Download Lesions to premotor area can cause apraxia: loss of the ability to

20. Primary motor cortex and premotor cortex
Primary motor cortex: BA 4
Premotor: BA 6 and others
Size of BA 4 (proportion of
body wt) is constant across
species, but BA 6 is 6x
larger in humans than
macaque monkeys.
Lesions to premotor area can
cause apraxia: loss of the
ability to plan and execute
complex voluntary motor
tasks.
21. Motor Homunculus
Primary motor cortex
M1
Brodmann’s area 4
22. Corticospinal and corticobulbar tracts
23. LCST and VCST
Lateral Corticospinal Tract (LCST)
3/4 of the CST axons
decussates in the medulla
limbs (arms, legs), especially distal muscles (feet, hands, fingers)
Ventral Corticospinal Tract (VCST)
1/4 of the CST axons
does not decussate in the medulla
terminates bilaterally in the medial part of the ventral horn
axial/proximal muscle movement (neck, shoulder, trunk, hip)
24. Lateral Corticospinal Tract Topography
25. Ventral Horn Topography
Lateral white matter
(LCST)
LCST
LCST
VCST
distal
muscles
proximal
muscles
VCST
proximal
muscles
distal
muscles
26. Directional tuning of an M1 neuron -- The experimental setup
27. Directional tuning of an M1 neuron -- Tuning curve
28. Directional tuning of M1 neurons -- Population Vector
29. Motor Neuron Pool and Motor Unit
Motor Neuron Pool
Motor Unit
30. Motor Neuron Pools
! (alpha) motor neurons
ventral horn of spinal cord
31. Motor Unit
Number of muscle fibers per
motor unit:
large leg muscles: 1000
fingers: 10
extraocular muscles: 3
32. Motor Unit
The fibers innervated by
a single alpha motor
neuron are distributed
throughout the muscle.
This makes the firing of each motor neuron cause a
distributed contraction (smoother muscle dynamics)
33. Neuromuscular Junction
Transmitter: Acetylcholine (ACh)
Excitation-Contraction Coupling
www.shelfieldpeonline.co.uk/assets/images/neuromuscular_junction.jpg
34. Neuromuscular Junction (Fig. 6.2)
Each synaptic vesicle of the
alpha motor neuron contains
about 10,000 ACh
molecules.
One acetylcholinesterase
(AChE) enzyme can break
down 5,000 molecules of
ACh per second!
35. Lower Motor Disorders
Lower Motor Disorders
Amyotropic Lateral Sclerosis (ALS)
death of lower and upper motor neurons
flaccid paralysis, areflexia, muscle atrophy
aka Lou Gehrig’s disease
Duchenne Muscular Dystrophy
death of skeletal muscle
x-linked recessive genetic mutation
gene for a muscle cytoskeletal protein (dystrophin)
Myasthenia Gravis
autoimmune destruction of skeletal muscle ACh receptors
alpha motor neurons and muscle not damaged
normal life expectancy with treatment
36. Myasthenia Gravis
myasthenia gravis causing
ptosis
1-min after i.v. injection of
acetylcholinesterase inhibitor
Images from Kandel, Jessel, and Schwartz, p. 299 (Fig. 16.1)
37. Proprioceptive (Ia and Ib) axons
Ia, Ib
Proprioception
Muscle Spindle
Touch
Merkel, Meissner,
Pacinian, Ruffini
A!
6-12 !m
35-75 m/s
Pain/Temp
Free nerve endings
A"
1-5 !m
5-30 m/s
0.2-1.5 !m
0.5-2 m/s
Pain/Temp/Itch Free nerve endings
C
13-20 !m 80-120 m/s
38. Muscle Proprioceptors: The Muscle Spindle
Muscle Spindle
Golgi Tendon Organ
(green)
a
(blue)
39. Muscle spindles compared to Golgi tendon organs
40. Muscle spindles compared to Golgi tendon organs
41. gamma
(!) motor neuron activity regulates muscle spindle responses
! motor neuron activation without "
! motor neuron activation with "
42. The knee-jerk (stretch) reflex
Ia
monosynaptic excitation
reciprocal disynaptic inhibition
43. Stretch reflex circuitry
44. Stretch reflex circuitry
Descending
command
Glutamate
Increased Ia
discharge
Ia
45. Autogenic inhibition reflex circuitry
(GABAergic)
disynaptic autogenic inhibition
disynaptic excitation of antagonist
46. Autogenic inhibition reflex circuitry
Descending
command
Force to
lift glass
GABAergic
inhibitory
interneuron
Increased Ib
discharge
Ib
Golgi Tedon Organ
Too much
force
47. Flexion-crossed extension reflex