KIN 340 Chapter 7: The Nervous System: Structure and Control of Movement
Neurotransmitter
-Chemical messenger released from presynaptic membrane -Binds to receptor on postsynaptic membrane -Causes depolarization of postsynaptic membrane
Kinesthesia
-Conscious recognition of the position of body parts -Limb movement rates
Reciprocal inhibition
-EPSPs to muscles to withdraw from stimulus -IPSPs to antagonistic muscles
Motor cortex through thalamus
-Forwards message sent down spinal neurons for "spinal tuning" and onto muscles -Feedback from muscle receptors and proprioceptors allows fine tuning of motor program
Golgi-type receptors
-Found in ligaments and around joints -Similar to free nerve endings
Central fatigue
-Higher brain centers and/or motor neurons -Depletion of excitatory neurotransmitters in the motor cortex resulting in reduced motor output to muscle
Pacinian corpuscles
-In tissues around joints -Detect rate of joint rotation
Free nerve endings
-Most abundant type of joint proprioceptors -Sensitive to touch and pressure -Initially strongly stimulated, then adapt
Cerebrum: Cerebral Cortex
-Organization of complex movement -Storage of learned experiences -Reception of sensory information
What is Resting Membrane Potential determined by?
-Permeability of plasma membrane to ions -Difference in ion concentrations across membrane Na+, K+, Cl-, and Ca++
Proprioceptors
-Receptors that provide CNS with information about body position -Located in joints and muscles
ANS: Parasympathetic division
-Releases acetylcholine (ACh) -Inhibits effector organ -After release, ACh is degraded by acetylcholinesterase
ANS: Sympathetic division
-Releases norepinephrine (NE) -Excites an effector organ -After stimulation, NE is removed from synapse or inactivated
Muscle Spindle
-Responds to changes in muscle length -Consists of: -Intrafusal fibers Run parallel to normal muscle fibers (extrafusal fibers) -Gamma motor neurons Stimulate intrafusal fibers to contract with extrafusal fibers (by alpha motor neuron) -Stretch reflex Stretch on muscle causes reflex contraction Knee-jerk reflex
Pathways of neural reflex
-Sensory nerve sends impulse to spinal column -Interneurons activate motor neurons -Motor neurons control movement of muscles
Structures and Processes Leading to Voluntary Movement
1) subcortical/cortical areas: initial drive to move 2) association cortex: movement design "rough draft" 3) Basal nuclei & cerebellum: refined movement design 4) Thalamus: relay station 5) Motor Cortex: Final executor of motor plan 6) Motor Units: Execution of desired movement
Irritability
Ability to respond to a stimulus and convert it to a neural impulse
PNS sensory division
Afferent fibers transmit impulses from receptors to CNS
Which of the following is not a type of proprioceptor? Golgi tendon organ Muscle spindle Pacinian corpuscles All of the above are proprioceptors
All of the above are proprioceptors
Central nervous system (CNS)
Brain and spinal cord
Sport-Related Concussions
Brain injury resulting from traumatic force Typically resolves within a few days -May or may not involve loss of consciousness May result in: Permanent brain damage or death due to brain swelling Second-impact syndrome -Second head injury before first has healed -Leads to cerebral swelling and death Same season repeat concussion Late-life consequences of repeated concussions -Alzheimer's disease
Axon
Carries electrical impulse away from cell body May be covered by Schwann cells, with gaps between these cells called nodes of Ranvier -Forms discontinuous myelin sheath along length of axon
Excitatory postsynaptic potentials (EPSP)
Causes depolarization
Central governor theory
Central control center regulates exercise performance -Reduces motor output to exercising muscle Protects against catastrophic disruptions of homeostasis More research needed on this mechanism Research suggests that fatigue is related to both central and peripheral factors
Which of the following is responsible for coordinating and monitoring complex movements? Cerebrum Midbrain Cerebellum Brain Stem
Cerebellum
Dendrites
Conduct impulses toward the cell body
Synapse
Contact points between axon of one neuron and dendrite of another neuron Small gap between presynaptic neuron and postsynaptic neuron
Neuron Cell body
Contains the nucleus
General Nervous System Functions
Control of the internal environment -With the endocrine system Voluntary control of movement Programming spinal cord reflexes Assimilation of experiences necessary for memory and learning
Cerebellum
Coordinates and monitors complex movement -Incorporates feedback from proprioceptors Has connections to: -Motor cortex -Brain stem -Spinal cord May initiate fast, ballistic movements
Explain how depolarization and repolarization occurs
Depolarization occurs as sodium channels open (potassium channels closed) and sodium goes into the cell causes the cell to become more positive. Repolarization occurs when potassium channels open (sodium channels close) and potassium goes out of the cell causing the cell to return to resting (negative) membrane potential.
Regular exercise can protect the brain against?
Disease (Alzheimer's) Certain types of brain injury (stroke)
PNS motor division
Efferent fibers transmit impulses from CNS to effector organs
Nerve impulse
Electrical signal carried the length of an axon -Initiated by stimulus that causes a change in the electrical charge of the neuron
How does exercise enhance brain health?
Enhances learning and memory Stimulates formation of new neurons Improves brain vascular function and blood flow Attenuates mechanisms driving depression Reduces peripheral factors for cognitive decline -Inflammation, hypertension, and insulin resistance
T/F: Repolarization is caused by the opening of sodium channels and the closing of potassium channels.
False
Vestibular Apparatus
Located in the inner ear Responsible for maintaining general equilibrium and balance -Maintains head position Sensitive to changes in linear and angular acceleration -Stimulated by head movement Also controls head and eye movement during exercise
Brain Stem
Major structures: -Medulla -Pons -Midbrain -Reticular formation Responsible for: -Many metabolic functions -Cardiorespiratory control -Complex reflexes
Golgi Tendon Organ (GTO)
Monitors tension developed in muscle -Prevents muscle damage during excessive force generation Stimulation results in reflex relaxation of muscle -Inhibitory neurons send IPSPs to muscle fibers Ability to voluntarily oppose GTO inhibition may be related to gains in strength
Cerebrum: Motor cortex
Motor control and voluntary movement
Motor unit
Motor neuron and all the muscle fibers it innervates
Resting Membrane Potential
Negative charge inside cells at rest (unequal distribution of charged ions) --5 to -100 mv (cell) -40 to -75 mv in neurons
Multiple Sclerosis
Neurological disease that destroys myelin sheaths of axons -Has genetic component -Due to immune attack on myelin
Peripheral nervous system (PNS)
Neurons outside the CNS
Which neurotransmitter is released from the sympathetic division of the Autonomic Nervous System? Norepinephrine Epinephrine Acetylcholine All of the above
Norepinephrine
Innervation ratio
Number of muscle fibers per motor neuron Low ratio in muscles that require fine motor control -23/1 in extraocular muscles Higher ratio in other muscles -1,000/1 or greater in large muscles
Explain the withdrawal reflex.
Occurs in response to sensory stimuli and is not dependent on higher brain centers. Example, someone steps on a pin. Sensory information is sent to the CNS which send efferent movement to the stimulated flexor (quads) to withdrawal the foot from the pin. The crossed-extensor reflex also occurs this situation. The person does not want to fall down when they remove their injured foot from the pin. Therefore, the opposite limb will support the body during the withdrawal reflex of the injured limb. Efferent signals are sent to the non-injured limb to stimulate the extensor (hamstring) and inhibit the flexor (quads) so that the limb stays straight for the person to stand on.
Action Potential
Occurs when a stimulus of sufficient strength depolarizes the cell -Opens Na+ channels, and Na+ diffuses into cell -Inside becomes more positive
All-or-none law
Once a nerve impulse is initiated, it will travel the length of the neuron
Crossed-extensor reflex
Opposite limb supports body during withdrawal of injured limb
Muscle Proprioceptors
Provide sensory feedback to nervous system -Tension development by muscle -Account of muscle length Muscle spindle Golgi tendon organ
Motor unit recruitment
Recruitment of more muscle fibers through motor unit activation
Withdrawal Reflex
Reflex contraction of skeletal muscle -Occurs in response to sensory input -Not dependent on higher brain centers
Somatic motor neurons of PNS
Responsible for carrying neural messages from spinal cord to skeletal muscles
Autonomic Nervous System
Responsible for maintaining internal environment -Effector organs not under voluntary control --Smooth muscle, cardiac muscle, and glands
Explain how a neuron's resting membrane potential is maintained.
Resting membrane potential is maintained by the concentrations of ions across the cell membrane. At rest more potassium is in the cell and more sodium is outside the cell. At rest almost all sodium channels are closed and a few potassium channels are open. This means more potassium is leaving the cell than sodium coming in which results in a negative resting charge.
Multiple Sclerosis and Nervous System Function
Results in progressive loss of nervous system function -Fatigue, muscle weakness, poor motor control, loss of balance, mental depression Exercise can improve functional capacity -Leads to improved quality of life
Repolarization
Return to resting membrane potential -K+ leaves the cell rapidly -Na+ channels close
Muscle Chemoreceptors
Sensitive to changes in the chemical environment surrounding a muscle -H+ ions, CO2, and K+ Provide CNS with information about metabolic rate of muscular activity -Important in regulation of cardiovascular and pulmonary responses to exercise
The size principle
Smallest motor units recruited first -Produce larger EPSP and result in action potential sooner
Spatial summation
Summing from several different presynaptic neurons
Temporal summation
Summing several EPSPs from one presynaptic neuron
Which of the following regarding the nervous system is incorrect? The CNS is comprised of the brain and spinal cord The PNS has an afferent and efferent division The CNS sends sensory information to the PNS. All of the above are correct.
The CNS sends sensory information to the PNS.
Explain the relationship between the PNS and CNS.
The central nervous system (CNS) uses sensory receptors through the sensory division of the PNS to gain sensory information from the periphery. The CNS then decides on an action and uses the motor division to execute motor output to skeletal muscles, smooth muscle, cardiac muscle, and/or glands.
How is the vestibular apparatus used during exercise?
The vestibular apparatus is located in the inner ear and is responsible for maintaining general equilibrium and balance by maintaining head position. The apparatus is sensitive to changes in linear and angular acceleration (two forms of motion that often occur with exercise).
Cerebellum and basal ganglia
These structures cooperate to form a precise movement plan
Conductivity
Transmission of the impulse along the axon
Types of motor units
Type S (slow) or type I fibers [smallest] Type FR (fast, fatigue resistant) or type IIa fibers [intermediate] Type FF (fast, fatigable) or type IIx fibers [largest]
Recruitment pattern during incremental exercise
Type S--> type FR--> type FF
Motor Functions of the Spinal Cord
Withdrawal reflex Other reflexes -Important for the control of voluntary movement Spinal tuning -Voluntary movement translated into appropriate muscle action --Higher brain centers concerned with general parameters of movement --Details of movement refined in spinal cord
Inhibitory neurotransmitters
cause the neuron to become more negative (hyperpolarized). This hyperpolarization of the membrane is called an inhibitory postsynaptic potential (IPSP).
Inhibitory postsynaptic potentials (IPSP)
causes hyperpolarization
Cerebellum movement
fast movements
excitatory neurotransmitter
increases neuronal permeability to sodium and results in excitatory postsynaptic potentials (EPSPs).
Synaptic transmission
occurs when sufficient amounts of a specific neurotransmitter are released from the presynaptic neuron
Subcortical and cortical motivation areas
send a "rough draft" of the movement
basal ganglia
slow, deliberate movements
Resting Membrane Potential maintained by?
sodium-potassium pump -Potassium tends to diffuse out of cell -Na+/K+ pump moves 2 K+ in and 3 Na+ out
