3 - The Nervous System

Question 1

What is the CNS and PNS?

Answer 1

CNS = spinal cord and brain
PNS = 12 cranial nerves and 31 spinal nerves

Question 2

What is the somatic nervous system?

Answer 2

Controls skeletal muscle under voluntary control including both incoming sensory (afferent) and outgoing motor (efferent) fibres from the brain and spinal cord

Question 3

What is the autonomic sensory system?

Answer 3

A division of the PNS that controls internal organs and the flight/flight response. Divided into

sympathetic: stimulates nervous activity (has pre/post ganglionic neurons)
parasympathetic: slows down the nervous system

Question 4

What is ganglia?

Answer 4

Ganglia are a group of cell bodies, from a number of segmental levels, or nerve cluster that occurs in the PNS. They act as intermediates between the PNS and CNS i.e. dorsal root ganglia. Should think about what territory is this ganglia supplying. Big nerve bundles.

Question 5

What is a plexus?

Answer 5

Branching network of nerves/vessels. Cervical, brachial, lumbosacral. Arise from the anterior rami of spinal nerves

Question 6

What is a dermatome and what is a myotome?

Answer 6

Dermatome = area of skin supplied by the cutaneous branches of a single nerve. This can be mapped in the body and is used to measure spinal cord damage
Myotome = the muscles innervated by a single spinal

Question 7

What are the spinal nerves?

Answer 7

8 cervical 
12 thoracic
5 lumbar
5 sacral
1 coccygeal

Question 8

What are the layers of the meninges and spaces?

Answer 8

Epidural space: 
Dura Mater:
Subdural space:
Arachnoid Mater:
Subarachnoid space:
Pia Mater:

Question 9

Epidural Space?

Answer 9

Contains fat which is the last to go. Small blood vessels with more veins than arteries. Put anaesthetics in here as is close to nerves but don’t have to penetrate tough dura mater. Between dura mater and vertebral wall

Question 10

Dura Mater

Answer 10

Robust, tough fibrous tissue that the scalpel struggles to get through. Tough mother.

Question 11

Subdural Space

Answer 11

VIRTUAL SPACE as dura mater and arachnoid are very close. Few arteries and veins. If you get brain shrinkage can get the space opening up and can tear the veins causing subdural haemorrhage. Short confusion and black-out - small bleeds

Question 12

What is a single segmental level?

Answer 12

Level at which a single spinal nerve leaves. Think cross section

Question 13

Why 8 cervical nerves but 7 vertebra?

Answer 13

1st comes out between skull and first vertebra

Question 14

When does the spinal cord finish?

Answer 14

At L1. At this point becomes cone shaped = Conus Medularis ends the spinal cord. From here on it is the Cauda Equina

Question 15

What direction does the spine protect the spinal cord?

Answer 15

Forwards and backwards but not elongation of spinal column - stops us being rigid. Structures in the spinal cord anchor it in place. If it wasn’t and you bent over the spinal cord would stretch and you would experience pain like a slipped disc everywhere

Question 16

Arachnoid Mater?

Answer 16

Web-like, shimmery nodes connect it here and there

Question 17

Subarachnoid space

Answer 17

IMPORTANT - lots of CSF. Largest reservoir

Question 18

Pia Mater

Answer 18

So closely adhered to spinal cord and nerves that you can’t distinguish it visually. Soft.

Question 19

What are the spinal nerves (motor and sensory) surrounded by?

Answer 19

A blend of the meninges. Epineurium.

Question 20

What are the sensory neurons?

Answer 20

Pseudounipolar neurons. Discriminative and non-discriminative.

Question 21

What is a spinal nerve?

Answer 21

A combination of the dorsal root and ventral root that will supply/take information to a particular level

Question 22

What are the 3 places the spinal nerves come from or go to?

Answer 22

1. Posterior Ramus: innervates back musculature. Small branch as small area.
2. Anterior Ramus: supplies muscles and organs of the front
   > both voluntary
3. Ramus Communicans: connects the spinal cord and the autonomic nervous system. It is a nerve that connects other nerves
   > involuntary

Question 23

What happens at the conus medullaris?

Answer 23

Spinal cord ends at conus medullaris at L1. A fibre continues and anchors into the coccyx. This is called the Filum Terminale (more white/blue and tighter than the other fibres). The Filum Terminale is a coming together of all the pia mater like the end of a sausage. It anchors and supports the spinal cord so when you bend over you don’t stretch the vertebral levels out of place

Question 24

Difference between discrim and non?

Answer 24

Discrim = what can you feel in the periperhy thats different at A than B
Non = responds to noxious stimuli that you should withdraw from or change behaviour

Question 25

What happens to the subarachnoid space after the conus medulairs?

Answer 25

The subarachnoid space and so CSF continues down with the filum terminale until S2 which is the lower limit of the subarachnoid space. Here the arachnoid mater also comes together around the pia mater to help form the filum terminale. This means all the CSF is above S2.

Question 26

What is the clinical important of the cauda equina and CSF filled subarachnoid space?

Answer 26

• if need some CSF (protein or bacteria or virus - meningitis - would accumulate around meninges)
• At the level of conus medullaris the chance of hitting the spinal cord is high as it is bigger
• at cauda equina you are less likely to hit a nerve or if you do it will likely bounce of the nerves and miss (may get twinge in leg)

Question 27

Where is the filum internum and externum?

Answer 27

Internum is above the lower limit of the subarachnoid space where there is CSF
Externum is below the lower limit where there is no CSF and the fibre consists of BOTH pia mater and arachnoid

Question 28

Denitculate Ligaments

Answer 28

• the arachnoid goes back and forth from being attached to the dura mater and the pia mater
• the arachnoid mater is attached to these by the denticulate ligaments (tooth like)
• if you didn’t have the ligaments then the arachnoid mater would close IN if the pressure increased or open more if pressure dropped. The ligaments give structure and ensure there is a CONSTANT volume of CSF around the spinal cord

Question 29

Ganglia?

Answer 29

Large bunch of nerves that come together from a group of spinal nerves - synonymous with plexus.