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Spinal Cord and Nerves
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The Nervous System
Coordinates the activity of muscles, organs,
senses, and actions
Made up of nervous tissue
Has 3 main functions:
1. Receives sensory Input
2. Integration
3. Dictates motor output
http://www.nationmaster.com/wikimir/images/upload.wikimedia.org/wikipedia/en/f/f0/ReflexArc1.jpg
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Structural Divisions of the
Nervous System
Central Nervous System (CNS)
Brain and spinal cord
Interprets incoming sensory signals
Dictates motor responses Peripheral Nervous System (PNS)
Nerves
Cranial nerves and spinal nerves
Nerve plexuses Enteric system
Communication between regions of
body and CNS
pg 34
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Review of Nervous Tissue
Features of Nervous Tissue
Neuron
Cell body
Dendrite
Axon
Myelin Sheath
Surrounds thicker axons
Forms insulating layer
Prevents leakage of electrical current Speeds up the impulse conduction
www.morphonix.com
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Review of Nervous Tissue
Neuroglia
Reflex Arc
Interneurons
Rapid, automatic motor response
Synapse
Action potential
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Organization of a Nerve
Endoneurium
Surrounds each axon (nerve fiber)
Myelinated and Unmyelinatedaxons
Motor and Sensory nerve fibers
Loose CT Perineurium
Bundles axons into fascicles
CT
Epineurium Bundles fascicles into a nerve
Fibrous CT
CT layers contain blood vessels
www.web-books.com
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Types of Nerve Signals/Fibers
Sensory (afferent)
Picked up by sensory receptors thru body
Carried by nerve fibers of PNS into CNS
Motor (efferent)
Carried away from the CNS by nerve fibers
into PNS
Innervate muscles and glands Causes these organs to contract or secrete
Remember: SAME
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Sensory and Motor Signals/Fibers
Somatic sensory Body senses
touch, pressure, temperature, vibration of body, musclesstretching, balance
Visceral sensory
Organ senses
Stretch, pain, temperature in organs
(eg) nausea, hunger, cramps
Somatic motor
Body movement Voluntary contraction of skeletal muscles
Visceral motor
Organ movement
Contraction of smooth muscle, glands
= Autonomic Nervous System (involuntary)
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CNSBrain
Spinal cord
PNSCranial nerves and
spinal nerves
Sensory (afferent)
division
Motor (efferent)
division
Somatic sensory
General: Touch,
pain, pressure,
vibration
Special: hearing,
equilibrium, vision,
smell
Visceral sensory
General: Stretch,
pain, temperature,
nausea, hunger
Special: Taste
Somatic motor
General: Motor
innervation of all
skeletal muscles
Visceral motor
General: Motor
innervation of smooth
muscle, cardiac
muscle, and glands;= ANS
Parasympatheticdivision Sympatheticdivision
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CNSSpinal Cord
Runs through vertebral canal of the vertebral column
Protected by bone, meninges, and cerebrospinal fluid
Spinal cord made of a core ofgray mattersurrounded by white
matter
31 pairs of spinal nerves branch off spinal cord throughintervertebral foramen
Functions in many ways:
Involved in sensory and motor innervation of body
inferior to the head (through spinal nerves)
Provides a 2-way conduction pathway for signals
between body and brain
Major center for reflexes
pg 101
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Meninges of Spinal Cord
Membranes surrounding the spinal cord
3 Layers of connective tissue
Functions
Protect spinal cord
Contains cerebrospinal fluid (CSF)
Protect blood vessels serving spinal cord
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Meninges of Spinal Cord
Dura mater (superficial)
Spinal dural sheath
Does not attach to bone
Merges w/epineurium of spinal roots & nerves Epidural space
Loose CT, fat and veins
Between dura mater and vertebra
Not present around brain
Subdural space
Between dura mater and arachnoid
pg 105
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Meninges of Spinal Cord
Arachnoid mater (middle)
Impermeable layer = barrier
Raised off pia mater by rootlets
Subarachnoid space
Between arachnoid and pia mater
Contains cerebrospinal fluid
Contains large blood vessels
*Runs to level of S2
Pia mater(deep)
Highly vascular
Adheres to brain/spinal cord tissue
Creates denticulate ligaments pg 105
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Regions of Spinal Cord
Cervical
Thoracic
Lumbar
Sacral Coccygeal
Cervical + Lumbosacral enlargements
Cauda equina
Conus medullaris Filum terminale
CT & pia mater
Attaches to coccyxpg 101, 109
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Gray Matter
Consists of neuron cell bodies, unmyelinated axons,
dendrites, and neuroglia
Shaped like an H
Gray commissure (crossbar)
Central canal
Posterior horns
Anterior horns
pg 102
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Gray Matter
Posterior horns
Consist of interneurons that transmit in from outside spinal cord into it
Dorsal root contain sensory fibers Somatic Sensory (SS)
Visceral Sensory (VS) Dorsal root gangliaclusters of cell bodies outside of CNS
Anterior horns
Cell bodies of motor neurons send info out of spinal cord to muscles and glands
Ventral Root contains Motor Fibers Visceral Motor
Somatic Motor
pg 102
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White Matter
Surrounds gray matter
Composed of myelinated and unmyelinated axons
Divided into white columns (funiculi) that create tracts
Tracts = bundles of axons traveling to similar destination
Posterior funiculus
Anterior funiculus
Lateral funiculus
Allow for communication between
Parts of the spinal cord
Spinal cord and brain
pg 102
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White Matter
3 types of nerve fibers:
Ascending
Carry sensory info from sensory neurons of body to brain
touch, pressure, pain, temperature
Descending Carry motor instructions from brain to spinal cord
Contraction of muscles and secretion of glands
controlling precise, skilled movement (e.g. writing, maintain
balance, create movement)
Commissural
Cross from one side of cord to the other
www.octc.kctcs.edu
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Spinal Nerves (31 Pairs)
Part of the PNS
Lie in intervertebral foramina
Send lateral branches to body
Named according to their point of attachment to spinal cord
segment
8 pairs of cervical spinal nerves; C1-C8
12 pairs of thoracic spinal nerves; T1-T12
5 pairs of lumbar spinal nerves; L1-L5
5 pairs of sacral spinal nerves; S1-S5 1 pair of coccygeal spinal nerves; C01
pg 110
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Spinal Nerves
Each spinal nerve connects to spinal cord via
posterior root (sensory) and anterior root (motor)
Each spinal nerve branches into a posterior ramus
and an anterior ramus
Anterior rami
Supply anterior and lateral regions of the neck,
trunk, and limbs Posterior rami
Supply the dorsum of the neck and trunk (back)
pg 42
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Recurrent Meningeal Nerves
Recurrent meningeal nerves branch from spinal nervesto supply intervertebral discs, dura mater, ligaments andblood vessels.
They access the vertebral canal via intervertebralforamina.
pg 105
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The Big Picture
Just lateral to the intervertebral foramen, each spinal
nerve then splits in 2
Dorsal Ramus
Ventral Ramus
RAMI contain BOTH Sensory and Motor fibers!!
Remember: Roots have sensory OR motor fibers, not both
pg 62
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Dermatomes
Area of skin innervated by cutaneous branches
of single spinal nerve
Clinical application for testing neurological
function
pg 40
CNS
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CNSBrain
Spinal cord
PNSCranial nerves andspinal nerves
Sensory (afferent)
division
Motor (efferent)
division
Somatic sensory
General: Touch,
pain, pressure,
vibration
Special: hearing,
equilibrium, vision,
smell
Visceral sensory
General: Stretch,
pain, temperature,
nausea, hunger
Special: Taste
Somatic motor
General: Motor
innervation of all
skeletal muscles
Visceral motor
General: Motor
innervation of smooth
muscle, cardiac
muscle, and glands;= ANS
Parasympathetic
division
Sympathetic
division
Autonomic
Nervous
System =
Visceral Motor
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Autonomic Nervous System
Visceral MotorFunction
Not controlled voluntarily
e.g. get nervous and sweat
Innervates smooth muscle, cardiac muscle, glands Regulates visceral function
Heart rate, blood pressure, digestion, urination
Has 2 divisions:
Parasympathetic
Sympathetic
i
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Autonomic Nervous System
Parasympathetic
rest and digest
Enables body to unwindand calm down
Most active when body atrest, normal activities
Routine maintenancefunctions
Most releaseacetylcholine
Axons branch less Craniosacral division
Fibers arise from brainand sacral spinal cord
Sympathetic
fight or flight
Mobilizes the body duringextreme situations
Becomes active when
extra metabolic effortneeded
Most releasenorepinephrine
Axons branch widely
Thoracolumbar division Fibers arise from
thoracic and lumbarparts of spinal cord
pg 42, 48
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Sympathetic Innervation
Comes from thoracolumbar regions (T1-L2)
Travels through anterior root and rami
Communicates with the sympathetic trunk
(via a connection called a ramus communicans)
Back to anterior rami (via another ramus
communicans) to spinal nerve to reach target
structures Can operate at same level of spinal cord (T1-L2)
or above a different level
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Parasympathetic Innvervation
Parasympathetic innervation comes fromcranio-sacral region of central nervous system
Cranial nerves III, VII and IX provide
parasympathetic innervation to structures of
head and neck CN X (Vagus) provides parasympathetic
innervation below neck to organs of thoracic &
abdominal cavities
Spinal nerves S2-S4 provide parasympathetic
innervation to inferior abdominal organs, pelvic
organs and tissue of perineum
Nerve fibers exit spinal cord through anterior roots
and then anterior rami into plexuses to serve organs
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Nervous System Overview
Sensory information (visceral and somatic)
travels along sensory nerves to the posterior
root into the spinal cord
The information is then processed by brain ora response is determined within the spinal
cord (e.g. in a reflex arc)
Motor information (visceral and somatic) goes
out of the spinal cord through the anterior root
along motor nerves to the body to make
muscles contract or glands secretepg 107
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Sympathetic Innervation at Same
Level of Spinal Cord
Sympathetic fibers providing innervation through spinal nerves at same
level of spinal cord (T1-L2)
Sympathetic fibers runs through anterior root into anterior ramus
It then connects to a whiteramus communicans, which leads to the
sympathetic chain ganglia and sympathetic trunk
Fibers then pass through the gray ramus communicans back out the
anterior ramus into a spinal nerve to body
pg 44
S th ti I ti t
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Sympathetic Innervation at
Different Level of Spinal Cord
Only from level T1-L2, so
Fibers may travel out anterior root and anterior
ramus
Through white ramus communicans up or downsympathetic trunk to different level of cord
Then through gray ramus communicans out
anterior root along spinal nerve to the body
pg 45