Bio 155 - Skeletal Muscle: Anatomy & Excitation + Contraction + Force, Work, and Energy

What are skeletal muscles?

• organs organized from smaller units

Describe the arrangement of thin and thick filaments in a sarcomere in terms of A&I bands

Describe Z&M lines in terms of the key biochemical features of thin and thick filaments

What is the contractile organelle within a muscle fibre? How are they organized?

• the muscle fibre in a contractile organelle is called the myofibril, which contains myofilaments

• these myofilaments are organized into repeating units called sarcomeres

Define the properties of muscle tissues, including key features shared between its subtypes

• muscle tissues: contract and produce mechanical forces (ex. walking)

• 3 subtypes

  • skeletal muscle tissue: moves the skeleton (this is our focus for lecture 6-8)

  • cardiac muscle tissue: pumps blood through the heart

  • smooth muscle tissue: blood vessels, digestive tract, and many more

Describe the organization of a skeletal muscle and the tissue types that it contains, including the relationship of muscle fibres to fascicles, and muscles to fascial compartments.

• each skeletal muscle is connected to the skeletal system via tendons (or aponeuroses)

• skeletal muscles are organized within layers of FASCIAE = connective tissue around ur bone that provides support

  • skeletal muscle —> muscle fascicle —> muscle fiber

5 main anatomical components of the musculoskeletal system (muscle, bone, tendons, ligaments and cartilage) in terms of tissue type and give examples of their roles

the skeletal and muscular systems are connected by a variety of connective tissue structures

1. cartilage

   • supportive connective tissue

   • found on joint surfaces, ears, nose, and vertebral disc (in between vertabrae)

2. ligaments

   • dense regular connective tissue

   • anchor bones to other bones

3. tendons

   • dense regular connective tissue

   • anchor bones to muscles

compare and contrast the gross anatomy and histology of bone and cartilage, including the composition of the matrix and diversity of distinct cell types

both bone and cartilage are connective tissues (meaning they both have dense, solid matrix)

• bones

  • their matrix (the ground substance) contains collagen, calcified and hydroxyapatite (calcium and phosphate perticpiated); more rigid

  • compact bone around the outside and spongy bone inside and on the ends of the bone

    1. compact

       • always have layers and layers around central holes

       • lots of solid matrix with little cells in-between layers

       • dense tissue with hallow tubes

       • so its COMPACT so its very good at resisting compression

    2. spongy

       • found on the inside of bone

       • all bones have a layer of compact bone around the outside and the inside will have hallow spaces filled with meshed work (aka. spongy bone)

       • doesn’t have as much tissues and matrix, so more spaces making it light and therefore can distribute forces

       • the hallow spaces in the sponge bone contains bone marrow

         • bone marrow

           • is a connective tissue but not a supportive connective tissue, instead it is where blood is created

  • bone tissues are highly vascularized (blood vessels running anywhere) and innervated (nerves through the bone tissue) and in the hallow spaces have bone marrow

    • ex. long bone (femur)

  • endosteum

    • the space between the spongy bone

    • endo = inside and osteum =bone

    • layer of epithelia tissue lining the surface of spongy bone between the bone and bone marrow

  • periosteum

    • on the outside of bone

    • perio = around perimeter, another epithelia layer

  • bone tissue contains many cell types with distinct roles

    1. osteogenics cells

       • cells that create new bone tissues and bone cells (the stem cells for bones)

       • found in the endosteum

       • osteogenic cells divides then the osteoblasts lays the new bone tissues

    2. osteoblasts

       • blast = builds

       • laying down the new bone tissues

       • MOST are found on the periosteum

       • once the osteoblasts become embedded in the bone matrix they become mature cells called osteocytes

    3. osteocytes

       • mature bone cells

       • maintain bone matrix and do a little of modification but can’t lay down lots of new matrix at one time like osteoblasts

       • found in the bone matrix, lacunae

    4. osteoclasts (maintains calcium levels)

       • clasts = clashes / removes bone matrix by dissolving it —> can make it rapidly

       • breaks down bone tissue by secreting acids and enzymes that dissolve the mineralized bone matrix, which contains calcium and phosphate

       • and as the bone matrix is broken down, calcium is released into the blood stream which helps increase blood calcium levels when they are low

       • found in the endosteum

• cartilage (cartilage are alrd matured, bc theyre not laying down new cartilage)

  • their matrix contains proteoglycans (glycoproteins which include chondroitin sulfates): more flexible, not as rigid as bone

  • cartilage are avascular (meaning no blood tissue)

  • all forms of cartilages contains cells called chondrocytes (cells responsible for cartilage formation)

    • chondrocytes resides in lacunae (the little holes in the matrix)

  • three subtypes of cartilage that differs in extracellular fibre composition

    1. hyaline cartilage

       • lots of proteoglycans

       • will look smooth and glassy bc it absorbs water

       • found on joint surfaces

    2. elastic cartilage

       • proteoglycans + elastin fibres

       • flexible and springs back and will look dark in histology

       • found in your ears and nose

    3. fibrocartilage

       • proteoglycans + collagen fibres

       • not a connective tissue

       • found in vertebrae discs

       • bit more tougher, handles squishing better, not very smooth/slidy BUT ITS TUFF

compare and contrast the different mechanisms of growth that occur in bones and in cartilaginous tissues, including how these processes alter following puberty

• cartilage

  • can grow through two methods

    1. cell division / growth proliferation (interstitial growth):

       • chondrocytes undergoes division

       • additional matrix secreted pushes cell apart

       • growth by division stops after adulthood

       • increase the size of cartilage and contributes to lengthening of long bones

    2. differentiation (new layer on top of the top surface, cartilage becomes thicker)

       • happens in childhood and continues on into adulthood

       • layers of cartilage is covered by a layer of connective tissue

       • cells differentiate into chondroblasts, then chondroblasts secrete new matrix and the chonroblasts will mature into chondrocytes

• bone

  • can also grow in 2 diff ways

    1. endochondral growth (means within cartilage)

       • taking a tissue that was cartilage and turning it into a bone

       • happens during embryological growth

       • as fetus grows, the initial skeletal is lay down with hyaline skeleton

       • as fetus grows and as blood vessels reach the bone, osteoblast colonizes the cartilage and starts growing from the inside and turning into bone tissue

       • you will grow LONGER

       • however, once the bone becomes ossified, your bone will stop growing longer

    2. appositional growth (adding layers to the outside surface of the bone)

       • grows wider

       • osteoclasts eats away the matrix in the endosteum (the inside) while the osteoblasts add new layers of bone to the surface

         • this happens so the bone doesn’t get too thick and heavy

    3. exceptions from bone growth

       • dermal (skull) and sesamoid bones ossify from non-cartilaginous connective tissue

       • bone tissues grow directly out from your connective tissue proper instead of cartilage

       • dermal bones ossify from within dermal tissue

       • sesamoid bones form within tendons

Describe the phases involved in bone repair and compare and contrast the capacity of repair in bone and cartilage

bone

• bone tissues repair itself well through a series of stages

• bone healing involves the growth of cartilage (only time when cartilage grows in adulthood)

• bone repairs starts with forming a new callulus (a cartilage)

• will continues to remodel over months to years

  • cartilage —> spongy bone —> compact

  • will takes a long time to fully remove cartilage

cartilage

• cartilage DOES NOT repair itself well

• intersitial growth no longer occurs after puberty

• however, appositional growth can occur into adulthood for fibrous and elastic cartilage

  • activates a dense connective tissue repair process instead of elastic cartilage

  • ex. piericing ur ear

• articular cartilage cannot undergo self-repair at all

  • therefore, if u damage ur joint surfaces ITS OVER

explain the pathological processes occurring in osteoarthritis and analyze the potential costs and benefits of treating osteoarthritis with total joint replacement

• bones is an organ filled with bone tissues

• bones are connected to each other using joints (articulations) with diff tissues which produces diff physical properties - 7 diff joints

  • diarthistis (free movement)

  • amphiarthrosis (little movement)

  • synarthrosis (no movement)

• synovial joints - the most complex and involve a lot of diff tissues including hyaline cartilage

  • surfaces of the joins will be covered by a layer of hyaline cartilage called the articular cartilage

    • articular cartilage is a subtype of hyaline cartilage

  • has fluids that lubricate the surfaces

• osteoarthritis

  • a degenerative disorder caused by damage to the articular cartilage

  • which will increase friction at the synovial joint —> inflammation —> more pressure on remaining cartilage —> more damage

explain the role of bone as mineral reservoir, and predict how the activity of the bone cells will respond to changes in body calcium levels

• bones act as a mineral reservoir for minerals, specially for calcium

• the balance between the amount of osteoblast and osteoclast activity help maintain calcium homeostasis

• negative feedback loop

  • If your calcium level drops, then your osteoclast will increase and your calcium levels will increase

    • breaking down your matrix will release calcium to your bone

SO1. Describe how tension generation by a muscle can be affected by physiological differences between the types of myofibres that make up a muscle.

• type l: generate low force but can sustain tension for long periods

• type llA: produce moderate force and are suited for activities requiring both strength and endurance

• type llB: generate highest force but fatigue quickly, perfect for short, explosive movements

SO2. Compare and contrast the different mechanisms skeletal muscles use to generate ATP at rest, at moderate activity and at peak activity, including nutrients used to generated ATP, aerobic vs anaerobic pathways, and the production of byproducts.

• Muscles get ATP = break down glucoses and other nutrients from either anaerobic or aerobic metabolism

• excitation and contraction in skeletal muscles are both a multi-step processes and requires ongoing energy input to maintain

• anaerobic

  • doesn’t require oxygen

  • takes place in the cytosol of the cell (outside of mitochondria)

  • fewer steps, so can produce ATP faster, however less ATP produced from a single glucose

  • only source we can get ATP fromis glucose, and can’t use fatty acids or other sources

• aerobic

  • requires oxygen

  • takes places in the mitochondria

    • remember function of mitochondria

  • needs steady oxygen supply, but will take longer to produce ATP

  • even tho its slow, it can produce a lot of ATP

  • can also use fatty acids

• phosphocreatine (enzyme)

  • doesnt need oxygen

  • very very fast

  • important bc it stores ATP, but limited

• how do they decide on how they’ll obtain their ATP?

  • resting muscles - aerobic metabolism

  • moderately active muscles (able to meet ATP demands) - aerobic metabolism

  • peak activity - anaerobic metabolism (lactate + creatine)

    • even if oxygen is available, its gonna take too long for aerobic to produce ATP

SO3. Define the term ‘muscle fatigue’ and identify at least two changes in physiological processes that contribute to the onset of fatigue.

• muscle fatigue is the reduced contractile tension for the asame (excitation) stimulus

• factors that affect excitation processes in skeletal muscle

  • depletion of ACh vesicle in MN axon terminal

  • Accumulation of potassium in T-tubules due to repeated APs

• factors that affect contracion

  • leakage of Ca2+ back into sarcoplasm

  • micotears in myofibrils

  • build-up of lactate and H+

SO4. Identify the key anatomical and physiological characteristics that distinguish Type I and Type IIA & IIB muscle fibres and analyze how these physiological differences would contribute to performance differences and training effects in an individual.

• type I: slow twitch

  • metabolism: primarily aerobic metabolism, utilizing oxygen for energy production

  • high fatigue resistance

  • slow contraction speed = less powerful but more enduring to muscle contractions

  • ideal for endurance activities (long-distance running, cycling)

• type llA (fast-twitch, oxidative)

  • ultilize both areobic and anaerobic pathways, allowing for more versatile energy production

  • moderately resistant to fatigue

  • faster contraction speed than type l fibers, but slower than type llB (ex. team sports)

• type llB

  • primarily anaerobic metabolism, relies on glycolysis for energy production

  • low fatigue resistance, leading to quick fatigue during prolonged exertion

  • fastest contraction speed, allowing for powerful bursts of force (ex. sprinting, heavy lifting)

SO5. Describe the patterns by which multiple motor units within the same muscle are used during synchronous and asynchronous recruitment.

• synchronous recruitment

  • all targeted motor units activate simultaneously

  • maximizes force and speed for short bursts of activity

• asynchronous recruitment

  • motor units activate in a staggered manner

  • sustains force and delays fatigue during longer-duration activities

SO6. Explain the difference between hypertrophy and hyperplasia in terms of muscle tissue growth and identify which mechanisms occur during adulthood.

hypertrophy: the increase in the size of individual muscle cells (muscle fibers)

• mechanism: occurs when muscle cells undergo increased protein synthesis, particularly of actin and myosin filaments, leading to larger muscle fibers

  • triggered by strength training

• occurs in adult hood

Hyperplasia: the increase in the number of muscle cells or fibers

• mechanism: involves in the formation of new muscle fibers

• does not occur in adulthood

Explain or apply different anatomical or functional rules for how to divide up the nervous system into components (e.g. CNS/PNS/ENS; Sensory/Integrative/Motor; Somatic/Autonomic)

Identify the four compartments of a neuronal cell and explain the basic functions of each compartment in
terms of information flow.

Explain the functions and key structural features of the four functional types of glia, and correctly identify which subtypes of glia are found in the CNS vs the PNS.

Compare and contrast the capacity of neurons in the CNS and PNS for repair, and the roles glial cells play
in neuronal repair

Identify which neuronal compartments and which glial cell types are associated with white vs gray matter

Use information about the organization of white and gray matter to make simple predictions about neurological symptoms arising from damage to different locations in spinal cord (e.g. sensory/motor,voluntary/involuntary)