1. Human Physiology Chapter 10 The Mechanisms of Body Function
Vander’s
Human Physiology
The Mechanisms of Body Function
Tenth Edition by
Widmaier • Raff • Strang
© The McGraw-Hill Companies, Inc.
Figures and tables from the book, with additional comments by:
John J. Lepri, Ph. D.,
The University of North Carolina at Greensboro

2. Figure 10-1 Motor commands from the brain have been modified by
a variety of
excitatory and
inhibitory control
systems, including
essential feedback
from sensory
afferent neurons,
along with vision
and balance cues
(not shown).

3. Planned
Voluntary
Movement
*Voluntary
movements,
learned
skills
Association
Cortex
Motor
Cortex
Loss of voluntary movement
& spastic paralysis (stroke)
Parkinson’s disease/dystonia
Basal
Ganglia
Proprioception
*Automatic
movements,
postural
adjustments
Reticulospinal
Cerebellum
Vestibulospinal
medullary
pontine
lateral
medial
Flexors
Extensors
Ataxia
Nystagmus
Extensors
Force  # action potentials/motor unit,
and # motor units active
Spinal
Reflexes
Stretch
Motor
Unit
= motor neurone + its muscle fibres
Pain
*Rapid,
protective
reflexes
Large, fast, fatigable/
Small, slow, fatigue-resistant
Skin,
Muscle,
Joint
Movement
Flaccid paralysis
Neuropathies
ICBruce2002

4. Figure 10-2 Side and cross-sectional views of some of the
neural components regulating motor commands.
Altered processing abilities in these components
can cause motor problems such as Parkinsonism.

6. Figure 10-3 Examples of the categories of information and their
underlying neuronal substrates modifying the
production of motor commands from the brain.

7. One motor unit consists of a
single motor neurone and the
muscle fibres it innervates.
Precisely controlled muscles,
like the extraocular muscles,
have low “Innervation ratios”
(number of muscle fibres per
motor neurone).
Less precisely controlled muscles,
like the postural muscles of the
back, have high innervation
ratios.
Each motor unit is controlled by
descending pathways from the
brainstem & motor cortex.

11. More action potentials in one motor
unit produce more force (frequency
code). Precise control of force, as in
suturing a wound.
More motor units active at the same
time produce more force (population
code). Gross control of force, as in
carrying a suitcase.
Diseases of the motor unit (such as
motor neurone disease, myasthenia
gravis, or the muscular dystrophies),
produce muscle weakness.

12. Figure 10-4 Acting on local reflex circuits and by relaying
impulses to the brain,
muscle spindles and
Golgi tendon organs
provide information
about muscle position
and stretch in order
to finely regulate the
speed and intensity
of muscle contraction.

13. Regardless of the reason for a change in length, the stretched spindle in scenario (a) generates a burst of action potentials as the muscle is lengthened; in scenario (b), the shortened spindle produces fewer action potentials from the spindle.

14. 13-19: (a) Activation of alpha motor neurons shortens the extrafusal muscle fibers; if the muscle spindle becomes slack, it no longer signals muscle length. (b) Activation of gamma motor neurons contracts the poles of the spindle, keeping its sensitivity.

15. Figure 10-6
Tapping the patellar tendon lengthens the stretch receptor in the associated extensor muscle in the thigh; responses include:
compensatory contraction
in that muscle (A and C),
relaxation in the opposing flexor (B), and sensory afferent delivery to the brain.
Note: NMJ = neuromuscular junction

16. Activation of Golgi tendon organs
Activation of Golgi tendon organs. Compared to when a muscle is contracting, passive stretch of the relaxed muscle produces less stretch of the tendon and fewer action potentials from the Golgi tendon organ.

17. 13-21: Muscle proprioceptors: (a) Spindles are parallel to the extrafusal fibers, GTOs are in series. (b) GTOs sense increased tension on the muscle.

18. Figure 10-8
Contraction of the extensor muscle on the thigh tenses the Golgi tendon organ and activates it to fire action potentials. Responses include:
Inhibition of the motor
neurons that innervate this
muscle (A), and excitation
in the opposing flexor’s motor neurons (B).
Note: NMJ = neuromuscular junction

19. 13-22: Reverse myotatic reflex.

20. 1 2 3 Figure 10-9 Pain sensory afferents detect pain in foot and
The neural components of the pain-withdrawal reflex in this example proceed as follows:
Pain sensory afferents
detect pain in foot and
send action potentials via
dorsal horn of spinal cord.
Interneurons in the cord
activate flexor muscles
on the “pained” side of
the body and extensor
muscles on the opposite
side of the body.
Muscles move body away
from painful stimulus. 1 2
Could alter to show 1, 2, 3 in sequence 3
Figure 10-9

22. Planned
Voluntary
Movement
*Voluntary
movements,
learned
skills
Association
Cortex
Motor
Cortex
Loss of voluntary movement
& spastic paralysis (stroke)
Parkinson’s disease/dystonia
Basal
Ganglia
Proprioception
*Automatic
movements,
postural
adjustments
Reticulospinal
Cerebellum
Vestibulospinal
medullary
pontine
lateral
medial
Flexors
Extensors
Ataxia
Nystagmus
Extensors
Force  # action potentials/motor unit,
and # motor units active
Spinal
Reflexes
Stretch
Motor
Unit
= motor neurone + its muscle fibres
Pain
*Rapid,
protective
reflexes
Large, fast, fatigable/
Small, slow, fatigue-resistant
Skin,
Muscle,
Joint
Movement
Flaccid paralysis
Neuropathies
ICBruce2002

24. Figure 10-13 Motor activity must be informed about the body’s
center of gravity in order to make adjustments
in the level of stimulation to muscles whose
contraction prevents unstable conditions (falling).

29. Figure 10-10 Extensive neural networks between the major
“motor areas” of the cerebral cortex permit
fine control of movement, utilizing sensory and
intentional signals to activate the appropriate
motor neurons at an appropriate level of stimulation.
Figure 10-10

30. Figure 10-12 Efferent motor commands from the cerebral cortex
are contralateral or “crossed,” meaning that the
left cortex controls
the muscles on
the right side of
the body (and
vice versa),
whereas the
brainstem
influences
ipsilateral
(same side)
motor activity.
Figure 10-12

31. The location and relative size of the cartoon body-
Somatotopic Map
The location and relative size of the cartoon body-
shapes represent the location and relative number
of motor-related neurons in the cerebral cortex.

32. Planned
Voluntary
Movement
*Voluntary
movements,
learned
skills
Association
Cortex
Motor
Cortex
Loss of voluntary movement
& spastic paralysis (stroke)
Parkinson’s disease/dystonia
Basal
Ganglia
Proprioception
*Automatic
movements,
postural
adjustments
Reticulospinal
Cerebellum
Vestibulospinal
medullary
pontine
lateral
medial
Flexors
Extensors
Ataxia
Nystagmus
Extensors
Force  # action potentials/motor unit,
and # motor units active
Spinal
Reflexes
Stretch
Motor
Unit
= motor neurone + its muscle fibres
Pain
*Rapid,
protective
reflexes
Large, fast, fatigable/
Small, slow, fatigue-resistant
Skin,
Muscle,
Joint
Movement
Flaccid paralysis
Neuropathies
ICBruce2002

34. THE VERY END