nervous tissue

Nerve tissue is involved in the transmission of

information throughout the body

electrochemical signals cause muscles to

contract or relax when needed to move body parts

nervous system allows us to

sense the world around us; 5 senses

Divisions of the Nervous System

CNS, PNS, ANS

CNS

brain and spinal cord

PNS

motor neurons and sensory neurons

motor neurons

efferent neurons; neurons that carry messages from spinal cord/brain to muscles and glands

sensory neurons

afferent neurons; neurons that carry messages from sensory organs to the brain and spinal cords

ANS

innervates organs and glands;

in both CNS and PNS;

parasympathetic and sympathetic

parasympathetic nervous system

rest and digest

sympathetic nervous system

fight or flight

enteric nervous system

the nervous system of the digestive tract;

operates independently and in conjunction with the ANS

2 general classes of nerve cells

neurons, glial cells

neurons

nerve cells, with highly excitable membranes;

10% of cells

Part of a neuron

cell body, dendrites, axon

cell body AKA soma

surrounded by cytoplasm, contains organelles

Nissl substance

RER found in cell body and dendrites, but not axon of neurons.

Dendrites

Branchlike parts of a neuron that are specialized to receive information from other neurons

axon

the extension of a neuron, ending in branching terminal fibers, through which messages pass to other neurons or to muscles or glands

neurons connect to each other by

electrochemical synapses

nerves

collections of hundreds of axons, 10% of cells

glial cells

support cells found in the nervous system, 90% of cells

cerebral cortex has

grey and white matter

gray matter

outer layer; composed of neurons and glia; 6 layers can be seen with light microscopy;

contains pyramidal cells

pyramidal cells

large neurons that allow conscious control of precise, skilled, skeletal muscle movements;

pyramidal cells shape

triangular shape;

Dendrites seen at base and apex of the pyramid;

axon is in middle of base

pyramidal cells H&E

see soma and proximal dendrites

pyramidal cells golgi stain

labels all dendrites and axons

white matter

inner layer; composed of axons (going to and from cortex

Cerebellum

A large structure of the hindbrain that controls fine motor skills;

has a 3 layered cortex

3 layered cortex of cerebellum

molecular;

purkinje;

granular

Molecular layer of cerebellum

outer most layer

Purkinje layer of cerebellum

visible as thin layer of globular shaped cells

Purkinje cells

flat cells in sequential planes, parallel to one another

purkinje cell nissl stain

only soma is visible

purkinje cell immunofluorescence stain

see massive dendritic tree extending towards molecular layer

granular cerebellum layer

innermost layer

Spinal cord gray and white matter

Central cavity surrounded by gray matter, with outer white matter

gray matter contains

cell bodies and dendrites

white matter contains

myelinated axons

Horns of the spinal cord

The extensions of the gray matter that form the letter "H"

dorsal horns

interneurons that receive somatic and visceral sensory input

ventral horns contain

motor neurons

motor neurons nissl stain

all one can see are the cell body (soma) and proximal dendrites;

can sometimes see beginning of the axon, the axon hillock and initial segment, can be seen

Motor neurons have cell bodies in the

CNS and send their axons into the PNS

In the PNS hundreds of

of axons travel together in bundles that we call nerves

White matter

axons from neurons at other levels of the brain and spinal cord

white matter has a high

lipid content

PNS begins

outside the spinal cord;

but within the vertebral column in the spinal canal, close to where sensory axons enter & motor axons leave the spinal cord

schwann cells

produce myelin in PNS;

only wrap around 1 axon

oligodendroglia

glial cells in the CNS that myelinate multiple axons

some neurons are in both the

CNS and PNS

neurons with cell bodies in PNS

sensory ganglia;

autonomic ganglia

sensory ganglia

no dendrites;

T shaped axon;

long peripheral branch of sensory ganglia

go to body

long central branch of sensory ganglia

enters spinal cord;

short stem axon of sensory ganglia

connect to soma

sensory neurons have some of the

longest axons in the body

sensory neuron cell bodies are located in the

dorsal root ganglia, which sits in the intervertebral foramina of the vertebral column

sensory ganglia structure

bipolar during early development;

becomes pseudounipolar

autonomic ganglia

Collections of nerve cell bodies, belonging to the autonomic division of the peripheral nervous system, that are found in various locations and innervate the major organs.

both divisions of the ANS have the same basic structure

have a two neuron chain between the CNS and their target organs.

A preganglionic neuron is located within the

spinal cord or brainstem;

The axon of this neuron passes out through the ventral roots and synapses on another neuron in a ganglion out in the body

ganglion

a small collection of neurons in the peripheral nervous system

autonomic ganglia are located in various places in the body. One well-known location is the

sympathetic chain

sympathetic chain ganglia

lies bilaterally adjacent to the vertebral column;

a series of tiny ganglia that contain ganglionic neurons AKA postganglionic neurons

postganglionic neurons have

short dendrites and unmyelinated axons

postganglionic neuron innervate

smooth muscle and glands

autonomic ganglion looks very much like the

dorsal root ganglion;

distinguish by looking for evidence of the dendrites on the autonomic neurons;

satellite cells of DRG more prominent

myelinated axons

axons covered with myelin sheaths

myelinated axons in light microscopy

tiny dark rings stacked on one another

myelinated axons in electron microscopy cross section

myelin layers aka lamellae;

Microtubules, neurofilaments, mitochondria

myelinated axons in electron microscopy longitudinal section

nodes of ranvier;

Myelin on either

Nodes of Ranvier

Gaps in the myelin sheath to which voltage-gated sodium channels are confined.

unmyelinated axons

no nodes of ranvier;

slow conduction;

Smaller diameter, but covered by cell membrane from Schwann cells

When a neuron is excited it generates an

electrical action potential that is conducted down its axon to its terminals synaptic boutons or a neuromuscular junction (NMJ)

Most axons have multiple

terminals;

These terminals connect to the dendrites and cell bodies of other neurons through synapses

Evidence of the synapse that can be seen with LM at

200-400x magnification is a tiny varicosity called a synaptic bouton.

a single axon may make only a few

few synapses upon one cell (5 or 10);

but receive hundreds of synapses from many different axons

At high magnification of a bouton, one can see

vesicles and synaptic specializations in both the bouton and the dendrite that it is contacting

synaptic cleft

The narrow gap that separates the presynaptic neuron from the postsynaptic cell.

Neurotrasmitters

chemical found in the synaptic vesicles that, when released, has an effect on the next cell;

released into synaptic cleft;

excites/inhibits

higher magnification of EM (50,000x magnification) reveals

bouton and synaptic vesicles with neurotransmitter

glial cells come from

neuroectoderm except microglia

neuroglial cells in cns

oligodendrocytes;

astrocytes;

ependymal;

microglia

Oligodendrocytes

Type of glial cell in the CNS that wrap axons in a myelin sheath.

fibrous astrocytes

in white matter;

long slender processes w/numerous filaments;

induce formation of blood brain barrier

protoplasmic astrocytes

in gray matter;

thick bushy processes;

induce formation of blood brain barrier

Blood Brain Barrier (BBB)

a selective mechanism that protects the brain from toxins and infections;

formed by endothelial tight junctions that divides blood and neuron extracellular space

Both types of astrocytes require

special stains to see more than their nuclei

ependymal cells

line ventricles in brain, central canal in spinal cord;

form choroid plexus

choroid plexus

produces CSF

microglia

macrophages of the CNS;

derived from bone marrow;

phagocytose injured tissue

Myelination of a single peripheral nerve axon occurs via

a series of Schwann cells

Cells in PNS

Schwann cells and satellite cells

schwann cells wraps a

wraps a single short-length portion of the axon

in the CNS oligodendroglia can

wrap short-length portions of several axons.

Schwann cells & oligodendroglia both wrap multiple

unmyelinated axons with single layer

satellite cells

found around ganglia neurons (e.g. DRG & autonomic ganglia)

satellite cells assist in

regeneration following peripheral nerve injury