1. Neuromotor Basis for Motor Control
Chapter 4
Neuromotor Basis for Motor Control
Concept: The neuromotor system forms the foundation for the control of movement

2. Introduction The Neuromotor System
Components of the central nervous system (CNS) and peripheral nervous system (PNS) involved in the control of coordinated movement
Focus of current chapter is CNS structure and function
Chapter 6 will include PNS related structure and function for tactile, visual, and proprioceptive sensory systems

3. The Neuron General Structure [see Fig. 4.1] Neuron = Nerve cell
Cell body
Contains nucleus
Dendrites
Extensions from cell body – range from 1 to thousands per neuron
Receive information from other cells
Axon (also known as a “nerve fiber”)
Extension from cell body – one per neuron with branches (known as collaterals)
Sends information from neuron
Neuron = Nerve cell
Basic component of the nervous system
Range in size from 4 to 100 microns

4. Types and Functions of Neurons
Three Types of Neurons
1. Sensory Neurons [see Fig. 4.2]
Also known as “afferent” neurons
Send information to CNS from sensory receptors
Unipolar – 1 axon; no dendrites
Cell body and most of the axon located in PNS; only axon central process enters CNS

5. Types and Functions of Neurons, cont’d
2. Motor Neurons [see Fig. 4.2]
Also known as “efferent” neurons
Two types influence voluntary movement:
1. Alpha motor neurons
Predominantly in spinal cord – axons synapse on skeletal muscles
2. Gamma motor neurons
In intrafusal fibers of skeletal muscles

6. Types and Functions of Neurons, cont’d
3. Interneurons [see Fig. 4.2]
Specialized neurons that originate and terminate in the brain or spinal cord
Function as connections between:
Axons from the brain and synapse on motor neurons
Axons from sensory nerves and the spinal nerves ascending to the brain

7. Central Nervous System (CNS)
Two components: Brain and spinal cord
The Brain
4 structural components most directly involved in the control of voluntary movement:
1. Cerebrum
2. Diencephalon
3. Cerebellum
4. Brainstem

8. Brain Components: 1. Cerebrum
One of two components of forebrain
Two halves
Right cerebral hemisphere
Left cerebral hemisphere
Covered by cerebral cortex
Gray tissue; 2- to 5-mm thick
Undulating covering of
Ridges – each is called a gyrus
Grooves – each is called a sulcus
Cortex motor neurons
Pyramidal cells
Nonpyramidal cells
Connected by the corpus callosum

9. Cerebral Cortex Four lobes Sensory cortex Frontal Parietal Occipital
Temporal
Sensory cortex
Posterior to central sulcus
Receives neuron axons specific to type of sensory information
Named according to nearest skull bone

10. Cerebral Cortex, cont’d
Association areas [see Fig. 4.4]
Location
Adjacent to specific sensory areas of sensory cortex
Function
To “associate” information from the several different sensory cortex areas
Allow the interaction between perceptual and higher-order cognitive functions
e.g., selection of the correct response in a choice-RT situation
Possible locations for transition between perception and action

11. Cerebral Cortex, cont’d
Primary motor cortex
Location & Structure
Frontal lobe just anterior to central sulcus
Contains motor neurons that send axons to skeletal muscles
Function
Involved in control of:
Initiation and coordination of movements for fine motor skills
Postural coordination

12. Cerebral Cortex, cont’d
Premotor area
Location: Anterior to the primary motor cortex
Functions include
Organization of movements before they are initiated
Rhythmic coordination during movement
-- enables transitions between sequential movements of a serial motor skill (e.g. keyboard typing, piano playing)
Control of movement based on observation of another person’s performing a skill

13. Cerebral Cortex, cont’d
Supplementary motor area (SMA)
Location: Medial surface of frontal lobe adjacent to portions of the primary motor cortex
Functions include involvement in the control of
Sequential movements
Preparation and organization of movement

14. Cerebral Cortex, cont’d
Parietal lobe
Location
One of the 4 lobes of the cerebral cortex
Function
Involved in the integration of movement preparation and execution
Interacts with the premotor cortex, primary motor cortex, and SMA before and during movement

15. Subcortical Brain Area Important in Motor Control
Basal Ganglia
Buried within cerebral hemispheres
Consist of 4 large nuclei
Caudate nucleus
Putamen
Substantia nigra
Globus pallidus
Function involves control of
Movement initiation
Antagonist muscles
during movement
Force
- Receive info from cerebral cortex and brainstem
- Send info to brainstem

16. Basal Ganglia, cont’d Parkinson’s Disease
Common disease associated with basal ganglia dysfunction
Lack of dopamine production by substantia nigra
Motor control problems [BART]
Bradykinesia (slow movement)
Akinesia (reduced amount of movement)
Rigidity of muscles
Tremor

17. Brain Components: 2. Diencephalon
2nd component of forebrain
Contains two groups of nuclei
Thalamus
Functions:
A type of relay station - receives and integrates sensory info from spinal cord and brainstem; sends info to cerebral cortex
Important role in control of attention, mood, and perception of pain
Hypothalamus
Critical center for the control of the endocrine system and body homeostasis

18. Brain Components: 3. Cerebellum
Location: Behind cerebrum and attached to brainstem [See Fig. 4.3]
Structure includes
Cortex covering
Two hemispheres
White matter under the cortex contains
Red nucleus – Where cerebellum’s motor neural pathways connect to spinal cord
Oculomotor nucleus

19. Brain Components: 3. Cerebellum cont’d
Functions
Involved in control of smooth and accurate movements
Clumsy movement results from dysfunction
Involved in control of eye-hand coordination, movement timing, posture
Serves as a type of movement error detection and correction system
Receives copy of motor neural signals sent from motor cortex to muscles (efference copy)
Involved in learning motor skills

20. Brain Components: 4. Brainstem
Location
Beneath cerebrum; connected to spinal cord
3 components involved in motor control
Pons
Medulla
Reticular formation
Functions
Pons
Involved in control of various body functions (e.g. chewing) and balance
Medulla
Regulatory center for internal physiologic processes (e.g. breathing)
Reticular formation
Integrator of sensory and motor info
Inhibits / Activates neural signals to skeletal muscles

21. Spinal Cord A complex neural system vitally involved in motor control
Structure [See Fig. 4.5]
Gray matter – H-shaped central portion
Consists of cell bodies and axons of neurons
Two pairs of “horns”
Dorsal (posterior) horns – Cells transmit sensory info
Ventral (anterior) horns – Contains alpha motor neurons with axons terminating on skeletal muscle
Interneurons (Renshaw cells) – In ventral horn

22. Sensory Neural Pathways
Several neural tracts (called ascending tracts)
Pass through spinal cord and brainstem
Connect to sensory areas of cerebral cortex and cerebellum
2 tracts to sensory cortex especially important for motor control
Dorsal column
Anterolateral system
Tract to cerebellum important for motor control
Spinocerebellar tract – Primary pathway for proprioceptive info

23. Motor Neural Pathways Descending tracts
Travel from brain through spinal cord
Pyramidal tracts (corticospinal tracts)
60% from motor cortex
Most fibers cross to other side body (decussation) in medulla of brainstem
Involved in control of fine motor skill performance
Nonpyramidal tracts (brainstem pathways)
Fibers do not cross to other side of body
Involved in postural control and control of hand and finger flexion – extension

24. The Motor Unit
An alpha motor neuron and all the skeletal muscle fibers it innervates [See Figure 4.6]
When a motor neuron activates (fires) all its connected muscle fibers contract
The ultimate end of the motor neural information
~ 200,000 alpha motor neurons in spinal cord
Number of muscle fibers served by a motor unit depends on type of movement associated with the muscle
Fine movements
e.g. eye muscles = 1 fiber / motor unit
Gross movements
e.g. posture control = many fibers (up to ~ 700) / motor unit

25. Motor Unit Recruitment
Amount of force generated by muscle contraction depends on number of muscle fibers activated
To increase force, need more motor units
Process of increasing number of motor units involved = recruitment
Recruitment follows “size principle”
Size = motor neuron cell body diameter
Size principle = recruit smallest motor units first (i.e., weakest force produced) then systematically increase size recruited until achieve desired force

26. From Intent to Action: The Neural Control of Voluntary Movement
Think about the entire process of deciding to perform a skill and actually performing it
The neural activity involved in this process typically follows a hierarchical organization pattern
From higher to lower levels of the neuromuscular system
This process is described conceptually in Figure 4.7 and Table 4.1

27. Neural Control of Voluntary Movement
1. Higher centers
Function - Form complex plans according to intent, communicates with the middle level via command neurons.
Structures – areas involved with memory and emotions, SMA, associations cortex
2. Middle level -
Function – converts plans to a number of smaller motor programs which determine the pattern of neural activation required.
Structures – sensorimotor cortex, cerebellum, basal nuclei, brainstem nuclei
Lowest level
Function – specifies tension of particular muscles and angle of joints at specific times necessary to carry out programs from middle control level
Structures – brainstem or spinal cord

28. From Intent to Action: Brain Structures Associated with Movement
Research by Carson and Kelso (2004)
Demonstrated there is more involved in understanding how we control voluntary coordinated movement than knowing which brain structures involved in which type of movements
Cognitive intention is a critical component
Experiment
Participants performed finger-flexion movement to a metronome
On the beat (synchronize)
Between beats (syncopate)
Task involved exactly the same movement but two different cognitive intentions
fMRI results showed
Different brain regions active for the two movement intentions