Module 2 (The Brain and Neurons): Brain Anatomy, Neurons and Communication, Measuring Brain Function, Plasticity and Learning

Question 1

Main Divisions of the Brain

Answer 1

Lower to higher order areas of the brain

• Brain Stem
• Cerebellum (hindbrain)
• Cerebrum (cerebral hemispheres - left and right, deivided by interhemispheric fissure- and forebrain)

Question 2

Grey Matter and White Matter

Answer 2

• Grey matter is the cerebral cortex; is folded surface of the brain containing body and connections of neurons. Folding maximises surface of the brain allowing large amounts of cortex to fit inside the skull
• White matter is the wiring of the brain; contains axons of neurons

Question 3

Four Lobes of the Brain

Answer 3

Frontal Lobe
* Executive functions - reasoning, planning, problem solving, inhibitory control, working memory
* Motor functions - premotor area (motor planning) and primary motor cortex (execution)
* Speech production (Broca’s area)

Parietal Lobe
* Sensory - primary somatosensory cortex, perception of touch; taste
* Sense of space and location - stability of world relative to our body position
* Spatial attention - direction attention and eye movement to explore visual world
* Links vision to action - represents spatial location of objects around us for guiding actions

Temporal lobe (primary auditory cortex, auditory association, sensory speech)
* Primary auditory cortex - perception of sound
* Language comprehension - Wernicke’s area
* Medial temporal lobe - limbic system, amygdala and hippocampus

Occipital lobe
* Primary visual cortex - all visual perception
* Different regions/group of neurons are sensitive to shape, colour, orientation and motion

Question 4

Limbic System (Medial Temporal Lobe)

Answer 4

Amygdala - Fear and arousal (responds to threat/danger, learning phobias)

Hippocampus - learning and memory (forming new episodic memories, damage causes anterograde amnesia)

Question 5

Broca and Wernicke’s Area

Answer 5

Broca’s Area - Left frontal lobe, responsible for speech production, damage causes Broca’s aphasisa which is characterised by slow speaking and difficulty finding words, can convey meaning and comprehension is unaffected

Wernickes’s Area - Left temporal lobe, responsible for speech comprehension, Wernicke’s aphasia is characterised fluent normal prosody nonense speech with no apparent meaning, unable to understand and comprehend language

Question 5

Corpus Collosum

Answer 5

• Neuron connections between the left and right hemispheres allowing brain communication between hemispheres
• Split brain patients are individuals whose corpus collosum has been cut - crucial in research finding specific functions of left and right brains

Question 6

Homunculus

Answer 6

Size of area on motor cortex dedicated to a muscle or part of the body is directly relative to the amount of sensitivty or fine motor control. This was discovered by mapping brain function through electrical stimulation of areas of the brain

Question 7

Brain Stem and Autonomic Nervous System

Answer 7

Brain Stem (Medulla) - autonomic nervous system functions and reflexes

Autonomic nervous system is a branch of the peripheral nervous system. Two divisions:
* Sympathetic - emotional arousal, stress, fear, fight-or-flight (increases heart-rate, respiration, perspiration and dilation of pupils)
* Parasympathetic - rest and digest, lowers heartrate and respiration, increase digestion

Question 8

Disorders of Conciousness

Answer 8

Persistant Vegetative State
* Severe damage to upper brain (hemispheres and cortex), if brainstem is not damaged autonomic nervous system functions can remain, patients have no conscious awareness

Lock-in syndrome (Amyotrophic Lateral Sclerosis or motor neuron disease or brain injury following accident)
* Intact cerebrum and brainstem but disconnected from spinal cord, normal cognitive function, vision and hearing but cannot move, patients fully concious and aware but unresponsive

Question 9

Cerebellem (Hind brain) and Movement

Answer 9

• Cerebellum is responsible for sense of balance and co-ordination of complex movement; Motor learning - fine adjustment of movement based on feedback loops
• Input from senses, primary motor cortex output, feedback from visions and sensation and outcome provides next input to adjust output.
• Planned actions compared with actual actions performed - when feedback matches prediction of planeed action the brain infers causality

Question 10

Neuron

Answer 10

Cell body: common to all cells, contain nucleus and all structures necessary for cell functioning (DNA)
Dendrites: unique to neurons, recieves signals, many per neuron recieves signal from many other neurons
Axon: unique to neurons, send signals from axon hillock to axon terminal, wrapped in myelin for efficient transmission along axon
Axon Terminal: Terminal buttons, form synapses with other neurons, secerte neurotransmitters to send signals across synapses

Question 11

Glial Cells

Answer 11

Brain contains neurons and glial cells, which are supporting cells for neurons. Three types:

• Oligodendrocytes - produce myelin sheath that wraps around axons
• Astrocytes - supplies nutrients from blood to neurons, maintains blood barrier
• Microglia - brains immune system, clean up foreign or toxic substances

Question 12

Myelin

Answer 12

Produced by oligodendrocytes wrapping around axon, essential for efficient communication and propagation of signals along axon.

Multiple sclerosis involves loss of myelin, disruption of efficient neural communication throughout the body.

Question 13

Synapses

Answer 13

Join axon terminals of one neurons to the dendrites of another. Send one way signals.

Question 14

Electrical Signals / Action Potentials

Answer 14

Always fixed size; either on or off

Action Potential: transmission of electrical signal along axon; input from other neurons via synapses increases membrane potential

• Input from other signals increases membrane potential, if voltage exceed threshold it triggers action potential.
• Depolarisation: membrane potential goes up to zero
• Repolarisation: membrane potential goes back to resting potential
• Refractory period: repolarisation undershoots
• Action potential begins at hillock then propagates down the entire axon

Question 15

Cell Membrane Wall

Answer 15

• ions and electrical potential across cell membrane - sodium and potassium positiviely charged ions
• Membrance potential is the difference of overall charge atr any given time.
• At rest, there are more positive ions outside than inside the cell. At rest it is -70 millivolts (resting potential)

Question 16

Ion Channels

Answer 16

channels in cell membrane wall open and close to pass or block movement of ions between intra- and extra cellular fluid (in and out of cell). Movement of ions changes electrical potential

Sodium Potassium Pump - constant pump of ions in and out of cell to maintain the resting potential. Ions outside cell want to get to more negative area inside the cell, sodium potassium pumps positive charges out of cell. Uses 25% of total body energy, 70% of brains energy.

Voltage Dependent Channels: Sodium channel opens once action potential theshold is reached, allowing for depolarisations, potassium channel opens at peak action potential to let potassium out of cell allowing for repolarisation

Question 17

Synapses

Answer 17

Depolarisation of axon terminal triggers release of neurotransmitter which acts on receptors of post-synaptic neuron to open ion channels and pass signals

Synaptic Vesicles - stores neurotransmitters in [re-synaptic terminal, joins cell membrane wall to release neurotransmitters into the synaptic cleft, recycled back into presynpatic terminal and repackaged into vesicles.

Neurotransmitter receptors - gates on post-synaptic neuron’s dendrites, NT joins with receptor, activates receptor to open ion channel.
* Lock and key - each receptor only bind to specific neurotransmitter, neurotransmitters only activate their type of receptor. Important for drug effects

Reuptake pump (clears neurotransmitter from synaptic cleft) and enzymes (break down neurotransmitter in synaptic cleft) stop neurotransmitters from signalling to post-synaptic neuron

Question 18

Dopamine and Parkinson’s Disease

Answer 18

• Caused by loss of dopamine in basal ganglia deep in brain
• primarily affects movement
• treated with L-DOPA

Question 19

Serotonin (Anti-Depressant Drugs) and Depression

Answer 19

Selective serotonin reuptake inhibitors (SSRIs; effecting reuptake pump) and monoamine oxidase inhibitors (MAOIs; effecting enzymes) act to keep serotonin in synaptic cleft for longer

Question 20

Reflexes

Answer 20

Sensory neurons (input) passes signal to motor neuron to cause reflex

Question 21

Excitatory and Inhibitory

Answer 21

Excitatory neurotransmitters brings membrane potential closer to threshold; depolarisation (allowing positive ions into cell). Excitatory Post-Synaptic Potential (EPSP)

Inhibitory neurotransmitters brings membrane potential further away from threshold; hyperpolerisation (allowing positive ions out or negative ions in). Inhibitory Post-Synaptic Potential (IPSP)

Question 22

Graded Potential - Neural integration

Answer 22

magnitude of membrane potential (and whether it reaches action potential) in post-synaptic neuron as a result of inhibitory and excitatory charges combined. Graded potential depends on strength of synapse connection.

Neural integration is the summing of all these inputs and integrating the information. Neurons receive many inputs but only produce one output. Brain is integrator of information that adapts with learning.

Question 23

Brain Lesions

Answer 23

Explains brain function by looking at changes in behaviour and ability after damage to part of a brain. Its assumed that changes in cognition and behaviour must be dependent on the damages area of the brain

Question 24

Single Neuron Recording

Answer 24

Placement of thin electrode into animals brain to record potential firing of single neuron. Measures what neuron encodes and detects. Best for localisation and timing of brain function. Problem: highly invasive

Question 25

EEGs (Electroencephalography)

Answer 25

Summed activity from action potentials in cortex cause electrical activity change on scalp, voltage changes are measured by elecrodes placed on scalp. Shows oscillations (waves) and frequency changes with brain states (sleep and alertness). Clinical uses: detecting stages of sleep and monotoring epileptic seizures.

Question 26

ERPs (Event-Related Potentials)

Answer 26

Brain activity related to specific event or stimulus; average of trials of EEG response to stimulus. Peaks represent different stages of processing stimulus. Shows precise time of information processing and direct mesure of neuron firing in brain.

Example: Autidort ERP and Face Processing (peak brain activity of viewing any stimulus is 100ms after seeing visual stimulus, however after viewing faces it peaks at 170ms)

Problems: difficult to accurately localise activity to specific brain areas, poor spatial resolution as it measure electrical potential across scalp.

Question 27

PET (Positron Emission Tomography)

Answer 27

Used from 1980 to late 90s. Now used to map neurotransmitters or receptors in the brain. Uses radioactive substances injected into bloodstream.

Question 28

MRI (Magnetic Resonance Imaging)

Answer 28

Studies brain anatomy

Question 29

fMRI (Functional Magnetic Resonance Imaging)

Answer 29

Studies brain function (brain activation) by measuring changes in blood oxygen level (BOLD signal). Active neurons use oxygen which is carried in blood to the brain and change blood oxygen level. Therefore, increase brain activity = increase blood flow = increase fMRI signal.

Question 30

Brain plasticity/Neuroplasticity

Answer 30

How the brain changes with learning and experience. Capability of the brain to alter its functional organisation as a result of experience.

Question 31

“Grandmother Cells” (Theory) and Spreading Activation Model (Theory)

Answer 31

Specific neurons are encoded to fire at specific concepts. Memory is represented by groups of neurons encoded to specific objects.

The neurons and concepts are inconnected and cause a spiderweb of firing neurons. Learning and memory is based on making and strenghtening connections between neurons that represent associated concepts

Question 32

Neurogenesis

Answer 32

Growing new brain cells. Neurons never regenerate or repair, damaged areas of the brain can never regrow. Neurons are constantly born throughout life through neural stem cells in hippocampus and subventricular zone for olfactory bulb

Question 33

Synaptogenesis and Environmental Enrichment

Answer 33

Generation of new synapses/brain connection. New synapses are constantly formed and strengthened with experience and learning.

Enriched conditions lead to growth of dendrites and more extensive synaptic connections

Question 34

Long Term Potentiation

Answer 34

Change in the structure of synapses to give stronger signal from pre-synaptic to post-synaptic neuron. Recall graded potentials.

Question 35

Hebb’s Law

Answer 35

Neurons that fire together wire together. Repeated firing of pre-synpatic and post synaptic neuron firing together strengthens synaptic connection, stengthens connections between paired stimuli or events. Brain pathways that are used often are strenghtened.

Question 36

Reorganisation

Answer 36

Repeated use of motor movement increased brain’s area in primary motor cortex dedicated to it. After damage, motor cortex can re-organise with use to recover function. In blind people, brain areas lacking normal input can that new functions with use.