PNB Exam #3: Key Terms & Definitions for Engineers

what can help neurons sent action potentials faster

myelinated neurons

myelination increases the ______________ by up to a factor of ___

- speed of conductivity

- 100

what is myeline

insulated wrapper produce by glia

(similar to rubber around chargers)

what is the function of myeline

- prevents local currents from dissipating into external environment

- gives increase in conduction velocity and efficiency

even though a myeline on its own doesn't create much change, why are myelinated axons so much faster?

- when you add up all of the small increases in efficiency = a big increase in overall neuron

what are the myelinated segments called

internodes

are the unmyelinated segments called

nodes of Ranvier

how would you describe an action potential traveling through a myelinated axon

- moves rapidly through internodes and pauses and recharges in nodes of Ranvier

what does being myelinated mean about ion channels

- there are fewer ion channels required to move action potential through the internodes

what are demyelination diseases

- very severe

- neurons do not have enough channels to propagate action potentials through internodes when myeline is gone

- efficiency is broken down

relationship with axon terminals and neurotransmitters

- axon terminals tend to have neurotransmitters made and ready to go: waiting for release

what helps release neurotransmitters

calcium allows vesicles to move to presynaptic membrane and attached to proteins called snares

- then vesicles exocytosis the neurotransmitters into synapse

what brings voltage gated calcium channels to threshold

- depolarizing sodium spreads from last part of axon segment into axon terminal

do calcium ion channels send calcium into or out of the cell

into

What is tetrotoxin?

drug that inhibits voltage gated sodium channels

4 properties of skeletal muscle

- excitability

- contractility

- elasticity

- extensibility

muscles (graded/action) potential compared to neurons

- muscles generate graded and action potentials through the same mechanisms are neurons

what do muscles use their action potential for

contraction (generates force)

muscles are able to always change in size due to their _____ property

elastic

do muscles have a resting length

yes

unlike other cells in the body, muscle cells do not lose ____ when it changes in size

- membrane integrity

what allows muscles to be stretched safely beyond resting length

its extensibility

what are the 3 main muscle functions

- heat

- movement

- posture

what is an important aspect in maintaining posture

- some muscles are contracted all the time

what do muscles produce as a byproduct of contraction and why is it important

heat

- muscles are important for thermoregulation or maintaining temperature homeostasis

- ex: why you shiver when cold

do muscle cells go through mitosis

no: differentiation of stem cells

What is a myosatellite cell?

multipotent stem cell

what is a immature muscle precursor

myoblast

2 other words for muscle cells

- myocytes

- muscle fibers

process of muscle cell differentiation

multipotent stem cell (myosatellite cell) -> immature muscle precursor (myoblast) -> tiny myoblasts line up next to each other -> mature into muscle cells

3 major types of muscle inside the body

- skeletal muscle

- cardiac muscle

- smooth muscle

which of the 3 major types of muscles in the body are multinucleated?

skeletal muscle

- has 3 or more nuclei per cell

why do skeletal muscles have more 3 or more nuclei per cell?

each individual myoblast has its own nucleus before it fuses to form a muscle fiber

shape of skeletal muscle and cardiac muscle

overall rectangular or cylindrical shape with striations going down the shorter axis of the cell

skeletal muscle has a _______ packed tissue : why?

- densely

- very little space between 2 adjacent skeletal muscle cells

organization of muscle cell from smallest to largest

- myofilaments (actin and myosin)

- myofibril

- muscle fibers (muscle cell/myocyte)

- fasciculus

- muscle belly

- tendon

muscle tissue is comprised of a network of bundles ____ which are made of ____

- fasciculus

- muscle fibers

what wraps the muscle belly

- epimysium

what wraps the fasciculus

- perimysium

What wraps each individual muscle fiber

- sarcolemma

what lays on top of the sarcolemma

- endomysium

what is created from arrangement of the contractile proteins inside the cell

myofibrils

is there variability among muscle fibers

yes: even within a single muscle

3 types of skeletal muscle

- Type I: slow twitch fibers (aerobic oxidative)

- Type IIa: fast twitch fibers (anaerobic glycolytic)

- Type IIb: fast twitch fibers (anerobic CP)

what is myoglobin

- oxygen binding protein

- hemoglobin counterpart

what color are type 1 fibers and why

- dark red (most myoglobin)

what are type 1 fibers

- really efficient in binding and trapping oxygen in the tissue which allows it to produce a lot of ATP

- can stay contracted for a long period of time

ex: postural muscles and muscles used for endurance

what color are type 2b fibers and why

- translucent

- little to no myoglobin

what are type 2b fibers

- rely entirely on anaerobic respiration

- less efficient in producing ATP

- fast fibers can only be used for a short burst of activity

ex: sprinting / weightlifting

what color are type 2a fibers and why

intermediate colors

- has some myoglobin

what are type 2a fibers

- have the ability to do a limited amount of aerobic respiration

relationship between the 3 types of muscle cells and other cells

- even though the 3 types are very different, they have more in common with each other than any other cell type

why are muscle cells different than the average cell type

- longer, thicker, more cylindrical

how do muscle cells match its function

- muscles only job is to contract -> crams as many myofibrils as possible inside the cell

- inside the cell has very little cytoplasmic space

- most of organelles inside of muscle tend to get pushed to periphery of the cell

what is the cytoplasm renamed in muscle cells?

sarcoplasm

what is the plasma membrane renamed in muscle cells?

sarcolemma

what is the endoplasmic reticulum renamed in muscle cells?

sarcoplasmic reticulum

what do contractile proteins arrange themselves into

- repeating units called sarcomeres

what are sarcomeres

basic units of muscle contractions

one myofibril contains ____ sarcomeres

many

3 structural proteins that make up most of the sarcomere

- myosin: thick filament

- actin: thin filament

- titan: tiny elastic filament

sarcomeres contract in a ___ manner, which is

- oscillatory

- bringing the ends towards the center (similar to an accordion)

2 regulatory elements of muscles

- troponin

- tropomyosin

what are the two different parts of myosin

- head and tail

why is the head of the myosin important

the heads contain an enzymatic domain that is able to break down and hydrolyze ATP into ADP and phosphate

two types of actin and what they are

G-actin: globular protein

F-actin: long filament

___ actin is a monomer and ___ actin is a polymer

- g actin

- f actin

what is tropomyosin

filamentous rope like protein that blocks the myosin binding site on actin

what is troponin

smaller protein made up of 3 subunits:

- TnT: binds to tropomyosin

- TnI: binds to actin

- TnC: binds to calcium

what needs to happen between actin and myosin for a muscle to contract

need to be bound together

what state is tropomyosin in at rest and why

- it blocks the myosin binding site on actin which prevents binding

- this is because there is low calcium levels in the cell

what state is tropomyosin in when a cell is depolarized and why

- depolarization = high calcium levels

- Ca2+ binds to TnC and causes tropomyosin to become ejected so binding can occur

what is a cross bridge

binding between actin and myosin

what are cross bridges necessary for

contraction

what does tropomyosin regulate

binding

skeletal muscle (and all types of muscle) require a __ signal to initiate muscle contraction

calcium

what is another requirement for muscle contraction

ATP: important for driving active transport and maintaining concentration gradients

skeletal muscle is one of the major consumers of ___ in the body

glucose

do skeletal muscles have a high concentration of mitochondria? why?

yes: allows them to meet great energetic demands

is polymerization of G actin into F actin ATP dependent?

yes

what is the most important role of ATP in muscles

- regulation of cross-bridge formation

myosin ATP hydrolysis triggers...

triggers conformational change

4 steps of myosin ATP hydrolysis

1) ATP binds to myosin -> myosin releases actin

2) myosin ATPase hydrolyzes and ATP -> ADP & phosphate -> myosin head rotates & binds to actin (cocked)

3) actin moved towards M line (powerstroke)

4) myosin releases APD & myosin and actin bind

can cross bridges form when ATP is bound to myosin

no

what happens to myosin and actin when ATP binds to myosin

- any existing cross bridges are broken

why does ATP turn into ADP when attached to myosin

- myosin head enzymatic and hydrolyzes it

do ADP and phosphate stay bonded to myosin even after they are hydrolyzed

yes

what do the ADP and phosphate do the to the myosin head

- causes it to twist in a high energy conformation and binds to actin

- cocked confirmation (similar to cocked gun)

what happens after myosin twists and attaches to actin

the phosphate is released which allows for the myosin head to stay bound, but then it untwists to a low energy state -> pulls actin closer to the center of the M-line

when can muscle contraction repeat

when calcium level in the cell stays high

what is rigor mortis

regulation of muscle contraction is broken down -> stiffening of muscles after death (partial contraction)

what are the two causes of rigor mortis

1: body stops producing ATP

- ATP is what breaks the cross bridges between myosin and actin (body is stuck in the position it was in)

2: calcium that is normally compartmentalized in the sarcoplasmic reticulum gets released into the cytosol which allows for new cross bridges

how long does it take for muscle proteins to break down and relax after death

48-72 hours

what happens to concentration gradient and membrane potential if there is no ATP

- concentration gradient breaks down

- membrane potential depolarizes

how long does rigor mortis usually last

between 18 and 36 hours (depending on condition)

what causes rigor mortis to stop

tissues begin to break down

- actin and myosin get degraded and their bonds are broken

why is rigor mortis important to forensic scientists

they can see how long a person has been dead based on its state of rigor mortis

what is the body farm at the University of Tennessee

placed dead bodies in all sorts of environmental conditions

- study time course of rigor mortis and accounts for every possible scenario that a medical examiner could encounter at a crime scene

- gives them a standard to compare it to

what is the issue with refrigerating meat? what is done to preserve meat to eat?

- myocytes contract in response to cold temperature

- electrical pulses prevent cold shortening at high voltage which depletes the muscle fiber of calcium

what is needed for the muscle fiber to release calcium

needs to fire an action potential