Part 2- Structure and Physiology of muscle

Question 1

What is slow muscle?

Answer 1

• active for prolonged periods of time(e.g posture)
• uses lots of energy therefore have mitochondria
• Myoglobin for oxygen storage
• red colour

Question 2

What is fast muscle?

Answer 2

• breifly active
• large sarcoplasmic reticulum for rapid release and uptake of calcium
• little myoglobin - white colour

Question 3

What are the 2 ways you can control the size of muscle contraction?

Answer 3

Spatial

temporal

Question 4

Define spatial summation

Answer 4

varying the number of active motor neurones

Question 5

Define temporal summation

Answer 5

varying the frequency of stimuli

Question 6

What is spatial summation?

Answer 6

lot of motor unit active means a lot of cells shorten which leads to bigger contraction

Question 7

What is a motor unit?

Answer 7

a single neuron and all the muscle fibres it innervates

Question 8

What is the response of a muscle to a single stimulus?

What are the 3 phases?

Answer 8

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

Question 9

Explain the steps of temporal summation

Answer 9

• 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

Question 10

What is a tetanus?

Answer 10

a large smooth contraction in response to a series of stimuli

Question 11

What are the 2 types of contraction?

Answer 11

Isometric- muscle doesnt shorten

Isotonic- muscle shorten

Question 12

What is the structure of cardiac muscle?

Answer 12

Striated - therefore means actin and myosin are arraned into sarcomeres

• fibres branched
• single central nucleus per fibre
• intercalated discs act as gap junction

Question 13

What ensures rapid conduction of action potentials?

Answer 13

the intercalated discs and branching of cardiac muslce

Question 14

What is the structure of smooth muscle?

Answer 14

• 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

Question 15

What are ocular structures which have smooth muscle?

Answer 15

iris and ciliary body

Question 16

What is the structure of smooth muscle FIBRE?

Answer 16

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

Question 17

Why is it good that smooth muscle contraction is slowand feeble?

Answer 17

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

Question 18

What happens if the muscle is too stretched in skeletal muscle?

Answer 18

the sarcomere will not contract

Question 19

What happens if the muscle is too stretched in smooth muscle?

Answer 19

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)

Question 20

What does the arrangement of sarcomere of a skeletal muscle do?

Answer 20

it is regular

so allows rapid and powerful contraction

Question 21

What is the similarity between smooth muscle and skeletal muscle contraction?

Answer 21

actin and myosin both slide over each other
calcium is involved
ATP is required

Question 22

What is the difference between smooth and skeletal muscle?

Answer 22

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.

Question 23

What are the 2 ways smooth muscle can be made to contract?

Answer 23

1. 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
2. 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

Question 24

What are the 2 types of smooth muscle ?

Answer 24

single unit

multi unit

Question 25

What is single unit (viscleral)?

Answer 25

individual fibres joined by gap junctions-large sheet acts as a unit- often spontaneously active
e.g. gut

Question 26

What is a multi unit?

Answer 26

muscle fibres independent of one another- rich nerve supply- contraction graded e.g large arteries