The Central Nervous System
Poudre High School
By: Ben Kirk
The Spinal Cord

Protection: Vertebral column primarily
Coverings:

–
–
–
Meninges: Connective tissue coverings around spinal
cord and brain
Spinal meninges cover and surround the spinal cord
Cranial meninges cover and surround the brain
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They meet at the magnum foramen of the skull, where they
become continuous.
Meningitis: Inflammation of the meninges
–
Infections (viral or bacterial) that are contagious: DORMS
The Spinal Cord

Meninges and Coverings:
– Epidural Space: Space between the spinal cord
and the vertebral column
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

Packed with adipose tissue (fat)
Common place for injections due to localized effects
Loss of sensation to total paralysis (giving birth)
– Dura Mater: Outer most layer “tough mother”
 Longitudinal, densely packed collagen fibers
 Very tough, protective covering
The Spinal Cord

Meninges and Coverings
– Arachnoid Mater: Middle Layer
 Delicate, web of elastin and collagen fibers
– Subarachnoid Space: Space between the
arachnoid mater and the pia mater


Filled with Cerebrospinal fluid
Spinal Tap: Remove fluid from this space
– Pia Mater: Inner most layer “Delicate Mother”
 Network of elastin and collagen fibers connected
directly to neural tissue of the spinal cord.
 Highly vascularized and nourished
The Spinal Cord
The Spinal Cord

General Features
– Length: 42-45 cm (16-18 inches)
 Extends from foramen magnum to 2nd lumbar
vertebrae (not entire length of vertebral column)
– Cauda Equina: lumbar and sacral nerves
extending distal from L2.
http://www.spineuniverse.com/displaygraphic.php/133/dp_caudaeq
uina-BB.gif
The Spinal Cord

General Features
– Cervical Enlargement: Contains upper
extremity nerves
– Lumbar Enlargement: Contains lower extremity
nerves
– 31 Spinal Segments (C8-T12-L5-S5-Cox1)
The Spinal Cord

Cross Sectional Structure
– Anterior Median fissure: large, anterior
indentation
– Posterior Median Sulcus: small, posterior
indentation
– Gray Matter: “H”/butterfly shape surrounded
by white matter

Cell bodies and dendrites
– White Matter: Surrounding gray matter
 Myelinated axons
The Spinal Cord

Cross Sectional Anatomy
http://en.wikipedia.org/wiki/Image:Medulla_spinalis_-_Section_-_Latin.png
The Spinal Cord

Functions:
– Impulse Conduction
 Spinothalamic Tracts: (Ascending) Pain,
temperature, deep pressure, crude touch
 Posterior Column Tracts: (Ascending)
proprioception, discriminative touch, pressure,
vibration
 Pyramidal Tracts: (Descending) Precise skeletal
muscle movements
 Extrapyramidal Tracts: (Descending) head
movement, muscle tone, posture, equilibrium
http://www.unm.edu/~jimmy/spinal_tracts.jpg
The Spinal Cord

Functions
– Reflex Center
 Reflex: An automatic, rapid, predictable response to
a stimuli
– Responds the same every time

Spinal Nerves:
– Dorsal Root (Posterior): Sensory Information TO the CNS
– Dorsal Root Ganglia: Swelling on dorsal root , composed
of sensory neuron cell bodies
– Ventral Root (Anterior): Motor Information to peripheral
effectors
• Dorsal and ventral roots converge in the periphery to
form spinal nerves
Spinal Nerves
http://www.coventrypainclinic.org.uk/treatment-nerverootblocks.htm
The Spinal Cord

Functions:
–
Reflex Arc: A single reflex (5 steps)
1.
2.
3.
Receptor: stimuli activates receptor and generates impulse
Activation of Sensory neuron: Impulse reaches spinal cord
via dorsal root
Information Processing: Sensory impulse relayed and
interpreted by interneuron or motor neuron directly
 If sufficient excitation, #4 occurs
4.
5.
Activation of Motor Neuron: Impulse sent via ventral root
Effector Response: Peripheral glands or muscles activated
 Have both EPSP and IPSP arcs
 Ex. Hot Stove
Spinal Nerves

Spinal Nerves: Part of the Somatic Nervous
System (SNS)
– Connect CNS to sensory receptors and peripheral
effectors (muscles and glands)
– 31 Pair

Names: Based on region and level of spinal cord
where they emerge
– 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal
– 1st pair exit between atlas and occipital bone, all others
exit through intervetebral foramen (between vertebrae)
Spinal Nerves

Composition:
– Anterior and Posterior roots attach peripherally
– Mixed Nerves: Both sensory and motor fibers

Distribution:
– Branches: Rami – Ventral and Dorsal
 Both sensory and motor axon bundles
 Dorsal: to back/posterior region
 Ventral: to anterior/ventral region
Spinal Nerves

Branches/Rami:
http://mywebpages.comcast.net/wnor/terminologyana
tplanes.htm
Spinal Nerves

Distribution:
– Plexuses: Ventral Rami of all spinal nerves
except T2-T11
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cervical, brachial, lumbar, sacral
Stretched/pulled plexuses (ex. Falling off a horse)
– Intercostal Nerves/Thoracic Nerves: T2-T11
 Muscles between ribs, abdominals, chest and back
Spinal Nerve Plexuses
Lumbar Plexus
Brachial Plexus