The document provides an overview of the nervous system, detailing its components such as the central and peripheral nervous systems, including neural structure and functions. It explores various neuron types, spinal cord anatomy, and the roles of the autonomic and somatic nervous systems. Additionally, it discusses reflex actions, sensory perception, and the specific functions of cranial and spinal nerves.

1. Nervous System

2. Nervous System Basics
● Central Nervous System: Made up of Brain and Spinal
Cord
● Peripheral Nervous system: Nerve Fibers/Bundles that
are Outside of the Brain and Spinal Cord
● 31 Spinal Nerve Pairs: 8 Cervical, 12 Thoracic, 5
Lumbar, 5 Sacral, 1 Coccygeal
● 12 Cranial Nerve Pairs: Cranial Nerves I-XII

3. Nervous System Divisions and Spinal Nerve Pairs

4. The Neuron
● The Anatomical unit of
the Nervous system: The
Neuron
● Cell body (Soma): The cell body
contains genetic information,
maintains the neuron’s
structure, and provides energy
to drive activities.
● Axon: Directs impulses away
from the cell body to transmit
the signal to additional nerve
cells or receptors. Neurons
usually have one main axon
● The term nerve fibers refers to
axons NOT dendrites
● Dendrites: The name is derived
from ‘dendron’ which means
tree. Like antennae, dendrites
receive and process signals from
the axons of other neurons.
● Increases the surface area to
receive signals from other

5. Dermatomes
● •A dermatome is an
area of skin in which
sensory nerves derive
from a single spinal
nerve root
● •The cervical and
brachial plexi provide
the dermatomes for
the shoulders and
upper extremites
● •The thoracic spinal
nerves provide
dermatomes to the
thoracic cage
● •The lumbo –sacral
plexi provide

6. Embryology of Nervous System
● By the end of the third
week the neural plate
inverts and comes
together to form the
neural fold that then
forms the neural tube
● The closure of the
neural tube
disconnects the
epidermis from the
neural tube which
creates the CNS
● Neural crest cells
differentiate into most
of the peripheral

7. Spinal Cord Development/Placement
●3 month
embryo-cord
occupies entire
space
●At birth, cord
terminates at L3
●In adult, cord
terminates at
L1-L2 disc
space

8. Know the Difference
between
Epidural=Between Dural
Space of Spinal Cord
Spinal-In the Spinal Space
Below the Spinal Cord

9. Special Osteology for Spinal Cord

10. Spinal Cord Functions
● Conduction- Nerve fibers conduct sensory and
motor signals up and down the spinal cord
● Neural Integration-spinal neurons receive input
from multiple sources, integrate it, and execute
appropriate out put
● Locomotion-spinal cord contain central pattern
generators. (i.e groups of neurons that coordinate
competitive sequences of contraction, like walking
● Reflexes- Involuntary responses to stimuli that are
vital to posture , coordination, and protection

11. Anatomic Superior Terminal Point of Spinal Cord: Foramen Magnum in the Skull
Anatomic Inferior End Point of Spinal Cord: Conus medullaris, Cauda Equina, Fillamentum Terminale

12. Cervical and Lumbar Enlargements for Plexi Formation (None in Thoracic)

13. ● Dura mater: thickest
covering and the most
superficial and dense in
collagen fibers that give it
a white color
● Arachnoid mater: a
spider-web like layer that
separates the layers into a
subarachnoid space which
is where the spinal fluid
flows
● Pia mater: which is the
deepest layer and directly
surround the spinal cord
● •There is also a fatty layer
called the epidural space
that lies outside the Dura

14. Spinal Columns and Nuclei (DON’T
MEMORIZE)
● Tracts are
aggregated into
columns (dorsal ,
lateral and ventral)
● Columns are divided
into tracts that
ascend (sensory)
and descend (motor)
● Decusitation-
crossing the midline
● Contralateral-
opposite side

15. Primary Arteries of the Spinal Cord
● Anterior spinal artery (1)
● Paired posterior spinal arteries (2)
● Contributions from Circle of Willis: Vertebral
arteries and ascending Cervical arteries
● Posterior intercostal arteries and Lumbar
arteries.
● Great radicular artery (of Adamkiewiscz)
○ From lower posterior intercostal or upper lumbar
artery
○ Usually on left

16. Primary Arteries of the Spinal Cord

17. Venous Drainage of the Spinal Cord
● The veins of the spinal cord have extrinsic and intrinsic veins:
● The intrinsic veins (sulcal and radial veins): drain the substance of
the cord to the extrinsic system.
● The extrinsic system: consists of anterior spinal vein which
accompanies the ASA till the filum terminale and continues as
filum terminale vein, the greatest spinal vein which traverses in
the posterior median sulcus along with two posterolateral veins
on either sides.
● The spinal veins drain into the anterior and posterior
radiculomedullary veins, which in turn drain into the
paravertebral and intervertebral plexuses. Finally, the venous
plexuses drain into the segmental veins, draining into the
ascending lumbar veins, azygos system, and pelvic venous
plexuses.

18. Primary Veins of the Spinal Cord

19. Peripheral Nervous System Basics and Function
● Peripheral Nervous system: Nerve Fibers/Bundles that are
Outside of the Brain and Spinal Cord
● 2 Groups: Somatic (Voluntary Motor) and Autonomic
(Involuntary Motor)
● 31 Spinal Nerve Pairs: 8 Cervical, 12 Thoracic, 5 Lumbar, 5
Sacral, 1 Coccygeal
● 12 Cranial Nerve Pairs: Cranial Nerves I-XII
● Function: To transmit Sensory and Motor information
between the effector organs of the body and the CNS

20. Peripheral Nerve Pairs

21. The Neuron-PNS Special aspects
● Similar Structure and
Function to CNS except the
following:
● Myelin sheath: a layer of
tissue which covers the
axon. Formed by glial
cells called Schwann
cells, the myelin sheath
provides insulation as
well as structural support
for the axon.
● Nodes of Ranvier: gaps
in the myelin sheath
which contain ion
channels. This allows ion
flux at intervals along the

22. Peripheral Nerve Anatomy
● Each peripheral nerve is a
bundle of neural axons,
encased in a sheet of
connective tissue and
aggregated in groups called
fascicles
● Peripheral nerve fascicles are
the equivalent of spinal tracts
in the CNS
● AXONAL INJURY
● Following transection or other
serious injury, that portion of
the axon distal to the injury
will undergo degeneration,
known as anterograde or
Wallerian degeneration.
● The axon stump proximal to the
injury will sprout and regrow at
the rate of 1-2 mm/day. If the
regenerating nerve fibers re-
enter the endoneural tube,

23. Remember SAME DAVE for PNS root Functions
●S=
sensory
●A=afferent
●M= motor
●E=efferent
D= dorsal
A= afferent
V= ventral
E= efferent

24. Peripheral Nervous System Afferent vs. Efferent
● Afferent nerve fibers transmit data from receptors in the
periphery (touch, temperature, vibration, proprioception)
to the central nervous system. It gives us the ability to
sense and perceive our surroundings. PERCEPTION
● Efferent nerve fibers transmit both conscious and
unconscious instructions from the central nervous
system to motor cells (including vasomotor and
secretomotor cells) in the periphery. This allows us to
physically (voluntarily or involuntarily) respond to the
perception input. RESPONSE

25. Somatosensory System
●The somatosensory
system is the part of
the sensory system
concerned with the
conscious perception
of touch, pressure,
pain, temperature,
position, movement,
and vibration, which
arise from the
muscles, joints, skin,
and fascia.
●This is where the signal
(sense) in perceived
and processed

26. Somatosensory Sensor Types
● There are a wide
variety of sensory
receptors that have the
ability to respond to
stimuli
○ Mechanoreceptors(
touch/pressure)
○ Thermoreceptors(h
eat)
○ Photoreceptors(ligh
t)
○ Chemoreceptors(ce
rtain chemicals)
○ Nociceptors(damagi
ng stimuli/Pain)

27. Peripheral Nervous System: Autonomic vs Somatic
● Somatic motor function
○ Voluntary-skeletal muscle
● Autonomic motor function
○ Involuntary-smooth, cardiac muscle,
Gland tissue
● Somatic sensory function
○ Precise, well localized (e.g. skin)
● Autonomic sensory function
○ Vague, poorly localized (e.g. visceral)

28. Autonomic Nervous System: Sympathetic and Parasympathetic
● The Sympathetic system that allows to body’s
response to stressful conditions “ fight or flight”
circumstances. Dilates pupils, speeds heart,
redistributes blood flow to skeletal muscular
beds.
● The Parasympathetic system which allows the
body to relax and provide basic homeostatic
function or “rest and digest”. Returns to baseline,
slows heart, redistributes blood flow to
splanchnic beds

29. Sympathetic Region Cervical: T1-T4
●Superior cervical
ganglia generally
control
sympathetic
responses to head
and neck organs
●The middle and
inferior (and
Stellate) ganglia
provide a
sympathetic

30. Sympathetic Region Thoracic: T5-T12
● T5-T9 ganglia greater splanchnic nerve: helps
with the motility of the foregut and provides
sympathetic innervation to the adrenal
medulla. Specifically, it supplies the stomach
duodenum, liver, gallbladder, pancreas,
adrenal medulla, and the spleen. Nerve
descends from thorax, pierces the crus of the
diaphragm and synapses primarily in the
celiac ganglion
● T10-T11 ganglia lesser splanchnic nerve:
courses lateral and in parallel to the greater
splanchnic nerves, over the anterior surface of
the spine and enters the abdomen in the
same manner - by traversing the ipsilateral
diaphragmatic crus. The lesser splanchnic
nerves terminate by synapsing within the
aorticorenal or superior mesenteric ganglia.
The corresponding postsynaptic fibers then
modulate the activity of the midgut
● T12 ganglion least splanchnic nerve: travel
lateral and parallel to the lesser splanchnic
nerves, over the anterior surface of the spine,
close to its lateral margin. It enters the
abdomen by passing beneath the medial
arcuate ligament and then joins the aorto-
renal ganglia, contributing to the sympathetic
innervation for the renal plexus. The fibers of
this nerve are sometimes joined by the lesser
splanchnic nerve. In this case, the lesser
splanchnic nerve gives off small branches to

31. Sympathetic Region Lumbar: L1-L2
● The lumbar splanchnic
nerves: arise from the
upper lumbar levels and
terminate in the inferior
mesenteric and hypogastric
ganglia. From these
prevertebral ganglia, the
postganglionic fibers
supply organs in the pelvis,
lower abdomen and lower
limb.
● The sacral splanchnic
nerves: are also a set of
nerves that run parallel to
one another on each side of
the body. They allow the
inferior hypogastric plexus
to connect with the sacral

32. Parasympathetic Connections
● Cell bodies of the parasympathetic
neurons are located in the
brainstem, in nuclei associated
with cranial nerves III,
Oculomotor nerve (CN 3): Light
reflex via constrictor pupillae
Accommodation via ciliary muscle
● Facial Nerve (CN 7): Motor to
salivary & lacrimal glands. Special
sensory (taste) to anterior tongue
● Glossopharyngeal Nerve (CN 9):
Motor to parotid gland. Sensory to
carotid body & sinus. Special
sensory (taste) to posterior tongue
● Vagus Nerve CN 10): Sensory to
carotid body. All parasympathetics
to thoracic viscera & to abdominal
viscera supplied by celiac and
superior mesenteric arteries
● Ventral horns of spinal cord
segments S2-4: control bladder
and reproductive organs

33. Autonomic Overview