2 - 10 29 Spinal Cord & PNS - PHYL 301

Peripheral Nervous System (PNS)

• Branches off the CNS to the rest of the body

• Spinal nerves

• Cranial nerves

Central Nervous System (CNS)

• Brain

• Spinal Cord

Spina Bifida

• Birth defect

• Folate (vitamin B 9 ) deficiency increases risk of spina bifida

• Caused by incomplete neural tube closure

• Location & severity varies

Which primary and secondary brain vesicles give rise to the Cerebrum?

Prosehow do i phrancephalon (forebrain) → Telencephalon → Cerebrum

Which primary and secondary brain vesicles give rise to the Eye cup, Thalamus, hypothalamus, and epithalamus?

Prosencephalon (forebrain) → Diencephalon → Eye cup, Thalamus, hypothalamus, and epithalamus

Which primary and secondary brain vesicles give rise to the Midbrain?

Mesencephalon (Midbrain) → Mesencephalon → Midbrain

Which primary and secondary brain vesicles give rise to the Pons and Cerebellum?

Rhombencephalon (Hindbrain) → Mesencephalon → Pons and Cerebellum

Which primary and secondary brain vesicles give rise to the Medulla Oblongata?

Rhombencephalon (Hindbrain) → Myelencephalon → Medulla

How How does the neural plate become the neural tube?does the neural plate become the neural tube?

1. Part of the ectoderm thickens to form the neural plate (neuroectoderm).

2. The center of the plate dips inward to form the neural groove, while the edges rise to form the neural folds.

3. The neural folds converge (move toward each other) and fuse, forming the neural tube beneath the surface ectoderm. Cells at the edges of the folds separate to form the neural crest.

The neural tube head end develops into the brain and the rest develops into the spinal cord.

Meninges

• Specialized membranes wrapping entire CNS

• Provide protection, physical stability, and shock absorption

• Spinal meninges continuous with cranial meninges

Meningeal layers

• Dura mater: Tough, fibrous outermost layer

• Arachnoid mater: Middle delicate meshwork layer

• Pia mater: Soft, innermost layer; adheres to CNS tissue

Dura mater

Tough, fibrous outermost layer

Arachnoid mater

Middle delicate meshwork layer

Pia mater

Soft, innermost layer; adheres to CNS tissue

What is the dura mater, and what type of tissue is it made of?

Tough, fibrous outermost layer of the meninges.

• made of dense irregular connective tissue.

How does the dura mater help stabilize the spinal cord?

Its cranial and sacral attachments help stabilize the spinal cord lengthwise within the vertebral canal

Where is the spinal epidural space?

Space between the dura mater and lining of the vertebral bones

What forms the coccygeal ligament?

The dura mater blends with the filum terminale, forming the ligament that anchors to the coccyx

Where is the arachnoid mater?

Middle meningeal layer, between the dura mater and pia mater

Arachnoid trabeculae and where do they extend from?

Thin, web-like strands that extend from the arachnoid mater to the pia mater

Where is the subarachnoid space, and what flows through it?

• Between arachnoid (middle) and pia (inner)mater

• Cerebrospinal fluid flows within subarachnoid space

Subdural space

• Potential space between the dura (outermost) mater and arachnoid mater

• Not found in healthy living people, but may appear in disease or in cadavers

What is the Pia Mater and what does it contain?

• Deepest meningeal layer

• Contains blood vessels in this layer

• Firmly bound to brain and spinal cord tissue

• Denticulate ligaments:

  • extensions of pia mater attach it and arachnoid mater to the dura mater

Meningitis

• -itis” = inflammation

• meningitis - acute inflammation of the meninges

• CSF should be sterile

• Many possible causes of infection

  • fungi

  • parasites

  • viruses

  • bacteria (e.g., Neisseria meningitidis)

Gray Matter

• Mostly consists of neuronal cell bodies (somas) and glial cells

• Surrounds central canal (inner butterfly)

• Forms horns

grAy = mAss = cell bodies

White matter

• Consists of axons (myelinated and unmyelinated)

• Axons organized into tracts or columns (outer)

• Generally superficial to gray matter

white outline, axons WX

What is a nucleus in the central nervous system?

Cluster of neuron cell bodies in the CNS (brain or spinal cord)

What is a ganglion?

cluster of neuron cell bodies in the PNS

• The dorsal root ganglion is one example.

What is a tract?

Bundle of axons within the CNS

What is a nerve?

Bundle of axons in the PNS, wrapped in connective tissue

• It can carry sensory signals, motor signals, or both

What does the posterior (dorsal) root carry?

Somatic Sensory (afferent) and viseral sensory nuclei signals into the spinal cord.

top

What does the Lateral horns (intermediate horns) carry?

Visceral motor unit nuclei

Middle

What does the anterior (ventral) root carry?

Somatic Motor (efferent) signals out of the spinal cord.

Bottom

Where is the dorsal root ganglion, and what does it contain?

Swelling on the dorsal root near the intervertebral foramen. It contains sensory neuron cell bodies

What are the three connective tissue layers of a spinal nerve?

Endoneurium wraps each axon.

Perineurium wraps each fascicle (bundle of axons).

Epineurium wraps the whole nerve

How does a typical spinal nerve form, and why is it mixed?

he dorsal and ventral roots join near the intervertebral foramen. The resulting spinal nerve carries both sensory and motor axons.

What are the two main branches of a spinal nerve, and what do they supply?

The dorsal ramus supplies the deep back muscles and skin of the back. The ventral ramus supplies the front and sides of the trunk and the limbs. Both rami are mixed.

Peripheral neuropathy

Condition resulting from peripheral nerve damage

• Many potential causes

  • Trauma, infection, Vitamin deficency, alchol use, type 2 diabetes

Peripheral neuropathy - Sensory Symptoms

• Numbess, Tingling, Pain

  • False signals, feeling sensations singals sent to wrong part

• Sharp, throbbing, freezing, or burning pain

Peripheral neuropathy - Motor Symptoms

• Muscle Weakness, paralysis

• Lack of coordination & falling

Peripheral neuropathy - Treatment

• Trauma

  • Medications, physical therapy, surgery, etc.

• infection

  • Medications (e.g. antibiotics)

• Vitamin deficency

  • Diet & supplements

• alchol use

  • Limit or discontinue alcohol

• type 2 diabetes

  • Weight, diet, & lifestyle management

Leprosy (Hansen's disease)

• Caused by Mycobacterium leprae bacteria

• Symptoms can take years to appear

• Can cause peripheral neuropathy

  • Loss of sensation

  • Paralysis of hands and feet

Prof. Alice Augusta Ball

• University of Hawaiʻi’s first female and African American chemistry professor

• 1915 – Developed early injectable treatment for leprosy from chaulmoogra tree

• Leprosy now curable with antibiotics

The 31 pairs of spinal nerves

• 8 cervical nerves

• 12 thoracic nerves

• 5 lumbar nerves

• 5 sacral nerves

• 1 coccygeal nerve

Main difference of cervical spinal nerves?

8 Cervical spinal nerves

Smallest to largest of Peripheral Nerve Connective Layers

Endometrium → Perineurium → Epineurium

Endoneurium

• Smallest, innermost

• Loose Connective Tissue

• Surrounds each axon (nerve fiber)

Perineurium

• Surrounds each Fascicle (fascicles), bundle of axons

• Connective Tissue

Epineurium

• Most outermost layer

• Irregular connective tissue

• Surrounding entire spinal nerve; continuous with dura mater

What are the main branches of a spinal nerve, how do they connect to the sympathetic nervous system?

• Main branches: The dorsal (posterior) ramus and ventral (anterior) ramus. Both carry sensory and motor fibers.

• Sympathetic connections: White and gray rami communicantes connect spinal nerves to the sympathetic trunk. T1–L2 have both. Gray rami are present at all spinal levels.

Dermatome

An area of skin supplied by sensory fibers from a single spinal nerve root

When neuron cell bodies are grouped together what is it called?

CNS: Nucleus

PNS: Ganglion (like dorsal root ganglion)

When axons are grouped together what is it called?

CNS: tract (carries signals in CNS)

PNS: Nerves (carries sensory, motor, or both signals)

Structure of nerve: Smallest to largest

Nerve fiber → fascicle (bundle of fibers) → whole peripheral nerve

wrapped in: endoneurium → perineurium → epineurium

Innervation

Distribution or supply of nerves to a body region

Which direction do signals travel in sensory innervation?

Receptors in the tissue → CNS

Sensory signals are afferent, meaning they travel toward the CNS

Which direction do signals travel in motor innervation?

CNS → muscles or glands

Motor signals are efferent, meaning they travel away from the CNS

Somatosensation Tests

• Tested along dermatomes

• Used in assessing spinal cord or brain damage

• Unequal/reduced/absent sensation may indicate nerve or CNS damage

Shingles

• Varicella-zoster virus (“chicken pox”)

  • Reactivates

• Painful rashes & blisters

• Affected area may feel painful, burning, tingling, numb sensations (or a combination!)

Shingles – Cause

• Viral latency

• Viruses lie dormant in nerves

• Can reappear later in life

  • Avg. age ~50+

  • 1 in 3 lifetime chance

  • the virus can remain dormant in sensory ganglia, such as a dorsal root ganglion

Shingles – Prevention

• Symptoms last ~2 to 4 weeks

• Antiviral drugs help with symptoms

• Vaccinations reduce chance of shingles

Nerve Plexus

Interwoven network of nerves (plexus = “to braid)

Cervical Plexus

• Ventral rami of C1 to C4 spinal nerves

• Some C5 spinal nerve fibers

• Cutaneous and muscular branches

  • Cutaneous branch innervates head, neck, & chest

Lesser occipital nerve (Cervical Plexus)

Innervates skin of neck and posterior head

Supraclavicular nerve (Cervical Plexus)

innervates skin of neck and shoulder

Great auricular nerve (Cervical Plexus)

innervates skin of neck and posterior ear

Transverse cervical nerve (Cervical Plexus)

innervates anterior triangle of the neck

Ansa cervicalis nerve

innervates five extrinsic laryngeal muscles

U shaped

Phrenic nerve

innervates diaphragm

Breathing