Brain Regions and Functions: Lectures 1-5

• Study notes from lectures 1-5

Lecture 1: Brain Regions and Cell Functions

• The amygdala coordinates sensory responses with emotional context.
• The hypothalamus regulates homeostasis, including heart rate and respiration.
• The premotor cortex develops motor plans for movements.
• The motor cortex sends signals to the spinal cord to activate muscles.
• The basal ganglion initiates and regulates motor patterns.
• The cerebellum fine-tunes motor actions based on proprioceptive feedback.
• The posterior parietal cortex integrates sensory information to create a 3D model of the body's position.
• The hippocampus encodes memory, aiding in learning and skill refinement.
• Neurons are the primary signaling units in the brain.
• Astrocytes maintain extracellular ion balance and contribute to the blood-brain barrier.
• Microglia act as immune cells, removing debris and pruning synapses.
• Oligodendrocytes (CNS) and Schwann cells (PNS) produce myelin to insulate axons.
• Ependymal cells line ventricles and produce cerebrospinal fluid (CSF).
• Fast axonal transport moves vesicular cargo at 200-400 mm/day.
• Slow axonal transport moves cytosolic proteins at 0.2-8 mm/day.
• Cerebrospinal fluid (CSF) is replaced approximately every 8 hours.
• Lipophilic molecules can diffuse freely, but hydrophilic substances require special transporters to cross the blood-brain barrier (BBB).

Lecture 2: Action Potentials and Ion Movement

• Sodium-potassium ATPase pumps 3 Na+ ions out and 2 K+ ions into the cell, establishing ionic gradients.
• Resting membrane potential is primarily established by sodium-potassium ATPase activity and potassium leak channels.
• During resting state, Na+ and K+ channels are closed.
• Depolarization involves opening of voltage-gated Na+ channels and Na+ influx.
• Repolarization involves inactivation of Na+ channels, opening of K+ channels, and K+ efflux.
• Hyperpolarization occurs when K+ channels remain open briefly before closing.
• The absolute refractory period occurs when voltage-gated Na+ channels are inactivated.
• Decreased extracellular K+ hyperpolarizes the cell.
• Increased extracellular Na+ amplifies depolarization.
• Lidocaine blocks voltage-gated Na+ channels, preventing depolarization.
• Myelination facilitates saltatory conduction, speeding up signal transmission.
• Larger axon diameter reduces resistance, increasing conduction velocity.

Lecture 3: Motor and Autonomic Systems

• Motor neurons act directly on skeletal muscle, while autonomic neurons act via a two-neuron chain.
• Motor control is voluntary, autonomic is involuntary.
• Motor targets skeletal muscle; autonomic targets smooth/cardiac muscle and glands.
• Myotatic reflexes involve stretching muscle spindles to trigger contraction.
• Inverse myotatic reflexes involve Golgi tendon organs detecting excessive contraction, triggering relaxation.
• The sympathetic system is associated with "fight or flight" and has a thoracolumbar origin.
• The parasympathetic system is associated with "rest and digest" and has a craniosacral origin.
• The sympathetic system uses norepinephrine/epinephrine and adrenergic receptors.
• The parasympathetic system uses acetylcholine and muscarinic receptors.
• Sympathetic activation increases heart rate, dilates bronchi, and decreases digestion.
• Parasympathetic activation decreases heart rate, constricts bronchi, and increases digestion.
• Synaptic vesicles vary in size and content.
• Sympathetic control shunts blood to skeletal muscle during exercise.
• Baroreflex and local axon reflexes regulate blood pressure and local responses to injury.
• Redness and swelling in skin injury are caused by substance P and CGRP release (antidromic action).
• Baroreceptors increase action potential frequency with higher pressure.
• Sympathetic neurons decrease firing rate with high pressure.
• Parasympathetic neurons increase firing rate to reduce heart rate.
• Vasovagal syncope is caused by sudden parasympathetic overshoot after intense emotional stimulation.
• Autonomic dysreflexia involves severe hypertension and bradycardia.

Lecture 4: Stimulus Detection and Modulation

• Stimulus strength is signaled by action potential frequency and the number of activated neurons.
• The two-point discrimination test reveals receptive field size.
• Lateral inhibition enhances contrast by suppressing neighboring neuron activity.
• Rapidly adapting receptors detect changes.
• Slowly adapting receptors provide constant feedback.
• TRP channels detect temperature, pain, and chemical stimuli.
• Peripheral sensitization is mediated by inflammatory mediators (prostaglandins, histamine) and substance P.
• The medial lemniscus pathway handles fine touch and proprioception.
• The lateral spinothalamic pathway handles pain and temperature.
• Non-painful stimuli activate inhibitory interneurons to reduce pain signaling.
• Brainstem neurons release endogenous opiates to suppress pain transmission.
• In men, heart attack pain radiates to the left arm due to somatic nerve convergence.
• In women, heart attack symptoms can include GI discomfort due to smaller vessel disease.

Lecture 5: Sensory Systems

• Taste and vestibular systems use specialized non-neuronal receptor cells.
• Taste buds contain taste cells that express taste receptors.
• The vestibular system uses hair cells with stereocilia and kinocilia.
• Olfactory receptors are bipolar neurons.
• Aging affects taste and smell more than touch.
• Olfactory neurons have a short lifespan (~60 days) and are replaced by stem cells.
• Taste cells turn over every 10-14 days.
• Approximately 350 active olfactory receptor family members are in humans.
• There are approximately 950 total GPCRs in the human genome.
• There are 43 bitter receptors (TAS2R family).
• There are 3 sweet receptors (combinations of TAS1R1-2-3).
• Head movement causes perilymph in semicircular canals to lag.
• This movement bends stereocilia of hair cells.
• Bending stereocilia opens stretch-activated ion channels, leading to hair cell depolarization.
• Depolarized hair cells release excitatory neurotransmitter.
• Amyloid plaques are followed by inflammation and neurofibrillary tangles (NFT) in Alzheimer's disease
• Rare familial mutations that increase amyloid production can cause Alzheimer's disease.
• Neurofibrillary tangles (NFTs) correlate better with the degree of dementia in Alzheimer's disease.
• APOE4 significantly increases AD risk.
• Each copy of APOE4 increases AD risk by approximately 3x.