THE NEURON :D“the basic working unit of the brain”

Neuroscience Society

Neurons

Transmit information to other nerve cells, muscle, or gland cells

between 1 billion and 100 billion neurons, depending on the species (humans = 100 billion)

Parts of a Neuron

Cell body Cytoplasm Nucleus

Dendrites Receive messages

Axon Transmit messages End at nerve terminals

Synapse: contact points

Myelin Sheath

Axons are covered with myelin sheath

Speed transmissions of electrical signals along axons

Two types of cells: Oligodendrocytes: brain Schwann: peripheral nervous system

Action Potential

Ion channels: selectively permeable, water-filled molecular tunnels that pass through the cell membrane and allow ions — electrically charged atoms — or small molecules to enter or leave the cell.

Ability to generate electrical impulse: charge b/e inside and outside of cell

Nerve impulses dramatic reversal in electrical potential (internal negative to positive)

Action potentials pass along axon at speeds up to several hundred miles per hour

Neurotransmitters

Brain’s “chemical messengers” Voltage changes trigger release Released at nerve terminals diffuse across

intrasynaptic space bind to receptors Neurotransmitter : receptor :: key : lock triggers a response, such as the generation

of an action potential, contraction of a muscle, stimulationof enzyme activity, or inhibition of neurotransmitter release from the target cell

Acetylcholine

First neurotransmitter. Identified 75 yrs ago

Released by neurons connected to voluntary muscles & muscles that control heartbeat

Formed at axon terminals Action potential calcium ion rushes in

ACh is released into synapse attach to ACh receptors broken down by acetylcholinesterase

Acetylcholine

Myasthenia gravis Caused by antibodies that block ACh

receptors Fatigue and muscle weakness

Alzheimer’s ACh-releasing neurons die Drugs that inhibit acetylcholinesterase

Amino Acids

Building blocks of proteins INHIBITORS:

Glycine Gama-aminobutyric acid (GABA)▪ Activity increased by benzodiazephines (eg. Valium) &

anticonvulsunt drugs▪ Huntington’s Disease: hereditary disorder (midlife).

GABA-producing neurons in brain regions that coordinate movement degenerate uncontrollable movements

ACTIVATORS: Glutamate Aspartate Activate N-methyl-d-aspartate (NMDA) receptors

Catacholamines

Dopamine and Norepinephrine in brain and peripheral nervous system

Dopamine’s three circuits: 1) control movement 2) psychiatric symptoms (psychosis) 3) regulate hormonal responses

Norepinephrine: Defincies occur in patients with: Alzheimer’s,

Parkinson’s, and Korsakoff’s Syndrome (cognitive disorder associated with chronic alcoholism)

Acute stress increases release from sympathetic nerves and the adrenal medulla

Catacholamines

1) Dopamine deficits Parkinson’s Disease muscle tremors, rigidity, and difficulty in moving Levodopa: a substance from which dopamine is

synthesized 2) Abnormalities Schizophrenia

drugs that block certain dopamine receptors in the brain are helpful in diminishing psychotic symptoms

3) regulate endocrine system dopamine directs the hypothalamus to manufacture

hormones and hold them in the pituitary gland for release into the bloodstream or to trigger the release of hormones held within cells in the pituitary

Serotonin

Present particularly in blood platelets and the lining of the digestive tract

Controls switches affecting various emotional states

Fluoxetine and other drugs that alter seretonin’s actions relieve symptoms of depression and OCD

Peptides

Chains of amino acids linked together Enkephalin: opiate produced by brain

and resembles morphine (opium derivative used to kill pain). Means: “in the head”

Endorphins: Act like opium or morphine to kill pain or cause sleepiness. Name comes from endogenous morphine

Opiod peptides may explain why injuries received during stress combat

Peptides

Activated by painful or tissue-damaging stimuli

Signals transmitted to central nervous system by special sensory neurons, small myelinated fibers, and tiny unmyelinated C fibers Some C fibers contain peptide called

substance P which causes sensation of burning pain

Active component of chili peppers (capsaicin) causes release of substance P

Trophic Factors

Small proteins in the brain Necessary for the development,

function, and survival of specific groups of neurons

Information about these proteins will be useful to design new therapies for degenerative diseases including Alzheimer’s and Parkinson’s

Hormones

Endocrine system = major communication system

SOURCES OF HORMONES: pancreas, kidneys, heart, adrenal glands, gonads, thyroid, parathyroid, thymus, and pituitary gland Pituitary secretes hormones into blood Endorphins are released from pituitary so they

can be hormones too System important for: basic behavioral

activities and regulation of body functions

Hormones

Brain contains receptors for thryoid hormones and six classes of steroid hormones: androgens, estrogens, progestins, glucocorticoids, mineralocorticoids, and vitamin D

Metabolic hormones: insulin (regulates glucose), insulinlike growth factor, ghrelin (stimulates hunger), and leptin (regulates energy intake)

Hormones

In response to stress and changes in our biological clocks, such as day and night cycles and jet lag, hormones enter the blood and travel to the brain and other organs

hormones alter production of gene products that participate in synaptic neurotransmission & the structure of brain cells

Circuitry of the brain can be altered in the course of a couple of hours to a day

Hormones are important for protection and adaptation

Stress hormones (Glucocorticoid cortisol) alter brain functions which is why SEVERE & PROLONGED STRESS CAN CAUSE PERMANENT BRAIN DAMAGE

Sex Hormones

Neurons in hypothalamus produce gonadotropin-releasing hormone (GnRH): acts on cells in the pituitary

GnRH causes two hormones in men & women to be released into bloodstream: Follicle-stimulating hormone (FSH) Luteinizing hormone (LH)

Men: FSH & LH bind to receptors in testes and release testosterone

Female: FSH & LH act on ovaries and release estrogen and progesterone

Increased levels of these decreased levels of FSH & LH

Sex Differences

Size and shape of brain structures in the hypothalamus

Arrangement of neurons in the cortex and hippocampus

Actually more similar than they are different Anatomical differences have also been

reported between the brains of heterosexual and homosexual men

hormones and genes act early in life to shape the brain in terms of sex-related differences in structure and function

Gases

Nitric oxide and Carbon monoxide Can be stored in any structure, not in synaptic

storage structures Made by enzymes when needed and released from

neurons by diffusion Don’t need receptors. They act on chemical

targets (enzymes?) Carbon monoxide: exact function is not known Nitric Oxide

Erection Intestine: Relaxation and normal movements of digestion Brain: Major regulator of intracellular messenger

molecule – Cyclic GMP Neuronal damage after excess glutamate release

(Stroke)

Second Messengers

Trigger biochemical communication after neurotransmitters at their receptor

Relay message of neurotransmitter from cell membrane to brain’s internal biochemical machinery

May endure from few milliseconds to up to several minutes

Before second messengers: ATP! Norepinephrine activated receptor binds G

protein on inside of membrane causes enzyme adenylyl cyclase to convert ATP to cyclic adenosine monophosophate (cAMP)