Peripheral Nervous System Flashcards
What is the PNS?
Peripheral nervous system contains nerves that originate in the brain and spinal cord but end peripherally.
Consists of motor, sensory, and autonomic neurons that innervate end-organs That include sensory receptors, muscles, and glands
T or F: The PNS consists 8 cranial nerves and 20 pairs of spinal nerves and all associated with ganglia and sensory receptors
False: the PNS consists of 12 cranial nerves and 31 pairs of spinal nerves and all associate with ganglia and sensory receptors
Where do sensory nervers originate?
Dorsal root ganglia
where do motor nerves originate?
Anterior horn of the spinal cord
What is the autonomic system divided into?
Sympathetic and parasympathetic nerves.
Where do the sympathetic nerves originate ?
Lateral horn of the thoracic spinal cord
Where do the parasympathetic nerves originate?
From the lateral gray matter of the sacral level of the spinal cord and from the brain stem itself
How are peripheral nerves typically classified?
By axon diameter and speed of conduction
List teh Sensory End-organ Receptors.
- Thermoreceptors
- Nociceptors
- Mechanoreceptors: Merkel’s disc, Ruffini’s corpuscle, Pacinian corpuscle, muscle spindle, free nerve endings, Golgi tendon organ (GTO)
- Chemoreceptors
- Photoreceptors
Axon
Projection of a nerve AWAY from the cell body that conducts impulses
Dendrite
An extension of the cell body that receives signals from other neurons
Endoneurium
Innermost covering of a peripheral nerve that surrounds each individual axon
Epineurium
Outermost covering of a peripheral nerve that surrounds the entire nerve and provides a buffer for the peripheral nerve
Motor unit
Single motor neuron and all of the muscle fibers that it innervates
Myelin
Proteins and lipids that form to crate a sheath around particular nerves; increases conductivity of the nerve impulse
Nerve conduction velocity
Measures the speed of a nerve impulse along the axon of a nerve
Neurons
Nerve cells that receive and send signals to other cells; comprised of a cell body, acon, and dendrites
Nodes of Ranvier
Brief gaps in myelination of an axon; serves to facilitate rapid conduction of a nerve impulse via jumping from gap node to gap node
Perineurium
Middle layer of covering surrounding hte peripheral nerve that envelopes fascicles or groups of axons and maintains the blood-nerve barrier
Saltatory conduction
An action potential moving along an axon in a jumping fashion from node to node; decreases the use of sodium potassium pumps and increases the speed of conduction
Schwann cell
Cells that cover the nerve fibers within the peripheral nervous system and fore the myelin sheath
Describe A Fibers.
- Large fibers
- Myelinated
- High conduction rate
What are the types of A Fibers?
Alpha
Beta
Gamma
Delta subsets
Describe an Alpha fiber.
(A fiber)
Alpha motor neurons, muscle spinal primary endings, GTOs, touch
Describe a Beta fiber.
( A fiber)
Touch, kinesthesia, muscles spindle secondary endings
Describe a gamma fiber
(A fiber)
Touch, pressure, gamma motor neurons
Describe a delta fiber.
(A fiber)
Pain, touch, pressure temperature
The sensory components of an A fiber include?
- Muscle spinal (primary afferent endings): primary for low-threshold stretch
- Muscle spinal (secondary afferent endings): receptors that respond to changes in length
- Golgi Tendon organ: responds to tension/stretch of a tendon
Describe B fibers.
- Medium fibers
- Myelinated
- Reasonably fast conduction
- preganglionic fibers of the autonomic nervous system
Describe C Fibers.
- Small fibers
- poorly Myelinated or unmyelinated
- slowed conduction rate
- postganglionic fibers of the sympathetic system
- exteroreceptors for pain, temperature, and touch
