Peripheral Nervous System

Question 1

Simply describe CNS and PNS

Answer 1

CNS is the brain and the spinal cord

PNS is outside CNS, so spinal and cranial nerves.

Question 2

How many spinal nerves are there? Where are they located?

Answer 2

31 pairs total

8 Cervical (even though there are only 7 cervical vertebrae)
12 Thoracic
5 Lumbar 
5 Sacral
1 Coccygeal

Question 3

How many cranial nerves? Where are they associated with?

Answer 3

12 total associated with cerebral hemisphere.

I and II cerebral hemisphere
III-X and XII are associated with brain stem
XI arises from cervical part of spinal cord.

Question 4

What are ganglia?

Answer 4

Ganglia are a collection of nerve bodies that are associated with the PNS and are found outside the CNS.

Question 5

T/F Cranial nerves do not have a ventral or dorsal root?

Answer 5

True.

Instead they have a cranial nerve ganglia

Question 6

Two types of ganglia? and their subtypes?

Answer 6

Sensory - which can be in the spinal ganglia (dorsal root ganglia)or in the cranial nerve ganglia.

Autonomic or Motor (visceral) - which can be either parasympathetic or sympathetic.

Question 7

What type of neurons are sensory ganglia?

Answer 7

They are pseudounipolar neurons.

Question 8

In the spinal cord, where is white matter and where is grey matter?

Answer 8

Grey matter is on the inside.
White matter is on the outside

The white matter is made of myelinated nerve matter.

Question 9

In which portions of the spinal cord can you find the lateral horn?
Why is this structure significant?

Answer 9

The lateral horn can be found from sections T1 to L2.

This structure is important because it is the source of pre-ganglionic neurons for the autonomic nervous system.

Question 10

What are two trends with variation in the grey and white matter in the spinal column as you go down it caudally?

Answer 10

Generally white matter decreases as you go caudally (and it results in smaller spinal cord).

Also the shape of the cord goes from oval shape to circular.

presence of lateral horn at T1-L2

Question 11

What is the dorsal horn of the spinal cord? What type of neurons are found there? What does it do?

Answer 11

The dorsal horn is also known as the sensory horn. It receives and process incoming somatosensory information.
It does this in two ways, it can send information to the CNS, or it can send information to the anterior horn (via interneurons).

side note - there are only multipolar neurons in the spinal cord.

Question 12

What is an interneuron?

Answer 12

Interneurons are in the spinal cord. They transmit information form the dorsal horn to the ventral horn.

Question 13

What is the lateral horn? Where is it found?

What is another name for the lateral horn?

Answer 13

The lateral horn is the part of the spinal cord that contains the pre-ganglionic cell bodies of the autonomic nervous system.

It is only found in the T1-L2 sections of the spinal cord.

Another name for it is the intermediolateral cell column.

Question 14

What is the ventral horn? What types of neurons are found in it?

Answer 14

The ventral horn is also known as the motor horn.
It has two types of neurons, alpha and gamma motor neurons.

Alpha motor neurons are the larger of the two. These send their axons to extrafusal skeletal muscle fibers. These are also known as lower motor neurons.

Gamma motor neurons are the smaller of the two. These send their axons to innervate intrafusal fibers of neuromuscular spindle.

Question 15

What is the dorsal column?

Answer 15

The dorsal column is the dorsal part of the white matter of the spinal cord.
The dorsal column carries modalities of discriminative touch and proprioception.
It is mostly axons whose cell bodies are located in the dorsal root ganglia.

Question 16

What is the lateral column? Does it differ from ventral column?

Answer 16

The lateral column contains ascending nerve fibers as well as descending motor fibers.
The sensory fibers have origin from the dorsal horn of grey matter, while the motor neurons have origin from higher up, i.e. the brain stem.
The ventral column is essentially the same thing as the lateral column.

Question 17

What are two subdivisions of the PNS?

What structures are involved in each?

Answer 17

The somatic and the visceral nervous system.

The somatic nervous system is involved in innervating the body or rather the skin and skeletal muscle.
These have motor neurons in the ventral root, and sensory neurons in the dorsal root.

The visceral nervous system affects the organs and smooth and cardiac muscle.
The visceral nervous system works via the sympathetic ganglion (or rather paravertebral ganglion).
Visceral motor neurons go through the paravetebral ganglion, while vsiceral sensory neurons go thorugh the dorsal root ganglion.

Question 18

What are supplied by the dorsal and ventral rami?

Answer 18

The dorsal ramus supplies the deep muscles of the back

The ventral ramus supplies (essentially) the rest of the body.

Question 19

How are cranial nerves different from spinal nerves? What different types of cranial nerves can you have?

Answer 19

Cranial nerves are different from spinal nerves in the sense that they do not have ventral/dorsal roots or dorsal/ventral rami. Instead they have only sensory and parasympathetic ganglia.

Also cranial nerves can be divided into one of three types:
Purely Motor
Purely Sensory
or Mixed

It is important to note that cranial nerves do not have sympathetic ganglia. They only have sensory ganglia and parasympathetic ganglia.