MS-1 FUND 1: 9:10-10:00
Monday, September 16, 2014
Dr. Will Brooks
Introduction to the Nervous System
Abbreviations: CNS= Central Nervous System ANS=Autonomic Nervous System
Nervous System CSF= Cerebrospinal Fluid DRG= Dorsal Root Ganglion
Transcriber: Mahmoud Elsayed
Editor: Avery Berlin
Page 1 of 4
PSNS= Parasympathetic Nervous System SNS= Sympathetic
Introductory Comments: Watch the short video podcast on MedMap to get the full information.
<ARS Question>
I.
Anatomy of the Central Nervous System (slide 4) 5:58
a. Cross Section of Central Canal: narrow and filled with CSF, in the center
i. Gray matter is shaped like a butterfly and has 3 types of horns. Know which side is ventral and which is
dorsal. Gray because of high density of neuron cell bodies and also contains glial cells.
1. Dorsal horn (green circle) contains neurons used for sensory neuron system
2. Ventral horn (red circle) contains neurons used for the motor neuron system, specifically somatic
motor (to our muscles)
3. Lateral horn only exists in the T1-L2 range and is used for the SNS
4. Intermediate zone is what is between the horns
ii. White matter- myelinated axons. Most of which are ascending to the brain (sensory) or descending (motor)
to the body. The axons will synapse with neuron somas inside gray matter.
b. Functional Organization of Gray Matter
i. For the dorsal horn, the soma of sensory fibers (unipolar) is external from the CNS in the DRG. From the
soma there are two axons in both directions, one from the sensory organ and another axon to the dorsal
horn through the dorsal root.
1. Dorsal Horn responsible for somatic and visceral sensation
ii. Ventral horn has somatic motor neurons that have their somas in the ventral horn and axons project out
through ventral roots.
1. E.g. All of your muscles, like your biceps, triceps, and pecks will be innervated by axons coming out
from the ventral horn.
iii. Lateral horn contains cell bodies used for visceral motor function in organs like the heart and GI muscles.
1. Only in T1-L2, because that is where out sympathetic nervous system originates
2. Parasympathetic is found in S2-S4 but doesn’t really show a lateral horn
c. Nerve Fiber types (ways we can divide all the axons):
i. Know that somatic goes to the body (skeletal muscles) and visceral goes to the organs.
ii. Know that efferent are leaving the CNS like motor fibers of the somatic and ANS.
iii. Afferent comes towards the CNS like sensory neurons from the body or viscera.
iv. General somatic efferent (GSE)
1. motor fibers to skeletal muscle
2. neuron soma house in ventral horn > axons exit via ventral roots
v. General somatic afferent (GSA)
1. convey sensory info from skin, joints, muscles (things you are aware of) to CNS
2. neurons are unipolar > soma housed in DRG
3. axons enter cord via dorsal roots > synapse in dorsal horn
vi. General visceral efferent (GVE)
1. motor fibers of ANS to visceral organs
2. preganglionic soma house in intermediate zone
3. axons exit cord via ventral roots
vii. General visceral afferent (GVA)
1. convey sensory info from visceral organs to CNS
2. neurons are unipolar > soma house in DRG
3. axons enter cord via dorsal roots > synapse in dorsal horn
d. Types of neurons:
i. Sensory- Pseudo-unipolar neuron (one cell body with long axon that extends in both directions)
1. Sensory organs sends signal through neuron to dorsal horn (passing the neuron cell body)
2. Soma is in DRG, also known as “spinal sensory ganglion”
ii. Somatic Motor - Multipolar neuron.
1. Sends signal from the ventral horn (where cell bodies are) through ventral root to effector organs
2. The axons will go to the muscle and innervate muscle fibers at the neuromuscular junction
iii. Special Sensory- Bipolar neuron
1. Found in retinal bipolar cells and olfactory epithelium, restricted to special sensory organs only.
II.
Protection of CNS (slide 10 ) 14:25
a. The brain and spinal cord have no scaffolding (no connective tissue to create a framework for it) so they have a
jelly-like consistency. Very easily injured, so it needs a special way to protect the CNS:
MS-1 FUND 1: 9:10-10:00
Monday, September 16, 2014
Dr. Will Brooks
Introduction to the Nervous System
Abbreviations: CNS= Central Nervous System ANS=Autonomic Nervous System
Nervous System CSF= Cerebrospinal Fluid DRG= Dorsal Root Ganglion
b.
c.
d.
e.
f.
g.
h.
Transcriber: Mahmoud Elsayed
Editor: Avery Berlin
Page 2 of 4
PSNS= Parasympathetic Nervous System SNS= Sympathetic
i. Bony cranium/vertebrae
ii. Meninges- 3 connective tissue layers between bone and CNS
1. Dura mater (tough mother)
2. Arachnoid mater (spider mother)
3. Pia mater (tender mother)
ii. CSF- fluid found between two of these meninges
Dura Mater: thick outermost layer
i. Periosteal layer- Attached to the surface of the cranium (basically fused with the periosteum of your skull)
ii. Meningeal layer-avascular layer found pressed against the periosteal layer
1. Therefore, both the periosteal and meningeal layers are pressed up against the skull
iii. Dural sinuses- can be found in certain areas where the two layers of dura mater split up – the meningeal
layer pulls away from the periosteal layer to create a triangular shaped space.
1. Covered in endothelial cells like veins and are used to drain CSF and eventually return it to venous
blood flow.
iv. Protrusions of meningeal layer into the brain to segment it and provide protection/support to large brain
structure areas.
1. Falx cerebri is a meningeal protrusion into the midline of the brain, separating the two hemispheres
2. The cavity formed by the Falx Cerebri protruding down makes a dural sinus that helps recycle CSF
Arachnoid Mater: avascular and thin membrane
i. Directly attached to the meningeal dura and follows its contours.
ii. Has arachnoid trabeculae (fibers) looks like spider web that connect the arachnoid to the pia mater.
iii. Deep to the arachnoid mater is the arachnoid space where the CSF lies.
iv. Has arachnoid villi which break through the meningeal layer into the dural sinuses is important for recycling
old CSF (pushes it out into sinuses)
Pia mater: thin delicate, innermost membrane
i. Adheres to the brain and spinal cord following contours of the gyri (bulge) and sulci (folds) like saran wrap.
ii. Cannot see this grossly, only microscopically
Meningeal Space: can be actual (normally present hollow space) or potential (only has a space during
pathological conditions)
i. Epidural space: above the dura, below the skull
1. Cranium has a potential space between skull and dura mater
2. Spine has actual space between periosteum (vertebrae) and dura mater
ii. Subdural space: potential space between dura mater and arachnoid in cranium and spine.
iii. Subarachnoid space: actual space between arachnoid and pia in the cranium and spine that contains the
CSF and arteries.
iv. No space deep to pia: astrocytes tightly adhere to inner surface of pia
Intracranial bleeds:
i. Epidural bleed caused usually by ruptured middle meningeal artery. Blood fills between cranium and dura
mater.
ii. Subdural bleed is venous blood that fills between dura mater and arachnoid mater. Arachnoid mater pulls
away making an actual space instead of potential space.
iii. Subarachnoid bleeding will release blood into an actual space and mixes with CSF.
<ARS Question>
Spinal meninges (different from cranial)
i. Spinal Duras
1. Only the meningeal layer of the dura mater continuous into the spinal cord. Not periosteal
2. The epidural space is an actual space between dura and bone and is filled with fat, loose connective
tissue, and venous vessels.
a. This is where you inject anesthesia when doing an epidural block
3. The duras cover the dorsal and ventral roots as they exit the intervertebral foramina and gradually
fading into the epineurium instead. (SN: He says perineurium but the slide says epineurium)
ii. Theca: a sac surrounding the spinal cord ending at S2
1. Made of dura and arachnoid mater
2. Filled with CSF and spinal cord or cauda equina
3. Pressure in this space causes lower back pain
iii. Lumbar cistern: area between L2 and the bottom of the thecal sac (S2)
1. Contains cauda equine
2. Location of lumbar puncture (L4-L5) because there is no spinal cord to damage in this region.
iv. MRI L-spine
MS-1 FUND 1: 9:10-10:00
Monday, September 16, 2014
Dr. Will Brooks
Introduction to the Nervous System
Abbreviations: CNS= Central Nervous System ANS=Autonomic Nervous System
Nervous System CSF= Cerebrospinal Fluid DRG= Dorsal Root Ganglion
Transcriber: Mahmoud Elsayed
Editor: Avery Berlin
Page 3 of 4
PSNS= Parasympathetic Nervous System SNS= Sympathetic
1. Note the lumbar cistern and cuada equina
2. Epidural space is an actual space filled with epidural fat and blood vessels.
3. Herniate disc between L3, L4
Peripheral Nervous system anatomy (slide 20 ) 28:00
a. As soon as we leave the dorsal/ventral roots we are in the peripheral nervous system
b. Spinal nerve branches
i. Dorsal Primary Ramus: innervate joints of spinal column, muscles of back and skin of back
1. Smaller branch
ii. Ventral Primary Ramus: innervates the lateral and ventral muscles and skin of trunk and extremities.
1. Much broader distribution area than dorsal
c. Peripheral Plexuses: network of spinal nerves that mix together before forming terminal nerve branches
i. Cervical plexus: C1-C5
ii. Brachial Plexus: C5-T1 (arm)
iii. Lumbosacral Plexus: L1-S4 (leg)
iv. 1 nerve containing axons from multiple spinal levels or it can also be thought as multiple spinal levels
merging together to form one nerve
d. Cranial Nerves- at least know their names and know that the number is a Roman Numeral
i. From I to XII: olfactory, optic, oculomotor, trochlear, trigeminal, adducens, facial, vestibulocochlear,
glossopharyngeal, vagus, accessory, hypoglossal.
ii. Use Mnemonics to memorize them.
1. Oh oh oh, to touch and feel very good velvet, AH!
ii. <Start by memorizing their names, you do not have to memorize their functions.>
IV. Dermatomes (slide 25 ) 33:02
a. Areas of the skin that are innervated by a single spinal nerve.
i. The vental ramus of spinal nerves will come around and some will come through the ribs to innervate your
skin, resulting in a stripe.
b. You should know:
i. T4- “milk will pour” where nipples are
ii. T6- where the xyphoid process is
iii. T10- where the umbilicus is (belly button)
iv. L1- where the inguinal ligament (between the ASIS and the pubic tubercle, it is the transition from your
trunk to your lower limbs)
v. Useful because - Sensory testing determines what level the spinal cord injury is.
vi. <For now just learn the trunk ones>
vii. If a patient comes to you with a shingles (Varicella zoster virus, same one that causes chicken pox) in a
layer of dermatome that is associated with the nipple, you should know that the virus is activated in the T4
spinal nerve.
1. Only on one side, only one dorsal root ganglion.
c. Dermatomes vs cutaneous nerves:
i. Dermatomes are supplied by nerves from a single segment (like in the trunk)
1. Many nerves same segment
ii. Cutaneous nerves branch out of a peripheral nerve (after a plexus) and often have a very confusing
mixture of nerves from different segments of the vertebrae (in the limbs)
1. So that nerve will be innervating a dermatome area, but it maybe innervating more than one
dermatome area.
1. In the limbs (because of the plexuses) Cutaneous map doesn’t match up with the dermatome map –
that is because the nerves (right side of slide 28) contain fibers (left side of slide 28) from more than
one spinal level.
2. Since there are not plexuses in the trunk, the cutaneous and dermatome map will match up.
iii. The overlap between them is poor because the plexus mixed the nerves together.
d. Myotomes: analogous to dermatome
i. Muscles innervated by single spinal nerve segment. Because most muscles receive from many spinal
segments, no map is drawn.
ii. All of your muscles are innervated by nerves, so you will have sensory problems, but also motor problems!
Thus testing motor function will tell you at what spinal cord levels a lesion might be found.
iii. Couple of different ways to test motor function:
1. Strength: elbow flexion against resistance (Can they flex it on their own? Against your resistance?)
III.
MS-1 FUND 1: 9:10-10:00
Monday, September 16, 2014
Dr. Will Brooks
Introduction to the Nervous System
Abbreviations: CNS= Central Nervous System ANS=Autonomic Nervous System
Nervous System CSF= Cerebrospinal Fluid DRG= Dorsal Root Ganglion
Transcriber: Mahmoud Elsayed
Editor: Avery Berlin
Page 4 of 4
PSNS= Parasympathetic Nervous System SNS= Sympathetic
2. Reflex testing- test myotomes based on nerve segments. Just remember 1,2,3,4,5,6,7,8 from
bottom to top. <Dr. Brooks said this is something every doctor should know, never forget>
a. Ankles (achilles tendon): S1,S2
b. Knee: L3, L4
c. Bicep: C5,C6
d. Tricep: C7,C8
ii. Why is your bicep reflex testing C5, C6?  because all of your peripheral nerves originate from those spinal
levels.
Aren’t blood and CSF still being drained by arachnoid villi?
Answer: Potentially yes, but you are getting more of a buildup than you can recycle so there is a buildup
of pressure and fluid that can be damaging.
Student Question 1:
<END OF LECTURE 43:27>