Neurons and Glia

two categories of cells in the nervous system

neurons and glia

neurons

nerve cells that recieve info, process it, and generate output

glia

(glial cells or neuroglia) suporting roles

2 ways that neurons communicate

electrical and chemical signals

when do neurons use electrical signals

to communicate within a neuron

when do neurons use chemical signals

to communicate between neurons

what encases neurons

cell membrane

cytoplasm

material inside the cell membrane; full of organelles

3 primary components of a neuron

1. cell body

2. dendrite

3. axon

other names for cell body

soma or perikaryon

cell body def

sit for synthesis of nearly all of the neuron’s enzymes, structural proteins, membrane components, organelles and some neurotransmitters

dendrites def

tapering extenstions of a cell body; specialized to receive information; increase surface area available for synaptic inputs

dendritic tree

totaly array of a neuron’s dendrites

in relation ot the cell body, how is information transmitted in the dendrites

distally → proximally

dendrite organelles

same as in cell body

dendritic spines

spiky protuberances that are preferred sites for synaptic inputs

axon

single output of a neuron; transmits actions potentials from cell body distally

what does the axon hillock give rise to

the initial segment

initial segment

just distal to axon hillock; most excitable part of neuron

what covers most axons

myelin

myelin def

glial membranes that increase the speed of APs

cytoskeleton

network of protein filaments contained within nearly all parts of neurons that give neurons their shape and assist in transport within the neuron

cell body

dendrite

neuron axon

axon hillock

3 types of cytoskeleton

1. microtubules

2. neurofilaments

3. microfilaments

axonal tranport def

active process by which cells send macromolecules and organelles along an axon

fast anterograde transport

material travels from cell body to the presynaptic temrinal along microtubules

fast retrograde transport

material travels from synapse back to the cell body along microtubules

poliovirus

can gain access ot the CNS thru fast retrograde transport causing poliomyelitis (polio)

herpes

the virus gains access to soma through retrograde transport

chemotherapy

stops cell division and also axonal transport; can lead to neuropathies and cancer pain

alzheimer’s disease

marked by neurofibrillary tangles, problem with tau proteins on microtubules; progressive degenerative brain disease

Chronic traumatic encephalophathy CTE

progressive degenerative brian disease found in athletes with a history of repetivie brain trauma, including symptomatic concussion as well as asymptomatic subconcussive hits to the head; marked by same neurofibrillary tangles as in AD; symptoms include behavioral, mood, and cognitive impairments

3 ways in which neurons are classified by shape

1. multipolar

2. bipolar

3. pseudounipolar

multipolar neuron

have multiple dendrites and a single axon; most common in vertebrates; designed to receive and accomodate large amounts of input

ex of multipolar neuron

spinal motor cell

bipolar neuron

have 2 primary processes that extend from cell body

two types of bipolar neurons

olfactory epithelium and retina

pseudounipolar

subclass of bipolar neurons; appear to have a single projection from the cell body that divides into two axonal roots and no true dendrites

what type of neuron is exclusive to pseuounipolar

sensory

location of sensory and motor neurons

lie partly in CNS and partly in PNS

sensory neurons reception

receptive to sensory input either directly or thorugh cconnections with receptor cells

motor neurons

end on muscles, gland, or other neurons

interneurons

located in a small area in the CNS (connectors)

projection neurons

neurons in the CNS with long axons that project to another part of the CNS

what types of neurons make up 99%

interneurons and projection neurons

synaptic transmission def

mechanism by which neurons communicate with each other

synapse

special zone of contact in whcih one neuron communicates with another

presynaptic element

distal end of axon

postsynaptic element

part of another neuron

synaptic cleft

separation between two elements

synaptic vesicles

structures that contain neurotransmitters are released from presynaptic element into the cleft and bind to receptor sites in postsynaptic membrane, causing an electrical signal in postsynaptic neuron

axodendritic synapse

axon of one cell to dendrite of another

axosomatic synapse

axon to soma

axoaxonic synapse

axon to axon

dendrodendrtic

dendrite to dentrite

what are the main PNS glia

schwann cells

satellite cells

2nd type of PNS glial cell, but flattened schwann cells

schwann cells are made of

lipid substance

schwann cells function (3)

1. facilitating regrowth of axons after peripheral nerve injury- glial cells provide the sheath

2. regulating extracellular ionic environment

3. metabolic suppoort

schwann cells role in myelination

schwann cells wrap around segments of most individual axons

what interrupts myelin sheaths

nodes of ranvier

internode

area of myelin between nodes of ranvier

internode relationship to schwann cell

one schwann cell myelinates one internode

what surrounds cell bodies

satellite cells

principal function of oligodendrocytes

form myelin sheaths

principle function of astrocytes

provide mechanical and metabolic support; response to injry

microglia function

phagocytosis; response to injury

ependymal cells function

line ventricles and choroid plexus, secrete CSF

what is the CNS counterpart of a schwann cell

oligodendrocytes

primary difference for oligodendrocytes

can produce several internodes and can do so on several different axons

astrocytes

largest of the CNS glia, highly branched

two types of astrocytes

protoplasmic and fibrous

protoplasmic astrocytes location

in gray matter

fibrous astrocytes location

in white matter

3 main roles of astrocytes

1. structural support

2. end-feet of astrocyte branches provide “carpet” over capillaries and neurons (part of blood brain barrier)

3. can multiply in response to CNS injury

what is the smallest CNS glia

microglia

what activates microglia and what happens

injury activates microglia to migrate and clean up debris

ependymal cells location

line the walls of ventricles and choroid plexus

ependymal cells function

produce and secrete CSF

gliomas

tumors of glial cell origin

what is usually the origin of a tumor in the PNS

schwann cells

schwannoma characteristics

usually encapsulated with no nerve fiber involvement; easily removed

neurofibroma

encapsulated but infiltrating nerves; difficult to remove

what is the origin of many brain tumors

astrocytic origin

astrocytoma

tumor of astrocytic origin

glioblastoma multiforme

grade IV astrocytoma

conditions that result in damge to the myelin sheath

demyelinating diseases

result of demyelinating disease

myelin sheath is damaged, nerve impulses slow or even stop, causing neurological problems

causes of demyelinating diseases

1. autoimmune disorders

2. metabolic abnormalities

3. viruses

4. trauma

5. toxic chemicals

demyelinating disease of the CNS

Multiple Sclerosis

what happens in MS

body produces antibodies that attack oligodendrocytes

etiology of MS

genetic predisposition with an environmental trigger

demyelination in MS

destruction of oligodendrocytes produces patches of demyelination

what replaces areas of demyelination in MS

astrocytic plaques which cuases slowed or blocked action potentials

prognosis of MS

variable, some may completely resolve, some linger

treatment of MS

• immunosuppressants

• rehabilitiation

demyelinating disease of the PNS

guillian-barre syndrome