Somatomotor control: The 1st motor neuron
Afferents:
- Spinal interneurons
- Muscle spindle dorsal root ganglion cells
- Pyramidal neurons in motor cortex (Betz cells)
Efferents:
- a-motor neuron: extrafusal (common) muscle fibers
- y-motor neuron: intrafusal muscle fibers (inside the muscle spindle)
Betz cells: the ability to suppress the reflexes of the brain. Only Betz cells directly terminate on the
2nd motor neurons
Motor columns are controlled differently. The
corticobulbospinalmotor system will address the inter- and
motor neurons in the bulb of the brain/spinal cord.
The secondary systems are located on the lateral side of the
vertebral column.
Cortico-bulbospinal system: consists of all components. Origin,
axons and course of axons and the termination.
Cortico-bulbospinal tract (C-Bst): axons and course of axons
Primary cortex:
- First cortical station in sensory processing
- Last cortical station in motor processing
Secondary cortex:
- Surrounds (some) primary sensory cortices
Associative cortex:
- The rest
- Processing inside the cortex
Every type of cortex has its own specific composition
Neocortex:
- 6 layers
- Most of the cerebrum
- Each layer its function
Allocrotex:
- Less than 6 layers
- Hippocampus
- Cingelute and parahippocampal gryi
- Insular cortex
,Function of layers
Input layers:
- Thalamus (IV)
- Cortex (III)
- Brainstem (III & V)
Output layers:
- Thalamus (VI)
- Cortex (II & III)
- Brainstem and spinal cord (V)
Giant pyramidal neurons
Pyramidal neurons are projection neurons. The Betz cells are only
present in the primary motor cortex. They are the largest neurons in
the CNS and have the thickest and fastest axons.
A thick soma leads to a lot of membrane to support.
Betz cells are the only 1st motor neurons that terminate on the 2nd
motor neurons. This projection is a minority but the axons are super
fast, and their control supersedes the control of the secondary systems
and is even able to inhibit some of the reflexes.
All other pyramidal cells in layer V of the motor cortex and the
premotor cortex project on interneurons, either directly or indirectly.
The Betz system is able to suppress the pain reflex (but not in all
cases), you have to be aware of the pain (f.e. you know something is
going to be hot). If you step in a needle you are not aware because the
spinal cord receives the information, not the brain.
Primary motor cortex:
- 55% from layer V pyramidal neurons
- 5% from layer V Betz cells
Premotor cortex
- 40% from layer V pyramidal neurons
Corticofugal projections
From layer V pyramidal neurons of all neocortical
areas. The cortico-bulbospinal projection is a subset of
the corticofugal system.
The pyramidal tract is the cortico-spinal projection.
Corticobulbar (go to the bulbar/brain stem) and
terminate from:
- Red nucleus
- Tectum
- Pons
- Reticular formation
- Vestibular nuclei
- Interneurons and motorneurons
Corticospinal (go to the spinal cord) and terminate
from:
, - Interneurons and motor neurons
Brainstem: general structure
Tectum:
- Covers the ventricular system
Tegmentum:
- Spinal cord look alike
Pes:
- Corticofugal axons (fiber bundle)
- Cerebral peduncle
Caudal to the pons the cortico-bulbospinal tract is renamed: the pyramidal tract.
Left hemisphere controls right body
All 1st motor neurons terminate on 2nd motor neurons on the contralateral
side. Some 1st motor neurons also terminate on 2nd motor neurons on the
ipsilateral side (on the same side).
Keep in mind that the 1st motor neurons are present in the cerebrum, so there
is crossing what means that the left side affects the right side of the body.
All 2nd motor neurons are innervated by axons from the contralateral motor
cortex. Some 2nd motor neurons are also innervated by axons from the
ipsilateral motor cortex with one exception, all spinal 2nd motor neurons
innervate ipsilateral muscles on the same side).
From primary motor cortex
Bilateral:
- Trigeminal motor nucleus (Vm)
- Mastication
- Dorsal facial motor nucleus (VIIm)
- Mimical musculature upper half of face
- Ambiguus nucleus (IX X)
- Swallowing
Contralateral
- Ventral facial motor nucleus (VIIm)
- Mimical musculature lower half of face
- Ventral horn upper cervical cord
- Sternocleidomastoid and trapezius muscles
- Hypoglossal nucleus (XII)
- Motor tongue
Not innovated at all:
- Oculomotor nuclei (control eye muscles, most of the eye movement is involuntary)
- Visceromotor nuclei in the brainstem (parasympathetic nuclei), autonomic nervous system
Afferents:
- Spinal interneurons
- Muscle spindle dorsal root ganglion cells
- Pyramidal neurons in motor cortex (Betz cells)
Efferents:
- a-motor neuron: extrafusal (common) muscle fibers
- y-motor neuron: intrafusal muscle fibers (inside the muscle spindle)
Betz cells: the ability to suppress the reflexes of the brain. Only Betz cells directly terminate on the
2nd motor neurons
Motor columns are controlled differently. The
corticobulbospinalmotor system will address the inter- and
motor neurons in the bulb of the brain/spinal cord.
The secondary systems are located on the lateral side of the
vertebral column.
Cortico-bulbospinal system: consists of all components. Origin,
axons and course of axons and the termination.
Cortico-bulbospinal tract (C-Bst): axons and course of axons
Primary cortex:
- First cortical station in sensory processing
- Last cortical station in motor processing
Secondary cortex:
- Surrounds (some) primary sensory cortices
Associative cortex:
- The rest
- Processing inside the cortex
Every type of cortex has its own specific composition
Neocortex:
- 6 layers
- Most of the cerebrum
- Each layer its function
Allocrotex:
- Less than 6 layers
- Hippocampus
- Cingelute and parahippocampal gryi
- Insular cortex
,Function of layers
Input layers:
- Thalamus (IV)
- Cortex (III)
- Brainstem (III & V)
Output layers:
- Thalamus (VI)
- Cortex (II & III)
- Brainstem and spinal cord (V)
Giant pyramidal neurons
Pyramidal neurons are projection neurons. The Betz cells are only
present in the primary motor cortex. They are the largest neurons in
the CNS and have the thickest and fastest axons.
A thick soma leads to a lot of membrane to support.
Betz cells are the only 1st motor neurons that terminate on the 2nd
motor neurons. This projection is a minority but the axons are super
fast, and their control supersedes the control of the secondary systems
and is even able to inhibit some of the reflexes.
All other pyramidal cells in layer V of the motor cortex and the
premotor cortex project on interneurons, either directly or indirectly.
The Betz system is able to suppress the pain reflex (but not in all
cases), you have to be aware of the pain (f.e. you know something is
going to be hot). If you step in a needle you are not aware because the
spinal cord receives the information, not the brain.
Primary motor cortex:
- 55% from layer V pyramidal neurons
- 5% from layer V Betz cells
Premotor cortex
- 40% from layer V pyramidal neurons
Corticofugal projections
From layer V pyramidal neurons of all neocortical
areas. The cortico-bulbospinal projection is a subset of
the corticofugal system.
The pyramidal tract is the cortico-spinal projection.
Corticobulbar (go to the bulbar/brain stem) and
terminate from:
- Red nucleus
- Tectum
- Pons
- Reticular formation
- Vestibular nuclei
- Interneurons and motorneurons
Corticospinal (go to the spinal cord) and terminate
from:
, - Interneurons and motor neurons
Brainstem: general structure
Tectum:
- Covers the ventricular system
Tegmentum:
- Spinal cord look alike
Pes:
- Corticofugal axons (fiber bundle)
- Cerebral peduncle
Caudal to the pons the cortico-bulbospinal tract is renamed: the pyramidal tract.
Left hemisphere controls right body
All 1st motor neurons terminate on 2nd motor neurons on the contralateral
side. Some 1st motor neurons also terminate on 2nd motor neurons on the
ipsilateral side (on the same side).
Keep in mind that the 1st motor neurons are present in the cerebrum, so there
is crossing what means that the left side affects the right side of the body.
All 2nd motor neurons are innervated by axons from the contralateral motor
cortex. Some 2nd motor neurons are also innervated by axons from the
ipsilateral motor cortex with one exception, all spinal 2nd motor neurons
innervate ipsilateral muscles on the same side).
From primary motor cortex
Bilateral:
- Trigeminal motor nucleus (Vm)
- Mastication
- Dorsal facial motor nucleus (VIIm)
- Mimical musculature upper half of face
- Ambiguus nucleus (IX X)
- Swallowing
Contralateral
- Ventral facial motor nucleus (VIIm)
- Mimical musculature lower half of face
- Ventral horn upper cervical cord
- Sternocleidomastoid and trapezius muscles
- Hypoglossal nucleus (XII)
- Motor tongue
Not innovated at all:
- Oculomotor nuclei (control eye muscles, most of the eye movement is involuntary)
- Visceromotor nuclei in the brainstem (parasympathetic nuclei), autonomic nervous system
