NEUROTRANSMITTERS

Excitatory and inhibitory neurotransmitters found in both PNS and CNS
Same neurotransmitter may be inhibitory in one location but excitatory in another
Type of receptors determines which response occurs
Neurons release up to 3 different neurotransmitters from their synaptic end bulbs

Ex. ACh

ACETYLCHOLINE

Excitatory at neuromuscular junction

Acts to open chemically gated ion channels

Inhibitory in parasympathetic fibers of Vagus nerve (cranial nerve X)

Innervates the heart
Slows the heart rate down

KNOWN NEUROTRANSMITTERS

60 known neurotransmitters
Parkinson's Disease, Alzheimer's Disease, depression, anxiety and schizophrenia are caused by neurotransmitter problems

1) acetylcholine
2) amino acids
3) biogenic amines
4) neuropeptides
5) gases

ACETYLCHOLINE

Released at NM junction
Released by axons of limbic system in brain
Destruction of these neurons is a hallmark of Alzheimer's Disease

AMINO ACIDS

Glutamate and aspartate are excitatory in the brain
GABA and glycine are inhibitory

GABA found primarily in the brain

Antianxiety drugs (valium) enhance the action of GABA

Glycine found primarily in the spinal cord

STRYCHNINE POISONING

Normally neurons release inhibitory glycine in spinal cord to motor neurons to prevent excessive muscular contraction

Strychnine binds and blocks glycine receptors

Result is massive tetanic contractions

BIOGENIC AMINES

Also called catecholamines
Actively transported back into the synaptic end bulbs after release
Reuptake by the neuron is required in order to recycle

NOREPINEPHRINE (NE) & EPINEPHRINE

May act as inhibitory or excitatory
Implicated in maintaining arousal, dreaming and mood regulation

DOPAMINE (DA)

Involved in emotional responses
Regulate gross automatic movements of skeletal muscles
Degeneration of neurons producing dopamine causes Parkinson's Disease

SEROTONIN (5-HT)

Induce sleep, sensory perception, temperature regulation and control of mood
Anti-depressant (Prozac) is a serotonin inhibitor of serotonin reuptake

Thus more serotonin available in synaptic cleft
Allowing signals to pass from neuron to neuron more easily

NEUROPEPTIDES

May also act as hormones

Angiotensin II - stimulates thirst
Oxytocin - improves memory
Antidiuretic hormone (ADH) - regulates water reabsorption
Enkaphalins and endorphins - analgesic effects

ENKAPHALLINS AND ENDORPHINS

linked to improved memory, learning, feelings of pleasure and euphoria
200 X stronger than morphine
acupuncture may increase release of enkaphalins and endorphins (opioids)

GASES

Nitric oxide (NO)
Released by endothelial cells lining blood vessels
Causes relaxation and vasodilation

Effect is to lower BP

Allow for erection of penis in males

NITRIC OXIDE

Phagocytic cells produce NO to kill microbes and tumor cells
In large quantities NO is toxic

ALTERATION OF IMPULSES AND SYNAPSES

Alkalosis
acidosis
hypnotics
caffeine
etc.

ALKALOSIS

Increase in the pH above 7.45
Increases the excitability of neurons
Impulses arise inappropriately
Light headedness, numbness, tingling, nervousness, muscle spasms

ACIDOSIS

Decrease in pH below 7.35
Progressive depression of neuron activity
Produces apathy and muscle weakness

EXCESSIVE PRESSURE

Causes blockage of nerve impulse

"go to sleep"

HYPNOTICS, TRANQUILIZERS, ANESTHETICS

Increase the threshold for excitation

CAFFEINE, BENZEDRINE, NICOTINE

Reduce threshold for excitation

CHEMICAL SYNAPSE MODIFICATION

Clostridium botulinum bacteria in some canned foods produce a toxin

Toxin inhibits the release of ACh if ingested
Weakens muscle contractions
Small amounts are very poisonous

Strabismus, uncontrolled winking, stuttering are uncontrollable muscle contraction

Can be helped by injections of botulinum toxin

MYASTHENIA GRAVIS

Weakened muscle condition brought on by antibodies blocking acetylcholine receptors
Neostigmine and phystigmine

anticholinesterase agents that inactivate acetylcholinesterase
Results in slow removal of acetylcholine

Used to treat myasthenia gravis

DIISOPROPYL FLUOROPHOSPHATE

Powerful nerve gas
Anticholinesterase agent active in many insecticides

CURARE

Plant derivative
South American Indians poisoned arrows and darts

Blocks acetylcholine receptors causing muscular paralysis

May be used during surgery to relax muscles

Neostigmine is antidote for curare

END OF NERVE