Neuro- Cell Types of the Nervous System

Central nervous system

aka CNS, made up of the brain and spinal cord, it analyzes and integrates motor and sensory information.

cerebral hemispheres + diencephalon + cerebellum + brainstem + spinal cord

diencephalon

Part of the brain located between the cerebral hemispheres and the brainstem, it includes structures such as the thalamus and hypothalamus, playing key roles in sensory processing and autonomic functions.

Peripheral nervous system

aka PNS, made up of sensory and motor components that connect the central nervous system to the rest of the body, facilitating communication between the CNS and limbs.

sensory components = ganglia + nerves + receptors at surface and w/in body

motor components = somatic motor system w/ motor nerves, visceral motor system (parasympathetic, sympathetic, & enteric divisions) controlling smooth muscles, and autonomic ganglia + nerves.

smooth & cardiac

autonomic nervous system controls ___ muscles as well as glands.

function of the sensory components of PNS

gathering information from internal and external environment and transferring it to the CNS

function of motor components of PNS

control skeletal aka striated muscles in somatic nervous system & smooth muscles in autonomic nervous system

2 main classes of nervous system cells

neurons + glia

neurons

related to anything neuronal, fundamental cellular unit of CNS and PNS.

specialized epidermal cells from embryonic perspective.

highly specialized in cell-cell communication

receive, process, and transfer information

unidirectional

neurons are ___

glia

NOT a nerve cell

metabolic and structural support to neurons

neural

anything within the nervous system

dendrites

processes coming out of the cell soma/body

receive input

can branch off and form a tree-like structure

extent of ___often correlated with the number of inputs

receive info from other neurons or the external environment and transfer it to the cell body and the axon

cell body/soma

contains all the nucleus and typical cellular organelles

axon

conductive part of neurons

only 1 per neuron

comes out/leaves cell soma

can branch off to form a collateral

axon collateral

secondary axon

branched off axon

presynaptic terminals

termina buttons, synaptic endings, axon terminals

ends of axon branches near target cell

polarized

neurons are ___ cells

The 3 parts of a synapse

presynaptic terminal + synaptic cleft + postsynaptic cell

primary target for sensory input

dendrites

antiparallel

the microtubule in dendrites run in an ___ fashion

mitochondria

__ are found all over the nerve cell

Purkinje cells

massive planar dendritic tree

cells of cerebral cortex

short axon

pyramidal cells

cerebral cortex

extended dendritic tree with basal dendrites (aka some dendrites close to the cell soma)

short axon

motor neurons of spinal cord

extremely long axon

multipolar neurons

conductive

axons are the ___ part of neurons

projection of nerve cell connecting soma to target

transfer information

specialized in electrical signal relaying

length ranges from few micrometers to meters depending on animals

microtubules for stability, integrity, and specialized vesicles transport

target, soma

The microtubules in the axon are always oriented with the + end toward the __ and the - end toward the __.

synaptic contact

specialized secretory apparatus containing neurotransmitters filled vesicles

presynaptic membrane immediately adjacent to postsynaptic membrane but NOT touching

most are chemical synapses

synaptic cleft

tiny space separating the presynaptic cell from the postsynaptic one

extracellular space where neurotransmitter diffuse

axo-dendritic

synapse between an axon and dendrite

axo-axonic

synapse connecting an axon to another

presynaptic terminal of one on top of the terminal buttons of the other

presynaptic cell has a control over the firing of the other—> one neuron antagonize the other

axo-somatic

synapse connecting the axon of a neuron to the soma of another neuron

en-passant

middle of axon on presynaptic neuron bumps/bubbles up to connect to another neuron while the axon continues to another target

dendritic spines

made of a head and a neck, multiple of them found on dendrites branches

dynamic aka change overtime

look like bubbly thorns

spine head

location of post-synaptic apparatus on dendrites

action potentials

aka nerve impulse

electrical signal of neurons

propagated from cell soma to terminus

axon hillock

region where the input captured by the dendrites is integrated and where the action potential is initiated

specialized region

link between soma and axon

unipolar cell

cell body on one end with axon connecting to dendrites

found a lot in invertebrates

bipolar cell

cell body in the middle with in dendrites on one side and axon on the other

found in the retina

pseudo unipolar cell

cell body in the middle but off to the side, bypassed by signal

still a single process coming off of it

number

neuron morphology based on the ___ of processes coming out of the cell soma

multipolar cell

multiple dendrites coming out of cell soma

input region

dendrites

integration

axon hillock (or right under dendrites in pseudo-unipolar cells)

conductible

axon

output

presynaptic terminals

sensory neurons

receive information from the external world via specialized receptors and transmit that sensory info to the CNS

PNS to CNS

long axon

pseudo-unipolar

motor neuron

end directly on muscles and transmit output from CNS to PNS

dendrites and cell soma in spinal cord

multipolar

projection neurons

cells projecting out of the nucleus or area aka axon leaves area cell soma is in

very long axon

soma and dendrites in cerebral cortex while axon leaves to spinal cord

interneurons

short axon

does not leave localized area aka both cell soma, dendrites and axon in the same area

usually in cerebral cortex/CNS

usually inhibitory

neural circuits

organized ensemble of neurons

shortest/simplest ones are reflex circuits like the knee jerk response

bypass the brain

reflex circuits are so fast because they ___

convergence

number of input to a single neuron

divergence

number of targets innervated by any 1 neuron

afferent neuron

nerve cells carry info from PNS to CNS

aka toward the brain

sensory neurons

efferent neurons

nerve cells that carry info from CNS to PNS

aka FROM the brain (or spinal cord)

motor neurons

glial cells

10 to 1 ratio in the brain

more common that neurons in the brain

Greek word for glue

glial cells in CNS

macroglia (astrocytes + oligodendrocytes + ependymal cells)

microglia (CNS immune cells)

glial cells in PNS

myelinating Schwann cells

non-myelinating Schwann cells

satellite cells

astrocyte

type of macroglia

• structural support = induce tight junction formation in endothelial cells = establish BBB

• metabolic support = get glucose form capillaries and make lactate from it to send it to neurons

• guide neuroblast migration and axon growth

• take up neurotransmitters overflow from synaptic cleft (using specific transport proteins and being up close to synaptic cleft)

• can act as stem cells/progenitors to new neurons (stimulated by exercise)

Blood brain barrier

established by astrocytes

tight junctions NOT allowing immune cells through unlike in the rest of the body

highly selective permeability barrier that separates circulating blood from the brain cerebrospinal fluid (CSF)

• protect brain from foreign substances

• protect brain from circulating hormones and neurotransmitters

• maintain constant environment

radial glia

“specialized astrocyte”

extent from ventricular surface all the way to pial surface (outer surface)

guide neuroblasts

glial stem cell

“specialized astrocyte” (really a progenitor/stem cell made of intermediate filaments, just like astrocytes)

divide to generate new neurons or new glia

Just in CNS, close to hippocampus and ventricular zone of cortex

oiligodendrocytes

type of macroglia

look like a spaceship

• generate the myelin sheath

• increases the speed of action potentials by enabling saltatory conduction (aka impulse jumps from node to node)

• can insulate up to 40 axons per glial cell

myelin sheath

characteristic feature of vertebrate CNS

laminated lipid-rich insulating wrapping

from oligodendrocytes membrane that wraps around itself and suck the cytoplasm out to be very compact

separated by node of Ranvier

node of Ranvier

a gap in the myelin sheath of a nerve, between adjacent Schwann cells/oligodendrocytes.

compaction

withdrawal of cytoplasm from the oligodendrocyte membrane during myelin sheath formation so that the sheath becomes compact

70-80

myelin sheath is made up of __-__ lipids

• cholesterol

• glycosphingolipids

• phospholipids

80

Myelin Basic protein (MBP) & Proteolipid protein (PLP) make up __ of proteins found in CNS myelin

MBP

major component of mammalian CNS

located on cytosolic surface of oligodendrocyte membrane via electrostatic interactions with negatively charged lipids = compact internodal myelin

involved in myelin formation and compaction aka mediate adhesion between cytosolic surfaces of myelin sheath.

anchor inner membranes

when mutated causes constant seizures, tremors, and shivers as well as early death because myelin is too thin or absent due to reduced amount of __

PLP

most abundant protein of mammalian CNS

highly conserved between species on PLP1 gene on X chromosome

hydrophobic protein (hydrophobic amino acid in cytoplasmic side of membrane reinforcing hydrophobic binding)

transmembrane protein (4 transmembrane domains)

compaction expels H2O and cytoplasm

stabilize myelin architecture because extracellular portion bind to other ___ proteins on adjacent myelin wraps

Palizaeus-Merzbacher disease

mutation in PLP protein gene causes this disease in humans

reduced amount of myelin (some compact some thin myelin as a result)

ependymal cell

cell of the epithelial layer lining the ventricle in CNS as well as central canal of spinal cord

have cilia that beat in coordination to circulate CSF

microvilli absorbing and producing CSF

choroid plexus

population of specialized ependymal cells and capillaries

microglia

part of CNS glia

immune cells of CNS

phagocytosis specialists aka professional phagocytes

only in CNS
5-15% cells in brain

phagocytosis

the uptake of particle materials by cells through engulfment

1. chemotaxis and adherence of microbe to phagocyte

2. ingestion of microbe by phagocyte

3. formation of phagosome (phagocytic vesicle)

4. fusion of phagosome with a lysosome to form phagolysosome

5. digestion of ingested microbe by enzymes

6. formation of residual body containing indigestible materials

7. discharge of waste materials

phagocytes

cells with the capacity to internalize and degrade microbes and particles matter

literally translate to “eating cells”