Psy 111 Basic concepts in Biopsychology

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Psy 111 Basic concepts in Biopsychology Lecture
12 Central motor systems
Website http//mentor.lscf.ucsb.edu/course/fall/p
syc111/
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Motor Pool
Motor neuron pool all the motor neurons that
innervate a single muscle
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Crossed-Extensor Reflex
Synergistic activation of muscles in one limb is
coupled to opposing control of contralateral
limb. e.g. flexsor reflex coupled to extension of
contralateral limb. Spinal Circuits form motor
commands for complex behavior
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Objectives

• Provide overview of cortex and motor function.
• Describe the descending motor pathways and their
  specific functions.
• Define the role of the primary motor cortex (M1)
  in activation of descending pathways and its
  relation to secondary and association motor
  cortices.
• Define the relation between M1 and motor units.
  Describe the encoding of motor commands in M1.
• Explain the connections of the basal ganglia and
  its relation between prefrontal cortex and motor
  cortices.
• Describe the role of the superior colliculus in
  motor action.
• Describe the role of the cerebellum in
  coordination of motor action.

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Motor Action is Preceded by Planning
Planning -serves to coordinate sensory input
(perception) to organize motor output. -is the
specialized function of the brain.
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Cortex and Brain Output Overview
Basics Organization Sensory Decision Command
Precentral Gyrus primary motor cortex (M1)
stimulate muscle contraction. Supplemental and
Premotor cortices secondary motor cortices (SMA
PMA) involved in coordination of input to
M1. Prefrontal cortex involved in executive
function ie conscious decisions Posterior
Parietal cortex involved in perception of body
surroundings input to PFC subcortical systems
(primarily brainstem, cerebellum)
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Sensorimotor System
Sensory info proceeds through primary sensory
cortices to association cortex in posterior
parietal area before being communicated to
association cortex in frontal lobe (prefrontal
cortex).
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Sensorimotor System Prefrontal Ctx

• Prefrontal cortex
• makes decision (executive function) with
  information from post parietal ctx
• sends commands to secondary motor cortex (via
  basal ganglia subcortical cortex-cortex loop).

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Secondary Motor Cortex
Premotor and Supplementary motor areas receive
input from basal ganglia and activate Primary
motor cortex
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Primary Motor Cortex
Primary motor cortex (M1) -controls activation
of motor neurons stimulate M1 produces
contraction of muscles. -somatotopic mapping
Primary Motor mapping is distorted based on
number of motor units. The more motor units
allows higher motor acuity.
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Single M1 Cell Activity Vectors
Individual neurons encode directional information
involved in motor neuron pool activation during
limb movement. (Note Broad tuning.)
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Population Vectors
Outputs of individual cells are summed to give a
population vector
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Population Vectors and Direction
Specific directions of movement correspond to
unique population vectors -many motor cortex
cells fire with each movement -cell activity is
summed to get population vector Motor acuity is
determined by number of neurons contributing to
motor pool
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Secondary Motor Cortex activation
Premotor area becomes active prior to motor
movements and is involved in planning of
movement. -poorly understood relation between
neural activity and function
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Motor Cortex control of Descending Paths

• All descending paths are under control of M1.
• M1 has direct projection to spinal motor neurons
  (cortiocospinal tract)
• M1 also projects to other descending pathways.
• Each paths interact with other brain structures
  to produce meaningful, coordinated behavior.

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Descending Pathways
Descending pathways travel down the spinal cord
allowing the brain to control spinal level
interneuron circuits.
As with sensory systems, there are independent
descending pathways serving specialized
functions. Lateral - voluntary movements under
direct cortical control Ventromedial - posture
and locomotion under brain stem control
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Lateral Pathways
Corticospinal tract - from neocortex to spinal
interneurons. Rubrospinal tract - from red
nucleus to spinal interneurons. (receives input
from motor ctx)
Lateral pathways control fine motor movements of
limbs. Redundancy allows some recovery after
damage.
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Ventromedial Paths
Ventromedial Paths coordinate sensory info with
motor control
Vestibulospinal - coordinates vestibular info
with motor control Tectospinal - coordinates
visual system info with motor control
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Ventromedial Paths
Reticulospinal tracts control extensors in
antigravity reflexes
Pontine reticulospinal - maintains posture via
extensor muscle control Medullary reticulospinal
- inhibits extensor muscle control These systems
are coordinated by Motor cortex.
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Descending Paths Reflexive Responses

• All descending paths are under control of M1.
• M1 has direct projection to spinal motor neurons
  (cortiocospinal tract)
• M1 also projects to other descending pathways.
• Tectum (superior and inferior colluculi) receive
  direct sensory input involved in orienting
  responses.

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Reflexive motor action.
SC critical for orienting response to visual
stimuli.
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Superior colliculus population vectors

• SC critical for orienting response to visual
  stimuli.
• Sensory input is organized topographically (like
  retina, LGN, etc)
• Population vectors encode direction of eye
  movement in two dimensions depending on visual
  input.

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Input from PFC Basal Ganglia/Thalamic Relay
Basal ganglia provides input from Prefrontal
cortex to Secondary motor cortex via the
ventrolateral thalamus. inter-cortical Loop
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Basal Ganglia
Basal ganglia subcortical forebrain structures
serve motor functions comprising a pathway from
PFC to SMA/PMA.
Structures of the basal ganglia are
interconnected by subcortical white matter.
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Circuitry of Basal Ganglia
Disinhibitory Circuit
Also, major input from substania nigra (dopamine)
and subthalamus both excitatory.
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Basal Ganglia Disorders
PD
HD
Parkinsons degeneration of dopamine neurons in
SN that are input to BG gt difficulty initiating
movement.
Huntingtons degeneration of GABA interneurons
in putamen gt uncontrolled ballistic movements
or chorea.
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Motor Loop and Cerebellum
Cerebellum -receives massive sensory input via
the pons (from several cortical
structures). -projects to thalamus (VLc) which
relays info to M1 -Coordinates ongoing motor
ouptut
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Structure of Cerebellum
Cerebellum is critical in coordination of muscle
activation. internal monitoring system for
motor output -Vermis projects to ventromedial
tracts (postural control) -hemispheres (lateral)
projects to VL Thalamus to M1 (voluntary control)
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Cerebellar Damage and Ataxia
Parkinsons
Cerebellum
Huntingtons
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Cortex and Motor Commands
Basics Organization Sensory Decision Command
Precentral Gyrus primary motor cortex (M1)
stimulate muscle contraction. Supplemental and
Premotor cortices secondary motor cortices (SMA
PMA) involved in coordination of input to
M1. Prefrontal cortex involved in executive
function ie conscious decisions Posterior
Parietal cortex involved in perception of body
surrounding input to PFC subcortical systems
(primarily cerebellum)
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Plasticity of the Motor Map
Remapping of M1 occurs when motor efferents are
disrupted. May be important during motor skill
learning.
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Motor Learning
Experience serves to make the motor system more
efficient (do more with less). Movement becomes
subconscious
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Cortical Organization of Langauge

• Wernicke-Geschwind Model
• Language localization intrahemispheric
  organization of language circuitry
• Brocas area (in frontal cortex) production
• Damage gt expressive aphasia
• Normal comprehension, speech is meaningful but
  awkward
• Wernickes area (in temporal cortex)
  comprehension
• Damage gt receptive aphasia
• Poor comprehension, speech sounds normal but
  has no meaning word salad

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Auditory and Visual Association Areas in Language
Perception
Motor side of language covered later.
Dorsal Stream (processes attributes)
Visual cortex

• Specialized for language production
• Identified in neuropsychology exams.
• Receives input from association areas in temporal
  cortex
• Assymmetrically localized on left side of brain.

• Specialized for language perception
• Identified in neuropsychology exams.
• Receives complex /high level auditory and visual
  inputs.
• Assymmetrically localized on left side of brain.

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