Neuroscience (L1-4) Flashcards
Multiple sclerosis
- Neurological condition caused by demyelination of axons, causing slower transmission
- Symptoms include fatigue, vision problems and difficulty walking
Propogation of an AP
- Initiated at the axon hillock
- Move down an axon using saltatory conduction (jumps between unmyelinated nodes of Ranvier)
- Myelin prevents any charge leakage through the axon
Blood-brain barrier
- Semi-permeable barrier between blood and brain
- Produced by tightly packed cells in the capillary walls of the brain
- Protects and helps to regulate the chemical balance of the brain
- Small uncharged, lipophilic molecules can cross
- Other substances access the brain via active transport
What is the…
- Central nervous system
- Peripheral nervous system
CNS - brain and spinal cord
PNS - connects CNS to the organs and muscle
What is the neuron doctrine?
- The idea that the brain consists of individual neurons
- Shown by Santiago Ramon y Cajal using staining techniques
Glial cells
- Astrocytes provide structure, supply neurons with nutrients and oxygen and modulate neurotransmission
- Microglia remove dead neuronal tissue and provide immune defence
- Oligodendrocytes (CNS) and Schwann cells (PNS) insulate nerve cells with myelin sheaths
Rett Syndrome
- Affects young females
- Caused by mutations in the MECP2 protein
- Symptoms include loss of speech and motor control, seizures, orthopedic and digestive problems, anxiety, etc.
Neurons
- Perform information processing tasks
- Specialised depending on their location
- Soma contains nucleus, mitochondria, ribosomes and ER
- Dendrites are branching fibres that receive info from other neurons via synaptic receptors
- Axons are thin fibres that transmit info to other neurons
Membrane potential
- Resting membrane potential = -70mV
- Penetrable for small uncharged molecules
Action potentials
- If stimulation exceeds the threshold of -55mV, an AP is triggered (all-or-none)
1. Na+ channels open = Na+ flows in = inside more positive = depolarisation to +40mV
2. K+ channels open = K+ flows out = repolarisation
3. Refractory period occurs where an action potential cannot be initiated
4. Na+/K+ pump restores resting potential by moving 3 Na+ out and 2 K+ in
Synapses
- Junctions at which signal is passed from one neuron to another
- Delay transmission (Charles Sherrington showed reflexes are slower than conduction along axon)
- Synaptic transmission is chemical (shown by Otto Loewi)
Neurotransmitters
- Synthesised by presynaptic neuron
- Stored in vesicles in axon terminal
- Released in synaptic cleft via Ca2+-dependent mechanism
- Bind to receptors on postsynpatic neuron
How do neurons work?
- Act as an information integrator and a decision maker
- Combine excitatory and inhibitory inputs to determine whether to fire
Receptors
- Protein embedded in the membrane that matches molecular shape of a neurotransmitter
- Ionotropic receptors are ligand-gated (fast and short-lived effect)
- Metabotropic receptors are GPCRs (slow and longer-lasting effect)
Excitatory postsynaptic potential (EPSP)
Depolarisation of the neuron that increases the rate of APs in the postsynaptic neuron
Inhibitory postsynaptic potential (IPSP)
Hyperpolarisation of the neuron that decreases the rate of APs in the postsynaptic neuron
Temporal summation
When rapid repeated sub-threshold stimulations of a presynaptic neuron accumulate
Spatial summation
When postsynaptic inputs arriving simultaneously at different locations on the dendrites are combined
What are the neurotransmitter differences between species?
- Variations in the number of synapses
- Amount of neurotransmitter release
- Sensitivity of receptors on postsynaptic cells
Acetylcholine (ACh)
- Involed in motor control
- Regulates attention, learning, memory and sleeping
- Involved in Alzheimer’s disease
Dopamine
- Influences movement, motivation, emotional pleasure and arousal
- High levels linked with schizophrenia
- Low levels linked with Parkinson’s disease
Glutamate
- Excitatory NT involved in learning and memory
- High levels linked with migraines and seizures
GABA
- Inhibitory NT
- Low levels linked to seizures, tremors and insomnia
Noradrenaline
- Controls mood and arousal
- Low levels linked to depression
Serotonin
- Regulates hunger, sleep, arousal and aggression
- Low levels linked to depression
Endorphins
- Act within pain pathways and emotion centres of the brain
- Low levels can lower pain threshold
How is the action of neurotransmitters terminated?
- Re-uptaken
- Degraded
- Reabsorption
Psychoactive drugs
- Drugs facilitate or inhibit transmission at synapses
- Agonists mimic and increase the effects of a NT
- Antagonists block the effects of a NT
Myasthenia Gravis
- Autoimmune disease caused by inhibition of ACh receptors
- Symptoms include fluctuating muscle weakness and fatiguability
- Treated with AChE inhibitors
Name two narcotics
Morphine and opiates
Name a hallucinogen
LSD
Abused drugs
- Most stimulate the release of dopamine from the nucleus accumbens
Cocaine
- Local anaesthetic (blocks Na+ channels to interfere with the propogation of APs)
- Stimulant (activates CNS to produce arousal and elevated mood)
- Potentiates the effect of dopamine and serotonin by blocking their reuptake
Autonomic nervous sytem
- Part of the peripheral nervous system
- Sympathetic division uses noradrenaline for ‘fight or flight’
- Parasympathetic division uses acetylcholine for ‘rest and digest’
What are the 3 planes of the brain?
- Coronal: view from the front
- Horizontal: view from above
- Sagittal: view from the side
Coordinate system of the brain
- Anterior (closer to front) or posterior (closer to back)
- Superior/dorsal (closer to top) or inferior/ventral (closer to bottom)
What are the 3 major parts of the brain formed during development?
- Hindbrain
- Midbrain
- Forebrain
- Hindbrain and midbrain form the brainstem
Hindbrain
- Medulla: coordinates heart rate, circulation and respiration (contains the reticular formation which regulates sleep and arousal)
- Pons: a major relay at which axonal projections become contralateral (cross sides)
- Cerebellum: controls fine motor skills, coordination, balance and cognitive functions
Midbrain
- Contains structures that have secondary roles in vision, audition and movement
- Superior colliculi: help guide eye movements and fixation of gaze
- Inferior colliculi: help sound localisation
- Substantia nigra: plays a role in reward, addiction and projects to the basal ganglia to integrate movements
- Tectum: orients an organism
- Tegmentum: involed in movement and arousal
Forebrain’s diencephalon
- Thalamus: relays and filters information from sensory organs and transmits it to the cortex
- Hypothalamus: regulates body temperature, hunger, thirst and sexual behaviour
- Mamillary bodies: relay for impulses coming from the amygdala & hippocampus
Forebrain’s limbic system
- Hippocampus: creating, storing and combining memories
- Amygdala: emotional behaviour and formation of emotional memories
- Cingulate cortex: linking behavioural outcomes to motivation and learning
Cerebral cortex
- Part of the forebrain
- Consists of grey matter
- Wrinkled/convoluted to increase SA
- Gyri are ridges
- Sulci are groves (called fissures if deep)
- Split into Broadmann’s map of 52 areas
Cerebral hemispheres
- Left and right hemispheres communicate via the corpus callosum (dense band of fibres at bottom of longitudinal fissure)
- Corpus callostomy is a surgical procedure that disconnects the cerebral hemispheres resulting in a condition called ‘split-brain’
- Each hemisphere has 4 lobes
Frontal lobe
- Anterior to the central sulcus and superior to the lateral fissure
- Important for movement and complex human capabilities
- Broca’s area - important for speech production
- Primary motor cortex
- Prefrontal cortex - plays a role in organizing, planning, decision making and impulse control (damage impairs impulse control)
- A frontal lobotomy is a surgical procedure that disconnects the prefrontal area from the rest of the brain
Parietal lobe
- Posterior to the central sulcus
- Important for body sensations and spatial localisation
- Primary somatosensory cortex
- Parietal association areas: combine info from body senses and vision
to dentify objects by touch, determine the location of limbs and locate objects in space
Occipital lobe
- At the posterior of the brain
- Processes visual information in the primary visual cortex
Temporal lobe
- Located laterally on the brain (sides)
- Primary auditory cortex
- Language, auditory and visual association areas (eg. Wernicke’s area for language comprehension and production)
What is phrenology?
- The correlation of brain anatomy with behaviour/personality
- Proposed by Franz Joseph Gall
How can brain lesions be stimulated?
- Invasive: use stimulating electrodes
- Non-invasive: trancranial magnetic stimulation (TMS) where neurons are excited/inhibited by externally applied electromagnetic field
How can the electromagnetic activity of a single neuron be recorded?
- Use of microelectrodes which impale the cells of interest
- A nano lead is implanted into an axon and records neural activity without stimulating it
What are grandmother cells?
- Responds to only one stimulus (eg. name/ image of a celebrity)
- Discovered by Quigora et al.
- Shows that visual info is stored in a localised way
How can the electromagnetic activity of a neuron population be recorded?
Electroencephalography (EEG)
- Measures brain activity on the scalp
- Sensitive to postsynaptic dendritic currents generated by a population of neurons that are active in synchrony
- Uses a cap with implanted electrodes placed in a specific arrangement
- Used for diagnosing epilepsy (displays spike and wave)
Event-related potentials (ERPs)
- EEG activity time-locked to an external event (eg. sound, visual signal)
- Good temporal resolution
- Poor spatial resolution
Magnetoencephalography (MEG)
- Recording of magnetic fields produced by electrical currents in the brain using arrays of SQUIDs
Neuron staining techniques
- Golgi staining - stains about 5% of neurons
- Myelin stains - stains axon
- Nissl stains - stains somas
CT scans
- Computerised tomography
- A contrast dye is injected into the blood
- Combines multiple x-ray photos from different angles
- Based on the fact that x-ray absorption varies with tissue density (higher density = lighter)
MRI
- Magnetic resonance imaging
- A strong magnetic field is applied and then ceased
- The energy released by molecules in the tissue as a result of the pulse is measured
- Differently charged molecules respond differently to the pulses, hence the energy signals reveal brain structures with different molecular composition
PET scan
- Positron emission tomography
- Measures local blood flow in a brain region using a radioactive tracer
fMRI
- Functional MRI
- Measures brain activity by detecting the levels of deoxyhemoglobin (BOLD response)
- Active neurons consume oxygen and convert oxyhemoglobin into deoxyhemoglobin
Syndactyly
A condition in which fingers are connected by skin tissue
Phantom pain
- When amputees experience pain in their missing limb
- Caused by neurons from other body areas invading area that normally receives input from the missing limb
What are the 3 main types of neurons?
- Sensory neurons receive information from the external world and convey it to the brain via the spinal cord
- Motor neurons carry signals from the spinal cord to the muscles to produce movement
- Interneurons connect sensory neurons, motor neurons and other interneurons
Spinal reflexes
Simple pathways that rapidly generate muscle contractions without input from the brain
Forebrain’s basal ganglia
- Basal ganglia: involved in planning behaviour and emotional expresion
- Pituitary gland: releases hormones
Central nervous system
- In vertebrates separates sensory (back) and motor (front) processing
- Higher levels perform more complex functions
What is meant by ‘degree of relatedness’?
The probability of sharing genes
Epigenetics
- The mechanisms of interaction between genes (nature) and the environment (nurture)
- Genes express themselves within an environment
- Genetic methylation silences a gene
Heritability
- A measure of the variability of behavioural traits among individuals that can be accounted for by genetic factors
- 0 = genes don’t contribute to individual differences
Phineas Gage
- Had an iron rod propelled through his frontal lobe
- Became irritable, irresponsive and indecisive
- Evidence that the frontal lobe is involved in emotion regulation, planning and decision making
Executive functions
- Hot EFs include impulses that take over our thoughts
- Cold EFs are logical choices that require rationality
What is prosopagnosia?
The inability to recognise faces
Hubel + Wiesel
- Inserted electrodes into the occipital lobes of anaesthetised cats and observed the AP signals
- Primary visual cortex are activated when a contrast between light and dark occurs in part of the visual field
- Each neuron responds to a particular orientation and are called feature detectors
