Neuro - Peripheral Nerves Flashcards
Name each of the four functional components found in a peripheral nerve and describe their functions.
- somatic afferent - pain, touch, temperature, and position sense
- somatic efferent - motor signals that control striated muscles
- visceral afferent - “visceral sensibility” like peristaltic activity, blood pressure, bladder fullness, etc.
- visceral efferent - autonomic nervous system; two neurons linked together
What tissues are innervated by somatic afferent neurons?
skin (pain, touch, temperature, conscious proprioception, awareness of limb position)
What tissues are innervated by somatic efferent neurons?
striated (voluntary) muscles
What tissues are innervated by visceral efferent neurons?
contraction of smooth muscle and secretion of glands; preganglionic and postganglionic neuron chains
What tissues are innervated by visceral afferent neurons?
organs to monitor internal environment like heart rate, blood pressure, smooth muscle contractility, and bladder/bowel fullness
What is the location of the preganglionic nerve cell bodies? The postganglionic nerve cell bodies?
- preganglionic - nerve cell body in CNS; axon extends to autonomic ganglion
- postganglionic - nerve cell body in autonomic ganglion; axon extends to visceral target
What are the functional components and target tissue of nerve fibers found in the posterior root?
- functional component - sensory (somatic afferent and visceral afferent)
- target tissue - skin, internal organs
What are the functional components and target tissue of nerve fibers found in the anterior root?
- functional component - motor (somatic efferent)
- target tissue - striated muscle, internal organs
What is the functional component and target tissue of nerve fibers found in the posterior ramus?
- functional component - sensory and motor
- target tissue - back
What is the functional component and target tissue of nerve fibers found in the anterior ramus?
- functional component - sensory and motor
- target tissue - anterior and lateral body as well as limbs
What is the function and relative speed of an A-alpha afferent nerve fiber?
- function - myotatic reflex
- velocity - 70-120 m/sec
What is the function and relative speed of an A-beta nerve fiber?
- function - deep touch
- velocity - 60-80 m/sec
What is the function and relative speed of an A-delta nerve fiber?
- function - light touch, fast pain
- velocity - 10-30 m/sec
What is the function and relative speed of a C nerve fiber?
- function - slow pain
- velocity - 0.5-2.5 m/sec
List the events seen during the degeneration of a nerve fiber.
- if an axon is crushed (or cut), the axon distal to the crush will degenerate
- the axon proximal to the crush will die back a short distance
- the cell body will respond by becoming more metabolically active (chromatolysis)
- the axon and myelin degenerate (but not Schwann cells) and macrophage cells engulf the debris
List the events seen during the regeneration of a nerve fiber.
- axons sprout and exhibit growth cones
- Schwann cells undergo mitosis and form guiding route for the growth cone
- Schwann cells produce new myelin
- greater number of Schwann cells means: shorter internodal distance and slower conduction time
What is the “knee jerk” reflex? How does it work? How is it modified?
- when the muscle is stretched (by hitting the knee), the neuromuscular spindle is also stretched
- A-alpha sensory fiber conducts stretch signal back to spinal cord
- sensory fiber has a single synapse with an alpha motor neuron which moves the extrafusal muscle fibers to move the limb
- this is monosynaptic and cannot be modified
What is the lower motor neuron?
the nerve cell body (located in the CNS) and its axon (located in the PNS) that innervates a striated muscle
What are the signs and symptoms of a lower motor neuron lesion?
- flaccid paralysis
- atonia - loss of normal muscle tone
- areflexia - loss of the stretch (myotatic) reflex
- fasciculations - spontaneous contraction of bundles of muscle fibers
- muscle atrophy
A lower motor neuron lesion results form a lesion of what?
- peripheral nerve
- anterior root
- anterior horn motor neurons
What is muscle tone?
slight contraction of the muscles that does not produce movement or active resistance, but gives the muscles firmness, assisting the stability of joints and the maintenance of posture
What is the neuroanatomical basis of muscle tone?
the activation of the gamma and alpha motor neurons
What are the functional components and target tissue of nerve fibers found in the anterior root?
- functional component - motor (somatic efferent)
- target tissue - striated muscle, internal organs
