The motor system
1 / 26

The Motor System - PowerPoint PPT Presentation

  • Uploaded on

The Motor System. Chapter 8. Overview. The motor system is divided into 4 components: Direct activation pathway Control circuits Indirect activation pathway Final common pathway. Direct activation pathway Largest, best-defined motor pathway

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
Download Presentation

PowerPoint Slideshow about ' The Motor System' - yvonne

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
The motor system

The Motor System

Chapter 8


  • The motor system is divided into 4 components:

    • Direct activation pathway

    • Control circuits

    • Indirect activation pathway

    • Final common pathway

  • Direct activation pathway

    • Largest, best-defined motor pathway

    • It is a “single neuron” pathway, extending from the cerebral cortex to the spinal cord (corticospinal tract)

    • Major function: to effect voluntary activity, particularly skilled movements under conscious control

  • Direct activation pathway

    • Origins:

      • Primary motor cortex

      • Premotor cortex

      • Supplementary motor cortex

    • Major neurotransmitters: glutamate (excitatory) and GABA (inhibitory)

    • Damage results in weakness, with loss of voluntary movements especially fine, skilled movements, but preservation of other forms of movements including segments reflexes

  • Control Circuits

    • 2 parallel pathways, the cerebellar and basal ganglia, control and modify motor activity

    • They both receive input from several motor and sensory cortical areas and project back to the cerebral cortex via the thalamus. They integrate and modulate motor activity primarily through the cerebral cortex and direct activation pathways.

  • Control Circuits

    • They also send information to the brainstem and the indirect activation pathways.

    • Basal ganglia

      • Concerned with learned, automatic behavior and with preparing and maintaining the background support, or posture, needed for voluntary motor activity. (Neurotransmitters: dopamine and GABA)

    • Cerebellum

      • Accomplishes the coordination and correction of movement errors of muscles during active movements. (Neurotransmitters: glutamate and GABA)

  • Indirect activation pathways

    • The older, more diffuse motor pathways, sometimes called extrapyramidal pathways

    • These pathways mediate the enormous number of automatic activities involved in normal motor function. For example, the maintenance of erect posture when sitting or standing requires the coordinated contraction of many muscles.

  • Indirect activation pathways

    • This coordination is under subconscious control and is mediated by the indirect activation pathways which are:

      • Reticulospinal

      • Vestibulospinal

      • Rubrospinal

    • Diseases affecting these pathways are manifested with abnormal muscle tone and reflexes.

  • Final common pathway

    • The somatic (skeletal) muscles that perform the voluntary movements are all under direct control of lower motor neurons and contract only in response to activation by these neurons.

    • These neurons are located in the ventral horn of the spinal cord and brainstem.

    • A lower motor neuron and the muscle fibers under its control constitute a motor unit.

    • The final common pathway consists of many motor units through which all activities in the motor system must act.

    • Neurotransmitter: acetylcholine

Motor homonculus
Motor homonculus

Internal capsule
Internal capsule

Corticobulbar fibers occupy a more anterior location in the posterior limb than the corticospinal

Clinical correlations
Clinical Correlations

Knowledge of the clinical manifestations of the diseases affecting the direct activation pathway comes from experimental studies and from observation of clinical disorders.

Disturbances of the corticospinal system may be irritative (positive) or paralytic (negative).

Clinical Correlations: irritative vs. paralytic

Irritative (seizures)

Jacksonian seizures – focal motor seizures starting from the distal upper extremity spreading proximally


Weakness – fine movements, skilled movements (distal muscles); no atrophy; presence of Babinski sign and primitive reflexes (upper motor neuron manifestations)

Control circuits
Control Circuits


learned, automatic behavior

preparing and maintaining the background support or posture needed for voluntary motor activity

Anatomy and Physiology

caudate nucleus, lentiform nucleus (putamen, globus pallidus), substantia nigra, subthalamic nucleus

striatum=caudate nucleus + putamen

striatum neurotransmitters: acetylcholine, dopamine (produced in the substantia nigra and transported to striatum via the nigrostriatal pathway)

Control circuits basal ganglia
Control Circuits: Basal Ganglia

Clinical Correlations:

excess discharge  slowing (hypokinesia)

lack of discharge  hyperactivity (involuntary movements)

Involuntary movements






Control circuits basal ganglia1
Control Circuits: Basal Ganglia

Clinical Correlation:


hypokinetic – quiet, weak, monotonous voice, poor articulation, short rushes of words, breathy quality

hyperkinetic – bursts of loudness, elevation of pitch, voice stoppages, distortion of vowels, disintegration of articulation

Control circuits1
Control Circuits


coordination and correction of movement errors of muscles during active movements

neurotransmitters: glutamate, GABA

Control circuits cerebellum
Control Circuits: Cerebellum

Functional subdivisions


Flocculonodular lobe connected with the vestibular nuclei through the inferior cerebellar peduncle

Controls and coordinates axial musculature and movements of the head and eyes

Control circuits cerebellum1
Control Circuits: Cerebellum

Functional subdivisions


Made up of vermis and paravermis

Its primary input is from dorsal spinocerebellar tract (via the inferior cerebellar peduncle) and the ventral spinocerebellar tract (via the superior cerebellar peduncle) which provide information about motor performance and motor neuron excitability, respectively.

Control circuits cerebellum2
Control Circuits: Cerebellum

Functional subdivisions


Made up of the lateral portions of the cerebellar hemispheres and receives inputs from pontine nuclei via the middle cerebellar peduncle

The output is from the dentate nucleus through the superior cerebellar peduncle

This subdivision is important in initiation of movement and in coordination of muscles (specifying direction, pattern, and intensity of movement)

Cerebellum clinical correlations
Cerebellum: Clinical Correlations

  • Flocculonodular Syndrome

    • Occurs with midline tumors in children

    • Produces truncal ataxia, with unsteadiness and falling and disturbances with gait and standing; with nystagmus

Cerebellum clinical correlations1
Cerebellum: Clinical Correlations

  • Anterior Lobe Syndrome

    • Commonly due to degenerative diseases of the adults

    • Produces severe gait ataxia (broad-based) without ataxia of the upper limbs, and mild ataxia of the legs

  • Cerebellar Hemisphere Disease

    • Produces limb ataxia with hypotonia, intention tremors, dyssynegria and dysmetria ipsilateral to the lesion

Cerebellum clinical correlations2
Cerebellum: Clinical Correlations

  • Disorders of speech also occur in cerebellar disease, particularly when it involves the vermis.

  • These disorders are manifested as irregularities of pitch, loudness, and rhythm and are known as ataxic dysarthria.

  • Many cerebellar diseases can be reversed if they are identified early and treated appropriately.

    • Cerebellar degeneration produced by vitamin E deficiency

    • Small cell lung carcinoma and ovarian cancers produce antibodies to Purkinje cells than cause cerebellar degeneration.

Final common pathway
Final Common Pathway

Motor unit – a lower motor neuron (ventral horn cell/CN nucleus) + muscle fibers under its control

alpha motor neuron

axon (nerve)


muscle fibers

Final common pathway – many motor units through which all activities in the motor system must act