Muscles Flashcards
What’s a fasciculation
Small, local, involuntary skeletal muscle contraction and relaxation (twitch)
Describe the origin of a skeletal muscle
Bone
Usually proximal
Greater mass and more stable during contraction than the insertion
Describe the insertion of a skeletal muscle
Bone, tendon or CT
Usually distal
Usually moved by contraction
What are the 3 arrangements of skeletal muscle
Circular
Parallel
Pennate
Describe circular skeletal muscle
Give examples
Fibres form concentric rings around sphincter or opening
Orbicularis occuli, orbicularis oris
What do circular skeletal muscles attach to
Skin
Ligaments
Fascia of other muscles
Describe parallel skeletal muscles
Fibres run parallel to force generating axis
What are the types of parallel skeletal muscle
Give an example of each
Strap - sartorius
Fusiform - biceps brachii
Fan shaped/convergent - Pectoralis major
Describe Pennate skeletal muscle
Has 1 or more aponeuroses through muscle body from tendon
Fascicles attach to aponeuroses at an angle (pennation angle) to direction of movement
Types of Pennate skeletal muscle
Give an example of each
Unipennate (fascicles on same side as tendon) - extensor digitorum longus
Bipennate (fascicles on both sides of tendon) - rectus femoris
Multipennate (central tendon branches) - deltoid
What separates compartments of muscle
Fascia
What is compartment syndrome
Bleeding within compartment exerts pressure on nerves and blood vessels
Symptoms of compartment syndrome
Constant poorly localised pain Paresthesia Compartment feels tense Swollen shiny skin Bruising and blistering Prolonged capillary refill time
Treatment of compartment syndrome
Fasciotomy
Define agonist
Main muscle responsible for a particular movement
Define antagonist
Opposes action of agonist
Define synergist
Assists agonist
Acting alone it can’t perform the movement of the agonist
Define neutraliser
Prevents unwanted actions that an agonist performs
Example: rotator cuff muscles prevent shoulder Flexion during elbow Flexion (biceps brachii)
Define fixator/stabiliser
Holds a body part immobile whilst another is moving
What are the types of muscle contraction
Isotonic contraction
Isometric contraction
Passive stretch
Describe isotonic contraction
Tension is constant
Muscle length changes
Types of isotonic contraction (describe)
Concentric - muscle shortens
Eccentric - muscle exerts force while extending
Effect of eccentric isotonic contraction
Damages muscles and causes delayed onset muscle pain
Describe isometric contraction
Muscle length is constant
Tension changes
When does isometric contraction occur
Load against muscle equals contractile force being generated
E.g. Holding weight in fixed position
Describe passive stretch
Give an example
Muscle is lengthened while in passive state
Example: hamstrings lengthen when touching toes
Describe first class lever Give example
Effort at one end, load at other end
Extension/Flexion of head
Describe second class lever Give an example
Effort at one end, load between effort and fulcrum
Plantar Flexion of foot
Describe third class lever Give an example
Effort between load and fulcrum
Lifting weight
What’s a motor unit
Alpha motor neurone and muscle fibres it innervates (connected by neuromuscular junction)
Demonstrate with examples the variety in muscle fibre number in motor units
Muscles that produce precise movements have few muscle fibres - inferior rectus has 9
Powerful movements have lots of muscle fibres - gastrocnemius has 2000
How do types of muscle fibres differ
Myosin heavy chain expression
What are the main types of muscle fibre
Slow oxidative type 1
Fast oxidative type 2a
Fast glycolytic type 2x
What’s the significance of the muscle fibres in each motor unit
All the same type
Therefore a motor unit is either fast, intermediate or slow contracting
Properties of type 1 muscle fibres
Aerobic High myoglobin Red Many mitochondria Rich capillary supply Fatigue resistant Recruited in standing and walking
Properties of type 2a muscle fibres
Aerobic High myoglobin Red/pink Many mitochondria Rich capillary supply Moderate fatigue resistance Recruited in walking and running
Properties of type 2x muscle fibres
Anaerobic Low myoglobin Pale Few mitochondria Poorer capillary supply Rapidly fatiguable Recruited in running, sprinting and jumping
What factors control contractile force
Size principle
Rate code
Describe size principle
Small motor neurones are recruited before larger ones
Therefore motor units are recruited in order of:
Slow type 1
Fast type 2a
Fast type 2x
Describe rate code and summation
More APs gives higher contractile force
Subsequent APs results in summation giving a slightly larger contractile force with each contraction. Limit where no further force can be produced is called tetany
What causes baseline muscle tone
Elasticity of muscle
Low level of motor neurone activity
What controls skeletal muscle tone
Motor control centres in brainstem
What is hypotonia
Lack of skeletal muscle tone
Causes of hypotonia
Cerebellum lesions
Lesions of sensory afferents from muscle spindles
Lower motor neurone lesions
Degeneration of muscle
Describe excitation contraction coupling
ACh release at neuromuscular junction opens L-type calcium channels in T tubules
These channels are in close association with ryanodine receptors in SER
Ryanodine receptors are activated by calcium influx
Calcium is released into sarcolemma and binds to troponin
Bonding sites on actin are revealed
Describe malignant hyperthermia
Rare dominant condition triggered by volatile anaesthetic agents and succinylcholine
Effect of malignant hyperthermia
Uncontrolled increase in oxidative metabolism and resulting increase in body temperature
Increase in intracellular Ca leads to increased rate of SERCA which leads to massive heat production
Treatment of malignant hyperthermia
Dantrolene
Antagonist of ryanodine receptor
Most common cause of malignant hyperthermia
Polymorphism (2 or more alleles at 1 locus) in ryanodine receptor
What is myotonia
Inability to relax muscles at will
Symptoms of myotonia congenita
Muscle stiffness enhanced by cold/inactivity and relieved by exercise
Muscle hypertrophy
Cause of myotonia congenita
Mutations in chloride channel (CLCN1)
What are intrafusal muscle fibres
Type of muscle fibre that facilitates proprioreception (unconscious perception of own body’s movement and spacial orientation)
Contains muscle spindle
What are muscle spindles
Sensory receptors in belly of intrafusal muscle fibres that respond to muscle stretch/length
Innervation of intrafusal fibres and function of neurones
Gamma motor neurone - keep fibres taught
Type 1a sensory neurone - relays rate of change in muscle length to CNS
Type 2 sensory neurone - provides position sense
What happens in patients with large fibre sensory neuropathy
Can perform accurate movements with eyes open but with eyes closed they are grossly inaccurate
Functions of skeletal muscle
Movement
Posture
Joint stability
Thermogenesis
What is sarcopenia
Loss of muscle mass due to loss of muscle fibres and reduced muscle cross sectional area
