Muscle Structure And Function

Question 1

How many muscles and joints I’m the body

Answer 1

650 muscles and 187 joints

Question 2

Describe cardiac muscle

Answer 2

Found in heart and circulates blood
Involuntary muscle contraction (ANS)
Small cells and limited ability to repair
Single nucleus in cardiac muscle cells
Many large mitochondria
Cardiac muscle required ATP for constant oxygen supply
Cardiac muscle cells also use lactic acid from skeletal muscle fibres to make ATP
Contraction speed is moderate
Branched cylindrical fibres with central nucleus,
Intercalated discs join neighbouring fibres
Striated muscle cells

Question 3

Skeletal muscle

Answer 3

Much larger muscle cells- up 30cm long
These cells can partially repair by satellite cells
Multinucleate cells
Under voluntary control (somatic ns)
Attached by tendons to bones
Contraction speed is fast
Long cylindrical fibres with many nuclei at the periphery and striated,

Question 4

Smooth muscle

Answer 4

Walls of organs like intestines, wall of blood vessels , stomach and oesophagus

Single nucleus in their cells

Fibre thickest in the middle and thinner at periphery - not striated

Can divide and repair itself If damaged- by pericytes

Involuntary muscle contractions (ANS)

Contraction speed is slow

Question 5

Connective tissue layers

Answer 5

Epimysium- connective tissue around whole muscle

Perimysium- divides muscle into small bundles - the perimysium surrounds fascicles

Endomyisum is connective tissue around individual muscle cell

Myofibril - smallest component makes up muscle fibres

Question 6

Size order of connective tissue

Answer 6

Largest is epimysium

Perimysium

Endomysium

Skeletal muscle fibre

Question 7

Functions of muscle tissue

Answer 7

Produce movement of body

Stabilise body positions

Regulate organ volumes eg, sphincter muscles empty bowel or bladder

Move substances through body eg, lymph, blood, air, urine, food or sperm. Also muscle pump in leg for venous return.

Produces heat - involuntary contractions , converts some energy to heat.

Question 8

Properties of muscle tissue

Answer 8

EEECC

Excitability - responding to a stimulus (chemicals released from nerve cells)

Extensibility - stretched without getting damaged

Elasticity- able to return to original shape after being stretched

Conductivity- ability to propagate electric signals over membrane so muscle fibres contract simultaneously.

Contractility- able to shorten and generate force

Question 9

Why is skeletal muscle multinucleate

Answer 9

In development, formed by many myoblasts that fuse together. Every myoblast has nucleus so muscle fibre has many nuclei.

Myoblasts that don’t fuse into muscle become satellite cells - muscle stem cells to repair muscle tissue damage.

Question 10

7 roles of skeletal muscle

Answer 10

Produce skeletal movement

Maintain body position

Support soft and hard tissues - eg, abdominal wall and pelvic floor support abdominal contents.

Guard body openings - sphincter muscles that can contract or close a bodily opening eg, control faeces removal from anus

Maintain body temperature

Store nutrient reserves like glycogen

Role in proprioception

Question 11

Connective tissue for skeletal muscles has:

Answer 11

Nerves

Blood vessels

Muscle tissue - muscle fibres

Question 12

EPIMYSIUM

Answer 12

Surrounds entire muscle

Exterior collagen layer - fibrous and irregular

Connects to deep fascia

Separates muscles from surrounding tissue and prevents friction between other muscles and bones

Question 13

PERIMYSIUM

Answer 13

Surrounds muscle fibres in fascicles

Made of 50% elastic and 50% collagen fibres

ContIns blood vessels and nerve supply to fascicles

Question 14

ENDOMYSIUM

Answer 14

Surrounds individual muscle cells
Has more elastic fibres
Loosely connects muscle fibres adjacent to each other
Contains capillaries and nerve fibres for muscle cells
Contains satellite cells stem cells

Question 15

What do the three layers form?

Answer 15

Endo, peri and epimysium combine to form a tendon or an aponeurosis (broad, sheet like fibrous tissue in wide attachment area)

Tendon transfers force from muscle to bone. Musc,e cells shorten and contract to pull on tendon which pulls on the bone to produce movement.

Question 16

In which layers will you find the nerves and blood vessels?

Answer 16

Perimysium contains blood vessels and nerves for fascicles

Endomysium contains capillaries and nerve fibres for muscle cells

Question 17

Nerve supply to muscles

Answer 17

Skeletal muscles innervated by peripheral nerves

Fascicles get innervated by a motor neurone

Each muscle cell is supplied by a single branch of the motor neurone

Motor nerve + muscle fibres it supplies = Motor unit

In strength training you get more motor units in the muscle and then processes slow down.

Question 18

Blood supply

Answer 18

Muscles have extensive vascular systems that:

Supply large amounts of oxygen for strong muscle contractions
Supply nutrients
Carry wastes away eg, lactic acid, oxygen, ADP, water

Each muscle cell is in contact with one or two capillaries
Nerve fibres and capillaries found in endomysium between individual cells.

Question 19

Development of skeletal muscle cells

Answer 19

Muscle cells develop by fusion of myoblasts.
Some myoblasts don’t fuse and they become satellite cells - stem cells to repair damaged muscle

So summary of skeletal muscle cells:
Long (30cm) and cylindrical
Develop through fusion of myoblasts (mesodermal cells)
Become very large
Multinucleate from fusion of many myoblasts
Nuclei around periphery of the cell
Contain many mitochondria (energy used for muscle contractions)

Question 20

Sarcolemma

Answer 20

Sarcolemma is muscle cell membrane

Surrounds the sarcoplasm

Sarcolpasm is filled wit tiny threads of myofibrils and myoglobin (red coloured oxygen-binding protein).

T tubules encircle each myofibrils

A change in transmembrane potential causes muscle contraction

Question 21

T transverse tubules

Answer 21

Invagination of the sarcolemma into the sarcoplasm

T tubule functions :
Filled with extracellular fluid
Carry muscle action potentials down into cell
Allows entire muscle fibre to contract simultaneously.

Mitochondria placed in rows along a muscle fibre. They are near the proteins that use ATP for contraction.

Question 22

Sarcoplasmic reticulum

Answer 22

Membranous structure around each myofibril

System of tubular sacs similar to a SER

Sarcoplasmic reticulum helps to transmit action potentials to the myofibril

They form terminal cisternae chambers at their ends that attaches to T tubules

Terminal cisternae store calcium ions + release them to start muscle contraction

Question 23

What is a triad?

Answer 23

A triad is 1 T tubule + 2 terminal cisternae

They concentrate calcium ions by ion pumps

Concentration of calcium in terminal cisternae is 40,000 times as much as the surrounding sarcoplasm.

Terminal cisternae release calcium ions into sarcomeres to begin muscle contractions

Question 24

Myofibrils and myofilaments

Answer 24

Each muscle cell filled with many threads called myofibrils, separated by sarocplasmic reticulum

Myofibrils made of many myofilaments

Myofilaments are contractile proteins of muscle (actin and myosin)

Question 25

Largest to smallest component of a muscle

Answer 25

Muscle 
Fascicles
Muscle fibres
Myofibrils 
Myofilaments 
Sarcomeres

Question 26

Myofilaments and the sarcomeres

Answer 26

Thick and thin filaments overlap each other in a pattern to form striations. (I bands and A bands).

I band = only actin
A band= myosin and actin

In overlap A band region, 6 actin filaments surround each myosin filament

Sarcomeres are small contractile units of the myofibrils. Ends of sarcomeres marked with a Z-line.

Middle of each sarcomeres has an M line

Around M line is the H zone with only myosin filaments

Question 27

Summary of sacrcomeres

Answer 27

Contractile units of muscle

Structural units of myofibrils

Form visible striations within myofibril

Transverse T tubules encircle sarcomeres near zones of overlap

Calcium ions released by SR cause thick and thin filaments to interact

Question 28

What is titin?

Answer 28

Muscle protein may be useful for eccentric contractions

Titin joins myosin to Z line and prevents it overstretchinf
So the muscle can return back to normal size