anatomy lecture 4 YAY

what is the basic function of all muscle tissue?

generating force (muscle tension)

what is the function of intercalated discs?

facilitate coordinated heart contraction and electrical conduction

what muscle type is made up of long, multinucleated cells arranged parallel to one another?

skeletal muscle tissue

what do skeletal muscles do?

extend nearly the entire length of muscle

what is skeletal muscle attached by?

connective tissue to skeleton

what is one distinct feature of cardiac muscle cells?

they are branched with one to two nuclei

what do intercalated discs do?

join adjacent cells and permit coordination of contraction

what do intercalated discs contain?

gap junctions and desmosomes

what links smooth muscle tissue?

gap junctions

types of muscle tissue (image)

what are the properties of muscle cells?

contractility, excitability, and conductivity, extensibility, and elasticity

what is contracility?

ability to contract (does not involve shortening of cell) and proteins in cell draw closer togehter

what is excitability?

ability to respond to stimulus (chemical, mechanical stretch, or local electrical signals)

what is conductivity?

ability to conduct electrical charges across entire plasma membrane

what is extensiblility?

ability to be stretch (up to 3 times resting length) without rupturing

what is elasticity?

ability to return to original length after stretching

what does the prefix sarco mean?

related to muscle

function of smooth endoplasmic reticulum (3)

lipid and carbohydrate synthesis, calcium (ca2+) storage, and detoxifying agent

function of sarcoplasmic reticulum

storing and releasing calcium ions (Ca2+)

function of rough endoplasmic reticulumn (3)

protein synthesis, bank of calcium, deliver calcium to myofibril for muscle contraction

what does the term tendon mean?

muscle to bone

what happens if you do flexion for biceps?

the triceps will relax

what happens if you do extension for triceps?

the biceps will relax

function of terminal cisternae? (2)

help deliver calcium to the sarcoplasm and are storage sites for calcium ions (Ca2+)

function of (transverse) T-tubles?

conduct impulses from the surface to the interior of the muscle fiber, helping calcium ions move for muscle contraction

what are the different kinds of myocyte (muscle cell)?

sarcoplasm, sarcolemma, sarcoplasmic reticulum

what is the sarcoplasm?

myocyte’s cytoplasm

what is the sarcolemma?

myocyte’s plasma membrane

what is a triad?

a structure consisting of terminal cisternae and transverse (T) tubles

what is cytosol?

the liquid part of a cytoplasm

what is the mitochondria?

powerhouse of cell

what is each myofibril made up of?

thousands of myofilaments

what proteins are present in myofibril?

contractile, regulatory, and structural proteins

function of contractile proteins

generate tension

function of regulatory protiens

dictate when a fiber may contact

function of structural proteins

maintain proper myofilament alignment and fiber stability

what are the three types of myofilaments

thick, thin, and elastic

what are thick filaments?

bundles of contractile protein myosin

what are thin filaments?

proteins actin, tropomyosin, and troponin

what are elastic filaments?

single massive, spring-like structural protein (titin)

function of elastic filaments

stabilizes myofibril structure and resists excessive stretching

what is myosin?

thick filament, has tail and big head connected by a neck

what does the head of myosin do?

has active site that binds with actin

what does actin have and what does it bind with?

it has an active site that binds with myosin heads

what happens to myosin and actin at the time of contraction?

the head of myosin attaches to actin’s active site and myosin pushes actin to the midline

what does tropomyosin do?

operates as security of actin active site and pins actin in place

function of troponin

pins tropomyosin in place

what is the unit function of a muscle?

sarcomere

myofilament arrangement of sarcomere image

what is the A band?

the whole length of myosin

whats the I band?

the lighter region containing only thin actin filaments

what does the I band do at the time of contraction?

shrinks and decreases in length

what is the zone of overlap?

overlapping actin and myosin

where is H zone found?

H zone is found in the middle of an A band IF there is a zone of overlap in the A band

what is the M line?

the middle of myosin

what is the Z disc?

found in the middle of I band and serves as the anchoring point for actin filaments in the sarcomere, the fundamental unit of muscle contraction

what form a fascicle?

multiple muscle fibers surrounded by endomysiumq

what is each fascicle surrounded by?

perimysium

what makes up a skeletal muscle?

bundles of fascicles surrounded by epimysium

what come together at the end of muscle to form a tendon?

perimysium and epimysium

what layer of thick connective tissue encloses skeletal muscles?

fascia

what is duchenne muscular atrophy?

a progressive and severe muscle-wasting disease primarily affecting boys, caused by a lack of the protein dystrophin

relaxed vs contracted sarcomere

what does sarcomere extend from?

one Z-disc to the next

what do myosin heads to?

attach to actin, pull thin filaments toward M line, bring Z-discs close togher

what makes the neuromuscular junction?

synpase between motor neuron and a skeletal muscle fiber

function to the neuromyscular junction

transmits nerve impulse/action potential from neuron to sarcolemma of muscle fiber

what does the axon terminal contain?

synaptic vesicles filled with neurotransmitter acetycholine (ACh)

what do neurotransmitters allow?

cell to cell communication

where is the synaptic cleft? what is it filled with?

space between axon terminal and muscle fiber, filled with collagen fibers and gel that anchors neuron in place

describe the motor end plate

folded surface that has many ligand-gated Na+ channels

what opens ligand-gated channels?

ACh is a ligand that does so, allowing Na+ to diffuse into muscle cell

when does neural transmission to a muscle fiber cease?

when acetylcholine is removed from the synaptic cleft

what are the muscle contraction phases?

excitation phase, excitation-contraction coupling, contraction phase

what is the excitation phase?

the process where a muscle cell receives and transmits an electrical signal, leading to a muscle contraction

what is excitation-contraction coupling?

the physiological process that transforms an electrical stimulus into a mechanical response, specifically muscle contraction

what is the contraction phase?

when a muscle generates tension, leading to shortening or movement of the muscle

why is calcium important for acetylcholine?

calcium is needed in order for acetylcholine to be released

why is calcium needed at the time of contraction for troponin

calcium binds troponin

what releases calcium ions?

sarcoplasmic reticulumn

what is hydrolysis of ATP responsible for?

recocking of myosin heads

why does myosin bind to ATP?

to release myosin heads from actin active sites

When does the release of ADP and Pi from myosin occur?

during the power stroke

when do the myosin heads return to their relaxed/low-energy state?

the power stroke

what does the power stroke do?

pulls the thin filaments toward the M lines

what are the sequence of events that occur in preparation for contraction?

Action potential arrives at triad, calcium is released from the terminal cisternae,
calcium binds to troponin, tropomyosin exposes the actin active sites

explain the cross bridge cycle briefly

myosin head binds to actin and forms a cross-bridge, pulls on actin filament resulting in power stroke, then detaches to bind to a new active site

what is crossbridge detachment?

myosin head separates from the actin filament

what causes myosin heads to be reactivated?

ATP binding and hydrolosis

why do calcium channels in the SR close during muscle fiber contraction?

the resting membrane potential is restored

what happens to calcium during muscle fiber relaxation?

calcium is pumped back into the sarcoplasmic reticulumn

when acetylcholinesterase in the synaptic cleft degrades acetylcholine, what happens?

ligand-gated sodium channels close

what does sarcolemma repolarization during relaxation do?

restores the resting membrane potential

what aspect of muscle relaxation requires ATP?

pumping calcium ions back into sarcoplasmic reticulum

what is rigor mortis?

progressive stiffening (contraction) of skeletal muscles that begins 3-4 hours after death

what happens to muscle fibers during rigor mortis?

muscle fibers are unable to relax without ATP

what is a muscle twitch?

smallest musle contraction

what are the three phases of twiches?

latent, contraction, relaxation, and refractory period

what does the latent period do?

time for action potential to propagate across sarcolemma

what does the contraction period do?

repeated crossbridge cycles generate tension