Transcript Neurological Control of Movement. Chapter 3.

Neurological Control of Movement
Chapter 20

Individual nerve fibers
are called neurons.

A typical neuron is
composed of three
regions:
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Regions of a Neuron

1. The cell body, or soma.
– Contains the nucleus.

2. The dendrites.
– Carry the impulses toward
the cell body.

3. The axon.
– The neuron’s transmitter.
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Nerve Function

Axon hillock.
– Cone-shaped region of axon
– Impulse conduction
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Nerve Function

Nerve impulse - an
electrical charge.

Resting membrane
potential (-70 mV)
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Sodium-potassium pump
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Nerve Function
Depolarization. (Excitation)
 Hyperpolarization. (Inhibition)

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Graded potentials

localized changes in
the membrane
potential.
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Threshold of excitation

Voltage above which an impulse must go to
excite a cell.
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Action potential

a rapid and substantial depolarization of the
neuron’s membrane.
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The chain of events for an action
potential are:
increased sodium permeability through
opening of the sodium gates.
 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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Nerve Transmission

Impulses also travel faster in neurons of
larger diameters.
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Nerve Communication

Neurons communicate with each other
across synapses.
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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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Nerve Communication

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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Nerve Communication
Neurons communicate with muscle cells at
neuromuscular junctions.
 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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Nerve Communication

The neurotransmitters most important to
regulation of exercise are acetylcholine and
norepinephrine.
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Summation
Excitatory postsynaptic potentials (EPSPs)
are depolarizations of the postsynaptic
membrane.
 Inhibitory postsynaptic potentials (IPSPs)
are hyperpolarizations of that membrane.

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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
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–
–
–
–
the cerebrum,
the diencephalon,
the cerebellum,
and the brain stem.
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Central Nervous System
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
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Sensory input can terminate at various
levels of the CNS. Not all of this
information reaches the brain.
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Sensory-Motor Integration
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Reflexes are the simplest form of motor
control.
– 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
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Muscle spindles trigger reflexive muscle
action when the muscle spindle is stretched.
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Sensory-Motor Integration
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Golgi tendon organs
trigger a reflex that
inhibits contraction if
the tendon fibers are
overstretched.
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Sensory-Motor Integration
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The primary motor cortex, located in the
frontal lobe, is the center of conscious
motor control.
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Sensory-Motor Integration
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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
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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
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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
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Motor units with smaller neurons (slowtwitch 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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Low Force
Moderate Force
Maximal Force
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