Spinal & Cranial Nerves

Cervical plexus is composed of:

Ventral rami of C-C4 Consists of cutaneous and muscular branches Cutaneous branch innervates: Head Chest Ventral rami of C-C4 Consists of cutaneous and muscular branches Cutaneous branch innervates: •Head •Neck •Chest

There are 31 pairs of spinal nerves

8 cervical nerves 12 thoracic nerves 5 lumbar nerves 5 sacral nerves 1 coccygeal nerve

The patterns of innervation from each spinal segment are among all humans

Each spinal segment innervates a particular dermatome

Each peripheral nerve consists of several layers of connective tissue:

Epineurium Perineurium Endoneurium

Gray Matter

Gray matter consists of the cell bodies of neurons organized into regions called horns. This area of the spinal cord acts as an integration and reflex processing center. Surrounding the gray matter is white matter

Higher centers and integration of reflexes

Higher Centers (like the cerebrum) •Enhance or suppress spinal reflexes •Modify information carried in descending tracts of the spinal cord

Spinal reflexes can be: Polysynaptic

Integrates motor output from several spinal segments

Endoneurium

Layer surrounding a single axon

Spinal Nerve Roots

Spinal nerves transfer signals between the body and the spinal cord. Each spinal nerve connects to the spinal cord through a dorsal and ventral root. The dorsal root also includes a ganglion, a coI lection of cell bodies of the sensory neurons. Dorsal roots transmit sensory signals. Ventral roots transmit motor signals

Cervical Innervation

The cervical plexus innervates skin and muscles of the neck. The phrenic nerves innervate the diaphragm.

Pathway of a reflex arc

1. Stimulus 2. Activation of a sensory receptor 3. Relay of information to the CNS 4. Information processing 5. Activation of a motor neuron 6. Activation of the effector organ 7. Response

Stretch reflex (patellar and postural reflexes)

1. Stimulus stretches a muscle 2. Activates a sensory neuron 3. Information is processed in the spinal cord 4. Motor neurons are activated 5. Muscle (effector) contracts

Dermatomes

A dermatome is a region of skin that is innervated by the sensory fibers from a single spinal nerve. Sensory signals travel from the skin through the dorsal root of the spinal nerve, into the spinal Cord and up to the brain. All the sacral, lumbar thoracic, and cervical spinal nerves innervate dermatomes except the first cervical spinal nerve (C) Which does not cOntain any sensory axons. instead, the sensory information from the skin of the facial region is conveved by cranial nerve V, the trigeminal nerve

Reflex

An immediate involuntary motor response

Motor (efferent)

Occulomotor (III), Trochlear (IV) Abducens (VI), Accessory (XI), Hypoglossal (XII)

Cervical Plexus

Major nerves of the cervical plexus include the transverse cervical, great auricular, lesser occipital, supraclavicular, and phrenic nerves.

Lumbosacral Plexus

Many nerves •Sciatic nerve •Femoral nerve •Innervates hips and legs

Motor Commands

Motor commands pass from the spinal cord through the ventral root of each spinal nerve and out Motor commands pass from the spinal cord through the ventral root of each spinal nerve and out to the body to trigger an action. This action is either skeletal muscle contraction or gland secretion.

Special sensory nerves (afferent)

Olfactory (), optic (II) Vestibulocochlear (VIII)

Epineurium

Outer layer-becomes continuous with the dura mater

Classification of Reflexes

Reflexes are classified according to: •Their development ~Innate or acquired •The site where information is processed ~Spinal or cranial •The nature of the resulting motor response ~Somatic, visceral, or autonomic •The complexity of the neural circuit ~Monosynaptic or polysynaptic

Sensory Signals

Sensory signals are passed into the spinal cord through the dorsal root of each spinal nerve. Cell bodies of sensory nerves are clustered in a bundle, the dorsal root ganglion.

Brachial Plexus

The organization of the brachial plexus: •Begin with the spinal cord •Ventral rami (roots) Trunks (superior middle, and inferior trunk) Divisions (anterior and posterior divisions) Cords (posterior, lateral, and medial cords) •Nerves

Spinal Cord

The spinal cord is a structure of the central nervous system formed by bundles of neurons and neuroglia that are protected by the meninges and enclosed inside the vertebral column. The spinal cord transmits signals between the brain and the rest of the body and controls reflexes.

Spine Cross Section

The spinal cord is protected by the meninges and enclosed in the vertebral canal, a hollow space inside the vertebrae. Spinal nerves, which form the majority of the peripheral nervous system, originate in the spinal cord. The dorsal roots arise from the posterior side, and the ventral roots arise from the anterior side. After leaving the vertebral column, the spinal nerves divide into rami, which branch to supply the body.

Spinal Nerve Regions

The spinal nerves are divided into 8 pairs of cervical nerves, 12 pairs of thoracic nerves, 5 pairs of lumbar nerves, and 5 pairs of sacral nerves.

Spinal Nerves

The spinal nerves arise from the spinal cord. Their branches are grouped into regions (cervical, thoracic, lumbar, and sacral) that cOrespond to the area of the vertebral column from which they originate. Many spinal nerves are also grouped into plexuses, networks of spinal nerves that innervate a specific region. The cervical plexus innervates the neck and thoracic cavity. The brachial plexus innervates the shoulder girdle and upper limbs. The lumbar and sacral plexuses (also called the lumbosacral plexus) innervates the pelvis and lower limbs.

Mixed motor/sensory

Trigeminal (V), Facial (VII), Glossopharyngeal (IX), Vagus (X)

white matter

formed by myelinated and unmyelinated axons organized into columns that down the spinal cord. information up and pass

Spinal reflexes can be: Monosynaptic

volves a single segment the spinal cord

The peripheral nerves sometimes group together to form a

• Interwoven network of peripheral nerves • Plexus means "to braid"

There are four nerve plexuses

•Cervical plexus •Brachial plexus •Lumbar plexus •Sacral plexus Sometimes the lumbar and sacral are combined to form the lumbosacral plexus

Perineurium

•Layer surrounding a fascicle •A fascicle is a bundle axons

Reflex arc

•The neural "wiring" of a single reflex •Begins at a sensory receptor and ends at a peripheral effector •No higher-order brain processing •Cortex