9. Motor Systems Flashcards
Somatomotor function is the activation of ____ muscle fibers (including those of head and neck of pharyngeal arch origin).
Somatomotor function can be characterized based on whether a movement occurs ____ or ____ – typically, movements are combinations of both.
All necessary interconnections in the CNS for such somatomotor function share a common final segment – terminating in a ____ located in either ____ or ____
skeletal automatically deliberately LMN brainstem spinal cord
Voluntary contraction of skeletal muscle requires the interaction of 2 neurons:
• an ____ and
• a ____
- Recall that the ____ motor neuron causes muscle contractions which generate movement, whereas the ____ motor neuron, independent of concrete movement, regulates normal muscle tone.
UMN
LMN
alpha
gamma
Upper Motor Neurons in ____ (primary motor cortex)
Descending axons forming the cortical output from M1 arise from the ____ in cortical layer ____
M1
pyramidal cells
5
Upper motor neurons
Responsible for:
• the initiation of ____ movement
• the maintenance of muscle ____ for support of the body against gravity
• the regulation of ____ to provide a stable background upon which to initiate voluntary activity
voluntary
tone
posture
In the spinal cord, cell bodies of two 2 sets of LMNs are found in ____ of the ventral horn of the spinal cord:
• Alpha motor neurons innervate ____ fibers in skeletal muscle at neuromuscular junctions.
• Gamma motor neurons innervate ____ fibers (muscle spindles) in skeletal muscle.
Alpha (and gamma) LMNs in the cord always lie on the ____ side of the midline of the skeletal muscles innervated by their axons
lamina IX
extrafusal
intrafusal
same
Let’s examine somatic spinal and brainstem reflexes and the involuntary contraction of skeletal muscle
A ____ is any response that occurs automatically without conscious effort.
The neural pathway involved in accomplishing reflex activity is known as a reflex arc, which typically includes five basic components:
- ____
- Afferent pathway
- ____
- Efferent pathway
- ____
reflex
sensory receptor
integrating center
efferent organ
Very simple (involuntary) motor processes such as reflexes may be executed directly in the ____ (spinal reflex) or ____ without involvement of ____ in higher centers of the CNS
The simplest of these involuntary processes is the ____
spinal cord
brainstem
UMN
monosynaptic stretch reflex
Monosynaptic Reflexes
• An afferent neuron originating at a stretch-detecting receptor in skeletal muscle terminates directly on an efferent neuron innervating the same skeletal muscle - causing ____ to counteract the stretch
• The integrating center is the ____ synapse within spinal cord or brainstem between the afferent and efferent pathways. The output of this system (whether or not the muscle contracts in response to passive stretch) depends on the extent of ____ of EPSPs at the cell body of the efferent neuron.
- Stretch reflex is a ____ (“one synapse”) reflex because the only synapse in the reflex arc is the one between the ____ neuron and the ____ neuron and serves as the integrating center.
- All other somatic reflexes are ____
contraction single summation monosynaptic afferent efferent polysynaptic
MONOSYNAPTIC REFLEX ARC
Changes in muscle stretch
• Activates an ____ muscle spindle fiber, that…
• Inputs to a ____ afferent neuron in a DRG that…
• Excites an ____ motor neuron in the ____ horn of the same cord segment that…
• Produces muscle contraction
intrafusal
proprioceptive
alpha
ventral
Deep Tendon
Reflexes (DTRs)
in both upper and
lower extremities employ ____ reflex arcs to assess both afferent and efferent pathway components
As each DTR involves specific spinal cord segments, an abnormal reflex can help localize a lesion to a specific levels of the cord.
* \_\_\_\_ * Quadriceps * \_\_\_\_ reflex
DTR GRADING!
monosynaptic
patellar
knee jerk
Quadriceps
tendon reflex: ____
Calcaneal (Achilles) tendon reflex: ____
Biceps tendon reflex: ____
Triceps tendon reflex: ____
L3/L4
S1/S2
C5/C6
C6/C7
Review:
How does a muscle contract reflexively?
Reflex contraction of skeletal muscle requires:
• ____
• ____ neuron
• ____
Stimulus: Muscle ____
But note: UMNs have a net ____ effect on such reflexes act like “brakes”
muscle sensory LMN stretch inhibitory
Recall the Jaw Jerk reflex
NOTES!
YA
LMN Lesion:
• Suppressed deep tendon reflexes (____)
• Muscle tone ____
• Muscle ____
• Ipsilateral____ as muscle is limp and unable to contract
• Spontaneous ____
The symptoms of ____ results from a loss of LMNs in the ventral horn caused by poliovirus
hyporeflexia decreased atrophy flaccid paralysis fasciculation
poliomyelitis
UMN Lesion:
• Elevated muscle stretch reflexes (____)
hyperreflexia
POLYSYNAPTIC REFLEX ARC
Noxious cutaneous stimulus
Information from cutaneous receptors act via ____ to excite ____ motor neurons and stimulate muscle contraction
interneurons
alpha
A classic polysynaptic spinal reflex is the ____ intended to protect the body from painful, damaging stimuli
Stimulation of ____ and ____ induces rapid contraction of ____ muscles to withdraw the body part in under .5 seconds
withdrawal reflex
thermoreceptors
nociceptors
flexor
How does a muscle contract voluntarily?
Voluntary contraction
of skeletal muscle requires two neurons: ____ + ____
UMN cell body is ____ to the LMN
The UMN axon must cross the ____ as it descends from the brain to the LMN
LMN is ____ to the innervated muscle
UMN LMN contralateral midline ipsilateral
The pyramidal system originates in ____ cortex and controls ____ movement (voluntary motor activity)
It is the most important pathway for ____ motor function!
All three components • \_\_\_\_ • Corticonuclear (Corticobulbar) • \_\_\_\_ pass through the \_\_\_\_ from the telencephalon, continuing to brainstem or spinal cord.
Corticonuclear fibers are distributed to to the motor nuclei of the ____
Corticospinal fibers descend to pyramids of the ____ and below
Corticoreticular fibers terminate in the diffusely distributed ____ of the brainstem and are involved in postural control and locomotor function.
motor
conscious
voluntary
corticospinal
corticoreticular
internal capsule
cranial nerves
caudal medulla
reticular formation
Primary motor cortex in the precentral gyrus (M1) is also known as ____ (based on cytoarchitectonic studies).
Its upper motor neurons encode for the ____, force, and velocity of a movement, and control individual muscles used in the execution of ____, deliberate movements.
As you will recall,
the primary motor cortex is arranged ____…
brodmann’s area 4
direction
skilled
somatotopically
The precentral gyrus contains a ____, which is a distorted orderly map of the skeletal muscles controlled by upper motor neurons in the ____ limbs and trunk.
In the homunculus, upper motor neurons that control cranial nerve-innervated muscles are represented close to the ____.
____-innervated musculature and muscles of the ____ are most heavily represented in the homunculus.
Proceeding ____ on the lateral aspect of the hemisphere are upper motor neurons that control neck, upper limb, and trunk muscles.
On the ____ aspect of the hemisphere is an extension of the primary motor cortex containing upper motor neurons that control pelvic and lower limb muscles.
motor homunculus
contralateral
lateral sulcus
cranial nerve
hands
dorsally
medial
BUT muscle contractions induced by ____ in M1 are only a small aspect of complex movement - other cortical regions, such as ____, are involved in and help coordinate such motor activity…
In fact, of the roughly 1 million fibers in the corticospinal tract, only ____ arise from primary motor cortex:
____ arise from premotor cortex and ____ from the parietal lobe
UMNs premotor cortex 30% 30% 40%
Descending pathways convey the axons of these upper motor neurons directly to lower motor neurons via the ____, Corticoreticular and ____ tracts
corticospinal
corticonuclear (corticobulbar)
In the pyramidal system, axons leaving the cerebral cortex begin their descent toward the
brainstem by way of the
____
They then converge and descend through the ____ limb of the ____
corona radiata
posterior
internal capsule
