Transcript Motor Systems - People Server at UNCW

Goal-Directed Behavior and
Reflexive Behavior
Goal-Directed
Reflex
Relatively Complex
Relatively Simple
Consciousness? Intention
Automatic
Plastic
Relatively Inplastic
Requires Cortex
Cortex not required
Learning /experiences are
major influence
Genetics are major influence
Goal-Directed Behaviors Require:
• Goal selection and prioritization
• Resistance to distracters
-Cross-modal Sensory integration
– Perception of target
– Awareness of location of movable body part
– Ability to aim movement of body part
– Ability to detect errors and re-adjust, (use
feedback)
– Ability to use feedback to control movement of
body part
Sensory-Motor Integration in the
frontal lobes
THE DLPFC: “The conductor”
Integrates cross modal input- may initiate goal-directed behaviors
Lesions of the dorsolateral frontal areas results in a
number of “executive” motor impairments. These
include perseveration, incoordination, motor
impersistence, apraxias and hypokinesia.
http://www.youtube.com/watch?v=p_uhP1vDfoo
The premotor and supplementary
motor ctx: “The sections”
Stimulation= complex sequences of behavior (aimless
behavior)
Damage to the secondary Motor
Cortex?
• Ideomotor Apraxia
• This apraxia is associated with great difficulty in the sequencing and
execution of movements. A common test of apraxia is to request the
patient to demonstrate the use of a tool or household implement (e.g.,
"Show me how to cut with scissors"). Difficulties are apparent when
the patient moves the hand randomly in space or uses the hand as
the object itself, such as using the forefinger and middle finger as
blades of the scissors. They have additional trouble sequencing the
correct series of movements and make errors in orienting their limbs
in space consistent with the desired action. Imitation of the
movements of others will usually improve performance but it is still
usually defective.
• Memories for skilled acts are probably stored in the angular gyrus of
the parietal lobe in the left hemisphere.
• http://www.youtube.com/watch?v=gewP1T7GYcc
The primary motor cortex; “the
instrument”
Stimulation = relatively simple fragments of behavior
TWO MAJOR DESCENDING PATHWAYS
FROM THE PRIMARY MOTOR CORTEX:
The Dorsolateral pathway
And the VM Path.
• The VM pathway does
not discretely decussate,
but does branch and
innervate contra lateral
segments in the spinal
cord.
DL vs VM descending motor paths
• Dorsolateral
• Ventromedial
• Decussates at
medullary pyramids
• Distal muscle groups
• More direct
• More volitional control
• Higher resolution of
control
• Does not cross
• Medial muscle groups
• Gives off spinal
collaterals
• Yoking
• Lower resolution of
control
Other Motor Pathways
• In addition there are other motor paths that
have relays in the brainstem
• These other paths innervate nuclei of the
RAS, cranial nerve nuclei, etc…
Descending paths get additional
inputs
Both pathways terminate in spinal
cord segments
According to part of the body they
control
On lower motor neurons
(alpha motor neurons)
Amyotropic lateral sclerosis (ALS)
disease of the alpha motor neurons
ALS
Alpha motor neurons project to
form part of spinal nerve pairs
Terminate on muscle fibers
At each spinal segment
Muscle groups are complex; attach
bone to bone via tendons and
ligaments
A muscle group has many fibers
The motor unit helps us understand
“resolution”
The motor unit: If ratio is high=low
resolution
The Neuromuscular junction (NMJ):
The receptive portion of muscle-the
motor end-plate
The NMJ ( sometimes called the
motor end-plate)
nACHr
End-plate potential
• Larger
• Longer
• Leads to Ca+ influx in sarcolema of
muscle
– Ca+ causes muscle contraction
muscle fibers encase myofibrils.
The casing is called the sarcolema
Muscle group
myofibril
Muscle fiber
End-plate potential causes ca+
influx into sarcolemma
Myofibrils in turn contain
“Actin and Myosin” filaments
When the NMJ is activated Actinmyosin interact to shorten the length of
a muscle fiber
Sliding filament model of muscular
contraction
Muscle shortens=work
Disease of the NMJ?
MG
MG
MG
Cortical vs Spinal control of
behavior
• Goal-directed
• Reflexive
• Complex
• Higher levels of
control
• Plastic
• Numerous reflexive
behaviors are
involved
• Simple
• Automatic
• inplastic
Spinal reflex ARCs
• Monosynaptic
– stretch
• Polysynaptic
– Withdrawal
– Antagonist muscle groups
– Synergistic muscle groups
– Polysegmental relexes
– Cross-spinal reflexes
A “monosynaptic” spinal reflex arcthe Stretch reflex
The stretch reflex involves
neuromuscular “spindles”
Stretch reflex regulates muscle
tension in every muscle group
The polysynaptic part of stretch
reflexes: inhibition of Antagonist
muscles
Spinal inhibition of antagonist muscles
require inhibitory interneurons
The “withdrawal reflex arc” a
polysynaptic spinal reflex
Also involves interneurons
And may involve more than one
spinal cord segment
And/or Cross spinal reflex arcs
The Goli tendon organ (GTO) reflex
Neural activity of spinal neurons
related to whole muscle group
activity
Lower motor neurons “the final
common pathway”
“the final common path: