MYTUTOR SUBJECT ANSWERS

336 views

How do muscle fibres contract?

Contraction occurs when an impulse from a motor neurone reaches the synapse at the junction with the muscle, the neuromuscular junction (NMJ). 

At the presynaptic membrane of the NMJ, depolarisation results in the entry of calcium ions. This causes vesicles in the membrane containing the neurotransmitter acetylcholine to fuse with the membrane and release the neurotransmitter into the synapse, this is known as exocytosis. The neurotransmitter molecules diffuse across the synaptic cleft and bind to complementary receptors on the post-synaptic membrane. This causes sodium ions to enter the post-synaptic membrane and the signal has been transmitted across the synapse. 

Synaptic transmission then affects the muscle fibres through the release of calcium ions from within the muscle. Muscle is made up broadly of actin and myosin fibres. Normally, actin is bound to a glycoprotein called tropomyosin - the release of calcium ions displaces tropomyosin from actin. This exposes binding sites on actin fibres and allows myosin to bind, forming cross-bridges.

ATP, attached to the head of the myosin molecule is hydrolysed to ADP. The energy released from this causes the myosin heads to alter their conformational shape. This pulls the actin filament past the myosin filament.

The cross-bridges then detach and reattach, in the same fashion, this time further along the actin filament. In this way, the formation of fibres gradually shortens, in contraction.

Emily B. GCSE Biology tutor, A Level Biology tutor, GCSE Chemistry tu...

8 months ago

Answered by Emily, an A Level Biology tutor with MyTutor


Still stuck? Get one-to-one help from a personally interviewed subject specialist

164 SUBJECT SPECIALISTS

Rebecca K. GCSE Biology tutor, A Level Biology tutor
£20 /hr

Rebecca K.

Degree: Biochemistry (Bachelors) - Kings, London University

Subjects offered:Biology

Biology

“Biology and Modern Greek tutor for one-to-one based sessions! Sessions are designed accordingly to the student's needs.”

MyTutor guarantee

£22 /hr

Upasana T.

Degree: Medicine (Bachelors) - Birmingham University

Subjects offered:Biology, Maths+ 1 more

Biology
Maths
Latin

“About me: Hi, my name is Upasana Topiwala and I am currently in my third year of medical school at the university of Birmingham. I've taken up tutoring in order to inspire my students to appreciate the importance of science in our liv...”

Nehemie M. A Level Biology tutor, GCSE Biology tutor, IB French tutor...
£20 /hr

Nehemie M.

Degree: Biochemistry with a Professional Placement (Bachelors) - Bath University

Subjects offered:Biology, French

Biology
French

“I am university student passionate about Biology and Chemistry who also speaks French!!!”

MyTutor guarantee

About the author

Emily B.

Currently unavailable: for new students

Degree: Medicine MBChB (Bachelors) - Birmingham University

Subjects offered:Biology, Human Biology+ 4 more

Biology
Human Biology
.UKCAT.
.BMAT (BioMedical Admissions)
-Personal Statements-
-Medical School Preparation-

“I am a medical student in my fourth year of the MBChB programme at the University of Birmingham. I am a bit of a geek and have always been absolutely fascinated by science and understanding ‘how things work’. I have experience tutorin...”

You may also like...

Other A Level Biology questions

The enzyme maltase breaks down maltose to glucose. This takes place at body temperature. Explain why maltase: 1) only breaks down maltose 2) allows this reaction to take place at normal body temperature

What are the modes of genetic inheritance?

What is the best method for Biology A level revision?

In genetics, what does co-dominance mean?

View A Level Biology tutors

We use cookies to improve your site experience. By continuing to use this website, we'll assume that you're OK with this. Dismiss

mtw:mercury1:status:ok