PNS / Spinal nerve / Cerebral Cortex (continued), Neuron / Synapse / Dendritic spines / PD-related changes

PNS / Somatic / Autonomic

PERIPHERAL NERVOUS SYSTEM (PNS) (Extension of Central CNS)

• SOMATIC SYSTEM (Reacts to Outside Stimuli)
• AUTONOMIC SYSTEM (Maintains homeostasis)
  • SYMPATHETIC SYSTEM
    • Origin: Thoracic / Lumbar
    • Response: Involuntary
  • PARASYMPATHETIC SYSTEM
    • Origin: Brain / Sacral
    • Response: Normal

Classification of nervous system

• Somatic nervous system
  • Cranial nerves (except optic n) — With the exception of the olfactory nerve (I) and optic nerve (II), all the nuclei are present in the brainstem.[3]
  • Spinal nerves (Js: sciatic n is a part of spinal nerve.)
• Autonomic nervous system
  • Sympathetic
  • Parasympathetic

Spinal nerve

The spinal nerves (and their dorsal & ventral roots) are part of the PNS.

Js: so this is nothing to do with SCI!

Each spinal nerve is a mixed nerve, formed from the combination of nerve fibers from its dorsal and ventral roots.

두 곳에서 별개로 시작 분기 → Dorsal root, ventral root → 둘이 일단 합쳐졌다가 → dorsal ramus, ventral ramus

Cauda Equina

ramus	territory	function
dorsal ramus	posterior portions of the trunk	carrying visceral motor, somatic motor, and sensory information to and from the skin and muscles of the back
ventral ramus	anterior parts of the trunk and the upper and lower limbs (hypaxial muscles)	carrying visceral motor, somatic motor, and sensory information to and from the ventrolateral body surface, structures in the body wall, and the limbs

Cerebral Cortex (6 layers)

Most of the neurons in the cerebral cortex are arranged vertically and most abundant neurons are the efferent pyramidal cells.

There are between 14 and 16 billion neurons in the cerebral cortex.

Layer	Name	Description
I	Molecular layer (lamina molecularis)	consists only a few nerve cells
II	External granular layer (lamina granularis externa)	relatively thin layer consisting of numerous small, densely packed neurons
III	Pyramidal layer or external pyramidal layer (lamina pyramidalis externa)	composed of medium-sized pyramidal nerve cells
IV	Inner granular layer (lamina granularis interna)	relatively thin layer composed of medium-sized cells / contains small, irregularly shaped nerve cells
V	Ganglionic or inner pyramidal layer (lamina pyramidalis interna)	includes large pyramidal cells
VI	Multiform layer (lamina multiformis)	small polymorphic and fusiform nerve cells

pyramidal layers are more developed in the motor centres and granular layers are more developed in sensory centres of the cerebral cortex.

very large giant pyramidal cells found in the layer V of the regions of the motor cortex are called Betz cells.

Neuron / Synapse

Spine (= ‘dendritic spine’): dendrite (= ‘dendritic shaft’) 에서 삐죽 나온 것

Synapse components: dendrite / dendritic spines / presynaptic terminal / mitochondria / Ca²⁺ channel / synaptic vesicle / synapse / presynaptic axon / NT receptors / NTs → synaptic cleft / postsynaptic density (PSD).

Scale: 1 μm.

Spiny dendrite of a striatal medium spiny neuron

Components: bouton / thin axon / postsynaptic spine / dendrite / spine head / spine neck.

Common types of dendritic spines

• mushroom
• stubby

(continues with thin / branched / filopodia in the next photo)

Asymmetric synapse (Gray’s Type I)

group	normal density	reduced density	increased density
	normal	PD	Cell therapy

[mainly Axo-spinous contact]

Dopaminergic terminals in the normal striatum predominantly synapse onto the neck, and glutamatergic endings onto the head, of dendritic spines (Freund et al., 1984; Groves, 1980).

PD

Dopamine depletion leads to a significant loss of dendritic spines.

↓ axo-spinous contact, ↑ axo-dendrite contact in the striatum

Cell therapy

↑ asymmetric synapses onto TH+ grafted cells in the striatum (NS synapse in the striatum 은 dopaminergic, symmetric, excitatory 인데, 병리적으로 glutamatergic, asymmetric, excitatory 으로 바뀌어서 dyskinesia 유발하는 것 아닌가 (Soderstrom et al. 2008, PMID))

non-TH+, asymmetric, perforated synapses

Uncertain Spans

location	transcription	uncertainty
Common types of dendritic spines	the partial list mushroom / stubby	the source figure includes additional spine types (thin, branched, filopodia) that are clipped on this capture.