Part 2- Structure and Physiology of muscle Flashcards
What is slow muscle?
- active for prolonged periods of time(e.g posture)
- uses lots of energy therefore have mitochondria
- Myoglobin for oxygen storage
- red colour
What is fast muscle?
- breifly active
- large sarcoplasmic reticulum for rapid release and uptake of calcium
- little myoglobin - white colour
What are the 2 ways you can control the size of muscle contraction?
Spatial
temporal
Define spatial summation
varying the number of active motor neurones
Define temporal summation
varying the frequency of stimuli
What is spatial summation?
lot of motor unit active means a lot of cells shorten which leads to bigger contraction
What is a motor unit?
a single neuron and all the muscle fibres it innervates
What is the response of a muscle to a single stimulus?
What are the 3 phases?
A muscle twitch
- Latent period: interval between stimulus and beginning of contraction
- Contraction period- when the muscle is shortening
- Relaxation Period- during which tension declines
Explain the steps of temporal summation
- When the time between stimuli is far apart, so observe seperate twitches
- When the time between stimuli is decreased, the 2nd contraction starts before the previous one is over- the amplitude of contraction is bigger
- the largest contraction- when the 2nd contraction begins before the muscle has relaxed from previous stimulus
What is a tetanus?
a large smooth contraction in response to a series of stimuli
What are the 2 types of contraction?
Isometric- muscle doesnt shorten
Isotonic- muscle shorten
What is the structure of cardiac muscle?
Striated - therefore means actin and myosin are arraned into sarcomeres
- fibres branched
- single central nucleus per fibre
- intercalated discs act as gap junction
What ensures rapid conduction of action potentials?
the intercalated discs and branching of cardiac muslce
What is the structure of smooth muscle?
- composed of small spindle shaped cells (20-500 x 5 um)
- No striations- means its actin and myosin cannot be arranged in sarcomeres; as there is little of them they are therefore then irregularly arranged
- one nucleus in centre
What are ocular structures which have smooth muscle?
iris and ciliary body
What is the structure of smooth muscle FIBRE?
Not arranged in sarcomere
less actin and myosin than skeletal
ratio is 16:1 actin:myosin in smooth muscle however in skeletal it is (2:1)
-No z- lines- actin and myosin are then connected to dense bodies or to the cell membrane
-Poorly developed SR- slow calcium released and pump very slow compared in the SR of skeletal muscle
-therefore contraction is slower and less powerful
Why is it good that smooth muscle contraction is slowand feeble?
it uses less energy (which is good as smooth muscle is continuously active)- e.g in the stomach, eye , blood vessels
- ones does not want to generate a lot of force
What happens if the muscle is too stretched in skeletal muscle?
the sarcomere will not contract
What happens if the muscle is too stretched in smooth muscle?
bladder and urine contain smooth muscle.
The more irregular arrangement of actin/myosin smooth muscle means there is always enough overlap to generate tension and release pee and give birth (e.g)
What does the arrangement of sarcomere of a skeletal muscle do?
it is regular
so allows rapid and powerful contraction
What is the similarity between smooth muscle and skeletal muscle contraction?
actin and myosin both slide over each other
calcium is involved
ATP is required
What is the difference between smooth and skeletal muscle?
SR is poorly developed in smooth muscle and calcium enters the cell from extracellular space
- smooth muscle has no troponin, instead calcium interacts with calmodulin.
- calmodulin activates myosin kinase
- this activates the myosin to form cross-bridges.
What are the 2 ways smooth muscle can be made to contract?
- depolarisation of the cell membrane-innervation is from the ANS (sympathetic & parasympathetic) – thus innervation can be either excitatory or inhibitory
(skeletal muscle innervation is by the somatic motor system)
innervation is from the ANS (sympathetic & parasympathetic) – thus innervation can be either excitatory or inhibitory
(skeletal muscle innervation is by the somatic motor system)
Nerve/smooth muscle junctions are diffuse (transmitter release from varicosities)
(skeletal muscle motor end plates more defined - chemically- Local tissue factors such as low oxygen levels or high carbon dioxide act on vascular smooth muscle to cause vasodilation
Hormones can cause smooth muscle to contraction – e.g. oxytocin stimulating uterine contraction during childbirth
What are the 2 types of smooth muscle ?
single unit
multi unit
What is single unit (viscleral)?
individual fibres joined by gap junctions-large sheet acts as a unit- often spontaneously active
e.g. gut
What is a multi unit?
muscle fibres independent of one another- rich nerve supply- contraction graded e.g large arteries
