Properties of the Motor Unit Flashcards
define motor unit
The minimal functional unit of the motor system. It consists of a somatic efferent (alpha-motoneuron) and all the extrafusal muscle fibres it supplies e.g.
extra-ocular muscles (1 neurone :10 fibres)
quadriceps (1 neurone:1000 fibres)
what are the 4 components of the motor system?
- Motoneurons (Neuronal tissue)
- Skeletal Muscles (Muscular tissue)
- The Neuromuscular Junction (where the neurone and muscle connect – specialised synapse).
- Connective tissue
what do the motor systems of the body work together to do?
Set muscle tone of the body – a small amount of sustained muscle contraction responsible for body posture
Bring about voluntary movement via antagonistic muscle pairs
define innervation ratio
The number of muscle fibres innervated by a single motor neurone.
Generally, the smaller the innervation ratio the more precise the movement.
where do the motor neurones originate from in the NS?
NS –> PNS –> efferent system –> somatic motor efferents (for upper motor neurones) –> alpha motor neurone (for lower motor neurone)
what are the 2 types of muscle?
striated
non- striated
what are the 2 muscles that are striated?
skeletal
cardiac
what is the muscle that is non- striated?
smooth
what are both striated and non-striated muscles made of?
Striated and non-striated muscles are both made of muscle tubulars.
In striated, however the tubulars are arranged in a PARALLEL formation.
In non-striated they run in EVERY direction.
define myogenic
what muscles are myogenic
generate their own electrical activity - ANS only controls rate & strength of contraction
Both cardiac and smooth muscle are myogenic
what are the 4 important functions of the skeletal muscle?
Set muscle tone of the body – a small amount of sustained muscle contraction responsible for body posture
Allow for voluntary movement via antagonistic muscle pairs
Stabilises joints
Generate heat – mechanical efficiency of skeletal muscle is 20% so 80% is lost by heat.
describe the general anatomy of skeletal muscles
The single cell of muscle is known as a myocyte - muscle fibre
Myofibrils are the most abundant organelle within them
Myocytes collect together form a fascicle
The neurovascular bundle (blood vessels) of any muscle runs in between and in parallel with muscle fascicles
Fascicles collect to form a muscle
what is the order in the organisation of the muscle starting from the most superficial layer first?
muscle –> fascicles –> muscle fibres –> myofibrils –> myofilaments
what are the 3 tissues that envelope the skeletal fibres?
Epimysium – CT enveloping all fascicles
Perimysium – CT enveloping a fascicle
Endomysium – CT enveloping each muscle fibre
what is the importance of tendons?
A tendon is a tough band of fibrous connective tissue
Attaches muscle to bone
It forms a point of confluence, bringing together the individual contractions of the myocytes to produce a combined action at a usually a joint.
Skeletal muscle can be classified according to the assemblies of their fascicles… what are these 5 classifications?
convergent/triangular
circular/sphincteric
parallel/strap
fusiform
Pennated Muscles
what are convergent/ triangular muscles?
muscle fibres converge to a small point on a tendon
allows for very strong contraction (i.e. pectoralis major)
what are circular/sphincteric muscles?
surround openings at orifices (i.e. orbicularis oris)
what are parallel/strap muscles?
fibres run parallel to each other
these are long muscles that cause large movements - not strong but good endurance (i.e. sternocleidomastoid)
what are fusiform muscles?
spindle-shaped
belly wider than points of origin & insertion (i.e. biceps brachii)
what are pennated muscles and what are the 3 types?
a muscle with fascicles that attach obliquely (in a slanting position) to its tendon.
unipennate – fibres diagonal to tendon - allows great strength (i.e. lumbricals)
bipennate – bilateral fibres run in opposing diagonals to central tendon - more power but less motion range (i.e. rectus femoris)
multipennate - multiple rows of diagonal fibres, with a central tendon which branches into two or more tendons - produce powerful contractions (i.e. deltoid muscle w/ anterior, posterior & middle sections)
what is structure of actin?
the thinner filament. They are connected to the Z line.
Actin filaments have binding sites for myosin heads.
what is the structure of myosin?
the thicker filament. Myosin filaments have globular heads that bind to the actin binding sites.
what is the binding site on actin called?
actin—myosin binding site