CogNeuro 1

Aristotle

Placed the seat of cognition and the soul in the heart.
His account of the mind includes sensation, imagination, memory, recollection, and reason
views most associated with vitalism and dualism. 

Descartes

Proposed reflexes as automatic responses to outside events
described nerves as “animal spirits,” and the pineal gland as the source in his model of the mind.
Views align with Cartesian dualism and mechanistic explanation of bodily responses. 

Dualism

The position that mental or spiritual processes and physical processes belong to different kinds of explanation or laws.

Mechanistic

When explaining a process, living thing, or event as if it works like a machine, governed strictly by physical cause and effect rather than purpose, emotion, or design

Vitalism

The view that living things have a nonphysical inner force that gives them life.
From Aristotle

Monism

• Physical and mental processes (substances) are governed by the same laws

• Animals purely physical automata

Reductionistic

Can be broken down into parts

Deterministic

Can be broken up

Gall

• Promoted phrenology

• Claimed that particular mental abilities occupied specific brain regions and that skull shape revealed a person’s traits

• Completely wrong but, encouraged testable questions about localization in the brain. 

Phrenology

• Brain organized around approximately 35 functions

• If individual uses these functions more than another person, that part of the brain grows larger and changes that shape if the skull

• Individual’s abilities and personality could be understood by studying the shape of his or her skull

• Lead to the popularity of scalp massages (phrenology spas) to study and understand skull

Flourens

• Commissioned by the French government to remove selected brain areas in animals and examined lost abilities

• Experiments led him to describe functional contributions of several nervous-system divisions as well as the action of the system as a whole. 

• “ If part of brain gone then function is gone ”

• 
  

Horsley and Clark

• Created the Horsley-Clarke Apparatus, laying the foundation for modern stereotaxic surgery

• Used a 3-D coordinate system to map out the brain

• Insulated wire could be lowered into deep brain structures

• To locate part of brain that required excision (CT) (for seizing tissue)

Fritsch and Hitzig

• Centrally occurring phenomena experienced peripherally

• Whether central or peripheral doesn't matter

• Could localize seizure foci to guide surgery

This thought process lead to the development of electrophysiology

• Used electrical stimulation of the cortex and observed movements on the opposite side of the body.

• Stimulation at particular cortical sites activated particular reactions, supporting localization of motor and emotional function. 

Ramon y Cajal

• Used staining methods to study nervous tissue

• Discovery of the Neuron

• Won Nobel piece prize with 1906 with Golgi

Golgi vs Cajal

• Golgi argued that neurons are joined together in a fine mesh work = “syncitium”

• Cajal argued that cells were distinct, joined by gap junctions = "synapses"

Golgi

• Helped introduce the silver chromate staining technique

• Won Nobel piece prize with 1906 with Cajal

Wernicke

• Linked a posterior sensory and association region in the brain to speech comprehension (Wernicke’s area)

• Wrote “The symptoms - complex of aphasia: a psychological study on an anatomical basis”

• Wernicke’s area is connected to the Broca’s by various fibers (arcuate fasciculus)

Broca

• Studied a patient called “Tan” whose speech was severely limited.

• connected a left frontal lesion to impaired speech production

• Broca’s area is motor-related region in the brain, related to speech production

• Wernicke’s area is connected to the Broca’s by various fibers (arcuate fasciculus)

Brodmann

• Mapped cortical regions by differences in cell structure, using a cytoarchitectonic method

• Labeled Broca’s area 44, and Brodmann Area as 17, 9, 46 and 44

Hughlings-Jackson

• Studied epilepsy and proposed that the central nervous system has a hierarchy reflecting evolutionary stages:

  • Neomammalian

  • Limbic (Paleomammilian)

  • Reptilian

Karl Lashley

• Tried to locate memory traces by training rats on mazes and then removing brain tissue

• Excise specific tissue in the brain to remove distinct part of a rats memory in a maze

• Developed 2 major principles of brain function with Penfield

  • Mass action 

    • Memory depends on amount of tissue available, not what tissue available

  • Equipotentiality

    • Brain areas are plastic in their function and can take over for parts that have been ablated 

Henry Dale

Argued for chemical synaptic transmission, stating: an action potential releases a chemical substance that initiates a response in the postsynaptic cell

John Eccles

Argued for electrical transmission in synapses, stating: that a current generated in one cell passes to another through a very narrow connection. 

Luria

• Known as the Father of modern neuropsychology

• Partnered with Lev Vygotsky to establish that human mental functions develop through social interaction, culture, and language rather than just biology.

• Proposed that the brain does not localize specific mental tasks to a single, isolated spot. Instead, it uses dynamic "functional systems" where multiple, distinct brain regions work together.

• Divided the brain into three main functional units:

  • Regulation of Arousal [ Brain Stem, Thalamus ]

  • Receives, analyzes, and stores sensory information [ Posterior Cortex ]

  • Plans, executes, programs, and controls conscious behavior [ Frontal and Prefrontal Lobes ]

Charles Bell

Worked together with Magendie, associated with the separation of spinal sensory and motor routes.

• Sensory signals enter dorsally

• motor signals leave ventrally. 

Francois Magendie

Together with Bell, associated with the separation of spinal sensory and motor routes.

• Sensory signals enter dorsally

• Motor signals leave ventrally

“Tan”

Broca’s patient was nicknamed for the repeated word he could say. The notes use the case to link left frontal damage with difficulty producing speech

The doctrine of the specific energies of nerves

A sensation reflects the nerve pathway activated, not only the kind of stimulus. Thus, activating the same sensory nerve in different ways can still produce its characteristic experience. 

“Extirpation of parts”

• Flourens removal of particular brain regions and then observing which abilities were lost.

• Process is known as “Ablation”

The sensory-motor homunculus

• place motor organization on the precentral gyrus and sensory organization on the postcentral gyrus

• distorted 3D map of the human body drawn across the surface of the brain

• created by penfield and boldrey

Astrocytes

Star-shaped cells in the central nervous system (CNS) that maintain the blood-brain barrier, regulate chemical concentrations, and provide structural support.

Oligodendrocytes

CNS cells that wrap around nerve fibers to form a protective, insulating myelin sheath.

Microglia

Small, immune-defense cells in the CNS that clear away cellular debris, waste, and pathogens through phagocytosis.

Ependymal cells

Lining cells with cilia that produce and circulate cerebrospinal fluid in the brain's ventricles and spinal canal.

Schwann cells

Peripheral nervous system (PNS) cells that create the myelin sheath around single nerve fibers

The anatomy of the neuron

• The cell body or soma contains the nucleus and supports cellular metabolism

• Dendrites receive input; the axon carries output and branches into terminal regions

• Axon Hillcock acts as the neuron's "trigger zone" or decision-making center. It adds up all incoming signals. If the total charge reaches a specific threshold, it starts an electrical signal called an action potential or Nerve impulse

• Myelin is a fatty insulating layer wrapped around sections of the axon. Acts like plastic coating on an electrical wire. It prevents the electrical signal from leaking out and protects the axon. This insulation helps electrical impulses travel much faster down the nerve fiber.

• Nodes of Ranvier boosts and renews the electrical signal as it travels. Because the signal "jumps" from one gap to the next (saltatory conduction), the impulse moves down the axon at a much higher speed than it would on a bare wire.

• Synaptic Terminals pass the message along to the next cell. When the electrical signal reaches these terminals, they release chemical messengers called neurotransmitters across a tiny gap (synapse) to stimulate the next neuron, muscle, or organ.

The resting potential

A resting neuron maintains a charge difference across its membrane, about −70 mV in these notes, with the inside relatively negative. Ion gradients, selective permeability, and active transport help maintain it.

The action potential and its propagation along the axon

When depolarization reaches the stated threshold near −50 mV, voltage-gated sodium channels open and 3 sodium enters. Potassium channels then open and 2 potassium leaves. The action potential travels along the axon without diminishing; refractory behavior helps keep propagation one-way. 

Graded potentials

Changes in membrane potential on the dendrites and cell body can be excitatory or inhibitory and vary in size. They weaken as they spread and can combine at the axon hillock

spatial summation

• Spatial summation combines signals arriving at different locations on a neuron, sufficient net depolarization at the axon hillock can trigger an action potential

• If enough excitatory (depolarizing) potentials sum at the axon hillock, that is if the depolarization sums to about -50 mV, a brief change in the membrane permeability occurs

Temporal summation

• Temporal summation combines signals arriving close together in time.

• If enough excitatory (depolarizing) potentials sum at the axon hillock, that is if the depolarization sums to about -50 mV, a brief change in the membrane permeability occurs

Voltage potential

• Voltage-gated Na⁺ channels open and sodium rushes into the cell during an action poteential

• Voltage gated K channels open, causing an outflow of potassium down the potential gradient

• After voltage-gated K channels close, so much K accumulated outside the cell that repolarization occurs so much so that there is an undershoot at the end of the AP sequence, Equilibrium potential of the cell is restored 

Threshold potential

• The critical level of membrane depolarization that a cell, such as a neuron or muscle cell, must reach to trigger an all-or-nothing action potential, typically around –55 mV

Ionic movements in the action potential

• Voltage-gated sodium channels permit sodium to enter during the rising phase.

• Potassium channels subsequently permit potassium to leave as the membrane potential returns toward rest and briefly undershoots.

Postsynaptic terminal.

• The receiving part of a cell that gets chemical signals from a neighboring neuron across a tiny gap called the synaptic cleft.

Presynaptic terminal

• the specialized end of a nerve fiber (axon) that releases chemical messages called neurotransmitters to communicate with a neighboring cell

• Arrival of an action potential permits vesicles to fuse with the presynaptic membrane and release transmitter into the synaptic cleft.

Neurotransmitter

• A chemical messenger stored in presynaptic vesicles.

• After release, it crosses the synaptic cleft and interacts with specific sites on the postsynaptic cell.

Plasma membrane

• The neuron has a selectively permeable lipid bilayer containing ion channels.

• At a chemical synapse, vesicles fuse with the presynaptic plasma membrane to release their contents

Teleodendria

• The small, extensively branched ends of an axon, these terminal branches are unmyelinated and end in synaptic terminals

Ions

• Electrically charged particles

  • Anions: negatively charged particles

  • Cations: positively charged particles

• Include: Na⁺ (sodium), K⁺ (potassium), Ca²⁺ (calcium), and Cl⁻ (chloride)

Forces of ionic movement

• Concentration (chemical) forces

  • Diffusion: movement of ions from region of high concentration to low

  • Osmosis: diffusion of fluid through semipermeable membrane from region of high concentration to low

• Hydrostatic forces

  • Gravity forces upon osmosis

  • Combination of these forces leads to dynamic equilibrium in the cellular environment

• The selective permeability of membranes:

  • Some ions permitted to cross easier than others

• Combined effects shape ionic equilibrium

Ion channels

Membrane-spanning proteins that permit selected ions to cross. Some remain open, while gated channels open or close under particular conditions and change membrane permeability

The sodium-potassium pump

Uses energy from ATP to move sodium out of the cell and potassium in, counteracting the gradual loss of their concentration gradients

Anions

Negatively charged ions

Cations

Positively charged ions

Sodium

• More concentrated outside a resting neuron in the notes.

• Both its concentration gradient and the electrical gradient favor entry

  • rapid entry through voltage-gated channels drives the rising phase of an action potential

Potassium

• More concentrated inside the resting neuron.

• Its outward movement through voltage-gated channels helps bring the membrane potential back down after the sodium-driven rise

Chloride

• more concentrated outside the cell.

• Its concentration gradient favors entry, while the negative electrical environment inside opposes further entry

Calcium

• An action potential allows calcium to enter at presynaptic active zones.

• The entry of leads vesicles to fuse with the membrane and release transmitter. 

The patellar reflex

• A tap below the kneecap stretches muscle spindles, activating sensory neurons that contact spinal alpha motor neurons.

• The motor output contracts the muscle.

• Monosynaptic in reaction

• additional coordinating and inhibitory signals

• In absence of rencha cell muscle still responds 

  • Response it still there, more like a seizure response

Decremental conduction

Passive spreading of a graded signal that becomes weaker the farther it travels

Saltatory conduction

Propagation along a myelinated axon in which the active signal is renewed at nodes of Ranvier. The notes say myelination greatly increases conduction speed

The synapse

The functional contact point between neurons. Chemical synapses have a cleft through which released neurotransmitter travels; electrical synapses pass ionic current through gap junctions

Ratios of synaptic contacts

• a typical neuron can receive input from about 1,000 other neurons and send output to about 1,000 cells

• The human neocortex averages approximately 7,000 synaptic connections (or a synapse-to-neuron ratio of about 7,000:1) per single neuron.

Electrical and chemical synapses

• Electrical synapses pass ionic current directly through gap junctions, have very little delay, and are usually bidirectional.

• Chemical synapses release a transmitter into a cleft, have a short delay, can amplify a signal, and are described as unidirectional. 

Mechanisms of exocytosis and reuptake

In exocytosis, an action potential permits calcium entry, prompting vesicles to fuse with the presynaptic membrane and release transmitter.

reuptake as a way to end transmission at the synpatic cleft, where a presynaptic neuron reabsorbs its own neurotransmitters from the synaptic cleft (the gap between nerve cells) after signaling is finished

Mechanisms of endocytosis

After vesicle fusion, membrane can be recovered to remake vesicles:

• Classical: 

  • Clathrin-coated pits

  • Concentrated intra-membranous particles into small packages

  • Important for slower release rates

  • Functions at Low calcium concentration

• Kiss-and-run:

  • Vesicles does not completely integrate with plasma membrane

  • Operation involves a "fusion pore" for faster faster release rates

  • Functions in the presence of high Ca levels

• Bulk endocytosis:

  • Excessive amounts of membrane reenter the terminal by budding off from uncoated pits

  • Occurs at active zones (only)

  • May be reserved for retrieval following very high release rates and may not be usually employed 

Receptor sites

ligand-gated receptors - open ion channels directly when transmitter binds
second-messenger receptors - activate an intracellular sequence before influencing channels

Vesicles

• Small packages at the presynaptic terminal that contain neurotransmitter.

• They dock at active zones, fuse during release, and can be recovered and refilled. 

Vesicle recovery

• Following release, vesicle membrane is retrieved by endocytosis.

• Recovered material moves through intracellular structures, is repackaged with transmitter, and returns to active zones

Methods of transmission termination.

• diffusion away from the cleft

• reuptake

• enzymatic breakdown

Refractory periods

• During the absolute refractory period, sodium channels that have just closed cannot immediately reopen.

• During the relative period, the membrane is hyperpolarized and some sodium channels remain refractory. 

Neuron cell types

multipolar neurons, with many dendrites and one axon

unipolar or pseudounipolar neurons, associated with sensation

bipolar neurons, discussed in sensory systems such as vision, hearing, and smell.

Active zones

• Specialized regions of a presynaptic terminal where vesicles dock and release transmitter.

• The notes mention microtubules guiding vesicles toward the membrane in some active zones. 

Cytoskeletal structures

Microfilaments are linked to transport of neurotransmitter-related material, and microtubules are described as guides for vesicles approaching release sites

Nucleus

Within a neuron, the nucleus is in the cell body and contains genetic material. In gross neuroanatomy, the same word can mean a collection of nerve cell bodies. 

Spinal cord

• The notes divide it into cervical, thoracic, lumbar, and sacral regions

• ascending and descending pathways in white matter

• sensory and motor cell groups in gray matter

Gyrus

A raised convolution or fold of the cerebral surface

Sulcus

An inward fold or groove of the cerebral surface

CSF

Cerebrospinal fluid cushions and nourishes the brain and spinal cord, helps remove waste, and carries chemical signals

• produced at choroid plexuses

• circulates through connected spaces

• returns to the blood through arachnoid structures. 

Blood brain barrier

A selective physical and chemical boundary that limits how changes in the blood affect the brain’s internal environment, area postrema is an exception

Nernst equation

The Nernst Equation relates the cell potential of an electrochemical cell to its standard potential and the concentrations or activities of the reacting species under non-standard conditions.

Glia

Support cells discussed in the notes include:

microglia which remove material

astroglia which contact neurons and vessels
oligodendroglia, which maintain central myelin. 

Oligodendroglia

Cells responsible for depositing and maintaining myelin around axons in the central nervous system

Schwann cells

The peripheral nervous system counterpart of oligodendroglia, able to support myelin repair after damage

Microglia

Small, mobile cells that remove dead or damaged material and participate in inflammatory responses. 

White matter

Regions composed mainly of axons; their pale appearance is due to the fatty myelin

Meninges

Three protective connective-tissue layers around the brain and spinal cord: outer dura, middle arachnoid, and inner pia.

associated with blood-vessel protection and cerebrospinal fluid

Hodgkin-Huxley cycle

rapid, self-amplifying positive feedback loop in excitable cells (like neurons) that drives the explosive upstroke of an action potential

Cytoskeleton

transport of vesicles and refer to microfilaments and microtubules

Spinothalamic pathway

trace first-order sensory input through spinal nerves, an early spinal synapse and crossing

second-order input to the ventral posterolateral thalamus

third-order input to the postcentral sensory cortex.

Lobes of the brain

four main neocortical lobes:

• frontal

• parietal

• occipital

• temporal.

Massa intermedia

a connection between the paired thalamic structures

Speech centers of the brain

Broca’s area is associated with speech output

Wernicke’s area is associated with sensory or association processes in speech

The arcuate fasciculus as a fiber connection between them and discuss the angular gyrus and other sensory regions in the language network

Up-regulation

An increase in available receptor sites when a neuron has received too little stimulation, according to the notes

Down-regulation

A decrease in available receptor sites when a neuron has received excessive stimulation, according to the notes

Neuroanatomy

The study of nervous-system structure.
Gross anatomy, which examines larger structures
Fine anatomy, which examines cells and their organization

Mechanisms of protection

The skull provides an outer layer of protection.

Meninges provide additional covering and support

Cerebrospinal fluid cushions the central nervous system

Blood Brain Barrier regulates exchange with blood.

Spinal anatomy

Spinal gray matter contains sensory and motor groups arranged in horns; surrounding white matter carries ascending and descending fibers in columns and tracts