Muscular System (Part 3) - Muscles of the Thoracic Limb
Summary
TLDRThis presentation segment delves into the anatomy of the thoracic limb muscles, distinguishing between intrinsic and extrinsic muscles and their roles around the shoulder, elbow, carpus, and digits. It highlights key muscles like the trapezius, rhomboid, serratus ventralis, and latissimus dorsi, detailing their functions and interactions. The discussion also covers muscles affecting the elbow, such as the triceps brachii and biceps brachii, emphasizing their extensor and flexor actions. The narrative concludes with a reminder of the multi-joint influence of these muscles, encouraging viewers to continue to the next module on pelvic limb muscles.
Takeaways
- 💪 The muscles of the thoracic limb are divided into intrinsic and extrinsic muscles, with intrinsic muscles located entirely within the limb and extrinsic muscles connecting different regions of the body.
- 🦾 Muscles can be further grouped by the joints they act upon, including muscles of the shoulder girdle, shoulder joint, elbow, carpus, and digits.
- 🏋️♀️ The trapezius muscle, a flat triangular muscle, swings the scapula forward and backward and is divided into two parts: the cervical (larger) and thoracic (smaller) parts.
- 🔍 Rhomboideus is a deeper, heavier muscle located beneath the trapezius and has three parts based on their location: capitis, cervicis, and thoracis.
- 🏗️ Serratus ventralis, a large fan-shaped muscle, forms a sling supporting the trunk between the thoracic limb, crucial for weight-bearing.
- 🏃♂️ Brachiocephalicus is the principal extensor of the shoulder, also acting as a flexor of the neck when the limb is weight-bearing, subdivided into clydobrachialis and clydoscephalicus.
- 🚶♀️ Latissimus dorsi is a strong flexor of the shoulder and assists in pulling the limb caudally or advancing the trunk when the limb is fixed.
- 🤸♂️ Triceps brachii is the strongest extensor of the elbow with four heads in dogs, including a long, lateral, medial, and accessory head, all inserting on the olecranon of the ulna.
- 🦵 Extensors of the carpus are found on the craniolateral aspect of the limb, including muscles like extensor carpi radialis and common digital extensor.
- 🤲 Flexors of the carpus and digits are found on the caudomedial side of the limb, including flexor carpi radialis and two digital flexors (superficial and deep digital flexor).
Q & A
What are the two types of muscles that make up the muscles of the thoracic limb?
-The muscles of the thoracic limb are composed of intrinsic and extrinsic muscles. Intrinsic muscles lie completely within one region of the body, having their origin and insertion in the bones of the thoracic limb. Extrinsic muscles run from one region of the body to another.
How are the muscles of the limb further grouped based on their function?
-The muscles can be grouped based on the joint of the limb they act with, which includes the muscles of the shoulder girdle, shoulder joint, elbow, carpus, and the digits.
What is the function of the trapezius muscle and how is it divided?
-The trapezius muscle helps swing the scapula forward and backward. It is divided into two parts: the cervical part (trapezius cervicalis), which is larger, and the thoracic part (trapezius thoracis), which is smaller.
What is the serratus ventralis muscle and its role?
-The serratus ventralis is the largest and most important muscle attaching the thoracic limb to the trunk. It is a large fan-shaped muscle that forms a sling supporting the trunk between the thoracic limb.
What is the main action of the brachiocephalicus muscle?
-The brachiocephalicus muscle is the principal extensor of the shoulder area and acts as a flexor of the neck. It raises and advances the shoulder.
Describe the latissimus dorsi muscle and its action.
-The latissimus dorsi is a wide triangular muscle and is a strong flexor of the shoulder. It also pulls the thoracic limb caudally or advances the trunk if the limb is fixed.
What are the two parts of the deltoid muscle and their respective locations?
-The deltoid muscle has two parts: the spinal part, which is thicker and fusiform in shape, and the acromial part, which is thinner and strap-like. They fuse before inserting and act together as a single unit.
Which muscle is considered the strongest extensor of the elbow and what are its heads?
-The triceps brachii is the strongest extensor of the elbow. It has three heads: the long head, which originates from the caudal border of the scapula, the lateral head from the lateral humeral diaphysis, and the medial head from the medial humeral diaphysis.
What is the role of the tensor fasciae antebrachii muscle?
-The tensor fasciae antebrachii muscle tenses the antebrachial fascia. It assists the triceps brachii in the extension of the elbow through its fascial connections.
How does the location of the pectoral muscles relate to their function?
-The pectoral muscles are strong adapters of the forelimb. The deep pectoral muscle (ascending pectoral) advances the trunk when the limb is fixed on the ground, while the superficial pectoral muscle, which is subdivided into a descending part and a transverse part, also plays a role in forelimb adaptation.
What is the main action of the superficial digital flexor muscle?
-The superficial digital flexor is the only muscle that flexes the distal interphalangeal joint. It also secondarily flexes the more proximal joints of the digit and the carpus, and supports the fat lock.
Outlines
💪 Thoracic Limb Muscles Overview
This section of the presentation focuses on the muscles of the thoracic limb, which are categorized into intrinsic and extrinsic muscles. Intrinsic muscles have their origin and insertion within the thoracic limb, while extrinsic muscles span across different body regions. Muscles are further grouped based on the joint they act upon, such as the shoulder girdle, shoulder joint, elbow, carpus, and digits. Each group is then subdivided into extensors, flexors, adductors, and abductors. The paragraph introduces the muscles acting on the shoulder girdle, including the trapezius muscle, which is divided into cervical and thoracic parts, and the rhomboidus muscle, which is composed of three parts based on their location. The serratus ventralis muscle, the largest and most important muscle attaching the thoracic limb to the trunk, is also discussed, along with the omotransversarius muscle.
🤚 Muscles Acting on the Shoulder Joint
The muscles acting on the shoulder joint are divided based on their primary action into extensors and flexors. The brachiocephalicus muscle, the principal extensor of the shoulder, is described, along with its subdivisions. The latissimus dorsi, a strong flexor of the shoulder, is mentioned, as well as the deltoid muscle, which has two parts that act together. The infraspinatus muscle is highlighted as a strong collateral ligament of the shoulder joint with multiple actions. The teres major and teres minor muscles are also flexors of the shoulder joint. The adductors of the shoulder, including the superficial and deep pectoral muscles, are discussed, along with the subscapularis and coracobrachialis muscles and their roles in shoulder stabilization and movement.
🤚💪 Muscles Acting on the Elbow and Carpus
This section discusses the muscles acting on the elbow and carpus. The triceps brachii, the strongest extensor of the elbow, is described, including its different heads and their origins. The anconus muscle, tensor fasciae antebrachii, and biceps brachii are also mentioned, with the latter being a primary flexor of the elbow. The paragraph continues to describe the muscles acting on the carpus, with the extensor carpi radialis being the largest and most prominent extensor. The common digital extensor, lateral digital extensor, and extensor carpi ulnaris are also discussed, along with the flexor carpi radialis and ulnaris. The digital flexors, including the superficial and deep digital flexors, are highlighted, with a focus on their role in flexing the distal interphalangeal joint and supporting the fat lock.
Mindmap
Keywords
💡Intrinsic Muscles
💡Extrinsic Muscles
💡Thoracic Limb
💡Trapezius Muscle
💡Rhomboid Muscle
💡Serratus Ventralis
💡Brachiocephalicus Muscle
💡Latissimus Dorsi
💡Deltoid Muscle
💡Triceps Brachii
💡Biceps Brachii
Highlights
The muscles of the thoracic limb are divided into intrinsic and extrinsic muscles.
Intrinsic muscles have their origin and insertion within the bones of the thoracic limb.
Extrinsic muscles run from one body region to another.
Muscles are further grouped based on the joint of the limb they act with.
The trapezius muscle is divided into cervical and thoracic parts.
The rhomboidus muscle is composed of three parts based on their area.
Serratus ventralis is the largest muscle attaching the thoracic limb to the trunk.
Oma transversarius assists in lateral flexion of the neck.
Brachiocephalicus is the principal extensor of the shoulder area.
Supraspinatus acts as a stabilizing ligament of the shoulder joint.
Latissimus dorsi is a strong flexor of the shoulder and pulls the limb caudally.
Deltoid muscle has two parts that act together as a single unit.
Infraspinatus acts as a collateral ligament of the shoulder joint.
Teres major is a strong flexor of the shoulder joint.
Adductors of the shoulder form the substance of the brisket and are divided into superficial and deep pectoral muscles.
Coracobrachialis is a small muscle that acts as an extensor of the shoulder joint.
Triceps brachii is the strongest extensor of the elbow.
Tensor fasciae antebrachii assists the triceps in the extension of the elbow.
Biceps brachii assists in holding the shoulder joint and flexes the elbow.
Flexors of the carpus include the flexor carpi radialis and flexor carpi ulnaris.
Digital flexors include the superficial and deep digital flexors.
Muscle actions are not exclusive to a particular joint; they can act on multiple joints.
Transcripts
welcome to part 3 of module 4.
this part of presentation will be
dealing with the muscles of the thoracic
limb
the muscles of the thoracic limb are
composed of intrinsic and extrinsic
muscles
as i recall an intrinsic muscle lies
completely within one region of the body
where they have their origin and
insertion in this case
the bones of the thoracic limb on the
other hand
extrinsic muscles run from one region
of the body to another moreover
the muscles can be grouped further based
on which joint of the limb they are
acting with
this include the muscles of the shoulder
girdle
muscles of the shoulder joint the elbow
muscles of the carpus and the muscles of
the digits
in addition the muscles within the
grouping are subgrouped further as to
whether they are
an extensor a flexor an adductor or
abductor let us begin with the muscles
acting on the shoulder girdle
the first muscle is a flat triangular
sheet of muscle as shown here
this is the trapezius muscle it is
divided into two parts
a cervical part or the trapezius
services
is larger compared to the thoracic part
or the trapezius thoracis
which is smaller this muscle helps swing
the scapula forward and backward
the next muscle is the rhomboidus if the
trapezius is removed or reflected
the rhomboidus muscle can be seen this
is a heavier muscle just dipped to the
trapezius
it is composed of three parts and were
named based on their area
at the neck region rhomboideus capitis
is a long
thin strap-like muscle that originates
on the occipital bone
rhomboideus services has more substance
and originates at the cervical rafi
rhomboideus thoracis is a short thick
expanse of muscle it originates on the
spinous process of the thoracic vertebra
four
to seven serratus ventralis is the
largest and the most
important muscle attaching the thoracic
limb to the trunk
it is a large fan-shaped muscle it forms
a sling that supports the trunk between
the thoracic limb
take note that in this image the
trapezius and the latissimus dorsi
muscles were reflected
to show the serratus ventralis muscle
oma transversarius is a separate muscle
of the shoulder region
it usually pulls the distal end of the
scapula forward
although with the limb in weight bearing
position it
instead assists a lateral flexion of the
neck
now let us discuss the muscles of the
shoulder joint
muscles under this section is divided
based on their main action
let us begin with the extensors first is
the brachiocephalicus muscle
from the name itself it extends from the
head or cephalic
to the arm or brachium this is a heavy
muscle
covering the cranial aspect of the point
of the shoulder
it raises and advances the shoulder it
is the principal extensor of the
shoulder
area and acts as a flexor of the neck
when the limb is weight bearing
this muscle is subdivided into
clydobrachialis
extending from the clavicular tendon to
the humerus
and clydoscephalicus extending from the
clavicular tendon to the head and neck
cephalicus may be further subdivided
into a mastoid part or the
clydomastoidus
attaching to the mastoid process of the
temporal bone
and a cervical part or the clydos
cervicalis
remember that the clavicular tendon
represents the vestigial clavicle
supraspinatus acts chiefly as a
stabilizing ligament of the shoulder
joint
this is a deep muscle attached to the
supraspinous fossa
for the flexors of the shoulder joint
let us begin with the latissimus dorsi
this is a wide triangular muscle and is
a strong flexor of the shoulder
also it pulls the thoracic limb caudally
or if the limb is fixed
it advances the trunk it is also known
as the broadest
muscle of the back the next flexor is
the deltoid use muscle
this muscle extends from the spine of
the scapula
to the deltoid tuberosity of the humerus
it has two parts which
fuse before they insert and act together
as a single unit
the scopular part is the thin and
shit-like
while the acromial part is a thicker and
is fusiform in shape
the infraspinatus muscle acts as a
strong collateral ligament of the
shoulder joint
and may abduct flex and outwardly rotate
the shoulder
this muscle is located filling the space
of the infraspinous fossa
the teres major as shown here is also a
strong flexor of the shoulder joint
the brachium is removed to show more of
the infraspinatus
and the teres major muscles also part of
the flexor of the shoulder
is the teres minor muscle this muscle
lies just distal to the infraspinatus
muscle
and has the same action with the
infraspinatus
now let us discuss the adductors of the
shoulder
muscles form the substance of the
brisket
commonly they are divided into the
superficial pectoral muscle
and the deep pectoral muscle the deep
pectoral muscle is also termed as the
ascending pectoral muscle because of the
ascending fashion of the muscle fibers
on the other hand the superficial
pectoral muscle
is further subdivided into a descending
part
and a transverse part the pectoral
muscles
are strong adapters of the forelimb and
the deep pectoral muscle also advances
the trunk when the limb is fixed on the
ground
to see other adapters of the shoulder
here is a medial view of the scapular
region
the subscapularis muscle stabilizes the
shoulder on the medial side
this muscle fills the space of the
subscapular fossa
the coracobrachialis on the other hand
is a small muscle
in which the location of the muscle
belly suggests
that it is a shoulder flexor but its
attachment makes it a muscle
of an extensor of that joint
now let us move to the muscles acting on
the elbow
since the elbow is a hinge joint the
muscles acting on it
are either flexors or extensors in
general
the extensors are located at the lateral
side while the flexors are seen at the
medial side of the limb
in quadrupeds the extensors are stronger
than the flexors because they support
the weight of the body
by maintaining the limb in extension
position
the first muscle is the triceps brachai
muscle
it is the strongest extensor of the
elbow
it fills the space between the scapula
and the humerus
from the name itself it has three heads
however in dogs
foreheads are present shown here is the
long head
which originates from the caudal border
of the scapula
the lateral head which originates from
the lateral
humeral diaphysis
to see the other heads of the triceps
brachii here is a dissected arm
showing the medial and lateral side for
orientation purposes
here is the long head and the lateral
head
which were previously discussed take
note that the lateral head is reflected
this time
the medial head originates from the
medial humeral diaphysis
the fourth and the additional head in
carnivores like dog is the accessory
head
it originates from the humerus between
the medial and the lateral heads
take note that all heads inserts on the
olecranon process
of the ulna
deep to the triceps brachii is a rather
small muscle called anconus
it covers the caudal aspect of the joint
capsule of the elbow
next is the tensor fasciae antebrachii
the muscle's name reflects its action on
the
antebrachial fascia or it tenses it
but through these fascial connections
the tensor fasciae antibrachi also
assist the triceps
in the extension of the elbow
as mentioned most of the flexors are
located at the medial side of the limb
one of the flexors of the elbow is the
biceps brachii
this muscle assists in holding the
shoulder joint in
a position and may extend it to some
extent
however the chief action is flexion of
the elbow
also classified as flexors are the
brachialis and the pronator teres muscle
the corpus and digits like the elbow act
essentially as a hinge joint the
extensors of the carpus
lie on the craniolateral aspect of the
limb while the flexors are found on the
codomedial side of the limb
here are the muscles of the antibrachium
in a lateral
cranial medial and cuddle view for
better visualization
take note that the muscle action is not
strictly on a certain joint
for example a muscle can be an extensor
of the corpus but
a flexor of the elbow what we will at in
this presentation
is their main action the first muscle is
the
extensor carpi radialis this is the
largest extensor of the carpus
this is also the most prominent muscle
on the front of the forearm and is the
most cranial muscle of the group
the common digital extensor is the
longest extensor muscle in the thoracic
limb
this muscle is an extensor of all joints
of the digit
including the fat lock it may also
assist in extending the carpus
and even in the flexing of the elbow
the lateral digital extensor originates
on the lateral collateral ligament
of the elbow and lateral radius and ulna
the insertion varies according to the
number of digits present
in the case of dog it has five
insertions
the extensor carpi ulnaris is formerly
known as the ulnaris lateralis
it is the most cuddle of the extensor
muscles
in most domestic animals this muscle
probably produce a weak flexion of the
carpus
although by origin and nerve supply it
belongs to the extensor group
it also produces some outward rotation
of the forearm
the extensor carpi oblicus or the
abductor police's longus or the abductor
digit 1
is a flat triangular extensor of the
carpus
lying deep to the digital extensor
muscles of the antebrachium
as you observed most of the extensors
are seen at the lateral side of the
antebrachium
for the flexors same views of the
antebrachial muscles are shown
let us first locate the flexor carpi
radialis
this is caudal to the radius which is
palpable directly beneath the skin
the flexor carpi ulnaris exerts
considerable leverage
as a flexor of the carpus by inserting
on the accessory carpal bone
it projects in a pulmonary direction
from the lateral aspect of the carpus
these muscles are of course primarily a
flexor of the carpus
but they may act slightly in the
extension of the elbow
there are two digital flexors here is
the superficial digital flexor
and a deeper dissection is needed to
expose the deep digital flexor as shown
here
it lies the closest to the metacarpal
bone
it is the only muscle that flexes the
distal interphalangeal joint
secondarily it also flexes the more
proximal joints of the digit
and the carpus it is also important in
supporting the fat lock
and that concludes our presentation on
part three of module four
just a point to remember the action of
each muscle is not exclusive to a
particular joint
it can be an extensor of a proximal
joint
but a flexor of a more distal joint
you may now proceed to part 4 of this
module which is focus on the muscles of
the pelvic limb
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