17-01-22 - Introduction to the Limbs Flashcards
At what week of embryonic does the formation of muscles begin?
- Muscle formation starts at week 4 of embryonic development
How does the formation of muscles process occur?
- Specialised cells migrate from somites and the lateral plate mesoderm
- Limb buds form from sclerotome, dermatome and myotomes, which will develop into limbs
What are the 3 different types of muscles?
- The 3 different types of muscle are skeletal muscles, smooth muscles, and cardiac muscles
What do skeletal muscles require to bring about movement?
- To bring about movement, skeletal muscles must attach to 2 bones that are connected to each other by a mobile/semi-mobile joint
- Skeletal muscles need at least 2 points of attachment
- These attachments are usually referred to as the origin and the insertion
What is the origin?
The origin is usually the proximal end of the muscle, which remains fixed/less mobile during muscular contraction
What is the insertion?
The insertion is usually the distal end of the muscle, which is movable
What can knowing the origin and the insertion indicate?
- Knowing the origin and insertion of a muscle, the kind of movement the contraction of this muscle brings about can be identified
What occurs when muscle contraction is stimulated?
- When muscle contraction is stimulated, the 2 ends of the muscle at the point of attachment (origin and insertion) will try and move closer to each other
What direction does the muscle contraction usually occur in? Why is this?
- When muscles contract and shorten, they usually shorten in the insertion to origin direction, as the origin is less mobile, though some muscles can shorten in both directions in different circumstances
What are the 2 different types of muscle contraction?
1) Isometric contraction
2) Isotonic contraction
What occurs during isometric contraction?
muscle tone changes (muscle length not changed)
What occurs during isotonic contraction?
muscle length changes (muscle tone not changed)
What is the prime mover?
Muscles(s) that play the primary role in moving a body part
What is fascia?
- Facia is connective tissue underneath skin and around muscles
How does deep fascia separate muscles into compartments?
- Deep fascia sends septae (intermuscular septae) between the muscles to separate them into compartments
What compartments are formed in the arm by intermuscular septae?
- The intermuscular septae divide the arm into an anterior (mostly flexor muscles) and a posterior (mostly extensor muscles) muscular compartment
Why is deep fascia of the lower limb thicker than deep fascia of the upper limb?
What is deep fascia of the thigh called?
How does it compare medially and laterally?
What is this called?
How is the thigh divided into 3 muscular compartments?
- Deep fascia of the lower limb is thicker than that of the upper limb as the muscles need to compress the veins during contraction for the venous blood to return to the heart against gravity (acts like a muscle pump)
- Deep fascia of the thigh is called fascia lata
- The fascia lata is thicker laterally, in the form of the iliotibial tract
- The fascia lata sends septae to divide the thigh into:
- Anterior (mainly extensor muscles)
- Medial (mainly adductor muscles)
- Posterior (mainly flexor muscles) muscular compartments
What is the deep fascia of the leg called?
What does the deep fascia of the leg form?
How does the crural fascia divide the leg into 4 muscular compartments?
- Deep fascia in the leg is continuous and as it goes from the thigh to the leg, it changes from fascia lata to crural fascia
- The crural fascia fuses with the tibia (medial long bone of the leg) as it is very superficial with no muscle
- The crural fascia of the leg forms the interosseal (IO) membrane
- The crural fascia of the leg sends septae to divide th leg into:
- Anterior (primarily extensor muscles)
- 2 Posterior (superficial and deep flexor)
- Lateral (peritoneal) muscular compartments
What are neurons?
How do they function?
What is their structure?
What are they supported by?
- Neurons are excitable nerve cells that transmit information through electrical signals or action potentials
- A typical neuron has a cell body (soma) and neurite(s).
- A neurite can either be an axon or dendrite.
- Axon is single, can be as long as 1m, covered with myelin or schwann sheath.
- Dendrites are multiple, thing, short extensions.
- Neurons are supported by Glilal cells (neuroglia).
What are the 5 steps of spinal nerve reflex?
- Sensory (afferent) information comes from the periphery, which would come through to the dorsal root ganglion
- After the dorsal root ganglion, the fibres form the dorsal root, which enters the dorsal horn of the spinal cord (this information ascends the spinal cord to the brain)
- After being processed by the brain, the motor (efferent) fibres descend the spinal cord and will exit from the ventral horn, which forms the ventral (motor) root to the periphery
- If the output is somatic (conscious) it will go straight to the periphery
- If the output is visceral (sympathetic nervous system), the pre-ganglionic fibres will exit the lateral horns and synapse in the sympathetic ganglion with post-synaptic fibres before entering the periphery (may be an effector)
- Ganglion – collection of cell bodies out with the CNS
- Sympathetic ganglion right next to spinal cord
- Parasympathetic ganglion right next to target structure
What is a dermatome?
What is a myotome?
- A dermatome is a strip of skin supplied by 1 spinal nerve
- A myotome is the group of skeletal muscles supplied by 1 spinal nerve
What are roots formed?
What are the 2 different kinds of roots?
How are spinal nerves formed?
What do spinal nerves divide in to?
• Rootlets converge to form roots
• There are 2 kinds of roots:
1) Ventral – motor (efferent)
2) Doral – sensory (afferent)
• Ventral and dorsal roots converge to become a spinal nerve, which is mixed motor and sensory
• Spinal nerves divide to form ventral and dorsal rami, which are mixed motor and sensory nerve fibres
Why are dermatomes so well organised in the thorax and abdomen but not the limbs?
Why do we have our thumb on the lateral side of our hand but our big toe on the medial side of the foot?
Why are the flexor muscles of the upper limb on the anterior aspect of the upper limb while flexor muscles of the lower limb are on the posterior aspect of the limb?
- Initially, both the thumb and hallux (big toe) are on the cranial side of each limb (point towards the head), and both the palm and sole face anteriorly (medially in these images)
- The upper limb then rotates laterally from its in-utero position
- The thumb moves from superior to lateral
- Flexor muscles group to an anterior position
- Extensors move to a posterior position
- The lower limb rotates medially
- The hallux moves from superior to medial
- Flexor muscle groups move from an anterior to a posterior position
- Extensors move to an anterior position
- The dermatomes rotate too while the limbs form, leading to the pattern of dermatomes seen on limbs
Where do spinal nerves emerge from?
Where do spinal nerves emerge in relation to their respective vertebrae?
What is a plexus?
What are the formed by?
- Spinal nerves emerge from the intervertebral foramen (Intervertebral foramina)
- C1 to C7 spinal nerves emerge above their respective vertebrae
- C8 spinal nerve emerges below the C7 vertebrae
- T1 and all the other spinal nerves below emerge below their respective vertebrae
- A plexus is a network of something, usually nerves, but can be arteries and veins
- The ventral ramus of all spinal nerves, with the exception of the thoracic region (excluding T1) will usually form plexuses
What nerves innervate the upper limb?
What are the 5 branches that innervate the upper limb?
- The upper limb is supplied by 5 termianl branches of the brachial plexus, which is formed in the axilla (armpit) by ventral rami (anterior branches) of spinal nerves
- The 5 terminal branches that innervate the upper limb:
- Musculocutaneous nerve
- Axillary nerve
- Radial nerve
- Median nerve
- Ulnar nerve
What plexus’ terminal branches are responsible for the neural innervation of muscles of the lower limb and pelvic girdle?
What is it derived from?
Where is it found?
- The terminal branches of the lumbo-sacral plexus is responsible for innervating the muscles of the lower limb and muscles of the pelvic girdle
- The lumbo-sacral plexus us derived from the ventral rami of L1-L5 and S1-S4
- The lumbo-sacral plexus is found within the psoas major on the posterior abdominal wall, and on the lateral side of the pelvis
What is the main arterial supply of the upper limbs and pectoral girdle?
What is the main arterial supply for the lower limbs and pelvic girdle?
- The main arterial supply for the upper limbs and pectoral girdle is the subclavian artery
- The main arterial supply for the lower limbs and the pelvic girdle is the external iliac artery
Where are superficial veins located in the upper limb?
What are the 2 superficial veins responsible for venous drainage in the upper limb?
What do these superficial veins divide into?
What are these superficial veins accompanied by?
What are they connected to?
What 2 things can these superficial veins be used for?
- Superficial veins are located in the superficial fascia of the upper limb
- The cephalic and basilic veins are superficial veins responsible for venous drainage of the upper limb
- The cephalic and basilic veins divide into dorsal and palmar venous networks in the hand
- These superficial veins are accompanied by arteries
- They are also connected to deep veins by perforating veins
- The cephalic vein can be used for an IV line
- The median cubital vein (aka median basilic vein) can be used for a venous sample
Where are the superficial veins of the lower limb found?
What are the main 2 superficial veins responsible for venous drainage in the lower limb?
Where are they found?
Why are connections between superficial and deep veins more important in the lower limbs than the upper limbs?
What direction does venous flow go?
What are the 3 ways venous return to the heart is aided?
- Superficial veins of the lower limb are found in the superficial fascia
- The great (long) saphenous vein runs from the foot to the groin
- The small (short) saphenous vein runs from the foot to eh popliteal fossa behind the knees
- Connections between superficial and deep veins are more important in the lower limbs than the upper limbs because blood is being pumped up the way against gravity towards the heart
- Venous flow goes from superficial veins to deep veins via perforating veins (aka perforators)
- How venous return to the heart is aided:
1. Veins can be associated with arteries – the artery pulsating aids movement of the blood within veins - These veins are known as venae comitantes – Latin for accompanying vein
- Muscular contraction (muscular pump) propels blood along the veins, with aid from the venous valves
- Respiratory pump – thoracic and abdomen pressure changes because of breathing, which aids in blood return to the heart.
What do lymph vessels follow?
Where does lymph in the upper limbs mainly drain to?
Where does lymph in the lower limbs mainly drain to?
- Lymph vessels follow the superficial or deep veins
- In the upper limbs, lymph mainly drains to the axillary lymph nodes
- In the lower limbs, lymph mainly drains to the inguinal lymph nodes
What can inability to perform movements indicate?
What movements of the upper limb are innervated by which spinal nerves?
- Inability to perform movements can indicate problems with joints, muscles, or spinal nerves responsible for the movement
What movements of the lower limb are innervated by which spinal nerves?
