Lecture 5 NS - CNS and PNS Anatomy

Question 1

What are the 2 structural divisions of the NS?

Answer 1

CNS and PNS

Question 2

What is in the CNS?

Answer 2

Brain and spinal cord

Question 3

What are the divisions of the brain (simplified)? FITB

Answer 3

Question 4

What is the function of the CNS?

Answer 4

Analyse all the sensory information, plan movements, control homeostasis, and higher functions described as behaviour but includes perception, cognition, decision making, judgement, setting of mood

Question 5

What is the function of the PNS?

Answer 5

Needs to get sensory information into CNS and responsible for carrying motor commands from CNS to body

Question 6

How is the brain separated into 3 segments?

Answer 6

Separated into these due to embryology of the brain

Question 7

Fill in the blanks of the spinal cord segment

Answer 7

Question 8

What is grey and white matter?

Answer 8

White matter contains cell bodies and grey matter contains bundles of axons -> richer capillary network

Question 9

Fill in the blanks of the cross section of the spinal cord

Answer 9

Question 10

How many of each vertebra are there?

Answer 10

Question 11

What is attached to the body of the spinal cord?

Answer 11

Pair of spinal nerves on each segment attached by dorsal and ventral roots, which join together to form the spinal nerve, short distance away from the spinal cord

Question 12

What are the divisions of the gray matter and what are the functions of each division?

Answer 12

Dorsal horn - sensory function, where axons coming in from PNS bring sensory information, which is then analysed by the interneurones Ventral horn - motor function, which carry the motor signal to the PNS then the skeletal muscle

Question 13

What is a ganglion?

Answer 13

A connective tissue capsule with neuronal cell bodies in it

Question 14

Where do the dorsal and ventral roots lie?

Answer 14

They lie in the cavity of the vertebral column, before they join to form the spinal nerve which occurs just as the spinal nerve is exiting the vertebral column via the intervertebral foramen

Question 15

How is the spinal cord segmented?

Answer 15

C1-7, T1-12, L1-5, S1-5

Question 16

Why is the spinal cord shorter than the vertebral column?

Answer 16

As the NS stops growing a long time before the bones do

Question 17

What is the difference between lumbar and sacral spinal segments and their corresponding vertebra?

Answer 17

They are much higher, as the spinal cord stops growing earlier than the vertebral column

Question 18

What is an advantage of the lumbar cistern?

Answer 18

It allows a space for lumbar punctures to go through because there is no chance of damaging the spinal cord

Question 19

What is the structure of the dorsal root ganglion?

Answer 19

Capsule of connective tissue surrounds it, with neurons and satellite cells surround the neurons, with axons entering and leaving the ganglion

Question 20

What are the features of the nerves?

Answer 20

Axons are grouped together into fasicles which are then packaged into nerves

Question 21

How do nerves survive wear and tear?

Answer 21

Due to connective tissue organisation -> have 3 layers: Epineurium, perineurium, endoneurium

Question 22

What is the epineurium?

Answer 22

Outer thick layer of loose connective tissue which ensheathes the whole nerve

Question 23

What is the perineurium?

Answer 23

Dense connective tissue capsule ensheathes individual fasicles

Question 24

What is the endoneurium?

Answer 24

Very delicate connective tissue around each axon -> very important for damaged neuron regeneration

Question 25

What is the difference between un and myelinated axons?

Answer 25

NB: both have schwann cells surrounding them but in unmyelinated many axons can be accommodated with one schwann cell -> thin axons don’t need schwann cells and very thick cells have thicker myelin sheath

Question 26

How are the functional components of the PNS arranged?

Answer 26

Question 27

What is the difference between somatic and autonomic components in the spinal cord?

Answer 27

NB: boundary between CNS and PNS are at the boundary of the spinal nerve

Question 28

Where does the dorsal ramus innervate?

Answer 28

It is short and innervated a strip of tissue on the back and the skin

Question 29

Where does the ventral ramus innervate?

Answer 29

Front and sides of trunk and the limbs

Question 30

What is the difference between dorsal roots and ramus?

Answer 30

Roots connect directly to spinal cord with one direction of information Ramus have both directions of information (sensory and motor)

Question 31

What does each spinal nerve (somatic) innervate?

Answer 31

Muscle (myotome) and skin (dermatome) in a particular part of the body

Question 32

What is the difference between spinal and peripheral nerve cutaneous innervation?

Question 33

What happens in a peripheral nerve injury?

Answer 33

PNS axons which are damaged will always try to regenerate-> in B the axon has degenerated and macrophages digest it -> presence of schwann cells encourage sprouting of axon and once on finds the target, all the other sprouts retract -> only difference between original and repaired is that internodal space is shorter so may take longer for AP to reach target

Question 34

What does the regeneration of the PNS axon depend on?

Answer 34

If damage to axon is too close to cell body, then it may give up and die. If distance between injury and target is too long, then chances of successful regeneration is low. Type of injury is important, if endoneurial tube is left intact then it acts as a guide but if not, axon buds can end up in a different endoneurial tube. If a lot of damage is done a neuroma can form which can lead to pain

Question 35

What are peripheral neuropathies?

Answer 35

They are progressive degeneration of nerves - usually distally (hands and feet leading to centre of body)

Question 36

What are the causes of peripheral neuropathy?

Answer 36

Metabolic (diabetes), infectious (leprosy), hereditary

Question 37

What does peripheral neuropathy affect?

Answer 37

Sensory and/or motor and may initially affect myelin or axon

Question 38

How to diagnose peripheral neuropathy?

Answer 38

Conduction velocity and nerve biopsy