Module 2 (The Brain and Neurons): Brain Anatomy, Neurons and Communication, Measuring Brain Function, Plasticity and Learning Flashcards
Main Divisions of the Brain
Lower to higher order areas of the brain
- Brain Stem
- Cerebellum (hindbrain)
- Cerebrum (cerebral hemispheres - left and right, deivided by interhemispheric fissure- and forebrain)
Grey Matter and White Matter
- 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
Four Lobes of the Brain
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
Limbic System (Medial Temporal Lobe)
Amygdala - Fear and arousal (responds to threat/danger, learning phobias)
Hippocampus - learning and memory (forming new episodic memories, damage causes anterograde amnesia)
Broca and Wernicke’s Area
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
Corpus Collosum
- 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
Homunculus
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
Brain Stem and Autonomic Nervous System
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
Disorders of Conciousness
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
Cerebellem (Hind brain) and Movement
- 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
Neuron
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
Glial Cells
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
Myelin
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.
Synapses
Join axon terminals of one neurons to the dendrites of another. Send one way signals.
Electrical Signals / Action Potentials
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
Cell Membrane Wall
- 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)
Ion Channels
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
Synapses
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
Dopamine and Parkinson’s Disease
- Caused by loss of dopamine in basal ganglia deep in brain
- primarily affects movement
- treated with L-DOPA
Serotonin (Anti-Depressant Drugs) and Depression
Selective serotonin reuptake inhibitors (SSRIs; effecting reuptake pump) and monoamine oxidase inhibitors (MAOIs; effecting enzymes) act to keep serotonin in synaptic cleft for longer
Reflexes
Sensory neurons (input) passes signal to motor neuron to cause reflex
Excitatory and Inhibitory
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)
Graded Potential - Neural integration
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.
Brain Lesions
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
