Chapter 19 - Neural Control in Exercise Physiology PDF

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Summary

Notes from the exercise physiology course at the University of Manitoba. These are from chapter 19 on the topic of neural control....

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Chapter 19 – Neural Control of Human Movement Neuromotor System Organization:  2 major parts: o CNS (brain and spinal cord) o PNS CNS – The Brain:  6 main areas: o Medulla oblongata o Pons o Midbrain o Cerebellum o Diencephalon o Telencephalon

o CNS – The Spinal Cord:  45 cm long, 1 cm in diameter  Encased by 33 vertebrae  Provides for two-way flow of communication between brain and periphery via nerve tracts and sensory receptors PNS:   

31 pairs of spinal nerves 12 pairs of cranial nerves o Important – vagus nerve 2 types of efferent neurons: o Somatic neurons  Innervate skeletal muscle o Autonomic neurons, which activate  Smooth muscle

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Cardiac muscle Sweat glands Salivary glands Some endocrine glands

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Autonomic – Sympathetic and Parasympathetic Nervous Systems:  Sympathetic

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o Heart [pacemaker (HR) and muscle fibres (SV)] o Smooth muscle o Sweat glands o Viscera Parasympathetic o Heart [pacemaker only (HR)] o Thorax o Abdomen o Pelvic regions

Reflex Arc:  Afferent neurons enter spinal cord via dorsal root o Transmit sensory input  Synapse with interneurons in spinal cord  Efferent signals return via anterior motor neurons to the effector organ

 Nerve Supply to Muscle:  Each muscle fibre is innervated

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The number of muscle fibres per motor neuron is related to a muscle’s function

Motor Unit Anatomy:  Motor unit – one motor neuron and the specific muscle fibres it innervates  Motor neuron pool – collection of motor neurons that innervate a single muscle

 Action Potential Propagation? Anterior = Motor Neuron Posterior = Sensory Neuron  Dendrites  Cell body  Axon  Myelin sheath  Nodes of Ranvier  Axon terminals  Motor end plate Neuromuscular Junction (Motor Endplate):  Electrical signal crosses a synapse  Interface between the end of a motor neuron and a muscle fibre  Anatomic features of a neuromuscular junction o Presynaptic terminals o Synaptic clef o Postsynaptic membrane

 Excitation:  The AP stimulates the sac-like vesicles at the NMJ to release ACh  Endplate potential  Action potential  Ach hydrolysis by cholinesterase ^ across synaptic clef? Action Potential:  Na+/K+ pump in cell membrane  Pumps: o 3 Na+ out o 2 K+ in o Effect?

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Regular AP:  Requires external stimulus for depolarization to AP threshold:  Resting membrane potential interior vs. exterior  Polarization – away from 0, negative 65-70mV

 o Resting membrane potential:  Electrical charge across membrane  Interior vs. exterior  Polarization (away from 0 mV)  RMP ~ -60 to -70 mV o Depolarization towards AP threshold:  EPSPs summate towards threshold  Packets of neurotransmitter (Ach) cause an EPSP o At AP threshold:  Voltage gates Na+ channels open  Na+ floods into cell, causing rapid depolarization/AP  Voltage-gated Na+ channels are momentarily inactivated  Membrane is refractory Resting Membrane Potential & AP Threshold:

AP Propagation? PACEMAKER AP:  Spontaneously depolarizes to AP threshold (e.g. Ca2+ leak in)  - AV and SA nodes

 Interneuronal Transmission?  Excitatory or inhibitory

 Neuromuscular Transmission?  At NMJ  Always excitatory Force and Fatigue with Different Fibre Types (again):

Number of Active Motor Units with Varying Intensities (again):

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