The Nervous SystemIncludes the brain, spinal cord and the nerves

What does it mean to be “brain-dead?”

Neurons = masses of nerve cells that transmit information (functional unit of the system)

1. Cell Body - contains the nucleus and other cell organelles2. Dendrites – shorter, more numerous, receive information3. Axons - single long fibers, conducts information away from the cell

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Two Divisions of the Nervous System

Central Nervous System (CNS)

Brain and spinal cord

Peripheral Nervous System (PNS)

Nerves throughout the body 31 pairs of spinal nerves 12 pairs of cranial nerves

Overall function -

coordinate the body’s

systems by receiving and

sending information;

maintaining homeostasis

● Sensory - gathers info from receptors in the body

● Integrative - determines where information is sent

● Motor - responds to signals, homeostasis

Motor Functions

Somatic Nervous System - skeletal; voluntary

Autonomic Nervous System

- smooth muscles, glands; involuntary

Autonomic Nervous System (2 branches)

Parasympathetic (rest and digest)

Sympathetic (fight or flight)

*autonomic conflict

Chromatophilic substance (rough ER) - transport system

Myelin -insulation surrounding axons

Nodes of Ranvier - gaps in the insulationNeurofibrils - fibers within the axon

Neuroglial Cells - Support for neurons

node of ranvier

1. Microglial Cells - Immune function; digest debris, kills bacteria

2. Oligodendrocytes - make myelin sheath that provides insulation around the axons

3. Astrocytes - connect blood vessels to neurons

I connect to blood vessels

4. Ependymal Cells - forms membranes around tissue

5. Schwann cells: form the insulating myelin sheath around the neurons in the PNS

(same function as oligodendrocytes, which are found in the CNS)

Myelin Sheaths - insulate axons

Schwann cells supply the myelin for peripheral neurons.

Oligodendrocytes myelinate the axons of the central nervous system.

Gaps in the sheath are called:NODES OF RANVIER

Which cell….

1. Creates myelin sheath

2. Has an immune function

3. Forms a membrane

4. Connects to a blood supply

Practice with neuroglia coloring!

Myelinated (white matter) – myelinated axonsUnmyelinated (grey matter) - unmyelinated

Functional: Sensory / Motor / Interneurons

Structural - Bipolar / Unipolar / Multipolar

Fun Facts about Neurons

-Longevity – can live and function for a lifetime-Do not divide – fetal neurons lose their ability to undergo mitosis; neural stem cells are an exception-High metabolic rate – require abundant oxygen and glucose

-The nerve fibers of newborns are unmyelinated - this causes their responses to stimuli to be coarse and sometimes involve the whole body. Try surprising a baby!

Cell Membrane PotentialResting Potential / Threshold Potential / Action Potential

Nerve Impulse = weak electric current, like a wave

1. Neuron membrane

maintains resting potential

2. Threshold stimulus is

received

3. Sodium channels open

4. Sodium ions diffuse inward,

depolarizing the membrane

5. Potassium channels open

6. Potassium ions diffuse

outward, repolarizing the

membrane

7. The resulting action potential causes a local bioelectric current that stimulates the membrane.

8. Wave of action potentials travel the length of the axon as a nerve impulse

Ions in the cell and outside the cell create a positive and negative side, which produces an electric current.

Depolarization:

loss of the difference in charge between the inside and outside of the plasma membrane of a muscle or nerve cell due to a change in permeability and migration of sodium ions to the interior

Nerve Impulse

Speed is proportional to the size of the axon

(greater diameter = faster impulse)

Myelinated axons conduct impulses faster than unmyelinated one

The SynapseSynapse = junction between two communicating neurons

Nerve pathway - nerve impulse travels from neuron to neuron

Dendrite → cell body → along axon -> synapse (gap) → dendrite

To complete the signal, a NEUROTRANSMITTER is released at the gap to signal the next neuron.

Receptors on the dendrite receive the chemical message

Anatomy of the SynapseA: Neuron (axon)B: Neuron (dendrite)

1. Mitochondria2. Vesicle 3. Receptor4. Synapse5. Receptor6. Calcium Channel7. Releases neurotransmitter8. Re-uptake

Types of Neurotransmitters

Excitatory - increase membrane permeability, increases chance for threshold to be achieved

Inhibitory - decrease membrane permeability, decrease chance for threshold to be achieved

Examples of Neurotransmitters

Acetylcholine - stimulates muscle contraction

Dopamine - mood, happiness

Serotonin = sleepiness and mood

Endorphins = pain reduction, mood

GABA

Reduces the activity of the neurons to which it binds (inhibitor).

● Most common type of receptor● 40% of all synapses work with

GABA● GABA has a tranquilising effect● Low levels of GABA associated

with anxiety and phobia

Sedatives bind to GABA receptors

(gamma-aminobutyric acid)

Agonist = molecule that has the same effect on the postsynaptic neuron as the neurotransmitter itself does.

Antagonist = molecule that blocks the effect that the neurotransmitter normally has on the postsynaptic neuron.

http://www.youtube.com/watch?v=GOK1tKFFIQI

Antidepressants

Zoloft is part of a class of drugs called selective serotonin reuptake inhibitors

it inhibits the uptake of serotonin back into the cell, keeping mood elevated for a longer time.

Drugs and Poisons that Affect Nerves

Curare - poison made from frog skin and causes paralysis by blocking Ach receptors at the neuromuscular junction.

Strychnine poisoning can be fatal to humans and animals and can occur by inhalation, swallowingIt prevents the proper operation of the chemical that controls nerve signals to the muscles. The chemical controlling nerve signals works like the body's “off switch” for muscles. When this “off switch” does not work correctly, muscles throughout the body have severe, painful spasms.

Read about Strychnine Poisoning

CocaineDopamine binds to receptors and is eventually recycled back into the neuron.

If cocaine is present, it attaches to the dopamine transporter and blocks the normal recycling process, resulting in a buildup of dopamine in the synapse, which contributes to the pleasurable effects of cocaine.

Your neurotransmitters on cocaine

Ecstasy (MDMA)The neurotransmitter serotonin is vital in regulating many of our basic functions. Serotonin is, among other things, the feel good neurotransmitter and helps to regulate body temp.

Our brain cells are recycle serotonin back into the cells and out of the synapse using serotonin reuptake transporters. Ecstasy essentially takes these upkeep transporters and reverses their roles. This causes a massive flood of serotonin from the brain cells into the synapse.

The most common cause of Ecstasy-related death is overheating (hyperthermia).

Heroin

Activates opiate receptorsBlocks release of GABAMore dopamine is released

DOPAMINE

Dopamine Receptors

Amphetamines

Mimic dopamine - binding to receptors

Dopamine does not re-enter the cell, depleting the cell’s supply

What Is PRIALT?PRIALT is a calcium channel blocker that could be used to inhibit pain transmission from the spinal cord

PRIALT does not bind to opioid receptors

*Why might this be an important chemical for combating heroin addiction?

http://www.hhmi.org/biointeractive/prialt-blocks-pain-signaling-mice

Check out Mouse Party!

Impulse ProcessingNeuronal pool - groups of neurons that make hundreds of synaptic connections and work together to perform a common function

These "pools" help us remember sequential tasks, like tying a shoe or riding a bike.

Nerve Pathways

Reflex arc = simple path, only includes a few neurons ( involuntary, instant)

Knee-jerk reflex = maintains uprightness

Withdrawal reflex = avoidance of painful stimuli

Disorders Related to Neurons

ALS - (Lou Gehrig’s Disease) Amyotrophic Lateral Sclerosis

Progressive degeneration of nerve cells in the spinal cord and brain

NEURODEGENERATIVE

- this means symptoms will get worse over time.

- most patients die within 5 years of diagnosis

EpilepsyEpileptic seizures are caused by excessive electrical activity within networks of neurons in the brain.

A fine balance between excitation and inhibition must be maintained in order for the brain to function normally.

If there is too much glutamate, neurons can become hyperexcitable and a seizure may result. Too little GABA (inhibitory) can also result in a seizure.

2 Minute Neuroscience - Epilepsy

Myasthenia Gravis

autoimmune disorder in which antibodies destroy neuromuscular connections

We did a case study on this during the muscle chapter, do you remember it?

Multiple Sclerosis (MS)Myelin around the nerve fibers is lost (autoimmune) and forms scar tissue called sclerosis. Nerves cannot conduct impulses to and from the brain.

Affects ability to walk, talk, swallow, and can affect vision.