Stof Neural Control of Movement
Motor unit = Motorneuron + axon + muscle fibers
Single motor unit innervates multiple muscle fibers.
Figure 1. Types of motor units.
Figure 2. At lower forces, the slow motor units are recruited, while at higher forces, faster motor units are recruited.
Two mechanisms in regulating muscle force:
1. Size principle of Henneman: Motor units are recruited in order of size from smallest to largest
depending upon the intensity. So at first the small units that don’t produce much force, are slow to
act and are resistance to fatigue are recruited. This minimizes the amount of fatigue an organism
experiences.
2. Summation of force as a function of firing frequency. High frequency causes summation of force,
which creates a fused tetanus.
Redundancy of muscles:
Multiple muscles act across a single joint. Furthermore, a muscle acts at multiple joints, which results
in multiple degrees of freedom.
, Monosynaptic reflex: Only occurs during muscle lengthening.
Long loop reflex: Also occurs in muscles that don’t change in length, but that are needed to produce
compensatory forces in the correct direction.
LE introduction on neuromuscular disorders (NMD)
Neuromuscular disorders: Disorders affecting a part of the peripheral
nervous system (PNS), which consists of:
- spinal cord: anterior horn cell + sensory ganglia
- nerve roots, plexuses, peripheral nerves
- neuromuscular junction
- muscle + skin sensory receptors
NMD categories
- Spinal cord / anterior horn cells:
- Spinal muscular atrophy
- Amyotrophic lateral sclerosis (ALS)
- Nerve roots:
- Guillain-Barré syndrome (GBS)
- Chronic inflammatory demyelinating polyradiculon… (CIDP)
- Brachial and lumbosacral plexus:
- Neuralgic Amyotrophy (NA)
- Peripheral nerves:
- Polyneuropathy
- Neuromuscular junction:
- Myasthenia Gravis
- Lambert Eaton Myasthenic Syndrome (LEMS)
- Muscle:
- Congenital or metabolic myopathies
- Muscular dystrophies (e.g. Duchenne’s muscular dystrophy)
Spinal muscular atrophy (SMA)
Anterior horn cells degenerate early because of loss
SMN1-gene. The less remaining SMN function, the
more severe the clinical syndrome. This leads to
three SMA types:
Type 1: never sits, usually death < 2 years old
Type 2: never walks
Type 3: loss of ambulation late teens
Amyotrophic lateral sclerosis (ALS)
Pure motor signs, including muscle twitches. Both upper and lower motor neurons are involved.
Average duration between start of disease and death is 3 years.
Hernia nuclei pulposi
Both motor and sensory signs. Distribution by root myotoma and dermatoma. It causes local pain
and radiating.
Guillain Barré syndrome
inflammation of spinal roots and peripheral nerves, which damages myeline. It is an auto-immune
Motor unit = Motorneuron + axon + muscle fibers
Single motor unit innervates multiple muscle fibers.
Figure 1. Types of motor units.
Figure 2. At lower forces, the slow motor units are recruited, while at higher forces, faster motor units are recruited.
Two mechanisms in regulating muscle force:
1. Size principle of Henneman: Motor units are recruited in order of size from smallest to largest
depending upon the intensity. So at first the small units that don’t produce much force, are slow to
act and are resistance to fatigue are recruited. This minimizes the amount of fatigue an organism
experiences.
2. Summation of force as a function of firing frequency. High frequency causes summation of force,
which creates a fused tetanus.
Redundancy of muscles:
Multiple muscles act across a single joint. Furthermore, a muscle acts at multiple joints, which results
in multiple degrees of freedom.
, Monosynaptic reflex: Only occurs during muscle lengthening.
Long loop reflex: Also occurs in muscles that don’t change in length, but that are needed to produce
compensatory forces in the correct direction.
LE introduction on neuromuscular disorders (NMD)
Neuromuscular disorders: Disorders affecting a part of the peripheral
nervous system (PNS), which consists of:
- spinal cord: anterior horn cell + sensory ganglia
- nerve roots, plexuses, peripheral nerves
- neuromuscular junction
- muscle + skin sensory receptors
NMD categories
- Spinal cord / anterior horn cells:
- Spinal muscular atrophy
- Amyotrophic lateral sclerosis (ALS)
- Nerve roots:
- Guillain-Barré syndrome (GBS)
- Chronic inflammatory demyelinating polyradiculon… (CIDP)
- Brachial and lumbosacral plexus:
- Neuralgic Amyotrophy (NA)
- Peripheral nerves:
- Polyneuropathy
- Neuromuscular junction:
- Myasthenia Gravis
- Lambert Eaton Myasthenic Syndrome (LEMS)
- Muscle:
- Congenital or metabolic myopathies
- Muscular dystrophies (e.g. Duchenne’s muscular dystrophy)
Spinal muscular atrophy (SMA)
Anterior horn cells degenerate early because of loss
SMN1-gene. The less remaining SMN function, the
more severe the clinical syndrome. This leads to
three SMA types:
Type 1: never sits, usually death < 2 years old
Type 2: never walks
Type 3: loss of ambulation late teens
Amyotrophic lateral sclerosis (ALS)
Pure motor signs, including muscle twitches. Both upper and lower motor neurons are involved.
Average duration between start of disease and death is 3 years.
Hernia nuclei pulposi
Both motor and sensory signs. Distribution by root myotoma and dermatoma. It causes local pain
and radiating.
Guillain Barré syndrome
inflammation of spinal roots and peripheral nerves, which damages myeline. It is an auto-immune
