peripheral nervous system Flashcards
Explain peripheral nerve origination and fucntion:
VE
SE
SA
- Visceral Efferent = from lat. horn = motor for vessels.
- Somatic efferent = from Ant. horn = motor for muscles
- Somatic Afferent = from post. horn = sensory for skin and muscles
Peripheral nerves have 3 meningeal coverings….describe each….
- Epineurium = outer most layer. most prominent around nerve trunks, provides tensile strength and is continuous with dura.
- Perineurium = middle layer. continuous with arachnoid and is blood-nerve barrier
- Endoneurium = innermost layer. surrounds individual nerve fibers.
Myelin is produced by____ in the CNS and by ______ in the PNS.
- Oligodendroglia
- Schwann cells
- Myelin is the cell membrane of both of these.
What is the node of ranvier?
An unmyelinated portion of axon between myelinated portions in the CNS, or the interface between successive myelin segments in PNS.
*Local anesthetics can act at the nodes.
Describe the 3 steps of salatory conduction:
- Membrane depolarization occurs at nodes.
- Depolarization renewed at next node.
- Conduction proceeds in either direction.
* Basically jumping from Node to node increasing velocity.
6 types of receptors:
- Chemoreceptors = taste, smell, pH metabolite concentrations.
- Photoreceptors = Retinal visual receptors.
- Thermoreceptor = Temperature
- Mechanoreceptors = respond to physical deformation, touch, muscle length & tension (auditory, vestibular receptors.)
- Nociceptor = pain!
- Porprioceptors (joints, muscle spindles)
Receptor potentials do what?
Encode intensity & duration of stimuli. Some are more sensitive than others and so they can reflect increased intensity.
What does receptor field do?
conveys info about the location of a stimulus, “wiring” patterns in ascending sensory pathways to cortex preserve location and nature information
All receptors can adapt except _______.
Nociceptors!
What are rapid adapting receptors?
Receptors that can adapt a lot…lol *pacinian corpuscles & hair follicles.
What are slow adapting receptors?
Only adapt a little & detect static position. * Muscle spindles
2 types of encapsulated receptors:
- Muscle spindles = detect muscle length!
(numerous in all skeletal muscle. Consists of a few small muscle fibers within a capsule around the middle third of the fibers. - Golgi tendon organs = detects Muscle tension!
(Consists of collagen bundles with sensory fibers that are surrounded by capsule, which when distorted stimulates the fibers.)
The spinal cord is organized into 31 segments, what are they?
8 cervical
12 thoracic
5 lumbar
5 sacral
1 coccygeal
_______ is the caudal end of spinal cord.
Conus Medullaris
The two regions on the Conus medularis are:
- Cervical enlargement = C5-T1 (neurons that supply the upper extremities)
- Lumbar enlargement = L2-L3 (neurons that supply the lower extremities)
______ enter the cord in the posterolateral sulcus.
Dorsal rootlets.
*FUN FACT: rootlets coalesce to form dorsal roots that each have a Dorsal root ganglion that contains bodies of SENSORY NEURONS.
_______ leave the cord from the anterolateral sulcus.
Ventral rootlets
*ventral rootlets coalesce to form ventral roots.
Describe spinal cord connectivity of sensory, motor and reflexes….
Sensory = afferent fibers enter cord via dorsal roots (Stay ipsilateral) and may terminate in post horn or ascend to medulla.
Motor = motor neurons located in anterior horns, leave cord thru ventral roots, activity modulated by defending fibers from rostral structures.
Reflexes = stereotyped motor outputs, involve neural circuits contained in cors
The posterior intermediate sulcus is present in what two cross-sections of spinal cord?
Cervical and Thoracic.
Describe the spinal cord gray matter of the posterior horn…
- Consistes of mostly interneurons
- contains substantia gelatinosa (Pain & Tempature)
- contains Lissauer’s tract (finely myleniated & unmyleinated fibers.
Describe spinal cord gray matter of the Anterior horn….
- contains motor neurons that control skeletal muscle ( known as lower motor neurons or alpha neurons)
- Contains Gamma -motor neurons, innervate muscle spindles.
- Two specialized columns in anterior horn at cervical levels.
1. Spinal accessory nucleus (caudal medulla to c5) CNXI
2. Phrenic nucleus, innervates diaphragm (c3,4,5)
Describe intermediate spinal cord gray matter..
- Preganglionic sympathetic neurons all in T1-L3. (Clarke’s nucelus found of medial surface of intermediate matter from T1-L2)
- S2-S4, sacral parasympathetic nucleus.
- Axons leave via anterior roots and supply pelvic viscera.
- Relay nucleus for transmission of info to cerebellum, proprioceptive info from leg
All reflexes involve interneurons except ________ reflex.
Stretch
Briefly describe the stretch reflex…
Simplest, monosynaptic so only 2 neurons and one synapse between them.
*believed to be important during movements and maintaining posture.
_______ can inhibit motor neurons/stimulated muscle.
Muscle tension /Golgi tendon organ
What 6 arteries are associated with blood flow to the spinal cord?
- Subclavian artery –> Vertebral artery—-> Anterior Spinal artery.
- Anterior spinal artery —> Radicular artery, Great vertebral radicular artery(Adamkiewicz) & Lumbar artery.
*Corona artery communicates Anterior spinal artery with Posterolateral artery
