Neurons have three components

name them

what are neurons commonly called

1. soma - cell body
2. dendrites - receptive process of neuron
3. axon - major outflow of neuron leads to synapse

"workhorse' of nervous system - couriering information

Name the classifications of neurons

3

1. bipolar - have 2 processes-one dendrite and one axon (found in pathways for special senses)
2. multipolar - most classic motor neuron - have one axon and several dendrites - ex: ant horn cells of SC
3. Pseudounipolar - one process that splits close to the soma into the dendrite and axon

in addition neurons are also classified as

sensory, motor and interneurons

Communication btwn neurons occurs

in many ways name some

1. axondendritic synapse
2. axosomatic synapse
3. axoaxonal synapse
4. en passant aka somatosomatic

Myelin

Axons are enclosed by what in the PNS...CNS

PNS = Schwann Cells

CNS = Oligodendrocytes

Myelin is made of what kind of cells

what is a single segment of myelin called

cells = glial cells

single segment = internode

note = a Schwann cell wraps only one internode(segment) of one axon while an oligodendrocyte may myelinate MANY axons but still only one segment(internode)

What are the gaps bwtn

internodes called

What is myelin made of

what does it do

Nodes of Ranvier

lipids and proteins

myelin acts as an insulator of nerve cells and enables saltatory conduction - it increases the velocity of the action potential

Nerve cell communication:

what is the resting membrane potential of a cell

-70mV (more negative inside cell)

pumps actively transport ions across cell membrane (ex: Na+ out and K+ in)

Nerve cell communication:

electrical signals

must alter the cell membranes permeability

happens via voltage gated channels: K+, Na+, Ca+, and Cl-.

At rest these channels are closed but an action potential occurs due to voltage gated channels and the membrane potential becomes reversed. This happens when a stimulus depolarizes the axon.

Action potentials are an "all or none"

what does this mean

After an action potential the cell returns to

a resting state, what does this entail

sodium channels close and potassium opens

and repolarization begins

The absolute refractory period begins right after the action potential occurs; during this period it is impossible to excite the cell

this helps to limit the rate of action potentials

Once an action potential occurs it continues

the velocity is dependent upon what

two factors

1. diameter of axon
2. presence of myelin sheath

bigger axons=faster

more myelin=faster

in myelinated fibers the signal jumps from node to node this is called saltatory conduction

communication from one neuron to the next

typical neuron has 1,000 to 10,000 synapses

1. electrically - transmitted through gap junctions
2. chemically - by release of neurotransmitters

• action potential reaches terminal button(end of axon) neurontransmitters are released
• terminal button = presynaptic afferent end releases NT across synaptic cleft to postsynaptic(efferent) end which receives the NT in its receptors

1. ligand gated ion channel
2. G-protein linked receptors

• a chemical messenger that binds to a protein receptor molecule which selectively allows ions to pass in or out of the ion channel
• sets up the postsynaptic potential which can then excite or inhibit the postsynaptic cell

• dont form ion channels but evoke action through a regulatory protein called G proteins
• when a NT binds to a receptor, G proteins are activated and released from the receptor to bind target enzymes to form a second messenger which allows them to affect cell metabolism and act as neuromodulators

EPSP/IPSP

Postsynaptic responses can lead to depolarization(excite) or repolarization(inhibit)

explain each

1. EPSP = depole due to opening of sodium and potassium channels
2. IPSP = hyperpolarization reducing the chance of a postsynaptic action potential due to opening of Cl- channels (Cl- are negative and thus neutralize the positive charge)

The strength of the signal can be variable(graded)

as it travels it decreases, and can be summed either spatially or temporally

Temporal Summation = summation of several EPSP's occuring close together in time due to rapid and successive firing of one or more presynaptic neurons; thus the previous potentials effects have not subsided before the next one occurs and the currents SUM.

Spatial summation = EPSPs arrive simulatenously from different presynaptic inputs. Basically several neurons synapsing at one neuron, summing their power to depolarize it at the same time.

An action potential occurs faster

with which temporal or spatial

Presynaptic inhibition:

allows for regulation of release of NT

and can modulate amplitude of IPSPs

it is the sum of all synaptic currents on a neuron - the decisions of nervous system activity

LTP = long term potentiation = synapses increase their effectivness with activity- becomes enhanced can last min to hours

LTD = long term depression = synapses decrease their effectiveness

LTP and LTD = assist in modulating the function of synapses (important in plasticity and learning)

only one

Neurontransmitters is released by each type of neuron. NT can cause either excitation or inhibition of the postsynaptic neuron

Neurontransmitters:

ACh

used in PNS some CNS including cerebral cortex, basal ganglia, limbic system and thalamus and spinal interneurons

EXCITATORY NT

Neurontransmitters:

Amino Acids

·         Glutamate (excitatory neurotransmitter, found in interneurons throughout the brain and spinal cord-most common neurotransmitter of the brain)

·         GABA (gamma aminobutyric acid: inhibitory neurotransmitter; found in interneurons in the spinal cord, cerebellum, basal ganglia and the cerebral cortex)

·         Glycine (inhibitory neurotransmitter; found in interneurons in the spinal cord and brainstem)

·         Aspartate: (excitiatory neurotransmitter; found in the spinal cord)

NT:

Monoamines

(act through the G protein coupled receptors)

·         Norepinephrine (inhibitory neurotransmitter; found in the brainstem, hypothalamus, also found in the PNS excitatory and inhibitory)

·         Epinephrine

·         Dopamine (inhibitory neurotransmitter; found in the basal ganglia and the limbic system)

·         Serotonin (inhibitory neurotransmitter; found in the brainstem)

·         Histamine

NT:

Neuroactive peptides

·         Opioid neuropeptides (excitatory)

o Enkephalins (found in pain pathways); Met-enkephalin and Leu-enkephalin

o Β-endorphin

o Dynorphin

·         Growth factors (epithelial growth factor)

·         Neuromodulators (calcitonin gene related peptide)

·         Substance P (a sensory system neurotransmitter-excitatory; found in pain pathways)

NT:

other

Gases

Nitric oxide

Carbon monoxide

1. ACh
2. Norepinepherine

1.     Choline must cross the cell membrane for the formation of acetylcholine (agent: hemicholinium-3 can stop this)

2.     There must be vesicles which take up the acetylcholine at the end of the axon in the region of the synapse (agent: vesamicol can stop this)

3.     Acetylcholine must be released to have the transmission of an impulse (agent: Botulinum toxin can stop this)

4.     There must be the formation and reformation of vesicles for storing acetylcholine (agent: Black widow spider venom can stop this)

5.     Ca++ ions must be present at the end of the axon for transmission of the impulse (agent: other metals such as magnesium can stop this)

6.     The ligand binding site must be available to the neurotransmitter (agent: Curare can stop this)

7. Chemical breakdown of ACh must take place and is reformed