Neuro - Descending Motor Systems Flashcards
What is a lower motor neuron?
- innervates striated muscles
- last neuron in chain of neurons
- includes A-alpha and A-gamma motor neurons
What are the signs and symptoms of a lower motor neuron lesion?
- atonia - loss of muscle tone
- areflexia - loss of myotatic (knee jerk) reflex
- flaccid paralysis - no muscle tone; patient cannot contract the muscle
- fasciculations - spontaneous muscle contractions
- atrophy - loss of muscle tissue
What are the signs and symptoms of a upper motor neuron lesion?
- spastic paralysis
- hypertonus (flexors of arms and extensors of leg)
- hyperreflexia - exaggerated knee jerk reflex
- negative plantar reflex (Babinski sign) - abnormal reflex on the bottom of the foot so when the foot is stroked, the toes curl upward
- atrophy of disuse
What is spastic paralysis?
chronic pathological condition in which the muscles are affected by persistent spasms and exaggerated tendon reflexes because of damage to motor nerves of the central nervous system
What is a flexor reflex?
- also called withdrawal reflex
- input from cutaneous receptor travels to the spinal cord and synapses with an alpha motor neuron via an interneuron
- for example, put your hand on a sharp needle and your arm pulls back quickly
What is a myotatic reflex?
- stretch spindle in the muscle is stretched
- A-alpha sensory fiber goes up to the dorsal horn of the spinal cord
- in a monosynaptic synapse, the A-alpha sensory fiber synapses directly with the alpha motor neuron
- alpha motor neuron goes back to the muscle to stimulate the motion
What is the neuroanatomical significance of the internal capsule?
a section of white matter in the brain that contains the axons descending from the motor cortex; part of the corticospinal (pyramidal) tract
What is the role of the periaqueductal gray? What are the side effects?
- deep brain stimulation and control of pain
- side effects: abnormal eye movements, smothered feeling, bladder fullness, nausea, vertigo, increased or decreased blood pressure
What is the neuroanatomical significance of the cerebral peduncle?
section of the midbrain carrying the motor neurons from the internal capsule to the basilar pons; part of the corticospinal (pyramidal) tract
What is the neuroanatomical significance of the pyramids?
section in the medulla that contains the descending motor neurons; also the site of decussation in which the neurons cross-over to the other side; part of the corticospinal (pyramidal) tract
What is the neuroanatomical significance of the posterolateral spinal cord?
(?)
What is the origin, termination, and function of the corticobulbar tract?
- origin - cortex
- termination - brainstem
- function - controls the muscles of the face, head, and neck by innervating the nuclei for CN V, VII, XI, and XII (and IX and X via the nucleus ambiguous)
What is the origin, termination, and function of the corticopontine tract?
- origin - cortex
- termination - basilar pons
- function - innervates the nuclei for CN V, VII, and XII
Identify the effect on leg and arm muscles of the activation of the corticospinal tract.
- extensor muscles in upper extremity
- flexor muscles in lower extremity
- control of hand musculature (primary effect!)
Identify the effect on leg and arm muscles of the activation of the rubrospinal tract.
control of proximal arm and leg musculature
