• Neural communication consists of two components

  • Electrical current w/in a neuron

  • chemical transmission between neurons

• Neurotransmitter: A chemical that is released from a nerve cell which thereby transmits an impulse from a nerve cell to another nerve, muscle, organ, or other tissue.

  • A neurotransmitter is a messenger of neurologic information from one cell to another

  • allows info to travel through the nervous sys

• most meds and verbal treatments exert effect by altering the functioning NTs

• Criteria for NT

  • chemical released onto a target cell:

  • substance exists in presynaptic axon terminal and is synthesized in presynaptic cells

  • is released when action potential reaches axon terminals

  • receptors for the substance exist on the post synaptic cell

  • blocking substance release prevents changes in postsynaptic cell

  • can activate (EPSP or IPSP) more than one neuron at a time (versatility in neurotransmitters)

  

Acetylcholine (ACH)

• General Charcteristics:

  • Found through the nerve sys

  • receptors called cholinergic primary NT secreted by afferent axons of the central NS

  • likely the first NT to have evolved

• Functions

  • All muscular movement is accomplished by the release of acetylcholine (EPSPs for voluntary muscles)

    • Nicotinic receptors --- excites voluntary muscles through the release of ACH

    • botulinum toxin --- improperly canned food --- prevents the release of ACH -- paralysis

  • inhibits target organs of the parasympathetic branch of the autonomic NS

    • increased heart rate, and blood pressure…allows the sympathetic NS to become active

    • Muscarinic - inhibits involuntary muscles

  • induces REM sleep; released from neurons in the Pons

    • Pons partially controls brain areas called the RAS (reticular activating system); controls overall brain arousal

    • when Pons (RAS) is inhibited by Ach, REM sleep occurs

    • Pons → releases Ach → inhibits RAS

• Cognitive functions of Ach

  • allows for movement of the voluntary muscles (released by efferent spinal and cranial nerves)

  • inhibits the parasympathetic NS, allows for activation of the sym NS

  • allows for induction of REM sleep by inhibiting the Pons

Dopamine

• Basic characteristics:

  • Pleasure and motivation (activates the nucleus accumben and septum)

    • site of action for many therapeutic and recreational drugs (cocaine, amphetamines)

    • source of many psychological disorders

  • receptors are called dopaminergic, different subclasses will be discussed w/ schizophrenia

  • associated w/ schizophrenia - drugs that block DA receptors can be used to treat schizophrenia

    (neuroleptic)

    • in schizophrenia, you have too many dopamine receptors and body produces too much dopamine

    • drugs such as cocaine dopamine worsen the effects of schizophrenia

  • neuroleptic: a type of antipsychotic; blocks dopamine receptors

  • referred as a receptor antagonist

• Mesolimbocortical Dopaminergic system

  • a neurological pathway

  • Associated with activity of the limbic system; associated with emotional experiences (love, joy, anger, hate, pleasure); also learning and memory

  • limbo - overactive in schizophrenia

  • activates nucleus accumbens, amygdala, and hippocampus

  • any substance (or activity) that activates these areas produce pleasure fear or other strong emotions --- not usually under conscious control

  • Mesolimbocortical Dopaminergic system also activates the pre-frontal cortex of the brain; associated with the ability to form long-term plans and goals

• Mesostriatal (also nigrostriatal) Dopamerningeic sys

  • not affected in schizophrenia,

  • associated with activity of the basal ganglia

  • basal ganglia: area of the brain associated with the passage of motor information from the PFC throughout the brain

  • damaged in Parkinson’s disease

  • passes motor info to cerebellum which organizes the movement and sends it to either the spinal or cranial nerves

  • Parkinson’s disease = damage to dopaminergic cells in the basal ganglia → loss of control over voluntary movement

  • Damage to the cerebellum (and dopamine), loss of balance = movement side effects associated with neuroleptic

    

• Implications for behavior and cognition

  • Most pleasurable activities (innate and external) activate DA neurons in the nucleus accumbens

  • Overactivity in the mesolimbic system (part of the mesolimbocortical) → hallucination and delusions

  • allows passage of movement info thru the brain

    • damaged in Parkison’s disease

  • allows PFC to produce IPSP to help regulate behavior

Norepinephrine (NE)

• Basic characteristics

  • aka adrenaline

  • only NT formed in the vesicle

  • comes from dopamine (precursor), if a specific enzyme is present, dopamine is converted to ME

  • receptors = noradrenergic; largely excitatory, similar in chemical nature to epinephrine which is a hormone associated with arousal

• Functions

  • Controls overall levels of arousal and wakefulness

    • activates sys call reticular activation sys (RAS)

  • begins in area of pons (discussed earlier) called Reticullar Formation-- controls overall levels of cortical arousal leads to alertness, active cortex

  • regulates circadian cycle - daily cycle of arousal

  • many antidepressant medication activate NE

    • combats lack of energy, arousal, and pleasure (depression symptoms)

    • Most stimulant drugs to activate NE (from Aderall to cocaine = produce arousal)

  • can be inhibited by Ach; this inability leads to many sleeping disorder

• Implications for cognition

  • creates EPSPs which enhance cortical activity

  • Makes us alert and active through activation of the Reticular Activating System

  • also activates limbic system and dopamine as result

  • Associated with psychology disorder such as depression and ADD

  • antidepressants increases NE

  • ADD under-active → seek out external stimulation

  • inability to inhibit could lead to sleep disorders

Serotonin (5-HT)

• Regulatory NT affecting many neural functions

  • many diff types of receptors (9 so far) --- referred to as serotinergic

  • source of many (most) anti-depressant meds

  • selective serotonin reuptake inhibitors (SSRI)

• important in regulating emotional behavior

  • related to depression (lo)

    • depression is related to low levels of serotonin

  • drugs that block 5-HT reuptake can be used to treat depression

    • Increases the nervous sys’ ability to utilize NE and DA (makes it more receptive) = agonist

    • serotonin increases receptor affinity for norepinephrine by activating an enzyme that changes the conformation of the receptor

• Important in regulation of reaction to pain

  • Found in the Raphe nuclei

  • When active the raphe nucleus inhibits transmission of pain to brain (thru activation of the endorphins)

  • RN activates 5-HT which activates endorphins which block the passage of pain through the spinal cord

Amino acids - GABA

• Inhibitory NTs found in CNS

• important in control of brain’s electrical activity and defense against stress and anxiety

  • major inhibitory NT in the mammalian brain

  • in many indivs. w/ anxiety, the brain shows decreased ability to utilize GABA (an abnormal genetic condition)

  • underactivity is associated w/ “out of control” brain activity such as seizures

• Receptors have binding sites that when activated make the neuron more sensitive to GABA

• anti-anxiety drugs (benzodiazepines) activate the companion sites

• when activated the affinity of the main receptor is increased (an allosteric activator)

  

• disruption of GABA neural systems associated w/ most anxiety-related disorders

• support animals increase GABA activity

Glutamate

• Principle excitatory NT

• important in learning and memory and overall brain activity

• most important receptor type is called and NMDA receptor

  • when NMDA receptor activated -- allows for physical changes of neurons, allow for the formation new memories

    • allows new dendritic branches to grow (only with NMDA)

  • associated w/ the process of increased dendritic branching = long-term potentiation

• glutamate works with NE to keep the brain active and alert - more general than NE

• drugs such as ketamine (sedative) block activity of glutamate receptors

• glutamate decreases GABA activity, helps brain stay active

  • inhibiting the inhibitor

• associated w/ a type of neuroplasticity

Endogenous opioids

• regulates the body’s response to pain

• activates circuitry which inhibits the passage of pain (emotional and physical) info

  • ultimate effect = produces IPSP which interferes w/ pain transmission

• 3 versions of endogenous opioids have been identified w/ each influencing different areas of brain

  • endorphins: reduce the perception of physical pain; activated by serotonin

  • enkephalins: found in limbic system, inhibits emotional pain

  • dynorphins: found in cortex, inhibits “cortical” pain (eg. existential pain, what ifs, etc.)

  • all of these are activated by narcotics

• narcotics (opioids) activate endorphins receptors -- associated with pain reduction (all three endogenous opioid receptors)]

• interesting fact - activity associated with estrogen levels in women

• lithium works on GABA

• inhibits manic episodes for BPD by activating GABA

• increases NE and 5HT (and DA) for depression for BPD