1. Spinal cord- 2
Descending tracts

3. Skeletal muscle Skeletal muscle Upper motor neurons in
primary motor cortex
Somatic motor nuclei
of brain stem
Skeletal muscle
Lower
motor
neurons
Somatic motor nuclei
of spinal cord
Skeletal muscle
In the somatic nervous system (SNS), an upper motor neuron in the CNS controls a lower-motor neuron in the brain stem or spinal cord. The axon of the lower-motor neuron has direct control over skeletal muscle fibers. Stimulation of the lower- motor neuron always has an excitatory effect on the skeletal muscle fibers.

4. Visceral motor nuclei in hypothalamus Preganglionic neuron
Visceral effectors
Autonomic nuclei in
brain stem
Ganglionic
neurons
Autonomic nuclei
in spinal cord
Preganglionic neuron
In the autonomic nervous system (ANS), the axon of a preganglionic neuron in the CNS controls ganglionic neurons in the periphery. Stimulation of the ganglionic neurons may lead to excitation or inhibition of the visceral effector innervated

5. First order neuron: has its cell body in the cerebral cortex
Second order neuron: an interneuron situated in the anterior gray column
Third order neuron: the lower motor neuron in the anterior gray column and
Innervates the skeletal muscle through the anterior root of spinal nerve
In some instances the axon of the first order neuron terminates directly on the third
order neuron

6. Motor tracts
•There are two major descending tracts
•Corticospinal tract (pyramidal) : Conscious control of skeletal muscles
•Subconscious tract (extrapyramidal): Subconscious regulation of balance, muscle tone, eye, hand, and upper limb position

8. •Corticobulbar tracts: conscious control over eye, jaw, and face muscles
•Lateral corticospinal tracts: conscious control over skeletal muscles (mostly distal muscles)
•Anterior corticospinal tracts: conscious control over skeletal muscles (mostly proximal muscles)
UMN
LMN
To skeletal
muscles
Corticobulbar tract
Motor
nuclei of
cranial nerves
Lateral corticospinal tract
MESENCEPHALON
To skeletal
muscles
Motor
nuclei of
cranial nerves
MEDULLA
OBLONGATA
Pyramids
Lateral corticospinal
tract
Anterior corticospinal
tract
To skeletal
muscles
Anterior corticospinal tract

9. Corticospinal tracts
The corticospinal tracts are often called the pyramidal tracts because they form pyramid-shaped enlargements on the anterior surface of the medulla
concerned with controlling skilled movements of the distal extremities (facilitation of alpha and gamma motor neurons which innervate the distal flexor muscles )
The upper motor neurons of these tracts originate in the precentral gyrus of the cerebral cortex
In medulla oblongata they form the medullary pyramids
Most of the fibers (85 percent) cross over (decussate) to the opposite side in the pyramidal decussation, where they continue to descend in the lateral funiculus of the spinal cord as the lateral corticospinal tract (LCST).
The tract descends all the way of spinal cord with fibers continually leaving it in order to synapse on interneurons in the anterior gray horn. ( Some even synapse directly on alpha and gamma motor neurons)
Those corticospinal fibers which do not decussate in the medulla continue descending on the same (ipsilateral) side of the cord and become the anterior corticospinal tract (ACST). This tract does not extend below the midthoracic level. Fibers leave the tract at various levels to cross over in the anterior white commissure to synapse on interneurons in the anterior gray horn.

10. The anterior corticospinal tract
acts on the proximal muscles of upper limb
(shoulder muscle) of the ipsilateral and
contralateral sides

11. corticospinal tract
for fine skilled movements

12. The Corticobulbar Tract
This tract is composed of fibers originating in the precentral gyrus of the lower quarter of the motor cortex.
The descending fibers terminate in the motor nuclei of cranial nerves III and IV in the midbrain; V, VI. and VII in the pons; and IX, X, XI, and XII in the medulla.
The corticobulbar fibers from one side of the brain project to the motor nuclei on both sides of the brainstem (bilateral input)
The corticobulbar input is bilateral to :
1- 5th
2- Part of 7th ( which supplies UPPER facial muscles)
3- 9th,10th,11th
4- 12th !!!!

13. These motor pathways are complex and multisynaptic, and regulate:
The Subconscious Motor Tracts
•Consists of four tracts involved in monitoring the subconscious motor control
•Vestibulospinal tracts
•Tectospinal tracts
•Reticulospinal tracts
•Rubrospinal tracts
Extrapyramidal tracts arise in the brainstem, but are under the influence of the cerebral cortex
These motor pathways are complex and multisynaptic, and regulate:
Axial muscles that maintain balance and posture
Muscles controlling coarse movements of the proximal portions of limbs
Head, neck, and eye movement

14. the anterior white column
Vestibulospinal tracts
Vestibular nuclei are situated in the pons and medulla beneath the floor of 4th ventricle
•Send information from the inner ear to monitor position of the head
• balance by facilitate the activity of the extensor muscles
The tract descends uncrossed through medulla and through spinal cord in
the anterior white column
Terminates by synapsing with interneurons of anterior gray column
The inner ear and the cerebellum facilitate the activity of extensor muscles
and inhibit the activity of flexor muscles in association with the maintenance of balance

16. ( balance by facilitate the activity of the extensor muscles )
Vestibulospinal tract
nerve cells in vestibular nucleus (in the pons and medulla oblongata
received afferents from inner ear and cerebellum
axons descend uncrossed
through medulla and through the length of spinal cord
synapse with neuron in the anterior gray column of the spinal cord
( balance by facilitate the activity of the extensor muscles )

18. by synapsing with interneurons
Tectospinal tracts
Concerned with reflex postural movements in response to visual stimuli
•Send information to the head, neck, and upper limbs in response to bright and sudden movements and loud noises
•The tectum area consists of superior and inferior colliculi
•Superior colliculi: receives visual information
•Inferior colliculi: receives auditory information
Arise from nerve cells in the superior colliculus
Most of the fibers cross the midline soon after their origin
The tract descends in the anterior white column close to Anterior median fissure
Majority of fibers terminate in the anterior gray horn in the upper cervical segments
by synapsing with interneurons

19. Tectospinal tract nerve cells in superior colliculus of the midbrain
nerve fibres/ axons
cross the mid line
terminate in the anterior gray column of upper cervical segments of spinal cord
( responsible for reflex movement of
head & neck in response to visual stimuli )

21. Reticulospinal tracts
• influence voluntary movements and reflex activity by facilitating or inhibiting the activity of alpha and gamma motor neurons
Reticular formation (RF): group of scattered nerve cells in the brain stem
From pons: axons of RF neurons descend uncrossed into the spinal cord
( pontine Reticulospinal tracts )
descend in the anterior white column as the medial reticulospinal tract (MRST)
activate the axial and proximal limb extensors
From medulla : axons of RF neurons descend crossed and uncrossed into the spinal cord
( medullary Reticulospinal tracts )
descend in the lateral white column as the lateral reticulospinal tract (LRST).
inhibit the axial and proximal limb extensors (and to a lesser degree it also excites axial
and proximal limb flexors)
The reticulospinal tracts exert both somatic and autonomic control
Has also descending autonomic fibers ( providing a pathway by which the hypothalamus
can control the sympathetic and sacral parasympathetic outflow)
Most of these fibers are derived from the lateral reticulospinal tract

23. Rubrospinal tracts
• facilitate the activity of flexors and
inhibit the activity of extensors
The axons of neurons in the red nucleus cross over near their point of origin and
descend contralaterally in the lateral funiculus of the cord adjacent to
the lateral corticospinal tract
Terminates by synapsing with interneurons of anterior gray column
It has connections with cerebral cortex and cerebellum

24. ( facilitate the activity of flexor muscles )
Rubrospinal tract
nerve cells in red nucleus
( tegmentum of midbrain at the level of superior colliculus )
nerve fibres / axons
cross the mid line
descend as rubrospinal tract
through pons and medulla oblongata
terminate anterior gray column of spinal cord
( facilitate the activity of flexor muscles )

26. Summary of somatic motor control
•Cerebral cortex initiates voluntary movement
•Information goes to the basal nuclei and cerebellum
•These structures modify and coordinate the movements so they are performed in a smooth manner
Information goes from the basal nuclei and cerebellum back to the cerebral cortex to constantly monitor position and muscle tone

27. Somatic Motor Control Motor Association areas Decision in frontal
lobes
Basal
nuclei
Cerebellum
The planning stage: When a conscious decision is made to perform a specific movement, information is relayed from the frontal lobes to motor association areas. These areas in turn relay the information to the cerebellum and basal nuclei.

28. Primary
motor
cortex
Motor
Association
areas
Movement: As the movement begins, the motor association areas send instructions to the primary motor cortex. Feedback from the basal nuclei and cerebellum modifies those commands, and output along the conscious and subconscious pathways directs involuntary adjustments in position and muscle tone
Basal
nuclei
Cerebellum
Other nuclei of the medial
and lateral pathways
Corticospinal pathway
Lower
motor
neurons
Motor activity