Download Neural Basis of Motor Control

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.
Neuron: Basic Unit of CNS
•  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
Differences
Axons
Dendrites
•  Take information away
from the soma
•  Generally only 1 axon per
cell
•  No ribosomes
•  Can have myelin
•  Branches further from the
soma
•  Bring information to the
soma
•  Rough surfaces (dendritic
spines)
•  Many dendrites per cell
•  Has ribosomes
•  No myelin insulation
•  Branches are near the
soma
Neuron Types
e.g. Retinal cells;
olfactory cells
2 axons one extending
toward the spinal cord
and other to skin or
muscle
e.g. Spinal motor
neuron (serves
many functions
Neuron Classification
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)
–  Gamma motor neurons which supply 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 and they
synapse on motor neurons and axons
from sensory nerves and spinal nerves
ascending to the brain.
Structures of Transmission
Communication
Neurons communicate with each other
through an electrochemical process.
Neurons contain some very specialized
structures (i.e., synapses) and chemicals
(i.e, neurotransmitters) that enable one
cell to communicate with another.
Electrochemical Charges
•  Chemicals cause an electrical signal.
•  Almost every chemical in our body is “electrically
charged.”
•  When they have an electrical charge, they are
call “ion.”
•  The important ions in the nervous system is:
–  Sodium & potassium (1 positive charge *)
–  Calcium (2 postive charges **)
–  Chloride (negative charge-)
Neural Transmission
•  Each axon is enclosed in cellular (myelin) sheath of lipid
material that insulates the axon.
•  The sheaths wrapped together in many layers is called
myelinated fibers. If it is only wrapped in one layer it is
called unmyelinated fibers.
•  Large myelintated fibers (1-2 mm) contain gaps called
nodes of Ranvier.
•  The myelinated fibers transmit neural messages up to
400 feet per second by jumping from one node to the
next. Unmyelinated fibers transmit messages up to 3
feet per second.
What turns the neural system on!
•  The on or off position is determined by the
distribution of charged ions (sometime called
particles).
•  Ions (+ or – charged) surround the inside and
outside of each cell.
•  When there is an unbalanced # of + or – ions on
each side it creates a membrane potential.
–  Resting membrane potential (polarization)
•  Unexcited cell (not sending a signal)
–  Action membrane potential (depolarization)
•  Excited cell (sending a signal)
•  Sodium (NA+) rushes which turns the cell on!
•  Transmission occurs as an “all or none” situation
Resting Membrane Potential
•  Inside of neuron is
negative to that of the
outside.
•  Ions on the inside and
outside are not
completely balanced
so some can flow in
and out of the cell.
Resting Membrane Potential
At rest, potassium ions (K
+) can cross through the
membrane easily.
Chloride ions (Cl-)and
sodium ions (Na+) have a
more difficult time
crossing. The negatively
charged protein
molecules (A-) inside the
neuron cannot cross the
membrane. The resting
membrane potential of a
neuron is about -70 mV
(mV=millivolt) - this
means that the inside of
the neuron is 70 mV less
than the outside.
There are more
sodium ions
outside the
neuron and more
potassium ions
inside the neuron.
Action Potential
An action potential
occurs when a neuron
send information
down an axon, away
from the soma.
Neuroscientists use
the words such as
“spike” or “impulse”
for the action
potential.
There is an explosion!
All or none
principle at
-55 mV.
Threshold
potential then
is -55 mv
Action potential is an
explosion of electrical
activities that is created
by a depolarization
current. This means that
some stimulus cause
resting potential to move
toward 0mV. When it
reaches about -55 mV a
neuron will fire an action
potential.
Action Potential (Depolarizing current)
A stimulus first causes sodium
channels to open. Because there
are many more sodium ions on the
outside, and the inside of the
neuron is negative relative to the
outside, sodium ions rush into the
neuron
Remember, sodium has a
positive charge, so the neuron
becomes more positive and
becomes depolarized. It takes
longer for potassium channels to
open. When they do open,
potassium rushes out of the cell,
reversing the depolarization. Also
at about this time, sodium
channels start to close. This
causes the action potential to go
back toward -70 mV (a
repolarization). Gradually, the ion
concentrations go back to resting
levels and the cell returns to -70
mV.
How does it transmit from one
Neuron to another?
Neural chains are created which is called synaptic
transmission
Without a synapse there is no communication between
neurons and target site such as muscles*
There is not an all or none transmission at the junction
(transmission may blocked, reduced, amplified or
changed)
Consists of pre-synaptic neuron (axon button), synaptic
cleft, and post-synaptic neuron (receiving axon)
The neurotransmitter is manufactured by
the neuron and stored in vesicles at the
axon terminal.
When the action potential reaches the
axon terminal, it causes the vesicles to
release the neurotransmitter molecules
into the synaptic cleft.
The neurotransmitter diffuses across
the cleft and binds to receptors on
the post-synaptic cell.
The neurotransmitter molecules are
released from the receptors and
diffuse back into the synaptic cleft.
Synaptic Transmission
Presynaptic neuron releases a
chemical transmitter.
Transmitter influences the
communication
Transmitter can be excitatory or
inhibitory.
Most common transmitter is
acteyclohline.
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
Occipital
Frontal
Temporal
Four Lobes
•  Frontal lobe controls voluntary movement.
•  Parietal lobe is a key player for controlling
perception of sensory information.
•  Occipital lobe is important for visual
perception.
•  Temporal lobe plays important roles in
memory, abstract thought, and judgment.
Sensory-Specific Areas (Figure 4.4 below)
Proximity of primary sensory and motor cortex areas and their
association areas allows interaction between perceptual and higherorder cognitive functions.
Cortex Areas Related to
Controlling Movement
• 
• 
• 
Primary motor cortex
–  Critical for movement initiation and coordination for fine motor skills.
Premotor area
–  Controls the organization of movements before they are initiated and
rhythmic coordination during movement that requires sequential
movements
Supplementary motor area (SMA)
–  Controls sequential movements and preparation and organization of movement.
• 
Parietal Lobe
–  Control of visual and auditory selective attention, visually tracking a target and grasphing.
–  Integration of movement preparation and execution processes by interacting with the
premotor cortex, primary motor cortex, and SMA
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
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
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
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
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
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.
Spinal Cord
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
Transportation of Movement information
from the Brain to the Muscles
•  Transport of movement information (descending
track) that will execute the movements:
–  Via two distinct motor neural 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.
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
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.
Producing a Motor Skill
Important part of performing a motor skill
comes from knowing “what to do” and
“how to do” the motor skill
–  What to do is called declarative knowledge
–  How to do the skill is called procedural
knowledge
Motor Control of Goal Oriented,
Voluntary Movement or Tasks
What to do (declarative knowledge) is a brain
function of planned movement.
-Involves the limbic & association cortex systems
- In short, limbic and association cortex function
cooperatively to guide goal-directed voluntary
movements.
Motor Control of Goal Oriented,
Voluntary Movement or Tasks
How to do it (procedural knowledge) is another
brain function associated with planned
movement.
- The projection system (basal ganglia,
cerebellum and the motor cortex) provides
detailed to motor and sensory information of how
to do it that matches with what to do (limbic or
association cortex systems) in the situation in
which the movements or skill is to be performed.
Controlling Voluntary
Coordinated Movement
•  Involves the limbic, association cortex, and
projection systems. For example:
–  basal ganglia (magnitude of movement)
–  cerebellum (detection & correction of errors)
–  pre and motor cortex (command center)
–  thalamus (relay station)
–  hypothalamus (body regulation)
–  frontal lobe of cerbral cortex (interprets)
THE END