muscles Flashcards
define muscular system
muscle tissue is specialised to contract when it is stimulated thus to exert a physical force on other tissues, organs or fluids
types of muscle
skeletal muscle
cardiac
smooth
cardiac muscle
only in heart
responsible for circulation of blood
cardiac muscles are; striated and shorter, branched and connected by intercalated discs
centrally located nucleus
smooth muscle
not innervated by motor neurons
those innervated are not under voluntary control
may contract or relax in response to:
- chemicals
- hormones
- local 02 conc
- physical factors
arranged In sheets, bundles or sheaths
cells bound together transmitting contractile forces
smooth muscle tissue have normal background level of activity, or smooth muscle tone
skeletal muscle
forms muscles responsible for movement of skeleton, locomotion, chewing and breathing
under voluntary control
origin, muscle belly and insertion
- include voluntary sphincters of eyelids, urethra and anus, diaphragm, tongue and some muscles of oesophagus
structure of skeletal muscle
muscle belly = covered in dense layer of collagen fibres, separating muscle from surrounding tissues and organs called epimysium
connected to deep fascia
epimysium encloses several muscle fasciculi
muscle fascicle = enclosed by connective tissue of perimysium
perimysium contains blood vessels and nerves
muscle fibre = delicate connective tissue surrounds each muscle fibre called endomysium, cell membrane contains sarcoplasm within which lies the myofibrils
myofibrils responsible for muscle contraction
microscopic structures of skeletal muscle
muscle cells are:
- cylindrical
- multinucleate
- striated
- packed with contractile proteins
muscle adaptation
highly plastic tissue
adapts to changes in activity pattern and loading
muscle size (atrophy and hypertrophy)
balance between protein synthesis/degradation
affected in diseased state
attachment of skeletal muscle
skeletal muscle attach to bones through extensions of their connective tissue components
indirect = muscle ends short of it bony destination and bridge is gapped by fibrous band or sheet called tendon
tendon can be broad sheet called aponeurosis
direct = little separation between muscle and bone
to naked eye, muscle tissue appears to emerge directly from bone
at microscopic level muscle fibres stop slightly short of bone and gap is spanned by collagen fibres
origins and insertions
most skeletal muscles are attached to a different bone at each end, so either muscle or tendon span at least 1 joint
when muscle contracts, it moves one bone relative to other
bony site of attachment at relatively stationary end is called origin
attachment site at more mobile end is called the insertion
functional groups of muscles
skeletal muscles seldom act independently but rather function in groups whose combined actions produce coordinated control of joint
agonist = contraction is chiefly responsible for producing particular movement
antagonist = action opposes that a particular agonist, stretches but will not usually relax completely
synergist:
- aids agonist
- stabilise joint or start movement
fixator:
- prevents unwanted movement and stabilises joints
skeletal muscle functional anatomy
- skeletal muscle required to perform large range of movements
- the size and shape of a muscle influences its capabilities
- longer a muscle fibre, greater range of movement it can generate
- increase in number of muscle fibres increases strength of the contraction
fascicle arrangment
fibres within fascicle are arranged in parallel
orientation of fascicles determines functional properties of muscle
fusiform = thick in middle, tapered at each end
parallel = fairly uniform width with parallel fascicles
circular muscle
fibres arranged concentrically around an opening or recess
triangular muscle
fan-shaped
broad at one end, narrow the other
