
False!


True!


False!

Broad generalizations are often made in popular psychology about one side or the other having characteristic labels such as "logical" or "creative".
These labels need to be treated carefully; although a lateral dominance is measurable , these characteristics are in fact existent in both sides , [1] and experimental evidence provides little support for correlating the structural differences between the sides with functional differences.
[2]


False!


True!


False!


False!

False!


True! The sciatic nerve can be over a meter long!


False! (well, sort of… it’s about as firm as tofu!)

Functions of the Nervous System:


A system of cells, tissue, and organs that regulate the body’s responses to external and internal stimuli.



Communication between organ systems.
Provides info about environmental conditions to all internal organs.
Translates environmental stimuli to messages understood by the cells

External stimuli: environmental factors that influence metabolic changes in a cell or physiological changes in tissues and organs.

Internal stimuli: cell secretions used to communicate info about a cell’s jobs and needs.


Neural tube – developmental struct

Stem cells

Neurons & neuroglia

 excitable cells
 receive, interpret, and transmit external and internal stimuli.

 maintain the excitability & health of neurons.

Don’t take part in communication.

Supportive.

•
•
•
Derived from the neural tube
Bidirectional communication with neuroglia and neurons.
Play a role in the development of the nervous system.


Categorized by their cell anatomy and mode of communication


Common features:

Axon:

Long process





Extends from cell body from the axon hillock
Transfers impulses to the terminus.
Usually one per neuron.
Some have branches (collaterals) that reach out to other neurons.
Job: initiate the electrical signal that will be transmitted from the axon to glands, muscles, other neurons.


Releases neurotransmitters—transmit info from one neuron to another.

Cells must possess neurotransmitter receptors if they are to respond to the stimulus

Cell body (soma): contains nucleus & organelles, ER and Golgi bodies that produce specialized enzymes and secretions needed for nerve cell communication.
Terminus: Releases neurotransmitters
Dendrite: antennae.
Receive stimuli from several sources
Axon Hillock: where the axon originates
Axon: long process that comes off the body; transfers impulses to the terminus.
Job: transmit electrical signal to glands, muscles, other neurons.


Neurons don’t directly touch the cells with which they communicate

Form a synapse: the junction where an impulse is transmitted from one neuron to another.

2. Pre-synaptic neuron: produces the neurotransmitter
4. Neurotransmitter: most pre-synaptic neurons produce 1 kind.
1. Synaptic Cleft: the space between the terminus of one neuron and the dendrites of another.
5. Receptor: Post-synaptic neurons an have a variety of neurotransmitter receptors.
3. Post-synaptic neuron: receives the neurotransmitter


Make up bulk of cells in the nervous system

Closely associated with neurons

High lipid content


White in appearance
Vulnerable to improper diet

Many types…


Astrocytes

Ependymal cells

Microglia

Oligodendrocytes
Not pictured:

Radial glia

Satellite cells

Schwann cells


A.k.a. macroglia

Largest class

Star-shaped, w/ many branches, or feet

Often associate w/ blood vessels




Control types of materials that pass from blood to neurons
Protects neurons from harmful agents
Creates blood-brain barrier
Mostly found in brain, spinal cord


Primary secretory cells

Line cavities of brain, spinal column

Produce cerebrospinal fluid (CSF)

Bathes, nourishes, protects brain, spinal cord

Cilia help circulate CSF


Highly variable

Found throughout nervous system

Many carry out phagocytosis, removing infectious agents, repair damage

Others produce secretions that maintain neuron health, assist in healing

Malfunctions often produce disorders


Large, w/ numerous branching processes

Wrap around axons of neurons

Form an insulating cover (myelin sheath)

Found only in brain, spinal cord

Speeds up nerve transmission


Found in developing nervous system

Provide framework for growing interconnections

In adults, assist maintenance of brain and eyes

Communicate “needs” of these cells


Small, numerous

Cover surface of neurons outside brain, spinal cord

Help maintain chemical environment

May help w/ nerve cell repair


Form myelin sheath around axons of neurons outside of brain, spinal cord (in PNS)

Gaps between cells called nodes of Ranvier

Help speed transmission

Functions of the Nervous System:


Materials diffuse from high  low concentration

Membranes act as a barrier to diffusion… they can be “selective” about what can pass


In general, things that are large/charged need special “permission” to pass through the membrane

They need a channel/gate that gives them a pathway
Ions, like Sodium (Na+), Potassium (K+), and
Chloride (Cl-) are normally not allowed through


In general, the following are true about ions:


They will repel each other (likes repel)
They will be attracted to an opposite charge


Neurons are excitable!

They transmit a signal that was received by the dendrites/cell body down through the axon

Cytoplasm must be ready!

Neurons transmit information to other cells via an action potential

Na+ gated channel
K+ gated channel
Na+/K+
Pump
K+ pore
(leaks)


Must maintain an excitable condition called
resting potential.


Chemically unstable condition
Sodium ion concentration higher outside cell than inside

Creates a diffusion potential; sodium “wants” to enter


Potassium ions higher inside cell than outside
A.k.a. a “salty banana”
Sodium/potassium pump maintains this potential

Na+
Na+
K+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+ Na+
Na+
Na+
Na+
Na+
Na+
K+
Na+
Na+
K+
K+
- PROTEIN K+
K+
K+
- PROTEIN -
K+ Na+
K+
- PROTEIN -
K+
K+
- PROTEIN -
K+
K+
Na+
- PROTEIN
- PROTEIN


Animation


Debatable… some have 6 phases




Depolarization
Repolarization
Hyperpolarization
Recovery phase


Cytoplasm’s charge starts at ~ -70 mV

Dendrites receive stimulus from a. another cell or b. the environment

Sodium channels open, allowing rapid influx


If enough channels open, cytoplasm’s charge reaches -55 mV = threshold
Required for an action potential to propagate, or travel, across the cell membrane


At threshold, more Na + channels open

Charge of cytoplasm increases to +30 mV

Each depolarized segment of axon depolarizes the adjacent segment… like falling dominoes


Potassium gated ion channels are also stimulated to open during a depolarization!

They are slower to respond

They don’t fully open enough to allow K+ ions to flow out until the sodium gates have both opened AND closed!


Sodium channels closed, and potassium channels finally open

K+ ions diffuse outward, causing the cell’s interior to become more negative (lost + ions)

Neuron is becoming repolarized.


Repolarization is rapid!

Cell moves past resting potential (-70 mv) and overshoots, reaching -90 mV.

K+ gated ion channels are slow to close as well…

This is hyperpolarization…


K+ gates on K+ channel proteins are slow to close, allowing this hyperpolarization

Why does this occur?
1.
2.
Prevents neuron from becoming stimulated during repolarization period
Prevents action potential from travelling both forward AND backward… becomes a unidirectional signal.
= REFRACTORY PERIOD


Sodium/Potassium pumps return cell to resting potential (Na+ outside, K+ inside)

Some cells send a second impulse before recovery is complete = tetany


Click here

-

Action potentials relatively slow (5  25 m/second)

To increase velocity, neurons’ axons are myelinated.


Reduces amount of membrane that must be depolarized
Stimulus “jumps” from node to node

10  120 meters/second!
-

Working with your partner, write a “story” that describes an action potential.

Axon

Cytoplasm

Dendrite

Depolarization

Diffusion Potential

Hyperpolarization

Influx

K+ gated ion channels

K+ ion

Na+ gated ion channels

Na+ ion

Na+/K+ pump

Outflux

Refractory period

Repolarization


When the terminus depolarizes, calcium ions diffuse into terminus



Stimulates movement of vesicles towards terminal knobs
Vesicles fuse w/ cell membrane, releasing contents
These vesicles contain neurotransmitters

Neurotransmitters diffuse across synaptic
cleft, binding to matching receptors on post- synaptic neuron




1. Synthesis and storage of neurotransmitters
2. Neurotransmitter release
3. Neurotransmitter binding to post-synaptic receptors

4. Inactivation of neurotransmitters


Synthesis occurs in nerve cell body, transferred to terminus
Inactivation occurs by degradation or
reuptake (for recycling)… many drugs affect these processes


Chemical signals that transfer action potential from affector (sensory neuron receptor) to an effector (motor neuron, muscle, gland)

Can be excitatory or inhibitory

Excitatory: helps depolarize post-synaptic neuron (move interior closer to threshold)

Inhibitory: hyperpolarize post-synaptic neuron (move interior farther from threshold)


Amino acids:


Usually in brain, spinal column
Aspartate, gamma-aminobutyric acid (GABA)
(inhibitory), glutamate (excitatory), glycine
(inhibitory)

Catecholamines: Excitatory; made from tyrosine


Ex. Epinephrine, norepinephrine, dopamine (both excitatory/inhibitory)
Associated w/ stress


Cholinergics: Excites muscle cells; made from dietary fats, other metabolic compounds

Acetylcholine most common

Monoamines: Related to catecholamines

Serotonin (made from tryptophan)

Inhibits catecholamine NT’s

Histamine: associated w/ pain sensations, stress

Function of the Nervous System


Key term: Innervate = supply a body part w/ nervous stimulation

Ex: Gland, muscle, neuron
Types of neural pathways (focus on the term!)

Axo-dendritic synapse: terminus  dendrite connection

Axo-somatic synapse: terminus  nerve cell body connection

Axo-axonic synapse: terminus  axon connection

Reverberating pathway (brain)


Neurons can stimulate themselves repeatedly until another stimulus stops it

Linked to important pathways in brain

Emotions, learning, memory

Breakdown in these pathways leads to disorders

Ex. Epilepsy (uncontrolled excitatory activity)


Type of communication that takes place between two neurons also significant:


Excitatory postsynaptic potential (EPSP) = action potential generated

In some pathways, may require multiple, simultaneous
EPSP’s to create an action potential
Inhibitory postsynaptic potential (IPSP) = action potential prevented

Hyperpolarizes the membrane
Many neurons have both EPSP and IPSP connections – allows decision-making in brain!

Functions of the Nervous System:


Sensory neuron (w/ receptor)  interneuron
(in spinal cord)  motor neuron
OR…

Afferent neuron  interneuron  Efferent neuron


Instantaneous, involuntary response to a stimulus

No intervention/conscious control required

Neurons arranged in a reflex arc


Stimulus excites an affector




Carry out physiological job = transduction
Convert a stimulus (touch/pain) into a message that can be relayed to cells
Part of sensory nerve’s dendrites
Transfers response to interneuron, which relays information to motor neuron

Motor neuron stimulates effector, which carries out task of the reflex

Interneurons communicate w/ brain

= certain reflexes can be “trained”, like urination and bowel movements

Function of the Nervous System:


Infectious: causes by microorganisms

Degenerative: progressive deterioration of a cell/tissue

Congenital: embryological/maturation errors

Toxicological: poisons that affect cell metabolism/communication

Traumatic: injuries resulting

Most common: bacterial

Release toxins into blood


Can inflame, kill neurons, neuroglia

Affect neuron communication
Ex. Botulism – toxin blocks action of acetylcholine

Produces flaccid paralysis (no muscle contraction)


Ex. Tetanus – toxin enhances acetylcholine

Prevents muscle relaxation
Endotoxins: produced as bacteria replicate, die

Cause immediate death to neuroglia and neurons


Commonly cause diseases

Examples


Encephalitis – inflammation of brain
Meningitis – inflammation of membranes surrounding brain, spinal cord

Fungal toxins similar to those from bacteria


Enter and infect nervous system cells

Varied:




Protista
Viruses: herpes, rabies
Viroids
Prions: Mad cow/BSE/Creutzfeldt-Jakob

Kill cells outright/produce inflammation

Carried by mosquitoes, biting insects


Amylotrophic lateral sclerosis (ALS) a.k.a.
Lou Gehrig’s disease


Faulty mitochondria
Gradual loss of muscle function

Demyelination


Loss of neuroglia around axons, bodies of neurons
Causes: metabolic, loss of blood flow


Results in slower neural impulses, eventual degeneration
Ex: Multiple sclerosis


Krabbe’s disease


Lack enzyme (galactosylceramide betagalactosidase) that prevents accumulation of toxic wastes in nerve cells
Buildup of harmful fats

Abnormal neuron functioning, diminished neuroglia maturation

Hirschsprung’s disease


Affects large intestine neurons
Nerve cells stop growing during development, causing loss of function of LI


Variety of sources:



Lead
Arsenic, cyanide (pesticides) – block cellular respiration, disabling neurons
Tetrodotoxins: inhibits flow of sodium into nerve cells


Neurons cannot be replaced once they die*

Injured neurons can be repaired




Intact neuroglia must be nearby
Can replicate if only a small number are killed
Rebuild damaged components of neurons
Redirect axons to original positions

Encouraged by growth factors

Stem cells show promise


Mitosis is rare!

Cells are so specialized, to divide would mean de-differentiating!

Remember neurons originate from stem cells, not other neurons

= Neurons and neuroglia stay with you throughout life

= They accumulate damage over your lifespan


The higher the cell’s metabolism, the greater the buildup of metabolic “oxidizing” byproducts



These come from mitochondria
Can alter DNA
 metabolic errors that can be fatal

Alcohol, drug abuse, smoking, air pollution accelerate cell aging


As one ages, consistent blood flow to tissues is lost

Neurons are highly susceptible to this



High metabolic needs
Obtain nutrients, ions for action potentials
Materials needed for NT’s

Become less responsive to stimuli

Glands, muscles, neurons


Loss of tonic control

= regular nerve communication with glands, muscles

Without tonic control…



Lose mobility
Loss of balance, posture
Lose muscle mass


Due to increased age

Refractory period longer

= fewer action potentials

Slows down impulses to muscles, delays sensory communication to brain, body

Wastes collect: plaques, tangles


Amyloid proteins = plaque
Tangles = changes in cell’s cytoplasm, changing shape

Lipofuscin = fatty, brown pigment that builds up; indicator of nerve cell pathology