Download 9. Motor

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Department of Neurology
Affiliated hospital of Jiangsu University
Motor
Descending (Motor) Pathways
Descending tracts deliver efferent impulses
from the brain to the spinal cord, and are
divided into two groups
• Direct pathways equivalent to the pyramidal
tracts
• Indirect pathways, essentially all others
Motor pathways involve two neurons (upper
and lower)
Pyramidal System concerned
with voluntary movement of the
skeletal m. and is composed of
two orders of neurons:
upper motor neuron
lower motor neuron
upper motor
neuron
lower motor
neuron
effector
Upper Motor Neurons
•
•
upper motor
Lie in the motor area of cerebral cortex
neuron
Connect directly or through interneurons to
lower motor neurons
Lower Motor Neurons
•
•
Include cranial motor nuclei and motor neurons
in anterior horn of spinal cord.
Their axons leave the CNS and extend through
peripheral nerves to supply skeletal muscles
The pyramidal system consists of
corticospinal tract
corticonuclear tract
lower motor
neuron
effector
Descending (Motor) Pathways
Upper motor neurons
• Cell bodies in the cerebral cortex
Lower motor neurons
• Cell bodies located in a motor nucleus of
the brainstem or spinal cord
Definition: Upper motor neuron
• It refers to the nerves that connect from the brain to
the spinal cord. It relays information to the lower
motor neurons.
• When the upper motor neurons are damaged the
result is muscle spasticity and very strong automatic
reflexes, such as the knee jerk reaction.
Definition: Lower motor neuron
• An efferent neuron which has its body located in the
anterior gray column of the spinal cord or in the
brainstem nuclei, and its axon passing by way of a
peripheral nerve to skeletal muscle.
• Also known as final common pathway.
Effects of Upper and Lower Motor Neuron Damage
UMN damage
LMN damage
Supranuclear paralysis
Infranuclear paralysis
Paralysis
Spastic
Flaccid
Muscle tone
Increased↑
Decreased↓
Tendon reflexes
Increased↑
Decreased↓
Pathological
reflexes
Positive (+)
Negatively (-)
Amyotrophy
No present
Distinctly
1. Direct (Pyramidal) System
• Direct pathways originate with the pyramidal
neurons in the precentral gyri
• Impulses are sent through the corticospinal tracts
and synapse in the anterior horn
• Stimulation of anterior horn neurons activates
skeletal muscles
• Parts of the direct pathway, called corticobulbar
tracts, innervate cranial nerve nuclei
• The direct pathway regulates fast and fine (skilled)
movements
Corticospinal tract
Upper motor neuron is the
Giant pyramidal cells (Betz
cells) and other pyramidal
cells in superior 2/3 of
precentral gyrus and ant.
part of paracentral lobule
Upper motor neuron
Corticospinal tract
Decussation of pyramid
Lateral corticospinal tract
Lower motor neuron
Anterior corticospinal tract
1. Corticospinal tract
Lower motor neuron
is the Motor neurons of
anterior horn of spinal
cord
Lateral corticospinal tract
Motor neurons of
anterior horn
Anterior
corticospinal tract
2. Corticonuclear Tract
Giant pyramidal cells and
other pyramidal cells in
lower 1/3 of precentral gyrus
upper motor neuron
Corticonuclear Tract
Genu of internal capsule
lower
motor
neuron
Brain stem
Cranial motor neuclei
Cranial nerves
Skeletal m. of the
head ,neck and face.
The Corticonuclear tract
send out fibers to end
Bilateral：
nucleus of oculomotor n., nucleus
trochlear n., motor nucleus of
trigeminal n., nucleus of abducent
n., ambiguus nucleus, nucleus of
accessory n., superior part of facial
nucleus.
facial nucleus
Contralateral:
inferior part of facial nucleus
hypoglossal nucleus
hypoglossal nucleus
Corticonuclear
tract
facial nucleus
Hypoglossal nucleus and inferior
part of facial nucleus receive only
the fibers from the contralateral
corticonuclear tract.
hypoglossal nucleus
The injury of the unilateral corticonuclear tract can
usually cause the paralysis of the contralateral glossal
m. and facial m. below the palpebral fissure.
• The paralysis caused by the injury of the upper motor
neuron is called the supranuclear paralysis.
• The paralysis caused by the injury of the lower motor
neuron is called the infranuclear paralysis.
Dept of Neurology, Medical College, Jiangsu University 16
Supranuclear paralysis of
facial n.
---- the paralysis of facial
m. in opposite side below
the pelpebral fissure
Infranuclear paralysis of
facial n.
---- the paralysis of facial
m. of same side
Supranuclear paralysis of
hypoglossal n.
---- when tongue extend,
the apex of tongue inclined
to the opposite side
Infranuclear paralysis of
hypoglossal n.
----when tongue extend, the
apex of tongue inclined to
the same side
2. Indirect (Extrapyramidal) System
• Includes the brainstem, motor nuclei, and all
motor pathways not part of pyramidal system
• Issue motor commands as a result of
subconscious processing
• Stimulate, facilitate, or inhibit LMN
• This system includes the vestibulospinal,
rubrospinal, reticulospinal, and tectospinal
tracts
2. Indirect (Extrapyramidal) System
These motor pathways are complex and
multisynaptic, and regulate:
• Axial muscles that maintain balance and posture
• Muscles controlling coarse
proximal portions of limbs
• Head, neck, and eye movement
movements
of
the
2. Indirect (Extrapyramidal) System
Rubrospinal tracts
• Controls muscle tone and movements of distal
muscles of the upper limbs
Vestibulospinal tracts
• Carry subconscious regulation of balance and
posture
Reticulospinal tract
• Carries subconscious regulation of reflex activity
Tectospinal tracts
• Carries subconscious regulation of visual and
auditory reflex stimulus
Upper motor neurons travel in several
pathways through the CNS
Tract
Pathway
Function
Corticospinal
tract
From the motor cortex
to lower motor neurons
in the ventral horn of
the spinal cord
The function of this pathway is
fine voluntary motor control of
the limbs. The pathway also
controls voluntary body posture
adjustments.
Corticobulbar
tract
From the motor cortex Involved in control of facial and
to several nuclei in the jaw musculature, swallowing
and tongue movements.
pons and medulla
From
the
superior Involved
in
involuntary
to lower adjustment of head position in
response to visual information.
motor neurons
Tectospinal tract/
Colliculospinal tract colliculus
Upper motor neurons travel in several
pathways through the CNS
Tract
Rubrospinal
tract
Pathway
Function
Involved
in
involuntary
From red nucleus to lower adjustment of arm position in
response
to
balance
motor neurons
information.
Vestibulospinal
tract
From vestibular nuclei,
which processes stimuli
from semicircular canals
to lower motor neurons
Reticulospinal
tract
From reticular formation Regulates involuntary motor
activities and assists in balance.
to lower motor neurons
Involved in control of facial
and
jaw
musculature,
swallowing
and
tongue
movements.
Spinal Cord Trauma: Paralysis
Paralysis – loss of motor function
Flaccid paralysis
• severe damage to the ventral root or anterior horn cells
• Lower motor neurons are damaged and impulses do not
reach muscles
• There is no voluntary or involuntary control of muscles
Spinal Cord Trauma: Paralysis
Spastic paralysis
• only upper motor neurons of the primary motor cortex
are damaged
• Spinal neurons remain intact and muscles are stimulated
irregularly
• There is no voluntary control of muscles
Spinal Cord Trauma: Transection
• Cross sectioning of the spinal cord at any level
results in total motor and sensory loss in regions
inferior to the cut
• Paraplegia – transection between T1 and L1
• Quadriplegia–transection in the cervical region
Example: Poliomyelitis
• Destruction of the anterior horn motor
neurons by the poliovirus
• Early symptoms – fever, headache, muscle
pain and weakness, and loss of somatic
reflexes
• Vaccines are available and can prevent
infection
Example: Amyotrophic Lateral Sclerosis (ALS)
• Lou Gehrig’s disease – neuromuscular
condition involving destruction of anterior
horn motor neurons and fibers of the
pyramidal tract
• Symptoms – loss of the ability to speak,
swallow, and breathe
• Death occurs within five years
• Linked to malfunctioning genes for glutamate
transporter and/or superoxide dismutase