Muscle, Bone, And Skin

Question 1

Three types of muscle tissue

Answer 1

1. Skeletal muscle
2. Cardiac muscle
3. Smooth muscle
   Types of muscle differ in structure, function, and nervous system innervation, but have properties in common

Question 2

How does a muscle generate force?

Answer 2

By contracting its cells

Mechanism of muscle contraction differs between three types of muscles

Question 3

Major functions of muscle

Answer 3

1. Body movement
2. Stabilization of body position
3. Movement of substances through the body
4. Generating heat to maintain body temperature

Question 4

Skeletal Muscle

Answer 4

Type of striated muscle that controls voluntary movements
Consciously controlled to produce specific desired movements
Innervated by the somatic system
Moves the body and allows running and lifting weights, thermoregulation, and movement of fluids in the cardiovascular and lymphatic systems
Connects one bone to another via a tendon (Tendon muscle to bone)

Question 5

Tendon

Answer 5

Connective tissues attaching muscle to bone

Fibrous, allowing them to store elastic potential energy

Question 6

Ligament

Answer 6

Connective tissue attaching bone to bone

Question 7

How does a muscle create movement at a joint?

Answer 7

Muscle stretches across a join to create movement
Origin of muscle is usually its attachment on the larger bone closer to the midpoint of the body (remains relatively stationary)
Insertion: Attachment at other end of muscle, on smaller bone farther from midpoint
- moves relative to larger bone as muscle contracts
Exact placement of origin and insertion of muscle determines how it moves a joint, and how much force, or torque a muscle contraction can make

Question 8

How do muscle agonist and antagonists work together to move?

Answer 8

Muscle whose contraction is primarily responsible for movement is called agonist, antagonist muscle stretches in response to agonist’s contraction and opposes movement so that motion is smooth and controlled
E.g. biceps and triceps function antagonistically
Muscle movements can also involve synergistic muscles
Synergistic: assists agonist by stabilizing origin bone or by positioning insertion bone during movement
Agonist, antagonistic, and synergistic muscles perform movement and maintenance of posture

Question 9

What other function does the contraction of skeletal muscle help with?

Answer 9

Peripheral circulatory assistance
Contraction of skeletal muscles help squeeze blood and lymph through respective vessels, aiding circulation
Thermoregulation
Contraction of skeletal muscle produces large amounts of heat
Shivering reflex: rapid contraction, or shaking, of skeletal muscle to warm the body
- Controlled by the hypothalamus upon stimulation by receptors in the skin and spinal cord
When necessary, energy stored as glycogen can be metabolized and used to power muscle contraction that provide heat to body

Question 10

How are most skeletal muscles class three levers?

Answer 10

Force applied by contraction of the muscle (via muscular attachment) is between the fulcrum (joint) and the load (part of body that moves)
Use more force to perform a given amount of work than would be used if there were no lever at all
Greater force than mg is required to lift a mass m
Shorter lever arm reduces bulk of body and increases range and control of movement

Question 11

Sarcomere

Answer 11

Smallest functional unit of contractile apparatus in skeletal muscle
composed of many strands of two kinds of protein filaments
Thick filaments: made of myosin
Several long myosin molecules wrap around each other to form one thick filament
Globular heads, myosin heads protrude along both ends of thick filament
Thin filaments: made of globular protein actin
Attached to actin are proteins troponin and tropomyosin (participate in mechanism of contraction)
Myosin and actin filaments overlap and slide past each other when muscles contract and relax

Question 12

Z line

Answer 12

Separates one sarcomere from the next

This is the location where actin filaments attach

Question 13

I band

Answer 13

Area containing actin only (including the Z line, so contains part of two sarcomeres)
From the end of one myosin filament to the end of another

Question 14

H zone

Answer 14

Area containing only myosin
Excludes the areas with actin
Changes with contraction

Question 15

A band

Answer 15

Area where myosin is present, including where it overlaps with actin
Includes the H zone

Question 16

M line

Answer 16

Midline of the myosin fibers in a sarcomere

Question 17

Myofibril

Answer 17

Sarcomeres are positioned end to end to form a myofibril
Each myofibril is surrounded by specialized endoplasmic reticulum of the muscle cell, the sarcoplasmic reticulum
Lodged between myofibrils are many mitochondria to create supplies of ATP required for muscle contraction
Modified cellular plasma membrane called sarcolemma wraps several myofibrils together to form muscle cell (AKA myocyte, or muscle fiber)

Question 18

Sarcoplasmic reticulum

Answer 18

Specialized endoplasmic reticulum of the muscle cell

Lumen of sarcoplasmic reticulum is filled with Ca2+ ions

Question 19

Fasciculus

Answer 19

Many muscle fibers/ cells are further bound together to form fasciculus
Many fasciculi make up a single muscle

Question 20

What is the heirarchical organization of the muscle?

Answer 20

Sarcomeres, smallest functional unit, line up end to end to form myofibrils, which are wrapped together by the sarcolemma to form a muscle cell
Many muscle cells bound together to form a fasciculus and many fasciculi form a muscle

Question 21

How does the nervous system control the contraction of a skeletal muscle?

Answer 21

Motor neuron in the somatic nervous system attaches to a muscle cell at a motor end plate, forming a neuromuscular junction
Motor end plate is region of highly excitable muscle, while neuromuscular junction is synapse between motor neuron and motor end plate
Action potential of neuron releases Acetylcholine into synaptic cleft, activating ion channels in sarcolemma of muscle cell and creating action potential that propagates along sarcolemma
AP moves deep into muscle cell, via small infoldings of sarcolemma called T-tubules, which facilitate uniform contraction of muscle by allowing rapid spread of APs
AP spread to sarcoplasmic reticulum, causing release of Ca2+ around sarcomere, which allows myosin and actin fibers to slide past each other, starting a contraction

Question 22

Sliding filament model

Answer 22

Myosin and actin work together by sliding alongside each other to create contractile force of skeletal muscle
Process of contraction requires the expenditure of energy in the form of ATP
Each myosin head crawls along the actin in a 5 stage cycle

Question 23

What is the 5 stage cycle of the sliding filament model?

Answer 23

1. In rest, myosin heads in high-energy “cocked” position w/ P & ADP group attached. Tropomyosin covers active sites on actin, heads can’t bind to actin
2. SNS increases Ca2+ levels in sarcomere, troponin changes configuration and pulls back tropomyosin, exposing active site. Myosin heads bind to actin, cross-bridges
3. Myosin heads expels P & ADP, bends into low energy position and drags actin. Called power stroke, causes shortening of sarcomere (contraction)
4. New ATP attaches to myosin head and release from active site. Active site covered by tropomyosin
5. ATP splits into P & ADP, and energy used to recock head into higher energy position. Cycle repeated many times to form contraction w/ Ca2+ actively pumped back into sarcoplasmic reticulum at end of each cycle

Question 24

How many muscle fibers are innervated by a single neuron?

Answer 24

2-2000 fibers
Neuron and muscle fibers that it innervates are called a motor unit
Motor units are independent of each other
Force of contracting muscle depends on the number and size of active motor units, as well as frequency of APs in each neuron of motor unit
Smaller units are activated firstk and larger motor units are recruited as needed
- result is smooth increase in force generated by muscle

Question 25

Motor Units

Answer 25

Muscle fibers that are innervated together Muscles requiring intricate movements, like those in the finger have small motor units Muscles requiring greater force and less finesse have larger motor units

Question 26

Muscle Fatigue

Answer 26

Can result from nervous or metabolic causes After sustained use of same motor unit, nerve supplying the unit can become temporarily unable to supply signals necessary to continue frequent, high intensity contraction of the muscle Metabolic fatigue can result from depletion of energy stores within the muscle or decreased sensitivity to effects of calcium in contracting muscle due to buildup of waste products from metabolism

Question 27

What happens when oxygen demands of metabolism exceed body’s supply of oxygen?

Answer 27

Muscle cells can switch from citric acid cycle and oxidative phosphorylation to anaerobic glycolysis to produce ATP Result is excess of lactic acid, which is later metabolized by body when O2 is avail Oxygen debt: need for increased oxygen after exercise in order to metabolize excess lactic acid

Question 28

What are the types of skeletal muscle fibers?

Answer 28

``` Type I (slow twitch or slow oxidative): slow contractile velocity, low amount of force, slow to fatigue and can be employed for long periods Type II (fast twitch) divided into two sub categories type IIa (fast oxidative( and type IIb (fast glycolytic): type IIa fast contractile velocity, resistant to fatigue, but not as resistant as type I, type IIb have rapid contractile velocity, generate great force, but fatigue quickly Differ in contractile velocity, maximum force production, and resistance to fatigue ```

Question 29

Type I muscle fibers

Answer 29

Appear red, contain large amounts of myoglobin, O2 storing protein similar to hemoglobin. Have large numbers of mitochondria, so efficiently use O2 to generate ATP Relatively slow contractile velocity, produce low amount of force Have advantage that they are slow to fatigue and can be employed for long periods of time due to mitochondria and high myoglobin content O2 and ATP necessary for long periods

Question 30

Type IIa muscle fibers

Answer 30

Red, so have myoglobin stores Have fast contractile velocity, resistant to fatigue, but not as resistant as type I Have long-term anaerobic activity

Question 31

Type IIb muscle fibers

Answer 31

Appear white due to low myoglobin content Contract rapidly and can generate a lot of force, but fatigue quickly Contain large amounts of glycogen Have short-term anaerobic activity

Question 32

How do muscles in the body differ in terms of compositions of different muscle fiber types?

Answer 32

Most muscles in body have mixture of fiber types Ratio of mixture depends on contraction requirements of muscle and genetics of individual Relative amounts of fiber types may influence a person’s natural aptitude for activities Large amounts of type I fibers are found in postural muscles Large amounts of type IIA found in upper legs, large amounts of type IIB fibers found in upper arms

Question 33

Hypertrophy

Answer 33

Increase in muscle cell diameter and change in muscle conformation due to repeated forceful, repetitive contractions Adult human skeletal muscle does not usually undergo mitosis to create new muscle cells Number of changes occur over time to meet need for increased strength; increased diameter of muscle fibers, increased numbers of sarcomeres and mitochondria, and lengthened sarcomeres

Question 34

Cardiac Muscle

Answer 34

Tissue that human heart is composed mainly of, involuntary nervous stimulation Specialized, electrically-excitable tissue, which permits propagation of electrical signals that cause the heart to beat normally Cardiac muscle is striated, which means it is composed of sarcomeres Each cardiac muscle cell contains only one nucleus, while skeletal muscle cells are multi-nucleated Cardiac muscle forms a net that contracts on itself like a squeezing fist

Question 35

Intercalated discs

Answer 35

Separate cardiac muscle cells Areas that contain gap junctions that allow an action potential to spread from one cardiac cell to next via electrical synapses Synchronize contraction of groups of cardiac muscle cells Coordination of contraction controls efficient pumping of blood through chambers of heart

Question 36

Why do cardiac muscle cells have numerous large mitochondria?

Answer 36

Heart must beat continuously for entire length of human life | Provide constant supply of ATP

Question 37

Where is nervous system control over cardiac muscle?

Answer 37

Involuntary, so innervated by autonomic nervous system Cardiac muscle is self-excitatory and modulates own rhythm through SA and AV node However, input from autonomic nervous system can affect contraction frequency and thus heart rate Sympathetic innervation increases heart rate, parasympathetic innervation via vagus nerve decreases heart rate

Question 38

How does cardiac muscle grow?

Answer 38

Hypertrophy, just like skeletal muscle | No actual mitosis

Question 39

Cardiac Muscle action potential

Answer 39

Exhibits a plateau after depolarization, created by slow voltage-gated Ca2+ channels which allow calcium to enter and maintain inside of membrane at positive potential difference Repolarization of cardiac muscle is slower and more frequent than skeletal muscle Plateau lengthens time of contraction, preventing new APs from starting in middle of previous contraction Without calcium, heart would beat far too quickly to serve as functional pump Gives heart enough time to refill with blood and prevents tetanus (sustained contraction) that can occur in skeletal muscle

Question 40

Smooth Muscle

Answer 40

Composes muscular layer of internal organs and blood vessels Contain only one nucleus, and contract involuntarily which means innervation from the autonomic nervous system Contain thick and thin filaments that aren’t organized into sarcomeres, also contain intermediate filaments Groups of spindle-shaped cells grouped in irregular bundles, uni-nucleated

Question 41

Intermediate filaments

Answer 41

Filaments present in smooth muscle which are attached to dense bodies spread throughout the cell Dense bodies: serve similar function to Z-lines of striated muscle When thin and thick filaments contract, cause intermediate filaments to pull dense bodies together (smooth muscle cells shrink length-wise during contraction)

Question 42

What are the two types of smooth muscle?

Answer 42

1. Single-unit or visceral, most common Connected by gap junctions that spread AP from single neuron through large group of cells, allowing cells to contract as single unit - Electrical synapses via gap junctions allow for faster signal transmission than chemical, simultaneous contraction - Small arteries / veins, stomach, intestines, uterus, and urinary bladder 2. Multi-unit - Each fiber directly attached to neuron, can contract independently from other fibers - Large arteries, bronchioles, pili muscles attached to hair follicles, and iris

Question 43

What are some signals that smooth muscle may contract or relax in response to?

Answer 43

Neural signals, hormones, changes in pH, O2, and CO2 levels, temperature, and ion concentration

Question 44

Is the vagus nerve part of the parasympathetic or sympathetic nervous system?

Answer 44

Parasympathetic

Question 45

If the heart is innervated by the vagus nerve, what effect will this have on heart rate?

Answer 45

Heart rate will slow, because vagus nerve is parasympathetic and excitation of parasympathetic nervous system inhibits heart rate

Question 46

Bone

Answer 46

Living connective tissue in the body | Contains four types of cells surrounded by extensive calcium/protein matrix composed of inorganic minerals and proteins

Question 47

Functions of bone

Answer 47

Support soft tissue, protection of internal organs, assistance in body movement, mineral (calcium) storage, blood cell production, and energy storage in form of adipose cells in bone marrow

Question 48

Four types of cells in bone tissue

Answer 48

1. Osteoprogenitor (osteogenic) cells differentiate into osteoblasts 2. Osteoblasts secrete collagen and organic compounds. Incapable of mitosis, releases matrix materials around themselves, become enveloped by matrix and differentiate into osteocytes 3. Osteocytes: incapable of mitosis, exchange nutrients and waste materials with blood. Osteoblast that has become trapped within bone cavity (lacuna) 4. Osteoclasts: resorb bone matrix, releasing minerals black into the blood, thought to develop from white blood cells called monocytes

Question 49

General structure of bones

Answer 49

Typical long bones have a long shaft (diaphysis) Two ends, each composed of metaphysis and epiphysis Sheet of cartilage between epiphysis and metaphysis is called epiphyseal plate, where long bones grow in length when stimulated by growth hormone (GH) during childhood/adolescence

Question 50

Two main types of bone structure

Answer 50

1. Spongy bone: trabecular or cancellous bone, contains red bone marrow, site of red blood cell development 2. Compact bone: cortical bone surrounds a hollow area inside the diaphysis known as medullary cavity, holds yellow bone marrow. Yellow bone marrow contains adipose cells for fat storage

Question 51

Bone Remodeling

Answer 51

Osteoclasts burrow tunnels through old compact bone Followed by osteoblasts which lay down new bone matrix onto tunnel walls, forming concentric rings, called lamillae Leave open spaces in center of lamellae known as Haversian canals

Question 52

Osteon

Answer 52

Entire system of lamellae and Haversian canal is called an osteon or Haverisan system Haversian canals and spaces allow for communication and nutrient exchange - Contain blood and lymph vessels - Connected by cross canals called Volkmann’s canals

Question 53

How do osteocytes that are trapped in lacuna exchange nutrients?

Answer 53

Spaces known as canalicculi

Question 54

How is remodeling subject to endocrine control?

Answer 54

Parathyroid hormone helps regulate Ca2+ levels in bloodstream by influencing bone High levels of parathyroid hormone signal osteoclasts to resorb bone to release Ca2+ Vitamin D helps restore Ca2+ stores in bone by promoting Ca2+ absorption through digestive system Calcitonin released by C cells of thyroid stimulates osteoblasts to store excess Ca2+

Question 55

How does bone help regulate mineral content of blood?

Answer 55

Osteoclasts release calcium into blood, osteoblasts use calcium and take from blood Calcium salts are only slightly soluble, so most calcium in blood is bound by proteins or phosphates (HPO42-) Too much free calcium in blood causes membranes to be hypo-excitable, leading to fatigue and memory loss, too little results in cramps and convulsions Ca2+ levels are maintained to generate large conc. Gradient w/ high Ca2+ out of cells and low Ca2+ in cytosol

Question 56

How is most of the body’s Ca2+ stored?

Answer 56

In bone matrix as the mineral hydroxy-apatite [Ca10(PO4)6(OH)2] Contributes to strength of bones Collagen fibers give bone great tensile strength (stretch) Hydroxyapatite crystals lie alongside collagen fibers, giving bone great compressive strength Some Ca2+ stored in form of slightly soluble calcium salts like CaHPO4- which buffer plasma Ca2+ levels Bone is reservoir to store excess Ca2+ and HPO42-

Question 57

Specialized bone types

Answer 57

1. Long: have shaft that is curved for strength - Composed of compact and spongy bone - Leg, arm, finger, and toe 2. Short: often roughly cuboidal in shape - ankle, wrist 3. Flat: provide organ protection and large areas for muscle attachment - skull, sternum, ribs, and shoulder blades 4. Irregular: irregular shape and variable amounts of compact and spongy bone - e.g. ossicles of ear

Question 58

Cartilage

Answer 58

Flexible, resilient connective tissue Composed primarily of collagen, great tensile strength Has no blood vessels or nerves except in its outside membrane

Question 59

What is the function of cartilage?

Answer 59

Gives shape and structure to various body parts (ears) | Serves important functions of providing cushion, connection, and elasticity to joints of body

Question 60

What are the three types of cartilage?

Answer 60

1. Hyaline: reduces friction, absorbs shock in joints, most common 2. Fibrocartilage 3. Elastic

Question 61

Joints

Answer 61

Locations where bones connect in ways that allow for varying amounts of movement, depending on type

Question 62

Hyaline Cartilage

Answer 62

Semi-rigid connective tissue composed of many chondrocytes Cells synthesize an extracellular matrix of proteoglycans, collagen, and water that keeps them apart from each other in spaces known as lacunae Strong, but compressible due to high water content Reduces friction between bones in kee joint as they move against each other

Question 63

Fibrous Joints

Answer 63

Occur betweent wo bones held closely and tightly together by fibrous connective tissue Permits extremely minimal movement Maintains fixed relationship between two bones E.g. teeth with mandible, skull bones after childhood

Question 64

Cartilaginous joints

Answer 64

Allow little movement Occur between two bones tightly connected by cartilage, such as ribs and sternum, or pubic symphysis in pelvis Slight flexibility of cartilaginous joints allows them to absorb some energy and can help in event of trauma

Question 65

Synovial joints

Answer 65

Wide range of movement possible, bones not bound directly by intervening cartilage Separated by a capsule filled with synovial fluid, which provides lubrication and nourishment to cartilage Synovial fluid contains phagocytotic cells that remove microbes and particles E.g. shoulder and knee

Question 66

Skin

Answer 66

Largest organ in the body with a wide variety of functions that contribute to homeostasis Has specific immune cells and unique patterns of innervation that help protect the body from pathogens Transmits information about environmental surroundings to rest of body

Question 67

Functions of the skin

Answer 67

1. Thermoregulation 2. Protection 3. Environmental sensory input 4. Osmoregulation 5. Immunity 6. Blood reservoir 7. Vitamin D synthesis

Question 68

How does the skin help regulate body temperature (thermoregulation)?

Answer 68

Heat from blood can be dissipated by endothermic evaporation of sweat, but most is dissipated by radiation (only effective if body temp > room temp) Vasodilation: more blood directed to surface capillaries for greater heat loss vasoconstriction: blood shunted away from capillaries of skin to reduce heat loss Thermoregulation through sweating, vasoconstriction, and vasodilation is under influence of hormonal control Hairs can erect via SNS stim of associated muscles, insulating warm air next to skin Skin has warmth and cold receptors

Question 69

How is the skin protection for the body?

Answer 69

Skin is a physical barrier to abrasion, pathogenic organisms, many chemicals, and ultraviolet radiation

Question 70

How does the skin receive environmental sensory input?

Answer 70

Skin gathers information from environment through many types of sensory receptors including thermoreceptors, mechanoreceptors, nociceptors

Question 71

How does the skin participate in osmoregulation?

Answer 71

Skin is relatively impermeable to water, protecting against dehydration Some water and salts are excreted through skin via diffusion Excretion and sweating are ways that skin contributes to osmoregulation, keeping conc. Of solutes in body fluids at appropriate level

Question 72

How does the skin contribute to the immune system?

Answer 72

Skin is one of the first lines of defense by preventing pathogenic organisms from entering the body via a physical barrier (innate immune system) Also has specialized cells of epidermis that are components of immune system

Question 73

How is the skin a blood reservoir?

Answer 73

Vessels in the dermis hold up to 10% of blood of resting adult

Question 74

How does the skin participate in Vitamin D synthesis?

Answer 74

UV radiation activates molecule in skin that is precursor to vitamin D Activated molecule modified by enzymes in liver and kidneys to produce vitamin D

Question 75

What are the two principal parts of the skin?

Answer 75

1. Superficial epidermis 2. Deeper dermis Beneath both layers is subcutaneous tissue called superficial fascia or hypodermis - Important heat insulator for body (fat layer), maintains normal core temps of body on cold days

Question 76

What is the primary purpose of the epidermis?

Answer 76

Protection from the environment | Avascular epithelial tissue (no blood vessels)

Question 77

Four major cell types of epidermis

Answer 77

1. Keratinocytes: 90% of epidermis, contain melanin, produce protein keratin (waterproofing) 2. Melanocytes: transfer melanin to keratinocytes 3. Langerhans cells: interact with helper T cells of immune system 4. Merkel cells: attach to sensory neurons and function in sensation of touch

Question 78

Four layers of epidermis

Answer 78

``` Stratum basale (SB), fourth from top layer, contains Merkel and stem cells Stratum spinosum (SS), third from top layer Stratum granulosum (SG), second from top layer Stratum corneum (SC), top layer Exposure to friction or pressure stimulates a fifth layer, causing thickened skin forming a protective callus ```

Question 79

How does skin move from deepest layers of epidermis to top over time?

Answer 79

Skin cells must be continually replaced with constant exposure to environment Stem cells continually divide to give rise to keratinocytes and other new replacement skin cells Keratinocytes once produced are pushed to top layer of epidermis, accumulating keratin and dying, losing cytoplasm, nucleus, and other organelles At outermost layer of skin, cells slough off body Process of keratinization, from birth of cell to sloughing off- 2-4 weeks Outermost layer of cell has 24-30 layers of flat, dead cells

Question 80

Dermis

Answer 80

Connective tissue derived from mesodermal cells Embedded with blood vessels, nerves, glands, and hair follicles Collagen and elastic fibers in dermis provide skin with strength, extensibility, and elasticity Sensors for touch: nociceptors, mechanoreceptors, and thermoceptors

Question 81

Hair

Answer 81

Column of keratinized cells held tightly together and plays a role in tactile sensation and thermoregulation Hair follicles are embedded in the dermis Arrector pili muscles that surround base of hair follicles allow them to become erect, trapping air close to skin to help maintain body heat As new cells added to base, hair grows

Question 82

Nails

Answer 82

Keratinized cells | Provide physical protection for skin

Question 83

Glands in dermis

Answer 83

Sebaceous (oil) gland: associated with hair follicle, empties oil direclty into follicle and onto skin Sweat glands: (1) Eccrine sweat glands: found over entire surface of skin and produce sweat in response to heat (2) Apocrine sweat glands: congregated in certain regions of dermis, produce an acrid-smelling sweat in response to stress