skeletal muscles are stimulated to contract by nerves and act as effectors
define antagonistic muscle pairs?
muscles that woke together in oppostion to move bones at joints e.g as one contracts, the other relaxes. this pulls a bone which is part of a joint
define neuromuscular junction?
the neuromusclar junction is synapse between a motor neurone and a skeletal muscle fibre
describe the sequence of events at a neuromuscular junction?
1. Depolarisation of membrane causes Ca2+ ion channels to open
2. Ca2+ enter by facilitated diffusion
3. causes vesicles to fuse with pre synaptic membrane
4. releasing acetylcholine into the synaptic cleft
5. acetylcholine diffuses across cleft
6. binds to receptors on the membrane of muscle fibre/sarcolemma
7. causes sodium ion channels to open
8. sodium ions diffuse in causing depolarisation of membrane of muscle fibre/sarcolemma and muscle contracts
9. the acetylchloine is hydrolysed by acetylcholinestase to prevent muscle being overstimulate
10. the chloine and ethanoic acid diffuse back into the pre synaptic neurone where they are recombined to synthesise acetylcholine using ATP produced by mitochondria
what is gross structure of skeletal muscle?
- in each fibre there are many myofibrals
- theses contain the contractile units called sarcomeres
- in each myofibril there are protein filaments made of actin and myosin
describe the compostion of the two types of bands?
only active filaments (thin) no overlap of myosin (thick) and actin (thin)
descibe the features and properties of each of the muscle tissue types?
Skeletal Smooth Cardiac
Cells Long multinucleate fibres Short and spindle-shaped; one nucleus per cell. Branched with intercalated discs joining cells at their ends; one nucleus per cell.
Appearance Striped / striated Unstriped / unstriated Striped / striated
Controlled by Voluntary NS Involuntary NS Myogenic;
Involuntary NS - controls RATE of contraction
Distribution Attached to the skeleton In tubular organs such as blood vessels, intestines, airways and reproductive system Heart
Function Movement and maintenance of posture Peristalsis, uterine contraction, control diameter of blood vessels/airways, reflexes e.g. pupil size
Contracts to pump blood around heart
Under a microscope
des
cells. skeletal. smooth. cardiac
______|___________|__________|__________|
appearance| striped/striated