Illinois State University Neurological Control of Movement Chapter 20 n Individual nerve fibers are...
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linois State University Neurological Control of Neurological Control of Movement Movement Chapter 20 Chapter 20 Individual Individual nerve fibers nerve fibers are called are called neurons neurons . . A typical A typical neuron is neuron is composed of composed of three regions: three regions:
Illinois State University Neurological Control of Movement Chapter 20 n Individual nerve fibers are called neurons. n A typical neuron is composed of three
Neurological Control of Movement. Chapter 3.A typical neuron is
composed of three regions:
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Contains the nucleus.
2. The dendrites.
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Threshold of excitation
Voltage above which an impulse must go to excite a cell.
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a rapid and substantial depolarization of the neuron’s
membrane.
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decreased sodium permeability as the gates close
and opening of the potassium gates and repolarization.
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Nerve Transmission
Myelinated neurons - the impulse travels through the axon by
jumping between nodes of Ranvier (gaps between the cells that form
the myelin sheath).
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This process, saltatory conduction, is 5 to 50 times faster than in
unmyelinated fibers of the same size.
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A synapse involves:
the axon terminals of the presynaptic neuron
the postsynaptic receptors on the dendrite or cell body of the next
neuron
the space (the synaptic cleft) between two neurons.
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Nerve Communication
A nerve impulse causes chemicals called neurotransmitters to be
released from the presynaptic axon terminals into the synaptic
cleft.
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Nerve Communication
Neurotransmitters diffuse across the cleft and are bound to the
postsynaptic receptors.
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Nerve Communication
Once neurotransmitters are bound, the impulse has been successfully
transmitted and the neurotransmitter is then either destroyed by
enzymes or actively returned to the presynaptic neuron for future
use.
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Neurotransmitter binding at the postsynaptic receptors opens ion
gates in that membrane and can cause depolarization (excitation) or
hyperpolarization (inhibition), depending on the specific
neurotransmitter and the receptors to which it binds.
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These involve presynaptic axon terminals (motor endplates), the
synaptic cleft, and receptors on the sarcolemma of the muscle
fiber.
The neuromuscular junction functions much like a neural
synapse.
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The neurotransmitters most important to regulation of exercise are
acetylcholine and norepinephrine.
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Summation
A single presynaptic terminal cannot generate enough of a
depolarization to fire an action potential.
Multiple signals are needed.
These may come from numerous neurons or from a single neuron when
numerous axon terminals release neurotransmitters repeatedly and
rapidly.
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Summation
The axon hillock keeps a running total of all EPSPs and
IPSPs.
When their sum meets or exceeds the threshold for depolarization,
an action potential occurs.
This process of accumulating incoming signals is known as
summation.
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Central Nervous System
The central nervous system is composed of the brain and the spinal
cord.
The four major divisions of the brain are
the cerebrum,
the diencephalon,
the cerebellum,
The cerebral cortex is your conscious brain.
The diencephalon includes the thalamus, which receives all sensory
input entering the brain, and the hypothalamus, which is a major
control center for homeostasis.
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Central Nervous System:
The cerebellum, which is connected to numerous parts of the brain,
is critical to movement.
The brain stem is composed of the midbrain, the pons, and the
medulla oblongata.
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Central Nervous System
The spinal cord carries both sensory (afferent) and motor
(efferent) fibers between the brain and the periphery.
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Central Nervous System
The brain has a pain control system called an analgesia
system.
The enkephalins and -endorphins are important opiate substances
that act on the opiate receptors in the analgesia system to help
reduce pain.
Exercise of long duration has been postulated to increase the
natural levels of these opiate substances.
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Peripheral Nervous System
The peripheral nervous system contains 43 pairs of nerves: 12
cranial and 31 spinal.
The PNS can be subdivided into the sensory and motor
divisions.
The motor division also includes the autonomic nervous
system.
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Peripheral Nervous System
The sensory division carries information from sensory receptors to
the CNS so that the CNS is constantly aware of your current status
and your environment.
The motor division carries motor impulses out from the CNS to the
muscles.
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Peripheral Nervous System
The autonomic nervous system includes the sympathetic nervous
system, which is your fight-or-flight system, and the
parasympathetic system, which is your housekeeping system.
Though these systems often oppose each other, they always function
together.
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Sensory-Motor Integration
Sensory-motor integration is the process by which your PNS relays
sensory input to your CNS, your CNS interprets this information,
and then it sends out the appropriate motor signal to elicit the
desired motor response.
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Sensory-Motor Integration
Sensory input can terminate at various levels of the CNS. Not all
of this information reaches the brain.
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These are not conscious responses.
For a given sensory stimulus, the motor response is always
identical and instantaneous.
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Sensory-Motor Integration
Muscle spindles trigger reflexive muscle action when the muscle
spindle is stretched.
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Sensory-Motor Integration
Golgi tendon organs trigger a reflex that inhibits contraction if
the tendon fibers are overstretched.
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Sensory-Motor Integration
The primary motor cortex, located in the frontal lobe, is the
center of conscious motor control.
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Sensory-Motor Integration
The basal ganglia, in the cerebral white matter, help initiate some
movements (sustained and repetitive ones) and help control posture
and muscle tone.
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Sensory-Motor Integration
The cerebellum is involved in all rapid and complex movement
processes and assists the primary motor cortex and the basal
ganglia.
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Cerebellum
It is an integration center that decides how to best execute the
desired movement given your body’s current position and your
muscles’ current status.
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Sensory-Motor Integration
Though not well understood, engrams are memorized motor patterns,
stored in both the sensory motor areas of the brain, that are
called upon as needed.
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Motor Units
Each muscle fiber is innervated by only one neuron, but each neuron
may innervate up to several thousand muscle fibers.
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Motor Units
All muscle fibers within a single motor unit are of the same fiber
type.
Motor units are recruited in an orderly manner, so that specific
ones are called on each time a specific activity is
performed.
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Motor Units
Motor units with smaller neurons (slow-twitch units) are called on
before those with larger neurons (fast twitch).
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Fiber Recruitment
Neuromuscular activity is graded on the basis of a fixed order of
recruitment from the available pool of motor units.
The more force that is needed to execute a certain movement, the
more motor units are recruited.
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