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Spinal Cord and Nerves
The Nervous System
 Coordinates the activity of muscles, organs,
senses, and actions
 Made up of nervous tissue
 Has 3 main functions:
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1. Receives sensory Input
2. Integration
3. Dictates motor output
Divisions of the Nervous System
 Central Nervous System (CNS)
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Brain and spinal cord
Interprets incoming sensory signals
Dictates motor responses
 Peripheral Nervous System (PNS)
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Ganglia
Nerves
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Cranial nerves and spinal nerves
Communication between regions of
body and CNS
Somatic
PNS
ANS
Sympathetic
Parasymp.
Enteric
CNS
PNS
 Nervous system structures outside the brain
and spinal cord
 Either somatic or visceral
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Visceral motor portion is the ANS
 Structural components:
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Sensory receptors
Motor endings
Nerves and ganglia
PNS - Nervous Tissue
 Made up of 2 cells:
 Neurons
 Conduct electrical
impulses
 Supporting cells
 Surround the
neurons
 Ex. Glial cells
The Neuron
 Nerve cells
 Transmit signals in form of
nerve impulses
 Have extreme longevity
 Do not divide
 High metabolic rate
Neuronal Anatomy
 Cell body (soma)
Most are in CNS
 Neuron processes
 Dendrites
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Toward cell body
Axons
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Transmit away from
cell body
 Synapses
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Site where neurons
communicate
Neuronal Anatomy
 Myelin sheath
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Fatty sheath that surrounds most nerve fibers
 Reflex arc
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Responses to a stimulus
 Interneuron
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Nerve cell that lies between a sensory neuron
and motor neuron in a reflex arc
Confined entirely within the CNS
PNS - Sensory and Motor Signals
 Divided by the body
regions they serve:
 Sensory division
 Somatic sensory
 Visceral sensory
 Motor division
 Somatic motor
 Visceral motor
Types of Nerve Signals/Fibers
 Sensory (afferent)
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Picked up by sensory receptors thru body
Carried by nerve fibers of PNS into CNS
 Motor (efferent)
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Carried away from the CNS by nerve fibers
into PNS
Innervate muscles and glands
Causes these organs to contract or secrete
 Remember: SAME
Sensory and Motor Signals/Fibers
 Somatic sensory
Body senses
 touch, pressure, temperature, vibration of body, muscles
stretching, 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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Spinal Nerves (31 Pairs)
 Part of the PNS (Somatic)
 Lie in intervertebral foramina
Send lateral branches to
body
 Named according to their point
of issue from the vertebral
column
 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
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Spinal Cord Segments
Spinal Nerves
 Each spinal nerve connected to spinal cord
via dorsal (sensory) and ventral (motor) root
 Spinal nerves branch into dorsal ramus and
ventral ramus
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Ventral ramus
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Connects to rami communicates, which then lead
to sympathetic chain ganglia
Supply anterior and lateral regions of the neck,
trunk, and limbs
Dorsal ramus
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Supply the dorsum of the neck and trunk (back)
Roots V. Rami
 Rami
 Lateral branches of
spinal nerves
 Each contains both
sensory fibers and
motor fibers
 Roots
 Lie medial to the spinal
nerves
 Strictly sensory
(dorsal) or motor
(ventral)
The Big Picture
 Just lateral to
intervertebral
foramen, each
spinal nerve then
splits in 2
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Dorsal Rami
Ventral Rami
 Contain BOTH
Sensory and
Motor fibers!!
Autonomic Nervous System
 Visceral Motor Function
 Not easily controlled by will
 Get nervous and sweat
 Innervate smooth muscle, cardiac muscle,
glands
 Regulate visceral function
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Heart rate, blood pressure, digestion, urination
 Has 2 divisions:
 Parasympathetic
 Sympathetic
ANS
 Parasympathetic
 Enables body to
unwind and calm down
 Most active when body
at rest
 Routine maintenance
functions
 Craniosacral division
 Fibers emerge from
brain and sacral
spinal cord
 Sympathetic
 “fight or flight”
 Mobilizes the body
during extreme
situations
 Becomes active when
extra metabolic effort
needed
 Thoracolumbar
division
 Fibers arise from
thoracic and lumbar
parts of spinal cord
ANS
 Includes a chain of 2 motor neurons
 Preganglionic neuron
 Preganglionic axon
 Ganglionic neuron
 Postganglionic axon
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Autonomic neuron synapses 2 neurons
PNS
 Somatic NS
 Autonomic NS
 Sympathetic division
 Parasympathetic
division
 Enteric division
Somatic Nervous System
 Innervates skeletal muscle
 Neurons runs from CNS directly to muscle
 Consists of single neuron plus skeletal
muscle cells
 Voluntary control
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Running, moving limbs, typing on a computer!
CNS – Spinal Cord
 Runs through vertebral canal of the vertebral
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column
Protected by bone, meninges, and
cerebrospinal fluid
Spinal cord made of a core of gray matter
surrounded by white matter
31 pairs of spinal nerves branch off spinal cord
through intervertebral foramen
Functions in many ways:
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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
Spinal Cord Growth
 Until 3rd month of
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development, does not
run to coccyx
As vertebral column
grows caudally, spinal
cord becomes more
rostral
At birth, ends at L3
During childhood,
terminates at L1 and L2
Adults runs from
medulla oblongata to L1
Regions of the Spinal Cord
 Cervical
 Thoracic
 Lumbar
 Sacral
 Coccygeal
 Cervical + Lumbar
enlargements
 Cauda equina
 Conus medullaris
 Filum terminale
Meninges of Brain and Spinal Cord
 Dura mater (superficial)
Spinal dural sheath
 Does not attach to bone
 Epidural space
 Fat and veins
 Between dura mater and
vertebra
 Subdural space
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Between dura mater and
arachnoid
Meninges of Brain and Spinal Cord
 Arachnoid mater (middle)
Impermeable layer =
barrier
 Raised off pia mater by
rootlets
 Subarachnoid space
 Between arachnoid and
pia mater
 Contains CSF
 Pia mater (deep)
 Highly vascular
 Adheres to brain/spinal
cord tissue
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Gray Mater
 Consists of neuron cell
bodies, unmyelinated
axons, dendrites, and
neuroglia
 Shaped like an “H”
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Gray commissure
(crossbar)
Central canal
 Posterior horns
 Anterior horns
Gray Mater
 Posterior horns
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Consist of interneurons that transmit in from outside spinal cord into it
Dorsal root contain sensory fibers
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Somatic Sensory (SS)
Visceral Sensory (VS)
Dorsal root ganglia - swelling in dorsal root that these interneurons pass
through
 Anterior horns
 Cell bodies of motor neurons send info out of spinal cord to muscles and
glands
 Ventral Root contains Motor Fibers
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Visceral Motor
Somatic Motor
White Mater
 Surrounds gray matter
 Composed of myelinated
and unmyelinated axons
 Divided into white
columns (funiculi)
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Posterior funiculus
Anterior funiculus
Lateral funiculus
 Allow for communication
between
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Parts of the spinal cord
Spinal cord and brain
White Mater
 3 types of nerve fibers:
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Ascending
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Descending
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Carry sensory info from sensory
neurons of body to brain
touch, pressure, pain, temperature
Carry motor instructions from brain
to spinal cord
Contraction of muscles and
secretion of glands
control precise, skilled movement =
writing, maintain balance, create
movement
Commissural
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Cross from one side of cord to the
other
Nervous System Overview