KIN 340 Chapter 7: The Nervous System: Structure and Control of Movement

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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


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