Module 3 Lecture 1 Flashcards
___________ controls the vast majority of skeletal muscles
Spinal cord
_____________ controls neck and arm region
Cervical
_____________ controls the torso and leg
thoracic
________________ has pelvic control
lumbar and sacral
___________ controls and plans our movement
Motor cortex
______________ areas of the brain do not generate movements they smooth movements
coordinating areas
ex- basal ganglia, cerebellum, the visual system
_____________is how the brain organizes auditory information
auditory system
Consists of all the muscles and the neurons
that control them
motor system
• The motor control comes from
– The spinal cord (programs)
– The brain
• Somatic motor system
– Skeletal muscles (33 somites)
– Nervous system controls them
– Voluntary
It was widely accepted
that reflexes occurred as
isolated activity within a _________________
a reflex arc
Reflexes are ___________
integrative activities
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ shared the Nobel prize with Edgar Adrian in 1932 for their discoveries regarding the functions of neurons
Sir Charles Scott Sherrington
(1857-1952)
The Sherrington’s law
The brain commands and control the _________________
motor programs in the spinal cord.
______________
– Muscles of the trunk
– To maintain posture
• Axial muscles
_____________
– Muscles of the shoulders, elbows, thighs, and knees
– Locomotion
• Proximal muscles
________________
– Muscles of the hands, feet, and digits
– Manipulations of objects
• Distal muscles
__________________Innervated by alpha motor neurons
Roots form mixed spinal nerves
skeletal muscles
How many spinal nerves are there
31 nerves
C1-8: _______________
spinal nerves
T1-12: ___________
thoracic nerves
L1-5:_________________
Lumbar nerves
S1-5:___________________
sacral nerves
1:_____________________
coccygeal
C3-T1
Innervate _______________
about
50 muscles
Motor neurons that innervate the proximal and distal muscles are found mainly
in the cervical and lumbar-sacral segment.
Neurons innervating the
axial muscle are medial to
to those innervating the
appendicular
Neurons innervating flexors are dorsal to
those
innervating extensors
Lower Motor Neurons
- Alpha motor neurons
* Gamma motor neurons
• Typical motor neurons that innervate the muscle
cells
Alpha Motor Neurons
What are the three types of inputs to alpha motor neurons
- input from upper motor neurons in the brain
- sensory input from muscle spindles
- input from spinal neurons
Sir Charles Scott Sherrington
When a muscle is stretched, it __________
tends to contract
_____________ are traditional muscles
extrafusal
___________ are special sensory muscles
intrafusal
__________ a group of muscle fibers which are innervated by unique nerves
muscle spindle
______________ wrap around the
muscle fibers of the spindle in the middle
Group Ia sensory axons wrap
_____________ stops the muscle from over stretching. Over stretching prevents the cross bridge cycle from working
muscle spindle
over stretching prevents the
cross bridge cycle from working
_______________ never stop firing because their function is to relay length information
1a motor neurons
Muscle spindles provide protection against overstretching because of ___________________________
1a sensory neurons which innervate alpha neurons causing contraction
What happens when you put weight on a muscle and the muscle lengthens
1A sensory neurons fire more than normal and they tell alpha motor neuron to control mechanism of firing
what makes 1a axons fast firing
more myelination and wider diameter
Group Ia Axons • Thickest myelin • Enter via the \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ • Synapse with \_\_\_\_\_\_\_\_\_\_\_\_\_ – Lots of synapses
dorsal root
interneurons and alpha motor
neurons
____________ gated channels on the 1A sensory motor neurons
stretch gated channels
-works when membrane is stretched open causing depolarization and action potentials
give an example of muscle mechano receptors
the knee jerk reflex. When tapping the tendon, the muscle briefly stretches
muscle spindles are inside the muscle and thus have specific
origin and insertion
When alpha motor neurons innervate the
extrafusal muscles, the _________.
As a result, the spindle becomes _________
The Ia sensory, will ________________
muscle contracts
slack (not stretched)-
not send a signal anymore
• Gamma MNs innervate___________________
specialized muscle fibers
within the spindle called intrafusal muscle fibers
__________________are located at the two ends of the
spindle
Gamma MNs
Feedback Loop (Homeostasis) • Control center: – Set point:\_\_\_\_\_\_\_\_\_\_\_\_\_ • Receptor: \_\_\_\_\_\_\_\_\_\_ • Effector: \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
a desired muscle length
Ia axons
alpha motor neurons and extrafusal fibers
Gamma Loop
• The gamma MN activity influences ________________________ if we are outside the
set point
the alpha motor neuron activities
• During most normal movements, alpha and
gamma motor neurons are
simultaneously
activated
________ controls th homeostasis loop
cerebellum
___________ when the muscle spindle is not parallel to extrafusal muscle. Brain is not sure about what is going on
hypotonia
___________
– Fiber is 50-100 um wide
– Fiber is 2-6 cm long
– Muscle has 103 – 109 fibers
– Muscle is controlled by about 100 alpha motor
neurons
– Alpha motor neuron innervates about 100-1000
muscle fibers
– A muscle fiber is innervated by only one alpha
motor neuron
• Extrafusal
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ – Known as muscle spindles – Embedded in the extrafusal fibers – A spindle consists of 8-12 muscle fibers – Sensory axon wraps around them – Continuously monitors length of muscle – Used for feedback control of movement – Innervated by gamma motor neuron
Intrafusal
When Do We Use the Ia Sensory?
always
when are the 1a sensory so valuable
- in extreme situations
- tight rope walking and extreme balance
what is the formula for gain
contraction/ stretching
Shared the Nobel prize with Cajal in 1906 in recognition
of their work on the structure of the nervous system
camillo Golgi
Golgi tendon organs:
When the muscle contracts, the_____________ fire action potential
sensory 1b axons
____________ is located in the tendon of the insertion muscle
Golgi tendon organ
The Ib sensory neuron may protect the muscle from being _____________
However, its normal function is to ________________
overloaded.
regulate muscle tension within an optimal range.
The 1b axons do not communicated directly with the alpha Motor neurons, it goes through ______________
an inhibitory neuron
Scottish surgeon and artist Charles Bell
showing a man in the throes of tetanus caused by
bacteria in the inhibitory neurons
activity of muscle spinal has nothing to do with the activity of
Golgi tendon
muscle spindle located in __________ to extra fusal muscles
series
Golgi tendon located in __________ to extra fusal muscle
parallel
What are the three Inputs to Alpha Motor Neurons:
Interneurons
- Upper motor neurons in brain
- sensory input from muscle spindles
- input from spinal neurons
Most of the innervation to the alpha motor
neurons comes from _______________
interneurons of the spinal
cord
Spinal interneurons receive inputs from
(3 places)
– Primary sensory axons
– Descending axons from the brain
– Collaterals of lower motor neurons axons
• Spinal neurons can form
– Inhibitory synapses
– Excitatory synapses
Spinal neurons can form
–_____________ (reciprocal inhibition)
–____________ (flexor withdrawal reflex and
cross extensor reflex)
inhibitory
excitatory
Flexor reflex
– Its speed depends on how ___________
painful the stimulus is
flexor reflex:
– The direction of the reflex depends on the
______________
location of the stimulus
flexor reflex:
– Slower than the ___________
stretch reflex
flexor reflex
– Activated by Aδ nociceptive axons that enter the
spinal cord and branch profusely and enter
_______________
different segment of the spinal cord
• Flexor reflex
– Nociceptive axons act on excitatory interneurons
that excite alpha motor neurons of ____________________
the flexors of the affected limb
flexor reflex
– At the same time, they activate the inhibitory
interneurons that synapse on the ______________
alpha motor
neurons of the extensors
___________ activates the same muscle intending to move
muscle tendon
_________ activates the opposite muscle intended to move
Golgi tendon
Aδ nociceptive axons __________
branch profusely
reflexes are helpful in
motor skills
• Root reflex: corner of the mouth
helpful for breast feeding
• Babinski reflex is the
toe fanning of a baby
The cross extensor reflex is the building block
for ____________
locomotion
Local circuits within the spinal cord
– Central pattern generator
– Neurons with pacemaker properties
– Able to control the timing and coordination
In bipeds, the movement of a single limb is a
cycle of _____________
two phases
Phase I:____________
• Limb is extended in contact with the ground to propel
forward
stance phase
Phase II: ___________
Limb is flexed to leave the ground and brought forward
swing phase
Locomotion is accomplished by ___________
higher centers
in the brain
Decerebrate prep: spinal cord and brain stem isolated by cut at “a” Animal can still walk on a treadmill
Spinal prep: cut at “b”
isolates hind limb spinal
segments yet animal can
still walk on a treadmil
Deafferented prep: yet
animal can still walk on a
treadmil
Conclusion
In conclusion, locomotion
– Is not dependent on sensory input
– Not dependent entirely on higher centers in the
brain
– It is dependent on spinal cord neurons that exhibit
a central pattern generator rhythm
_________
- work on their own
- have their own action potentials
central pattern generators
compare cpg vs reflex
CPG: does not rely on sensory information as much
Reflex: rely on sensory information
