BIO 168 Unit 4 - Muscles & Nervous System

Describe skeletal muscle.

• smooth, parallel sheets with striations

• multiple nuclei between muscle fibers

• found mostly attached to skeleton

Describe cardiac muscle.

•  parallel sheets (kinda looks like some split and/or join)

• have striations and intercalated discs

• larger nuclei

• found in the heart

Describe smooth muscle.

•  stacked, flat smooth muscle cells each with one large

• centrally located nucleus

• found in walls of nearly every hollow organ, blood vessels, eyes, skin, and ducts of certain glands 

What is a fasicle?

• bundle of muscle fibers or axons

What is a sarcomere?

•  functional unit of skeletal muscle and cardiac muscle

What is a myofibril?

• bundles of mycofilaments within skeletal and cardiac muscle cells

• rod-like, microscopic organelles within muscle cells

What is the sarcoplasmic reticulum?

•  endoplasmic reticulum found in muscle cells

• stores calcium ions required for contraction

What is the sarcolemma?

• plasma membrane of muscle cell

What are t-tubules?

•  invaginations of the sarcolemma that connect the sarcolemma to the sarcoplasmic reticulum

What is a triad?

•  a t-tubule flanked by two terminal cisternae of the sarcoplasmic reticulum

What is the epimysium?

• layer of dense irregular connective tissue that covers the entire (skeletal) muscle

What is perimysium?

• layer of dense irregular connective tissue that covers skeletal muscle fascicles

What is endomysium?

•  layer of areolar connective tissue that covers individual skeletal muscle fibers

What is rigor mortis?

• The state after death where all skeletal muscles are locked into a contracted position and the body of the deceased becomes rigid. 

• Occurs because after a few hours after the heart stops beating, ATP levels in skeletal muscle fibers become exhausted, sarcoplasmic reticulum loses the ability to return Ca2+ to SR with Ca2+ pumps (needs ATP). Thus, the Ca2+ already present in sarcoplasm and the Ca2+ that leaks out of SR trigger the sustained contraction of muscles

What is the excitation-contraction coupling theory?

What is crossbridge cycling?

What is concentric muscle contraction?

What is eccentric muscle contraction?

What is isotonic muscle contraction?

What is isometric muscle contraction?

What are the 3 phases of a muscle twitch?

• latent

• contraction

• relaxation

• *refractory

What is happening in the latent period of muscle contraction?

•  brief delay after the stimulus

• action potential spreads through sarcolemma and calcium is released from SR

• no contraction yet 

What is happening in the contraction period of muscle contraction?

• calcium ions bind to troponin

• cross-bridge forms and actin is pulled, muscle shortens

What is happening in the relaxation period of muscle contraction?

• calcium ion is pumped back into SR

• troponin-tropomyosin blocks actin sites

• tension decreases

What is happening in the refractory period of muscle contraction?

• muscle temporarily cannot respond to another stimulus while it resets electrically after contraction

What are type I muscle fibers?

What are type II muscle fibers?

What is myoglobin?

• A protein that binds to oxygen when the muscle is at rest and releases it for use during muscle contraction. 

What is the sliding filament theory?

• Calcium ions are released from the SR and cause myosin heads on thick filaments to bind to actin of thin filaments, pulling the thin filaments past thick filaments toward the center of the sarcomere.

• Causes the muscle fiber to shorten and contract.

• This process requires ATP. 

What is the role of calcium in muscle contraction?

What is the role of calcium in muscle relaxation?

What are the steps of the neuromuscular junction?

When and what is ATP needed for in muscle contraction?

What is an agonist?

• a muscle that contracts to produce a particular movement

What is an antagonist?

•  a muscle whose actions oppose those of the agonist

What is a synergist?

•  a muscle that assists the agonist

What is a fixator?

• synergists that assist the agonist by preventing movement at a joint and thereby stabilizing the agonist

What is a first-class lever?

• fulcrum in the middle of force and resistance (scissors, neck looking up)

What is a second-class lever?

• resistance is between the fulcrum and force (wheelbarrow, foot is plantar flexed)

What is a third-class lever?

•  force/effort is between resistance and fulcrum (tweezers, elbow)

What is actin?

• contractile

• contains myosin binding site where myosin heads attach to generate force

What is myosin?

• contractile

• heads that bind to actin.

• During contraction myosin heads bind to actin and pull it toward the center of the sarcomere, shortening the muscle

What is troponin?

• regulatory

• contains binding site for Ca2+

What is tropomysin?

•  regulatory

• on a resting muscle it lies over the binding sites of actin, blocking myosin from attached (and thereby blocking contraction)

What is titin (connectin)?

•  structural

• stabilizes the position of the thick filament and maintains thick filament alignment within a sarcomere

What is acteylcholinesterase?

• An enzyme that resides in the synaptic cleft and quickly breaks down acetylcholine molecules (neurotransmitter that triggers muscle contractions) following their release from the cleft.

• This prevents continuous contraction of the muscle and allows for muscle relaxation. 

What is the absolute refractory period?

• phase overlapping the depolarization and the first two-thirds of the repolarization phases where the neuron cannot fire a second action potential.

What is the relative refractory period?

• phase overlapping the final third of repolarization and the hyperpolarization phase.

• The sodium channels have reset but the membrane is hyperpolarized and thereby farther away from the threshold potential.

• Thus, a much stronger-than-normal stimulus is required to trigger another action potential.

What are astrocytes?

• forms blood-brain barrier

• regulate interstitial fluid composition

• provides structural support and organization to CNS

• assists with neuronal development

• alters synaptic activity

• replicates to occupy space of dying neurons

What are oligodendrytes?

•  produces myelin sheath (therefore allows faster propagation of action potentials)

What are microglia?

• phagocytizes microorganisms and other potentially harmful substances, phagocytizes unnecessary synapses between neurons. 

What are ependymal cells?

• lines ventricles of brain and central canal of spinal cord, assists in production and circulation of the CSF

What are schwann cells?

• PNS

•  (neurolemmocyte)

• produces myelin sheath (therefore allows faster propagation of action potentials)

What are satellite cells?

• PNS

•  insulates PNS cell bodies, regulates nutrient and waste exchange for cell bodies in ganglia

How are the effects of a neurotransmitter terminated?

• They are removed from the synaptic cleft via diffusion, enzymatic degradation, or reuptake into surrounding glial cells. 

Where is calcium stored in the muscle cell?

• Sarcoplasmic reticulum (SR)

What are the functions of the muscular system?

• Create motion

• Posture

• Store substances through sphincters

• Move substances through peristalsis

• Generate heat

What are the 4 characteristics of muscles?

• Excitability → can respond to stimulus

• Contractibility → can shorten and generate force

• Elasticity → can return to original length after stretching

• Extensibility → ability to stretch without damage

What is the z-disc?

• narrow, plate-shaped regions of dense material that separate one sarcomere from the next

What types of filaments are in the H zone?

• thick filaments only

What types of filaments are in the I band?

• thin filaments only

What types of filaments are in the A band?

• both thick and thin filaments

What are the 4 types of muscle twitches?

• single twitch

• wave summation

• unfused tetanus

• fused tetanus

What is wave summation?

• occurs when a second action potential triggers muscle contraction before the first contraction has finished

• results in a stronger contraction

What is fused tetanus?

What is unfused tetanus?