Session 2 Flashcards
What are the various arrangements of skeletal muscle?
Circular - Orbicularis Oris
Convergent - Pec Major
Parallel - Sartorius
Unipennate - Extensor digitorum longus
Multipennate: Deltoid
Fusiform (amorphous structureless fibres): Biceps brachii
Bipennate: Rectus femoris
Describe the structure of skeletal muscle
Epimysium: tough outer connective tissue layer, continuous with tendon - distribute force onto tendon
Perimysium: surrounds fascicles (bundles of muscle fibres)
Endomysium: surrounds individual muscle fibres A fascicle is a functional unit
Describe the types of levers
First class levers: (skull is balanced on top of the cervical vertebrae) see - saw arrangement (most efficient)
Second class levers e.g. In the leg: not very efficient
Third class levers: least mechanically efficient - biceps brachii at the elbow joint (fulcrum)
Define the muscle groups
Agonists: prime movers (main muscles responsible for a particular movement)
Antagonists oppose agonists. Agonist-antagonist allow control of fine movement.
Synergists: help agonists by producing the same movement or by reducing undesirable movements (neutralising extra motion).
Fixators: (specialised Synergists) - hold a bone still or stabilize the origin of a prime mover so all the tension can be used to move the insertion bone. The postural muscles that stabilize the vertebral column are fixators.
Discuss Compartment Syndrome
Each group of muscles in the limbs together with nearby neurovascular structures is contained within an enclosed space surrounded by fascia. The tough fascia do not easily stretch or expand easily so the pressure inside the compartment can easily increase if bleeding or swelling occurs.
Compartment Syndrome occurs when there is bleeding inside, increasing the pressure on the muscle therefore causing nerve damage due to decreased blood supply.
This can case paraesthesia, pain, swelling and movement restriction.
Describe Isotonic Contraction
Constant tension (constant force and equal tone), variable muscle length - the muscle changes length and moves the load
Two types:
Concentric ( muscle shortens e.g. Biceps shorten and flex the elbow joint when lifting load with the arm)
Eccentric (muscle exerts a force while being extended e.g. Walking downhill - can cause delayed onset muscle soreness)
Describe Isometric Contraction
Constant length, variable tension e.g. Hand grip. Muscle is exerting a force but length stays the same - muscles do not shorten.
What are the Muscle Fibre Types?
Type I (Slow Oxidative)
Type IIa (Fast Oxidative)
Type IIb (Fast glycolytic)
(2 types of fast twitch fibres and 1 type slow twitch)
Describe Type I muscle fibres
Slow oxidative
Aerobic
High myoglobin levels
Red colour
Many mitochondria
Rich capillary supply
Fatigue resistant
Endurance activities, posture
Describe Type IIa Muscle Fibres
Fast oxidative
Aerobic
High myoglobin levels
Red to pink colour
Many mitochondria
Rich capillary supply
Moderate fatigue resistance
Walking, sprinting
Describe Type IIb Muscle Fibres
Fast Glycolytic
Anaerobic glycolysis
Low myoglobin levels
White (pale) colour
Few mitochondria
Poorer capillary supply
Rapidly fatigable
Short, intense movements
Describe the feedback control of movement
Muscle spindles are proprioreceptors (sensory receptors) within the belly of a muscle. They detect changes in the length of this muscle and convey this information via sensory neurones to the brain to determine the position of body parts.
The responses of muscle spindles to changes in length also play an important role in regulating the contraction of muscles, by activating motoneurones via the stretch reflex to resist muscle stretch.
Where and what are Muscle Spindles?
Found within the belly of muscles, embedded in extrafusal muscle fibres.
Muscle spindles are composed of 3-12 intrafusal muscle fibres.
Muscle spindles are also known as proprioreceptors.
What is a Motor Unit?
A motor neurone and the muscle fibres it innervates.
A single motor neurone will innervate a particular number of muscle fibres.
The fewer muscle fibres a motor neurone innervates, the finer the control of movement
Describe Communication between Neurones and Muscle
‘Crosstalk’
Signalling molecules communicate between nerve and muscle.
Atrophy of nerve or muscle can lead to atrophy of the corresponding neurone or muscle.
Maintaining crosstalk is really important.
Examples: neurotrophins, cytokines, insulin-like growth factors