Introduction to Somatic and Autonomic Nervous Systems

What are the two main components of the nervous system?

Central nervous system (CNS) and Peripheral nervous system (PNS)

What makes up the CNS?

Brain and spinal cord

What makes up the PNS

Cranial, spinal, and splanchnic nerves

What are the divisions of the PNS?

Somatic nervous system (SNS) and Visceral nervous system (Autonomic nervous system - ANS)

What are the divisions of the visceral nervous system of PNS?

Visceromotor and viscerosensory

What are the divisions of the SNS?

Somatomotor and Somatosensory

What does visceromotor control?

Controls involuntary contraction of smooth muscle, cardiac muscle, and glands

What does viscerosensory control?

Modulates internal regulation (ex/ blood pressure, chemistry, respiration)

What are the 3 functions of the nervous system?

Sensory, integration, and motor (combined to maintain homeostatic state)

Describe the sensory function of the nervous system.

Collection of information from sensory receptors regarding internal and external environments.

Describe the integration function of the nervous system.

Processing sensory signals for decision-making

Describe the motor function of the nervous system.

Executing responses after decisions are made.

What does the SNS innervate?

Skeletal muscle and the body wall

Efferent

From the brain

Afferent

To the brain

What do the somatomotor nerves of SNS control?

Controls voluntary reflex contractions of skeletal muscles

What regions/structures are innervated of somatomotor nerves?

All skeletal muscles io head and neck regions + limbs

What do somatosensory nerves of SNS do?

Provides sensory innervation to skin, muscles, and joints

What regions/structures to somatosensory nerves provide sensation to?

Pain/temp/touch to skin, cornea, and certain mucosa - ex/ oral mucosa

Which is more precise temporally and spatially - SNS or ANS?

SNS

For the SNS, one motor neuron acts on _________ striated muscle motor units.

One

Which has no divergence of stimuli - SNS or ANS?

SNS

Why is pain from the ANS more diffused and dull?

Lots of divergent stimuli, therefore pain signals pass through multiple pathways.

What does the ANS innervate?

Internal organs, smooth muscle, cardiac muscle, and glands (most innervate structures in the viscera)

What kinds of responses are innervated by ANS?

Responses that are not under voluntary or congitive control

What do visceromotor nerves control?

Innervate involuntary contraction of smooth muscle and glands

What do viscerosensory nerves control?

Modulate internal conditions (ex/ blood pressure and respiration)

What nerves sends messages from viscerosensory to the brain?

Splanchnic nerves

What is viscerosensory pain?

Pain from an organ

What is the path that viscerosensory pain travels?

Splanchnic n., Sympathetic trunk, White communicating ramus, Ventral ramus, Spinal n., DRG (along T1-L2)

What are examples of viscerosensory reflex?

Vomiting, cough, chemoreceptors, baroreceptors

What is the path that the viscerosensory reflex travels along?

Parasympathetic pathway (cell bodies in vagal sensory ganglia)

What components of the nervous system work together to maintain homeostasis in the face of challenging external conditions?

Parasympathetic and sympathetic act in concert along with the somatic motor system to regulate normal or emergency behavior.

For the ANS, one motor neuron acts on _________ muscle cells.

Many

Sympathetic and parasympathetic nerves are a part of the [SNS/ANS]

ANS

What is the main function of the spinal cord?

Major conduit by which motor information travels from the cortex to the the peripheral nerves and sensory information travels from the peripheral nerves to the cortex

Name the meningeal layers from inside → outside

Pia mater → Arachnoid mater → Dura mater

What are denticulate ligaments?

Derived from Pia mater and divide dorsal and ventral sides of spinal cord

Where does the spinal cord sit within the vertebrae?

Vertebral foramen

How do dorsal and ventral roots exit the vertebral column?

Through intervertebral foramen

What are conus medullaris?

Sacral spinal cord segments that terminate at L1-2 vertebral level.

What is the filum terminale (composition and function)?

Derived from pia mater. Extension of conus medullaris that anchors spinal cord to sacrum.

What makes up the cauda equina?

Dorsal and ventral roots + Filum terminale

What is are dural sleeves?

Extension of dural mater that pass through the sacrum and allow dorsal and ventral roots to exit the sacrum (present in all levels - cervical, thoracic, lumbar, and sacrum)

What makes up white matter?

Myelinated axons

Where is the location of white matter in the spinal cord?

In the periphery

What makes up gray matter?

Cell bodies and unmyelinated axons

What type of neurons are in the dorsal horn?

Sensory neurons

What type of neurons are in the ventral horn?

Motor neurons

What type of neurons are in the lateral horns of thoracic spinal cords?

Sympathetic neuron

Unique feature of cervical and lumbar spinal cord (relative to ventral/dorsal horn)

Large ventral horns that contain cell bodies of motor neurons that innervate the upper and lower limbs respectively.

Unique feature of thoracic spinal cord

Have lateral horns that house the cell bodies for sympathetic (preganglionic) neurons with relatively small ventral horns

Where is the epidural space?

Space between the dura mater and vertebral column containing fat and blood vessels/

How many segments contribute to spinal nerves? Include the split between the different levels.

31 segments (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal)

Spinal cord segment

Region of the spinal cord that contribute to the formation of an individual spinal nerve

Spinal cord level

Location of an individual spinal cord segment along the spinal cord

In a newborn, the length of the spinal cord is ______ than the length of the vertebral column.

Shorter

Why are lumbar punctures performed between L3 and L4 vertebrae?

Performed at the level of cauda equina in adults to avoid damaging the spinal cord (rational behind why can only be performed in adults)

Components of spinal nerves

Sensory component (sensory info from body back to CNS) and motor component (execute motor commands from CNS and ANS)

List the main plexuses from superior → inferior

Cervical plexus, Brachial plexus, Intercostal nerves, Lumbar plexus, and Sacral plexus

Path of motor neuron from ventral horn → ventral ramus

Ventral horn, Ventral root, Spinal n., Ventral ramus

Path of sensory receptor from dorsal ramus → dorsal horn

Dorsal ramus, Spinal n., DRG, Dorsal root, Dorsal horn

Spinal nerve is made up of ______ and ______.

Dorsal root (afferent - sensory) and ventral root (efferent - motor)

Rami definition

Spinal n. branch that travels out to the periphery (carry motor, sensory, and autonomics)

What does the dorsal rami carry?

Sensory and motor info to and from the midline muscles and skin of the back (innervates deep back muscles and overlying skin)

What does the ventral rami carry?

Sensory and motor info to the remainder of the muscles and skins from the trunk and limns (innervate all other parts of “body wall”)

Which is larger, dorsal ramus or ventral ramus?

Ventral

What makes up a sensory strip on the body wall?

Cutaneous branches of the dorsal and ventral rami

Dermatome

Localized area of the body wall innervated by sensory fibers from the dorsal and ventral primary rami of each spinal cord segment

T4 dermatome

Nipple area

T10 dermatome

Umbilicus

T12/L1 dermatome

Pubic region

Why does anesthetizing one spinal nerve or dorsal root not provide anesthesia?

Dermatomes overlap (need to provide anesthesia to multiple spinal nerves)

Sympathetic nerves cell body location

Lateral horn at T1 to L2

How do sympathetic nerves leave the CNS?

Ventral roots of T1 to L2

Where do sympathetic nerves go once they leave the CNS?

All areas of the body (including the body wall)

Are 2nd neuron cell bodies (SNS) in ganglia associated with target organ?

No, ganglia are not associated with target organ

If destined for skin and thoracic viscera, where are cell bodies located?

Paravertebral ganglia of the sympathetic trunk

If destined for abdominopelvic viscera, where are cell bodies located?

Prevertebral ganglia

Sympathetic trunk

Paired conduits for sympathetic axons with ganglia spread along the trunks (sites for synapses) that run from the base of the skull to the tip of the coccyx

Superior cervical ganglion

Large ganglion at the super end of the sympathetic chain near C2

How are sympathetic signals amplified?

2 neuron system

General path of sympathetics

Lateral horn of T1-L2 segments, Ventral root, Spinal n., Ventral ramus, White communicating ramus, Sympathetic trunk … target

GVE Sympathetics: Pathway to body wall structure at same level

Lateral horn of T1-L2, Ventral root, Spinal n., Ventral ramus, White communicating ramus, Sympathetic trunk, Chain ganglia, Gray ramus (at same level), Dorsal/Ventral ramus (depending on target)

GVE Sympathetics: Pathway to body wall structures in the head, neck, and limbs

Lateral horn of T1-4, Ventral root, Spinal n., Ventral ramus, White communicating ramus, Sympathetic trunk (ascends), Synapse at cervical chain ganglia, Gray rami, Dorsal/Ventral rami

GVE Sympathetics: Pathway to body wall structures in the lumbar and sacral revions

Lateral horn of T12-L2, Ventral root, Spinal n., Ventral ramus, White communicating ramus, Sympathetic trunk (descends), Synapses at lumbar and sacral chain ganglia, Gray rami, Dorsal/Ventral rami

GVE Sympathetics: Pathway to thoracic viscera

Lateral horn of T1-4, Ventral root, Spinal n., Ventral ramus, White communicating ramus, Sypathetic trunk, Synapses at thoracic chain ganglia, Exit sympathetic trunk through splanchnic n. (connected to thoracic organ)

GVE Sympathetics: Pathway to abdominal viscera

Lateral horn of T5-12, Ventral root, Spinal n., Ventral ramus, White communicating ramus, Sympathetic trunk, Enter thoracic splanchnic n., Preaortic ganglia, Synapse, Connect to target organ

Parasympathetic nerve cell body location

Lateral horn of spinal cord at S2, 3, and 4

How do parasympathetic nerves leave the CNS

Cranial nerves and ventral roots of S2, 3, and 4

How do 2nd neuron cell bodies of parasympathetic nerves differ from sympathetic nerves?

Ganglia are associated with target organs

Do parasympathetic nerves go to body wall structures?

No, only goes to “internal core”

List the paired parasympathetic ganglia of the head.

Otic, ciliary, submandibular, and pterygopalatine

Nerve components of dorsal and ventral rami

Somatomotor, somatosensory, visceromotor fibers

Nerve components of cutaneous nerves

Somatosensory and visceromotor fibers

Nerve components of motor nerve (skeletal muscle)

Somatomotor, somatosensory, visceromotor fibers

What are the 5 special senses

Smell, Vision, Hearing, Balance, Taste

Which CN only have special sensory components?

Olfactory (I) - Smell; Optic (II) - Vision; Vestibulochoclear (VIII) - Hearing and balance

Which CN only have somatomotor components?

Trochlear (IV); Abducent (VI); Accessory (XI); Hypoglossal (XII)

Which CN has 2 nerve components?

Oculomotor (CN III) - SM and Parasymp/Pre