Neurotransmitters, Synapses, Neural Communication and Hormones Flashcards
Outline the electrical synapse
“Gap junctions”
Very small gap between two neurones (2-4 nm)
§
The facing membranes have large channels that allow ions to move directly from one cell to the other
Transmission from one neuron to the next is similar to action potential conduction along the axon
Very fast –no time delay
Rare in human CNS (eye movements)
NEAR-INSTANTANEOUS TRANSMISSION
outline the chemical synapse
There is a gap between the axon of one neurone and the dendrite of the next one
Small gap but much larger than gap junctions (20-40 nm)
Each neurone has many (typically ca 1000) synapses
Slower (ca 1ms)
Chemical synapses Specialized structures for transmitting chemical signals from one neuron (presynaptic neuron) to another (postsynaptic neuron) Neurons are separated by small gap = synaptic cleft
How does the chemical synapse work?
- Action potential arrives at presynaptic membrane
- Voltage-gated Ca2+ channels open, Ca2+ diffuses into cell
- Synaptic vesicles fuse with membrane, releasing neurotransmitter molecules into synaptic cleft 4. Transmitter binds to postsynaptic receptors, opening ion channels
- If channel is for Na+: → depolarization= excitatory postsynaptic potential (EPSP) If channel is for Cl-: → hyperpolarization= inhibitory postsynaptic potential (IPSP)
- EPSP/IPSP propagated along membrane
what is a receptor in terms of neurones?
Receptors are membrane proteinsthat bind neurotransmitters
Each receptor type can bind only a specific neurotransmitter
– lock-and-key principle: when a transmitter molecule binds to the receptor, the receptor changes shape, causing an ion channel to open
Fast= Ionotropic receptors
These control the ion channel directly § When bound to the transmitter the ion channel opens and ions flow across the membrane § Also known as ligand-gated ion channels
slow= metabrotropic receptors
These also bind with the neurotransmitter but do not open the ion channel
They activate G-Proteins that subsequently control the ion channel
what i the differecne between tempral and spatial summation
temporal: many EPSPs/IPSPs occur at the same time
spatial: many axons converge on one neuron
what happens when EPSPS/IPSPS reach the axon hilllock?
If net charge (sum of EPSPs+IPSPs) is below threshold (
what is a neurotransmitter?
A chemical released by one neuron that affects another neuron or an effector organ (e.g., muscle, gland, blood vessel)
where are neurotransmitters qualities?
. Synthesized in the presynaptic neuron
- Localized to vesicles in the presynaptic neuron
- Released from the presynaptic neuron under physiological conditions
- Rabidly removed from the synaptic cleft by uptake or degradation
- Presence of receptor on the post-synaptic neuron
- Binding to the receptor elicits a biological response
give the 7 steps to neurotransmitters
neurotransmitters are synthathised from precursors under the influence of enzymes
- stored in vesicles
- neurotransmitter molecules that leak from their vescicles are destroyed by enzymes
- Action potential cause vesicles to fuse wit hsynpase and release neurotransmitters
- some of it binds with auto receptor and inhibit subsequent neurotransmitter release
- rest of it binds to receptors
- released neurotransmitters are deactivated either by uptake orenzyme degredation
give some excitatory neurones in the CNS
Acetylcholine Aspartate Dopamine Histamine Norepinephrine Epinephrine Glutamate Serotonin
give some inhibitory neurones in the CNS
GABA Glycine
explain the many types of communication in the CNS
Point-to-point= Restricts synaptic communication
hormonal communication= Secretes chemicals into the blood stream to affect the entire body
interconnected neurones in the ANS= Simultaneously controls responses in many internal organs.
Diffuse modulatory systems:
Specific neurotransmitter. Regulate arousal, mood, motivation, sexual behavior, emotion, sleep, etc.
what is a DMS
diffuse modulatory systems
Modulatory system affect wide areas to make them more or less excitable or more or less synchronously active etc.
Messages that must be widely broadcast through the brain use diffuse modulatory systems
The brain uses many of these mechanisms each requiring a specific neurotransmitter
Connections are widely dispersed throughout the brain
Important in motor control, memory, mood, motivation, and metabolic state
Heavily involved in many psychiatric disorders
outline DMS within the brain
Core of each system has a small number of neurons § Neurons of the diffuse system arise from this central core
The core is in the brain stem
Each neuron has tremendous affect because it can connect to as many as 100,000 neurons
Neurotransmitters are released into the extracellular fluid and can diffuse to many neurons
what is the Noradrenergic Locus Coeruleus
Makes some of the most diffuse connections in the brain
Involved in regulation of attention, arousal, sleep wake cycles, learning and memory, anxiety, pain, mood and brain metabolism
Activated by new, unexpected, non-painful sensory stimuli
General arousal to interesting events in the outside world
Increase brain responsiveness, speeding information processing
Outline the Serotonergic Raphe Nuclei
Caudal innervate spinal cord and modulate pain-related sensation
Rostral innervate brain
Fire most during wakefulness
Part of reticular activating system
Involved in sleep wake cycles and stages of sleep
Control of mood and emotional behaviors
Outline the Cholinergic Basal Forebrain
General function not completely understood
First cells to die in the course of Alzheimer’s disease
Implicated in arousal, sleep wake cycles, learning and memory
Arousal, Sleep, Learning, Memory
what is the Dopaminergic Substantia Nigra
Neurons project from Substantia Nigrato striatum Control voluntary movements
Degeneration results in Parkinson’s disease
Ventral tegmental area projects to frontal cortex and limbic system
Reward system that reinforces adaptive behaviors
Motor control and Reword
Outline bipsych depressino and its treatment
predominant mental health problem worldwide MENTAL HEALTH IN ENGLAND
An estimated 1 in 6 people experienced a ‘common mental disorder’ like depression or anxiety in the past week.
Younger people, people living in deprived areas, and people with disabilities are all less likely than average to recover from their condition after psychological thera
Some types may be due to lack of seretoninn
treatment: SSRI’s
what is the difference between a drug antonist and antagonist?
ANTAGONISTIC drugs blockthe effects of neurotransmitters
Novacaine Caffeine
AGONIST drugs mimic or increasethe effects of neurotransmitters
Heroin LSD Cocaine
How do drugs alter neurotransmitter activity?
Drugs alter various stages of synaptic processing
Increasing number of action potentials
Release transmitters from vesicles without impulses
Blocking re-uptake
Blocking receptors
Producing more neurotransmitter
Preventing neuro transmitter release
what does drug abuse do to the brain?
Almost all abused drugs stimulate dopamine release in the nucleus accumbens Feelings of pleasure
Methamphetamine (”METH”) alters Dopaminetransmission in 2 ways:
(1) Enters dopamine vesicles in axon terminal causing release of transmitter
(2) Blocks dopamine transporters from re-uptakingdopamine This results in > dopamine in the synaptic cleft = neurones fire more= eurphoria
What is the effects of LSD?
Lysergic Acid Diethylamide (LSD) LSD, Brain & Behaviour Serotoninergic Hallucinogen Physical Effects • Dilated pupils • Higher or lower body temperature • Sweating or chills (“goose bumps”) • Sleeplessness • Dry mouth, Tremors Mental Effects mental: • Delusions • Visual hallucinations • An artificial sense of euphoria or certainty • Distortion of one’s sense of time and identity • Severe, terrifying thoughts and feelings • Fear of losing control • Panic attacks • Flashbacks • Severe depression or psychosis
What does alcohol do to the brain?
It alters neuronal membranes, ion channels, enzymes, and receptors
• Binds directly to receptors for: Acetylcholine Serotonin GABA Glutamate
Outline hormonal communication
Hormones
Chemicals secreted by one cell group travel through blood to targets Released from endocrine glands
Explain the 9 steps involved in hormonal communication
- Gradual, often long-lasting, effect
- Change likelihood of behaviour
- Hormones and behaviour interact
- Many different hormones affect many different body parts & behaviours
- Produced in small amounts (often in bursts)
- Many have rhythmic release
- Hormones interact with other hormones
- All vertebrate hormones have similar structures, but not necessarily similar effects
- Can only affect cells with the appropriate receptor proteins
give examples of 2 different hormones
Protein:
Comprise amino acids
Protein and amine hormones faster than steroids
Bind to receptor, activate second messenger
Second messenger alters cell function
steroid:
These are derived from cholesterol from the diet
Bind directly to membrane receptors
Much slower
Affect the long-term production of proteins within the target cells
give some examples of howhormones use negative feedback
Autocrine feedback endocrine cell senses the increase of its own hormone and switches off hormone release
Target cell feedback target cell releases another substance when stimulated by the hormone which subsequently inhibits hormone release in the endocrine cell
what is the endocrine system??
what is homeostasis
All glands of the body and hormones produced by those glands
By regulating the functions of organs in the body, these glands help to maintain the bodys homeostasis
cellular metabolism, reproduction, sexual development, sugar and mineral homeostasis, heart rate, digestion…
What are the hypothalalmus and pituitary complexes
Hypothalamus is located below the thalamus and forms the walls of the third ventricle
It can be divided into several nuclei: each nucleus has a very specific function
Pituitary is connected to the base of the hypothalamus
outline the hypothalmus function
and structure
Integrates somatic and visceral responses in accordance with the needs of the brain
Homeostasis–maintains the body’s internal environment in a narrow physiologic range
Temperature, blood volume and pressure, pH, oxygen levels
A tiny lesion in the hypothalamus can be lethal
Three zones: Lateral, Medial, Periventricular
Connections are extensive
Periventricularis most highly connected to the pituitary Controls: circadian rhythms and ANS to viscera
what is the function and structure of the pituitary glands?
It is the “mastergland” of the body It produces many hormones that travel throughout the body, directing processes or stimulating otherglands to produce other hormones
Posterior Pituitary Gland
Connected with hypothalamus
Neuro-hormones are produced in the magnocelluarhypothalamus and released at the pituitary
Oxytocin Released to initiate uterine contraction or milk let-down Can be triggered by somatic, visual or auditory stimuli or inhibited by stress
Vasopressin Antidiuretic Hormone Regulate blood volume and pressure
Anterior Pituitary Gland
§ Connected with hypothalamus § Parvocellular neurosecretory cells release tropic factors that cause the production of hormones in the anterior pituitary
what hormoes does the anterior pituitary gland use?
ACTH- controls the adrenal cortex (kidneys)
TSH–controls the release of thyroid hormones
FSH–controls growth of ovary follicles/sperm Prolactin–promotes milk production
LH–promotes rupture of follicles/increase in testosterone
Growth hormone –promotes growth of cells/tissues
what does oxytocin do?
Oxytocin: § Involved in reproductive and social behaviour
§ Stimulates contractions
§ May promote bonding (e.g. Scheele et al 2012) by influencing social distance
§ Triggers the milk let-down reflex
what does the penial gland do?
Activated by sympathetic nervous system
Releases melatonin (amine) at night
Influences puberty and reproductive condition
In human, important for sleep rhythms
