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Part 7
Control of Motor Function
Muscle controlled by nerve
 Motor unit: A single  nerve fiber + skeletal
muscle fibers
Motor functions of the spinal cord
Motor neurons at anterior horns of the cord gray
matter
 Types of motor neurons

motor neuron

A  motor nerve fiber large skeletal muscle
fibers


motor neuron


Final road of the cord reflex
A  motor nerve fiber intrafusal fibers
 motor neuron
Section of spinal cord -- Spinal shock

Definition

Spinal animal

Causes
The cord reflexes

Stretch reflex

Flexor reflex

Crossed extensor reflex
Muscle stretch reflex (myotatic reflex)

Definition
Whenever a muscle is stretched suddenly,
excitation of the spindles causes reflex
contraction of the large skeletal muscle fibers of
the same muscle and also of closely allied
synergistic muscles.
 Types of stretch reflex
1. Tendon reflex
(dynamic stretch
reflex)

Rapid tretch
instantaneous, strong
reflex contraction

Monosynaptic reflex
2. Muscle tonus (static
stretch reflex)

Slow stretch weaker
continuous contraction

Polysynaptic reflex
 Reflex
arc of stretch reflex
1. Sensory receptors
-- Muscle spindle
Intrafusal fibers: sensitive
to length change of muscle.
 Nuclear
bag muscle fiber
 Nuclear
chain muscle fiber
Nuclear bag fiber: mainly response to change of muscle length
Nuclear chain fiber: mainly response to length of muscle
Sensory receptors -Golgi tendon organ
 Sensitive to
change of
tension
 Providing
a negative
feedback that prevents
too much tension on the
muscle.
2. Afferent fibers of stretch reflex


Muscle spindle

Ia fiber (spiral endings)

II fiber (flower-spray ending)
Golgi tendon organ

Ib fiber
3. Neural center: motor neurons in anterior
horn
4. Efferent fibers: large  motor nerve fibers
5. The final effector: Extrafusal skeletal muscle
fibers
Flexor reflex
 Nociceptive reflex
 Withdrawal reflex
or pain reflex
Crossed
extensor
reflex
Brain stem control of motor function
 Struction
 Medulla,

and function
pons, and mesencephalon
Reticular system
 Facilitatory
and inhibitory area
 Regulation of muscle tonus
Decerebrate rigidity
 Sectioned
below the midlevel of the
mesencephalon
 Strain of antigravity muscles
 Neck,
trunk and extensors of the legs
Causes of decerebrate rigidity


-decerebrate rigidity
Blockage of the inhibitory input to the medullary reticular area from
the cerebral cortex and basal ganglia inhibitor system to - motor
neuron becomes low functional  increase muscle tonus
a-decerebrate rigidity
Increase a-motor neuron activity by vestibular nucleus de-inhibition
Cerebellum and its motor functions
How is it that the cerebellum is so important when
it has no direct ability to cause muscle contraction?
Anatomical functional areas of
Cerebellum

Anterior lobe

Posterior lobe

Flocculonodular lobe
Motor functions of cerebellum
1. Vestibulocerebellum
 Flocculonodular
 Controlling
lobes
equilibrium and
postural nystagmus
2. Spinocerebellum
 Vermis
of the posterior and anterior cerebellum
 Coordinating the
movements of the distal portion of
the limbs and modulating muscle tonus
Clinical abnormalities of Spinocerebellum

Ataxia

Intention tremor

Hypotonia
3. Corticocerebellum
 Large
lateral zones of the
cerebellar hemispheres
 To
plan, sequence and time
complex movements
Basal ganglia and their motor functions
Basal ganglia
 Caudate nucleus
 Putamen
 Globus
pallidus
 Substantia nigra
 Subthalamic nucleus
 Red
nucleus
Motor Function:
Responsible for the
smooth and proper
implementation of
voluntary movements
Damage to the basal ganglia
1. Parkinson’s disease
(Paralysis agitans )

Symptom

Rigidity

Static tremor

Akinesia and
bradykinesia
 Treatment
with L-Dopa
2. Huntington’s disease (Chorea)
 Symptom

Flicking movement

Distortional movements

Dementia
Cerebral cortex control
of motor function
Motor cortex
 Primary
motor cortex(4)
 Premotor
area(6)
 Supplementary
motor area
Characters of primary motor cortex
Transmission of signals from the
motor cortex to the muscles
1. Pyramidal system (Corticospinal tract)
 Pathway:
Motor cortex (pyramidal cells) internal capsule
forming the pyramids of the medulla cross to
the opposite side in the lower medulla spinal
cord (motor neurons)
 Function:
 Direct
pathway
 Concerned
more
discrete and detailed
movements
2. Extrapyramidal
system
 The
accessory pathway
that involve the basal
ganglia, cerebellum, and
nuclei of the brain stem
 Function
Regulation of cerebral cortex
on somatic movement
Flaccid paralysis
 Spastic paralysis: Babinski’s sign

General Questions

Terms
 Spinal shock
 Stretch
reflex
 Decerebrate rigidity

Describe the regulation of cerebral cortex on somatic
movement

What is the decerebrate rigidity? Please describe the
main mechanism.