2. Neuromuscular transmission

4. Motor Unit Motor Unit : is the motor neuron and all the muscle
fibers it supplies
all of these fibers will have the same type (either fast twitch or slow twitch). When a motor unit is activated

5. The Neuromuscular junction consists of
Axon Terminal : contains
around 300,000 vesicles which contain the neurotransmitter acetylcholine (Ach).
Synaptic Cleft :
20 – 30 nm ( nanometers ) space
between the axon terminal & the
muscle cell membrane. It contains
the enzyme cholinesterase which
can destroy Ach .

6. Synaptic transmission ***
Synapse is the junction between two neurones where electrical activity of one neurone is transmitted to the other

7. Acetylcholine (1)
Ach is synthesized locally in the cytoplasm of the nerve terminal, from active acetate (acetylcoenzyme A) and choline.
Then it is rapidly absorbed into the synaptic vesicles and stored there.
The synaptic vesicles themselves are made by the Golgi Apparatus in the nerve soma ( cell-body).
Then they are carried by Axoplasmic Transport to the nerve terminal , which contains around 300,000 vesicles .
Each vesicle is then filled with around 10,000 Ach molecules .
acetate is a derivative of acetic acid This term includes salts and esters
 Golgi transport of lipids around the cell

8. Steps involved:
AP at the synaptic knob -----» Ca channels open (increase Ca permeability) -----»
release of neurotransmitter (NT) from synaptic knob to synaptic cleft -----»
NT combines with specific receptors on the other membrane -----» postsynaptic potential -----» AP will result

9. Neuromuscular transmission

10. Neuromuscular transmission ***
Transmission of impulse from nerve to muscle (neuromuscular junction)
Steps:
AP at nerve knob -----» increase Ca permeability (Ca inter synaptic knob) -----» release of Acetylcholine (Ach) -----» Ach combine with receptors on motor end plate -----» Na permeability increase -----» end plate potential develop -----» AP spread on the membrane -----» muscle contraction

11. Molecular basis of muscle contraction ***
Anatomical consideration:
Muscle fibre
Sarcomere
Myosin (thick filament):
Cross-bridge
Actin (thin filament)
Regulatory protein: (Troponin,Tropomyosin)
Actin

12. Events of muscle contraction: ***
Acetylcholine released by motor nerve »»»»» EPP »»»»» depolarization of CM (muscle AP) »»»»»
Spread of AP into sarcoplasmic reticulum »»»»»release of Ca into the cytoplasm
»»»»» Ca combines with troponin »»»»» troponin pull tropomyosin sideway »»»»» exposing the active site on actin »»»»» myosin heads with ATP on them, attached to actin active site
»»»»» Resulting in formation of high energy actin-myosin complex »»»»» activation of ATP ase (on myosin heads) »»»»» energy released, which is used for sliding of actin & myosin

13.  T-tubule of muscle is a deep invaginationof the sarcolemma which is the plasma membrane, only found in skeletal and cardiac muscle cells

15. Events of muscle contraction:
When a new ATP occupies the vacant site on the myosin head, this triggers detachment of myosin from actin
The free myosin swings back to its original position, & attached to another actin, & the cycle repeat its self

16. Events of muscle contraction:
When ca is pumped back into sarcoplasmic reticulum
»»»»» ca detached from troponin »»»»» tropomyosin return to its original position
»»»»» covering active sit on actin »»»»» prevent formation of cross bridge »»»»» relaxation

17. Muscle contraction ****
1- simple muscle twitch:
The mechanical response (contraction) to single AP (single stimulus)
2- Summation of contraction:
Spatial summation:
the response of single motor unites are added together to produce a strong muscle contraction
Temporal summation:
when frequency of stimulation increased (on the same motor unite), the degree of summation increased, producing stronger contraction

19. Types of muscle contraction:
1- Isometric contraction:
No change in muscle length, but increase in muscle tension (e.g. standing)
2- Isotonic contraction:
Constant tension, with change in muscle length (e.g. lifting a loud)

21. ELECTROMYOGRAPHY AND MOTOR NERVE CONDUCTION VELOCITY

22. ELECTROMYOGRAPHY (EMG)
It’s a recording of electrical activity of the muscle by inserting needle electrode in the belly of the muscles or by applying the surface electrodes.
The potentials recorded on volitional effort are derived from motor units of the muscle, hence known as motor unit potentials (MUPs). 22

23. Electromyography (EMG) is a technique for evaluating and recording physiologic properties of muscles at rest and while contracting. 23

24. A motor unit is defined as one motor neuron and all of the muscle fibers it innervates.
A motor unit is defined as one motor neuron and all of the muscle fibers it innervates. When a motor unit fires, the impulse (called an action potential) is carried down the motor neuron to the muscle. The area where the nerve contacts the muscle is called the neuromuscular junction, or the motor end plate. After the action potential is transmitted across the neuromuscular junction, an action potential is elicited in all of the innervated muscle fibres of that particular motor unit. The sum of all this electrical activity is known as a motor unit action potential (MUAP). This electrophysiologic activity from multiple motor units is typically evaluated during an EMG. The composition of the motor unit, the number of muscle fibres per motor unit, the metabolic type of muscle fibres and many other factors affect the shape of the motor unit potentials in the myogram. 24 24