movements and audition motor section 7mboyle/cogs17/pdf-files...descending tracts purpose: bring...
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Section 7: Motor
Movements and Audition
Lexi Franklin7/22/19
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Descending Tracts● Purpose:
○ Bring motor decisions from higher
cortical levels to lower levels of the
CNS
● Produces a Motor Response in 2 Ways:○ Skeletal muscles
○ Autonomic motor
■ Glands
■ Smooth muscle
■ Heart
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Motor Cortex
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Premotor Area (PMA)● Purpose
○ Plans the motor activity
● Receives info from the ascending tracts of the CNS○ Cerebellum
■ Body positions
■ Tendon and muscle tension
○ Sensory cortical regions
● After the plan, the descending fibers will execute it
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PMA Neurons● Do not have a direct connection
to the muscles● Motor programs in the PMA
stimulate M1 neurons● M1 neurons do not have planning
capacity
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3 Important Parts of the PMA● Broca’s Area
○ Plans speech ○ Connects to the area in M1 associated with
speech that controls:■ Facial expressions, larynx, pharynx,
and tongue ○ Broca’s aphasia
■ Damage causes speech production errors
● Frontal Eye Field ○ Controls eye movements on the
contralateral side
● Premotor Area Homunculus○ Body mapped with motor purpose ○ Controls bilateral primitive movements ○ Also in M1
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Supplementary Motor Area (SMA)● Primitive movements● Controls lower body movements
○ Truck control: lower spine and hip movements
● Controls bilateral movement
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3 Levels of Control and Corresponding Brain Regions
● Strategy○ Plans the movement/goal
○ Brain regions: cortex and basal ganglia
● Tactics○ Controls muscle sequences to execute the goal
○ Brain regions: motor cortex and cerebellum
● Execution○ Adjusts posture and movement to achieve the goal
○ Brain regions: brain stem and spinal cord
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Pyramidal Decussation Stop 1: Layer 5 of Cortex
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Pyramidal Decussation Stop 2: Internal Capsule
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Pyramidal Decussation Stop 3: Midbrain
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Pyramidal Decussation Stop 4: Pons
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Pyramidal Decussation Stop 5: Medulla
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Two Tracts in the Spinal Cord ● Dorsal Lateral Corticospinal
Tract○ Made up of fibers that cross in the
pyramids of the medulla
■ “Decussation of the pyramids”
○ Controls further away, distal skeletal
muscles
● Ventral Corticospinal Tract○ Made up of fibers that do not cross in
the medulla
■ Instead cross in the spinal cord
○ Controls closer, axial & truncal
muscles
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Audition
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Sound Waves● Range: 20 Hz to 20,000 Hz
○ Units: Hertz (HZ) -> cycles per second
● Pitch/Frequency○ High pitch = high frequency
● Intensity/Amplitude○ High intensity is louder
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Outer Ear● Purpose:
○ Collect sounds
○ Orientation
○ Localization
● Parts:○ Pinna: individually distinct outer ear
○ Auditory canal: channel where
molecules move and ink to the
eardrum
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Middle Ear● Tympanic Membrane
○ Also called the eardrum ○ Connects to the ossicles
● Ossicles○ Made up of 3 bones: malleus, incus, and
stapes○ Transfers the movement of the tympanic
membrane to the oval window ○ Amplifies the force of the sound
■ Need to convert the sound energy into a more powerful signal since the cochlear fluid is harder to vibrate than the air molecules
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Inner Ear: Cochlea● Fluid filled chambers:
○ Scala vestibuli○ Scala media○ Scala tympani
● Membranes: Reissner’s and Basilar ● Types of fluids:
○ Perilymph○ Endolymph
● Purpose:○ Converts sound to neural signals
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Place Coding● Base of the Basilar Membrane
○ Closest to the oval window
○ Narrow and stiff
○ Moved most by high frequencies
● Apex of the Basilar Membrane○ Far end of the cochlea
○ Wide and floppy
○ Moved most by low frequencies
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Organ of Corti Anatomy ● In the scala media
● Hair cells between 2 membranes○ Tectorial membrane on top
○ Basilar membrane on bottom
● Hair Cells○ Depolarize or hyperpolarize depending on
which direction the cilia bend ○ As the basilar membrane moves from the
sound waves, the cilia bend ○ Inner Hair Cells
■ Divergent connections■ For details
○ Outer Hair Cells■ Act as cochlear amplifiers ■ Convergent connection
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Transduction of Hair Cells ● Basilar membrane bends the cilia
○ Tip links stretch and open the K+
channels
○ Hair cell depolarizes when K+ enters
the cell
● Ca++ channels then open which causes the release of glutamate
● Receptors on the spiral ganglion receive the signal
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Pinna
Auditory Canal
Ossicles
Cochlea
Tympanic Membrane
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Scala Media
Scala Tympani
Basilar Membrane
Reissner’s Membrane
Scala Vestibuli