STRUCTURE AND FUNCTION OF THE MUSCULAR SYSTEM


what is a muscle

  • specialised bundles of fibre

  • highly cellular well vascularised tissues

  • which has the ability to shorten and lengthen

  • responsible for most types of body movement


what are the function of muscles

  • movement - initiation and control

  • stability - posture

  • heat production

  • assist circulation


what are properties of muscles

  • contractility

  • elasticity

  • extensibility

  • electrical excitability


what are the types of muscle

  • muscle I - smooth muscle

  • muscle II - striated muscle


describe smooth muscle and where they're found

  • spindle shaped cells, central nuclei, arranged to form sheets

  • walls of hollow organs and structures


describe skeletal muscle

  • long thin fibre cells that contain many nuclei and mitochondria

  • the individual fibres are 10-100 micro meters on diameter

  • 0-30 cm in length

  • fibres embed into connective tissue and are bound into bundles

  • contraction initiated by nerve impulses generated externally


EACH SKELETAL MUSCLE IS A DISCRETE ORGAN COVERED WITH DENSE CONNECTIVE TISSSUE ORGANISED INTO BUNDLES OR FASICLES AND HAS THE SARCOMERE AS THE BASIC CONTRACTILE UNIT


describe cardiac muscle

  • similar in structure to skeletal muscle

  • but has autorythmycity

  • long duration action potentials


describe muscle metabolism

  • energy needed for contraction is provided by stored ATP

  • this source is limited to sustain contraction further ATP is produced from the interaction of ADP with creatine kinase

- from stored glycogen via anaerobic pathway of glycolysis (which produces lactic acid)

- by aerobic respiration


when can skeletal muscle contraction only occur

  • if there's ongoing impulse to continue the release of calcium which keeps the myosin binding sites open

  • there's insufficient ATP


muscle = grouping of fascicles

fascicles = grouping of muscle fibres

muscle fibres = bundle of myofibrils

myofibrils = bundle of myofilaments


what is the epimysium

the overcoat of dense connective tissue on whole muscle


what is the perimysium

connective tissue around the fascicles


what is the endomysium

connective tissue around each individual fibre


skeletal muscles also include

  • other cells

  • excitatory elements

  • feedback systems

  • connections to supporting structures - by non contractile collagen rich attachments

- tendon

- aponeurosis?

- direct

  • circulatory/neural mechanisms


what are functional requirements of skeletal muscle

  • adaptability

  • - to enable alterations to contraction speed

  • - alterations in intensity

  • - variable speed of reaction

  • - efficiency

  • achieved by adaptations of structure, metabolism and activation


what are structural adaptations of skeletal muscle

  • sarcomere arrangement

  • fascicle arrangement


what are metabolic adaptations of skeletal muscle

  • muscle fibre type

  • blood supply and energy source

  • classified by rate of contraction/fatigue and energy source


what are different types of muscle fibre

  • slow twitch/type I - oxidative aerobic (darker due to more myoglobin)

  • fast twitch/type II

- type IIa - intermediate oxidative-glycolytic

- type IIb - glycolytic (lightest)


what are neurological adaptations of skeletal muscle - which are needed to produce muscle contractions which vary in length and intensity which are graded muscle responses produced by neurologically

  • changing the stimulus strength

  • changing the stimulus frequency

  • ensuring optimal performance

  • ensuring readiness for action


what are the most common patterns of fascicle arrangement

  • parallel

  • pennate

  • convergent

  • circular


how is movement initiated and recruited

  • by motor nerves


what is a motor unit

  • one neuron and all the muscle fibres it supplies


how do motor nerves initiate and recruit movement

  • arises in anterior of horn of the spinal cord leave via ventral root

  • and enters the muscle and branches to supply different groups of muscle fibre

  • individual axons branch to supple a number of individual muscle fibres


what does cyclical contraction mean

  • when not all motor units fire at the same time


what are the proprioceptors in skeletal muscle known as

  • muscle spindles

  • golgi tendon organs


what do muscle spindles do

  • detect muscle length and communicate this via the sensory nerves to the CNS

  • the activation leads to the excitation of the muscle where its situation and inhibition of the antagonist


what do the golgi muscle tendon organs do and where are they located

  • they detect the degree of tension generated

  • activation leads to inhibition of the muscle where it's situated and excitation of the antagonist

  • located at the junction of a tendon and a muscle


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how are muscles named

  • location

  • function

  • shape

  • direction of fibres

  • number of heads

  • points of attachment

  • size


what is active insufficiency

  • the inability of bi/multi articulate muscles to generate full contraction force in a shortened or lengthened position


what is passive insufficiency

  • the inability to reach full ROM due to the limit of muscle length across more than one point


explain the process of skeletal muscle fibre

  • release of Ca reveals the myosin binding site on actin

  • the hydrolysis of ATP energises the myosin heads to attach to myosin binding sites to from cross bridges

  • power stroke draws actin in

  • the recycling of ATP and Ca causes cross bridges to break to ensure they're ready for the next cycle