Lecture 5 - The Structure and Function of Muscle cells Flashcards Preview

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Flashcards in Lecture 5 - The Structure and Function of Muscle cells Deck (45):

What are the 3 types of muscle?

skeletal  - also called striated and voluntary muscle

cardiac - only find it in the heart



What separates muscle cells from each other ?

connective tissue (epimysium)


what are the functional stages of sarcomeres?

Resting stage

Contracted stage

Stretched stage


What are the 5 stages of the contraction cycle?

Stage 1: Attachment

The myosin head is tightly bound to the actin molecule of the thin filament (rigor state). 

Stage 2: Release

ATP binds to the myosin head and induces the release from the actin therefore without ATP

the muscle would remain in a state of rigour. The muscle is now relaxed. 

Stage 3: Bending

The ATP causes further changes to the myosin head causing it to bend. The bending movement initiates the breakdown of ATP to ADP +inorganic phosphate both of which remain in the myosin head. 

Stage 4: Force generation

The myosin head binds to the new site and the inorganic phosphate is released. The effects are twofold:

- It increases the binding affinity of the myosin for the actin.

- The myosin head generates a force to straighten up and in doing so forces the thin filament

along the thick filament creating the power stroke and shortening the sarcomere. During this

stage the ADP is lost form the myosin head. 

Stage 5: Reattachement

The release of the ADP results in the reattachment of the myosin head to the actin filament

and the rigour state is re-established. 


where do you find smooth muscle?

Blood vessels

Gastrointestinal tract and gallbladder

Ureter and urinary bladder Uterus

Respiratory system



function of skeletal muscle?

Support and Movement. Skeletal muscles move the body. Skeletal muscle contractions pull on tendons, which are attached to bones. If contraction of the muscle causes the muscle to shorten, the bone and, thus, the body part will move.


Z line

A band?

H band?

I band?

M line?

Actin and Myosin?


where do you find cardiac muscle?

in the heart


arrangemet of skeletal muscle?

it is connectec to connective tissue(tendons) and the tendons are then connected to the bone

the muscle itself is surrounded by a connective tissue known as the epimysium

inside of the connective tissue we can see bundles that are surrounded byperimysium and this allows the blood vessels and nerves to reach the bundles

inside of these bundles we find muscle fibres (muscle cells) that are seperated from each other by more connective tissue and this tissue is called endomysium



What are the three layers of connective tissue in skeletal muscle??





muscle fibres vary in lenght in diameter?

becasue they have different roles

E.g. eye muscles, gluteus maximus


structure of muscle fibre?

Surrounded by connective tissue endomysium

and surrounded by the cell membrane sarcolemma

small amount of sarcoplasm (the cytoplasm of striated muscle cells)

and a number of mitochondria (not shown on the picture)

(the number depends on what kind of muscle it is)

it is packed full of myofibrils and they are the ones that contain the contractile elements (the sarcomeres)

multi nucleated - that are pushed towards the edge



what is the Sarcoplasmic Reticulum and the ‘T’ System ??

The sarcoplasmic reticulum is arranged as a repeating series of networks around the myofibrils extending from one A-I junction to the next. Where they meet is termed the terminal cisterna. They act as reservoirs for Ca2+. Mitochondria are also present toe provide the energy for muscle contraction.

The plasma membrane invaginates transversely forming a tubular system, T tubules, between the cisternae. They contain voltage-sensor proteins which are activated when the membranes depolarizes inducing the sarcoplasmic reticulum to release Ca2+.

The T tubules and the adjacent cisternae form a triad. 


How Does Skeletal Muscle Innervation & Excitation Work??

Each muscle fibres needs to be innervated as they are electrically separated from each other.


Ach is released form the motor end plate (1) which binds to nicotinic receptors , which incorporate a channel. The channel opens causing a small depolarisation which opens voltage gated Na+ channels causing a larger depolarisation (action potential, 2) which spreads over the plasma membrane and via the T tubules (3). 


Ca2+ (5) is released in to the sarcoplasm and binds to the troponin complex which causes changes in the tropomyosin allowing the myosin head to attach and thus contraction is initiated.

Decreases in Ca2+ causes Ca2+ to unbind from the troponin allowing tropomyosin to recover the binding sites (9). 


Calcium release and crossbridge formation in skeletal muscle


Length tension relationship??

The tension a muscle can generate is related to the number of crossbridges formed between the thick and thin filaments. In an elongated fibre there are very few crossbridges and therefore little power can be generated. As the sarcomere shortens more crossbridges form and the force increases until the crossbridges reach the Z disc and there are no new binding sites and therefore the tension decreases rapidly. 


what kind of muscle is cardiac muscle??




what percentage of the cardiac muscle cell is mitochondria?



Arrangement of Muscle Fibres in cardiac muscle??

he spiral arrangement of the ventricular muscles results ion the upward squeezing of the ventricular blood from the apex during ventricular contraction.

The intercalated discs contain desmosomes which transfer the force from cell to cell and gap junction that allow for the passage of electrical signals 


What is this??

Cardiac muscle


What is this? 

What are the black dots?

Cardiac muscle



Does skeletal muscle have intercalated discs?



Cardiac Muscle T Tubule ‘Diad’ 


In cardiac muscle the action potential originates spontaneously in the pacemaker cells and spreads through gap junctions to the contractile cells. what does this look like??


Contraction and Relaxation of Cardiac Muscle ??

The action potential enters from an adjacent cell opening the calcium gated voltage channels and Ca2+ enters the cell which induces local release of calcium. The Ca2+ binds to troponin to initiate contraction.
Relaxation occurs when Ca2+ unbinds from troponin and the Ca2+ is pumped back into the sarcoplasmic reticulum to be stored ready for the next contraction. 


Cardiac muscle properties??

Like skeletal muscle cardiac muscle cells contain organised myofibrils but there are important differences.

- Cardiac muscle cells are relatively small (10-20μm in diameter and 50-100μm).

- A cardiac cell typically has a single centrally placed nucleus

- The T tubules are short and broad and there are no triads.

- The sarcoplasmic reticulum lacks terminal cisternae

- Cardiac muscle is almost completely dependent on aerobic metabolism and therefore the

cells contain large numbers of mitochondria. There are glycogen and lipid inclusions which

are stores of energy and the myoglobin store oxygen.

- Each cardiac cell contact several others via intercalated discs.


Intercalated discs are formed from the plasma membrane of two adjacent cells which are extensively intertwined and bound together by gap junctions and desmosomes. The binding together of the cells mechanically, chemically and electrically results in their acting together. The sarcomeres of cardiac muscle have the same banding pattern as skeletal muscle but unlike skeletal muscle form branching fibrillar networks continuous in three dimension throughout the cytoplasm

Cardiac muscle contracts without neural stimulation. The pacemaker are specialised cardiac muscle cells which are more excitable than the others and therefore contract first. Innervation of these cells by the nervous system can adjust the rate at which they contract. 


Where is smooth muscle found??

Smooth muscle is important in maintaining homeostasis and is found in the walls of :

- blood vessels

- Gastrointestinal tract and gallbladder

- Ureter and urinary bladder

- Uterus

- Respiratory system

- Eye 


What is this??


Smooth muscle cells have a single nucleus with a diameter about 5 μm and length from 20 to 500μm 


Structure of smooth muscle?

Each cell is surrounded by a basal lamina, and there is a small amount of connective tissue between cells – allows for passage of nerve tracts and blood vessels 


contraction pattern of smooth muscle??

Depending on location smooth muscle has a different contraction pattern. In the oesophagus it is phasic, contracting only when food enters whilst in the intestine there is phasic contraction and relaxation to push the contents along the gut. Tonic contraction is found in sphincters which only relax to open allowing material to pass through. Vascular smooth muscle has variable tonic contraction which can control the pressure and quantity of blood in a particular tissue. 


Contraction of Smooth Muscle ??

Smooth muscle cells have cytoplasm filled with filaments of actin, and lesser amount of myosin.

Less ordered than striated muscle (hence no striations).

Electrical excitation spreads from cell to cell via gap junctions

Contraction controlled by hormones or balance between sympathetic and parasympathetic divisions of the autonomic nervous system. 




Regulatory proteins in skeletal muscle??




contraction of smooth muscle cells (Ca2+)

Ca2+ enters the cell and induces release of Ca2+ from the sarcoplasmic reticulum. Ca2+ binds to calmodulin (CaM) (different from smooth and cardiac muscle). Calmodulin activates myosin light chain kinase (MLCK) resulting in phosphorylation which leads to the activation of the myosin head to attach to actin. In the presence of ATP the myosin head bends producing contraction. 


Thin filament attachment in skeletal muscle??

Z disc


Thin filament attachment in cardiac muscle??

Z disc


Thin filament attachment in smooth muscle??

Dense bodies


Regulatory proteins in cardiac muscle??




Regulatory proteins in smooth muscle?

Calmoduln Light chain myokinase


Ca2+ source in skeletal muscle?

Sarcoplasmic reticulum 


Ca2+ source in cardiac muscle??

Sarcoplasmic reticulum and extracellular fluid 


Ca2+ source in smooth muscle?

Mainly extracellular fluid 


Ca2+ receptor in skeletal muscle?

Troponin of thin filament 


Ca2+ receptor in cardiac muscle?

Troponin of thin filament 


Ca2+ receptor is smooth muscle?

Calmodulin of thick filament