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Chapter 32
Control of Motor Function
by Nervous System
Contents

Motor Unit and Final Common Pathway
 Spinal Reflexes
 Function of Brain Stem
 Function of the Basal Ganglion
 Function of Cerebellum
 Function of the Cortex
organization of motor subsystems
Section 1. Motor Unit and
Final Common Pathway
•Every striated
muscle has
encapsulated
muscle fibers
scattered
throughout the
muscle called
muscle spindles.
•Extrafusal and
intrafusal fibers
The extrafusal muscle
fibers are innervated
by Alpha motor
neuron
The intrafusal muscle
fibers are innervated
by Gamma motor
neurons
Motor units
A single motor neuron (a motor) and all
(extrafusal) muscle fibers it innervates
 The physiological functional unit in muscle
(not the cell)

 All cells in motor unit contract synchronously
Motor units and innervation ratio
Innervation ratio
Fibers per motor
neuron
Extraocular muscle 3:1
Gastrocnemius 2000:1
Purves Fig. 16.4
•The muscle cells of
a motor unit are not
grouped, but are
interspersed among
cells from other
motor units
•The coordinated
movement needs
the activation of
several motors
Overview - organization of
motor systems
Motor Cortex
Brain Stem
Spinal Cord
a-motor
neuron
Final common
pathway
Skeletal muscle
Final common path - a-motor neuron
(-)
(+)
muscle
fibers
Transmitter?
Schwann
cells
motor nerve
fiber
(-)
(+)
axon
hillock
Receptors?
acetylcholine
esterase
NM junction
Final Common Pathway,

a motor pathway consisting of the
motor neurons by which nerve
impulses from many central sources
pass to a muscle in the periphery.
Section 2. Spinal Reflexes

Somatic reflexes mediated by the spinal cord
– May occur without the involvement of higher brain
centers
– Was facilitated or inhibited by brain

For example
– Stretch reflex
– Deep tendon reflex
– Crossed extensor reflex
– Superficial reflex
Part 1 Stretch Reflex
1 Anatomy of Muscle Spindle

3-10 intrafusal muscle fibers
 detect change in the length
of the muscle
-- stretch receptors that report
the stretching of the muscle to
the spine.

The central region and
peripheral region of the
intrafusal fibers
Anatomy of Muscle Spindle

Intrafusal fibers are wrapped by two types of
afferent endings
– Primary sensory endings


Type Ia fibers
Innervate the center of the spindle
– Secondary sensory endings


Type II fibers
Associated with the ends of the nuclear chain fiber
Components of muscle spindle
Afferent
axons
Ia
II
Nuclear Bag
Fiber
} Primary
ending
Secondary
}
ending
Nuclear Chain
Fiber
Anatomy of Muscle Spindle

Primary sensory endings
– Type Ia fibers

Stimulated by both the rate and amount of stretch (dynamic
response)
Anatomy of Muscle Spindle

Secondary sensory endings
– Type II fibers

stimulated only by degree of stretch (static response)
Anatomy of Muscle Spindle

The contractile region of the intrafusal muscle
fibers are limited to their ends
– only these areas contain actin and myosin filaments
– are innervated by gamma () efferent fibers
2. Muscle
stretch reflex
Muscle stretch reflex
Definition: Whenever a muscle is stretched, excitation of the
spindles causes reflexive contraction of the same muscle
from which the signal originated and also of closely allied
synergistic muscle.
The basic circuit: Spindle
Ia or II nerve fiber dorsal
root of the spinal cord synapses with anterior motor
neurons a -motor N. F. the same M. from whence the M.
spindle fiber originated.
Circuit of the Strength Reflex
The Stretch Reflex

Exciting a muscle spindle
occurs in two ways
– Applying a force that
lengthens the entire
muscle
– Activating the  motor
neurons that stimulate
the distal ends of the
intrafusal fibers to
contact,

thus stretching the midportion of the spindle
(internal stretch)
The Stretch Reflex

Whatever the
stimulus, when the
spindles are
activated
 their associated
sensory neurons
transmit impulses
at a higher
frequency to the
spinal cord
The Stretch Reflex

The reflexive muscle contraction resists further stretching of
the muscle
The Stretch Reflex

Branches of the afferent fibers also synapse with interneurons that inhibit motor neurons controlling the
antagonistic muscles
•Inhibition of the antagonistic muscles is called
reciprocal inhibition
•causes the antagonists to relax
The types of the Stretch Flex
1) Tendon reflex (dynamic
stretch reflex)
 Caused by rapid stretch of the
muscle, as knee-jerk reflex
 Transmitted from the IA sensory
ending of the M. S.
 Causes an instantaneous, strong
reflexive contraction of the same
muscle;
 Opposing sudden changes in
length of the M
A monosynaptic pathway
 being over within 0.7 ms
The types of the Stretch Flex
2) Muscle tonus (static stretch reflex):
 Caused by a weaker and continues stretch of the muscle,
 Transmitted from the IA and II sensory ending of the M. S.
 Multiple synaptic pathway, continues for a prolonged period.
 Non-synchronized contraction,
 M. C. for at least many seconds or minutes, maintaining the
posture of the body.
The Stretch Reflex

most important in large extensor muscles
which sustain upright posture
 Contractions of the postural muscles of the
spine are almost continuously regulated by
stretch reflexes (Muscle tonus )
3 Gamma impact on afferent
response
Muscle spindle: motor
innervation

Gamma
motoneurons:
– Innervate the
poles of the
fibers.
-LOOP
Descending influence (UMN)
Muscle spindle
1a

Activation of the -loop
results in increased
muscle tone
a
MUSCLE
Functional significance of gamma
impact on spindle activity

The tension of intrafusal fibers is maintained during
active contraction by gamma activity.
 The system is informed about very small changes in
muscle length.
Part 2. The Deep Tendon Reflex
Structure and Innervation of
Golgi Organ





Located in the muscle
tendon junction.
Connective tissue
encapsulating collagen
fibers and nerve
endings.
Attached to 10-20
muscle fibers and
several MUs.
Ib afferent fiber.
sensitive to tension
Golgi tendon organ: response
properties

Less frequent than muscle spindle
 Sensitive to the change of tension caused by the
passive stretch or active contraction
The Deep Tendon Reflex

When muscle
tension increases
moderately during
muscle contraction
or passive
stretching,
 GTO receptors are
activated and
afferent impulses are
transmitted to the
spinal cord
The Deep Tendon Reflex

motor neurons in
the spinal cord
supplying the
contracting muscle
are inhibited
 antagonistic muscle
are activated
The Deep Tendon Reflex

cause muscle relaxation and
lengthening in response to
the muscle’s contraction
– opposite of those elicited
by stretch reflexes

help ensure smooth onset
and termination of muscle
contraction

important in activities
involving rapid switching
between flexion and
extension such as in running
Compare spindle and golgi
Compare spindle and golgi
Part 3. The Crossed
Extensor Reflex



The reflex occur when you
step on a sharp object
There is a rapid lifting of
the affected foot (ipsilateral
withdrawal reflex )
the contralateral response
activates the extensor
muscles of the opposite leg
(contralateral extensor
reflex)
– support the weight shifted
to it
Part 4. Superficial Reflexes

elicited by gentle cutaneous stimulation
 dependent upon functional upper motor
pathways
– Babinski reflex
Babinski reflex - an UMN sign
 Adult
response - plantar flexion of the big toe and adduction
of the smaller toes
 Pathological (Infant) response - dorsoflexion (extension) of
the big toe and fanning of the other toes
 Indicative of upper motor neuron damage
Part 5. Spinal cord transection and spinal shock
Concept: When the spinal cord is suddenly
transected in the upper neck, essentially all
cord functions, including the cord reflexes,
immediately become depressed to the point of
total silence.
(spinal animal)
During spinal shock:
complete loss of all reflexes
no muscle tone, paralysis
complete anesthesia,
no peristalsis, bladder and rectal reflexes absent
(no defecation and micturition )
no sweating
arterial blood Pressure decrease（40 mmHg）
the reason: The normal activity of the spinal
cord neurons depends on continual tonic
excitation from higher centers
(the reticulospinal-, vestibulospinalcorticospinal tracts).
The recovery of spinal neurons excitability.
Section 3. Role of the brain stem
Support of the Body Against
Gravity – Roles of the Reticular and
Vestibular nuclei
Facilitated and inhibitory area
Areas in the cat brain where stimulation produces facilitation (+) or
inhibition (-) of stretch reflexes. 1. motor cortex; 2. Basal ganglia; 3.
Cerebellum; 4. Reticular inhibitory area; 5. Reticular facilitated area; 6.
Vestibular nuclei.
1. Facilitated area—roles of the reticular and vestibular
nuclei.：
(1) The pontine reticular nuclei
 Located slightly posteriorly and laterally in the pons and extending
to the mesencephalon
 Transmit excitatory signals downward into the cord (the pontine
reticulospinal tract)
1. motor cortex;
2. Basal ganglia;
3. Cerebellum;
4. Reticular
inhibitory area;
5. Reticular
facilitated area;
6. Vestibular nuclei.
(2) The vestibular nuclei
 selectively control the excitatory signals to the different
antigravity muscle to maintain equilibrium in response to
signals from the vestibular apparatus.
1. motor cortex;
2. Basal ganglia;
3. Cerebellum;
4. Reticular
inhibitory area;
5. Reticular
facilitated area;
6. Vestibular
nuclei.
MOTOR TRACTS & LOWER MOTOR NEURON
MOTOR CORTEX
MIDBRAIN &
RED NUCLEUS
(Rubrospinal Tract)
UPPER MOTOR NEURON
(Corticospinal Tracts)
VESTIBULAR NUCLEI
(Vestibulospinal Tract)
PONS & MEDULLA
RETICULAR FORMATION
(Reticulospinal Tracts)
LOWER (ALPHA) MOTOR NEURON
THE FINAL COMMON PATHWAY
SKELETAL
MUSCLE
Properties of the Facilitated Area
 Terminate on the motor neurons that exciting antigravity muscle of the
body (the muscle of vertebral column and the extensor muscle of the
limbs).
 Have a high degree of natural (spontaneous) excitability.
 Receive especially strong excitatory signals from vestibular nuclei and
the deep nuclei of the cerebellum.
 Cause powerful excitation of the antigravity muscle throughout the
body (facilitate a standing position), supporting the body against gravity.
1. motor cortex; 2. Basal
ganglia; 3. Cerebellum; 4.
Reticular inhibitory area;
5. Reticular facilitated
area; 6. Vestibular nuclei.
2. Inhibitory area –medullary reticular system
(1) Extend the entire extent to the medulla, lying ventrally and
medially near the middle.
(2) Transmit inhibitory signals to the same antigravity anterior
motor neurons (medullary reticulospinal tract).
1. motor cortex
2. Basal ganglia
3. Cerebellum
4. Reticular
inhibitory area
5. Reticular
facilitated area
6. Vestibular
nuclei.
MOTOR TRACTS & LOWER MOTOR NEURON
MOTOR CORTEX
MIDBRAIN &
RED NUCLEUS
(Rubrospinal Tract)
UPPER MOTOR NEURON
(Corticospinal Tracts)
VESTIBULAR NUCLEI
(Vestibulospinal Tract)
PONS & MEDULLA
RETICULAR FORMATION
(Reticulospinal Tracts)
LOWER (ALPHA) MOTOR NEURON
THE FINAL COMMON PATHWAY
SKELETAL
MUSCLE
(3) Receive collaterals from the corticospinal tract, the rubrospinal
tracts, and other motor pathways.
These collaterals activate the medullary reticular inhibitory system
to balance the excitatory signals from the pontine reticular system.
1. motor cortex
2. Basal ganglia
3. Cerebellum
4. Reticular
inhibitory area
5. Reticular
facilitated area
6. Vestibular
nuclei.
Areas in the cat brain where stimulation produces facilitation
(+) or inhibition (-) of stretch reflexes. 1. motor cortex; 2.
Basal ganglia; 3. Cerebellum; 4. Reticular inhibitory area; 5.
Reticular facilitated area; 6. Vestibular nuclei.
Decerebrate Rigidity
• Decerebrate Rigidity: transection of the brainstem at
midbrain level (above vestibular nuclei and below red
nucleus)
• Symptoms include:
– extensor rigidity or posturing in both upper and lower
limbs
•Results from:
–loss of input from inhibitory medullary reticular formation
(activity of this center is dependent on input from higher
centers).
–active facilitation from pontine reticular formation
(intrinsically active, and receives afferent input from spinal
cord).
•The extensor rigidity is -loop dependent
–section the dorsal roots interrupts the -loop, and the
rigidity is relieved. This is -rigidity.
THE -LOOP?
Descending influence (UMN)
Muscle spindle
1a

Activation of the -loop
results in increased
muscle tone
a
MUSCLE
Section 4. The Cerebellum and its Motor
Functions
Cerebellar Input/Output Circuit
Function of the cerebellum

Based on cerebral intent and external
conditions
– tracks and modifies millisecond-to-millisecond
muscle contractions
– produce smooth, reproducible movements
Without normal cerebellar function,
movements appear jerky and uncontrolled
Functional Divisions-cerebellum
• Vestibulocerebellum (flocculonodular lobe)
The vestibulocerebellum
input-vestibular nuclei
output-vestibular nuclei
Function 1: Control of the equilibrium and
postural movements.
controlling the balance between agonist and
antagonist M. contractions of the spine, hips,
and shoulders during rapid changes in body
positions.
Function 1: Control of the equilibrium and
postural movements. （Cont.）
During running
 Receive the signals from the periphery how rapidly
and in which directions the body parts are moving
Calculate the rates and direction where the different
parts of body will be during the next few ms.
anticipatory correction (feed-forward control)
the key to the brain’s progression to the next
sequential movement.
Function 2 regulate the eye
movement
– Through vestibulo-ocular reflex
 keep the eyes still in space when the head moves
– Damage of the flocculonofular lobe result in
positional nystagmus (位置性眼震颤）
The VOR: Definition

A eye movement reflex
 Stimulated by head movements
 Moves the eyes opposite of the head
 Helps keep the retinal image stabilized
The VOR contributes to clear vision during head movements
Cerebellar Nystagmus

Horizontal oscillating eye movement
•Spinocerebellum (vermis & intermediate)
•Spinocerebellum (vermis
& intermediate)
–input–somatic sensory information via
spinocerebellar tracts
–Branch from corticospinal
tract
–Output
–Thamalus – motor cortex
–-fastigial (顶） and interposed（中间
核） nuclei → vestibular nuclei,
reticular formation and red nucleus →
vestibulospinal tract, reticulospinal tract
and rubrospinal tract → motor neurons
of anterior horn
Function of spinocerebellum

Provide the circuitry for coordinating the movements
of the distal portions of the limbs, especially the
hands and fingers
– Compared the “intentions ” from the motor cortex and red
nucleus, with the “performance” from the peripheral parts
of the limbs
– Send corrective output signals to the motor neurons
– Provides smooth, coordinate movements
– Feedback control
•Cerebrocerebellum (lateral zone)
input- from the cerebral cortex via a relay in pontine nuclei
output- to dentate nucleus → dorsal thalamus and red nucleus→
primary motor cortex → corticospinal tract → motor neurons of anterior
horn
Cerebrocerebellum (functions)

Planning and programming of sequential
movements
– Panning (计划形成）: begins in the sensory
and promotor area of the cortex and transmitted
to the cerebrocerebellum
– Programming （运动程序编制）: what will
be happening during the next sequential
movement a fraction of the second later….
•Vestibulocerebellum (flocculonodular lobe)
Balance and body equilibrium
•Spinocerebellum (vermis & intermediate)
Rectify voluntary movement
•Cerebrocerebellum (lateral zone)
Plan voluntary movement
Clinical Abnormalities of the
Cerebellum
Dysmetria （辨距障碍） and Ataxia (共济失调）
 Past pointing: （过指）
 Failure of progression

– Dysdiadochokinesia (轮替运动障碍）
– Dysarthria （构音障碍）

Intention tremor
Dysmetria （辨距障碍） and Ataxia
(共济失调）
Past Pointing
Dysdiadochokinesia (轮替运动障碍）
Intention Tremor

Present during
reaching movement
 Not at rest
Section 5 The motor functions of
basal ganglia
Components of Basal Ganglia
Caudate
Putamen
GPe
GPi
1. Corpus Striatum(纹状体）
Caudate Nucleus （尾状核） Putamen (壳核）
Globus Pallidus (苍白球，GP)
Components of Basal Ganglia
2. Substantia Nigra （SN）
Pars Compacta (SNc)
Pars Reticulata (SNr)
STN
3. Subthalamic Nucleus (STN)
SN (r & c)
Basal Ganglia
Connections
•Circuit of connections
–cortex to basal ganglia to
thalamus to cortex
–Helps to program
automatic movement
sequences (walking and arm
swinging or laughing at a
joke)
•Output from basal ganglia
to reticular formation
–reduces muscle tone
–damage produces
rigidity of Parkinson’s
disease
cortex to basal ganglia to thalamus to cortex
somatosensory
cortices
motor cortices
excitation
D1
Putamen
inhibition
D1 & D2
GPe
Dopamine
receptors
D2
GPi
Thalamus
STN
GPe/i: Globus pallidus
internal/external
STN: Subthalamus
Nucleus
SNc: Pars Compacta
SNc
(part of substantia Nigra)
• Direct Pathway:
– Disinhibition of the thalamus facilitates cortically mediated
behaviors
somatosensory
cortices
motor cortices
excitation
inhibition
D1
Putamen
D1 & D2
Dopamine
receptors
GPe
D2
GPi
Thalamus
GPe/i: Globus pallidus
internal/external
STN: Subthalamus Nucleus
STN
SNc: Pars Compacta (part
of substantia nigra))
SNc
•Indirect pathway:
–Inhibition of the thalamus inhibits cortically mediated behaviors
somatosensory
cortices
motor cortices
excitation
D1
Putamen
inhibition
D1 & D2
GPe
Dopamine
receptors
D2
GPi
Thalamus
STN
SNc
GPe/i: Globus pallidus
internal/external
STN: Subthalamus Nucleus
SNc: Pars Compacta (part
of substantia nigra)
Medical Remarks
• Hypokinetic disorders result from overactivity in the indirect pathway.
example: Decreased level of dopamine supply in nigrostriatal
pathway results in akinesia, bradykinesia, and rigidity in Parkinson’s
disease (PD).
somatosensory
cortices
motor cortices
excitation
inhibition
Putamen
D1
D1 & D2
Dopamine
receptors
GPe
D2
GPi
GPe/i: Globus pallidus
internal/external
Thalamus
STN
SNc
STN: Subthalamus
Nucleus
SNc: Pars Compacta
(part of substantia
nigra)
Parkinson’s
Disease
PD
Disease of mesostriatal
dopaminergic system
Muhammad Ali in Alanta Olympic
normal
Parkinson’s Disease
Substantia Nigra,
Pars Compacta (SNc)
DOPAminergic Neuron
Clinical Feature (1)
Slowness of Movement
- Difficulty in Initiation and Cessation
of Movement
Parkinson’s Disease
Clinical Feature (2)
Resting Tremor
Parkinsonian Posture
Rigidity-Cogwheel Rigidity
•Hyperkinetic disorders result from underactivity in the indirect pathway.
example: Lesions of STN result in Ballism. Damage to the pathway
from Putamen to GPe results in Chorea, both of them are involuntary
limb movements.
somatosensory
cortices
motor cortices
excitation
D1
Putamen
inhibition
D1 & D2
GPe
Dopamine
receptors
D2
GPi
Thalamus
STN
GPe/i: Globus pallidus
internal/external
STN: Subthalamus
Nucleus
SNc: Pars Compacta
SNc
(part of substantia nigra)
SYDENHAM’S CHOREA （风湿性舞蹈病）
Clinical Feature
- Fine, disorganized , and
random movements of
extremities, face and
tongue
- Accompanied by
Muscular Hypotonia
- Typical exaggeration of
associated movements
during voluntary activity
- Usually recovers
spontaneously
in 1 to 4 months
Principal Pathologic Lesion: Corpus Striatum
HUNTINGTON’S CHOREA
亨廷顿舞蹈症
Clinical Feature
- Predominantly autosomal dominantly
inherited chronic fatal disease
(Gene: chromosome 4)
- Insidious onset: Usually 40-50
- Choreic movements in onset
- Frequently associated with
emotional disturbances
- Ultimately, grotesque gait and sever
dysarthria, progressive dementia
ensues.
Principal Pathologic Lesion:
Corpus Striatum (esp. caudate nucleus)
and Cerebral Cortex
HEMIBALLISM （半侧投掷症）
Clinical Feature
Lesion: Subthalamic
- Usually results from CVA
(Cerebrovascular Accident)
involving subthalamic nucleus
- sudden onset
- Violent, writhing, involuntary
movements of wide excursion
confined to one half of the body
- The movements are continuous
and often exhausting but cease
during sleep
- Sometimes fatal due to exhaustion
- Could be controlled by
phenothiazines and stereotaxic
Nucleus surgery
Section VI Control of muscle
function by the motor cortex
•Two principal
components
–Primary Motor
Cortex
–Premotor Areas
The primary motor cortex
The topographical representations of the different
muscle areas of the body in the primary motor cortex
Characteristics of the PMC:
1, It has predominant influence on
the opposite side of the body (except
some portions of the face)
2. It is organized in a homunculus pattern with inversed order
3. The degree of representation is proportional to the
discreteness (number of motor unit) of movement required of
the respective part of the body. (Face and fingers have large
representative)
4. Stimulation of a certain part of PMC can cause very specific
muscle contractions but not coordinate movement.
•Projects directly
–to the spinal cord to regulate movement
–Via the Corticospinal Tract
–The pyramidal system
•Projects indirectly
–Via the Brain stem to regulate movement
–extrapyramidal system
Descending Spinal Pathways
pyramidal system

Direct
 Control muscle tone
and conscious skilled
movements
 Direct synapse of
upper motor neurons
of cerebral cortex with
lower motor neurons
in brainstem or spinal
cord
Descending Spinal Pathways
extrapyramidal system




Indirect
coordination of head &
eye movements
coordinated function of
trunk & extremity
musculature to
maintaining posture and
balance
Synapse in some
intermediate nucleus
rather than directly with
lower motor neurons
• Premotor area composed of supplementary motor
area and lateral Premotor area
Premotor Areas
•Receive information from parietal （顶） and
prefrontal （前） areas
•Project to primary motor cortex and spinal cord
•For planning and coordination of complex planned
movements