Lecture 4a - Peripheral Nervous System

ANAT 305 - Cross Sectional Anatomy. University of Alberta

What are the two portions of the nervous system

The CNS and the PNS

What are the two portions of the CNS

the brain (cerebrum, cerebellum, and brainstem)

the spinal cord

What are the two components of the PNS

The somatic nervous system and the autonomic nervous system

what can both the somatic and autonomic nervous system be split into

motor and sensory subdivision

What are the two portions of the motor subdivision of the ANS

the sympathetic and parasympathetic nervous systems

What regions of the spinal cord control the sympathetic motor ANS, and what type of response does it generate

The sympathetic motor ANS is primarily controlled by the thoracic and lumbar regions of the spinal cord, generating a 'fight or flight' response.

What regions of the spinal cord control the parasympathetic motor ANS, and what type of response does it generate

The parasympathetic motor ANS is primarily controlled by the brainstem and sacral regions of the spinal cord, generating a 'rest and digest' response.

What are sensory autonomic nerves sensitive to?

stretch, ischemia, and chemoreception

• They detect changes in the internal environment, such as blood pressure, oxygen levels, and chemical composition.

Is the pain sensation from sensory autonomic nerves well or poorly localized

Pain sensation from sensory autonomic nerves is poorly localized, often resulting in diffuse discomfort that is not easily traced to a specific source.

visceral afferent pain fibres in the sensory autonomic nervous sytem travel back to the spinal cord via what two nerves?

1. sympathetic nerves

2. vagus nerve

what is the origin of somatic structures

somatic mesoderm. which gives rise to skeletal muscles and skin.

what do somatic strucures include

skin, muscles, bone of the body wall, and parital membranes

• pleura, pericardium, peritoneum, periosteum

Where do somatic structures get their motor nerve supply from

spinal nerves (both segmental and non-segmental)

where do somatic structures get their sensory nerve supply from

spinal nerves (both segmental and non-segmental)

• these respond to modalities like pain, temperature touch and chemical stimuli

Describe somatic pain

it is sharp and well localized

what is the origin of the visceral / splanchnic structures

the splanchnic mesoderm

what do splanchnic structures include

viscera

• heart, lungs, liver, glands, smooth muscle, gut, uterus

Visceral membranes

where do splanchnic structures get their motor supply from?

the autonomic nervous system

• sympathetic = thoracolumbar (T1-L2)

• parasympathetic = craniosacral (III, IX, X, and S2-4)

where do splanchnic structures get their sensory nerve supply from ?

the autonomic nervous system

• visceral afferents travel with the sympathetics and the vagus nerve

• respond to stretch and ischemia

describe splanchnic structure pain

Splanchnic structure pain is often poorly localized and can be described as deep, aching sensations.

what do the branchial arche structures include

head and neck structures

where do branchial arch structures get both their motor and sensory nerve supply

Cranial nerves

the ____ and ____ are key to understanding the concept of pain

the spinal nerves and ANS

Spinal nerves supply _____ structures

somatic (body wall, extremeties) structures

• skeletal muscle, bone, parietal membranes and then become cutaneous to supply their dermatomes

what are dermatomes?

Areas of skin supplied by specific spinal nerves, which correlate to segments of the spinal cord.

Describe what is going on in the sensory neuron of this diagram

A sensory input (cold) travels along a sensory neuron (yellow) in the skin

• this can be dorsal (posterior) or vental (anterior)

the sensory axon runs along the dorsal root and reaches the dorsal root ganglion and passes to spinal cord where it synpases with a second order neuron that travels up to the thalamus and cerbral cortex via the spinothalamic tract where the brain activates a sympathetic response

Describe what is going on in the sympathetic neuron of this diagram

the preganglionc sympathetic neuron originates in the intermediolateral cell column (lateral) horn at T1-L2 (thoracolumbar since sympathetic)

• its axon exits via the ventral root and joins the spinal nerve entering the white ramus (myelinated) communicanes and synapses in the sympathetic ganglion with a postganglioninc neuron

the post ganglionic neuron leaves the ganglion via the gray ramus communicans (non-myelinated) where it regoins the spinal nerve then follows the dorsal and ventral rami to reach the skin to innervate muscles

describe what is going on in the red motor neuron

If instead the sensory input was pain, instead of going to the brain first, an internuron excites a motor neuron in the ventral horn for a reflex arc

• the motor neuron sends out it’s axon through the ventral root, passing into the spinal nerve and then out into the primary rmaus to reach skeletal muscles to move

how many pairs of spinal nerves do we have and where do they arise from?

There are 31 pairs of spinal nerves, which arise from the spinal cord and are organized into cervical, thoracic, lumbar, sacral, and coccygeal regions.

what do spinal nerves supply before coming cutaneous

skeletal muscles, parietal membranes

what are dermatomes

Bands of skin supplied by cutaneous branches of a single segmental spinal nerve.

Where are dertmatomes arranged in a segmental ladder-like fashion?

the thorax and abdomen

Why are dermatomes in the extremities and head/neck non-segmental?

Because innervation there is mixed through plexuses, not simple segmental nerves.

which dermatome responds to the sternal angle

T2

which dermatome respodns to the nipple

T4

which dermatome responds to the xiphoid process

T7

which dermatome responds to the umbilicus

T10

which dermatome responds to the suprapubic region

L1

Are all dorsal primary rami from C1 to Coccygeal 1 arranged segmentally?

yes

are all ventral primary rami arranged segmentally?

no

what are the only segmentally arranged ventral rami

the ventral rami of the thoracic spinals nerves T1-T12

What are the T1-T11 nerves called

intercostal nerves

the intercostal nerves are actually the ___

the ventral primary rami of thoracic spinal nerves T1-T11

what do the intercostal nerves supply?

the intercostal muscles, parietal

pleura, periosteum of ribs, diaphragm and the

superficial fascia and skin of the thoracic and

abdominal walls

what is the T12 nerve called

the subcostal nerve

what happens to the other spinal nerves (not T1-12) that are non-segmental

they form nerve plexuses that innervate various regions of the body.

what region of the spine does the cervical plexus innervate

C1-C4

what region of the spine does the brachial plexus innervate

C5-T1

What region of the spine does the lumbar plexus innervate

L1-L4

Segmental spinal nerves definition

segmental spinal nerves are nerves that arise from certain spine levles and innervate somatic structures derived from the somites of that same level.

• for example: spinal nerve T1 will supply somatic structures derived from the T1 somites and T1 somatic mesoderm

Non-segmental spinal nerves definition

where the ventral primary rami of spinal nerves are non-segmental, they join to form a nerve plexus

nerve plexus definition

a network of interjoining nerves

motor innervation to the thoracic and abdominal ciscera is provided by what fibres?

sympathetic autonomic fibres arising from the spinal cord via the sympathetic trunk

what spine segments have the symptathetic nerves to provide motor innervation to the thorax

T1-T5

what spine segments have the symptathetic nerves to provide motor innervation to the abdomen

T6 - L2

where are ALL preganglionic sympathetic neuroins located

in the lateral horn of the spinal cord, specifically in the thoracolumbar region (T1 to L2).

Once the preganglionic neuron arives at the sympathetic trunk it has five options, what is the first option?

Synapses in the sympathetic ganglion at the same level, and the postganglionic neuron leaves with the spinal nerve at that same level to be distributed to smooth muscle in somatic structures

• skeletal muscle, skin

Once the preganglionic neuron arives at the sympathetic trunk it has five options, what is the second option?

it synapses in the sympathetic ganglion at the same level and the postganglionic neuron tracks up or down the trunk to exit with the spinal nerves above or below T1 or L2 levels

Once the preganglionic neuron arives at the sympathetic trunk it has five options, what is the third option?

it synpases with the sympathetic ganglion at the same level and the postganglionic neuron tracks up or down the trunk until it find a direct nerve branch going to the thorax

• cardiac nerves, pulmonary plexus

Once the preganglionic neuron arives at the sympathetic trunk it has five options, what is the fourth option?

It DOES NOT synapse at the same level, but tracks up or down the trunk to synpase to reach the ganglia of the cervical or sacral region.

• example: tracks up to superior cervical ganglion to reach structures in the ehad and neck via the ICA nerve and plexus

Once the preganglionic neuron arives at the sympathetic trunk it has five options, what is the fifth option?

it DOES NOT synpase at the same level, but tracks up or down the trunk until it finds a splanchnic nerve the synpase in the abdominal prevertebral ganglion to reach abdominal organs via blood vessels

• example: tracks down to the celiac ganglion to reach the foregut via the celiac artery

What are splanchnic nerves?

Nerves that arise from the sympathetic nervous system and innervate the abdominal and pelvic organs. They carry preganglionic sympathetic fibers to various ganglia in the abdominal cavity.

• do not synapse at sympathetic chain ganglia, they pass through and synpase in prevertebral ganglia near abdominal aorta

what are visceral afferent fibres

sensory fibres from the viscera that respond to stretch, ischemia and chemoreception

where are white ramus communicans

found in the sympathetic nervous system and are only present at Levels T1-L2

where are gray ramus communicans found

Gray ramus communicans are found in the sympathetic nervous system and are present at all levels of the spinal cord.

what pathways does sensory innervation from the gut take to the brain?

visceral afferent pathways that go through the splanic nerve and then to the spinal trunk before reaching the dorsal root ganglia in the spinal cord.

• central pain pathways will ascend adjaced to the spinothalmic tracts —> thalamus —> cerebral cortex

what pathways does sensory information from the heart take to get to the brain

Visceral afferent pathways via the cardiac nerves to the spinal trunk, then to the dorsal root ganglia, ultimately reaching the thalamus and cerebral cortex.

• can also take the vagus nerve for parasympathetic signals to the brainstem

1

cerebrum

2

spinal cord

3

superior cervical ganglion

4

middler cervical ganglion

5

inferior cervical ganglion

6

preganglionic sympathathetic neurons (T1 —> L2/3)

7

sublingual and submandibular glands

8

cardiac and esophageal plexus

9

pulmonary plexus

10

greater splanchnic nerve

where does the greater splanchnic nerve synapse

the celiac ganlgion and plexus

11

celiac plexus and ganglia

13 (yes I know it is out of order)

lesser splanchnic nerve

where does the lesser splanchnic nerve synapse

at the aorticorenal ganglion and plexus

12

aorticorenal plexus

14

least splanchnic nerve

where does the least splanchnic nerve synapse

at the renal ganglion and plexus

18 (I know it’s out of order)

renal plexus

15

superior mesenteric plexus

16

lumbar splanchnic nerve

where does the lumbar splanchnic nerve synpase

in the inferior mesenteric ganglion and synaptic plexus.

17

inferior mesenteric plexus

1

cerebrum

2

spinal cord

CN ?

CN III - oculomotor nerve

Where does CN III synpase

At the ciliar ganglion

3

ciliary ganglion

CN ??

CN VII - facial nerve

Where does the facial nerve synpase (2 ganglion)

At the pterygopalatine and submandibular ganglia.

4

pterygopalatine ganglion

5

Submandibular ganglion

CN ???

CN IX - glossopharyngeal nerve

where does the glossopharyngeal nerve synpase

The glossopharyngeal nerve synapses at the otic ganglion