Lecture 7: Motor System II Flashcards
Motor (pyramidal) pathway is composed of:
2 order neurons
Motor (pyramidal) pathway is composed of 2 order neurons:
-1st order neuron: upper motor neuron
-2nd order neuron: lower motor neuron
1st order neuron (of the motor pathway) : upper motor neuron starts at __ and ends at
Starts at the MOTOR CORTEX and ends at the VENTRAL (ANTERIOR) HORN of the spinal cord
1st order neuron: upper motor neuron: stimulates and modulates:
The activity of the lower motor neuron
Motor pathway: 1st order neuron have the __ fibers of the CNS
Longest fibers of the CNS!
2nd order neuron of the motor neurons: Lower motor neuron starts at __ and ends at __
Starts at the anterior horn of the spinal cord and ends at the neuromuscular
junction.
2nd order neuron of the motor patway: lower motor neuron: exits _
muscles
2nd order neuron of the motor pathway: Lower motor neuron is integrated in __
The circuit of motor reflexes
Motor cortex is located in:
Frontal lobe
Motor cortex is located in the frontal lobe and divided into
3 sub areas
Motor cortex is located in the frontal lobe and divided into 3 sub areas:
- Primary motor cortex
- Premotor area
- Supplemental motor area
Motor association cortex is composed of (2):
(1) Premotor area
(2) Supplemental motor area
Primary motor cortex:
Located in the
PRECENTRAL GYRUS (frontal lobe)
Primary motor cortex:
Map of a motor representation of body muscles.
Primary motor cortex has unequal:
Topographic representation
Primary motor cortex: Penfield’s homunculus:
small muscles with low innervation ratio have greatest representation (e.g. fingers, hand, face)
Primary motor cortex: Stimulation of specific primary motor area (e.g. Legs) leads to:
Contraction of
muscles of the associated region of the body (i.e. Legs).
Map of the body representation in the cortex: output: motor cortex
Left hemisphere section controls the body’s right side
Map of the body representation in the cortex: Input: sensory cortex:
Left hemisphere section receives input from the body’s right side
Organization of the Primary Motor Cortex has __ horizontal layers
6
Layer 5 of the primary motor cortex (2) :
(1) House of the UPPER MOTOR NEURONS (giant pyramidal neurons=Betz cells)
(2) DESCENDING OUTPUT layer (i.e. gives rise to descending pyramidal tracts.
Betz cells
Giant pyramidal neurons
Primary motor cortex: Layers 2-4:
INPUT LAYERS from other
cortical areas (e.g. motor association
cortex, somatosensory cortex…)
Primary motor cortex: layer 6:
CORTICAL OUTPUT layer gives
rise to cortico-cortical fibers
Organization of the primary cortex is in __ and __
6 Horizontal layers and vertical columns
Primary motor cortex: Vertical columns: structure
< 1 mm in diameter, high density of neurons (thousands each).
Primary motor cortex: VERTICAL COLUMNS function as:
FUNCTIONAL UNIT : each column stimulates a single muscle or a group of synergistic muscles (motor units)
PREMOTOR AREA: organization
Topographical organization similar to
primary motor cortex.
(works to coordinate movements in a more complex way than the primary motor cortex alone)
Premotor area:INTEGRATIVE PROCESSING SYSTEM :
Uses information from input (sensory, visual…) to determine output (motor) response
(plan and prepare appropriate motor responses)
Premotor area functions as:
an INTEGRATIVE PROCESSING SYSTEM to PLAN MOVEMENT
Premotor area: FUNCTION:
PLANNING MOVEMENT
Activation of the premotor area results in
more complex patterns of movement (e.g.
position the shoulders and arm so that the
hands are properly oriented to perform
specific tasks).
premotor area works in concert with:
other motor areas
(primary motor, basal ganglia, thalamus,
cerebellum …).
Supplemental motor area (SMA): specific _
topographical organization
Supplemental motor area (SMA): often elicits:
BILATERAL movements (e.g., grasping of both hands).
Often elicits bilateral movements (e.g., grasping of both hands).
Supplemental motor area (SMA)
Supplemental motor area (SMA): functions:
in concert with premotor area for control of POSTURE and
position (e.g., positional movements of the head and eyes).
control of posture and
position (e.g., positional movements of the head and eyes).
Supplemental motor area + other premotor areas
Motor cortex-Specialized Areas: Broca’s area: Dedicated to:
Motor speech production (i.e.
word formulation)
Broca’ s area: located in:
the dominant hemisphere (i.e. left
hemisphere for a right-handed person).
Broca’s area: Damage causes
Language production deficits
(inability to form words): Broca’s (or motor) aphasia.
Broca’s (or motor)
aphasia.
language production deficits
(inability to form words)
Motor cortex: 3 specialized areas:
(1) Broca’s area
(2) Hand skills area
(3) Eye movement and head rotation areas
Motor Cortex-Specialized Areas: Hand skills area are for performing:
Coordinated and Purposeful hand movements.
Motor cortex: hand skills: damage causes:
MOTOR APPRAXIA:
the inability to perform coordinated
hand movements
Motor apraxia:
The inability to perform coordinated
hand movements
Motor Cortex- Specialized Areas: eye movement and head rotation areas purpose (2):
(1) For coordinated voluntary head and eye movements towards specific objects.
(2) Modulate the vestibulo-ocular reflex.
Pyramidal/cortico-spinal pathway: upper motor neuron (1st order neuon) fibers originate mostly from:
The primary motor cortex (but also from premotor/SMA areas)
Pyramidal/Cortico-spinal pathway: MAJORITY of fibers UMN (75-90%):
DECUSSATE (cross to opposite side) in the MEDULLA (pyramids)
Pyramidal/Cortico-spinal pathway: MAJORITY of fibers (75-90%) UMN DECUSSATE in the:
MEDULLA
Pyramidal/Cortico-spinal pathway: MAJORITY of fibers (75-90%) UMN that decussate in medulla form:
the LATERAL CORTICOSPINAL TRACTS
Pyramidal/Cortico-spinal pathway: MAJORITY of fibers (75-90%) UMN that decussate in medulla synapse:
with the lower motor neuron at the LATERAL VENTRAL HORN of the spinal cord.
Pyramidal/Cortico-spinal pathway: MAJORITY of fibers (75-90%) UMN that decussate in medulla STIMULATE:
distal (limb) muscles (arms and legs)
Pyramidal/Cortico-Spinal pathway: minority of fibers (25-10%) UMN :
DO NOT DECUSSATE in the Medulla
Pyramidal/Cortico-Spinal pathway: minority of fibers (25-10%) UMN decussate in:
the spinal cord
Pyramidal/Cortico-Spinal pathway: minority of fibers (25-10%) UMN synapse with the lower motor neuron at the :
MEDIAL VENTRAL HORN of the spinal cord
Pyramidal/Cortico-Spinal pathway: minority of fibers (25-10%) UMN Stimulate:
Proximal (axial) muscles (trunk)
Pyramidal/Cortico-Spinal Pathway, Lower motor neuron (2nd order neuron), cell body located in:
VENTRAL HORN of the spinal cord
Pyramidal/Cortico-Spinal Pathway, Lower motor neuron (2nd order neuron) leaves the spinal cord through:
the VENTRAL ROOT
Pyramidal/Cortico-Spinal Pathway, Lower motor neuron (2nd order neuron) has what kind of distribution:
SEGMENTAL DISTRIBUTION
Pyramidal/Cortico-Spinal Pathway, Lower motor neuron (2nd order neuron), at the periphery:
motor nerves meet with sensory nerves to form mixed nerves
The cortico-bulbar pathway stimulate:
FACIAL MUSCLES
The cortico-bulbar motor pathway has __ order neurons:
2
The cortico-bulbar motor pathway 1st order neuron (upper motor neuron) originates from:
PRIMARY MOTOR CORTEX and PREMOTOR AREAS (cingulate gyrus)
Cortico bulbar motor pathway: first order neuron synapses __ with the __ at the __
BILATERALLY with the 2nd order neuron (LOWER MOTOR NEURON) at different levels of the brainstem
Cortico-Bulbar Pathway: 2nd order neuron (lower motor neuron) leaves the brainstem through:
many cranial nerves
Cortico-Bulbar Pathway: 2nd order neuron (lower motor neuron) leaves the brainstem through many cranial nerves (3)
(1) Trigeminal (V) nerve
(2) Facial (VII) nerve
(3) Hypoglassal (XII) nerve
Trigeminal = _ nerve
V nerve
Trigeminal (v) nerve stimulate:
Skeletal muscles of MASTICATION
Facial (VII) nerve stimulate:
skeletal muscles of FACIAL EXPRESSION
Facial = __ nerve
VII
Hypoglossal nerve (XII) nerve stimulate:
skeletal muscles of TONGUE
Hypoglossal nerve = __ nerve
XII
The activity of upper MNs in the cortex:
CONTROLS MOVEMENT, rather than individual muscles
contraction (i.e. coordination function)
The UMN (upper motor neurons) have an__ of the motor reflexes
INHIBITORY control on the MOTOR REFLEXES
Stimulation of the motor cortex (i.e. upper MNs) initiates:
the excitation of several muscles and simultaneous
suppression of others.
A particular movement (e.g. hand movement) can be
elicited by stimulation of
widely separated cortical sites.
Regions responsible for initiating different movement:
Overlap substantially
The force generated by contracting muscles (i.e.
magnitude) depends on:
The firing rate of upper MNs.
The firing rate of upper MNs dictates:
the force generated by contracting muscles
The direction of the force produced by muscles depends on:
The activity the upper MNs.
Extrapyramidal pathways =
Accessory (indirect pathways)
Extrapyramidal pathways: Signals are relayed through multiple accessory pathways involving (3):
basal ganglia, cerebellum, brainstem nuclei.
(Accessory (indirect) motor pathways refer to motor control pathways that do not directly synapse with lower motor neurons (LMNs) but instead influence movement indirectly through interneurons in the brainstem and spinal cord. )
Most of the extrapyramidal pathways
modulate movement through
the pyramidal pathway (UMN & LMN).
Extrapyramidal pathways =
Accessory (indirect pathways)
Extrapyramidal pathways (4) :
(1) BASAL GANGLIA PATHWAYS
(2) CEREBELLUM PATHWAYS
(3)VESTIBULOSPINAL TRACTS PATHWAY
(4) CORTICOVORUBROSPINAL PATHWAY
Extrapyramidal pathways: Basal ganglia pathways:
Complex motor actions
Extrapyramidal pathways: Cerebellum pathways:
Movement Coordination
Extrapyramidal pathways: Vestibulospinal tracts pathway:
Antigravity and equilibrium
Extrapyramidal pathways: Corticorubrospinal pathway:
fine motor control
The Cortico-Rubro-Spinal pathway serves as
an
alternative pathway to transmit cortical motor
signals to the spinal cord (Accessory route).
Cortico Rubro spinal pathway:
motor cortex -> red nucleus -> spinal cord
Stimulation of red nucleus causes
motor
movement in specific groups of muscles but not as
precise as primary motor cortex.
Input from primary motor cortex to the red nucleus
(midbrain):
Corticorubral tracts.
Cortico-rubro-spinal pathway:Primary motor cortex fibers synapse in:
the lower
portion of the red nucleus called the MAGNOCELLULAR PORTION.
Cortico-rubro-spinal tract: magnocellular portion fibers give rise to:
Rubrospinal tract
Rubrospinal tract:
(1) Decussates in lower Medulla
(2) Descends adjacent and anterior to the pyramidal tract
(3) Terminates mostly on interneurons but also on motor
neurons (LMNs).
Rubrospinal tract decussates in:
lower medulla
Rubrospinal tract descends:
adjacent and anterior to the pyramidal tract
Rubrospinal tract terminates :
Mostly on interneurons but also on motor neurons (LMNs)
Abnormality in the stretch reflexes response suggests that there may be
damage to
the lower motor neuron or upper motor neuron
Hyporeflexia
weak (or absent) reflex response:
Hyporeflexia: the problem is in the:
LOWER MOTOR NEURON
hyporoflexia: disruption of either:
afferent or efferent fibers (PNS) in the stretch reflex loop (e.g.,
cut in the fibers, neuropathies, nerve or root compression…).
Hyporeflexia: localisation of a spinal segment:
(1) Pastellar reflex corresponds to L4
(2) Biceps reflex corresponds to C5-C6
Hyperreflexia:
STRONG reflex response:
Hyperreflexia: the problem is in:
the upper motor neuron (the upper motor neuron has an INHIBITORY control on the stretch reflex)
The upper motor neuron has an ___ control on the stretch reflex.
inhibitory
Loss of central command on the spinal cord leads to:
An ENHANCED stretch reflex
The distribution of facial weakness provides:
Important
localizing clues indicating whether the underlying injury
involves the UPPER MOTOR NEURON (UMN) or the LOWER MOTOR NEURON (LMN)
Injury to the PRIMARY MOTOR CORTEX (LESION A) causes:
A weakness of THE CONTRALATERAL INFERIOR FACIAL MUSCLES
Injury to the PRIMARY MOTOR CORTEX (lesion A) causes a
weakness of THE CONTRALATERAL INFERIOR FACIAL MUSCLES (2) :
(1) Input to INFERIOR FACIAL MUSCLES from the UMN in
the PRIMARY MOTOR CORTEX is LOST.
(2) Input to superior facial muscles from the UNM
in the premotor areas (cingulate gyrus) remains
intact because this input projects bilaterally.
Injury to corticobulbar tract (lesion B) causes a weakness of:
the contralateral inferior facial muscles:
Injury to CORTICOBULBAR TRACT (LESION B) causes a
weakness of the CONTRALATERAL INFERIOR FACIAL MUSCLES:
(1) Input to INFERIOR FACIAL MUSCLES from the UMN in PRIMARY MOTOR CORTEX is LOST.
(2) Input to SUPERIOR FACIAL MUSCLES from the UNM in the
PREMOTOR AREAS (cingulate gyrus) remains INTACT because
this input projects BILATERALLY
Injury to the FACIAL MOTOR NUCLEUS or its NERVE (lesion C) causes:
a WEAKNESS of ALL MUSCLES OF FACIAL EXPRESSION on the SAME SIDE of the lesion (input to superior and inferior facial muscles from LMN is lost)
Injury to the facial motor nucleus or its nerve (lesion
C) causes a weakness of all muscles of facial
expression on the same side of the lesion:
input to superior and inferior facial muscles from LMN
is lost.
Aphasia is:
A disorder in the comprehension and/or expression of speech
Broca’s (motor) aphasia:
Loss of the ability to produce speech
Wernicke’s (non-motor) aphasia (fluent aphasia):
Not coherent speech
Broca’s aphasia: Characterized by:
the LOSS of the ability to
produce SPEECH (i.e. inability to form words)
Lesion in the Broca’s area:
a lesion in the posterior inferior
frontal gyrus (inferior part of the motor cortex).
For that is also called motor aphasia.
Lesion in Broca’s area, which is located in __, results in __, also known as __
Lesion in Broca’s area, which is located in the posterior inferior frontal gyrus (part of the inferior motor cortex), results in Broca’s aphasia, also known as motor aphasia
Broca’s aphasia: mostly caused by:
a stroke
A stroke affecting Broca’s area often extends to the motor cortex, leading to __
contralateral hemiplegia (paralysis on the opposite side of the body)
Broca’s aphasia: varies from:
The complete loss of the ability to
speak to struggle to speak (non-fluent speech).
Broca’s aphasia: possibility of:
recovery by speech therapy
Myasthenia gravis:
a NEUROMUSCULAR DISEASE that causes weakness in the
muscles (e.g. drooping of eyelids, difficulty
swallowing, shortness of breath)
Myasthenia gravis: pathology at:
the NEUROMUSCULAR JUNCTION
Myasthenia gravis: acetylcohline receptors on the muscle cell membrane are:
-BLOCKED (or DESTROYED) by
antibodies (autoimmune disease),
- REDUCED transmission (binding) of Ach in the muscle
- IMPAIRED MUSCLE CONTRACTION
Myasthenia gravis treatment:
CHOLINESTERASE INHIBITORS
Treatment of myasthenia gravis : cholinesterase inhibitors:
Inhibit acetylcholinesterase, preventing ACh breakdown.
Increases ACh levels in the synaptic cleft, improving nerve-muscle signaling.
Upper motor neuron lesion: site of the lesion:
Cortex
Brainstem
Spinal cord
Upper motor neuron lesions: muscle weakness:
Yes (plegia)
Upper motor neuron lesion: muscle tone:
increased (spasticity)
upper motor neuron lesion: muscle atrophy:
disuse atrophy
Upper motor neuron lesion:fasciculation (muscle twitching)
No fasciculations
Upper motor neuron lesion: Tendon / stretch reflex:
hyperreflexia (strong reflex)
Upper motor neuron lesions: Babinski sign (plantar reflex):
positive babinski sign
Lower motor neuron lesion: site of the lesion:
Anterior horn
Roots
Nerves
Neuromuscular junction
Lower motor neuron lesion: muscle weakness:
Yes (myopathy)
Lower motor neuron lesion: muscle tone:
Decreased (hypotonia)
Lower motor neuron lesion: muscle atrophy:
Denervation atrophy
Lower motor neuron lesion: fasciculation (muscle twitching):
Fasciculations
Lower motor neuron lesion: tendon / stretch reflex:
hyporeflexia (weak reflex)
lower motor neuron lesion: babinski sign (plantar reflex):
Negative babinski sign
