Peripheral motor function
Purves et al., chapter 16, 1, 9
The Biology Department at SLU has a faculty member, Dr.
Fisher, who does research on muscle
Review of some muscle physiology mostly not in book
Sliding filament - well covered in Bio 106 & cell - only reviewed here
Ca2+ binding to troponin gets tropomyosin off actin sites
myosin can bind actin, ATP unbinds - explaining rigor mortis in ATP depletion
Duchenne (and Becker) muscular dystrophy X linked
additional protein - dystrophin - also in brain axon terminals
Excitation - contraction coupling
Fig (not in 5th edition)
Axon and collaterals go to the huge NMJs of one motor unit
Here is a picture
from our histology course of the neuromuscular junction.
Here is a transmission electron micrograph of a portion of a neuromuscular
junction. Note the folds, increasing the area on the muscle cell. Note
the space with electron density in the cleft. Note the numerous vesicles.
t-tubules get excitation to near sarcoplasmic reticulum
dyhydropyridine (blocking drug) receptor in t-tubule
homology to sodium channel - voltage sensitive
ryanodine receptor in sarcoplasmic reticulum same family as IP3 receptor
coupled with t-tubule
Nervous control of muscle
Fig. 16.6 p. 358
In BL A347 (General Physiology Lab)
one lab goup stimulated the forearm of subject Joel with increasing frequency
and obtained this
record of finger twitches using a sensitive force transducer; this was our
non-invasive equivalent of a tetanus experiment.
Recall that "tetanus" was the term for the disorder caused by
the clostridial toxin that cleaved synaptobrevin (vSNARE).
twitches summate (to tetanus)
Types of muscle (review) - best seen in turkey
slow, actually tonic, oxidative (and hence dark meat because of hemoglobin,
myoglobin and cytochrome)
fast fatigable, phasic, glycolytic
It is possible to stain, in this case for ATPase, to show mixed
muscle cells in a muscle (dark is slow, aerobic).
autonomic nervous system (controls smooth muscle and influences cardiac
Fig. 16.5 p. 357
In 1932, Sir Charles Sherrington won the Nobel
Prize. He originated our understanding of the motor unit..
(see also Fig (section opener))
One spinal motor neuron connects to several muscle cells scattered through
How many cells innervated depends on how fine vs gross the muscle's control:
13 muscle cells per nerve in extraocular muscle
1730 in calf
Fig. 16.2BC p 355
Motor unit pool - motor units to one muscle.
Spinal motor neuron cell bodies are labeled by injection of marker into
the muscle (soleus vs gastrocnemius)
Also (this is a different point) each motor neuron innervates only one type
(white meat, dark meat) of muscle.
Fig. 16.10 B p 363
Stretch reflex - simplest behavior
Ia sensory -> alpha motor neuron -> muscle
alpha motor neuron to striated muscle
gamma motor neuron to intrafusal muscle (fusimotor system) to preset stretch
on stretch receptor
Fig. 1.7 A,B p. 12
Fig 9.7A p 197
This pathway was also described for proprioception and in introduction
With inhibitory interneuron, there is an inhibition of the antagonistic
Up to and beyond fixed action pattersn (FAPs)
built up from complex of reflexes - with many other influences
Sir Charles Sherrington Integrative action of the nervous system (1906)
Prize (with Adrian) "discoveries regarding the function of neurons"
Fig. 16.14 p 367
how this integrates in spinal cord
crossed extensor reflex
Fig. 16.12 p 366
Golgi tendon organ
Fig. 16.13 p. 367
via Ib (slower than Ia) acts through inhibitory interneuron
to mediate the clasp-knife reflex -give up if stretch is too strong
More on the anatomy of the spinal cord
Fig. 16.3 p. 356
axial (proximal) vs distal muscles - medial vs lateral
flexors vs extensors - dorsal vs ventral
Fig3. A2 p. 719
Fig. A5A p. 721 (appendix)
cervical vs. lumbar enlargements
- for all the extra motor neurons for the arms vs legs respectively
Lou Gehrig's farewell speech
Amyoropic Lateral Sclerosis (ALS) Box 16.D
Lou Gehrig's disease
- he died in 1941 after playing baseball for the New York Yankees (retired
in 1939) and (until recently) holding the record for consecutive games played
a familial variety is on chromosome 21 and codes for copper/zinc superoxide
P. Aebischer & A.C. Kato, Playing defense against Lou Gehrig's Disease,
Scientific American, November 2007, pp. 86-93
Cells die from cell terminal back in to cell body
Interesting that bladder and eye movement spared
Most die in a few years, Physicist Stephen Hawkins lived 4 decades
Exam questions from 2005 - 2011 relating to this outline
How do dihydropyridine and ryanodine receptors interact to enable interaction
of sliding filaments?
calcium channel in t-tubule interacts with calcium channel in sarcoplasmic
reticulum for calcium release
How localized, to spinal segments, would you expect to find the alpha motor
neurons for a muscle like the gastrocnemius or the soleus?
might be spread over 5 segments
Say something about mototopic organization of motor neurons in the ventral
proximal muscles are medial, flexors are dorsal
You withdraw one supporting leg because you stepped on something painful.
What happens to the opposite leg's flexor?
it is inhibited via interneurons
Binding to troponin, helping with the release of vesicles at the "presynaptic"
membrane of the neuromuscular junction, release from sarcoplasmic reticulum.
Name a yet one additional location or channel for the action of calcium
ions in excitation ­p; contraction coupling.
T-tubules carry action potentials into cell with DHP calcium channels
The numbers 13 vs 1730 were given for extraocular vs gastrocnemius muscles
respectively (and explained in terms of muscles for fine vs gross movement
respectively). 13 and 1730 what?
Number of muscle cells (fibers) per motor unit (one spinal motor neuron)
For a Golgi tendon organ in the tendon of the biceps, answer either (1)
How would the muscle react from stimulation? Or (2) What is the sensory
Muscle is inhibited from contracting (via inhibitory interneuron); Ib
How is it that, in the knee-jerk reflex, the flexor is inhibited from contracting?
Through an inhibitory interneuron
I have located a spinal motor neuron for the triceps in the ventral horn.
Where should I look, relative to that cell, for neurons that would mediate
making a fist?
(using that diagram of making a muscle superimposed on the ventral gray
matter) lateral to that neuron
What do dihydropyridine and ryanodine receptors have to do with each other?
dihydropyridine in t tubules interact with ryanodine in sarcoplasmic reticulum,
Make a statement about how many different metabolic muscle types connect
to one motor unit.
each motor unit has only one metabolic type
How would you go about visualizing the cell bodies of all the spinal motor
neurons that connect to one muscle?
backfill from the nerve
Pick one: (1) What is the source of the signal that comes up the Ib afferent?
(2) What is the function of the signal that comes up the Ib afferent?
Golgi tendon organ, let go (as opposed to contract
What is the function of the enzyme deficient in familial amyotropic lateral
get rid of superoxide
What cells degenerate in ALS (amyotrophic lateral sclerosis, Lou Gehrig's
spinal motor neurons
Relative to adjacent areas, what would be more plentiful in the cervical
spinal motor neurons
In the ventral horn of the spinal cord, where are motor neurons controlling
the hand relative to those controlling the shoulders?
Where is the cell body for the stretch receptor involved in the monosynaptic
dorsal root ganglion
What are gamma motor neurons used for?
to preset stretch in intrafusal muscle fibers
The sensitivity for the reflex can be preset by the fusimotor system. What
type of nerve and what type of muscle are used in this efferent system?
gamma motor neuron to intrafusal system
What muscles are excited and inhibited in the crossed-extensor reflex?
ipsi + flexor to withdraw, - extensor, contra + extensor to support and
Consecutive muscle twitches that come close enough together in time fuse
to a steady and stronger contraction. What is this called?
One motor neuron connects to quite a few muscle cells. What is this called?
There's a muscle protein called "dystrophin." Why did they give
it that name?
it is the product of a gene that, if mutant, leads to Duchenne (or Becker)
Name a Ca2+ channel relevant to excitation-contraction coupling.
dihydropyridine receptor and ryanodine receptor (also synaptic calcium channel)
I compared 13 for extraocular muscle and 1730 for gastrocnemius. 13 and
muscle cells per neuron in a motor unit
In the knee-jerk reflex, the flexor is inhibited. How?
there is an inhibitory interneuron
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