Session 4 Flashcards
What are parallel muscles and what are the three different types?
Fibres run parallel to force generating axis.
Strap - eg sartorius
Fusiform - wider and cylindrical shaped in the centre, taper off at ends. Eg biceps brachii.
Fan shaped - fibres converge at one end, eg pectoralis major
What are circular muscles?
Where fibres form a concentric ring around a sphincter. Tend not to attach to bones. Eg orbicularis oculi around the eye
Define: agonist, antagonist, synergist, neutraliser and fixator.
Agonist - the prime muscle(s) responsible for a particular movement.
Antagonist - oppose prime movers. Important for the fine control of the movement.
Synergist - assist prime movers. Acting alone they cannot perform the movement of the agonist.
Neutralisers - prevent unwanted actions that the agonist can perform. Eg the rotator cuff muscles prevent flexion of the elbow whilst the bicep flexes the elbow.
Fixators - hold a joint stable whilst another one is moving
What is isotonic contraction and what are the two different types?
Where the tension within the muscle remains constant and the length changes.
Concentric contraction - where the muscle shortens
Eccentric contraction - where the muscle lengthens. Can result in delayed onset muscle pain.
What is the contraction called when the muscle is generating tension but not shortening?
Isometric contraction
What is a motor unit?
An Alpha-motor neurone and the group of individual muscle fibres it innervates
What is the advantage of big or small motor units?
Muscles that perform precise fine movements have a low number of muscle fibres per motor unit. Powerful muscles have a high number.
What form of myosin heavy chain do the different types of muscle fibres possess?
Slow/type I muscle fibres - type I myosin heavy chain (slow oxidative)
Fast/type II muscle fibres - type IIA (fast oxidative). Type IIX (fast glycolytic).
What factors does the contractile force produced by a muscle depend on?
The size principle - small motor neurones are recruited before large ones, generally meaning that slow fibres are recruited first.
The rate code - the frequency that the muscle fibres are stimulated by their motor neurone. Consecutive APs in a repetitive train result in summation, giving a slightly larger force with each contraction. Eventually a limit, called tetany, is reached.
What causes baseline muscle tone?
Motor neurone activity
Muscle elasticity
What is hypotonia and what can cause it?
A lack of skeletal muscle tone. Caused by damage to the motor cortex/cerebellum/spinal cord or myopathy.
What are pennate muscles and what are the three different types?
They have one or more aponeurosis running through the muscle body. The fascicles attach to the aponeurosis at an angle (pennation angle).
Unipennate - all fascicles on the same side of the tendon eg extensor digitorum longus of foot
Bipennate - fascicles on both sides of central tendon eg rectus femoris
Multipennate - central tendon branches eg deltoid
What are the articulating surfaces of the elbow joint?
Trochlear notch of the ulna with the trochlea of the humerus.
Head of the radius with the capitulum of the humerus.
Outline the stability of the elbow joint
Weak anteriorly and Posteriorly. Joint capsule strengthened medially and laterally by collateral ligaments.
What is malignant hypothermia and how is it treated?
A rare life-threatening condition triggered by some volatile anaesthetic agents and succinylcholine, a neuromuscular blocking agent. Leads to uncontrolled increase in oxidative metabolism, hence body temperature.
Polymorphism in the ryanodine receptor is the most common cause. The receptor become activated and leads to a massive increase in intercellular Ca2+ from stores. The SERCA pump works at an increased rate, consuming ATP.
Dantrolene is administered which antagonised the ryanodine receptors.
