TAMU BIOL 319 (A&P Part 2)

Set for the second practical of BIOL 319 at Texas A&M University. Made the summer of 2024.

Where is smooth muscle?

Walls of hollow organs

How does smooth muscle move?

involuntary, slow and rhythmically to propel substances through channels of the body

How does cardiac muscle move?

involuntary, intrinsic contraction rhythm altered by nervous system

How much of the body’s mass is skeletal muscle?

40%

What do skeletal muscles do?

majority of locomotion and support of skeleton

What are skeletal muscles made up of?

muscle fibers/cells organized in fascicles

What is an upper motor neuron lesion?

loss of muscle function bc of stroke damaging neurons in the brain

How does skeletal muscle move?

voluntary, powerful, can rapidly contract but tires rapidly

What is excitability?

the electric charge differential in the cell membrane can be changes upon stimulation to produce an intracellular muscle response

What is contractility?

muscle cells shorten when stimulated

What is extensibility?

muscle cells can stretch, sometimes more than resting length

What is elasticity?

muscle cells can return to resting cell length after being stretched

Functions of muscles?

generate movement, maintain posture and balance, stabilize joints, generate heat to maintain body temperature

What is in a skeletal muscle?

muscle fibers, nerves, blood vessels, connective tissues

Where do blood vessels and nerves enter the skeletal muscle?

near the center, then branch out through connective tissue sheaths

What is this?

Gamma efferent fibers

What is this?

Intrafusal muscle fibers

What is this?

Flower spray endings

What is this?

Annulospiral endings

What are annulospiral endings?

endings of large axons, wrap around center of muscle spindle, stimulated by degree and rate of stretch

What are flower spray endings?

small axons, ends of muscle spindles, stimulated by amount of stretch

What are gamma efferent fibers?

from small motor neurons of spinal cord, innervate contractile ends of intrafusal fibers, stimulate them to contract with rest of muscle

What are efferent fibers/alpha efferent fibers?

from large alpha motor neurons, stimulate contraction in extrafusal fibers

What is external stretch?

muscle spindle is stretched when muscle lengthens, eg. when weight is applied or antagonistic muscle contracts

What is internal stretch?

gamma motor neurons cause intrafusal fiber ends to contract which stretches spindle middle, increases rate of firing of anulospiral and flower spray endings

What is alpha-gamma coactivation?

descending motor pathway fibers synapse with alpha and gamma motor neurons so extrafusal and intrafusal fiber ends contract simultaneously

What type of muscle is autorhythmic?

Skeletal Muscle

Tendons

Connective tissues that attach muscle to bone; rope-like extensions that are made up of mostly collagen

Why are the connective tissue sheaths of muscles continuous with each other and with tendons?

To transfer the force of the contracting muscle fibers to the structure (like bone) to be moved

Direct Attachment

When the periosteum or perichondrium is fused with the muscle’s epimysium

Indirect Attachment

The more durable, smaller, and more common attachment type, like a tendon or aponeurosis; can blend into the fascia of other muscles to form an attachment

Interacting Joints or Articular Surfaces

Allows for an almost frictionless movement of the adjacent bones

Joints

Pivot points for motion when skeletal muscle contracts

Antagonistic muscle

The muscle that relaxes

Myofilament(s) that A Bands contain

Actin and Myosin

Myofilament(s) that I Bands contain

Actin

Myofilament(s) that H Bands contain

Myosin

Myofilament(s) that Z Line contain

Actin

Myofilament(s) that M Line contain?

Myosin

Alpha-Actin

The protein that the z line is mostly made up of

Titin

Protein that makes up elastic filaments and runs from the Z Line to the thick filaments

Agonist

Muscle that contracts

Terminal Cisterns

Large perpendicular cross channels of the sarcolemma that are always found in pairs

T Tubules

Elongated tube extensions of the sarcolemma that dive deeply into the cell

What type of contraction is this?

Twitch

What type of contraction is this?

Unfused/incomplete tetanus

What type of contraction is this?

Fused/complete tetanus

What type of contraction is this?

Wave summation

What is the order of neurons from least to most sensitive?

3 → 2 → 1

What does this image represent?

Summation

What does this image represent?

Size principal of recruitment (voltage)

What phase of an isometric twitch is shown?

Period of relaxation

What phase of an isometric twitch is shown?

Period of contraction

What phase of an isometric twitch is shown?

Period of latency

What is this?

Axon terminal

What is this?

Motor end plate

What is this?

Calcium

What is this?

Voltage gated calcium channels

What is this?

Vesicle containing acetylcholine

What is this?

Acetylcholine

What is this?

Nicotinic acetylcholine receptor

What is this?

Cell body

What is this?

Nucleus

What is this?

Dendrites

What is this?

Myelin sheath

What is this?

Axon

What is this?

Synaptic cleft

What is this?

Extrafusal fibers

What is this?

Flower spray endings

What is this?

Annulospiral endings

What is this?

Gamma efferent fibers

What is this?

Alpha efferent fibers

What is this?

Intrafusal fibers

What happens during this step of cross-bridge formation?

A myosin head in high-energy configuration binds to an exposed myosin-binding site on actin

What happens during this step of cross-bridge formation?

ADP and inorganic phosphate are released from myosin head, returning it to its low-energy state, resulting in a power stroke

What happens during this step of cross-bridge formation?

ATP binds to myosin head, causing detachment

What happens during this step of cross-bridge formation?

Hydrolysis of ATP into ADP and inorganic phosphate repositions the myosin head into its high-energy configuration

What are the steps of cross bridge formation?

binding, power stroke, detaching, and cocking

Cross bridge

globular myosin links thick and thin filaments together and swivel as motors to shorten sarcomere

Dystrophin

links thin filaments to sarcolemma, causes muscular dystrophy when not enough

How many thick filaments surround each thin filament?

3

How many thin filaments surround each thick filament?

6

Sarcoplasmic reticulum

smooth ER, surrounds myofibrils, abundant mitochondria and glycogen granules around it, controls calcium levels

Triad

a T tubule and the terminal cisterns on either side

Integral membrane proteins of T tubule

voltage sensors

Integral membrane proteins of terminal cisterns

gated channels for release of calcium

Polarization

inside of the cell has a more negative charge than outside

3 steps of an action potential

1. Depolarization: acetylcholine binds to receptor and opens ion channels for Na and K. Na enters cell and K leaves. Make inner surface of sarcolemma less negative

2. Muscle action potential: more voltage-gated Na channels open as charge increases

3. Repolarization: Na channels close and K channels open. Membrane becomes more negative as K leaves cell. Na and K gradient differences are restored by ATPase pump that moves Na out and K in

Refractory period

muscle cell cannot be stimulated again until sufficiently repolarized

Excitation-contraction coupling

muscle action potential travels along sarcolemma, T tubules change shape, terminal cisterns release calcium, calcium removes inhibitory action of tropomyosin, exposes myosin-binding sites on actin, cross bridge cycling starts

Motor unit

a motor neuron and all the muscle fibers it innervates, smaller unit=finer control of movement

How many neuromuscular junctions does each muscle fiber have?

1

Synaptic end bulb/axon terminal

end of an axon

Synaptic cleft

space between the axon terminal and muscle, filled with extracellular fluid with collagen and glycoproteins

Acetylcholinesterase

in synaptic cleft, breaks down acetylcholine into acetic acid and choline to terminate the signal for fine muscle control

Myasthenia gravis

deficient acetylcholine receptors due to autoimmune destruction, symptoms are difficulty talking and swallowing, drooping upper eyelids, generalized muscle weakness

Isometric contraction

contraction but muscle fibers maintain constant length, thin filaments do not move when cross bridges form, tension increases but length is constant

Isotonic contraction

muscle fibers shorten or lengthen, muscle tension is constant but length changes

Concentric isotonic contractions

muscle length decreases

Eccentric isotonic contractions

muscle length increases