Neuromuscular System and Fatigue Flashcards
Describe the 3 main components of nervous tissue
- Neurons (aka nerve cells) - communicate via travelling action potentials
- Glial Cells - highly abundant cells that protect neurons, but dont generate action potentials
- Neurotransmitters - chemical substances such as acteylcholine that facilitate synapses
Describe the 4 main components of neurons
- Cell body - includes regular cell components
- Dendrites - extends from cell body and recieve chemical messages
- Axon - propagates imulses and can be coated in myelin sheath
- Axon Terminals - Site of synapse and where neurotransmitters are stored
Describe sensory (afferent) neurons and give the 6 exampes
- Monitor and provide information
- Impulses recieved by brain
- Proprioceptors, baroreceptors (detect stretch of blood vessels), mechanoreceptor, chemoreceptor, thermoreceptor, nociceptors (detect pain)
Describe motor (efferent) neurons
- Command/instructions
- Transfer impulses to effectors in thei periphery (muscles and glands)
- Triggers muscles to contract and glands to secrete
Describe the CNS
- Brain and spinal cord
- Processes incoming sensory information
- Decides necessary action
What are the parts of the peripheral NS?
- Autonomic NS (split into sympathetic and para)
- Somatic NS
Describe the Somatic NS
- Voluntary
- Sensory neurons provide information from the periphery eg limbs
- Motor neurons send impulses from CNS to skeletal muscles only
Describe the autonomic NS
- Involuntary
- Sensory neurons provide information from organs
- Motor neurons send impulses from CNS to smooth muscle, cardiac muscle and glands
Describe the sympathetic and parasympathetic NS
- Sympathetic - helps to support emergency actions (fight or flight), increases HR
- Parasympathetic - takes care of quieter body functions (rest and digest), decreases HR
Describe action potentials
- Electrical impulse, primary method of communication in neurons
- Originate in cell body
- Transferred by axon terminals
- Recieved by dendrites
How to action potentials occur?
- Due to changes in membrane potential due to the movement of sodium
- Rapid movement of sodium into cell causes depolarisation
- This leads to generation of AP
- Cells must repolarise before this process can repeat
Describe electrical synapses
- Electrical impulse passed to next cell
- Occurs in cardiac muscle cells
- Fast and immediately stimulates neighbouring cells
Describe chemical synapses
- Electrical impulse converted into a chemical signal (NT)
- Initiates a new impulse in the neighbouring cell eg muscle
- Slower than electrical
What are the 3 steps of communication across a neuromuscular junction?
- AP stimulates release of acetylcholine
- Acetylcholine diffuses over synaptic cleft and binds to receptor
- Causes sodium to flow into muscle cell, initiating an AP across muscle membrane
What is a motor unit?
Motor neuron and all innervated muscle fibres
Describe the 3 main skeletal muscle tissue structures
- Epimysium - surrounds the whole muscle and separates muscle from other organs
- Perimysium - surrounds bundles of fibres and allows them to be stimulated
- Endomysium - surrounds each individual muscle fibre (cell)
Describe the 4 structures of skeletal muscle cells/fibres
- Sarcolemma - cell membrane, lipid bilayer that conducts APs
- Myofibrils - functional units within fibres
- Sarcoplasmic reticulum - network of tubular channels that propagate APs
- T tubules - tube systems between sarcoplasmic reticulum that propagate APs to deeper interior
What is the first step of the contraction of the sarcomere/sliding filament model?
- Cross bridge formation
- Calcium binds to troponin
- Exposes binding site on tropomyosin
- Myosin heads attach to actin binding sites
What is the second step of the contraction of the sarcomere/sliding filament model after myosin heads attach to actin binding sites?
- Power stroke
- Myosin head releases ADP and Pi
- Myosin head uses full energy to pull actin filament
- Actin and Z discs move towards centre of sarcomere
What is the third step of the contraction of the sarcomere/sliding filament model after actin and Z discs are moved towards the centre of the sarcomere?
- Detachment of sarcomere
- ATP required to move myosin
- Enables myosin to reset
What is the fourth step of the contraction of the sarcomere/sliding filament model after myosin is reset?
- Resetting of myosin head
- ATP is hydrolysed into ADP + Pi
- Energy released energises myosin head
- Ready to repeat cycle
Describe type 1 motor units
- Slow oxidative
- Smallest fibre diameter
- Many mitochondria
- Slow contraction velocity
- High fatigue resistance
- Order of recruitment - first
Describe type IIa motor units
- Fast oxidative glycolytic
- Intermediate fibre diameter
- Many mitochondria
- Fast contraction velocity
- Intermediate fatigue resistance
- Order of recruitment - second
Describe type IIx motor units
- Fast glycolytic
- Largest fibre diameter
- Few mitochondria
- Fast contraction velocity
- Low fatigue resistance
- Order of recruitment - third
Define fatigue
Any exercise-induced reduction in the ability to exert muscle force/power, regardless of whether the task is sustained
What is peripheral fatigue?
- Loss of force producing capacity due to process at or below NM junction
- Often chemical/metabolic nature
- Alters force, contractile velocity and relaxation rate
What is central fatigue (neural aspect)?
- Loss of force producing capacity due to processes above the NM junction (essentially CNS)
What is the typical voluntary activation in humans?
90-95%
What are examples of task related and physiological/individual characteristics for muscle fatigue?
- Task - dynamic vs isometric, sustained vs intermittent, intensity of exercise, exercising muscle mass, exercise duration
- Physiological - sex, fibre type, training history, metabolic capacity
Which type of fatigue is associated with high intensity, short duration?
Peripheral
