PNS

What are the two main divisions of the PNS

Somatic Nervous System

Autonomic nervous system

Autonomic Nervous System

consists of heart muscles, smooth muscles and glands

divides further into sympathetic and parasympathetic

Somatic Nervous System

consists of voluntary skeletal muscles, skin, fascia, connective tissue, bone, and cartilage

Segmental Innervation

Dermatomes and myotomes labelled with a letter and a number based on the spinal nerve innervating a specific segment

Peripheral innervation

Innervations carried by branches of a plexus, labelled with names of peripheral nerves

2 Types of Somatic Fibers

General Somatic Afferent (GSA)

General Somatic Efferent (GSE)

GSA

General Somatic Afferent fibers

Transmit FROM the body TO the CNS

Sensory information from body wall: skin, skeletal muscles, fascia, cartilage

Exteroceptive sensations - pain, temperature, touch, pressure

Proprioceptive sensations

GSE

General Somatic Efferent fibers

Transmit TO body FROM CNS

Transmit impulses to skeletal muscles

2 Types of Visceral Fibers

General Visceral Afferent (GVA)

General Visceral Efferent (GVE)

GVA

General Visceral Afferent fibers

Sensory information

Transmits pain or subconscious visceral reflex sensations FROM hollow organs and blood vessels TO the CNS

Ex. of sensory information: bloating, digestion, gas

GVE

General VIsceral Efferent fibers

Transmits TO smooth muscle, modified cardiac muscle, and glandular tissues FROM the CNS

Consists of presynaptic/preganglionic fibers and postsynaptic/postganglionic fibers

Where are the cell bodies of presynaptic/preganglionic fibers?

in the spinal cord

Where are the cell bodies of postsynaptic/postganglionic fibers?

in peripheral ganglia

GSE vs GVE

GSE transmits through a single neuron travelling to a somatic organ

GVE transmits through presynaptic fibers and postsynaptic fibers

Somites

A bilteral row of biscuit-like structures which represent our primal spinal cord

Tissues will give rise to muscle, bone, and other connective tissue

Sclerotomes

Originate from medial sides of somites

Migrate ventrally to surround notochord and will make up body of vertebrae

Migrate dorsally to surround neural tube to create neural arch of vertebrae

Nerves and Somites

Develop in bilateral pairs that serve the dermis-forming and muscle forming tissue of some adjacent somites

Motor Neurons

Send processes peripherally into posterior and anterior dermatomyotome

Develop in the anterior neural tube

Sensory Neurons

Send peripheral processes into regions of dermatomyotome and central processes into posterior neural tube

Develop in neural crests

Somatic Sensory and Motor Nerve Fibers

Organized segmentally along neural tubes

Becomes part of all spinal nerves and some cranial nerves

Ganglia

Cluster of cell bodies

Derived from neural crest

Located OUTSIDE of the CNS

Myotome

Unilateral mass of muscle supplied by a single spinal nerve

Dermatomyotomes

Lateral aspect of somite

Give rise to skeletal muscles and dermis of the skin

Deep back muscles and overlying dermis originate from dermatomyotomes that migrate posteriorly

Hypaxial muscles of anterolateral trunk and limbs and associated dermis arise from dermatomyotomes that migrate anteriorly

Dermatomes

Unilateral area of skin supplied by a single pair of spinal nerves

Often there is overlapping of innervation zones

No C1 dermatome

Important Dermatomes

C2 - Innervates back of head (highest dermatome)

C4 - top of the shoulders

C6 - thumb

C7 - middle finger

C8 - little finger

T4 - level of nipples ;)

T10 - level of umbiculus

T12/L1 - skin along inguinal crease

L4 - big toe

S1 - little toe and sole of foot

What does C2 innervate?

Back of head

What does C4 innervate?

Top of shoulders

What does C6 innervate?

Thumb

What does C7 innervate?

Middle finger

What does C8 innervate?

Little finger

What does T4 innervate?

Level of nipples

What does T10 innervate?

Level of umbilicus

What does T12/L1 innervate?

Skin along inguinal crease

What does L4 innervate?

Big toe

What does S1 innervate?

Little toe and sole of foot

What does S4/S5/Cocc 1 innervate?

Skin around the anus ;)

Nerve Fiber Components

Neurolemma

Dendrites

Axon

Soma

Neurolemma

Consists of cell membranes of Schwann cells surrounding the axon

Myelinate or unmelinated

Dendrites

Receive signals

Axon

Send signals

Soma

Cell body

Label This Diagram

Connective Tissue Coverings of Nerves

Endoneurium

Perineurium

Epineurium

Afferent Division

Flows towards the brain

Somatic and visceral sensory

Special sensory

Efferent Divisions

Flows away from the brain

Somatic and autonomic motor

Autonomic motor divides into: parasympathetic, sympathetic, and enteric

Neuron

Bundle of axons

Ganglia

Bundle of soma

Ventral Root Ganglia

Sympathetic

Each spinal cord segment has two ventral roots that connect by a white ramus to a spinal sympathetic ganglion

Dorsal Root Ganglia

Spinal ganglia - close to the spinal cord

A collection of neuronal cell bodies of sensory neurons near the spinal cord

Most common type of sensory ganglia in the body

Autonomic Ganglia

Sympathetic Ganglia

Parasympathetic Ganglia

Spinal Nerves (definition and how many of each)

Exit the spinal cord through intervertebral foramina

Arise from spinal cord as rootlets and converge to form 2 nerve roots: anterior/ventral nerve root and posterior/dorsal nerve root

8 cervical

12 thoracic

5 lumbar

5 sacral

1 coccygeal

Anterior/Ventral Nerve Root

Efferent fibers

Pass FROM nerve cell bodies in anterior and lateral horns of spinal cord gray matter TO effector organs located peripherally

Interwoven networks of nerves formed by ventral rami of adjacent spinal nerves

Plexuses of Ventral Nerve Root

Cranial plexus

Brachial plexus

Lumbar plexus

Sacral plexus

Coccygeal plexus

Cranial plexus made up of

C1-C4

Brachial plexus made up of

C5-T1

Lumbar plexus made up of

L1-L4

Sacral plexus made up of

L4-S4

Coccygeal plexus

S4-Co1

Posterior/Dorsal Nerve Root

Afferent fibers

Move FROM soma in sensory endings in dorsal root ganglia that extend peripherally to sensory endings and centrally to posterior horn

Dorsal and Ventral Root Labeled

Cranial Nerves

Exit the cranial cavity through foramina in cranium

Named from most anterior and superior to most inferior and posterior

Arise in bilateral pairs

Little overlap in innervations

Communicate only between cranial nerves and upper cervical nerves

Which two cranial nerves branch off the cerebrum instead of the brainstem?

CN I and CN II

List all the Optic Nerves

CN I = olfactory

CN II = optic

CN III = oculomotor

CN IV = trochlear

CN V = trigeminal

CN VI = abducens

CN VII = facial

CN VIII = vestibulocochlear

CN IX = glossopharyngeal

CN X = vagus

CN XI = spinal accessory

CN XII = hypoglossal

Visceral and Motor Nerve Fiber Pathways

Cranial Nerves of GSA?

CN II and VIII

Cranial Nerves of SVE

Muscles of facial expression = CN VII

Muscles of mastication = CN V

Pharyngeal muscles (swallowing) = CN IX, X

Laryngeal muscles (speaking) = CN X

Trapexius and sternocleidomastoid = CN XI

Send and receive motor stimuli to all skeletal muscles derived from pharyngeal arches **

Cranial Nerves of SVA

CN I = olfactory

CN VII, IX, and X = gustation

receive olfactory stimuli and gustatory stimuli **

Nerves of GSE

Send motor stimuli to all skeletal muscles except those derived from pharyngeal arches

Nerves of GVE

Send motor stimuli to smooth muscles, cardiac muscle, and glandular tissues

Nerves of GSA

Receive sensory stimuli from somatic structures such as skin, superficial and deep fasciae, skeletal muscles, bones, joints, ligaments and tendons

Nerves of GVA

Receive sensory stimuli from visceral organs

Nerves of SSA

Receive visual and auditory stimuli through CN II and VIII

Gray Matter

Made up of soma of nerve fibers

Gray because of the high nucleus concentration

Deep to white fibers

Found in anterior/ventral horn and posterior/dorsal horn

Anterior/Ventral Horn

Lower motor neuron from the ventral horn

Somatic efferent signals

Send OUT signals

Posterior/Dorsal Horn

Somatic afferent signals

RECEIVES signals

White Matter

Outermost layer of spinal nerve

Primarily made up of myelinated axons

White because Schwann cells make up the myelination of the fibers

Where do the Ventral and Dorsal Nerve Roots Unite?

Within or proximal to intervertebral foramen as they emerge from the spinal column

What is formed by the uniting of the ventral and dorsal nerve roots?

Mixed spinal nerve —> both sensory and motor

Will immediately divide into 2 rami - dorsal and ventral ramus

Ventral Ramus (supply?) (location?) (merge?) (become?)

Supplies nerve fibers to: skin, hypaxial muscles of anterior and lateral regions of trunk, and upper and lower limbs

Remain in trunk

Merge in limbs with 1 or more other ventral ramus - form somatic nerve plexuses; fibers intermingle and multisegmented peripheral nerves emerge

Will become motor and cutaneous nerves

Neurons of the PNS

Sensory Neurons

Visceral and sensory are processes of pseudounipolar neurons with cell bodies OUTSIDE the CNS

In spinal or cranial sensory ganglia

Motor Neurons

Motor fibers of nerve are axons of multipolar neurons

Cell bodies of somatic motor and presynaptic visceral motor neuron are located IN the CNS in gray matter of spinal cord

Transverse Section Showing Rami

Referred Pain

Occurs when sensory information comes to the spinal cord but is interpreted as coming from another location innervated by the same spinal cord level

Viscero-Somatic Referred Pain

Stimulus acting on a visceral organ, sensation appearing in somatic structure

Somato-Somatic Referred Pain

Stimulus acting on a somatic structure, sensation appearing in a different somatic structure

Somatic Nervous System

Provides sensory and motor innervation to all parts of the body EXCEPT viscera

Transmits touch, pain, temperature, and position from sensory receptors

Most reach the conscious level

Innervate only skeletal muscle

Autonomic Nervous System

Visceral nervous system

Innervates smooth muscle, modified cardiac muscle and glandular cells

Efferent fibers accompanied by afferent fibers

Efferent autonomic regulation depends on feedback from sensory organs

Major Functions of Autonomic Nervous System

Regulate heartbeat

Smooth muscle contraction

Glandular secretions to maintain homeostasis

Efferent Fibers Divide Into:

Parasympathetic - BREAK PEDAL

Sympathetic - GAS PEDAL

Parasympathetic vs Sympathetic Anatomically

Location of presynaptic cell bodies

Which nerve conducts presynaptic fibers from CNS

Conduction of Impulses

Involves a series of 2 multipolar neurons: presynaptic/preganglionic neurons and postsynaptic/postganglionic neurons

Presynaptic/Preganglionic Neurons

Soma located in gray matter in CNS

Fibers (axons) synapse on soma of postsynaptic neuron

Postsynaptic/Postganglionic Neuron

Somas outside CNS in autonomic ganglia

Fibers (axons) terminate on effector organ

Reflex Arc

All neurons function in reflex arcs

Receptor picks up stimulus —> sends stimulus to afferent neuron —> brain/CNS —> efferent neuron (preganglionic and postganglionic) —> vector organ —> issues a response

Parasympathetic System (origin) (types) (purpose)

Craniosacral origin = brainstem, S2-S4

Types: cranial and intramural (intramural is embedded in wall of vector organ)

Energy conserving - rest and digesr

LONG presynaptic neuron axons

SHORT postsynaptic neuron axons

Parasympathetic Pathways

Sympathetic (origin) (types) (purpose)

Thoracolumbar origin

Types: paravertebral and prevertebral/preaortic

Energy expending - fight or flight

SHORT preganglionic neuron axon

LONG postganglionic neuron axon

Sympathetic Pathways

Where are the cell bodies of the sympathetic division?

Cell bodies are in intermediolateral cell columns (IML) or in nuclei of spinal cord

• Gray matter of T1-L2/3

• IMLs are organized somatotopically