Muscle Tissue | Skeletal, Cardiac, and Smooth

Summary

In this educational video, Dr. Mike explains the three muscle types in the human body: skeletal, cardiac, and smooth. He compares their functions, structures, and how they contract. Skeletal muscles enable voluntary movement, cardiac muscles control the heartbeat involuntarily, and smooth muscles move substances through organs like the digestive system. He delves into their microscopic structures, explaining the differences in their nuclei, appearance, and striations. Dr. Mike also highlights how cardiac and smooth muscles work without conscious control, contrasting them with the voluntary actions of skeletal muscles.

Takeaways

• 💪 Muscle tissue is one of the four body tissues and is responsible for mechanical work, allowing movement, blood flow, and substance transport.
• ⚡ Muscles are excitable tissues, meaning they can be stimulated to perform an action like contraction.
• 🧠 Skeletal muscle is voluntary, meaning we consciously control it, while cardiac and smooth muscles are involuntary and work automatically.
• 🧬 Skeletal muscle cells are cylindrical and multinucleated, while cardiac muscle cells are branched and uni/binucleated, and smooth muscle cells are spindle-shaped and uninucleated.
• 🏋️ Skeletal muscle has the greatest capacity for growth (hypertrophy) because of its multiple nuclei, which allows for efficient protein synthesis.
• 🔍 Skeletal and cardiac muscles are striated, showing stripe-like patterns due to the arrangement of actin and myosin filaments. Smooth muscle lacks these striations.
• 🔗 Cardiac muscle cells are connected by intercalated discs and gap junctions, allowing for coordinated contractions across the heart muscle.
• 🩸 Smooth muscle contracts in multiple directions to help move substances through hollow organs, such as the digestive tract and blood vessels.
• 🧩 Sarcomeres are the smallest contractile units in skeletal and cardiac muscle, where myosin heads bind to actin to facilitate contraction.
• 🫀 Cardiac muscle contracts as a unit, with electrical signals spreading through gap junctions, enabling the heart to beat in a coordinated manner.

Q & A

What are the three different types of muscle tissue in the body?

The three types of muscle tissue are skeletal muscle, cardiac muscle, and smooth muscle.

What is the primary function of muscle tissue?

The primary function of muscle tissue is to perform mechanical work, which allows for movement of the body, blood flow, and movement of substances through organs like the digestive and reproductive systems.

What does it mean for muscle tissue to be 'excitable'?

Excitable tissue can respond to stimuli. For muscle tissue, this means it can be excited to contract when stimulated, helping to move the body, pump blood, or push substances through organs.

What distinguishes skeletal muscle from cardiac and smooth muscle in terms of control?

Skeletal muscle is under voluntary control, meaning we consciously move it, while cardiac and smooth muscle are involuntary, functioning without conscious effort.

How do the shapes of skeletal, cardiac, and smooth muscle cells differ?

Skeletal muscle cells are cylindrical, cardiac muscle cells are branched, and smooth muscle cells are spindle-shaped.

Why does skeletal muscle have multiple nuclei, while cardiac and smooth muscle cells have fewer?

Skeletal muscle is multinucleated to support greater capacity for growth and protein synthesis, which is important for hypertrophy (muscle growth). Cardiac muscle has one or two nuclei, and smooth muscle has only one nucleus due to their lower capacity for growth.

What are striations, and which muscle types have them?

Striations are stripe-like patterns seen under a microscope, created by the arrangement of actin and myosin filaments. Both skeletal and cardiac muscles have striations, while smooth muscle does not.

What is the role of actin and myosin in muscle contraction?

Actin and myosin are proteins that interact during muscle contraction. Myosin binds to actin and pulls on it, shortening the muscle fibers and creating contraction.

How does the arrangement of actin and myosin differ between smooth muscle and the other two muscle types?

In skeletal and cardiac muscle, actin and myosin are arranged in parallel, allowing for uniform contraction. In smooth muscle, they are arranged in a more random, criss-cross pattern, allowing the muscle to contract in multiple directions.

How do cardiac muscle cells communicate with each other during contraction?

Cardiac muscle cells are connected by intercalated discs, which contain gap junctions that allow electrical signals to pass from cell to cell. This enables the entire heart to contract in unison during a heartbeat.

Outlines

00:00

💪 Introduction to Muscle Types and Functions

Dr. Mike introduces the three types of muscle tissue—skeletal, cardiac, and smooth—and their functions. He explains that muscle tissue is excitable and plays a key role in movement, whether it's conscious movement of the body, involuntary movement in the heart, or movement of substances in internal organs like the digestive system. Muscles contract when excited, and different muscle types are responsible for various movements in the body.

05:03

🦴 Skeletal Muscle: Structure and Function

Dr. Mike describes skeletal muscle as attached to the skeleton, allowing for voluntary movement. He uses the example of the biceps brachii to show how skeletal muscle contraction results in joint movement. Skeletal muscle is consciously controlled (voluntary) and has a cylindrical structure under a microscope. It is also multi-nucleated, meaning it has many nuclei, giving it a high capacity for growth, or hypertrophy.

10:03

❤️ Cardiac Muscle: Involuntary but Essential

Cardiac muscle, responsible for pumping blood, contracts involuntarily. Dr. Mike highlights the importance of this feature, as conscious control over heartbeats would be exhausting. Cardiac muscle is branched, has one or two nuclei (uni- or binucleated), and also shows striations similar to skeletal muscle. This muscle type doesn't have the same hypertrophy potential as skeletal muscle.

15:04

🌀 Smooth Muscle: Structure and Function in Organ Systems

Smooth muscle, found in the digestive, urinary, reproductive tracts, and blood vessels, contracts involuntarily and lacks striations, appearing smooth under the microscope. It has a spindle-shaped structure and only one nucleus (uninucleated). Its unique arrangement allows for contractions in multiple directions, which is vital for processes like peristalsis, moving substances through the body.

🔬 Striations and Sarcomeres: Muscle Contraction Mechanics

Dr. Mike explains how striations in skeletal and cardiac muscles are due to the arrangement of myosin and actin filaments. These proteins overlap and form sarcomeres, the smallest contractile units of muscle. Myosin heads bind to actin and move along it, shortening the muscle and causing contraction. This organized structure is key for the efficient function of these muscle types.

🧬 Muscle Growth and Hypertrophy

Skeletal muscle's capacity for growth (hypertrophy) is tied to its multi-nucleated structure. More nuclei allow for more protein synthesis, essential for muscle repair and growth. When skeletal muscle is stressed during exercise, growth factors are released, leading to increased protein production and muscle growth. In contrast, cardiac and smooth muscles have less capacity for hypertrophy due to their fewer nuclei.

⚙️ Communication Between Muscle Cells

Dr. Mike describes how muscle cells, especially cardiac muscle, communicate through structures like gap junctions and intercalated discs. In cardiac muscle, electrical signals spread quickly, causing synchronized contractions (a process known as syncytium). This communication ensures that the heart contracts as a unified organ. Skeletal muscle, however, requires individual nerve signals for each cell, while smooth muscle cells contract in a coordinated manner due to their structural organization.

🌀 Peristalsis and Smooth Muscle Contraction

Smooth muscle's ability to contract in multiple directions is vital for moving substances through hollow organs. Dr. Mike compares this action to squeezing a tennis ball through a stocking, where the muscle shortens the tube and narrows its diameter. This process, known as peristalsis, allows smooth muscle to propel substances through organs like the intestines or blood vessels.

🔗 Structural Differences Between Muscle Types

Dr. Mike concludes by summarizing the structural differences between the three muscle types. Skeletal muscle cells are arranged in parallel for efficient shortening during contraction. Cardiac muscle cells, due to their branching and gap junctions, work together to contract the heart in unison. Smooth muscle cells, arranged in a mishmash pattern, contract in various directions to facilitate movement through tubular organs.

📚 Recap and Social Media Outro

Dr. Mike wraps up the video by reviewing the main differences between skeletal, cardiac, and smooth muscles, emphasizing their functions, structures, and the types of movement they control. He encourages viewers to follow him on social media for more educational content and invites them to like and subscribe to his channel for future videos.

Keywords

💡Skeletal Muscle

Skeletal muscle is a type of muscle tissue that is attached to bones and is responsible for voluntary movement. In the video, it is explained that skeletal muscles contract to move parts of the skeleton, such as in the example of the biceps brachii, which flexes the elbow and shoulder joints. This type of muscle is consciously controlled and has the unique ability to grow (hypertrophy) due to its multinucleated cells.

💡Cardiac Muscle

Cardiac muscle is the type of muscle tissue found in the heart. It is responsible for involuntary contraction that allows the heart to pump blood throughout the body. The video highlights that cardiac muscle cells are branched and connected through intercalated discs, enabling synchronized contraction of the heart. Unlike skeletal muscle, it is not controlled consciously, which is vital for continuous heart function.

💡Smooth Muscle

Smooth muscle is a type of involuntary muscle found in the walls of hollow organs such as the digestive tract, blood vessels, and the urinary system. In the video, it is explained that smooth muscle contracts in multiple directions to move substances through these organs, such as food through the digestive system or blood through vessels. It lacks striations (unlike skeletal and cardiac muscle), giving it a 'smooth' appearance under a microscope.

💡Voluntary Movement

Voluntary movement refers to muscle actions that are consciously controlled by the individual. In the video, this term is associated with skeletal muscle, which enables movements like walking, lifting, or bending joints. The ability to consciously decide when to contract these muscles differentiates them from the involuntary movements controlled by cardiac and smooth muscles.

💡Involuntary Movement

Involuntary movement is the automatic and unconscious contraction of muscles, as seen in cardiac and smooth muscle. The video emphasizes how cardiac muscle contracts involuntarily to pump blood, and smooth muscle contracts involuntarily to move substances through the digestive and urinary tracts. This action is crucial for bodily functions that require constant operation without conscious thought, such as heartbeats and digestion.

💡Striations

Striations are the visible stripes seen in skeletal and cardiac muscles under a microscope, caused by the regular arrangement of actin and myosin filaments. The video explains that these striations are not found in smooth muscle, which lacks this organized structure. Striations are a key feature that helps distinguish muscle types and relate to the mechanical function of muscle contraction.

💡Hypertrophy

Hypertrophy refers to the growth of muscle tissue, particularly skeletal muscle, in response to stress or resistance (such as weightlifting). The video explains that skeletal muscle can grow because it is multinucleated, which increases its capacity for protein synthesis. This process allows muscles to increase in size and strength as they adapt to physical demands.

💡Intercalated Discs

Intercalated discs are specialized structures in cardiac muscle that connect individual muscle cells. The video highlights their importance in facilitating synchronized contraction of the heart by allowing electrical signals to pass between cells. This structural feature ensures that the heart contracts as a unified organ, pumping blood efficiently.

💡Gap Junctions

Gap junctions are channels that allow communication between neighboring cardiac muscle cells. In the video, it is explained that these junctions enable the electrical signals responsible for heartbeats to pass from one cell to another, ensuring coordinated contraction. They play a critical role in the heart's ability to function as a single unit during each contraction cycle.

💡Sarcomere

A sarcomere is the basic contractile unit of muscle fibers, composed of actin and myosin proteins. The video describes how these proteins interact to produce muscle contraction. In skeletal and cardiac muscle, the sarcomeres are arranged in series and parallel, creating striations and allowing for the powerful, coordinated contractions necessary for movement and heart function.

Highlights

Introduction of the three types of muscle tissue: skeletal, cardiac, and smooth muscle.

Muscle tissue is one of the four primary tissues of the body, alongside epithelial, nervous, and connective tissue.

Muscle tissue performs mechanical work, enabling movement, blood circulation, and digestion.

Skeletal muscle is voluntary, allowing conscious movement, and is attached to the skeleton to facilitate locomotion.

Cardiac muscle is involuntary and responsible for the heart's rhythmic contractions, pumping blood through the body.

Smooth muscle is also involuntary and found in hollow organs, helping to move substances through the digestive, renal, and reproductive tracts.

Skeletal muscle fibers are cylindrical and multi-nucleated, which allows them to grow through hypertrophy.

Cardiac muscle fibers are branched and either uni- or bi-nucleated, with intercalated discs connecting the cells for synchronized contraction.

Smooth muscle fibers are spindle-shaped and uni-nucleated, lacking the ability to grow significantly due to their single nucleus.

Both skeletal and cardiac muscles are striated due to the arrangement of contractile proteins (actin and myosin).

Smooth muscle lacks striations because its contractile proteins are arranged in a more random, less structured fashion.

Skeletal muscle grows through hypertrophy by synthesizing more proteins in response to stress, which is facilitated by the many nuclei in its cells.

Cardiac muscle cells communicate through gap junctions, allowing for coordinated contraction throughout the heart muscle.

Smooth muscle cells contract in multiple directions, aiding in peristalsis, the movement of substances through tubes like the digestive tract.

The lecture concludes with an emphasis on the structural and functional differences between the three muscle types and how these adaptations suit their respective roles in the body.

Transcripts

hi everybody Dr Mike here in this video

we're taking a look at the three

different muscle types of the body

skeletal cardiac and smooth and we're

going to compare and contrast each of

them

[Music]

importantly we need to begin by talking

about what muscle tissue is it's one of

the four tissues of the body we've got

epithelial we've got nervous we've got

connective and we've got muscle tissue

and the job of muscle tissue is to

perform mechanical work it allows for us

to move whether it's to move our body

consciously whether it's to move the

blood into and out of the heart or

whether it's to move various substances

through our digestive tract our renal

system or our reproductive tract all of

this occurs because of muscles and

muscles are excitable tissue this is

really important for students to

understand excitable tissue there's only

a couple of different excitable tissue

types in the body you've got nervous

tissue endocrine tissue and muscle

tissue now a tissue being excitable

means it has the capacity to do

something it can be excited like me it

can do nothing but when it's excited

something happens so nervous tissue when

nothing's happened it doesn't fire any

signals off but it can be excited to

send what we call an action potential a

signal for communication the endocrine

system when these cells aren't doing

anything nothing's happening but they

can be excited to do something which is

to release hormones into the bloodstream

and muscle tissue when they're not doing

anything they just sit there but they

can be excited to contract and when

muscles contract and shorten they can

help move things around so if it's

skeletal muscle when this muscle

contracts it moves the skeleton and

allows for locomotion when cardiac

muscle contracts it decreases the volume

of these little cavities inside the

heart known as atra and ventricles and

pushes blood around the body and the

smooth muscle that lines the inside

hollow organs of our digestive tract our

renal tract and our reproductive tract

and also our blood vessels when they

contract they help push substances

through the body so that's really

important for you to understand let's

first begin with skeletal muscle

skeletal muscle is muscle that's

attached to our skeleton and generally

speaking these muscles cross joints for

example I've drawn up the biceps brachii

it crosses both the shoulder joint and

the elbow joint and when you excite

skeletal muscle to contract it will

shorten and if it shortens and it

shortens across joints those joints move

so

contract biceps brachii

I get elbow flexion I can track biceps

brachii I get shoulder flexion and this

is the result of skeletal muscle now all

skeletal muscle contracts consciously we

must write that down so it is conscious

let's say voluntary is a better one it's

voluntary

movement

voluntary movement now compare that to

something like cardiac right do you

consciously tell your heart to contract

no thank God we don't because imagine

how much mental time and energy it would

take to constantly tell our heart to

beat once every second it would be

horrible so cardiac muscle is

involuntary and like I said you should

be grateful for that smooth muscle this

is going to be the muscle that lines the

inside of our hollow organs like I said

a digestive tract so our esophagus our

stomach our small large intestines all

the way through and our urinary tract so

our ureters our bladder our urethra and

our reproductive tract and our blood

vessels as well this is all smooth

muscle again you don't tell this muscle

to contract so it contracts in

voluntarily

please

I'll just write involuntary like I did

for the other one so only one is

voluntary contraction that's skeletal

muscle I want you to think about what

these cells look like under a microscope

because it tells you a lot about their

function so if I were to draw up

skeletal muscle and see what it looks

like under a microscope what you'll find

for skeletal muscle is number one it's

shaped like a cylinder compare that to

cardiac muscle if I were to compare

cardiac muscle under a microscope what

you'll find is that it's branched

and then if I were to compare that to

smooth muscle under a microscope it

has this shape to it like a spindle

shape like an eye all right so that's

the first thing that's how they look

under the microscope quite different

than nuclei we must talk about the

nuclear because it's very important

particularly for skeletal muscle now the

nuclei we know houses DNA and if we look

at skeletal muscle you're actually going

to find that it is multi

nucleated multi-nuclear let's write this

down let's write down the fact that it

is

cylinder shaped

let's write down the fact that cardiac

is Branched

and write down that smooth muscle is

spindle shaped

and then let's write down that skeletal

muscle is multi

nucleated

has many nuclei

if we compare that to cardiac it's uni

or by nucleated and it's usually found

right in the center so let's write uni

or sometimes by nucleated

and then let's compare this to smooth

muscle which is uni nucleated

now again and it's sitting right in the

center

what's so important about look

the nuclei well it's really important

for skeletal muscle think why which of

these three muscles or muscle types do

you think has the capacity to grow most

hypertrophy is the term that we use for

muscle growth or tissue growth really

it's skeletal muscle you go to the gym

you lift weights the whole reason why

muscle grows or skeletal muscle grows is

because you expose it to stress and that

stress is a heavy load and that muscle

goes this is difficult I don't want it

to be this difficult next time so I'm

going to release growth factors and I'm

going to stimulate the synthesis of more

proteins to allow for muscle contraction

to occur we know that proteins are made

from the DNA in our nuclei DNA gets

transcribed into RNA RNA gets translated

into amino acids which fold into

proteins and proteins can be used for

contraction and growth and that's what

happens with skeletal muscle so the more

nuclei the more capacity you have for

hypertrophy and growth and that's why

skeletal muscle has so many nuclei our

heart has less of a capacity hence why

it's uni or binucleated and as smooth

Muscle really doesn't have the capacity

for hypertrophy hence why it's only

uni-nucleated let's talk a little bit

about their appearance as well because

what you're going to find is down the

microscope skeletal muscle

has these Stripes like these tiger

looking Stripes to it so does cardiac

cardiac has these Stripes as well

we call these Stripes striations so

let's write this down so this is

striated

skeletal muscle this is also striated

this is cardiac muscle but smooth muscle

now this is where the name comes from

right skeletal muscle makes sense it's

attached to the skeleton cardiac muscles

easy It lines the ventricles and atria

of our heart smooth muscle tells you

nothing about where it is but about what

it looks like under the microscope

smooth muscle looks smooth it does not

have those striations so let's write

this down let's write striations

and then let's put a

cross through it no striations what are

these striations these striations are

the protein

microfilaments that allow for

contraction to occur so if I were to

take either cardiac sorry cardiac or

skeletal and have a look at it in a bit

more detail it's going to look a little

bit like this

you're going to have two major types of

proteins you're going to have

what's called myosin

and this myosin has these little Golf

Club looking heads to them like this

these little arms and golf club looking

heads

and they need to bind to the second

protein and that second protein is

called actin so let's draw up some actin

so here's some actin

now we're going to have these things

called Z discs over here

and what was actually what we've

actually just drawn up here is what we

call a sarcomere so this actual thing

here called a sarcomere

is actually the smallest contractile

unit of muscle what happens is the mice

and heads bind to the actin they walk

along it and they shorten the whole

thing that's contraction if you shorten

a contraction shorten and contract this

you're going to shorten and contract the

muscle tissue so you've got the myosin

which is the blue I'll write that down

for you we've got the myosin

and you've got the actin

now I was saying to you about the

striations what are the striations well

can you see here that you've got Parts

where both proteins overlap so you've

got an area here no overlap

here overlap no overlap overlap no

overlap when you look at that under a

microscope you get stripes the areas of

overlap look darker and they're the

striations which tells you that in both

skeletal muscle and cardiac muscle actin

and myosin are arranged in this fashion

for contraction to occur but when we

look at

smooth muscle it's not arranged in this

fashion in and the reason why is this

because they're arranged in series and

parallel right so basically take this

sarcomere and go boom boom boom boom and

then go boom boom boom boom and add them

in series and parallel so they're all in

the same direction so that when they

contract the whole thing shortens which

means when skeletal muscle contracts the

whole thing

shortens when cardiac muscle contracts

the whole thing

shortens but the difference here was

smooth muscle is that they're not

arranged in series and parallel they're

arranged in what seems to be this

mishmash different shape and if it's

arranged in this mishmash shape you

don't get these pattern striations and

why would we want our smooth muscle to

be arranged in a weird way because we

don't just want contraction of our

smooth muscle to go like that we want

contraction of our smooth muscle to go

in many directions

why well because smooth muscle is not

just straight like skeletal muscle where

we want it to shorten like this and bend

the joint or cardiac muscle where we

wanted to shorten and contract over

ventricle we have smooth muscle lining a

tube and so if we've got a tube like

this

what you want is you want to narrow the

diameter of that tube similar to what

happens here but you also want to

shorten the length of the tube and this

is how things move through if you were

to get a tennis ball put it into a

stocking and you were to squeeze that

tennis ball through the stockings what

you're doing is you're narrowing the

diameter but you're also shortening the

tube and that's peristalsis that's how

things move through tubes and it can

only happen if the uni uh sorry if the

smooth muscle cells have their

contractile proteins arranged in what

looks like a mishmash sort of random way

so hopefully that makes sense to you so

we've got voluntary fiskeletal

involuntary for cardiac involuntary for

smooth we've got multi-nucleated for

skeletal we've got uni or binucleated

for cardiac and we've got uni nucleated

for smooth we've got uh cylinder shaped

for skeletal branched for cardiac and

we've got spindle shaped for our smooth

muscle all right what's the next thing

we need to look at we need to have a

look at

how are they connected to one another so

what you'll find here for the skeletal

is that they're simply just sitting on

top of each other like parallel right so

you're going to have

there's one there

there's one there

there's one there right

when we look at cardiac it's going to be

attached like this

because it's branched it wants to be

attached to other ones like this

so you've got all these branches

attached to each other

now why is this the case this is

important because

little for a second because because it's

rained arranged in parallel it's like

that on purpose take them you're going

to have the it arranged for the biceps

for example these big long

cylindrical cells like this right

like that I know my lines aren't very

straight but it's like that so that when

it contracts

it shortens like that that's easy but

the branching because it moves around

these ventricles and Atria they're

actually connected

through little gaps

called Gap Junctions you've got these

intercalated discs that hold each cell

together intercalated discs they hold

each one together and then you've got

these Gap Junctions let's write this

down you've got intercalated discs

enter

collated

discs right which hold things together

and then you've got Gap Junctions

which allow for communication

talk to each other

now why do we want them to talk to each

other here's the thing you probably are

aware that when a heart contracts you

don't just contract one part of the

heart muscle you contract all of the

heart muscle but the stimulus for

contraction begins in one spot the

sinoatrial node it begins at around

about

up here

an electrical signal gets sent

in this fashion

around the tissue now the electrical

signal needs to spread through the

muscle now it spreads through these Gap

Junctions so if you start an action

potential or you know sodium jumping

into this cell it gets the spread to

this one and spreads to this one so when

that contracts that contracts and then

that contracts and it contracts in what

we call a sensation it means that if you

stimulate one muscle cell to contract

all the rest will contract that's not

the same here you need a different motor

neuron innervating each of these muscle

cells if I have a motor neuron coming

down it needs to innovate that one it

needs to innervate that one it needs to

innovate that one to tell it to contract

not the case here you only need to

innovate this first one

and it spreads the signal to the rest

and they all act as one when all muscle

cells act as one we call that a

sin session

spelled that wrong see I shouldn't

shouldn't talk at the same time sin

I've probably spelled it wrong again but

anyway the term is sensation I promise

you that it's just that my spelling is

pretty poor

and then when we've got smooth muscle

they're going to be connected as well

like this

so I've got a spindle I'm going to have

another spindle

I'm gonna have another spindle

we're gonna have another spindle

I'm gonna have another spindle like that

and again it's so they contract in

multiple directions to help move things

through

all right so these are the similarities

and differences between skeletal cardiac

and smooth muscle and I hope that it

helps hi everyone Dr Mike here if you

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