Chapter 1b - Neuromuscular Anatomy and Physiology Flashcards
What is a motor unit, what does it consist of?
The functional unit of the neuromotor system consisting of the motor neuron and all the muscle fibers it innervates. Motor unit function will depends on the morphological and physiological characteristics of the muscle fibers innervated by the motor neuron.
What is a motor neuron? What about myelin sheath / nodes?
Consists of an alpha motor neuron (cell body), axon and dendrites. The motor neuron transmits nerve impulses from the spinal cord to the muscle fiber. Myelin sheath surrounds the axon, with nodes interrupting the myelin every 1-2 millimeters. The alternating myelin and nodes allow electrical current. Terminal branches end at NMJ
What is a NMJ (aka motor end plate)
The functional connection (chemical synapse) between the end of the myelinated motor neuron and the muscle fibers. Transmits nerve impulse from motor neuron to muscle fiber. The action potential reaches the terminal branches, and ACh is released across the synaptic space, stimulating the sarcolemma. When enough Ach is release, an action potential is generated.
What are muscle spindles?
Muscle spindles are proprioceptors that sense the rate and magnitude of increases in muscle tension as the muscle lengthens with an eccentric contraction. As a muscle spindle is lengthened, activates a sensory neuron in the spindle that activates the spinal cord. Motor neurons activate the muscle, causing a reflexive action called the stretch reflex
What are golgi tendon organ (GTO) ?
Mechanoreceptors that lie parallel to extrafusal muscle fibers near the musculotendinous junction and detect tension changes in an active muscle., acting as feedback monitors. They protect the muscles from injury, by reflex inhibition, they prohibit excessive tension buildup in a muscle.
What is reciprocal inhibition (GTO). What is autogenic inhibition.
Reciprocal inhibition - Occurs when a contracting muscle stimulates the GTO, causing the opposing muscle to relax.
Autogenic inhibition - The increased tension caused by muscle shortening stimulates to relax the muscle via the inhibitory neuron.
The big difference is that autogenic inhibition involves the relaxation of one group to allow the other to relax. Reciprocal inhibition involves the relaxation of the muscle that is contracting to allow the antagonistic muscle to contract.
What is the Somatic nervous system?
It innervates skeletal muscles and is responsible for conscious control of voluntary movement.
What is the autonomic nervous system, what are the two types.
The ANS innervates smooth and cardiac muscle, as well as glands. It’s also responsible for visceral muscle actions ( pumping the heart, digestion) Aka the involvuntary nervous system, is not under control.
Two parts - sympathetic and parasympathetic.
Explain the Sympathetic NS and Parasympathetic NS
Sympathetic - Prepares the body for action, aka fight or flight. During exercise, the SNS will direct blood away from the digestive tract and skin and towards the heart, muscles and brain. Physiological responses include - increased BP, HR, blood glucose, sweating, dialation of pupils and lung broncioles.
Parasympathetic - aka resting and digestion system. Conserves body energy by maintaining activities at a baseline. PNS is responsible for digestive tract motility, smooth muscle activity, associated with urination and defication, pupil constriction and gland secretion.
Explain motor unit recruitment patterns. What are two ways motor units modulate force.
Motor units only contain one type of muscle fiber (type I, type IIa, type IIb). Ability to recruit force is required for all sports. Two ways motor units modulate force are summation and size principle.
Explain the two ways motor units modulate force - summation and size principle.
Summation - Dependent on how often motor units are activated. Single activation will cause a minimal muscle twitch with little force production, but is continued to be activated with higher frequency, can be sunmmative effect of twitches leading to greater force production.
Size principle - Depends on how many motor units are activated. If more force is needed for activity, more motor units will be recruited. Smaller motor units are recruited first, and if more force is needed, we hit the larger ones.
Explain selective recruitment
This is an exception to the size principle. Under some circumstances, trained athletes can inhibit the activation of small motor units. This allows larger motor units to be activated immediately when rapid force production is needed (e.g vertical jump)
Explain what is nerve conduction and EMG
When an electric impulse from the motor neuron arrives at the motor junction, ACH is released converting the impulse into chemical stimulus. Generates action potential, a wave of depolarization, that travels through the muscle fiber, through the t-tubules, causing the release of Ca, initiates actin myosin movements.
EMG - Electromyography - used to assess the quality and quantity of the electrical activity within the skeletal muscles resulting from neural activation by motor units. Greater neural activation is implicated when there is an increase in EMG signal.
