Chapter 9 Flashcards
Motor cortex plans and
initiates movement
Basal ganglia and cerebellum
coordinate movement
Spinal cord conducts
information to the muscles
Initiating and producing movement requires
the interaction of information from the senses and the entire brain
Sequential Production of Movement (1-8)
1.visual info required to locate target 2.frontal motor areas plan the reach and command the movement 3.spinal cord carries information to hand 4.motor neurons carry message to muscles of the hand and forearm 5. sensory receptors on the fingers send messages to sensory cortex saying that the cup has been grapst 6. spinal cord carries sensory information to the brain 7.basal ganglia judge grasp forces and cerebellum corrects movement errors 8. sensory cortex receives message that cup has been graspt
Parietal cortex (Brodmann areas 5 and 7)
integrates information from the senses and initiates movements based on sensory information
prefrontal cortex
plans movements based on experiences, goals, and sensory input
Premotor cortex
coordinates whole-body movements and organizes action sequences
Primary motor cortex
produces simple movements, such as hand movements to use or manipulate tools
order of movement within the brain
parietal cortex sends goals - prefrontalcortex plans - premotor cortex sequences - motor cortex executes
As movement complexity increases
additional brain areas are recruited to coordinate the movement
Electrical stimulation of the precentral gyrus triggered
triggered movements of different parts of the body
Stimulation of the cortex immediately anterior to the primary motor cortex also elicited
movement
The motor homunculus is similar to the somatosensory homunculus, with the body represented
upside down, the feet in the central fissure, and the head near the inferior lateral surface
The motor homunculus has larger representations for the
hands and tongue, areas associated with fine motor control
Original mapping of the motor cortex was relatively crude, using
large electrodes
Brief electrical stimulation produces movement of
a specific body part
longer stimulations result in
ethological behaviors, or behaviors the animal might use in everyday activities
ethological behaviors
Defensive postures
Reaching movements
Climbing and leaping postures
Ethological movements
include the part of the body to be moved, the destination to which the movement is directed, and the function of the movement
Organization of the homunculus is somewhat maintained by the
ethological movements
hand movments and the homunculus
Hand movements are ventral
hand movements from hand to mouth and the homunculus
Movements of hand to mouth are most ventral
More complex, whole-body movements are in
premotor area
Ethological movements can be elicited from
parietal cortex stimulation
Movements evoked from the parietal lobe map - dorsal stimulation
Stepping movements
Movements evoked from the parietal lobe map - ventral stimulation
Hand movements
Movements evoked from the parietal lobe map - most ventral stimulation
Mouth movements
The pincer grip is a developmental milestone in the
first few months of life that gets refined over time
Damage to cortical motor areas impairs
the entire movement, not just the one part of the body or muscle that corresponds to the damage
Movements to replace the impaired movement are controlled by an
intact part of the cortex, such as the pincer grip being replaced by the whole hand grip
Evidence from stroke studies suggests that movements are encoded
in multiple places in the cortex
Damage to the primary motor cortex produces
muscle weakness and impairs individual movements
Damage to premotor cortex impairs
complex movements involving multiple body parts
Movements coordinated by the motor planning areas
integrate and refine more basic movements, such as walking or climbing movements
The role of the neocortex and motor planning areas seems to involve
blending these prelearned movements
Corticomotor-Neuron Activity in monkeys lifting weights
Electrodes implanted into the wrist area of the primary motor cortex,Neuronal activity increased while the monkey was planning the movement, before actually moving, Activity increased further during the actual movement, Neuronal activity was even higher when there was more weight on the bar, Neurons encode direction, firing during flexion movements but not during extension, Movement is encoded by a population of neurons, not a single cell
Many movements are learned and are modified based on our
interaction with others
Mirror neurons are found in the
ventral premotor areas
Mirror neurons are found in the ventral premotor area and are active both when the animal is
performing a movement and when it observes someone else making that same movement
Some mirror neurons are specific to the
size of the target object
Some mirror neurons discharge only when the object is
in reach
Core mirror neurons are less
specific and respond to broad classes of movement
Additional mirror neurons have been identified in the
temporal and parietal lobes
Basal ganglia, cerebellum, and brainstem are important for the
control of movement
Basal ganglia includes the
caudate, putamen, and globus pallidus
Basal ganglia receive input from the
cortex and the substantia nigra in the midbrain
Basal ganglia receive input from the cortex and the substantia nigra in the midbrain and send projections
back to these areas
Hyperkinetic symptoms Result from damage to the
caudate and putamen
Hyperkinetic disorders
Huntington disease, Tourette syndrome
Hypokinetic symptoms Result from loss of
dopamine input from the substantia nigra
Hypokinetic symptoms Associated with difficulty
making voluntary movements
Hypokinetic disorders
Parkinsons disease
the role of the basal ganglia is to
modulate movements
basial ganglia and movement force and movement disorders
One hypothesis is that the basal ganglia control movement force, and the movement disorders are issues with too much or too little force
Output from the interior portion of the globus pallidus (GPi) projects
to the thalamus and motor cortex
If the predominant input to GPi is inhibitory, then the region
fails to inhibit the thalamus and movement occurs
If the predominant input is excitatory, then the GPi
inhibits the thalamus and movement is prevented
Decreasing activity in the GPi
descreases the symptoms of Parkinson disease
Cerebellum is important for
acquiring and maintaining motor skills
Cerebellum includes two
hemispheres and a small horizontal lobe, the flocculus
Different parts of the cerebellum are involved in
different aspects of motor control
Flocculus receives information from the
vestibular system and is involved in balance
Midline areas of the cerebellum control the
midline of the body
Lateral areas of the cerebellum are involved in
movements of the limbs and hands
Cerebellum is important in
timing movements
Damage to the cerebellum impairs the ability to
move at a regular rhythm
Damage to the cerebellum also impairs the ability to accurately
perceive time
Cerebellum is important for monitoring
movement accuracy
cerebellar experiments and throwing darts
2 groups were given glasses that distorted their vision and were asked to throw darts initially patients with an intact cerebellum adjusted their throws so that they hit the target Patients with cerebellar damage were unable to adjust their movements to hit the target,When the goggles were removed, patients with an intact cerebellum threw incorrectly again and had to compensate, but patients with cerebellar damage were on target and did not have to correct
Cerebellum and Motor Feedback 1
If the movement does not reach the intended target, some adjustment is needed
Cerebellum and Motor Feedback 2
Cortex sends the motor command to the spinal cord, but sends a copy to the cerebellum
Cerebellum and Motor Feedback 3
Sensory information from the muscles and the visual system is sent to the cerebellum
Cerebellum and Motor Feedback 4
Cerebellum compares the intention (motor output) with the results (sensory input) and generates a correction to achieve the desired result
Cognitive processes, such as language, use a similar error correction strategy based in the
cerebellum
Main motor control pathway originates in the
motor cortex
multiple pathways originate in the
brainstem
Spinal cord pathways provide input about
balance and posture to refine the movement commanded by the cortex
Movements specified by the brainstem tend to be
coarse movements of the entire body
Electrical stimulation of brainstem areas produces behaviors such as
an arched back and erect hair in a cat or walking or running behaviors
The timing of the behavior depended on the timing of the
stimulation
the intensity of the behavior was determined by the
magnitude of the stimulation
The spinal cord is the final
pathway to convert motor plans into movements
Corticospinal and corticobulbar tracts project from
the cortex to the spinal cord
Corticobulbar tracts control
facial movements
Corticospinal tracts influence
movement of the limbs, digits, and body
Corticospinal tracts originate in
somatosensory areas, motor cortex, and premotor cortex
Input from somatosensory areas modulates
afferent sensory information
Input from motor areas projects to
motor neurons of the brainstem and spinal cord to influence movement
Corticobulbar and corticospinal tracts originate in layer
V
Approximately 95% of the descending motor pathways decussate on the
ventral surface of the brainstem, resulting in a bump called the pyramids
The lateral corticospinal tract decussates and influences the movements of
limbs and digits contralateral to the hemisphere where the motor command originated
The anterior corticospinal tract does not decussate and controls
movements of the trunk
Motor neurons of the spinal cord provide the output connection between the
nervous system and the muscles
Neurons from the corticospinal tracts synapse on both
interneurons and motor neurons
Spinal motor neurons and interneurons are arranged in a
homunculus
Lateral motor neurons influence the
fingers and hand
Intermediate motor neurons control the
limbs
Medial motor neurons control the
trunk
Muscles that control the limbs are arranged in
pairs
Extensor muscles move the limb
away from the trunk
Flexor muscles move the limb
toward the trunk
Circuits in the spinal cord cause one muscle of the pair to
relax while the other muscle is excited
