Lecture 1 Muscles & Connective Tissue Flashcards
How many skeletal muscles are there and how are they normally present?
~640
Present as bilateral pairs
What are the 2 key principles of muscles?
- They can only pull NOT PUSH.
- Can only act on joints that they cross
Why do muscles produce force?
- Provide stability (trunk in upright position)
- Propel body segments
Where do muscles attach?
At least 2 sites of attchment
Origin: stationary anchor point located proximally
Insertion: mobile attachment point located distally
What muscle type doesn’t have at least 2 site of attachment?
Circular muscles
Is muscle contraction symmetrical?
Yes. Equal force is exerted on the origin and insertion.
Why would the position of the origin and insertion become inverted?
If the usual insertion becomes fixed and the origin becomes mobile.
What is the action of a muscle a function of?
- The orientation of its fibres and the relation of these fibres to the joint.
- The starting position of the joint.
How do muscles normally work?
Together. They rarely work in isolation.
What are agonists and antagonists?
Agonists: prime muscle, responsible for the particular movement
Antagonist: oppose the movement of the agonist (required for fine control of movement)
What are synergists?
Muscles that act to assist a prime mover.
Acting alone they can’t perform the movement of the agonist, but their angle of pull assits the agonist.
What are neutralisers?
Prevent unwanted action of an agonist.
What are fixators?
Stabilisers.
Act to hold a body part immobile whilst another part is moving.
e.g. most proximal joints are stabilised whilst distal joints move
What is concentric contraction?
Contraction causing shortening of the muscle.
Most common.
e.g. biceps- full extension of elbow to full flexion
What is eccentric contraction?
Muscle lengthens as it contracts.
e.g. lowering a dumbbell, biceps are contracting to reduce rate at which dumbbell is lowered but biceps is legnthening
What is isometric contraction?
No change in length of the contracting muscle.
e.g. carrying an object
Does the length of the muscle affect the amount of force it produces during isometric contraction?
Yes, it depends on the length of the muscle during contraction.
Each muscle has an optimum length at which the maximum isometric force is produced.
What are the different arrangements of skeletal muscle fibres?
Parallel: strap, fusiform, triangular (fan shaped)
Pennate: uni/bi/multi
Circular
What is the most common fibre arrangement?
Parallel to the force generating axis.
Strap: fibres run longitudinally, like a belt/strap
Fusiform: cylindrical, wider in centre tapering off at the ends
Triangular: fibres converge at one end
What is the structure of pennate muscles?
Have one or more aponeuroses running through muscle body from tendon.
Fasicles of muscle fibres attach to aponeuroses at an angle to the direction of movement.
Uni- all fasicles on same side of tendon
Bi- fasicles on both sides of the tendon
Multi- central tendon branches into several tendons from which fasicles originate
Do pennate/parallel muscles produce a greater force?
Pennate produces more force for the same amount of muscle, beacuse it has a greater number of muscle fibres.
-but shortening achieved is less (conflict b/w force & movement)
What is the structure of circular muscles?
Fibres form concentric rings around a sphincter/opening.
-attach to skin, ligaments, fascia, muscles rather than to bone
What does a fascial compartment contain?
Muscles,nerves, blood vessels
What do muscles within a compartment have in common?
They share a common innervation and action. Each compartment has a separate nerve/blood supply.
Why are connective tissues called connective tissues?
They are all physically connected with each other.
What is fascia?
Band/sheet of connective tissue.
What is superficial fascia?
Subcutaneous fatty layer.
Often called the subcutis/hypodermis
Not always found immediately below the skin, it also surrounds organs, glands and neurovascular bundles.
What is the purpose of the superficial fascia?
- Storage medium for fat and water.
- passageway for lymphatics, nerves & blood vessels
- protective padding for organs
What is the deep fascia, and what is it made of?
Thickened elaboration of epimysium enveloping muscle compartments.
Made of collagen bundles and elastin fibres orientated in wavy pattern parallel to direction of pull.
-flexible and resists great unidirectional forces
What are the palmar creases of the hand due to?
The adhesion of the deep fascia to the skin.
What are tendons, ligaments and aponeuroses?
Tendons: connect muscle to bone
Ligaments: connect bone to bone
Aponeuroses: connect muscle to muscle
What do tendons and ligaments have in common?
They both have a poor blood supply which impedes healing.
What do tendons and ligaments consist of?
Dense regular connective tissue fasicicles, enclosed with dense irregular connective tissue sheaths.
Tendons: low elastin to collagen ratio
How are tendons anchored to bone?
Sharpey’s fibres
What impedes the healing of tendons?
- poor blood supply
- low water content: limiting diffusion of nutrients
What is the major role of ligaments?
Stabilise joints and limit their range of movement.
-some store energy to assist with propulsion
What are peri-articular ligaments?
Comprise thickening of the capsule that srrounds synovial joints, acting as reinforcement.
What are aponeuroses?
Sheet like structures similar to tendons.
-join muscles of the body
What is Hilton’s Law?
Nerves supplying the muscles moving the joint also supply the joint capsule and the skin overlying the insertions of these muscles.
What organises groups of cells into tissues?
Segmentation.
- Repeating pattern of subunits called segments arranged along the longitudinal axis.
- involved in patterning and segregation of groups of cells
- generates regional properties for cell groups and organises them into tissues
What is segmentation controlled by?
Hox genes.
- Expressed in segmental pattern in cranio-caudal axis.
- the order that the hox genes are encoded on the chromosomes is reflected in the order they are expressed in the body
What do the hox genes determine?
They determine the different types of vertebrae and the type of limb that will develop from a limb bud.
What are homeotic mutations?
Mutation to the hox genes, causing tissues to alter their normal differentiation pattern.
e. g. generation of 6th lumbar vertebra in place of 1st sacral vertebra
e. g. mutation in hox genes governing digits=extra digits
e. g. mutation in cervical spine resulting in additional ribs (cervical ribs)
How do cervical ribs present clinically?
Compress nearby arteries and nerves leading to thoracic outlet syndrome. Pain in shoulders and neck, numbness in fingers.
What are serially homologous?
Upper and lower limbs (extremely similar development)
When do limb buds first appear?
4th week of development- appear as small lateral projections in the coronal plane.
What are limb buds and how do they form limbs?
They consist of mesenchyme covered by a layer of ectoderm.
- at the tip of the bud, ectodermal cells divide to form an apical ectodermal ridge
- limb buds elongate via proliferation of mesenchyme
What is the purpose of the apical ectodermal ridge?
It exerts an inductive influence on the limb mesenchyme, promoting development of the limbs.
In what week does endochondrial ossification occur?
Week 12.
Where does the hyaline cartilage remain?
In the epiphyseal end plates in children to allow for bone elongationg and at articular surfaces of joints.
How does muscle mass develop in the limb buds?
Myoblasts aggregate and develop large muscle mass in the buds.
-muscle mass separates into dorsal (extensor) and ventral (flexor) components
What are the pre-axial and post-axial borders of the limbs?
Pre-axial: cranial (top of arm as if your are standing like a star)
Post-axial: caudal (tail)
How do the limbs rotate?
Upper and lower limbs rotate in opposite directions.
Upper: rotate externally 90 degrees on longitudinal axis so elbows face backwards, extensor muscles lie on posterior aspects of limb
Lower: rotate internally 90 degrees so future knees face forwards and muscles lie on the anterior aspect of limb
What does the limb rotation explain?
The spiral pattern of dermatomes in the lower limb.
