4.1 Neuromuscular Function Flashcards
1
Q
Motor unit
A
A single motoneuron & the muscle fibres which it innervates (supply with nerves)
2
Q
Parts of a motor unit
A
Dendrite, cell body, nucleus, axon, motor end plate, synapse and muscle
3
Q
Dendrites
A
- Link neuron to neuron
- allows information to flow between nerves
4
Q
Soma/Cell Body
A
- Contains the nucleus but does not incorporate the dendrites or axon
5
Q
Nucleus
A
- Membrane-enclosed organelle
- Has the cell’s DNA
- Controls the cell
6
Q
Axon
A
- Main component of nerve signal transmission
- Has a cover made of myelin (protein)
- makes sure electrical signal is insulated
- has Nodes of Ranvier (gaps) - aids in transmission of info
7
Q
Motor End Plate
A
- Where the neuron meets the muscle fibre
8
Q
Synapse
A
- Gap between neuron and muscle fibre
- Transmission of electrical nerve signals happens across
9
Q
Muscle
A
- Transmission of electrical nerve signal stimulates muscle (to contract)
10
Q
Neurotransmitters
A
Chemicals that are used for communication between a neurone at the synapse and another cell
11
Q
Role of neurotransmitters in stimulating skeletal muscle contraction
A
- Acetylcholine (ACh) is the primary neurotransmitter for the motor neurons that innervate skeletal muscle
- Muscular contractions start w/ electrical impulse
- generated either voluntarily by brain or by reflex
- Electrical impulses travel along motoneuron through motor end plate
- When a signal reaches the synapse, neurotransmitter ACh is released
- ACh changes electrical state of muscle & causes signal called the action potential to travel along muscle fibres
- When nerve is no longer stimulated, ACh is removed by cholinesterase
- Cholinesterase (enzyme) is present in synaptic cleft + rapidly breaks down ACh into acetate + choline
- necessary to allow a neuron to return to its resting state after activation
12
Q
Contracted state of sarcomere
A
- Contracted state of sarcomere:
- H-zones disappear
- I-band narrows
- light bands shorten
- A-band remains the same
- dark bands remain the same
13
Q
Parts of the muscle (getting smaller and smaller)
A
SKELETAL MUSCLE ⇒ MUSCLE FIBRES ⇒ MYOFIBRILS ⇒ MYOFILAMENTS
14
Q
Sliding filmanet theory
A
- Relaxed muscle - regulatory protein tropomyosin binds protein sites on actin
- Motor neuron sends a signal to muscle fibre to contract ⇒ sarcoplasmic reticulum releases calcium ions
- Calcium ions bind to a protein called troponin & causes it to change shape ⇒ tropomyosin moves + unblock actin’s binding sites
- Myosin heads bind to site & swivel towards centre of sarcomere
- moving actin filament a small distance
- ATP causes breaking of cross-bridges
- when ATP attaches to myosin head ⇒ head detaches from binding site
- ATP hydrolyses ⇒ ADP + phosphate
- Hydrolysis provides energy for myosin head to cock
- cock: swivel outwards away from centre of sarcomere
- New cross-bridges are formed by myosin binding to actin’s binding site adjacent to ones previously occupied
- each head binds to a site one position further from centre of sarcomere
- Energy stored in myosin head when cocked causes it to swivel inwards towards centre ⇒ moving actin a small distance
15
Q
Slow twitch muscle fibres (Type I)
A
- slow nerve transmission speeds
- small muscle forces
- can maintain contractions for a long time ⇒ fatigue resistant
e.g. walking, jogging
