FORM & FUNCTION (Components of PNS)

Question 1

Functional organization of the NS:

Answer 1

1. Somatic
2. Autonomic

Question 2

Somatic:

Answer 2

-conscious afferent and efferent (ex. pain, temperature)
-voluntary motor control (ex. muscle)

Question 3

Autonomic:

Answer 3

-unconscious efferent
-involuntary motor control of internal organs to maintain homeostasis
*entirely EFFERENT

Question 4

Autonomic divisions:

Answer 4

-sympathetic
-parasympathetic

Question 5

Somatic afferents:

Answer 5

-sensory fibers from skin, muscle, joints, tendons

Question 6

Visceral afferents:

Answer 6

-sensory fibers from visceral organs
-some result in conscious sensations, but others do not
-NOT considered part of autonomic NS

Question 7

Components of PNS:

Answer 7

1. Nerves (bundles of nerve fibers)
2. Nerve endings
3. Ganglia (cell bodies): sensory vs. autonomic ganglia

Question 8

Myelination:

Answer 8

-speeds up the conduction of electrical impulses along axons

Question 9

Axons in CNS are myelinated by:

Answer 9

-oligodendrocytes

Question 10

Axons in PNS are myelinated by:

Answer 10

-Schwann cells
*each cell myelinates a single internode

Question 11

How is myelination formed?

Answer 11

1. Neurolemmocyte starts to wrap around a portion of an axon
2. N. cytoplasm and N. PM begin to form consecutive layers around axon
3. Overlapping inner layers of N. PM form the myeline sheath
   4.Eventually N. cytoplasm and N. nucleus are pushed to periphery of the cell as the sheath is formed

Question 12

How is an unmyelinated nerve fiber formed?

Answer 12

1. Neurolemmocyte starts to envelope multiple axons
2. Unmyelinated axons are enveloped by the neurolemmocyte, but there are no myelin sheath wraps around each axon

Question 13

Nodes of Ranvier:

Answer 13

-areas of myelinated axon that are not covered by myelin sheath

Question 14

Internode:

Answer 14

-area between two nodes

Question 15

Paranode:

Answer 15

-transitional zone of myeline sheath (ex. on either side of node)

Question 16

Connective tissue layers of PNS:

Answer 16

-endoneurium
-perineurium
-epineurium
*PNS nerve fibers are grouped into bundles to form nerves

Question 17

Endoneurium:

Answer 17

-surrounds axons

Question 18

Perineurium:

Answer 18

-surrounds axon fascicles
-blood-nerve barrier using tight junctions

Question 19

Epineurium:

Answer 19

-surrounds the entire nerve

Question 20

Mixture of myelinated and unmyelinated axons:

Answer 20

-most nerves in PNS are a mixture
-different functions and have different conductions speeds

Question 21

Rapid signal transmission axons:

Answer 21

-usually myelinated
Ex. sensory and motor pathways, somatic NS

Question 22

Unmyelinated axons commonly found in:

Answer 22

-autonomic nervous system
-slow signal conduction

Question 23

Nerve endings of PNS:

Answer 23

-afferent nerves
-efferent nerves

Question 24

Afferent nerves:

Answer 24

Contain sensory receptors
-free nerve endings
-encapsulated nerve endings

Question 25

Free nerve endings:

Answer 25

-most common
Ex. somatic and visceral sense of pain (nociceptors) and temperature (thermoreceptors)

Question 26

Encapsulated nerve endings

Answer 26

-ensheathed by a connective tissue capsule
Ex. mechanoreceptors in the inner dermis, proprioceptors in skeletal muscles

Question 27

Efferent nerves:

Answer 27

-innervate target organs
Ex. neuromuscular junction

Question 28

Neuromuscular junction:

Answer 28

-motor endplate
-synapse between motor neuron and muscle fiber

Question 29

Ganglia:

Answer 29

-part of PNS
-ovoid structures containing neuronal cell bodies and glial cells supported by connective tissues
-relay station to transmit nerve impulses
-sensory or autonomic

Question 30

Glial cells:

Answer 30

-satellite cells

Question 31

Sensory ganglion:

Answer 31

-the impulse travels toward the CNS
-located in cranial and spinal nerves

Question 32

Autonomic ganglion:

Answer 32

-the impulse travels away from the CNS
-controls involuntary movement
-2 neuron circuits of the sympathetic and parasympathetic NS

Question 33

Histological differences between autonomic and sensory ganglion:

Answer 33

1.Location of nucleus
-on side (autonomic) vs. center (sensory)
2. Size of neuron
-smaller (autonomic) vs. bigger (sensory)
3. distribution of Nissi substances:
-edge of cell (autonomic) vs. evenly distributed (sensory)