Five Flashcards
What does the somatomotor system include? What is the difference between command and control components? What happens when a command component is damaged? Control? What is muscle tone? What are reflexes? What are 3 types of voluntary muscle movement, how are they developed, and generally where are the muscles located that perform them?
The somatomotor system includes all neural structures/systems responsible for the initiation and regulation of any movements occurring as the result of contraction of striated, skeletal, or voluntary muscles.
Clinically, damage to command structures generally results in the loss of movements (paralysis, paresis) whereas damage to control structures generally results in abnormal movements (ataxia, dyskinesia). Alteration in muscle tone and reflexes can also occur with damage to the motor system.
Tone – Static- Background Activity
Reflexes – Dynamic - Automatic Response to a Sensory Stimulus
Voluntary
- Postural Inborn Subconscious Axial/Proximal Muscles
- Stereotype Inborn Subconscious Axial/Proximal Muscles
- Highly Skilled Acquired Conscious Distal Muscles/Proximal/Axial M.
What is muscle tone? What are 2 types of abnormal muscle tone? What are 4 types of localization of abnormal muscle tone?
Resistance to Passive Lengthening of Muscle
- Normal
- Abnormal
- Increased – Hypertonicity - Spasticity / Rigidity
- Decreased – Hypotonicity - Flaccidity
- Localization
Segmental
Unilateral vs Bilateral
Antigravity Muscles (flexors upper limb, extensors lower limb)
All Muscles (agonist and antagonists)
What are reflexes? What are 2 types of motor reflexes? What are 3 types of abnormal statuses of muscle reflexes? What are they called? What are the 2 possible statuses of superficial cutaneous reflexes?
Automatic Motor Response to a Specific Sensory Stimulus
Types of Motor Reflexes
• Status of Muscle Reflexes
Normal
Abnormal
Absent - Areflexia
Diminished - Hyporeflexia
Exaggerated - Hyperreflexia
• Status of Superficial Cutaneous Reflexes
Normal
Abnormal
How are normal voluntary movements defined? What are 3 types of abnormal voluntary movements? What are 2 things to keep in mind concerning abnormal voluntary movements?
Normal
• Age Appropriate Strength and Speed
Abnormal
- Absent or Weak - Paralysis or Paresis
- Involuntary - Dyskinesia
- Uncoordinated - Ataxic
- Localization
- Type of Movements Affected
Which neurons can command the contraction of skeletal muscles? Where are they located? Where do their axons synapse? What is a synonym for them? Why are they called the final common pathway?
Lower Motor Neurons
• Spinal and Brainstem Motor Neurons Whose
Axons Enter the PNS and Synapse on Extrafusal Skeletal Muscle Fibers (motor end plate)
• Sole Connection Between CNS and Skeletal
Muscles - Final Common Pathway
• LMNs = alpha motor neurons Extrafusal
What is a motor unit? What determines how many muscle fibers are in a motor unit? Give examples of muscles that would have few fibers in the motor unit? That would have many?
The alpha motoneuron, its axon, and the muscle fibers it innervates form a motor unit. The number of muscle fibers within a motor unit varies considerably depending upon the delicacy or coarseness of the movement produced by the muscle. Thus, motor units in muscles involved in delicate movements, such as the extraocular, lumbrical, or interossei include less than a dozen muscle fibers. In contrast, motor units within muscles involved in coarse movements, such as the biceps, gluteus maximus, or soleus may contain as
many as a thousand fibers.
What are two disorders of the motor unit? Generally, what is the location of the movements they
Myopathy – Muscles Disorder
Proximal Movements
Neuropathy – LMN or Axon Disorder
Distal Movements
What do spinal LMNs control? Where are spinal LMNs located? What does the medial column innervate? What does the lateral column innervate? How are the lateral spinal LMNs somatotopically organized? Where is the lateral column largest?
Body muscles.
Spinal lower motor neurons are in medial and lateral cell columns in lamina IX of the anterior horn. The medial column innervates the axial muscles of the trunk and neck, whereas the lateral column supplies chiefly the limb muscles. The lateral column is largest in the cervical and lumbosacral enlargements. Lower motor neurons in the lateral
columns are somatotopically organized in respect to limb muscles. In general, the more lateral the lower motor neuron in the ventral horn, the more distal the limb muscles innervated by it.
What do brainstem LMNs control? Where is the nucleus ambiguus located? Which nerves does it control? Which muscles does it supply? Where is the hypoglossal nucleus located? Which muscles does it supply? Where is the motor trigeminal nucleus located? Which muscles does it control? Where is the abducent nucleus located? Which muscles does it control? Where is the facial nucleus located? Where is the facial nucleus located? Which muscles does it supply? Where is the oculomotor nucleus located? Which muscles does it supply? Where is the trochlear nucleus located? Which muscles does it innervate? Which are the only motor neurons that innervate a contralateral muscle?
Head and neck muscles.
The nucleus ambiguus, which extends through most of the medulla, gives axons that travel in the glossopharyngeal (IX), the vagus (X), and the cranial part of the accessory (XI) nerves to supply the skeletal muscles of the palate, pharynx, larynx, and upper esophagus. (lateral to hypoglossal)
The hypoglossal (XII) nucleus, which supplies the tongue muscles, is in the floor of the caudal part of the fourth ventricle. (medial to hypoglossal in medulla)
The motor trigeminal (V) nucleus (masticator nucleus) is at midpontine levels and supplies mainly the muscles of mastication.
The abducent (VI) nucleus, found in the caudal pons, supplies the lateral rectus muscle. (medial to facial)
The facial (VII) nucleus, located at caudal pontine levels, supplies chiefly the muscles of facial expression. (lateral to abducent)
The oculomotor (III) nucleus in the midbrain at the level of the superior colliculus innervates the superior palpebral, inferior oblique, and the superior, medial, and inferior recti muscles.
The trochlear (IV) nucleus, located in the midbrain at the level of the inferior colliculus, innervates the contralateral superior oblique muscle, the only lower motor neurons to innervate a muscle in the opposite side of the body. (caudal to oculomotor)
What are 4 reasons why reflexes are functionally important?
• Clinical Status of the Motor System
• Automatic Correction/Compensation to
Changes in Muscle Length and Muscle Tension
• Awareness of Limb Movements
Conscious (Proprioception) and Subconscious
• Protection
What is the most simple reflex pathway? What causes them to become more complex? What happens as they become more complex? What are two fundamental types of reflexes that cause contraction of skel. muscle? What determines which type they are?
Monosynaptic
More interneurons—>more complex (polysynaptic)—>more modifiable
Reflexes that cause contraction of skeletal muscle fibers are of two fundamental types depending upon the location of the sensory receptor in muscle or skin (muscle or cutaneous).
What are 2 things that can cause a muscle reflex?
What are 3 names for one of the things that can cause a muscle reflex? What are 2 names for the other thing? What are 3 examples of a cutaneous reflex?
Muscle – length or tension
Lengthening, Stretch or Myotatic or Deep Tendon • Patellar • Ankle • Biceps • Triceps
Shortening, Inverse or Golgi Tendon Organ
Cutaneous
• Flexor Plantar Response
• Flexor Reflex or Withdrawal Reflex
• Crossed Extensor Reflex
Where are muscle spindle cells located? What do they consist of? What is the morphological difference between nuclear bag cells and nuclear chain fibers? What 2 things are the muscle spindles innervated by and where? What does the muscle spindle sense? What type of afferent axons are connected nuclear bag fibers? What are its characteristics? What info do they transmit about stretch? Same questions for nuclear chain fibers? What do efferent gamma motor neurons do?
The Muscle Spindle and the Stretch Reflex
Embedded in parallel with large extrafusal skeletal muscle cells are specialized intrafusal muscle spindles that respond to stretch of that muscle (Fig. 2).
The encapsulated spindle consists of elongated intrafusal cells that contain contractile fibers only at the poles and a central non-contractile region containing the cell’s nuclei.
In some spindle cells the nuclei are closely grouped together at the center of the cell and are identified as nuclear bag fibers. In other spindle cells the nuclei are linearly aligned forming nuclear chain fibers.
Small diameter axons of gamma (γ) motor neurons synapse on the polar ends of the spindle cells and large diameter sensory afferent axons innervate the more central parts of the cells.
When a muscle stretches its embedded spindles stretch as well and conversely when the muscle shortens due to contraction the spindle becomes slack. An increase in muscle length is “sensed” by the spindle and this information is transmitted to the CNS by sensory afferent axons. Group Ia large diameter, heavily myelinated and rapid conducting
axons are the principal afferents to transmit information about changes in muscle length to the spinal cord. Generally nuclear bag fibers transmit information about the rate of stretch (group Ia, fast) and nuclear chain fiber report on the amount of stretch (group II, slow)
Under normal conditions the sensitivity of the muscle spindle is automatically maintained by the mechanism consisting of alpha-gamma co-activation. Higher motor centers command movements by the contraction of extrafusal muscle fibers by descending projections to alpha motor neurons. These pathways also activate homologous gamma motor neurons which then simultaneously activate the intrafusal muscle fibers to contract. When the extrafusal fibers contract and shorten, the spindles also shorten, thereby maintaining continuous responsiveness to stretch (Gamma Motor Innervation Resets Spindle Sensitivity)
What is the golgi tendon organ like morpho? What type of axon is involved? What kind of information does it transmit? How many interneurons are involved? What do they do? What is the purpose of the inverse stretch reflex?
Embedded at the musculotendenous junction are Golgi tendon organs. These receptors are oriented in series with the muscle and are responsive to muscle tension. The slender Golgi tendon organ consists of an encapsulated matrix of interwoven collagen fibers. A single Group Ib primary sensory axon is intertwined with the collagen fiber bundles.
Stretching the collagen fibers compresses the group Ib nerve endings and initiates the generation of action potentials transmitted centrally. Recordings from single Ib axons in humans have shown there is a direct correlation in the firing frequency of Ib fibers and the force generated by the contracting muscle (Tension)
The inverse stretch reflex is a disynaptic circuit: an excitatory sensory afferent neuron, an inhibitory interneuron and the excitatory alpha motor neuron. The inhibitory interneuron inserted between the excitatory sensory afferent and the motor neuron, however, results in a response just opposite to the monosynaptic stretch reflex. Activation of the Golgi tendon organ results in synaptic inhibition of the alpha motor neuron and concomitant relaxation of the muscle. This reflex is protective to prevent the development of supranormal muscle tension and possible skeletomuscular injury.
How is the stretch reflex tested? How is it graded? What is considered normal? What is abnormal? What is the babinski response?
The monosynaptic stretch reflex is tested clinically using a reflex hammer to tap a tendon, thereby quickly stretching the attached muscle. Skeletal muscle reflexes are qualitatively graded on a scale of 0-5 with scores of +2, and +3 being considered normal if symmetric and scores of 0 (areflexia), +1 (hyporeflexia) and +4 and +5 (hyperreflexia) being characterized as abnormal (Fig. 4).
Abnormal Cutaneous Reflexes
Following damage to motor pathways in the CNS the cutaneous flexor plantar reflex becomes abnormal with the large toe extending or dorsiflexing and the other toes fanning apart when the sole of the foot is stimulated. This abnormal cutaneous reflex is called the extensor plantar or Babinski response and is a hallmark sign of damage to the pyramidal system. In Figure 5 the downward curved arrows on each side indicate the normal flexor
plantar response. If an extensor plantar response is present the arrow would be up going in direction.
