IMAT Biology Lesson 6.10 | Anatomy and Physiology | Muscle Contraction

Summary

This video from Med School EU delves into the skeletal system, focusing on the innervation of skeletal muscles by the nervous system. It covers muscle anatomy, including striations due to myosin and actin filaments, and physiology, particularly the sliding filament model of muscle contraction. The lecture explains the role of the sarcomere, sarcolemma, T tubules, and sarcoplasmic reticulum in muscle function. It also discusses the neuromuscular junction's role in initiating muscle contractions and the sources of ATP for muscle activity, including creatine phosphate, aerobic respiration, and lactate fermentation.

Takeaways

• 📚 The lecture focuses on the skeletal system, specifically the innervation of skeletal muscles by the nervous system and the anatomy and physiology of muscle contraction.
• 💪 Skeletal muscles are composed of striated muscle fibers, characterized by the presence of thick and thin filaments made up of myosin and actin, respectively.
• 🔬 The structure of a muscle fiber includes A, I, and M bands, and Z lines, which are crucial for defining the sarcomere, the basic contractile unit of muscle tissue.
• 🔍 Under a light microscope, the striations of skeletal muscle are visible due to the arrangement of thick and thin filaments, which are essential for muscle contraction.
• 🏋️‍♂️ Muscle contraction occurs through the sliding filament model, where thin filaments slide over thick filaments, causing the Z lines to move closer together.
• 🔄 The M line remains constant during contraction, while the A band and I band undergo changes in size, reflecting the movement of actin filaments towards the myosin filaments.
• 🌐 The sarcolemma, a cell surface membrane, plays a key role in muscle contraction, along with the T tubules and sarcoplasmic reticulum, which are involved in the propagation of action potentials and calcium release.
• 🚀 The neuromuscular junction is where the neuron communicates with the muscle fiber, initiating muscle contraction through the release of acetylcholine, which triggers action potentials in the muscle.
• 🔑 Calcium ions are pivotal in muscle contraction, as their release from the sarcoplasmic reticulum and binding to troponin cause a conformational change that enables myosin to bind with actin.
• ⚡ ATP is essential for muscle contraction, but its role is to terminate each contraction cycle by facilitating the release of myosin heads from actin, not to activate the contraction itself.
• 🔄 ATP supply for muscle contraction comes from various sources, including creatine phosphate for immediate contraction, stored ATP, aerobic respiration in the mitochondria, and lactate fermentation.

Q & A

What is the primary focus of the lecture in the provided script?

The lecture primarily focuses on the skeletal system, specifically discussing the anatomy and physiology of muscle innervation and contraction.

What are striations in skeletal muscle, and what causes them?

Striations in skeletal muscle are the banded patterns visible under a light microscope, caused by the arrangement of thick and thin filaments composed of myosin and actin, respectively.

What are the main components of the thick and thin filaments in skeletal muscle?

The thick filaments are primarily composed of myosin, while the thin filaments are mainly composed of actin.

What is the role of the Z line in skeletal muscle structure?

The Z line is important as it marks the sarcomere, which is the contractile unit of muscle, and it holds the thin filaments together.

What happens to the sarcomere during muscle contraction?

During muscle contraction, the sarcomere shortens as the Z lines move closer together, and the actin filaments slide over the myosin filaments.

What is the sliding filament model, and how does it explain muscle contraction?

The sliding filament model describes the process of muscle contraction where the thin actin filaments slide over the thick myosin filaments, pulling the Z lines closer and causing the muscle to contract.

What is the role of the sarcolemma in muscle fibers?

The sarcolemma is the cell surface membrane of muscle fibers that covers them and has T tubules, which are important for muscle contraction.

What is the function of the T tubules and sarcoplasmic reticulum in muscle contraction?

The T tubules are involved in the transmission of the action potential from the sarcolemma to the interior of the muscle fiber, while the sarcoplasmic reticulum releases calcium ions necessary for muscle contraction.

How does the neuromuscular junction facilitate muscle contraction?

The neuromuscular junction is where the motor neuron binds to the sarcolemma, releasing acetylcholine that triggers action potentials in the muscle, leading to contraction.

What are the sources of ATP for muscle contraction, and how do they differ based on the type of activity?

ATP for muscle contraction comes from creatine phosphate for immediate contraction, stored ATP for short-duration activities, aerobic respiration for sustained activities, and lactate fermentation for high-intensity, short-duration activities.

How does the calcium cycle within the sarcoplasmic reticulum contribute to muscle contraction and relaxation?

Calcium is released from the sarcoplasmic reticulum during contraction to facilitate the binding of myosin to actin. After contraction, calcium is actively transported back into the sarcoplasmic reticulum, allowing the muscle to relax.

Outlines

00:00

💪 Anatomy and Physiology of Skeletal Muscle

This paragraph introduces the lecture on the skeletal system, focusing on the innervation of skeletal muscles by the nervous system. It delves into the anatomy of striated muscle, explaining the structure of thick and thin filaments composed of myosin and actin, respectively. The concept of striations is explored, and the role of the Z line in defining sarcomeres, the contractile units of muscle, is highlighted. The paragraph also explains the sliding filament model of muscle contraction, detailing the changes in the A band, I band, Z line, and H band during contraction.

05:02

🔬 The Sliding Filament Model and Muscle Fiber Bundles

This section expands on the sliding filament model of muscle contraction, discussing the role of T tubules and the sarcoplasmic reticulum (SR) in the process. It describes the structure of a muscle fiber bundle, including the sarcolemma, and explains how action potentials from the brain or spine are received and transmitted. The paragraph also covers the role of troponin and tropomyosin in muscle contraction and relaxation, and the importance of ATP in the muscle contraction cycle.

10:04

🚀 Neuromuscular Junction and Calcium's Role in Contraction

The paragraph discusses the neuromuscular junction, where neurons bind to the sarcolemma and initiate muscle contraction through the release of acetylcholine. It explains how the action potential travels along the sarcolemma and down the T tubules, triggering the release of calcium from the SR. The influx of calcium ions causes a conformational change in troponin, allowing myosin heads to bind with actin and initiate contraction. The paragraph also touches on the refractory period and the recycling of calcium for subsequent contractions.

15:05

🔄 ATP Supply and Muscle Contraction Mechanisms

This paragraph focuses on the sources of ATP that power muscle contractions. It explains the immediate use of creatine phosphate for the first contraction, the role of stored ATP, and the subsequent reliance on aerobic respiration in the mitochondria for sustained activity. The paragraph also mentions lactate fermentation as a source of ATP, particularly relevant for short-duration, high-intensity activities. It concludes by emphasizing the coordinated and rapid nature of muscle contraction due to the swift movement of electrical stimuli.

20:06

👀 Upcoming Lecture on the Anatomy and Physiology of the Eye

The final paragraph teases the next lecture in the series, which will cover the anatomy and physiology of the eye. While it does not provide specific details about the content, it signals a continuation of the comprehensive approach to understanding the human body, moving from the skeletal system to the intricacies of the visual system.

Keywords

💡Skeletal System

The skeletal system is the framework of bones in the body that supports and protects the various organs and provides attachment points for muscles. In the context of the video, the focus is on the skeletal muscles and how they are innervated by the nervous system, which is essential for movement and posture.

💡Striated Muscle

Striated muscle, also known as skeletal muscle, is characterized by its striped or banded appearance under a microscope due to the arrangement of thick and thin filaments. The script discusses striations as a key feature of skeletal muscle, which are important for muscle contraction and the sliding filament model.

💡Myosin

Myosin is a protein that forms the thick filaments in muscle fibers. It plays a crucial role in muscle contraction by interacting with actin, the protein that forms the thin filaments. The script explains that myosin is responsible for the formation of the A band in the sarcomere, which is central to the sliding filament model of muscle contraction.

💡Actin

Actin is a globular protein that forms the thin filaments in muscle fibers. It is essential for muscle contraction as it interacts with myosin to produce movement. In the script, actin is described as being part of the I band and is involved in the sliding process during muscle contraction.

💡Sarcomere

A sarcomere is the functional unit of muscle contraction, extending from one Z line to the next. It includes the A band, I band, and H zone, and is where the sliding of actin and myosin filaments occurs. The script describes the sarcomere as the basic unit of contraction in skeletal muscle.

💡Z Line

The Z line, also known as the Z disc, is a protein structure that anchors the thin actin filaments and marks the boundary of a sarcomere. The script explains that the Z line is crucial for defining the sarcomere and changes in its position are indicative of muscle contraction.

💡M Line

The M line is a structure in the middle of the A band where the myosin filaments are anchored. It plays a role in maintaining the integrity of the sarcomere during contraction. The script mentions the M line as a constant structure during muscle contraction.

💡Sliding Filament Model

The sliding filament model is the mechanism by which muscle contraction occurs. It describes the process where the actin filaments slide over the myosin filaments, pulling the Z lines closer together and causing the muscle to contract. The script provides a detailed explanation of this model as the primary method of muscle contraction.

💡Neuromuscular Junction

The neuromuscular junction is the connection between a motor neuron and a muscle fiber. It is where the electrical signal from the neuron is transmitted to the muscle, initiating contraction. The script describes the process of how an action potential at the neuromuscular junction leads to the release of acetylcholine and subsequent muscle contraction.

💡Sarcoplasmic Reticulum (SR)

The sarcoplasmic reticulum is a network of membranous sacs within muscle cells that store and release calcium ions. It plays a critical role in muscle contraction by releasing calcium in response to an action potential, which then triggers the interaction between actin and myosin. The script explains the SR's role in the release and reuptake of calcium during muscle contraction.

💡ATP

ATP, or adenosine triphosphate, is the primary energy currency of the cell and is essential for muscle contraction. It provides the energy needed for the myosin heads to detach from the actin filaments, allowing the cycle of contraction to continue. The script discusses ATP's role in terminating muscle contraction and its supply through creatine phosphate, aerobic respiration, and lactate fermentation.

Highlights

Introduction to the skeletal system lecture focusing on skeletal muscle innervation by the nervous system.

Explanation of striated muscle structure, highlighting the roles of myosin in thick filaments and actin in thin filaments.

Description of sarcomere as the contractile unit of muscle, marked by Z lines and M lines.

Muscle contraction process explained through the sliding filament model.

Details on how the I band shrinks and Z lines move closer during muscle contraction.

Importance of the sarcolemma and T tubules in muscle contraction physiology.

Role of the sarcoplasmic reticulum (SR) in calcium release for muscle activation.

ATP's role in muscle contraction, specifically its use in disconnecting myosin heads from actin.

Neuromuscular junction's function in transmitting signals from the brain or spine to activate muscles.

Acetylcholine's role in binding to receptors at the motor plate, initiating muscle action potentials.

Calcium's function in changing troponin shape to enable myosin binding with actin during contraction.

ATP's indirect role in activating muscle contraction by facilitating the release of myosin heads.

Creatine phosphate's contribution to immediate muscle contraction and its conversion to ATP.

Aerobic respiration's role in sustained muscle contractions, especially in long-duration activities.

Lactate fermentation as a source of ATP for high-intensity, short-duration activities.

Different energy sources for muscle contractions based on activity duration and intensity.

Conclusion of the lecture with a summary of muscle contraction mechanisms and energy sources.

Transcripts

[Music]

hi everyone my name is andre and welcome

to med school eu in today's lecture we

are going to discuss the skeletal system

so we are primarily going to talk about

how skeletal muscle is innervated

by the nervous system so we will discuss

the anatomy and physiology of muscle

innervation

the first thing we must talk about is

the skeletal muscle anatomy so we're

going to go over striated muscle and the

structure of it so that you get a good

understanding of the anatomy before we

learn the physiology of muscle

contraction

and the the first thing i wanted to

discuss here is going to be the

striations what depicts striations what

makes up striations and why does a

skeletal muscle look this way if we look

under the light microscope

well that is primarily because there are

thick and thin filaments so these thick

filaments are made up primarily of

meiosin

and the thin filaments are going to be

made up primarily of

actin

and

it is depicted in this diagram so if we

were to take

a side view of a muscle fiber this

would be the muscle fiber if we take the

side view the thick filaments are

represented by the a band right here

and the thin filaments so actin

represented by i band now these lines

that connect

the actin so the thin filaments that

holds the thin filaments together the

two sides of the thin filaments it's

called the z line

and the z line is very important because

it is the way we mark

the sarco sarcomere and the sarcomere is

the

unit of is a contractile unit

so

here it would be labeled as sarcomere

that's going from the z line to the next

z line each z line represents a

sarcomere so the distance between the

two z lines

is the distance and the length of the

sarcomere now another line that would be

important here as well is the m line

and this line is the middle

of

the

myosin connection so the thick filament

is connected through

the m line and

the same thing is here so if we're

looking at the different diagram

depiction we've got m line

right here right down in the middle of

the thick filament these are obviously

actin filaments

and these are myosin filaments

and

the way that contraction happens is the

thin filaments are going to slide over

the thick filaments

in this

orientation

and they will close in and make

things shorter so let's discuss what

actually gets smaller

when a contraction occurs when we're

talking about muscle contraction in

essence

what's going to happen

is everything is going to shrink

everything is going to contract and get

shorter

and so you will see these z lines are

not going to be

so far apart they will actually move

closer together

in this

orientation

and they will move closer together

because the muscle is contracting and

the actin is sliding against the myosin

so myosin is going to stay there m line

will stay constant

the h band will be smaller because the

thin filaments are going to move in more

probably towards something

like this over here so they're going to

move all the way in

closer to the m line

so if we were to talk about

like a summary of what occurs

is we would basically have

the m line is going to remain constant

the a band

will be

constant the i band

is going to shrink so it'll get smaller

z lines

will move

closer

to

the m

lines

finally the h band is also going to

shrink just like the eye band so this is

just a basic summary of contraction of

skeletal muscle and what happens

to the sarcomere and sarcomere is

basically just a

point of the measurement of a single

unit of a contractile muscle so if we

were to take contractile unit that is

able to contract the smallest one you

would be able to detect is going to be

the sarcomere and based on that

depiction

these will be the changes observed when

you have a contraction of the muscle

now if we just kind of zoom out of the

muscle because of course it's not simply

depicted by the muscle fiber but all of

these muscle fibers will be composed

together into a muscle fiber bundle

and so there will be multiple muscle

fibers that are covered under a single

cell surface membrane the cell surface

membrane is

going to be called the sarcolemma now of

course this would be the mitochondrion

now if we're looking at the sarcolemma

it's going to have these little holes

sticking out that is going to continue

on downwards inside of the muscle fiber

or going around it

now that's going to be the entrance to

the t tubule

and you will see that the t tubule is

going to be very important

in terms of muscle contraction and we're

going to go over the physiology

of that as well

and also the uh this little mesh in

between the t tubules

that's going to be called the

sarcoplasmic reticulum

the

so we're going to depict it as sr

and so this muscle fiber if we were to

make a full circle of it

it would of course have multiple

of these units and these units are going

to be called myofibril

so what we noted previously is that the

sarcomeres in each myofibril will get

shorter as the z discs are pulled closer

together towards the m line now this

diagram is going to show how this

happens if we are to zoom in

on the muscle contraction

and

it is known this entire mechanism is

known as the sliding filament model and

the sliding filament model is what's

typically used to teach a muscle

contraction and how it is

depicted in its physiology so let's

discuss that in greater detail first of

all let's label a lot of this

anatomy that we have to go through in

order to provide

a better understanding of the physiology

so here we have the m line right and

right through the middle we talked about

this before

now all of these little

balls right here

are going to be actin molecules so

that's

actin now this this one right here

that's right around the act and it's

wrapped all around it it's called

troponin finally this long one is going

to be called the tropomyosin

and so the first thing that occurs right

here

is when a muscle's relaxed the

tropomyosin and the troponin are sitting

in a position in the actin filament that

prevents meiosine from binding so as you

can see if we're zooming in on this

actin right here

we could see that during a relaxation

period when the muscle is not

contracting the tropomyosin and the

troponin are going to be in positions

where it blocks the binding of the

myosin

head the troponin and the tropomyosin

right here in the second stage

are going to change shape and allow

meiosin so this is the meiosin head

they're going to allow this meiosis and

head to bind with the actin and attach

to it so as you can see here the

attachment

occurs all along the actins now if we're

looking at the next stage of the sliding

filament

model and this comes into play to

actually understanding what the sliding

filament represents is because now

the meiosin head is going to pull

the actin to the left side so from here

it's going to pull to the left from here

it's going to pull to the right

pulling the thin filaments towards the m

line and the z lines are going to come

closer together

and this occurs as the meiosine head

tilts

and pulling the actin in those

directions and finally the last thing

that occurs part 4

is that atp is hydrolyzed so we're going

to have atp

hydrolysis

and this atp hydrolysis causes the

release

of myosin heads that spring back and

repeat the binding

and the tilting process so this keeps

going as a cycle

and then it will begin right at the

start

each time and so atp a lot there's a lot

of misconception here is that atp is

used

in order to cause the muscle contraction

and

that is inherently not true i mean

indirectly it is true but

what is atp used for the hydrolysis of

atp is used to

disconnect the myosin head with the

actin so it's used to terminate

each muscle

contraction it is not used to activate

it and what's used to activate it we are

going to describe

in the next slide because there's quite

a bit of physiology involved with that

and this leads us to the discussion

about the neuromuscular

junction

and so here we have a lovely depiction

of

what's going on

in terms of the neurons so this would be

the neuron binding

on to the sarcolemma so this is the

muscle fiber

cell

membrane

and the sarcolemma is going to have of

course these bindings along with the

neurons in order to

receive impulses from the brain or the

the spine in order to activate the

skeletal muscle

and how this occurs is very similar to

what we saw with the connection between

two neurons in our last lecture at the

neuromuscular junction this is a

neuromuscular so there's a muscle

involved on the receiving end

in this junction we have a little bit of

further physiology to deal with so we're

going to discuss that however the

beginning of it is going to be exactly

the same the signal is going to come in

through the axon so the electrical

stimuli there's going to be action

potential

that will be occurring throughout the

neuron once it reaches its terminal ends

it's going to get the

calcium inside

the cell so calcium two plus is going to

enter inside the cell and is gonna cause

a release of the

neurotransmitter

acetylcholine and so what it's gonna do

is it's gonna

go over and bind with the membranes here

and it's going to release

its acetylcholine that will be

a ch

so the acetylcholine will then be

released all over the synaptic cleft

and it binds to receptors in the motor

and plate so this

all of this right here is called the

motor

and plate and this motor and plate is

the mechanism that triggers

action potentials inside the muscle and

we're going to talk about that so these

little acetylcholines are going to bind

to the receptors here and again these

are ligand

gated receptors we've discussed this

previously because they are gated by

chemicals so

again if acetylcholine is released it is

going to be activated

and what it's going to do is the action

potential is going to propagate along

the sarcolemma

and down the t tubules so how does it

happen well there's going to be an

influx of positive charges with n a

plus

and this occurs throughout the motor end

plate

and this continues to occur

all over here because the signal is

going to continue to travel this way

and so the sodiums are going to continue

to depolarize the membrane and they're

going to continue to make the membrane

more positive

and that will continue to create action

potentials all along the sarcolemma and

eventually it will head down the t

tubule as well so this

is the t tubule here and this right here

is the sr sarcoplasmic

reticulum so once the signal heads down

the t tubule what's going to happen is

it's going to the action potential will

trigger calcium release

from the sarcoplasmic reticulum

and so we're going to have this calcium

released all over from

the sarcoplasmic reticulum

from both sides here

because this the signal went down

the t tubule and it causes the opening

of the calcium

channels and so now there's going to be

all this

influx of calcium two plus

in essence the calcium two plus from the

sarcoplasmic reticulum that is released

due to the action potential will now

travel

to the troponin

and the troponin so if we were to label

let's say troponin would be right here

the troponin would then change its shape

because of the release of the calcium

and now the meiosis and heads are going

to bind and make a binding with the

actin because the troponin will then

cause tropomyosin

to remove its blockage of the meiosis

head and now it's going to be bonded it

will then

do its cross-bridge cycling so that the

muscle fiber will contract

and then again it's going to bring back

and it's going to go back to its

original shape because atp will cause

the breakage of these bonds and what

occurs next is that the tropomyosin

blocks meiosis mining sites because atp

was released

and then what happens to all of these

calcium channels is that they're going

to open on this side

of the sarcoplasmic reticulum and now

all of the calcium will then be brought

back

into sarcoplasmic reticulum for another

cycle of

contraction and of course this occurs

all over

the entire muscle so the entire muscle

is going to contract

extremely quickly because of this

movement of electrical stimuli the

action potential and it's going to move

and depolarize the membranes extremely

fast almost simultaneously

and so the contraction will be very

coordinated

because of that

as type of stimulation but the important

thing to note here is that the calcium

is actively going to be transported

back into the sarcoplasmic reticulum by

these calcium transport pumps so the

transport pumps are typically going to

be closed but as soon as atp binds

and

forces the

dismissal of myosin head from actin

then it's going to open these calcium

channels

that the active channels to push the

calcium back into cycloplasmic reticulum

and basically be ready for the next

contraction that's going to be the

refractory period between one

contraction

and the next is this recycling of

calcium and finally the last thing i

wanted to discuss

is going to be the way

that atp is supplied for muscle

contraction so we are going to have atp

readily available inside the muscle

ready to go as soon as we like and

that's going to be due to

creatine

phosphate so that first contraction that

first immediate contraction is going to

happen due to the creatine phosphate

that will provide the extra phosphate in

order for

the atp to be formed and provide the

initial contraction or provide the

disengagement of myosin from the actin

because without it the contraction would

not typically

proceed uh the next major source so

that's that's going to be uh one source

another source is just straight atp that

would be stored but this is going to be

in very

low amounts typically the first

contraction the first couple of forceful

contractions

are going to be done by

the creatine phosphate that will create

atp

and typically within about 30 seconds or

so

of activity

is when the aerobic

respiration will come in with the

mitochondria is producing a whole lot

of

atp so that's going to be done by

aerobic

respiration and the final asset of atp

is going to be made by lactate

fermentation so if you would like to go

ahead and review these two units we

talked about in cellular

respiration we talked about the lactate

fermentation how it happens and why it

happens as well as the aerobic

respiration when the

pyruvates actually enter into the

mitochondria and they proceed to make a

whole lot of atp and so typically if you

are a long distance runner you would be

relying on the aerobic respiration

whereas if you're somebody like usain

bolt you would be relying more on the

creatine phosphate supply because

the duration of your activity is about

10 seconds long and therefore you're not

going to be using your aerobic

respiration

supplies

because your the length of your activity

will not be reached by that time

however if you're running a marathon

then of course aerobic respiration and

lactate fermentation are the two main

sources

of atp for your muscles in order to

continuously cycle through

the muscle contraction this concludes

our video and our unit on the muscle

and the skeletal system and in the next

video we are going to talk about more

anatomy of the body and more

particularly we will discuss the anatomy

and the physiology of the eye

[Music]

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