Chapter 9 Anatomy

Describe the structure, function, and location of skeletal muscle

structure- skeletal muscles are the longest and have striations

function0 enables you to move body different directions

location- attaches to bones and skin

describe the structure, function, and location of cardiac muscle

structure- striated

function- contracts at steady rate

location- walls of heart

describe the structure, function, and location of smooth muscle

structure- not striated, spindle shaped, uninucleate

function- forces substances through internal body channels with involuntary contractions

location- walls of hallow organs

Describe the four main characteristics of muscle

excitability- ability to receive + respond to stimuli

contractabily- ability to shorten forcibly when stimulated

extensibility- ability to stretch

elasticity- ability to recoil to resting length

Describe the 4 important functions of muscles

1. Movement: responsible for all locomotion and manipulation

2. Posture: maintaining sitting and standing positions.

3. Joint Stability: Muscle tendons crossing over joints help stabilize joints during movement.

4. Heat Production: Muscle contractions generate heat

Describe the importance of nerve and blood supply to muscle

– skeletal muscle has nerves supplying every fiber to control

activity

• Contracting muscle fibers require huge amounts of oxygen and nutrients

Describe the importance connective tissue sheaths to muscle and explain the structure of epimysium, perimysium, and endomysium of connective tissue sheaths

Epimysium: dense irregular

connective tissue surrounding entire

muscle

– Perimysium: fibrous connective

tissue surrounding fascicles

– Endomysium: fine areolar

connective tissue surrounding each

muscle fiber

Describe insertion and orgin as it relates to muscle attachment to bone and explain the two different ways muscle attach to bone

Insertion- attachment to moveable bone

orgin- attachment to immoveable bone

direct- epimysium fused to perimysium of bone/cartilage

indirect-connective tissue wrapping extends beyond muscle

Describe the function of glyosomes and myoglobin in muscle

glycosomes- stores glycogen

myoglobin- stores O2

Describe the structure of striations, sacromeres, and myofilaments of skeletal muscle

Striations

• stripes forms from repeating dark and light bans along length of mycrofibril.

Sacromeres

• contractile unit- a band w half I band

• 2 discs

• line up end to end

Myofilaments

• arrangement of actin + myosin

Describe the molecular composition and function of thick and thin myofilaments

• Thick Filaments

  • Myosin

  • Protein filaments with protruding heads. They use ATP to attach to thin filaments and pull them inward to contract the muscle.

• Thin Filaments

  • Actin, Tropomyosin, Troponin

  • anchor for pulling and control center

Describe the functions of tropomyosin, troponin, titin, dystrophin, nebulin, myomesin and C proteins

• Tropomyosin: Blocks actin to keep muscle relaxed.

• Troponin: Binds calcium to unlock contraction.

• Titin: Elastic spring that prevents overstretching.

• Dystrophin: Anchors inside of cell to membrane for protection.

• Nebulin: Ruler that sets thin filament length.

• Myomesin: Holds thick filaments together at the center

• C-Protein: Bundles thick filaments and regulates myosin heads.

Describe Duchenne musclar dystrophy and explain the consequences of having it

• What it is: An X-linked genetic disease mostly affecting young boys that causes progressive muscle loss.

• Cause: A defective protein makes muscle cell membranes tear easily.

• Outcome: Leads to severe weakness in limb, chest, and heart muscles

Describe the structure and function of sacroplasmic reticulum

network of smooth endoplasmic reticulum tubules

– regulates Calcium by storing and releasing it

Describe the structure and function of T tubules

Tube formed by protrusion of

sarcolemma deep into cell interior

• Allow electrical nerve transmissions

to reach deep into interior of each

muscle fiber

Describe triad relationships and explain their functions

A triad is a 3-part structure made of 1 T-tubule sandwiched between 2 SR sacs.

Functions

• T-Tubule: Directs the electrical signal deep into the muscle fiber.

• SR Sacs: Store and release calcium.

• Overall: Converts an electrical signal into calcium release to trigger muscle contraction.

Describe sliding filament of skeletal muscle contraction

• Activate cross bridges to generate force

• during contraction, thin filaments slide past thick filaments, causing actin and myosin to overlap more

Describe the functions of the two classes of ion channels present in muscle tissue

chemically gated- opened w chemical signal

voltage gated- open/ close in response to voltage changes in membrane potential

Describe the 6 events that occur at neuromuscular junction for skeletal muscle to contract

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1. AP Arrives: Signal reaches axon terminal.

2. Calcium Enters: Voltage-gated channels open; calcium enters neuron.

3. ACh Released: Calcium causes ACh release into synaptic cleft.

4. ACh Binds: ACh diffuses to sarcolemma receptors.

5. Sodium Enters: Gates open; sodium enters, creating end plate potential.

6. ACh Degraded: Acetylcholinesterase breaks down ACh.

Describe the 3 steps to generate an action potential for skeletal muscle contraction

1. End Plate Potential: ACh opens ion channels on the muscle membrane, allowing Na+ to flow in and make the inside less negative.

2. Depolarization: If depolarization reaches threshold, voltage-gated Na+ channels open, firing an unstoppable action potential across the muscle fiber.

3. Repolarization: Na+ channels close and K+ channels open, sending K+ out to reset the electrical voltage.

Describe excitation- contraction coupling of skeletal muscle contraction

1. AP Travels Down T-Tubules: Electrical signal spreads deep into the muscle fiber.

2. Ca2+ Released: Signal triggers SR sacs to dump calcium into the cell.

3. Sites Exposed: Calcium binds to troponin, shifting tropomyosin off actin's binding sites.

4. Contraction Triggered: Myosin grabs actin and pulls, shortening the muscle.

Describe the 4 steps of cross bridge cycling for skeletal muscle contraction

1. Cross bridge formation: high-

energy myosin head attaches to

actin thin filament active site

2. Working stroke: myosin

head pivots and pulls thin filament

toward M line

3. Cross bridge detachment: ATP

attaches to myosin head, causing

cross bridge to detach

4. Cocking of myosin head: energy

from hydrolysis of ATP “cocks”

myosin head into high-energy

state

Describe how and why rigor mortis occurs

• muscles began to stiffen 3-4 hours after death

• calcium levels began to increase because ATP is no longer being synthesized, so calcium cannot be pumped back into SR

• muscles stay contracted until muscle proteins break down

Describe isometric and isotonic muscle contraction

Isometric contraction: no shortening; muscle tension increases but does not

exceed load

Isotonic contraction: muscle shortens because muscle tension exceeds load

Describe the three phases of a muscle twitch

• Latent period: no muscle tension

• Period of contraction: tension increases

• Period of relaxation: tension declines to 0

Describe graded muscle responses and explain wave summation, unfused and fused tetanus

• Graded Response: Muscle strength adjusts by changing stimulus frequency or strength.

• Wave Summation: Fast signals add up into a stronger force.

• Unfused Tetanus: Faster signals cause a sustained, shaky contraction.

• Fused Tetanus: Fastest signals cause a smooth, max contraction (leads to fatigue).

Describe muscle recruitment including the three types of stimuli involved

• Subthreshold stimulus: Stimulus not strong enough, so no contraction

• Threshold stimulus: stimulus is strong enough to cause first observable contraction

Maximal stimulus: strongest stimulus that increases maximum contractile force

Describe isotonic, concentric, eccentric and isometric muscle contraction

Isotonic: muscle changes in length and moves load eg.

• Concentric: Muscle shortens and does work (eg. bicep curl up)

• Eccentric: muscle lengthens and generates force (eg. bicep curl down)

Isometric: Load is greater than maximum tension the muscle can generate. Muscle neither shortens or lengthens. eg. holding weight

Describe the three ways ATP is generated to provide energy for muscle contractions

• Creatine phosphate: Quickly makes ATP from ADP; provides energy for about 15 seconds.

• Anaerobic glycolysis: Breaks down glucose without oxygen; produces ATP quickly but also lactic acid.

• Aerobic respiration: Uses oxygen in mitochondria to produce lots of ATP; used during longer activities.

Describe muscle fatigue and explain the possible causes of it

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The physiological inability to contract despite continued stimulation

Causes:

• Ionic imbalance - levels of Na+, K+ and Ca2+ can change and distrupt membrane potential

• Increased organic phosphate - interferes with calcium release and muscle power.

• Decreased ATP & Increased magnesium - As ATP decreases, magnesium increases and interferes with T-tubule proteins

• Decreased glycogen

Describe the four reasons why excess postexercise oxygen consumption is required

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• Oxygen reserves are replenished

• Lactic acid is reconverted to pyruvic acid

• Glycogen stores are replaced

• ATP and creatine phosphate reserves are resynthesized

Describe the four fsctors that influence the force of muscle contraction

1. Number of muscle fibers stimulated: more recruited = greater force

2. Relative size of fibers: bulkier muscles = hold more tension

3. Frequency of stimulation: higher frequency = greater force

4. Degree of muscle stretch: generate more force when sarcomeres are stretched to 80–120% of resting rate.

Describe the two ways that muscle fiber types can be classified

1. Speed of contraction:

• Speed which myosin ATPases split ATP

• Pattern of electrical activity of motor neurons

2. Metabolic pathways used for ATP synthases

• Oxidative fibers:

• Glycolytic fibers:

Describe the influence of slow oxidative fibers, fast oxidative fibers, and fast glycolytic fibers on muscle contraction

Slow oxidative fibers: low intensity, endurabce activities eg. maintaining posture

Fast oxidative fibers: Medium intensity activities eg. sprinting or walking

Fast glycolyctic fibers: short term intense or powerful activities eg. swinging a bat

Describe load and recruitment in terms of muscle contraction

Load: muscles contract fastest with no load

• Greater load = shorten duration and slower contraction

Recruitment: more units contracting = faster and longer contraction

Describe how muscles adapt to aerobic and resistance exercise

• Aerobic exercise: Increases capillaries and mitochondria which improves endurance and resistance to fatigue.

• Resistance exercise: Increases muscle fiber size and myofilaments which improves muscle strength and size.

Describe the five differences between smooth and skeletal muscle

• S.H.E.A.T

1. Smooth muscle fibers are spindle shaped

2. Smooth muscle has no connective tissue sheaths

3. Smooth muscle has less elaborate SR and no T tubules

4. Autonomic varicosities

5. Sarcolemma contains tiny pouch like infoldings called caveolae

Describe the six differences between smooth muscle fibers and skeletal muscle fibers

Smooth muscle…

1. Fibers are electrically connected via gap junctions, skeletal are electrically isolated

2. Thick filaments are fewer and have myosin heads

3. No troponin complex

4. thick and thin filaments arranged diagonally

5. Intermediate filaments dense body network

6. dense bodies

Describe the mechanisms of contraction of smooth muscle

• Slow synchronised contractions

• Cells electronically coupled by gap junctions

• Some cells are self excitatory

  • Act as pacemakers

Describe how smooth muscle contraction is similar to skeletal muscle contraction

• Actin and myosin interact by sliding filament mechanism

• Final trigger increases intracellular Ca2+ level

• ATP energizes sliding process

• Contraction stops when Ca2+ is no longer available

Describe how smooth muscle contraction differs from skeletal muscle contraction

• Some Ca2+ still obtained from SR but mostly from extracellular space

• Ca2+ binds to calmodulin, not toponin

• Activated calmodulin then activates myosin kinase

• Activated myosin kinase phosphorylates myosin head, activating it

  • Leads to crossbridge formation with actin

Describe why the contraction of smooth muscle is energy efficient

• Slower to contract and relax but maintains contraction for long periods with little energy cost

• Slower ATPases

• Makes ATP via aerobic respiration

Describe the two ways smooth muscle contraction is regulated

Neural regulation:

• Neurotransmitters binding causes either graded or action potential

• Results in Ca2+ increase

Hormones and local chemicals:

• Some smooth muscle have no nerve supply

• Some smooth muscle respond to both neural and chemical stimuli

Describe the two special features of smooth muscle contraction

1. Response to stretch

• Stress relaxation response: responds to stress only briefly then adapts to new length

2. Length and tension changes

• Can contract when between half and twice resting length

Describe the structure, function and location of unitary smooth muscle

Structure & Function: All common characteristics of smooth muscle

Location: Found in hollow organs except heart

Describe he structure, function and location of multiunit smooth muscle

Structure: Similar to skeletal muscle, independent muscle fibers. Controlled by autonomic nervous system and hormones.

Location: Large airways, lungs, large arteries

Describe the developmental aspects of muscle

• All muscle tissues develop from embryonic myoblasts

• Multinucleated skeletal muscle cells

• Regeneration:

  • Skeletal muscle: limited

  • Smooth muscle: regenerates throughout life

• Males have more muscle mass than females

• With age muscles weaken