Nerves

Question 1

What is a neuron ?

Answer 1

A neuron is a functional unit of the nervous system

Question 2

What is the basic structure of a neuron ?

Answer 2

A neuron has cell body, dendrites and axon, axon hillock

Question 3

What are the three major types of neuron ?

Answer 3

bipolar, multipolar, and pseudounipolar

Question 4

Draw the three main types of neuron

Answer 4

-

Question 5

What is myelin ?

Answer 5

Myelin is lipid and protein substance. Secreted by Schwann cells (glial cell) around some axons in the PNS. Produced by Oligodendrocytes in the CNS. For neurons having an myelin sheath increase velocity of impulse conduction (insulation).

Question 6

What are the membranes which wrap around a nerve cell ?

Answer 6

The first covering is the epineurium then the perineurium and finally the endoneurium

Question 7

What is the blood supply to the nerves called?

Answer 7

The blood supply for the nerve is called the vase nervorum.

Question 8

what is a dermatome ?

Answer 8

Area of skin supplied by a single spinal nerve

Question 9

what is a myotome ?

Answer 9

Part of muscle supplied by a single spinal nerve. One muscle myotome may involve multiple spinal segments. Useful to test motor or sensory loss of one or more spinal nerves/segments by testing joint movement or an area of skin

Question 10

what is a motor unit ?

Answer 10

muscles fibres supplied by one motor neuron

Question 11

What are motor unit end plates ?

Answer 11

The neuromuscular junction. Where the axon meets the muscle.

Question 12

How many pairs of cranial nerves are there ?

Answer 12

12

Question 13

How many pairs of spinal nerves are there ?

Answer 13

31

Question 14

Describe the path of a nerves signal through the spinal chord

Answer 14

Sensory information detected by the sensory neurons and passed along the rami.
Signal enters the dorsal root and moves into the spinal chord.
Moves through the CNS
Enters a motor neuron and moves out through the ventral root
Moves into the rami
Connects with a NMJ

Question 15

What does the rami contain ?

Answer 15

Both sensory and motor neurons

Question 16

What does the dorsal root contain ?

Answer 16

Sensory nerves

Question 17

What does the ventral root contain ?

Answer 17

Motor nerves

Question 18

Which part of the vertebrate does the rami run through ?

Answer 18

Runs through the intervertebral foramen

Question 19

What two groups can our peripheral nerves system be divided into ?

Answer 19

Somatic (Voluntary)

Autonomic (Involuntary)

Question 20

What is the somatic nervous system used for ?

Answer 20

Regulating voluntary control of body movements

Question 21

What can the autonomic nervous system be divided into ?

Answer 21

Sympathetic

Parasympathetic

Question 22

What is the sympathetic nervous system used for ?

Answer 22

‘fight or flight’ responses.

Question 23

What is the parasympathetic nervous system used for ?

Answer 23

rest and digest responses

Question 24

Which region does the sympathetic nerves flow out from?

Answer 24

T1-L2/3

Question 25

Where are sympathetic neuron bodies found ?

Answer 25

Lateral horn of the spinal chord

Question 26

What is contained in the dorsal root ganglion ?

Answer 26

cell bodies of sensory neurons

Question 27

How does sympathetic nerves get to every level of the body ?

Answer 27

Although outflow of sympathetic nerves only occurs in the T1 – L2 region all regions of our body require sympathetic nerves. Therefore preganglionic fibres travel up or down the paravertebral sympathetic ganglia , only synapsing at the sympathetic ganglion levels higher of lower and enter the spinal nerve occurring at that vertebral level. Thus every spinal nerve therefore carries postganglionic sympathetic fibres plus their normal sensory and motor fibres.

Question 28

Where is the outflow for the parasympathetic region ?

Answer 28

Craniosacral region.
S2-S4
Cranial nerve III, VII, IX, X

Question 29

Describe the paravertebral sympathetic ganglia

Answer 29

The paravertebral sympathetic ganglia are paired meaning that there is one on each side of the vertebral bodies from C1 – S5. The ability to move superiorly and inferiorly along the chain that results in the mass response (mass distribution mechanism) of the sympathetic nervous system

Question 30

Describe the basic pathway of sympathetic nerves. i.e. they can synapse in the chain at the same level

Answer 30

Sympathetic fibres originate in the lateral horn cells between spinal levels T1-L2(3).

They travel in the ventral root of the spinal nerve to the mixed spinal nerve (MSN).

They leave the MSN via a white (myelinated) ramus communicans as preganglionic fibres to enter the sympathetic ganglion of the same vertebral level.

After synapsing in the sympathetic chain ganglion, they re-enter the spinal nerve via the grey (unmyelinated) ramus communicans as postganlionic fibres and are distributed in both dorsal and ventral rami of the spinal nerve.

The rami then go to supply skin and body wall structures such as arrector pili muscles, blood vessels and glands at that vertebral level (dermatome) with sympathetic input.

Question 31

Sometimes however this is not the path of the sympathetic nerves. Other ways include….

Answer 31

1. they can run up or down the chain and synapse at a different level
2. they can pass straight through the chain and synapse elsewhere, eg. in an autonomic nerve ganglion or plexus in the thorax or abdomen
3. They can synapse in the sympathetic chain and then run as postganglionic fibres to thoracic organs (thoracic organ supplying splanchnic nerves T1-T4)
4. They can run through without synapsing with the sympathetic chain and synapse with the preaortic ganglia before running as postganglionic fibres to abdominal organs (T5-L2/3)

Question 32

Which region of the spinal chord supplies the face and head ?

Answer 32

Superior, middle and inferior cervical ganglion

Cranial nerves

Question 33

What is Horners’ Syndrome ?

Answer 33

Damage to the cervical fibres supplying the face and head.

Question 34

What are the symptoms of Horner’s syndrome?

Answer 34

Partial ptosis - Dropping of the upper eyelid
Miosis - Constriction of the pupil
Anhydrosis - Decreased sweating