Neural Basis of Motor Control

Chapter 4

Neurological Perspective

“A basic understanding of the physiology underlying the control of voluntary movement establishes a more comprehensive appreciation and awareness of capabilities and limitations of the people with whom a practitioner works.” (Magill, pg 65)

Nervous System

Nerves (Neurons) inside or outside the: – Central Nervous System (Nerves inside)

•  Brain and •  Spinal cord

– Peripheral Nervous System (Nerves outside CNS) •  Efferent nerves (motor) •  Afferent nerves (sensory)

Neural Activity

The focus of this chapter will be how the nervous system controls voluntary, coordinated movement.

Concept 1: The Neuron

•  Neuron are similar to other cells

It has a cell membrane, a nucleus that contains genes, contains cytoplasm, mitochrondria, and organelles. It carries out basic cellar processes such as protein synthesis and energy production

Neuron: Basic Unit of CNS

•  Neuron is a nerve

Axon takes information away from the cell body (soma) - the neuron has only one

Dendrites bring information to the cell body (soma) -neuron may have none

to as many as 1000 dendrites

Summary of Differences

Axons •  Take information away

from the soma •  Generally only 1 axon per

cell •  No ribosomes •  Can have myelin •  Branches further from the

soma

Dendrites •  Bring information to the

soma •  Rough surfaces (dendritic

spines) •  Many dendrites per cell •  Has ribosomes •  No myelin insulation •  Branches are near the

soma

Concept 2: Types of Neurons

Neurons are classified by direction that they send information:

1.  Sensory (afferent) neurons sends information from sensory receptors (e.g. skin, eyes, ears)

2.  Motor (efferent) neurons sends information AWAY from the CNS to muscles or organs.

3.  Inter-neurons: send information between sensory and motor neuron; most are located in CNS.

Sensory Neurons

•  They are unipolar, that is, they have no dentrites and only one axon.

•  Most sensory neuron are in the peripheral nervous system

Motor Neuron

•  Two types

– Alpha motor neurons (predominately in spinal cord and referred to as the motor horn cells). Has many dendrites and long branch axons that connects directly to skeletal muscle fibers.

– Gamma motor neurons supplies a portion of skeletal muscle called intrafusal fibers.

Interneurons

•  Originate and terminate in the brain or spinal cord

•  They function as connections between axons descending from the brain.

•  They synapse on motor neurons and axons from sensory nerves and spinal nerves ascending to the brain.

Concept 3: Central Nervous System

•  Functions as the command center •  Comprises the the brain and spinal cord •  Integrates and organizes sensory and

motor information to control movement

CNS Components most involved in Motor Control

•  Cerebrum

•  Diencephalon

•  Cerebellum

•  Brainstem

Cerebrum •  Divided into two the right and left cerebral hemispheres •  Each hemisphere is covering with gray matter of 2-5 mm thick, folded tissue

of nerve cell bodies called the cerebral cortex •  The gray matter contains neurons that send signals from the cortex to other

parts of the CNS (pyramidal cells) or non pyramidal cells. •  Each hemisphere of the cortex consist of four lobes

Parietal Frontal Occipital Temporal

Sensory-Specific Areas (Figure 4.4 below)

Proximity of primary sensory and motor cortex areas and their association areas allows interaction between perceptual and higher-order cognitive functions.

Diencephalon

•  Diencephalon (contains the thalamus & Hypothalamus) lies between cerebrum and the brainstem

–  Hypothalamus lies under the Thalamus controls the endocrine and the body homeostasis including temperature, hunger, thirst, and regulation of carbohydrate energy use.

–  Thalamus is a relay station for sensory and motor information that transmits pulses from one cerebral hemisphere to another and interconnects the other areas of the brain, plays important roll in controlling attention, mood, & perception of pain.

Thalamus

Hypothalamus

Cerebellum

1.  Attaches to the brain stem & Located behind the cerebral hemispheres

2.  Regulates the accuracy & smoothness of movement.

3.  Controls eye-hand movements

4.  Movement timing

5.  Posture Control

6.  It detects errors and corrects errors in movement*

cerebellum

Important Subcortical Component

•  Basal ganglia plays critical role in planning and initiating movement, control of antagonist muscles during movement, and the control of force.

•  People with Parkinson’s disease and cerebral palsy affect the basal ganglia’s functions

•  People with basal ganglia limitations experience:

–  Bradykinesia (slow movements) –  Akinesia (reduced amount of movements) –  Tremor –  Muscular rigidity

Basal ganglia

Concept 4: The Brain Stem

•  Consists of the pons, medulla or medulla oblongata, and reticular formation

Pons 1.  Pons considered to be part of the brainstem.

2.  Top of the brain stem

3.  Bridge between cerebral cortex and cerebellum

4.  Connects the two hemispheres of the cerebellum

5.  Acts as a relay for the auditory system and movement

6.  Involved in controlling chewing, swallowing, salivating, and respiration

7.  Plays a role in balance Pons

Medulla or Medulla Oblongata 1.  Considered to be part of the brainstem

2.  Serves as regulatory agent for various internal physiologic processes such as heart beat, respiration, and gastrointestinal functions.

3.  Site where sensory (ascending) and motor neural (descending) pathways cross over the body midline and merge on their way to the cerebellum and cerebral cortex.

medulla

Reticular Formation

Located just above pons and contains the reticular formation which is considered to be part of the brainstem)

Plays a major role in arousal, consciousness, states of sleep, and relaxation

Primary role is as an integrator of sensory and motor neural impulses, that is, inhibits or increases neural impluses which in turn influences skeletal muscle activity.

Reticular

Concept 5: Limbic system

Limbic system controls behaviors including emotions, motivation, and learning which provides impetus for goal directed movement in environmental contexts.

Pleasure center of the brain.

Consists of the frontal and temporal lobes of cerebral cortex, thalamus, hypothalamus, and interconnections nerves of CNS

Hummm! How does this all relate to learning a motor skill?

•  http://med.stanford.edu/alumni/media/video/jennifer-raymond.html

Concept 6: Spinal Cord Two major portions of the spinal cord are the gray and white matter.

Gray matter is butterfly shape, central part of spinal cord, containing 2 pairs of horns.

Dorsal horn involve cells are involved in transmitting sensory information.

Ventral horns contain Alpha Motor Neuron whose axons terminate on skeletal muscles.

Spinal cord contains interneurons call Renshaw cells. Nerve fibers descend from the brain terminate on interneurons which influence Alpha Motor Neuron activity.

Concept 7: Transportation of sensory information to the brain

•  Sensory neural pathway (ascending track) –  Passes through the spinal cord to brain stem to

thalamus to the sensory areas of cerebral cortex and to the cerebellum

–  There are different specific ascending tracks: •  Vision has it’s own track to the cerebral cortex •  Audition has it own track to the cerebral cortex •  Sensory information has it own tracks to the cerebral cortex.

–  Ascending tracks cross at the brain stem from one side of the body to another which means information from one side of the body is received in the opposite side of the brain.

Next Slide

Concept 8: Transportation of Movement information from the Brain to the Muscles

•  Motor neural pathway. Transport of movement information (descending track) that will execute the movements: –  Two distinct pathways that function together

•  Pyramidal (corticospinal tract) –  Transmits neural information that arises from the cerebral

cortex with axons projecting into the spinal cord that cross over to the opposite side of the body.

–  Primarily associated with fine motor skills (mostly discrete in nature or what neural scientists call – fractionated movements).

•  Extrapyramidal (brainstem pathways) –  Transmits neural information that arises in the brainstem with

axons descending into the spinal cord with many of fibers not crossing over to the opposite side of the body

–  Chiefly found in the reticular formation of the pons and medulla. –  Primarily associated with postural control and muscle control of

flexion and extension of hands and fingers.

Concept 9: Motor Unit

The end of transmission of motor neural information is the motor unit.

Commonly defined as the Alpha motor neuron and muscle fibers it innervates (motor unit)

Connection between an Alpha motor neuron and skeletal muscle occurs at the neuromuscular junction located at the middle of the muscle.

This synapse allows nerve impulses to be transmitted so he muscle contracts and movement occurs.

Alpha Motor Neuron

Concept 10: Performing a Voluntary Motor Skills

Neural system is hierarchical organized.

1.  One needs to have cognitive intent to move.

2.  Various structures work both hierarchically (top-down or down-up) and in parallel (same time).

3.  Different neural activity occurs when we perform different skills.

THE END