Human Anatomy and Physiology I - Chapter 9

Exam 2, Liberty University

what are the three types of muscle tissue?

skeletal, smooth, cardiac

where are the locations of skeletal muscles?

all over the body

what are the functions of skeletal muscles?

locomotion, facial expressions, posture, respiratory movements

under what control are skeletal muscles?

voluntary

where are the locations of smooth muscles?

walls of hollow organs, blood vessels, eye, glands, skin

what are the functions of smooth muscles?

propel urine, mix food, pupils contractions, blood flow

under what control are smooth muscles?

involuntary

where is the location of cardiac muscle?

heart

what are the functions of cardiac muscle?

pump blood throughout the body

under what control is cardiac muscle?

involuntary

what are the seven functions of the muscular system?

movement, posture, respiration, heat, communication, heart contraction, organ/vessel contraction

contractility definition

ability of a muscle to shorten with force

excitability definition

capacity of a muscle to respond to an electrical stimulus

extensibility definition

muscle stretched beyond normal resting length and still contracts

elasticity definition

ability of a muscle to recoil to original resting length after stretched

what composes skeletal muscles?

muscle fiber cells, connective tissue, blood vessels, nerves

describe skeletal muscle cells (fibers)

long, cylindrical, multinucleated

describe the appearance of skeletal muscle

striated, light and dark banding

what are the three layers of connective tissue coverings

epimysium, perimysium, endomysium

epimysium definition

dense irregular connective, surrounds whole muscle

perimysium definition

loose connective tissue, surrounds fascicles

fascicle definition

group of muscle fibers

endomysium definition

loose connective tissues, surrounds individual skeletal muscle fibers

what kind of tissue is muscular fascia?

connective tissue sheet

what does muscular fascia do?

hold muscles together, separate into functional groups

what do motor neurons do?

stimulate muscle fibers to contract

where are the cell bodies of motor neurons found?

brain or spinal cord

how do motor neuron axons reach skeletal muscle fibers?

they extend through nerves

why do motor neuron axons branch

so that each muscle fiber is innervated

neuromuscular junction definition

contact point between motor neuron muscle fiber

where are the nuclei located in a skeletal muscle fiber?

several found in sarcolemma

what is the sarcolemma?

cell membrane of muscle fibers

what are transverse tubules (T-tubules)?

inward folds of sarcolemma, reach center of fiber

what fills most of the cytoplasm in a muscle fiber?

myofibrils

what is a muscle fiber’s cytoplasm called?

sarcoplasm

what are myofibrils made out of?

myofilaments

what are the two types of myofilaments

actin and myosin

what are the other names for actin and myosin filaments?

thin and thick filaments

sarcomeres definition

highly ordered repeating units of myofilaments

sarcoplasmic reticulum definition (smooth ER)

calcium regulation and storage

what forms actin (thin) myofilaments?

two strands of fibrous actin, double helix

where are the ends of the actin myofilament attached?

z disc of sarcomere

what are fibrous actin strands made of?

globular actin monomers

how many globular actin monomers per strand?

200 per strand

what is the function of the active site on each g actin monomer

binds to myosin during muscle contraction

what is tropomyosin?

elongated protein in thin filaments

where is tropomyosin located on the thin filament?

winds along groove of actin double helix

what do the three subunits of troponin do?

bind to actin, tropomyosin, calcium ions

what else does troponin do?

hold tropomyosin over active sites

what does the tropomyosin/troponin complex do?

regulate interaction between thin and thick filaments

what are myosin molecules shaped like?

two golf club heads, myosin chain rods

what do myosin heads bind to during muscle contraction?

active sites on actin molecules, cross bridges

how are myosin heads connected to the rod portion of the myosin molecule?

hinge region, bend and straighten during contraction

what enzyme activity do myosin heads have?

act as ATPase enzymes, break down ATP

sarcomere definition

basic functional unit of muscle fiber

z disk definition

protein network where actin filaments attach

titin filament definition

elastic amino acid chain that make muscles extensible

I band appearance (striation)

end of one thick filament to the start of another

A band appearance (striation)

length of thick filaments

H zone appearance (striation)

A band region, thin and thick filaments do not overlap

M line appearance (striation)

middle of H zone, delicate filaments hold myosin in place

what happens during muscle contraction?

actin slides over myosin, shortening sarcomeres

doa chin and myosin filaments change length during contraction?

no, they overlap

what causes skeletal muscle contraction?

shortening of sarcomeres

how do sarcomeres lengthen during relaxation?

external forces, opposing muscle contraction

what are antagonistic muscles?

muscles that produce opposite effect of each other

synapse definition

axon terminal resting in an invagination of sarcolemma

parts of the neuromuscular junction (NMJ)

presynaptic terminal, synaptic cleft, postsynaptic membrane

presynaptic terminal definition

axon terminal with synaptic vesicles

what do synaptic vesicles contain?

neurotransmitters

what is the synaptic cleft?

space between axon and postsynaptic membrane

what is the postsynaptic membrane?

sarcolemma of the muscle cell

three key points in action potential

all excitable cells are polarized, polarized cells have charge difference, charge difference is known as membrane potential

membrane potential definition

numerical charge difference between inside and outside of cell

why is the inside of a cell more negative than the outside?

because of large negative charged protein molecules inside of the cell

where is potassium more concentrated?

inside the cell

why doesn’t all K+ leak out of the cell?

negatively charge proteins inside the cell attract and hold some ions back

where is sodium more concentrated?

outside the cell

what maintains the difference in Na+ and K+ concentrations across the membrane?

the sodium potassium pump

why is the resting membrane potential important?

it must exist for an AP to occur

approximately what is the resting membrane potential in millivolts (mV)?

-70 mV

what are the two main types of ion channels?

ligand gated, voltage gated

what is a ligand?

a molecule that binds to a receptor

what is a receptor?

a protein or glycoprotein with a specific receptor site for a ligand

give an example of aligned in the nervous system

acetylcholine

when does a ligand-gated ion channel open?

when a neurotransmitter binds to its receptor site

when does a voltage-gated ion channel open or close?

in response to small voltage changes across plasma membrane

are ion channels specific to certain ions?

yes

wha ion has a higher concentration inside the plasma membrane?

potassium

what ion has a higher concentration outside the plasma membrane?

sodium

which ion is the plasma membrane more permeable to?

K+

what is the ratio of sodium to potassium going in and out of the cell through the sodium-potassium pump?

3 sodiums, 2 potassiums

what is used to measure the resting membrane potential?

an oscilloscope

are there more leaky K+ channels or Na+ channels in the membrane?

K+ channels

what happens because of the greater number of K+ channels?

K+ diffuses out of the cell, inside more negative

what process maintains the uneven Na+ and K+ distribution across the membrane?

active transport by the sodium-potassium pump

what triggers and action potential?

excitation of the cell membrane

what happens after excitation in an action potential?

ion channels open

what changes when ion channels open?

membrane permeability changes

what occurs when ions diffuse through open channels?

the charge across plasma membrane changes