Neurotransmitters and behaviour

what is a neuron

core componentof the NS (brain, spinal cord (CNS) and ganglia (PNS)

What is the soma

• complex cell body

• axon and dendrites extrude from it

• review and processes information

dendrites

• branch profusely and get thinner with each branching

• receives information from other neurons

axon

• leaves soma at the axon hillock

• extend for great distances and has hundreds of branches

• sends information to other neurons

Three types of neurons (functional)

• afferent (sensory)

• efferent (motor)

• interneuron (association)

Afferent neuron

• convey information from tissues and organs into the CNS

• simplest form of neuron

• stimulus can come from exteroreceptors or intereceptors

Stuctural types of sensory neuron

• bipolar (retina)

• somatosensory (skin and muscle)

Efferent neuron

• transmit nerve impulses from brain to affectors

Where are efferent neurons located

• in the lower brain stem and spinal cord

What is the structure of efferent neurons

• extensive dendritic networks and large axons that connect to muscle

Interneurons

• connect neurons within specific regions of the CNS

• link sensory and motor neurons

• allow brain and spinal cord to process and integrate information

• branch extensively

why are interneurons important for reflexes

process sensory information from sensory neurons and relayed to motor neurons

what’s different about the knee jerk reflex compared to other reflexes

there is a direct connection from sensory to motor neuron

what receives synaptic signals from other neurons

soma and dendrites

how are signals transmitted to other neurons

down the axon > axon terminal > receiving dendrite/body

how do neurons communicate

neurotransmission/synaptic transmission (electrical signals that turn into chemical energy) via the synapse

what triggers the release of neurotransmitters

action potential

action potential

quick electric pulse that neurons use to communicate with each other

cell membrane of neurons

forms border of neuron

seperates the inside environment from the outside environment

controls movement of substances in and out of the neuron

external layer contain receptors (specialised proteins) that respond to specific molecules

what does extracellular fluid contain

water

ions

nutrients

signalling molecules

what is the cell membrane made out of

lipids and proteins

ligand-gated channel

allow ions to pass through the membrain in response to the binding of a neurotransmitter

mechanically-gated channel

open in response to mechanical stress (i.e touch, hearing)

always open/leaky channel

passive ion channels that are always open to maintain homeostasis

voltage-gated

activated by changes in the electrical membrane potential near the channel (i.e action potential)

located at axon and synapse

directionally propagate electical signals

iron-specific (only allow one type of ion to pass through)

• activation gate

• inactivation gate

what is the function of gated channels

receive information

maintain homeostasis

detect stimuli

send message

activation gate

opens when neuron receives the right signal allowing specific ions to flow through

inactivation gate

closes shortly after channel opens stopping flow and activation of ions

what is the purpose of inactivation and activation gates

• speed and efficency

• ions only briefly flow into cell membrane for a period of time before it resets

what triggers the opening and closing of voltage gated channels

changing ion concentration between the intra and extracellular fluid (Na+, K+, Ca2+ and Cl-)

At resting potential, the inside of the neuron is more * relative to the outside

negatively charged

What is the charge of a neuron at resting potential

-70mv

why is intracellular fluid more negatively charged than the outside

The is a higher concentration of the protein anions and potassium inside the axon relative to the ouside

what is in the extracellular fluid

chloride and sodium

how is resting potential of the neuron maintained

• ungated channels allow K+ and Cl- pass freely

• Gated sodium channels keep out Na+

Graded potentials

• small changes in the cell membrane

• excitory: make the inside of the neuron more positive (depolarisation)

• inhibitory: makes the inside of the neuron more negative (hyperpolarisation)

Depolarisation

-50mv threshold reached > voltage gated channels open > influx of sodium ions into the cell > rapid positive change in intracellular fluid (depolarisation)

saltutory conduction

when the electrical signal skips between the nodes of ranvier down the axon

faster

what stimulates the release of neurotransmitters

action potentials

what type of channels are on the post synaptic neuron

ligand gated

neurotransmitter

1. chemiscal must be synthesised/made in the neuron or be present in it

2. when released the chemical must produce a response in target

3. same response must occur when the chemical is experimentally placed on the target

4. must be a mechanim for removing the chemical following its work

excitatory neurotransmitters

increase likelihood of action potential threshold (depolarisation)

more on dendrites

wider gap

inhibitory neurotransmitter

decrease likelihood of action potential (hyperpolarise)

more on cell body

what determines whether a neurotrasnmitter is excitory or inhibitory

depends on

• type of channel coupled to receptor

• concentration of permeant ions inside and outside the cell (charge)

classes of neurotransmitters

1. small molecule neurotransmitters

2. peptide neurotransmitters (neuropeptides)

small molecule neurotransmitters

• derived from the food we eat

• eat > gut > small intestine absorb nutrients into blood > cell body of neuron

• packaged ready to use in axon terminals

• quickly replaced following release

• communicate and quick firing rate

• acetylcholine, histamine, amines (dopamine, serotonin). amino acids (glutamate, glycine)

acetylcholine

• one type of small molecule neurotransmitter

• functions in both PNS and CNS

• neuromodulator

• key NT for parasympathetic nervous system

• primarly excitatory NT

acetylcholine

• type of small molecule NT

• fundamental to cholinergic system (network of neurons that use acetylcholine)

• muscle activation (PNS)

• effects as a neuromodulator upon plasticity, arousal and reward

• forebrain networks: learning, decision making and attention (CNS)

serotonin

• small molecule neurotransmitter

• primarily an excitory neurotransmitter

• found in neurons of the raphe nucei region of the pons and upper brain stem > extend to forebrain and other parts

• regulate sleep and wakefulness, mood, aggression, appretite, arousal, perception of pain

• implicated in anxiety, depression, cognitive symptoms of schizophrenia, memory problems, appetite regulation and psychotic experiences

peptide neurotransmitters (neuropeptides)

• made on the neuron’s cell body

• responsible for the synthesis of proteins in cells on ribosomes

• packaged in the membrane into vesicles > transported to the axon terminal

• slow production and not easily replaced

endorphins

• neuropeptide

• naturally occur in the body

• opiod receptors and reduce pain

• contribute to pleasure and wellbeing

• released during exercise, stress, laughter and other rewarding experiences

• motivation, emotion, attachment and stress regulation

what is the main neurotransmitter used in motor neurons to make movement possible

acetylcholine

motor neurone disease (MND)

progressive disease that attacks the motor neurons in the brain and spinal cord

amyothrophic lateral sclerosis (ALS)

• type of MND

• stuff muscles, muscle twitching, gradual muscle wasting

• lose ability to speak, swallow and breath, progress to frontotemporal dementia

how does acetylcholine control the sympathic nervous system

• activates the SNS to release noradrenaline

• prepares the body for fight or flight

how does acetylcholine control the parasympathic nervous system

• activates PNS

• neurons release acetylcholine

• prepares body for rest and digest

activating system

network of neurons that uses one primary neurotransmitter to regulate brain activity

these neurons have cell bodies clustered in specific brain regions and send axons through the brain

four activating CNS systems

• cholinergic

• dopaminergic

• noradrenergic

• serotonergic

cholinergic system

• use acetylcholine to communicate with other neurons

• cognitive functions: attention, memory and emotional processing

• cholinergic input from the basal forebrain helps maintain sustained attention

• supports attentional processing of important, including threat-related stimuli

alzheimer’s disease

• neurogenerative disease characterised clinically by insideous, chronic and progressive cognitive decline

what are the two key neuronal changes that take place in the brain during alzheimer’s

1. loss of cholinergic cells in the forebrain (medication to increase acetylcholine in the forebrain (donepezil)

2. neuritic plaques in the cerebral cortex (amyloid) which are associated with neurofibrillary tangles

changes trigger inflammation and deterioration of cholinergic cells

dopaminergic system

neural pathways in the brain that transmit dopamine

8 dopaminergic pathways

1. mesolimbic

2. mesocortical

3. nigrostriatal

4. tuberoinfundibular

nigrostriatal pathway

• projects from substantia nigra upwards to the striatum

• striatim is the primary input to the basal ganglia system

• parkinsons disease results in loss of dopaminergic innervation to the striatum and other basal ganglia

• symptoms result from the progressive degeneration of dopamine-producing cells of the substantia nigra

mesolimbic pathway

• begins in the ventral tegmental area of the midbrain and connects to the nucleus accumbens, amygdala, hippocampis and prefrontal corex

• role in motivation, pleasure, reward, reinforcement and learning

• addiction (too much), schizophrenia and depression (too less)

what causes addiction

• increased dopamine release in the mesolimbic pathway

methamphetamine

• meth blocks receptors of original neuron so seratonin cannot be reuptaken and goes to next neuron > floods it > damages receptors of the next neuron'

• abnormal neuroplastic changes in brain structures

• changes to white matter integrity

• reduced hippocampal volume

• reduction in grey matter in the cingulate cortex

• limbic cortex

• paralimbic cortex

• regions involved in emotion, memory and decision making

• overstimulation of the amygdala: aggression, distruption of inhibitory circuits, ODC, hyperactive dopaminergic signal transduction, stimulant psychosis

noradrenergic system

• norepinephrine

• originate in the locus coeruleus and lateral tegmental field (medulla, pons of brain stem)

• emotion: depression mania stability of mood

• mobilises brain and body for action

what are the behavioural affects of norepinephrine

• increases arousal and alertness

• promotes vigigilance

• enhances formation

• retrieval of memory

• focuses attentions

• increases restlessness and anxiety

what are the physiological effects of norepinephrine

• increased heart rate and blood pressure

• triggers release of glucose from energy stores

• increases blood flow to skeletal muscles

• reduces blood flow to the gastrointestinal system

when is norepinephrine released

norepinephrine releases lowest during sleep, rises during wakefulness and reaches its highest levels in situations of stress and danger

locus coeruleus is important for…

wakefulness

where is the serotonergic system located

• originated in the dorsal and median raphe in the midbrain

• dorsal raphe is on the midline of the brainstep and is one of the raphe nuclei extending to most parts of the CNS

serotonergic system responsible for producing…

serotonin

how many serotonin receptors subtypes are in the serotonergic system and what is the effect of this

• 15

• produces diversity of signalling so one neurotransmittercan produce very different effects

what is the function of the serotonergic system

• maintains activity in forebrain and plays role in wakefulness

• regulate sleep/wake cycles

• precursor for melatonin

• regulated circadium rhythm

what is the reduced function of the serotonergic system associated with?

insomnia and depression

what is enhanced function of the seotonergic system associated with?

weight loss and suppressed diet

what psychopathological disorders is linked with serotonergic dysfunctions?

• anxiety

• eating disorders

• schizophenia

• impule constrol disorders

• autism

• aggressive behaviours

• depression

what do antidepressents do

• increase serotonin levels in the synapse

• blocks reactants

what are the symptoms of high serotonin levels due to MDMA and antidepressents together

• agitation

• fever

• sweating

• muscle rigidiy

• rapid heart rate

• death