lecture 17 motor- how the brain moves the body Flashcards
brain control of movement still important
movements appear effortless as long as there is steady stream of sensory information
successively higher levels of the motor hierarchy specify increasingly more complex aspects of a motor task
reflexive (lowest) then rhythmic then voluntary (highest)
learned movements become reflexive with practice
upper motor neurons important for voluntary movements
wilder penfield
area 6
posterior parietal (areas 5/7)
wilder penfield
1st stimulated cortex and found that the weakest stimulation strengths could give twitches in individual muscles only if the stimulation was localize just anterior to the central sulcus in an area known as m1 or area 4
area 6 (premotor cortex)
stimulation elicits movement, but they are more complex (limb instead of single muscle twitch)
posterior parietal area (areas 5/7)
essential for initiation of purposive movements like brushing teeth
upper motor neuron system
brainstem and cerebral cortex neurons
essential for initiation of voluntary movements
when we make a movement in a particular direction a subset of m1 neurons fire
likely that sequential activity of subsets of neurons underlie sequential motor programs
these cells descend to synapse on interneurons and the lower motor neurons
the upper motor neurons in cortex are mapped the same way the sensory cortex is mapped
somatotopic map in m1: homunculus
wilder penfield
over-representation of brain regions that are required for most complicated motor behaviors
hierarchial system
spinal cod, brain stem, and cortex contain motor control circuits
each level receives sensory info
each level can organize movements
some are unconscious (balance, breathing)
cerebellum and basal ganglia critical for motor acts
basal ganglia absence: huntington’s (too much movement, hyperkinetic)
parkinsons (too little movement, hypokinetic)
cerebellar damage: balance problems called ataxias
parkinsons
initiation of willed movements is inhibited because of more tonic (continuous) inhibition of the thalamic input to the premotor cortex
hypokinetic
huntingtons
initiation of movement is augmented because of less tonic inhibition of the thalamic input to the premotor cortex
hyperkinetic
voluntary movements controlled by a movement “plan” that is indifferent to which muscles are being used
whereas sensory systems generate an internal representation of the actual world, voluntary movements reverse the task and begin with an internal representation
brain represents the outcome of motor actions in a way that is independent of the specific muscles used or the way the goal is achieved
unvoluntary movements
can’t resist them (blinks, holding breath, tics)
pathological urge can be voluntarily resisted but not for too long (intrinsic tendency to reach threshold)
Primary motor cortex
Contains
upper motor neurons, which
control contralateral body parts.
Stimulation of specific sites in
motor cortex usually leads to
coordinated movements across
multiple joints. Large neurons in
layer 5 send their axons down the
spine to synapse onto lower
motor neurons and interneurons
in the spinal cord.
Provides commands to initiate
voluntary movement and control
complex movement. Primary
motor cortex is topographically
organized. The motor cortex, in
coordination with other areas of
the brain integrates information
from multiple sensory systems
and sends depending axons to
the motor control regions of the
brainstem, to spinal cord
interneurons, and to lower motor
neurons themselves.
Neurons in motor cortex are tuned to different parameters of movement, including direction,
velocity, joint angle etc. There is some evidence that stimulation of specific sites in motor
cortex can lead to coordinated movements across multiple joints
Premotor cortex
Contains neurons that help plan more complicated actions. Also contains mirror neurons, which are active not only when planning/performing complicated actions, but also when watching the same types of actions
Basal ganglia
A group of nuclei lying deep in the subcortical white matter of the frontal lobes
that organize motor behavior. The major components are the striatum (caudate and putamen),
substantial nigra, globus pallidus external segment (GPe) and globus pallidus internal segment
(GPi) which connects to nuclei in the thalamus and brain stem. The basal ganglia is essential
for motor initiation and control, habit formation and reward-based learning. Contains 2 different
pathways the direct and indirect pathway
Direct pathway
a subset of projection neurons (medium spiny neurons) link the striatum directly to the basal ganglia output: GPi and the substantia nigra. Since both the striatum and globus pallidus are GABAergic, activating this pathway, provides less inhibition to the thalamus and brain stem
Indirect pathway
a subset of medium spiny neurons in the striatum project to the GPe,
which in turn projects to the GPi. Because there is a chain of inhibitory connections
(disinhibition), activating this pathway provides more inhibition to the thalamus and brainstem
Parkinson’s disease
A neurodegenerative disease with symptoms that include shaking,
rigidity, slowness and difficulty walking. Dopaminergic neurons which help activate the direct
pathway degenerate, this leads to an increase in the GPi activity and causing more inhibition to
the thalamus
Huntington’s disease
A genetic disease that is characterized by abnormal, hyperkinetic movements. Caused by the degeneration of medium spiny neurons in the striatum that
specifically project to the GPe, resulting in the inactivation of the indirect pathway and
decreased inhibition to the thalamus
Cerebellum
structure located dorsal to the pons and medulla that plays an important role in motor coordination, motor learning and other cognitive functions. The cerebellum influences movements primarily by modifying the activity patterns of upper motor neurons. A primary
function of the cerebellum is to detect the difference or “motor error” between an intended
movement and the actual movement and thus modulate the upper motor neurons to reduce
the error. These corrections can be made both during the movement and as a form of motor learning
Brain computer interface
uses brain signals to control either devices or muscles using
bidirectional communication between the nervous system and a computer
Describe the major cortical regions and the type of motor responses elicited by neurons
located within each region
Describe the organization of
upper motor neurons in M1
Understand how rather
straight forward
connectivities generate
complex behaviors such as
walking, balance and even
writing
Understand how rather
straight forward
connectivities generate
complex behaviors such as
walking, balance and even
writing
Which is the definition of a motor unit?
A single motor neuron and skeletal muscle fibers innervated by that motor neuron’s axonal terminals
Which is the way that motor neurons are mapped within the ventral horn?
Based on the physical location of the muscles in the body.
Which of the following describes Henneman’s Size principle?
Motor neurons innervating the same muscle are recruited to activate different sets of muscle fibers sequentially with the smallest fibers activated first
Larger muscles receive innervation from more and more powerful motor neurons
Motor neurons innervating the same muscle are recruited to activate different sets of muscle fibers sequentially with the largest fibers activated first
The size of the ventral horn of the spinal cord is larger in the cervical and lumbar enlargement
Motor neurons innervating the same muscle are recruited to activate different sets of muscle fibers sequentially with the smallest fibers activated first
The firing of primary motor cortical neurons occurs precisely at the onset of a muscle contraction.
true or false
False
Stimulating two adjacent areas in M1 will result in _____.
movement of two adjacent areas on the ipsilateral side of the body
movement of two muscle groups that are close in size on the contralateral side of the body
movement of two muscle groups that are close in size on the ipsilateral side of the body
movement of two adjacent areas on the contralateral side of the body
movement of two adjacent areas on the contralateral side of the body
Upper motor neurons _____ .
affect motor patterns only indirectly via their inputs to the basal ganglia
have cell bodies that are located in the ventral horn of the spinal cord
synapse on local circuit neurons and/or lower motor neurons
control the upper half of the torso
synapse on local circuit neurons and/or lower motor neurons
The hallmark of Parkinson’s disease is:
Reduced movements that the patient cannot control (hypokinetic)
