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‫االسراء اية ‪58‬‬
Somatic Motor System
By
Dr. Abdel Aziz M. Hussein
Assist prof of Physiology
• Origin:
• From area (6) and area (4) → descends to corpus
striatum → Globus pallidus→ from the globus pallidus
fibers pass to;
1. Reticular formation
2. Vestibular nuclei
3. Red nucleus
4. Tectum of midbrain.
• From these nuclei the following extrapyramidal tracts
arise:
Motor areas 4 and 6
Corpus striatum
Basal Ganglia
Globus pallidus
RF
Ret.Spin T.
Vest. Nuclei
Red Nucl. Tectum
Vest.Spin.T. Rubrospin. T. Tectospin. T.
Cerebrum
Cerebellum
Basal ganglia
Red nucleus
Rubrospinal T.
Lateral AHCs
++
Functions:
1. Mediates motor signals concerned with the skilled
voluntary movements performed by distal limb
muscle.
2. Also facilitates  &  motor neurons of the distal
flexors
Medullary RF
Pontine RF
Lateral RST.
Medial RST
-- ++ -Medial AHCs
• Functions:
• a. Medial R.S.T.
• It mediates facilitatory effect on the motor neurons of
the antigravity ms to maintain postural support.
• b. Lateral R.S.T.
• It inhibits the tone in the antigravity ms under some
postural conditions, which provides background to
perform other motor activities.
Medial VN
Medial VST.
Lateral V.N.
Lateral VST
++++ ++
Medial AHCs
• Functions:
• a. Lateral V.S.T.
• It is facilitatory to  &  motor neurons of the
antigravity ms to maintain body posture & equilibrium
in response to impulses from the vestibular apparatus
which evoked by charges in head position or exposure
to acceleration.
• b. Medial V.S.T.
• It is facilitatory to  &  motor neurons of the neck and
upper limb muscles that are involved in regulation of
the head & upper limb position during exposure to
acceleratory movements
Superior colliculus
Inferior colliculus
Medial T.S.T
Lateral TST
++++
Medial AHCs
• Functions:
• This tract mediates reflex turning of the head in
response to sudden visual or auditory stimuli.
MOTOR
CORTEX
INTERNAL
CAPSULE
BRAIN STEM
SPINAL
CORD
Def.,
• It is the damage of upper motor neuron in the higher
center or the descending motor tract.
Causes
1. Trauma
2. Tumour
3. Vascular disorders as thrombosis or hemorrhage.
Sites:
• Most common site of UMNL is the internal capsule.
Internal capsule
Motor loss
Sensory loss
Loss of somatic
Hemiplegia
sensations, vision
and hearing
1. Contralateral paralysis (loss of only voluntary
movements) of the distal ms of the limbs, lower
facial ms and ms of the tongue.
2. Contralateral paresis (weakness i.e., the ms
retains some movements) of the axial ms and
upper facial ms.
•
Axial ms are supplied by descending motor tracts
other than CBS whereas ms of the upper face
are ipsilaterally innervated by CBS tract.
3) Spasticity (increased ms tone) of the skeletal ms
due to increased supraspinal facilitation to -motor
neurons.
• A lesion at the level of internal capsule interrupts the
descending inhibitory cortical fibers which feeds the
inhibitory reticulospinal tract leaving the facilitatory
vestibulospinal and reticulospinal to act.
• This spasticity is of the clasp-knife type
Facilitatory RF
and VST
Inhibitory RF
4) Exaggerated tendon jerk & clonus: due to increased
supraspinal facilitation.
5) Positive Babinski's sign
6) The paralyzed ms show no or minimal atrophy as the
lower motor neuron is intact and the ms contracts
reflexly.
7) Normal response of the paralyzed ms to electric
stimulation
a) Faradic current produces clonic or tetanic
contractions
b) Galvanic current produces contractions that occur
only at closing (make) and opening (break) of the
circuits.
CCC > ACC > AOC > COC
1) Contralateral hemianaesthesia i.e. loss of all
sensations on the opposite side of the body
2) Contralateral homonymous hemianopia i.e., loss of
vision in the two opposite halves of the field of vision
3) Bilateral diminution of hearing acuity.
No complete loss of hearing as both ears are bilaterally
represented in both cortices.
Def.,
• It is damage of the lower motor neurons (the spinal
AHCS and the cranial motor nuclei or their axons)
resulting in skeletal ms paralysis
Causes
1. Trauma
2. Neuropathy
I) Structural changes
In Nerve (degeneration and regeneration
In muscle (atrophy and increase Ach receptors
II) Functional changes
1. Flaccid paralysis
2. Fasciculation and fibrillation
3. Dennervation supersensitivity
4. Reaction of degeneration
Retrograde degeneration
Wallerian degeneration
Regeneration
Atrophy of muscles
A) Flaccid paralysis:
Paralysis of denervated ms with loss of all types of
movements; "voluntary, postural and reflex".
All reflexes are lost including stretch reflex resulting in
loss of ms tone and tendon jerk (flaccidity).
The extent of paralysis is usually limited to a small
group of ms
B) Fasiculations and fibrillations:
• Appears few days or weeks after denervation
• Disappear when the motor nerve completely
degenerates or successful re-innervation of the ms
occurs.
B) Fasiculations :
• Synchronous visible contraction of the motor unit (all ms fibers)
supplied by the injured axon.
• Result from spontaneous generation of action potential (injury
potentials) in distal segment of the injured axon
B) Fibrillations:
• As degeneration of the injured axon continues, the
axon terminals are now separate from the main axon
and hence, from each other.
• Injury potentials are still generated along the terminals
leading to asynchronous contraction of the individual
ms fibers attached to terminals.
• Invisible to the observer and detected only by
electromyogram (EMG).
Fibrillations
C) Denervation supersensitivity:
• Denervated ms becomes supersensitive to
acetylcholine.
• This is due to increase in the number of A.Ch.
receptors which cover the entire surface of ms cell
membrane.
D) Reaction of degeneration:
• - This means abnormal response of the denervated
muscle to electric stimulation.
• Reaction of degeneration (response of denervated ms):
• INCOMPLETE REACTION:
• i) Faradic current produces no response.
• The denervated muscle has a prolonged chronaxia.
• The faradic current is faster than the excitation time
needed to produce a response.
• ii) Galvanic current produces an abnormal response.
• The response in general is weaker than normal and ACC >
CCC.
D) Reaction of degeneration:
COMPLETE REACTION:
• When the denervation is prolonged, the ms is
atrophied and fibrosed.
• Thus, no response occurs to both faradic and galvanic
currents.
THANKS