5.5.10 muscle Flashcards
define cardiac muscle
found in heart walls
define involuntary muscle
smooth muscle that contracts without conscious control
define neuromuscular junction
structure at which a nerve meets the muscle; similar in action to a synapse
define skeletal (striated) muscle
muscle under voluntary control
how is contraction achieved
interaction between 2 protein filaments - actin & myosin - in muscle cells
what does muscle need to elongate
an antagonist
3 types of muscle
- involuntary (smooth)
- cardiac
- voluntary (skeletal/striated) muscle
describe the structure of involuntary (smooth) muscle
- consists of individual cells, tapered at both ends = spindle-shaped
- at rest, each cell ~500 micrometers long & ~5 micrometers wide
- each cell contains nucleus & bundles of action/myosin
contractions of involuntary (smooth) muscle
- slow & regularly
- does not tire quickly
- controlled by autonomic nervous system
where is involuntary (smooth) muscle found
- walls of tubular structures (eg. digestive system, blood vessels)
- usually arranged in longitudinal & circular layers that oppose each other
describe structure of cardiac muscle
- individual cells form long fibres, which branch forming cross-bridges between
- cross-bridges help to ensure electrical simulation spreads evenly over walls of chambers
- when muscle contracts, arrangement also ensures contraction is squeezing action (not one-dimensional)
- cells joined by intercalated discs = specialised cell surface membranes fused to produce gap junctions which allow free diffusion of ions between cells
- action potentials pass easily & quickly along/between cardiac muscle fibres
describe the contraction of cardiac muscle
- contracts & relaxes continuously throughout life
- can contract powerfully
- doesn’t fatigue easily
- some muscle fibres in heart (purkyne fibres) modified to carry electrical impulses = coordinate contraction of chamber walls
- myogenic = initiate own contraction
- rate of contraction normally controlled by SAN
what does cardiac muscle appear like under the microscope
striated (striped)
where is skeletal muscle found
joints in the skeleton
what does contraction of skeletal muscle cause
- movement of skeleton by bending or straightening the joint
- muscles arranged in antagonistic pairs
describe the structure of skeletal muscle
- muscle cells form fibres ~100 micrometers in diameter
- each fibre = multinucleate & surrounded by sarcolemma (membrane)
- muscle cell cytoplasm is called the sarcoplasm
- sarcoplasm specialised to contain many mitochondria & extensive sarcoplasmic reticulum
- contents of fibres arranged into many myofibrils (contractile elements)
- myofibrils divided into chain of subunits called sarcomeres
- sarcomeres contain protein filaments actin & myosin
how are actin & myosin arranged in voluntary (skeletal/striated) muscle
- arranged in banded pattern
- gives muscle striped appearance
- dark bands = A bands
- lighter bands = I bands
describe the contractions of voluntary (skeletal) muscle
- contracts quickly & powerfully
- fatigues quickly
- stimulated by somatic nervous system
describe the steps involved in the stimulation of a contraction at a neuromuscular joint
- action potentials arriving at end of axon open calcium ion channels, allowing them to flood in
- vesicles of acetylcholine move towards & fuse with end membrane
- acetylcholine molecules diffuse across gap & fuse with receptors in sarcolemma
- sodium ion channels open, allowing sodium ions to enter muscle fibre, causing depolarisation of sarcolemma
- wave of depolarisation spreads along sarcolemma & down transverse tubules into muscle fibre
define a motor unit
- when many motor neurones divide & connect to several muscle fibres
- all these muscle fibres contract together, providing stronger contraction
what can the electrical activity of muscles be investigated using
electromyograph (EMG)
what does the amplitude of the EMG recording reflect
number & size of motor units involved in contraction - more powerful contraction is seen as higher amplitude
