KIN 210: Nervous System and Exercise

• KIN 210: Principles of Exercise
• Class is held on Tuesdays and Thursdays from 9:10 AM to 10:00 AM in Wells Hall, Room B115
• Instructor is Chad Wiggins, PhD
• Lab to be held this week
• You should dress for exercise for the lab

The Nervous System and Exercise

• The nervous system has an effect on exercise

Synapse

• It denotes the site of neuron-to-muscle communication
• Uses acetylcholine (ACh) as its neurotransmitter
• It is excitatory
• It passes an action potential (AP) along to the muscle

Postsynaptic Cell

• This equals the muscle fiber
• Acetylcholine diffuses across the synaptic cleft and binds to a receptor at the motor end plate
• This step causes depolarization
• AP moves along the plasmalemma, down the T-tubules
• It undergoes repolarization, the refractory period

Central Nervous System

• Comprises the brain and spinal cord

Peripheral Nervous System

• Includes sensory (afferent) and effector (efferent) nerves
• Effector nerves are further divided into autonomic and somatic components
• Autonomic nerves are split into sympathetic and parasympathetic branches

The Autonomic Nervous System

• Controls involuntary internal functions
• It governs exercise-related autonomic regulation like heart rate, blood pressure, lung function, and breathing rate
• Has two complementary divisions
• Sympathetic nervous system
• Parasympathetic nervous system

The Sympathetic Nervous System

• Prepares the body for exercise
• Involves the "fight or flight" response
• Sympathetic stimulation increases
• Heart rate and blood pressure
• Blood flow to muscles
• Airway diameter (bronchodilation)
• Metabolic rate, glucose levels, and free fatty acid (FFA) levels
• Mental activity

The Parasympathetic Nervous System

• Focuses on "rest and digest" functions
• It is active at rest and counteracts the effects of the sympathetic nervous system
• Parasympathetic stimulation
• Digestion and urination
• Conservation of energy
• Decreases heart rate
• Affects the diameter of vessels and airways

Impact on Target Organs

• Heart Muscle: Increased rate and force of contraction via sympathetic effects, decreased rate via parasympathetic effects
• Heart (Coronary Blood Vessels): Causes vasodilation with sympathetic activity, vasoconstriction with parasympathetic activity
• Lungs: Sympathetic activity causes bronchodilation and mildly constricts blood vessels whereas parasympathetic activity causes bronchoconstriction
• Blood Vessels: Sympathetic activity increases blood pressure
• It causes vasoconstriction in abdominal viscera and skin to divert blood and causes vasodilation in skeletal muscles during exercise
• Parasympathetic activity has little or no effect
• Liver: Sympathetic activity stimulates glucose release while parasympathetic has no effect
• Cellular Metabolism: Sympathetic activity increases the metabolic rate; parasympathetic has no effect
• Adipose Tissue: Sympathetic activity stimulates lipolysis and parasympathetic has no effect
• Sweat Glands: Sympathetic activity increases sweating, parasympathetic has no effect
• Adrenal Glands: Sympathetic activity stimulates the secretion of epinephrine and norepinephrine; parasympathetic has no effect
• Digestive system: Sympathetic activity decreases activity of glands and muscles and constricts sphincters, parasympathetic increases peristalsis and glandular secretion, and relaxes sphincters
• Kidney: Sympathetic activity causes vasoconstriction and decreases urine formation; parasympathetic has no effect

Ion Channel States During Action Potential

• Na+ channels are closed and mostly outside the cell
• K+ channels are closed and mostly inside the cell
• Na+ channels open, Na+ rushes in
• K+ channels remain closed and no movement in or out
• Na+ channels close, no movement in or out
• K+ channels open, K+ moves to the outside of the cell
• Na+ channels remain closed, no movement in or out
• K+ channels remain open and K+ is still moving outside
• Na+ channels remain closed, but can open with a strong enough stimulus
• K+ channels close but are "leaky" and allow K+ to leak out

Brain Lobes

• Frontal lobe controls general intellect and motor control
• Temporal lobe controls auditory input and interpretation
• Parietal lobe controls general sensory input and interpretation
• Occipital lobe controls visual input and interpretation
• Insular controls emotion and self-perception

Spinal Cord Regions

• Cervical controls head and neck; diaphragm; deltoids and biceps; wrist extenders; triceps; and hands
• Thoracic controls chest and abdominal muscles
• Lumbar affects lumbar nerves
• Sacrum affects bowel, bladder, and sexual function

Peripheral Nervous System Receptors

• Joint kinesthetic receptors are sensitive to joint angles and rate of angle change, sensing joint position and movement
• Golgi tendon organs sense changes in stretch and strength of muscle contraction
• Muscle spindles sense changes in muscle length, tension, and speed of movement

Exercise and Fatigue Definitions

• Fatigue refers to decrements in muscular performance with continued effort, accompanied by sensations of tiredness
• It also refers to the inability to maintain the required force/power output to continue muscular work at a given intensity

Causes of Fatigue

• Fatigue is a complex phenomenon that depends on the type and intensity of exercise
• It depends on the muscle fiber type and training status, and diet
• There are four major causes
• Inadequate energy delivery/metabolism
• Accumulation of metabolic by-products
• Failure of the muscle contractile mechanism
• Altered neural control of muscle contraction

Peripheral Fatigue

• Includes decreased rate of energy delivery, PCr depletion, and glycogen depletion
• It includes a build up of metabolic byproducts such as excess Pi, lactic acid dissociation, H+ accumulation, and ROS accumulation
• It causes the failure of the muscle fiber's contractile mechanism
• The cause also includes reduced Ach concentrations, cholinesterase activity, altered stimulation thresholds, receptor activation changes, and K level changes

Central Fatigue

• Includes alterations in the neural control of muscle contraction
• Influenced by the intensity of exercise, the duration of exercise, the fiber type of the involved muscles, and the subject's training status, age, and diet
• Humidity is also a factor

Inadequate Energy and Metabolism as a Cause of Fatigue

• Includes phosphocreatine (PCr) depletion
• Also involved is blood glucose depletion and glycogen depletion

Accumulation of Metabolic By-Products

• These include inorganic phosphate (P₁) from the breakdown of PCr and ATP
• Heat retained during exercise
• Hydrogen Ion (H+) accumulation from metabolism