Hand Muscles

Summary

This tutorial delves into the intrinsic muscles of the hand, focusing on the thenar, hypothenar, lumbrical, and interosseous muscles. It explains their actions, innervation by the median and ulnar nerves, and the unique function of the lumbricals in flexing the metacarpophalangeal joints and extending the interphalangeal joints. The video script also covers the anatomy and function of the adductor pollicis and the interosseous muscles, highlighting their role in thumb movement and finger abduction/adduction, respectively.

Takeaways

• 🤚 The intrinsic hand muscles originate and insert in the hand, providing dexterity but less power compared to extrinsic muscles.
• 👍 The thenar muscles act on the thumb, including the abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis, and are innervated by the recurrent branch of the median nerve.
• 🤞 The hypothenar muscles act on the pinky finger, with actions of abduction, flexion, and opposition, and are innervated by the ulnar nerve after it traverses Guyon's canal.
• 🤌 The lumbrical muscles arise from the flexor digitorum profundus tendons and have a unique action of flexing the metacarpophalangeal (MCP) joint while extending the interphalangeal (IP) joints.
• 🔄 The median nerve provides innervation to the first two lumbrical muscles for the index and middle finger, while the ulnar nerve innervates the third and fourth lumbricals for the ring and pinky fingers.
• 🤏 The adductor pollicis has a transverse and an oblique head, both originating from the third metacarpal and carpal bones, and is responsible for thumb adduction.
• 👐 The interosseous muscles, with a dorsal and palmar set, are involved in the abduction and adduction of the fingers, respectively, and are innervated by the ulnar nerve.
• 🔑 The acronym 'PAD' stands for palmar interossei muscles that adduct the digits, while 'DAB' stands for dorsal interossei muscles that abduct the metacarpophalangeal joints.
• 🛤️ The median nerve courses through the carpal tunnel and sends branches to the thenar muscles and the first two lumbricals, while the ulnar nerve traverses Guyon's canal to innervate the hypothenar muscles and the third and fourth lumbricals.
• 🔍 The knowledge of the actions and innervation of these hand muscles is crucial for understanding conditions like claw hand and for medical board preparation.

Q & A

What are the intrinsic hand muscles?

The intrinsic hand muscles are muscles that originate and insert in the hand. They are responsible for fine motor movements and dexterity, unlike the extrinsic muscles which provide power but less dexterity.

What are the three main muscles that act on the thumb?

The three main muscles that act on the thumb are the abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis. These muscles are responsible for thumb abduction, flexion, and opposition, respectively.

Which nerve provides motor innervation to the thenar muscles?

The median nerve provides motor innervation to the thenar muscles. It sends a branch called the recurrent branch of the median nerve after traversing the carpal tunnel.

What is the role of the hypothenar muscles in hand function?

The hypothenar muscles act on the pinky finger. They include the abductor digiti minimi, flexor digiti minimi, and opponens digiti minimi, and are responsible for abduction, flexion, and opposition of the pinky finger.

How does the median nerve innervate the hypothenar muscles?

The median nerve innervates the hypothenar muscles after traversing the carpal tunnel and sending a branch called the recurrent branch of the median nerve.

What are the lumbar muscles and what is their function?

The lumbar muscles are four in number and arise from the flexor digitorum profundus tendons. They help in flexing the metacarpophalangeal (MCP) joints and extending the interphalangeal (IP) joints, contributing to fine hand movements.

Which nerve innervates the lumbar muscles?

The median nerve innervates the first two lumbar muscles (for the index and middle fingers), while the ulnar nerve innervates the third and fourth lumbar muscles (for the ring and pinky fingers).

What is the function of the adductor pollicis muscle?

The adductor pollicis muscle, which has a transverse head and an oblique head, is responsible for adducting the thumb towards the palm.

What are the interosseous muscles and how do they affect finger movements?

The interosseous muscles are two sets: the dorsal and palmar interosseous muscles. The dorsal interosseous muscles abduct the fingers away from the midline, while the palmar interosseous muscles adduct the fingers towards the midline.

Which nerve innervates the interosseous muscles?

The interosseous muscles are innervated by the ulnar nerve, which also provides innervation to the hypothenar muscles.

What is the significance of the extensor expansion hood in relation to the lumbar muscles?

The extensor expansion hood is significant because the pull of the lumbar muscles on this hood helps in flexing the MCP joints and extending the IP joints, contributing to the unique action of the lumbar muscles.

Outlines

00:00

🤚 Intrinsic Hand Muscles and Their Functions

This paragraph delves into the anatomy and function of the intrinsic hand muscles, focusing on the thenar, hypothenar, lumbrical, and interosseous muscles. The thenar muscles, which include the abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis, are responsible for thumb movements such as abduction, flexion, and opposition, crucial for dexterity in tasks like buttoning a collar or shaking hands. These muscles are innervated by the recurrent branch of the median nerve after it traverses the carpal tunnel. The hypothenar muscles, which act on the pinky finger, include the abductor digiti minimi, flexor digiti minimi, and opponens digiti minimi, and are also innervated by the ulnar nerve after passing through Guyon's canal. The paragraph emphasizes the importance of these muscles for fine motor skills and their representation in the somatotopic map of the precentral gyrus.

05:00

🤌 Lumbrical Muscles and Their Unique Actions

The second paragraph discusses the unique action of the lumbrical muscles, which arise from the flexor digitorum profundus tendons and insert on the extensor expansion hood. These muscles have the distinct function of flexing the metacarpophalangeal (MCP) joints while simultaneously extending the interphalangeal (IP) joints. This dual action is facilitated by the lumbrical muscles' position relative to the MCP and IP joints. The median nerve, after sending a branch to the thenar muscles, innervates the first two lumbricals, while the ulnar nerve, after traversing Guyon's canal, innervates the remaining two lumbricals that act on the ring and pinky fingers. The paragraph also touches on the clinical relevance of understanding these muscle actions for diagnosing conditions like claw hand.

Keywords

💡Intrinsic hand muscles

Intrinsic hand muscles are those that both originate and insert within the hand itself. They are essential for fine motor control and dexterity, as opposed to the extrinsic muscles which have their origins in the forearm or arm and insert into the hand via long tendons. In the video, the intrinsic muscles are highlighted for their importance in hand function, particularly in tasks requiring precision and agility.

💡Thenar muscles

The thenar muscles are a group of muscles located on the palmar side of the thumb that are responsible for its movement. They include the abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis. The video emphasizes the role of these muscles in providing the thumb with its opposable function, which is crucial for activities like grasping objects and performing intricate hand movements.

💡Hypothenar muscles

The hypothenar muscles are located on the medial side of the hand and are responsible for the movement of the little finger. Comprising the abductor digiti minimi, flexor digiti minimi, and opponens digiti minimi, these muscles allow for the fine control of the pinky, contributing to the overall dexterity of the hand. The script discusses these muscles in the context of their actions and innervation.

💡Lumbrical muscles

Lumbrical muscles are small muscles in the hand that arise from the tendons of the flexor digitorum profundus. They play a unique role in hand function by flexing the metacarpophalangeal (MCP) joints and extending the interphalangeal (IP) joints. The video script illustrates this dual action, which is important for understanding the complex movements of the fingers.

💡Gon's canal

Gon's canal is a tunnel-like structure in the hand through which the ulnar nerve passes. The video mentions this anatomical feature in the context of the ulnar nerve's path and its role in innervating the hypothenar muscles and other structures in the hand, emphasizing the canal's importance in hand function and nerve distribution.

💡Median nerve

The median nerve is a major nerve in the arm that provides sensation and motor function to the hand. In the video, the median nerve is discussed in relation to its branches, such as the recurrent branch, which innervates the thenar muscles after the nerve traverses the carpal tunnel. This nerve's pathway and function are central to the video's explanation of hand muscle innervation.

💡Adductor pollicis

The adductor pollicis is a muscle located in the thenar eminence that adducts the thumb towards the palm. It is composed of a transverse head and an oblique head, both of which originate from the third metacarpal and carpal bones. The video script describes the muscle's action and its contribution to the thumb's ability to perform precise movements.

💡Interosseous muscles

The interosseous muscles are a group of four dorsal and three palmar muscles located between the metacarpal bones of the hand. They are responsible for the abduction and adduction of the fingers. The video script refers to these muscles as 'PADs and DABs' due to their actions of palmar adduction and dorsal abduction, respectively, and their innervation by the ulnar nerve.

💡Carpal tunnel

The carpal tunnel is a narrow passageway at the wrist through which the median nerve and flexor tendons pass. The video script explains that the median nerve sends branches to the thenar muscles after traversing the carpal tunnel, highlighting the tunnel's significance in hand anatomy and function.

💡Extensor expansion hood

The extensor expansion hood is a fibrous structure found on the dorsal surface of the fingers, which plays a role in finger extension. The video script describes how the lumbrical muscles attach to this hood and how their contraction affects both the flexion of the MCP joints and the extension of the IP joints, demonstrating the hood's role in finger movement mechanics.

Highlights

Introduction to intrinsic hand muscles, which originate and insert in the hand, providing dexterity.

Extrinsic hand muscles, like FDP, FDS, FPL, EDC, originate in the forearm and have long tendons in the hand, providing power.

Thear muscles act on the thumb, including abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis.

The median nerve innervates the thenar muscles through the recurrent branch after traversing the carpal tunnel.

Hypothenar muscles act on the pinky, including abductor digiti minimi, flexor digiti minimi, and opponens digiti minimi.

The ulnar nerve provides innervation to the hypothenar muscles after traversing Guyon's canal.

Lumbrical muscles arise from the flexor digitorum profundus tendons and insert on the extensor expansion hood.

Lumbrical muscles uniquely flex the MCP joint and extend the IP joints, affecting hand movement.

The median nerve innervates the first two lumbrical muscles, affecting the index and middle finger.

The ulnar nerve innervates the third and fourth lumbrical muscles, affecting the ring and pinky fingers.

The adductor pollicis has a transverse head and an oblique head, both originating from the third metacarpal and carpal bones.

The adductor pollicis muscle contracts to perform thumb adduction.

The dorsal and palmar interossei muscles are responsible for abduction and adduction of the fingers.

The dorsal interossei muscles are involved in abduction at the metacarpophalangeal joints.

The palmar interossei muscles adduct the digits, pulling them towards the midline.

The interossei muscles are often referred to as 'PADs' (palmar adduct) and 'DABs' (dorsal abduct).

The ulnar nerve innervates the interossei muscles, affecting finger movement.

Transcripts

okay let's talk about the hand muscles

now in this uh tutorial we're going to

talk about the uh theer hypothenar

muscles and the adductor policis the

lumbal and the Neurosis muscles their

actions and their ination and we'll

throughout this we'll talk about gon's

Canal okay hand and the Hand muscles

I've called this called the intrinsic

hand muscles because these are muscles

that are originate and insert in the

hand there's a lot of tendons that go to

the hand like fdp fds FPL EDC but these

muscles originate in the forearm or even

in the arm in some cases and then their

long tendons go into the hand so they

have great power not a lot of dexterity

our intrinsic hand muscles the following

list don't have as much power in fact

they're fatigued easier but they have a

lot of dexterity which is also why if

you remember in the homunculus so much

time so much uh uh

somatotopic um space has been or uh

dedicated to hand muscles in the preor

pre Central gyrus all right let's start

with the thear muscles thear muscles are

muscles that act on the thumb and

there's three of them abductor Pocus

brevis flexor Pocus brevis and

opponent's Pocus and there they are for

the abbreviations

afo on the thumb muscles and whether you

can identify those three individual

muscles on a picture or Cav doesn't

matter to me the main thing is to

recognize the actions we have an

abductor of the thumb a flexer of the

thumb and an opposer of the thumb

opposition or opponent's pules think

thumb touching Pinky and so find

dexterity of the thumb like uh buttoning

Your Collar grabbing a hammer shaking a

hand and so the ination of these muscles

is by the median nerve the median nerve

courses through the carpal tunnel and

then after traversing the carpal tunnel

it sends a branch backwards called the

recurrent branch of the median nerve or

sometimes simply the recurrent median

nerve which then provides motor

inovation of the thear muscles the key

to it is the recurrent median nerve

Branch innervates the muscles after

traversing the carpal tunnel and there's

also other branches that go to the

lumbal and your digits now the

hypothenar muscles are muscles that act

on your pinky and there's three of them

abductor digiti minimi digiti minimi

means minimi small digit flexor Digi I

minimi and opponent's Digi I minimi and

so again I don't care if you can

identify these three individual muscles

on a picture or the Cav because it's a

group but it's the actions we have

muscles that will one of these muscles

will abduct the pinky one will Flex the

pinky and one will oppose pinky touching

the thumb fine movement of that small

finger and so now if we take a look at

that allner nerve as it courses into the

hand it traverses this tunnel formed by

a connective tissue attaching to the

pistoor Bone that's called gon canal and

after the aler nerve traverses gon's

Canal now enters into the hand and gives

innervation to the hypothenar muscles as

well as a bunch of other muscles in the

hand and some

skin the next group are called the

lumbal and the lumbal are forign num so

I'm going to ghost through so we can see

a little bit easier and these four

lumbal muscles arise from the flexor

digitorum profundus tendons all four of

them and then these tendons coarse up so

they arise or they originate on the the

front of the hand also called The Palmer

surface or sometimes volar surface of

the hand and then the tendons course to

the back of the digits so to best see

the insertion of these four muscles

let's take a look at a lateral view of

the digit where there's a metacarpal

there's a proximal middle and distal

fangi so between the metacarpal and

fangi is the mCP

metacarpal fenial joint and then our pip

and dip are interial joints for proximal

and

distal then we've got the same picture

except now we've overlaid muscles and

tendons so in turquoise there is a

lumbrical muscle it's arising from the

FTP tendon and then notice its

attachment is on that dark blue

structure called the extensor expansion

Hood this extensor expansion hood is is

primarily found on the dorsal surface or

posterior surface of the digits but

recognize that part of this Hood crosses

in front of the mCP joint that's going

to become significant here in a minute

so the pull of the lumle with the lumle

now contracts that first dotted Arrow

represents the vector pull and and and

see that it is in front of the mCP joint

and because of that it would cause

flection of the mCP joint in other words

lumle lumbal Flex the mCP joint point

but look at that second dotted Arrow

it's on the backside of the extensor

expansion hood on the back of the IP

joints and as a result when the lumbal

contract in addition to flexing the mCP

joint lumbal extend the IP joints this

is what makes it unique and recall that

the mCP joint extension is primarily

from the extensor digit torm communis

and the extension of the IP joints is

primarily from the lumbal this uh uh

knowledge of this will be helpful in

trying to figure out all those claw

hands that you're using and you're

studying for your

boards okay so this is a left hand this

is a light embalmed caber which means uh

the tissue doesn't fix because it's not

used with from aldhy so it can move when

you pull on muscles and this was done by

Jordan Barker um a previous student and

now Orthopedic residence so there's our

mCP joint there's the PIP and dip joints

outlined in Orange is a a lumbal that's

the first lumle muscle there's the

extensor expansion Hood starting and

then continuing on the dorsum of the

finger now I'm going to go onto this

video and watch now what happens so

there we've got tending pulling on that

Lumber comb now watch what happens to

the mCP and the IP joint flexion and

extension again one more time flexion of

the mCP extension of the IP joints

there's our

lumber now uh the interation of these

lumbal muscles is unique remember how

the fdp was funky the flexor digitorum

profundus in its interation the exact

same thing happens with these lumbal

where the median nerve after traversing

the carpal tunnel and sending a branch

to the recurrent median will then

innervate those first two lumbal going

to your index and square finger

now the olner nerve courses through

gon's canal and it interat the

hypothenar muscles it

intervesicle including the third and

fourth Lumber or the lumber that act on

the ring finger and the pinky and so if

you can remember what nerves inovate the

two bellies of the fdp you'll always

remember what nerves inovate these two

different Lumber Co

muscles next is the adductor pocis and

that it has a Traverse head and an

oblique head both of which they come

basically from that third metacarpal and

carpal bones and go to the proximal

failings of the thumb and when this

muscle contracts it will do that motion

which is thumb adduction from here to

there next is our interos muscles

there's two of them a dorsal and a

pulmer interus muscles and so in purple

we have the dorsal interus muscle and

that dot dorsal inosi muscles there's

four of them that dotted line that goes

down the swear finger shows where what

you're using as the midline for what's

considered ab and AD duction when the

dorsal and aasi muscles contract the ab

duct they pull the fingers away from the

midline in this fashion you'll notice

that I didn't show the pinky abducting

when I go from here to here because the

Pinky has its own abductor on the

hypothenar muscles and so I also put on

this page dab da because the dorsal D

inosi muscles abduct AB the metacarpal

fangel joints dab now the pulmer inosi

muscles in Orange there's three of them

and these pulmonar oi muscles are going

to adduct they pull the fingers towards

the midline the adduct the digits and so

you'll notice I put the acronym pad P

pal osus muscles will adduct the digits

hence pad and this is often why you'll

hear these neosi muscles referred to as

the pads and dabs and these muscles are

inovated by the oler Nerf