Ohio University Perey BIOS 1300 Exam 4

myology=

muscle

what are functions of skeletal muscle?

1. movement of the skeleton and skin

2. posture and body position

3. supporting and protecting soft tissues

4. gatekeepers at entrances and exits

5. generating body heat

6. amino acid reserve (in times of need)

7. glycemic control

8. social cohesions in humans

skeletal muscles are organs. What make up these organs?

1. muscle tissue

2. connective tissue

3. blood vessels

4. nerves

what is the structure of skeletal muscle?

1. muscle fiber (muscle cells that are multinucleate)

2. endomysium-around each muscle fiber

3. fascicles

-bundles of muscle fibers surrounded by..

4. perimysium

-fibrous connective tissue sheath

-blood vessels

-nerves

5. epimysium

-dense irregular connective tissues

-sheath around whole muscle

what is the endomysium made of and contain?

1. fine areolar connective tissue

2. capillaries

3. terminal branches of axons (neurons)

4. myosatellite cells

what is around each muscle fiber?

endomysium

what is around whole muscle?

epimysium

what is the relationship between endomysium, epimysium, and perimysium?

all connected

endomysium-->perimysium-->epimysium

what are the different muscle connections?

direct and indirect

what are the two kinds of indirect connection?

1. tendon

-cord of dense regular connective tissue

2. aponeurosis

-tendinous sheet of dense regular connective tissue

what does a tendon do?

connects skeletal muscle to bone

what does a aponeurosis do?

connects muscles to other muscles or bone

-wide area of attachment

what are some examples of aponeurosis?

1. epicranial aponeurosis

2. aponeurosis of the external oblique

what is direct connection?

epimysium fused to attachment sites

-fibrous: collagen

what are the functional groups of muscle?

1. agonists

2. antagonists

3. synergists

4. fixators

what is a agonist?

prime mover

-major responsibility for producing specific movement

-can be more than one agonist

what is a antagonist?

opposed movement of agonist

-controls motion

-muscles can only pull

-prime mover and antagonist on opposite sides of joint

what is a synergist?

helps prime mover

-adds extra force to same movement or stabilizes joint

-may reduce unnecessary movement

what is a fixator?

synergist that immobilizes bone or muscles origin

what do the functions of muscles depend on?

movement

What are the three types of muscle tissue?

1. Skeletal

-voluntary muscles

2. Cardiac

-heart

3. Smooth

-involuntary

-walls of hollow organs

what is the general function of muscle tissue?

movement

what are the common properties of muscle tissue?

1. excitability

2. contractility

3. extensibility

4. elasticity

What is excitability?

ability to receive and respond to stimuli

-from brain

-possibly externally

What is contractility?

-muscle cells shorten when stimulated

-generate force (only pull)

What is extensibility?

ability to stretch past resting position

-can also generate pulling force

What is elasticity?

ability to return to resting length

what is EMS?

electronic muscle stimulation

what are the characteristics of skeletal muscle fibers? (cells)

1. very large

-100 um diameter

-3-30 cm long

2.striations

-arrangement and alignment of protein fibers

3. multinucleate

what is the process of skeletal muscle fibers formation?

fusion of embryonic my oblasts

-each contributes one nucleus

-a few do not fuse and become myosatellite cells

What are myosatellite cells?

stem cells for muscle cells

-quiescent=dormant

-until damage they divide and differentiate into myoblasts and repair

What is the sarcoplasm?

muscle cell cytoplasm

What is the sarcolemma?

muscle fiber plasma membrane

What are myofibrils?

as long as muscle fiber

-where the action is at

-actively shorten = contraction

-uses ATP

where is the mitochondria of skeletal muscle fiber?

-under sarcolemma

-between myofibrils

what does the mitochondria need?

lots of ATP

what are glycogen granules? what is the purpose?

little "lumps" of glycogen

-glucose storage

(carbo-loading)

What is the resting membrane potential?

1. cells maintain resting membrane potential

-membrane polarization

-differential ion transport (Na+/K+ pump)

2. negative charge inside

-3+ out, 2+ in

3. electrochemical gradient

how does sarcolemma use resting membrane potential?

on signal from neuron to contact

-sudden change in sarcolemma potential

-wave down full length of fiber

how does the signal reach interior quickly?

transverse tubules = T tubules

-tubes of sarcolemma projecting into sarcoplasm (part of sarcolemma)

What is the sarcoplasmic reticulum?

specialized smooth endoplasmic reticulum for muscle cells

-tubular network around myofibrils

what is the function of the sarcoplasmic reticulum?

stores and releases calcium

what are triads?

1. terminal cisterna

-enlarges chamber of SR

-where SR meets t tubule

Triad=

-2 terminal cisternae + 1 T tubule

2. t tubules tightly bound to cisternae

-by transmembrane proteins

-but separate compartments

what are myofilaments?

make up myofibrils

-parallel protein fibers

-really where the action is at

what are the two kinds of Myofilaments?

1. thin

-made of actin

2. thick

-made of myosin

what are sarcomeres?

functional units of myofibrils

-repeating

-highly organized

how many sarcomeres are there per cm?

1000

(for 30 cm muscle fiber: 30,000 sarcomeres per myofibril)

what are sarcomeres made of?

1. think filaments

2. thick filaments

3. proteins that stabilize thick and thin filaments

4. proteins that regulate interactions between thick and think filaments

what are the interactions between thick and thin filaments?

contraction

sarcomere set up?

z disc to z disc

-interdigitating thick and thin filaments

what is the skeletal muscle structural hierarchy?

muscle -> fascicle -> muscle fiber -> myofibril -> sarcomere -> myofilaments -> actin or myosin

what is the I band?

-light band

-only thin filaments and titin (titin extends from thick filaments)

-z line (or disc)

what is the A band?

-dark

-thick and thin together

-M line

what are the A band subdivisions?

H band

-no think filament

-M line

zone of overlap

What are thin filaments?

1. actin

-double helix strand

-myosin binding site

2. regulatory proteins

-tropomyosin (controls access to myosin binding site)

-troponin (binds Ca2+ and controls tropomyosin)

what are thick filaments?

1. myosin

-binds actin

-motor molecule

-has ATPase activity

what are elastic filaments?

spring back after stretching

-made of titin

What is titin?

largest protein: 34,350 aminos

-extends from Z disc to M line

what is the function of titin?

forms core of thick filaments

what happens during contraction?

1. Z lines get closer

2. I band narrows

3. H band narrows

4. A bands stay the same

-thick and thin filaments don't shrink

5. filaments slide past each other

what is contraction?

sarcomeres in a myofibril shorten together

-entire muscle fiber shortens

what are connections?

myofibrils anchored:

-to each other

-to sarcolemma (by costameres)

All at Z discs

What are costameres?

connects Z discs to sarcolemma

-multi-protein complexes

-transmission of force to sarcolemma, endomysium and outward

What is muscular dystrophy?

diverse group of inherited myopathies

-progressive muscle weakness and wasting

What are Duchenne and Becker Muscular Dystrophy?

mutations in dystrophin gene

-1 in every 4000 males

-very rare in females but are carries

-loss of ability to walk

-cardiomyopathy

what are the steps of a skeletal muscle contraction?

1. neuron fires a signal

2. signal travels down axon

3. signal crosses NMJ

4. signal travels down sarcolemma and T tubules (excitation-contraction coupling)

5. SR releases Ca++

6. myofibrils contract (sliding filaments)(cross-bridge cycle)

What does NMJ stand for?

neuromuscular junction

Motor neuron =

nerve cell that controls muscles

-axon branches to several muscle fibers

motor unit =

1 neuron + muscle fibers it controls

axon =

sending "wire"

-one per neuron

what is the synapse?

where a neuron communicates with a target cell

-signal transmitted:

-neuron -> neuron

-neuron -> muscle

-neuron -> gland

what are the 2 types of synapses?

1. Electrical

2. Chemical

what are electrical synapses? what is an example?

have gap junctions

-very fast

-rare

example:

retina

what are chemical synapses? what does it contain?

cells do not touch

-space = synaptic cleft

contains:

-neurotransmitter

-presynaptic membrane

-postsynaptic membrane

What is a neurotransmitter?

chemical that carries signal across synapse

-vesicles

what is the function of presynaptic membrane?

-sends signal

-releases neurotransmitter

what is the function of postsynaptic membrane?

-receives signal

-receptor proteins

what is NMJ?

where neuron meets muscle

-1 per muscle fiber

-1 axon terminal branche

-several terminal buttons

what are axon terminals (buttons)?

enlarged end of axon

what does the motor neuron do in NMJ?

releases acetylcholine

-ACh

-Neurotransmitter

-diffuses across synapse

what is a motor endplate in NMJ?

-shallow depression in muscle fiber

-ACh receptors (AChR)

-junction folds

-more surface area = more receptors

What are ligand-gated ion channels?

transmembrane receptors with "gates"

-not GPCR

Ligand = signaling molecule

-like a key for the gates

what is an example of ligand-gated ion channels?

ACh receptors

-for Na+ and K+

-bind ACh --> open (transient binding)

what happens when it is time for a muscle to contract?

1. motor neuron releases acetylcholine

2. ACh diffused to motor endplate

3. ACh receptors

4. acetylcholinesterase (AChE)

What is acetylcholinesterase?

-enzyme

-free in synapse and in end plate membrane

-breaks down ACh (inactivates)

What is action potential?

electrical signal

-sudden change in voltage across membrane

-runs down axon or muscle fiber

-wave-like

what are the events of NMJ?

1. neuron fires AP down axon

-AP arrives at axon terminal

2. Axon AP triggers exocytosis

-ACh released

3. ACh binds to AChR

-AChR opens

-sodium goes into cell

-allows passage of (+) ions

-net flow of (+) charge inward

4. AP initiated in sarcolemma

-travels down full length of muscle fibers into T-tubules

5. acetylcholinesterase breaks down ACh

-terminates signal

-AChR's close

what happens when a motor end plate potential changes?

depolarization

-polarization flips

-inside becomes (+)

What are voltage-gated ion channels?

membrane proteins

-allow passage of ions

gates that open and close

-sensitive to voltage

-closed at rest

-open when triggered (threshold voltage)

what are voltage-gated Na+ channels? where are the found?

transmembrane proteins

-found throughout sarcolemma and T tubules

what are the players (parts) of excitation-contraction coupling?

-AP

-Triad

-Ca++ channels in SR

-Troponin

-Tropomyosin

-Thin/Thick Filaments

what is the excitation part in excitation-contraction coupling?

AP in neuron arrives at NMJ

-ACh released

AP initiated in muscle fiber

-down T-tubules

what is the coupling part of excitation-contraction coupling?

-AP activates voltage sensor in T-tubules

-Voltage sensors open Ca++ channels in Sarcoplasmic reticulum

Is the SR close or far from myofibrils?

Really Close

-quick diffusion

what proteins are in excitation-contraction coupling?

transmembrane proteins

-Ca++ released from SR and diffusion into sarcomeres

what are the events of excitation-contraction coupling?

1. Ca++ from SR

2. Ca++ binds to troponin

3. Troponin-Tropomyosin changes shape

4. Binding site exposed

(this happens just before the cross-bridge cycle)

how are excitation-contraction coupling and cross-bridge cycle connected?

myosin interacts with actin = cross-bridge

what is cross-bridge cycle?

-sliding filaments

-contraction

what happens when returning back to rest?

Ca++ constantly pumped from SR (ATP)

After AP:

-Ca++ channels close

-Ca++ in sarcoplasm drops

-Troponin returns to "resting" shape

-Tropomyosin blocks actin

what are the steps of the cross-bridge cycle?

1. cross-bridge formation

2. The power stroke

3. cross-bridge detachment

4. myosin reactivation