Download Spinal Nerves and Nerve Plexus

Spinal Cord and Spinal Nerves
Spinal Cord
• Enclosed in the vertebral canal, extends from the foramen
magnum of the skull to the first or second lumbar vertebra
where it terminates in the cone shaped conus medullaris
Spinal Cord
• Spinal meninges;
 Dura Mater – outer
 Arachnoid Mater – middle
 Pia Mater – inner
Spinal Cord
• Dura Mater – composed of dense, irregular connective tissue
Spinal Cord
• Arachnoid Mater – It is an avascular covering with a spider’s
web arrangement of delicate collagen fibers and some elastic
fibers
Spinal Cord
• Pia Mater – A vascular and thin transparent connective tissue
layer composed of interlacing bundles of collagen fibers and
some fine elastic fibers
Spinal Cord
• Subarachnoid space – between the arachnoid mater and pia
mater which contains cerebrospinal fluid
Spinal Cord
The dura mater and arachnoid meningeal coverings extend
beyond the conus medullaris, approximately to the level of S2
Spinal Cord
• Filium terminale – a fibrous extension of the pia mater, extends
farther and attaches to the posterior coccyx
Spinal Cord
• 31 pairs of spinal nerves, which exit via the intervertebral
foramina
Spinal Cord
• Since the spinal cord doesn’t extend to the end of the vertebral
column, the spinal nerves emerging from the inferior end must
travel through the vertebral canal until reaching the appropriate
intervertebral foramina
Spinal Cord
• This collection of spinal nerves are called the cauda equina
Spinal Cord / Gray Matter
• Looks like an H
Spinal Cord / Gray Matter
• Posterior or dorsal horns – posterior projections
Spinal Cord / Gray Matter
• Anterior or ventral horns – anterior projections that contain cell
bodies of motor neurons
Spinal Cord / Gray Matter
• Lateral Horns – In the thoracic and lumbar regions there is a
lateral outpocketing of gray matter
Spinal Cord / Gray Matter
• Gray commissure – central area of gray matter
Spinal Cord / Gray Matter
• Dorsal root – Sensory fibers enter the cord here
Spinal Cord / Gray Matter
• Dorsal Root Ganglia – Cell bodies of sensory neurons located
here
Spinal Cord / Gray Matter
• Ventral Roots – Motor neurons leave the cord here
Spinal Cord / Gray Matter
• Spinal nerves – are formed from the fusion of the dorsal and
ventral roots
Spinal Cord / Gray Matter
Spinal Nerves;
8 pairs of cervical nerves
12 pairs of thoracic nerves
5 pairs of lumbar nerves
5 pairs of sacral nerves
1 pair of coccygeal nerves
Spinal Cord / White Matter
• The anterior median fissure and the posterior median
sulcus divide the spinal cord into R. and L. sides
Spinal Cord / White Matter
• White matter is divided into columns;
Posterior Funiculus, Anterior Funiculus, and Lateral Funiculus
Spinal Cord / White Matter
• Each column contains distinct bundles of nerve axons called
tracts
Spinal Cord / White Matter
Two Types of Tracts
1. Sensory (ascending) tracts – conduct nerve impulses toward
the brain
Spinal Cord / White Matter
2. Motor (descending) tracts – conduct impulses down the cord
Connective Tissue Coverings of Spinal Nerves
• A fiber is a single axon within an endoneurium
Connective Tissue Coverings of Spinal Nerves
• A fascicle is a bundle of fibers within a perineurium
Connective Tissue Coverings of Spinal Nerves
• A nerve is a bundle of fascicles within an epineurium
Spinal Nerves and Nerve Plexus
• Each nerve divides into dorsal and ventral rami
Spinal Nerves and Nerve Plexus
• Rami contains both motor and sensory rami
Spinal Nerves and Nerve Plexus
• Dorsal rami – serve the skin and musculture of the posterior
body trunk at their approximate level of emergence
Spinal Nerves and Nerve Plexus
• Ventral rami of spinal nerves T2 –T12 – pass anteriorly to
supply the muscles of intercostal spaces, and the skin and
muscles of the anterior and lateral trunk
Spinal Nerves and Nerve Plexus
• Ventral rami of all other nerves – form complex networks of
nerves called plexuses
Spinal Nerves and Nerve Plexus
• The plexuses diverge again to form peripheral nerves
Spinal Nerves and Nerve Plexus
Four Plexuses
• Cervical
• Brachial
• Lumbar
• Sacral
Spinal Nerves and Nerve Plexus
• Cervical Plexus
Supplies the skin and muscles of the head, neck, and upper part
of the shoulders and diaphragm
Spinal Nerves and Nerve Plexus
• Damage to the spinal cord above the origin of the phrenic
nerves causes respiratory arrest.
Spinal Nerves and Nerve Plexus
• Breathing stops because the phrenic nerves stops sending
impulses to the diaphragm
Spinal Nerves and Nerve Plexus
• Brachial Plexus
Supplies the upper extremities and a number of neck and
shoulder muscles
Spinal Nerves and Nerve Plexus
• In carpal tunnel syndrome there is damage to the median nerve
Spinal Nerves and Nerve Plexus
• Lumbar Plexus
Supplies the anterolateral abdominal wall, external genitals, and
part of the lower extremities
Spinal Nerves and Nerve Plexus
• Femoral Nerve - Largest nerve arising from the lumbar plexus
Spinal Nerves and Nerve Plexus
4. Sacral Plexus
Supplies the buttocks and part of the lower extremities
Spinal Nerves and Nerve Plexus
• Sciatic Nerve – Largest nerve arising form the sacral plexus
Spinal Nerves and Nerve Plexus
• Sciatica – Pain that extends from the buttock down the back
of the leg due to injury to the sciatic nerve
Spinal Cord Physiology
• The white matter tracts are highways for nerve impulse
conduction to and from the brain
Spinal Cord Physiology
• The gray matter receives and integrates incoming and outgoing
information
Spinal Cord Physiology / Sensory Tracts
Sensory information from receptors travels up the spinal cord via
the;
• Spinothalamic tracts
• Posterior column tract
Spinal Cord Physiology / Sensory Tracts
 Spinothalamic tracts carry pain, touch, and temperature
impulses
Spinal Cord Physiology / Sensory Tracts
 Posterior columns carry proprioception and vibration
Spinal Cord Physiology / Motor Tracts
Motor info. travels from the brain down the spinal cord to muscles
and glands via the;
• Pyramidal tracts
• Extrapyramidal tracts
Spinal Cord Physiology / Motor Tracts
 Pyramidal tracts control voluntary, purposeful motor
movement of eyes, mouth, face, arms, and legs
Spinal Cord Physiology / Motor Tracts
 Extrapyramidal tracts control more complex things like the
accessory adjustments we make to muscle tone to adjust our
posture
Spinal Cord Physiology / Reflexes
• The gray matter of the spinal cord serves as an integrating
center for spinal reflexes
Spinal Cord Physiology / Reflexes
• A reflex is a fast, predictable, automatic response to changes in
the environment that helps to maintain homeostasis
Spinal Cord Physiology / Reflex Arc
Five functional components;
• Receptor
• Sensory Neuron
• Motor Neuron
• Integrating Center Neuron
• Effector
Stretch Reflex
1. Slight stretching of a muscle stimulates sensory receptors in
the muscle called muscle spindles
Stretch Reflex
2. In response to being stretched the muscle spindle generates
a nerve impulse along a somatic sensory neuron and enters the
spinal cord via the posterior root
Stretch Reflex
3. In the integrating center of the spinal cord the sensory neuron
makes an excitatory synapse with a motor neuron in the anterior
gray horn
Stretch Reflex
4. If the excitation is strong enough a nerve impulse is
propagated along the motor neuron which extends from the
spinal cord to the muscle
Stretch Reflex
5. ACh is released at the NMJ which triggers a muscle action
potential in the stretched muscle (effector) and the muscle
contracts