6.control of muscle tone

8/3/2019 6.Control of Muscle Tone

1/30

Control of Muscle Tone

By Dr D Fisher


2/30


3/30

Cerebellar Awareness'

After MS stimulation (stretch) APs are conductedalong the afferent fiber (Ia)

It enters into the spinal cord and divides into

several collaterals. Some of these collaterals synapse on the cell

bodies of neurons which ascend to thecerebellum (anterior and posterior

spinocerebellar tracts). Thus, at all times the cerebellum is aware of the

state of stretch in muscles, in other words theTONE of muscles.


4/30

Cerebellar Awareness'


5/30

Coactivation of Gamma Efferents

Whenever a motor command descends from the

motor cortex and synapses on neural cell bodies

which innervate muscles, collaterals from these

descending fibers also synapse on thecorresponding cell bodies (gamma efferents)

which innervates the ends of the intrafusal

muscle fibers.

This is important so that as the extrafusal

muscle fibers contract and shorten, the intrafusal

also shorten and remain taunt.


6/30


This enables the MS to always respond to

stretch even immediately after contraction

of a muscle. In other words the coactivation of gamma

efferents avoids 'silent periods' which

would occur if the intrafusal muscle fibers

did not contract simultaneously with theextrafusal muscle fibers.


7/30



8/30

The Golgi Tendon Organ

The Golgi tendon organ is a receptor

found within the tendons of muscle.

It detects tension >100 grams in the

tendon.

It is innervated with a 1b afferent fiber.


9/30


10/30

The Golgi Tendon Organ


11/30


12/30

Summary

Golgi tendon organs detects tension in thetendon.

Afferent neurons conduct action potentialsto the spinal cord.

Afferent neurons synapse with inhibitory(inter) association neurons (secretesGABA) which in turn synapse with alphamotor neurons.

Inhibition of the alpha motor neuronscauses muscle relaxation, relieving thetension in the muscle.


13/30

Control ofSkeletal Muscle

The prefrontal area has association areas

for the motivation and foresight to plan

and initiate movements.

In the premotor area motor functions are

organized before they are initiated in the

Motor Cortex.

The motor cortex (primary motor cortex) is

found on the precentral gyrus.


14/30


15/30

Homunculus


16/30

Homunculus

Definition: It is the literal representation ofconnected parts of the human body on thesurface of the brain.

The surface of the postcentral gyrus providesthe literal somatosensory homunculus,

while the surface of the precentral gyrusprovides the literal motor homunculus.

Please note that the sensory homunculus isalmost a mirror image of the motor homunculus.


17/30

The Somatic MotorSystem

The Somatic motor system (SMS) can be

divided roughly into 3 components:

The Pyramidal System

Extrapyramidal System

Cerebellar System


18/30

The Pyramidal System

(direct system) Involved with fine, discrete and precise

voluntary control of movement.

The command arises from the precentralgyrus (where the somatic motor cortexresides).

Fibers from the cortex descend to the

spinal cord where they synapse on theanterior horn motor neurons (alpha andgamma).


19/30

Descending Spinal Pathways

Direct Control muscle tone

and conscious skilledmovements

Direct synapse of uppermotor neurons ofcerebral cortex withlower motor neurons inbrainstem or spinal cord

Tracts

Corticospinal

Lateral

Anterior corticobulbar


20/30

The Extrapyramidal System

(indirect system)

Its main function is to provide course

background voluntary movement.

Arises from various sites on the cerebralcortex.

Interconnected with the pyramidal system.

The EPS is directly connected to theBasal Ganglia


21/30

Descending Spinal Pathways

Indirect Synapse in some

intermediate nucleus

rather than directlywith lower motorneurons

EPS Tracts Rubrospinal

Vestibulospinal

Reticulospinal

Testospinal tract


22/30

The Cerebellar Component

Function: To enable smoothcoordinated movement

plays an important role in themaintenance of posture andequilibrium.

Sends fibers via the cerebellar-spinal

tract to modulate the activity of thealpha (lower motor neurons) as well asthe gamma motor neurons.


23/30

The Cerebellar Functions

The cerebellum receives information from a

wide array of senses:

Pressure and touch

Positional receptors: Spindle and Golgi tendonorgans

Eyes and ears

A copy of the command signal is sent from the

cerebral cortex to the cerebellum, where itacts as a comparator.


24/30

Cerebellar Comparator

Function


25/30


26/30

The Basal Ganglia

What is the Basal Ganglia?

Paired masses of gray matter in each cerebral

hemisphere

Largest Nuclei Corpus Striatum:

Caudate nucleus

Lentiform nucleus:

Putamen and globus pallidus

Claustrum and amygdaloid

Substantia nigra, subthalamic nucleus and red

nucleus.


27/30

Neural Connections of the Basal

Ganglia

The basal ganglia are interconnected by

many fibers.

They have fibers connected to the:

Cerebral cortex (ascending fibers)

Thalamus and Hypothalamus Descending fibers to Gamma motor fibers

(sp.Cord)


28/30

Clinical Manifestation

Abnormal body movements: Tremor (uncontrollable shaking)

Involuntary movements of the skeletal muscles

Paralysis Akinesis: (destruction of the caudate(most affected site in strokes) results in paralysis inthe opposite side of the body).

Globus pallidus: mostly concerned with muscle tonefor specific body movements.

Lesion in the subthalamic nucleus hemiballisms,jerky movements, spontaneous movements of thearms (affects the extremities legs and arms)


29/30


30/30

Other Clinical Manifestations

Parkinsonism:

Concentration of dopamine in certain of

the basal ganglia is reduced. Treatmentinvolves giving the patient L-dopa which

passes the B-B Barrier.

Alzheimers:

Related to the degeneration ofsubstantia

innominata (basal ganglia nuclei)

6.control of muscle tone

Documents