Neuroanatomy: Brain Structures, Function, Learning & Memory

• Study notes on neuroanatomy, neural activity, learning and memory

Key Brain Structures and Functions

• Cerebellum coordinates movement and balance
• Pons exists
• Thalamus is a sensory relay station which processes and transmits information
• Hypothalamus regulates homeostasis, hunger, thirst and the endocrine system
• Pituitary gland exists
• Corpus callosum connects the two hemispheres, facilitating communication
• The cingulate cortex exists
• Occipital lobe processes vision
• Temporal lobe processes auditory information, memory, and language comprehension
• Parietal lobe processes sensory information and spatial awareness
• Frontal lobe is responsible for decision-making, problem-solving, and motor function

Key Landmarks and Structures

• Central fissure exists
• Precentral gyrus is the location of the primary motor cortex, which controls voluntary movements
• Postcentral gyrus is the location of the primary somatosensory cortex, which processes touch
• Lateral fissure exists
• Longitudinal fissure exists
• Superior temporal gyrus exists
• Caudate nucleus (head & tail) exists
• Basal ganglia controls motor function and learning
• Limbic system processes emotion, motivation, and memory; it includes the hippocampus, amygdala, and fornix
• Hippocampus controls learning and memory
• Amygdala processes emotion, particularly fear
• Superior colliculus exists
• Inferior colliculus exists
• Optic chiasm exists
• Fornix exists
• Ventricles (Lateral & Third) exist

Neuron Structures

• Soma is the cell body and contains the nucleus
• Dendrites receive incoming signals
• Axon initial segment generates action potentials
• Axons transmit electrical impulses
• Myelin insulates the axon and speeds up signal transmission
• Terminal buttons release neurotransmitters
• Synaptic cleft is the gap where neurotransmitters transfer signals

Neural Activity: Action Potential and Synaptic Transmission

• Presynaptic neuron sends signals
• Postsynaptic neuron receives signals
• EPSP (Excitatory Postsynaptic Potential) depolarizes the membrane, increasing the likelihood of firing
• IPSP (Inhibitory Postsynaptic Potential) hyperpolarizes the membrane, decreasing the likelihood of firing
• Action potential starts when the threshold is met at the axon initial segment
• Threshold of excitation is the minimum voltage to trigger an action potential, which is -65mV
• Action potential is an electrical impulse traveling down the axon
• All-or-nothing principle describes how an action potential either occurs fully or not at all
• Voltage-gated ion channels open or close in response to voltage changes
• Terminal buttons release neurotransmitters into the synaptic cleft
• Synaptic vesicles store neurotransmitters
• Neurotransmitters are chemical messengers like dopamine, serotonin, and glutamate
• Receptors bind neurotransmitters to trigger a response
• Ionotropic receptors directly open ion channels
• Metabotropic receptors trigger secondary messengers for a slower response
• Reuptake/recycling is the process of neurotransmitters being reabsorbed

Electrical Communication (Inside the Neuron)

• Electrical communication happens within a neuron travelling from the dendrites, cell body, axon then to axon terminals
• Dendrites receive signals from other neurons
• Cell body (soma) processes incoming signals
• the action potential starts at the axon hillock if the signal is strong enough
• Axon is the pathway that carries the action potential
• Myelin sheath is a fatty covering that speeds up the signal
• Nodes of Ranvier are gaps in myelin where the signal "jumps" to move faster
• Axon terminals are where the signal is sent to the next neuron

Electrical Communication Steps

• Resting state at -70 mV where the neuron is at rest with Sodium outside and Potassium within the cell, maintained by the sodium-potassium pump
• Depolarization happens when the neuron receives enough input, the axon hillock opens voltage-gated sodium channels, Sodium rushes in making it positive (~+30 mV)
• Repolarization happens when Potassium channels open and lets Potassium out to restore negativity inside
• Hyperpolarization happens when too much Potassium leaves making the neuron extra negative, the sodium-potassium pump restores balance again
• Propagation is the movement or transmission of the signals, action potential "jumps" between Nodes of Ranvier in myelated neurons speeding up transmission (saltatory conduction).

Chemical Communication (Between Neurons) Synaptic Transmission

• Happens at the Synapse, the tiny gap between neurons
• Axon terminals (presynaptic neuron) is where the signals are sent from the end of a neuron
• Synaptic vesicles are sacs in the axon terminal filled with neurotransmitters
• Synaptic Cleft is the space between two neurons
• Receptors (Postsynaptic Neuron) are proteins on the next neuron that catch neurotransmitters

Chemical Communication Steps

• First, action potential reaches the presynaptic neuron, which opens voltage-gated Calcium channels and triggers synaptic vesicles to releases neurotransmitters
• Neurotransmitters (like dopamine or acetylcholine) cross the synaptic cleft during neurotransmitter release
• The neurotransmitters then attach to receptors on the postsynaptic neuron which may trigger a new action potential if enough binds
• Neurotransmitter removal sees Enzymes breaking them down, or they are reabsorbed (reuptake) to stop the signal

Electrical and Chemical Communication Notes

• Electrical signal travels through the neuron (from dendrites to axon terminals)
• Chemical signal happens at the synapse where neurotransmitters pass the message
• The next neuron fires a new action potential continuing the signal if it is strong enough

Learning and Memory

• Long-Term Potentiation (LTP) is a process where connections between neurons become stronger with frequent activation
• Presynaptic neuron releases neurotransmitters
• Postsynaptic neuron strengthens synapse with repeated stimulation
• EPSP strengthens synapse by increasing response
• NMDA receptor is a key receptor in synaptic plasticity and requires glutamate and depolarization
• AMPA receptor facilitates fast synaptic transmission
• Glutamate is the main excitatory neurotransmitter
• Magnesium ion blocks NMDA receptors at rest
• Calcium ions enters through NMDA receptors triggering synaptic strengthening
• Sodium ions enters though AMPA receptors depolarizing the neuron
• Efficiency is enhanced synaptic transmission from repeated activation
• Synapse is the site of learning and memory formation

Two Different Types of Memory

• Explicit memory is conscious recall of facts and events
• Implicit memory is used for skills and habits

Two Factors That Enhance Memory

• Active recall is a memorization method that involves actively retrieving information from memory, rather than passively reading or reviewing it
• Spaced repetition is a learning technique that involves reviewing material at increasing intervals over time, which helps to improve retention and recall

Neural Structures Involved in Learning and Memory

• Hippocampus consolidates new memories
• Amygdala aids emotional memory formation

Case Study: H.M.

• H.M.'s medial temporal lobes including the hippocampus and amygdala were removed
• Anterograde explicit memory was impaired
• Implicit and short-term memory remained intact
• Mirror drawing tasks tested implicit memory
• Digit span tasks tested working memory
• Recall tests tested explicit memory

Explore neuroanatomy with notes on brain structures, neural activity, learning, and memory. Key areas like the cerebellum, thalamus, and cortex are examined. Understand how these components contribute to overall brain function.