S2
Fig. 10.10a
Each region has
a homunculus
Decision to move
S4
Fig. 10.01
Initiates motor command
Coordinates
secondary movements
Corticospinal and
corticobulbar
tracts
Balance and
complex
learned
movements
Pathways?
Other inputs:
Vestibular &
Visual!
Reflex
Examples of
motor
disorders:
Huntington’s
Disease and
Cerebellar
Disorder
S5
Jack Nicholson
One Flew Over the Cuckoo’s Nest
Frontal lobotomy
S 16
Pyramidal tract
Fig. 10.12
Corticospinal tract
Corticobulbar tract
Fine motor control, esp. of extremeties
Extra-Pyramidal tracts
Reticulospinal tract
Vestibulospinal tract
Originate in brainstem,
more involved with posture and equilibrium
Diagram is not accurate:
This is not a monosynaptic
pathway! Descending axons
synapse onto interneurons
which then synapse onto
motoneurons.
Descending Pathways
S 17
Who Cares?
Video of Huntington’s Chorea
Video of Cerebellar Dysfunction
Locked-in Syndrome
S6
Local control
• Muscle spindle
Spindle
Afferent
gamma motoneurons
– Stretch receptor
– Intrafusal muscle fiber
• What is their role?
• The stretch reflex…
– Follow the reflex arc
– Be able to differentiate
function of afferent fibers,
alpha motor neurons, and
gamma motor neurons
Motor units of
alpha motoneurons
S7
Fig. 10.05ab
This doesn’t happen!
S8
Fig. 10.05c
Co-activation of alpha and gamma
motoneurons insures that the
stretch of muscle can be detected
regardless of the initial length or
state of contraction of that muscle.
S9
Fig. 10.06
Proprioception
pathway via dorsal
column-medial
lemniscus pathway
One component
of Stretch reflex is
monosynaptic
Most common
example:
patellar reflex =
“knee jerk reflex”
Synergistic
&
Antagonistic
Muscles
S 10
Stretch Reflex
Monosynpatic excitation of motoneurons of
that muscle and synergistic muscles
and polysynaptic inhibition of motoneurons
to antagonistic muscles.
Recall frog reflex lab and existence of spinal
reflexes in single-pithed frogs.
Also, example Christopher Reeve and
patellar reflex.
S 11
Fig. 10.07
S 12
Golgi tendon organs
involved in a reflex to
oppose excessive
muscle tension.
Not monosynaptic.
Not shown in text diagram:
ascending axons in dorsal
column-medial lemniscus tract.
S 13
Other proprioceptors
Joint angle detectors and cutaneous mechanoreceptors also
contribute to sense of body position (proproiception.)
Plus vision and vestibular inputs!
S 15 Something is incorrect on this figure from another textbook.
Find it!