Illinois State University Neurological Control of Movement Chapter 20 n Individual nerve fibers are...

Neurological Control of Movement. Chapter 3.A typical neuron is composed of three regions:
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Contains the nucleus.
2. The dendrites.
Threshold of excitation
Voltage above which an impulse must go to excite a cell.
a rapid and substantial depolarization of the neuron’s membrane.
decreased sodium permeability as the gates close
and opening of the potassium gates and repolarization.
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).
This process, saltatory conduction, is 5 to 50 times faster than in unmyelinated fibers of the same size.
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.
Nerve Communication
A nerve impulse causes chemicals called neurotransmitters to be released from the presynaptic axon terminals into the synaptic cleft.
Nerve Communication
Neurotransmitters diffuse across the cleft and are bound to the postsynaptic receptors.
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.
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.
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.
The neurotransmitters most important to regulation of exercise are acetylcholine and norepinephrine.
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.
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.
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.
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.
The spinal cord carries both sensory (afferent) and motor (efferent) fibers between the brain and the periphery.
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.
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.
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.
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.
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.
Sensory input can terminate at various levels of the CNS. Not all of this information reaches the brain.
These are not conscious responses.
For a given sensory stimulus, the motor response is always identical and instantaneous.
Muscle spindles trigger reflexive muscle action when the muscle spindle is stretched.
Golgi tendon organs trigger a reflex that inhibits contraction if the tendon fibers are overstretched.
The primary motor cortex, located in the frontal lobe, is the center of conscious motor control.
The basal ganglia, in the cerebral white matter, help initiate some movements (sustained and repetitive ones) and help control posture and muscle tone.
The cerebellum is involved in all rapid and complex movement processes and assists the primary motor cortex and the basal ganglia.
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.
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.
Motor Units
Each muscle fiber is innervated by only one neuron, but each neuron may innervate up to several thousand muscle fibers.
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.
Motor Units
Motor units with smaller neurons (slow-twitch units) are called on before those with larger neurons (fast twitch).
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.

Illinois State University Neurological Control of Movement Chapter 20 n Individual nerve fibers are...

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