Intro To Nerves, Plexuses DLA

Question 1

What is the central nervous system?

Answer 1

Brain and spinal cord

-Receives information from and sends information to the body serves as the central control unit

Question 2

What is the PNS?

Answer 2

Everything out of the CNS

The pathways (nerves) that communicate from the body structures to the CNS and vice versa

Question 3

What are the components of the nervous system?

Answer 3

Autonomic nervous system
The ‘autonomic’ control of the body

Contains both central and peripheral components

Somatic- relating to the body (muscles, skin, bones)

Visceral-relating to the organs (heart,vessels, digestive etc.)

Question 4

What are the components of the CNS

Answer 4

Brain

Spinal cord

Question 5

What are the components of the peripheral nervous system?

Answer 5

Spinal nerves (31 pairs)- from spinal cord

Cranial nerves(12 pairs)- from brain and brain stem

Somatic nerve plexuses

Visceral nerve plexuses

Enteric nerve plexuses

Sensory nerve plexuses

Autonomic nervous system sympathetic-fight or flight
Parasympathetic- rest and digest

Question 6

What are the two types of tissue that makes up the internal arrangement of the spinal cord?

Answer 6

Made up of two types of tissue:
- Inner gray matter (nuclei)- cell bodies of neurons and glial cells

-Outer white matter(tracts)- myelinated axons, neural ‘highways”

Question 7

What are the segments of the spinal cord?

Answer 7

Cervical, thoracic, lumbar, sacral and coccygeal

Question 8

Neural cell bodies of the same function…

Answer 8

Are collected in the same area

Question 9

What are tracts?

Answer 9

Composed of axons that serve the same function and travel in the same direction

Question 10

Explain the general concept of afferent fibers arrangement

Answer 10

The general arrangement is a three neuron chain

First order arises at the organ and has two processes, one on either side of the cell body

The cell body is located in a ganglion located outside of the CNS (spinal cord/ brainstem) synapses on the next neuron in the chain

The second order arises from thee grey horn of the spinal cord or brainstem nucleus and synapses in the thalamus.

The third order arises from the thalamus and ends in the cortex

Olfactory is an exception as the thalamus is one of its elements

Question 11

Describe the general arrangement of motor fibers

Answer 11

The general arrangement is a two neuron chain

The first (upper motor neuron-UMN) arises in the cortex and synapses in the ventral horn of the spinal cord or in the brainstem on the nucleus of the corresponding cranial nerve.

The second (lower motor neuron-LMN)- arises from the brainstem nucleus and ends in the muscle it supplies

Question 12

How are sympathetic efferent fibers different from motor system?

Answer 12

Similar. To motor system but synapses at the sympathetic chain

Question 13

How are parasympathetic fibers different from the motor system?

Answer 13

Similar to the motor system but synapses in the parasympathetic ganglion

Question 14

Where does the spinal cord start and end? Where does it start and end?

Answer 14

Spinal cord begins at medulla oblangata (foramen magnum) ends at vertebral level L1-L2 (conus Medilarus)

Two enlargements: cervical & lumbar regions

Question 15

What are the 31 spinal nerve pairs?

Answer 15

8 cervical (C1-C8)

12 thoracic (T1-T12)

5 lumbar(L1-L5)

5 sacral (S1-S5)

1 coccygeal (Co1)

Question 16

What is the cauda equina?

Answer 16

Horses tail

Spinal nerve roots that exit from the lumbar and sacral region travels in the lumbar cistern towards their respective exit points from the vertebral canal

Question 17

Where are sensiry neurablast found?

Answer 17

In DRG forming primary sensory nerves

Question 18

Where are motor neurobkast?

Answer 18

Motor neuroblast (from basal plate of intermediate layer) forming somatic motor neuron

Motor neuroblast (from basal placate of intermediate layer) forming visceral motor neuron (pre-ganglionic sympathetic)

Motor neuroblast (from neuracrest) forming visceral motor neuron (post-ganglionic sympathetic) in sympathetic chain ganglion

Question 19

A spinal nerve and it’s branches contain ….

Answer 19

Mixed fibers (sensory/motor/autonomic)

Question 20

Explain the typical spinal nerve course

Answer 20

Dorsal (posterior) ramus- supplies intrinsic back muscles (motor) and skin over that area(sensory)

Ventral (anterior) Ramus- supplies all other muscle (motor) and skin over that area (sensory)

Sympathetic chain ganglia run down the length of the vertebral bodies (bilateral)

Sympathetic chain ganglia communicate with spinal nerve via grey (unmyelinated) and white (myelinated) rami communicants

Question 21

What is a plexus?

Answer 21

A network of intersecting nerves from different levels or sources that combine to form new nerves with specific targets

Question 22

What are the somatic plexuses?

Answer 22

Form from the ventral rami of spinal nerves

C1-C5= cervical plexus

C5-T1= brachial plexus

L1-L4= lumbar plexus

L5-S4= sacral plexus

Combination of somatic sensory, somatic motor and sympathetic nerve fibers

Question 23

What are types of the visceral plexuses?

Answer 23

Combination of sympathetic, parasympathetic and visceral afferent fibers
E.g., hypogastric, celiac

Question 24

What is the significance of a somatic plexus?

Answer 24

Muscles are formed from several myotomes

• Since myotomes are supplied by nerves that develop from the same segments
• The plexuses form to supply the muscles
• The plexuses are subject to much variation
• As a result, injury doesn’t necessarily lead to the expected clinical picture

Question 25

Where are the receptors of the somatic nervous system?

Answer 25

Conscious sensation: pain, pressure, touch, temperature, proprioception

Question 26

Where are the visceral receptors for the visceral PNS?

Answer 26

Organs and tissues

Distention, inflammation, ischemia, physiological changes (eg decreased oxygen and increased CO2), Abnormal muscle spasm