Understanding the Brain Flashcards
(22 cards)
Week 1
Define neuroscience
- The scientific study of the nervous system
- Interdisciplinary
- The study of how the nervous system controls behaviour, thoughts and emotions
The Nervous System
- Network of neurons in the brain, spinal cord and periphery
- CNS - brain & spinal cord
- PNS - nerves (cranial & spinal), ganglia (mass of nerve cell bodies)
Week 1
The importance of neuroscience
- Behaviour is initiated by the nervous system - neuroscience can therefore be used to help understand it
- Advance of neuroimaging and measures of brain function
Week 1
Historical notions of the brain and neuroscience
- Neolithic period - cranial trepanation
- Blunt force cranial trauma
- Ancient Egypt - earliest written reference to the brain, body mummified and organs preserved except for the brain
- Ancient Greece
- Hippocrates - brain is responsible for emotions
- Aristotle - heart is responsible for everything, brain is not
- Roman Empire
- Galen - brain is the ruling organ of the body & is responsible for common sense, cognition and memory
- Dark Ages - not much new discovery, mostly translations
- Renaissance
- Leonardo da Vinci - sensation, cognition & memory attributed to the 3 ventricles
- Vesalius - Identified errors in Galen’s anatomy, added detail to understanding of brain structure
- Descartes - Reflexive theory, dualism, fluid-mechanical theory of brain function
- 18th & 19th century - four key insights:
- Nerves are wires
- Luigi Galvani - stimulation of nerves in frogs caused muscle contractions
- Hermann von Helmholtz - human physiology is subject to the laws of nature, measured speed of nerve conduction (~90ft/sec) - Localisation of specific brain functions
- Muller - proposed the ‘law of specific nerve energies’
- Marie-Jean Pierre Flourens - experimental ablations (intellect = cerebral cortex; vital bodily functions = lower brain; coordination & motor control = cerebellum)
- Broca - damage to left frontal coretx = difficulties in language production
- Frtisch & Hitzig - muscle contractions contralateral to brain hemisphere - Involvement of neurons
- Golgi - proposed ‘reticular theory’, invented a new staining technique
- Santiago Ramón y Cajal - proposed the ‘neuron doctrine’, worked out nerual circuitry of many brain regions - Evolution of the brain
- Darwin - natural selection, ‘On the origin of species’
- Nerves are wires
Week 1
Evolution
- Gradual change in the structure and physiology of a species - generally producing more complex organisms - as a result of natural selection
The Vertebrain
- Vertebrate brains are similar in organisation
- All have a forebrain, midbrain & hindbrain
- Brain areas may be specialised in distinct ways in response to environmental constraints
How Human Brains Have Evolved
- Brain size increased
- Proportion of different areas have changed
- Folding of cerebral cortex increased
Proportion Between Brain and Body
- There is no relationship between brain size and complexity of behaviour
- However, there is a relationship between proportional brain size and behaviour
- Differences in evolutionary development of parts of the brain have more effect on behaviour than brain size
Evolution in Hominids
1. Australopithecus robustus
2. Homo habilis
3. Homo erectus
4. Homo sapiens neanderthalensis
5. Homo sapiens sapiens
- The high, straight forehead of modern humans is due to expansion of the cortex, especially the prefrontal cortex
The Neocortex
- Size increased in primates
- Flexible & almost infinite learning abilities
- Reflects growing complexity of social lives
- Growth of certain parts responsible for social skills (e.g., language) because they improved this ability
The Prefrontal Cortex
- Developed greatly in primates
- Primarily for voluntary motor control in other species
- Responsible for planning & abstract reasoning abilities in humans
- Humans have a larger volume of white matter compared to most other primates
- White matter provides greater connectivity between PFC & rest of brain
- Connectivity is vital for working memory functioning
Folding
- Increase in cortex folding allows more cortical surface area to fit inside the skull
- This allows better organisation of complex behaviours
Week 2
Outline the structure of the nervous system
The Nervous System
- Network of neurons in the brain, spinal cord and periphery
- CNS - brain & spinal cord
- PNS - nerves (cranial & spinal), ganglia (mass of nerve cell bodies)
CNS: Spinal Cord
- Continuous with brain stem
- Long conical structure
- Mediates transmission of information between brain & body
- Coordinates certain reflexes
- Conduit for sensory & motor information
- Protected by vertebrae (24 vertebra)
- Core of grey matter surrounded by white matter
- Spinal nerves split into dorsal & ventral roots before entering spinal cord
- Afferent - away from body (sensory), back of spinal cord
- Efferent - to effectors (motor), front of the spinal cord
PNS
- Connects CNS to limbs & organs via cranial and spinal nerves
- Neuron axons grouped into bundles
- 43 pairs - 12 cranial nerve pairs, 31 spinal nerve pairs
PNS: Cranial Nerves
- 12 pairs
- 10 -> brainstem
- I & II -> forebrain
- Information between brain and body above the neck, except for the Vagus nerve - gut & enteric system
PNS Divisions
- Somatic Nervous System
- Autonomic Nervous System
> Sympathetic
> Parasympathetic
> Enteric
Week 2
Understand the importance of ions in neuron potentials
- Neuronal membrane is particularly impermeable to ions due to its charge
- Fluid environment contains ions
Ions move via:
- Concentration gradients (diffusion)
- Electrical force (electrostatic pressure)
- Specialised proteins (e.g., channels & pumps) allow ion transport through bilayer
- Ion channels/leak channels - acts as a gate
- Allow selected ions to rush down gradients of concentration & electric potential
Ion Pumps
- Energy consuming
- Active transport - against gradient
- Maintains and builds gradients
- Slower
Week 2
Identify the characteristics of an action potential
- Brief electrical impulse that provides the basis for conduction of information along an axon
- Created when ion channels open, and ions rush across the membrane
- ‘All-or-nothing’ - AP only occurs if threshold of -55mV is reached
- Large change in membrane potential (-70 to +30mV)
- Standard size and shape
- Very rapid (1-4 ms)
- Frequent (hundreds per second) - depending on stimulus intensity
Week 2
Explain how the action potential moves along and between axons
- Depolarisation: inside becomes more positive
- Repolarisation: inside becomes more negative
- Hyperpolarisation: more negative than at rest
- Signal travels away from cell body towards axon terminals
- No decay
- Termed AP propagation
- AP first generated in axon hillock
Week 2
Explain how neurons communicate with other neurons
- AP is first generated at axon hillock, where it passes information to the next neuron (or target cell)
AP Propagation
- Na+ ions spread away from site of AP, depolarises cell
- Triggers another AP in this nearby area
- Next AP occurs as previous AP starts to die out
- APs are triggered one after another all the way to axon terminals
- If axon branches, each branch continues AP
- AP stays the same size
- Domino effect - saltatory jumping of action potential from node to node (of Ranvier)
Synapses
- Neurotransmitters release from vesicles in terminal ends of axon
- Excite, inhibit or modulate postsynaptic cell
- 2 (or more) neurotransmitters released from each neuron
Week 3
Meninges
- Tough connective tissue covering the CNS and some of the PNS
- Layers:
- Dura mater - outer layer; thick, tough & flexible but not stretchable
- Arachnoid membrane - middle layer, between dura mater & pia mater, soft & spongy
- Pia mater - clings to surface of brain & spinal cord, thin & delicate, smaller surface blood vessels
- Subarachnoid space - fluid-filled space between arachnoid membrane & pia mater, cushions brain
CNS:
- Covered by 3 layers of meninges
- Dura mater
- Arachnoid membrane
- Pia mater
PNS
- Two layers fuse
- Dura and pia mater fuse
- Sheath protects spinal and cranial nerves, and the automatic ganglia
- Arachnoid membrane (CSF) not present
Week 3
Glia
- Supporting cells of the nervous system
- Several types, each with a special role:
- Astrocytes
- Microglia
- Oligodendrocytes
- Schwann cells
Astrocytes
- Physical support - ‘neuron glue’
- Nourish neurons - wrap blood vessels to receive, store & release nutrients to neurons
- Help control chemical composition of extracellular fluid
- Surround & isolate synapse (limit NT dispersion)
- Phagocytosis:
- Clean up debris (e.g., dead cells) in the brain
- Special astrocytes move around CNS engulfing & digesting debris (phagocytosis)
- Form scar tissue in place of dead tissue
Microglia
- Smallest glial cells
- Phagocytes
- Representative of immune system in brain
- Protect brain from invading microorganisms
- Primarily responsible for inflammatory reaction in response to brain damage
- Thought to have a role in:
- Neurodegenerative disorders (Alzheimers & Parkinsons)
- Viral infections (HIV)
Oligodendrocytes
- Central NS
- Wrap several axons
- Contain fatty tissue called myelin that wraps around neuron axons
- Forms insulating coating: myelin sheath
Schwann Cells
- Peripheral NS
- Wrap individual axons
- Contain fatty tissue called myelin that wraps around neuron axons
- Forms insulating coating: myelin sheath
Week 3
Ventricular System
- Ventricles - hollow spaces within the brain, filled with cerebrospinal fluid
- Interconnected
- CSF - clear fluid (similar to blood plasma)
Four ventricles:
- Lateral ventricles - largest, centre of telencephalon
- 3rd ventricle - midline in centre of diencephalon
- Cerebral aqueduct - long tube in mesencephalon, connects 3rd & 4th ventricles
- 4th ventricle - between cerebellum & pons
Central functions:
1. Production and flow of CSF
2. Protection of the CNS and maintenance
Week 3
Cerebrospinal fluid
- Extracted from blood
- Consists of ions, water, protein and glucose
- Produced constantly from the choroid plexus
- Total vol is ~125 ml
- Takes 3 hours for half to be replaced
CSF Flow
- Produced by the choroid plexus of lateral ventricles
- Flows to 3rd ventricle where more is produced
- Flows through cerebral aqueduct to 4th ventricle
- Leaves ventricles to flow into subarachnoid space around CNS
- Reabsorbed into blood stream through arachnoid granulations
Vital Functions
1. Protection - buffer against shock
2. Buoyancy - allows brain to ‘float’ - reduces weight on base
3. Waste reduction - immunological protection - removes waste/harmful chemicals, particularly during sleep
4. Transport - transports hormones throughout brain
Hydrocephalus
- Accumulation of CSF within cerebral ventricles
- Leads to ventricular dilation
- Two types:
- Obstructive - blockage to natural ventricular drainage system & CSF flow
- Communicating - reduced absorbance of CSF by arachnoid villi
Week 3
Blood brain barrier
- Brain receives 15-20% of body’s blood supply
- Nutrients & oxygen carried to brain by blood vessels
Basic Blood Function
1. Brings materials necessary for brain function
- Oxygen
- Nutrients (carbohydrates, amino acids, fats, vitamins)
- Hormones
2. Blood removes materials from the brain
- Carbon dioxide
- Lactate
- Hormones
- Ammonia
Blood-Brain Barrier
- Semi-permeable barrier between blood and brain - some substances can cross, others cannot
- In most parts of the body, capillaries are lined with endothelial cells - small spaces exist between endothelial cells so substances can move across capillary walls
- In the brain, no spaces exist between endothelial cells & substances cannot pass over capillary wall
BBB Functions
1. Protects brain from ‘foreign substances’ in blood that may injure the brain
2. Protects brain from hormones & neurotransmitters in the rest of the body
3. Maintains a constant environment for the brain
Substances
- Lipid soluble molecules can penetrate fairly easily via lipid membranes of cells
- Water soluble molecules can only use specialised carrier-mediated transport mechanisms
- Active transport allows some substances to move across capillary walls (e.g., glucose transporters)
- Barrier is weaker in some areas
Week 4
Synapse Structure
- Junction between the terminal button of an axon and the membrane of another axon
- Conduit of information from one neuron to another
- Information travels in one direction
Structure
- Presynaptic axon - terminal containing NTs, mitochondria and other organelles
- Postsynaptic ending - receptor sites for neurotransmitters
- Synaptic cleft
Postsynaptic Receptors
- Direct receptor (ionotropic)
- Binding site for a NT
- Ion channel opens when NT molecule binds
- Indirect receptor (metabotropic)
- Only binding site for a NT
- Activates enzyme
- Ion channel opens elsewhere
Week 4
Synaptic Transmission
- Action potential arrives at axon terminal, triggering Ca2+ ions to move into the cell
- Ca2+ ions cause the migration of vesicles containing NTs to the pre-synaptic membrane
- The vesicles fuse to pre-synaptic membrane and break open, releasing NTs into the synaptic cleft
- NTs diffuse across the synaptic cleft towards post-synaptic membrane
- NTs bind to receptor sites on the post-synaptic membrane with ‘lock and key’ specificity - specific NT binds to specific receptors
- This binding opens NT-dependent ion channels which change the excitability of the post-synaptic cell (more or less likely to fire an action potential
Week 4
Excitatory / Inhibitory Post-Synaptic Potentials
Postsynaptic Potential
- Ions move across post-synaptic membrane and alter the membrane potential
- Depolarising (excitatory) = increased likelihood of AP
- Hyperpolarising (inhibitory) = decreased likelihood of AP
- Depolarisation > threshold (-55mV) triggers AP
Na+ Channels
- Excitatory postsynaptic potentials
- Na+ channels open -> Na+ move into neuron -> depolarisation, increased AP likelihood
K+ Channels
- Produce inhibitory postsynaptic potentials
- K+ channels open -> K+ leaves neuron -> hyperpolarisation, decreased AP likelihood
Cl- Channels
- Cl- channels open
- Rest - nothing happens - forces balance
- Depolarised - Cl- enters neuron -> stabilisation, decreased AP likelihood
Week 4
Role of Neurotransmitters
Acetylcholine
- Excitatory
- CNS and PNS
- Role in muscle contractions, memory, motivation, libido, sleep and learning
- Imbalances: Alzheimer’s, seizures, muscle spasms
Serotonin
- Monoamines
- Excitatory or inhibitory
- Regulates mood, sleep patterns, libido, anxiety, appetite and pain
- Imbalances: SAD, anxiety, depression, impulsivity, fibromyalgia, chronic pain
- Medications: SSRIs & SNRIs
Dopamine
- Monoamines
- Excitatory or inhibitory
- Role in focus, concentration, memory, sleep, mood and motivation, as well as learning, pleasure and arousal
- Dysfunctions: Parkinson’s, schizophrenia, bipolar disorder, restless legs syndrome, ADHD
Nor/epinephrine
- Monoamines
- Responsible for fight-or-flight response
- Released into blood as a hormone - blood vessel contraction & increased heart rate
- Increased heart rate, breathing, blood pressure, blood sugar, blood flow to muscles, attention & focus
- Excess epinephrine can lead to high blood pressure, diabetes, heart disease, etc.
- As a drug, epinephrine is used to treat anaphylaxis, asthma attacks, cardiac arrest and severe infections
Endorphins
- Peptides
- Inhibitory
- Role in perception of pain, ‘feel good’ feelings
- Low levels may play a role in fibromyalgia and some types of headaches
GABA
- Most common inhibitory neurotransmitter
- Regulates brain activity to prevent problems with anxiety, irritability, concentration, sleep, seizures and depression
- Contributes to motor control, vision, regulation of anxiety and many other cortical functions
- Drugs that increase GABA in the brain are used to treat epilepsy & calm trembling in Huntington’s
Glutamate
- Amino acids
- Most common excitatory neurotransmitter
- Used to synthesise GABA
- Key role in cognitive functions like thinking, learning and memory
- Imbalances associated with Alzheimer’s, dementia, Parkinson’s, Huntington’s, and seizures
Week 4
Influence of Drugs on NTs
- Exogenous chemicals
- Unnecessary for normal functioning
- Alter molecular functions
- Psychological or behavioural effects
- Natural or artificial
Agonists
- Facilitate or mimic action of a NT
- Facilitate postsynaptic effects
Antagonists
- Inhibit action of a neurotransmitter
- Block postsynaptic effects
Mechanisms of Drug Action
1. Synthesis - alter NT synthesis in presynaptic neuron
2. Storage - alter NT storage in presynaptic terminal
3. Release - changes NT release from presynaptic cell
4. Receptors - act on NT receptors (agonists open, antagonists close)
5. Reuptake - modify removal of NTs from synaptic cleft, agonists reduce or block reuptake
6. Destruction - NT destruction in synaptic cleft
Week 5
Sub-Regions of the Forebrain
Week 5
Cerebral cortex
Week 5
Thalamus, Limbic System, Basal Ganglia
