Articular discs (menisci): Fibrocartilage separates articular surfaces to improve "fit" of bone ends, stabilize joint, and reduce wear and tear

Structures Associated with Synovial Joints

Bursae: Sacs lined with synovial membrane, contain synovial fluid, reduce friction where ligaments, muscles, skin, tendons, or bones rub together
Tendon sheaths: Elongated bursa wrapped completely around tendon subjected to friction

Three Stabilizing Factors at Synovial Joints

Shapes of articular surfaces (minor role)
Ligament number and location (limited role)
Tendons that cross joint (most important)
Muscle tone keeps tendons taut
Extremely important in reinforcing shoulder and knee joints and arches of foot

Synovial Joints: Range of Motion

Nonaxial-slipping movements only
Uniaxial-movement in one plane
Biaxial-movement in two planes
Multiaxial-movement in or around all three planes

Movements at Synovial Joints

Shapes of joint surfaces Determine movements allowed Determine classification of synovial joints Six structural types of synovial joints:
- Plane Joints
- Hinge Joints
- Pivot Joints
- Condylar Joints
- Saddle Joints
- Ball-and-Socket Joints

Muscle Tissue

Types of muscle tissue:
- Skeletal muscle: striated, voluntary
- Cardiac muscle: striated, involuntary
- Smooth muscle: non striated, involuntary

The Muscular System

Voluntary Movement – walking, standing, sitting, being upright, balance, facial expression
Involuntary Muscle Action – Cardiovascular control, respiration, digestion, elimination, reflexes
Protection – through reflex, cover and surround viscera, support internal organs
Miscellaneous – produce heat, maintain temperature, provide shape to body

Skeletal Muscle

Skeletal muscle: striated/voluntary
- Made of bundles of muscle fibers
- Provide the force to move bones

Skeletal Muscle and Connective Tissue Sheaths

Bone, tendon, epimysium, fascicle, perimysium, blood vessel, endomysium, muscle fiber

Structure of a Muscle

Myofilaments: (muscle version of microfilaments); myosin (thick) and actin (thin); contained in sarcomeres
Myofibrils: hundreds to thousands in muscle cells; parallel along muscle fiber length; contain sarcomeres; 80% of cellular volume
Muscle Fiber: muscle cell; also called myocyte
Fascicle: a bundle of muscle fibers
Muscle Body: a bundle of fascicles

Skeletal Muscle Cells

Myocytes = muscle fibers = muscle cell
"myo" = muscle; "cyte" = cell
Multinucleated
Diameter: 10–100µm (10x size of average body cell)
Length: some 30cm in length

Skeletal Muscle Fibers

Sarcolemma: plasma membrane of a muscle cell
Sarcoplasm: cytoplasm of a muscle cell
Sarcoplasmic reticulum: smooth endoplasmic reticulum in muscle fibers
There are large amounts of stored glycogen (glycosomes) and myoglobin: a red pigment that stores oxygen

Muscle Attachments

Muscle Attachments can be direct or indirect:
Direct is epimysium of a muscle fiber directly fuses to the periosteum of a bone or perichondrium of cartilage
Indirect is connective tissue wrappings extend beyond the muscle tissue itself into a tendon or aponeurosis

Tendons and Aponeurosis

Tendons: connects muscle to bone, cordlike extensions of connective tissue, inserts into bone that does most of the movement; example: Achilles tendon
Aponeurosis: a broad, flat sheet of tendon that attaches skeletal muscle to other muscles or muscles to bones

Skeletal Muscle Contractions

Contractility: ability to shorten, change shape, and thicken (muscle cells have this)
Excitability: ability to respond to external stimuli by changing their resting membrane potential (neurons and muscle cells have this)

Motor Impulses to Muscles

Nerves that send signals to muscle fibers are called Motor Neurons
Motor neuron connects (innervates) to a group of muscle fibers
Motor nerve and the muscle fibers it innervates = Motor Unit
Neuromuscular junction: where a motor neuron contacts the skeletal muscle

Neuromuscular Junction

Motor neuron releases a chemical called a neurotransmitter
In skeletal muscle the kind of neurotransmitter used is called acetylcholine [ACh]
When ACh lands on the receptors, a muscle contraction is triggered.
This begins an electrical impulse called an action potential that calls the muscle into action

Action Potential Generated at Neuromuscular Junction

An end plate potential is generated at the neuromuscular junction (see Figure 9.8).

Basic Understanding of energy

The ability to propagate electric signals allows nerve and muscle to be excitable and communicate with one another
All living cells maintain a separation of charge across the cell membrane that a net negative charge exists in the intracellular environment
This difference allows for potential electrical energy
Balanced between Na+ and K+
The potential across the cell is called the Resting Membrane Potential (RMP)

Physiologic Responses: Electrophysiologic Effects

Depolarization is the process which initiates inflow of Na+ ions into the cell and creates action potential in the neuron cell
Repolarization is the process which returns the neuron cell into its resting potential after depolarization by stopping the inflow of Na+ ions into the cell and sending more K+ ions out of the neuron cell

Excitation: Depolarization

Voltage dependent Na+ Channel
Voltage dependent K+ Channel
Sodium Ion (Na+)
Potassium Ion (K+)

Steps to Skeletal Muscle Excitation

Action potential arrives at the axon terminal of the motor neuron
Ca2+ channels open
Ca2+ enters the axon terminal
Ca2+ triggers ACh to be released from the neuron in the synaptic cleft
ACh diffuses to receptors on the sarcolemma of the muscle cell
Opens channels on the sarcolemma ,allows sodium ions (Na+) into the muscle fiber and potassium ions (K+) out.

Steps to Skeletal Muscle Excitation (continued)

More Na+ flows into the muscle cell, than K+ flows out of the muscle cell
This changes the charge inside of the cell at that area, changing the resting membrane potential
This depolarizes the area (making that area more positive)
At a certain charge inside the cell an action potential is triggered
the action potential spreads along the muscle cell membrane, resulting in the opening of other Na+ channels along the membrane
An action potential is propagated/spread in all directions along the membrane

Action Potential: Depolarization

Repolarization

Occurs when there is a restoration of the original charge in the muscle cell and across the sarcolemma
This is caused by Na+ channels closing and K+ channels opening
K+ flows out of the cell, following its concentration gradient, which makes the inside of the cell more negative again

Muscle Contraction in Sarcomere

Ca2+ is stored in the sarcoplasmic reticulum (SR)
Terminal cisterns are tubules of SR that surround each myofibril along with longitudinal tubules of SR; they are on each side of the T-tubule (sarcolemma protruding into cell)
When an action potential is triggered, electricity flowing through the cell triggers the SR to release Ca2+
Ca2+ allows the muscle to contract

Sarcoplasmic Reticulum and T Tubules to Myofibrils of Skeletal Muscle

Muscle Excitation

Muscle Contraction

Contractile subunits inside a myocyte is called the sarcomere
Sarcomere consists of myosin (thick) filaments with actin (thin) filaments (protein filaments)