1. Nervous tissue histology

• Excitable plasma membrane

• Specialization for fast conduction (myelination/nodes of Ranvier)

• Specializations for immune production (BBB)

• CT for insulation

• Blood and nerve supply for large nerves

Characteristics of peripheral nervous tissue

• Nerve cells (neurons)

• Supporting cells

  • Schwann cells

  • Satellite cells

  • Fibroblasts

• Perineural sheath (blood-nerve barrier)

Cells of PNS

Neurons composed of:

• Nerve cell body aka soma, perikaryon

• Cytoplasmic processes:

  • Afferent (dendrites)

  • Efferent (axons aka nerve fibers)

Dendrite afferent or efferent?

Afferent

Axons/nerve fibers afferent or efferent?

Efferent

the three nerve cell types:

• pseudounipolar

• bipolar

• multipolar

neuron cell process

extensions of a neuron cell, primarily the dendrites which receive signals from other neurons, and the axon which transmits the electrical signal away from the cell body to other neurons

• the dendrites "listen" to incoming signals while the axon "speaks" by sending signals out. 

cytoplasmic processes (neuron cell processes)

• axons (1/neuron)

  • ensheathed by Schwann cells

  • may be myelinated

• dendrites (many per motor neuron)

major characteristic of axon?

no Nissl bodies

what is an axon hillock?

a cone-shaped part of a neuron that controls when an electrical impulse is sent. It's located where the axon connects to the cell body.

• Receives signals from other neurons and the environment

• Determines if the neuron should send an action potential

• Generates action potentials

nerve cell for sensory

• one cell process that extends from the cell body (soma)

• one axon that splits into two branches

• no dendrites

pseudounipolar

nerve cell for sensory and sensory organs (e.g. olfactory epithelium)

• two cell processes (axon and dendrite) extend from soma

bipolar

nerve cell for somatic motor and visceral motor

• many cell processes

  • typically one axon and many dendrites

multipolar

PNS neuron cell bodies are clustered in

• nuclei (CNS), multipolar neurons

• ganglia

  • dorsal root: cranial sensory nerve ganglia (sensory)

  • autonomic ganglia: visceral motor (parasympathetic, sympathetic, enteric)

ganglia

collection of neuron cell bodies located outside the central nervous system, within the PNS

characteristics of soma

• large euchromatic nucleus

• prominent nucleolus (w/in nucleus where ribosomes are assembled)

• Nissl substance (rER cluster for protein synthesis)

• ex: dorsal rot ganglion, cranial sensory nerve ganglion

• pseudounipolar neurons

• morphology: central nucleus, ring of satellite cells

• synapses: none

sensory neurons

sensory neurons

• ex: sympathetic, parasympathetic, enteric

• multipolar neurons

• morphology: eccentric nucleus, dispersed satellite cells

• synapses: abundant

autonomic neurons

autonomic neurons (visceral)

describe organization of a peripheral nerve

ex: median nerve is comprised of outer connective tissue called epineurium surrounding many individual nerve bundles each wrapped by perineurium. The nerve bundles are comprised of many somatic sensory, somatic motor, and/or autonomic unmyelinated neurons. Inbetween the different nerve fibers is insulating tissue endometrium. there are also blood vessels in nerves

cell bodies of motor neurons originate in?

ventral root

cell bodies of sensory neurons originate in?

dorsal root ganglion

cell bodies of sympathetic neuron originate in?

ventral root

what happens when dorsal and ventral roots come together?

it is now called a spinal nerve

somatic motor neurons

striated muscle

autonomic unmyelinated neurons

smooth muscle and enterorecptors of ANS

somatic sensory neurons

pacinian corpuscle

6 nerve bindles in this cross section of a nerve

explain Schwann cells myelinated vs unmyelinated

• Schwann cell can only surround one myelinated axon because it takes a lot of energy; sheath

• for unmyelinated one Schwann cell can surround many unmyelinated axons

*actually one Schwann cell will myelinate a single axonal region and it takes many into invest in full length of an axon. its the sheath that makes it thicl

what is not well-preserved in most preparations?

myelin which is lipid rich

define neurokeratin

where is neurokeratin found?

protein in myelin sheath of axon; protein residue after lipids extracted during tissue process

found in myelinated nerves only (Schwann cells can be around non-myelinated)

what are the two types of myelin interruptions?

Schmidt Lanterman incisures (clefts)

Schmidt-Lanterman incisures (clefts)

small gaps when myelin sheaths shift during rolling/formation

Nodes of Ranvier

T or F: most of the autonomic pathway is myelinated

FALSE

which CT layer has:

• tight junctions

• gap junctions

• restrict cell entry (no lymphocytes and plasma cells; dye placed in blood vessel? won’t stain nerve)

• control transport

• are contractile

perineurium

do myelinated fibers have Schwann cells? blood-nerve barrier? neuorkeratin? is their main represented group autonomic fibers?

• Schwann cells: yes

• blood-nerve barrier: yes

• neurokeratin: no

• autonomic fibers: they are the majority

• many axon to 1 Schwann cell relationship

define Guillain-barre syndrome

life threatening PNS disease caused by T cell mediated immune response against myelin (leads to exposed fiber and damaged myelin)

which neuron types have myelin sheaths?

somatic sensory and somatic motor; so Guillain-barre syndrome would damage these