Ross University Semester 1

1. Introduction to the
Nervous System
Nicole M. Reeves, Ph.D.
Department of Anatomy
NicoleReeves@RossU.edu
Recommended Reading
COA : 7th Edition
Pages: 46-56
*Practice questions can be found on Canvas*

2. Learning Objectives
• Understand that the nervous system is divided into central and peripheral components
and be able to describe the parts of each
• Describe the parts of a neuron and how the nomenclature of those parts differ
depending upon location
• Describe the differences between the somatic and autonomic nervous systems and the
components of each
• Trace the pathway of somatic efferent information & what those efferent axons are
called
• Trace the pathway of somatic afferent information and what those afferent axons are
called
• Understand the difference between a dorsal root, ventral root, dorsal primary rami,
ventral primary rami, and the axon types that they carry
• Describe the arterial supply and venous drainage of the spinal cord
• Use the information provided from the lecture, along with the learning objectives from
the applicable gross anatomy laboratories, as your knowledge base required for
practical examinations 2

3. Organization of the Nervous System
• Central Nervous System (CNS)
• Brain
• Spinal cord
• Cerebellum, brainstem, diencephalon, cranial nerves
I and II
• Peripheral Nervous System (PNS)
• Spinal nerves
• Cranial nerves (CN III-XII)
• Ganglia (Dorsal root ganglia & autonomic ganglia)
3

4. Organization of the spinal cord and spinal nerves 31 pairs of
spinal nerves
8 Cervical!!
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
9
10
11
12
1
2
3
4
5
1
2
3
4
5
1
12 Thoracic
5 Lumbar
5 Sacral
1 Coccygeal!!
Cervical
enlargement
Lumbar
enlargement
• The spinal cord, with the brain, forms
the Central Nervous System (CNS)
• The 31 pairs of spinal nerves arising
from the spinal cord form part of the
Peripheral Nervous System (PNS)
• 33 vertebral bodies
• The spinal cord has two
enlargements, cervical & lumbar,
where there are more nerves for
innervation of the limbs
4

5. Spinal nerves & vertebral levels
• Cervical nerves course SUPERIOR to
their corresponding vertebra, while all
others course INFERIOR to their
corresponding vertebra
• C1 spinal nerve courses SUPERIOR to
the C1 vertebra
• NOTE: C8 spinal nerve courses inferior to
the C7 vertebra, superior to the T1
vertebra
• T1 spinal nerve courses INFERIOR to the
T1 vertebra 5

6. Parts of a neuron
• This entire structure is a neuron!
6
• Information
receiving end
• Synaptic end –
information transfer

7. Information flow through neurons
7

8. Information flow through neurons
8

9. Motor neuron
9

10. Axon
Fascicle
Peripheral Nerve
Axons
• Hundreds to thousands of axons can be contained in a fascicle and
several fasicles can create a peripheral nerve!
10

11. Nomenclature of CNS and PNS
• Nomenclature differs depending on if you are in the Central Nervous System (CNS)
or Peripheral Nervous System (PNS)
11
CNS PNS
Axons of neurons form
_______.
Tracts
(you will learn in Neuro block,
Semester 2)
Nerves
(some nerves form
interconnected plexii, such
as the cervical plexus,
brachial plexus, lumbar
plexus, sacral plexus
Neuronal cell bodies
_______ .
are called nuclei and are
scattered throughout cortex
and brainstem levels
are in ganglia
(such as the dorsal root
ganglia, cranial nerve
ganglia, autonomic ganglia)

12. Nervous system
Central Nervous
System (CNS) – brain
and spinal cord –
receives and processes
information; initiates
action
Peripheral Nervous
System (PNS) –
transmits signals
between CNS and the
rest of the body
Somatic Nervous
System –
communicates with skin
(sensation), bones,
skeletal muscles
Voluntary motor -
(Efferent), General
Somatic Efferent (GSE)
axons
Somatic sensory -
(Afferent), General
Somatic Afferent (GSA)
axons
Autonomic
Nervous system –
communicates with
organs, glands, smooth
muscle
Visceral motor –
(Efferent) General
Visceral Efferent (GVE)
axons
Sympathetic –
prepares the body for
stressful or energetic
activity; “fight or flight”
Parasympathetic –
directs maintenance
activities; “rest and
digest”
Enteric – governs
function of the
gastrointestinal (GI)
tract
Visceral Sensory –
(Afferent) General
Visceral Afferent (GVA)
axons
12
Components of the Nervous System

13. Organization of the Somatic (Voluntary) Motor System
• Somatic motor pathways have a 2-neuron
chain, from the cortex
• Upper Motor Neurons (UMN), in Primary Motor
Cortex, send a signal along somatic motor
axons - general somatic efferent (GSE) type –
to the ventral horn of the spinal cord
• The ventral horn contains the Lower Motor
Neurons (LMN) which will then send a signal
out along axons in the ventral root and into the
peripheral or spinal nerve
13

14. Dorsal
Ventral
Organization of the Somatic (Voluntary) Motor System
• Sensory axons, or General Somatic Afferent (GSA)
type axons, are traveling in the spinal nerve to enter
the dorsal root and subsequently become a tract
within the spinal cord to reach the cortex (brain)
DRG
Dorsal
primary
rami
Ventral
primary
rami
Ventral Root
“Mixed” Spinal
Nerve
Dorsal
Root
• Voluntary motor axons, or General
Somatic Efferent (GSE) type axons, are
descending from the cortex (brain),
synapse in the spinal cord and then
travel out the ventral root to enter the
spinal nerve and peripheral nerve to
ultimately innervate voluntary
musculature
=Synapse
DRG = Doral root ganglia

15. Arterial Supply of the Spinal Cord
15
• 2 posterior spinal arteries – arise directly
or indirectly from vertebral arteries
• 1 anterior spinal artery – branch from
vertebral artery
• Spinal arteries are reinforced by radicular
arteries, branches from segmental
arteries, ascending cervical a., deep
cervical a., posterior intercostal aa.,
lumbar aa., sacral aa.

16. Venous Drainage of the Spinal Cord
16
• There are usually 3 anterior and 3 posterior
spinal veins
• The veins communicate freely with each
other and drain into the anterior and
posterior medullary veins
• The veins join the internal vertebral
(epidural) plexus & these communicate
with dural sinuses & then the vertebral
veins
• Internal vertebral plexus also
communicates with the external vertebral
plexuses on the external aspect of the
vertebrae