Neurology Test 1 Slides 1-3

Brain is comprised of

• close to 90-billion neurons and 100-trillion connections called synapses

  • 16-B in cortex, 70-b in cerebellum (80% of total), 1.5-b in BS

• 62,000 miles of axons (> 2-times around the world)

• Possible neural circuits — 10 followed by 1-million zeros

• Human brain can hold more than one quadrillion bytes of info

• our brains have the capacity to direct their own development over 75% of brain development occurs after birth

• Glial cells, the helping cells of the nervous system, outnumber neurons 10:1 and have their own communication system

  • involved in strengthening synapses between neurons

  • facilitating neuron to neuron communications

How many synapses do we have in the brain?

100,000,000,000,000

Magnetic Resonance Imaging (MRI)

• An MRI scan is a common procedure used by hospitals around the world

• MRI uses a strong magnetic field and radio waves to create detailed images of the organs and tissues within the body. An adaptation to an MRI is a fMRI

Diffusion tensor imaging (DTI)

• DTI is a recently developed MRI technique that can measure macroscopic axonal organization in nervous system tissues

Components of the nervous system

• Central Nervous System: Cerebrum, Cerebellum, Brainstem, & Spinal Cord

• Peripheral Nervous System:

• Sensory Components: sensory ganglia & nerves, sensory receptors

• Motor Components:

  • Visceral Motor System: Autonomic Ganglia and nerves

  • Somatic Motor System: Motor Nerves

• Effectors: smooth muscles, cardiac muscles, glands, skeletal muscles

• Internal & External Environnement

Grey Matter

cell bodies

White Matter

• Axons

• Classified into 3 types:

  • Commissural

  • Association

  • Projection

Cerebral White Matter

• Projection fibers - descend through the internal capsule

• Commissural fibers - corpus callosum, anterior & posterior commissures, & commissure of fornix

• Association fibers - short and long association fiber

Fissure/Sulcus/Gyrus

Flashcard: "A fold in the brain's surface. Fissures are deep grooves that divide the brain into major regions. Sulci are shallower grooves, and gyri are the raised folds between them. They increase the brain's surface area, allowing for more neural connections."

tract or pathway neurology

Flashcard: Tract or Pathway Neurology

• Refers to the specialized neural pathways in the central nervous system.

• These tracts transmit information between different areas of the brain or spinal cord.

• Examples include the corticospinal tract for voluntary motor control and the optic tract for visual information processing.

• Damage to these tracts can result in specific neurological deficits.

• Understanding tract or pathway neurology helps in diagnosing and treating various neurological conditions.

Fasciculus, Peduncle

A fasciculus is a bundle of nerve fibers that carry similar information. A peduncle is a stalk-like structure that connects different parts of the brain.

Lemniscus

Bundle of nerve fibers in the brainstem that carries sensory information related to pain, temperature, touch, and proprioception from the spinal cord to the thalamus.

Nucleus (in CNS)

Flashcard: The central part of the central nervous system (CNS), responsible for controlling and coordinating bodily functions. It contains the cell bodies of neurons and plays a crucial role in information processing and signal transmission.

Ganglion (in PNS)

Ipsilateral, contralateral, bilateral

Frontal Lobe of the cerebral hemisphere

prefrontal cortex, motor area, pre-motor area, motor speech area

Parietal Lobe of the cerebral hemisphere

primary sensory area, sensory association area

Temporal Lobe of the cerebral hemisphere

auditory cortex, auditory association area

Occipital Lobe of the cerebral hemisphere

visual cortex, visual association area

Limbic Lobe of the cerebral hemisphere

emotion, memory, olfactory

Insular Lobe of the cerebral hemisphere

Gustatory cortex

Frontal Lobe

• The frontal lobe is the area of the brain responsible for movement and higher cognitive functions

• These include: problem solving, spontaneity, memory, language (Broca’s Motor Speech Area), Motivation, Judgement, Impulse control, social & sexual behavior

Temporal Lobe

• The temporal lobe plays a role in hearing (primary auditory cortex), comprehension of speech (Wernicke’s area), facial recognition, & memory.

Parietal Lobe

The parietal lobe plays a role in our sensations of touch, smell, & taste. It is also involved with multi-sensory processing, & visual-spatial awareness

• It is a key structure in eye-hand coordination

Occipital Lobe

• The occipital lobe is at the rear of the brain and controls vision and object recognition

• We have over 30 visual processing areas in the brain located throughout the cortex

Limbic Lobe

• The limbic lobe is located deep in the brain and makes up the limbic system

• This system is involved with memory, learning, and emotions

Insular Lobe

• The insular lobe is located deep in the lateral fissure

• Involved with pain, emotions, taste, vestibular, and visceral-sensations

Frontal Lobe: Sulci & Gyri

3 sulci:

• Precentral sulcus

• Superior frontal sulcus

• Inferior frontal sulcus

4 gyri:

• Precentral gyrus

• Superior frontal gyrus

• middle gyrus

• inferior gyrus

Parietal Lobe: Sulci & Gyri

2 sulci:

• Post-central sulcus

• Intra-parietal (arcuate) sulcus

Gyri:

• Post-central gyrus

• Superior parietal lobule

• Inferior parietal lobule:

  • Superior marginal gyrus

  • Agnular gyrus

  • 2nd pareitooccipital arcus

Temporal Lobe: Sulci & Gyri

2 sulci:

• Superior temporal sulcus

• inferior temporal sulcus

3 gyri:

• superior temporal gyrus

• Middle temporal gyrus

• Inferior Temporal Gyrus

Occipital Lobe: Sulci & Gyri

2 sulci:

• Superior occipital sulcus

• Inferior occipital sulcus

Gyri:

• Superior Occipital gyrus

• Middle Occipital gyrus

• Inferior Occipital gyrus

Insular Lobe

• Anterior insular lobule (short insular gyri):

  • Anterior short insular gyrus

  • Middle short insular gyrus

  • Posterior short insular gyrus

• Posterior insular lobule (Long insular gyri):

  • Anterior long insular gyrus

  • Posterior long insular gyrus

Key Gyri of the Frontal Lobe

One lateral surface:

• Precentral gyrus: primary motor area - contains a motor map (homunculus) controlling movement on contralateral side

• Superior, Middle Frontal Gyrus

• Inferior Frontal Gyrus: on dominant hemispheres (90% + on left side) contains Broca’s (motor) speech rate

Key Gyri of the Parietal Lobe

Lateral Surface

• Postcentral Gyrus: primary somesthetic area - sensations from contralateral side

• Superior Parietal Lobule - Visuospatial info

• Inferior Parietal Lobule (Supramarginal & Angular Gyri) - word recognition

Gyri of the Temporal Lobe

Lateral surface

• Superior temporal gyrus - on dominant hemisphere contains Wernicke’s (oral comprehension) area

• middle temporal gyrus

• inferior temporal gyrus

Basal-Medial surface

• Para hippocampal gyrus - contains hippocampus for memory & learning

• Occipitotemporal gyrus (Fusiform Gyrus) - facial/object recognition

• Uncus - Medial extension of PHG - olfaction

Gyri of the Occipital Lobe

Lateral Surface

• Lateral Occipital Gyri - vision

Medial surface

• cuneus & lingual gyrus separated by calcarine sulcus - vision

Thalamus

• means “inner room” in Greek, as it sits deep in the brain at the top of the brain stem

• often called the gateway to the cerebral cortex, as nearly all sensory inputs pass through it to the higher levels of the brain

Hypothalamus

• sits under the thalamus and controls many critical bodily functions: ANS, emotions, body temp, food/water intake, sleep cycles and endocrine system

Other important structures

• brainstem: contains 10 of the CNS (controls vital respiratory and cardiac functions)

• midbrain

• pons

• medulla oblongata

• cerebellum (sometimes)

Basal Ganglia

involved with automated movements

Cerebellum

connected to BS and is the center for balance and coordination

Ectoderm 18-20 days (3 Primary layers)

• (outer layer) - CNS/PNS & skin

• Neuroepithelia cells are the stem cells of the ectoderm and future nervous system

Mesoderm 18-20 days (3 Primary layers)

• middle layer - muscle, skeleton, & notochord

Endoderm 18-20 days (3 Primary layers)

• (inner layer) - lining of viscera

Notochord: key structure of ectoderm at 18-20 days

• (mesodermal origin) - centroid marker & induces development of neural plate

• Derived from special mesodermal cells called mesenchyme cells

Neural Plate: key structure of ectoderm at 18-20 days

• (future CNS) forms a groove - neural groove

• Neural plate cells are basically stem cells

Neural crest: key structure of ectoderm at 18-20 days

• (future PNS) comprise neural fold tips

Coinciding with folding of neural groove are Somites: key structure of ectoderm at 18-20 days

• non-neural tissue forming skeletal & muscular systems

What we see is the following tube/foldings:

• The notochord induces the overlying ectoderm to differentiate into the neural plate

• Sonic hedgehog is the primary mediator to signal this induction

• When the neural plate has begins its folding, the neural groove forms the base of the developing neural tube and the neural crests comprise the neural fold tips

• The neural crests produce biological mediators: bone morphogenetic proteins (BMPs) and Wnt, which signal the dorsal neural tube to form the roof plate

• The roof plate then uses these same mediators to form the bilateral alar plates

• The notochord signals the base of the neural tube to form the floor plate (again, via sonic hedgehog,) and the floor plate uses shh to form the bilateral basal plates

Cell Migration in Neural Tube

• Inner lining of neurotube contains neuroepithelial cells

  • Germinal layer - differentiates into neuroblasts (neurons) & glioblasts (glial cells)

• Forms future ependymal layer (forms choroid plexus cells producing CSF), marginal layer (white) and mantle layer (gray)

• Migration of cells - mediated by glioblast cells:

  • moving out [radial migration]

  • Moving up [tangential migration]

Axonal Growth & Synaptogenesis

• Once migration is complete axons and dendrites grow

• Growth cone at tip of axonal extensions, extends filopodia that releases chemicals, guiding growth to other cells - forms synapses

  • Glial cells assist in process

Sulcus Limitans

separates CNS into Motor and Sensory structures

Brain Divisions: Brain begins with three developmental divisions

• Prosencephalon

• Mesencephalon

• Rhombencephalon

Prosencephalon:

• Telencephalon - cerebral cortex, cerebral white matter, basal ganglia

• Diencephalon - thalamus, hypothalamus, subthalamus, epithalamus

Mesencephalon:

Mesencephalon - midbrain

Rhombencephalon:

• Metencephalon - cerebellum, pons

• Myelencephalon - Medulla oblongata

First Weeks:

• Neural Groove

• Neural Tube

• Neuroepithelium

• Brain

• Spinal cord

5-6 Weeks

• Forebrain

• Telencephalon

• Diencephalon

• Midbrain

• Hindbrain

• Pons

• Medulla

• Spinal Cord

Telencephalon (Forebrain at 9-Months)

• 2 cerebral hemispheres

• form a “cap” over inner brain structures

General Functions of Forebrain (Telencephalon) Structures

• Hippocampus

• Formation of long-term memory

Visual Cortex

high-level visual processing

Temporal Cortex

auditory & visual processing, and receptive language

Parietal cortex

sensory integration and visual motor processing

Frontal cortex

higher-level cognition, motor control, and expressive language

Diencephalon - Thalamus

• relay station for all sensory information

• entering the cortex (except for olfaction)

Diencephalon - Hypothalamus

Intersection of CNS & hormone system; coordination of autonomic functions

Midbrain

basic auditory & visual processing

Hind Brain: Pons, Medulla, Cerebellum

controls respiration, digestion, circulation, & some aspects of motor control

Over-proliferation & pruning

• The number of synapses reaches a maximum early in childhood

• after this, pruning begins - by 16, only half of the original synapses remain - this normal winnowing process of cell death is called apoptosis and is triggered by factors called neurotrophins (NGF & BDNF)

• Cortical development and axon myelination continues throughout infancy into late adolescence

Myelination

• Increases the speed of conduction

• begins before birth in primary motor & sensory areas

• Continues into adolescence in certain brain area (e.g. frontal lobes)

Acephaly: Abnormal Embryological Development

incomplete closure of neural tube at cranial end

Spina Bifida: Abnormal Embryological Development

• Incomplete closure of neural tube at caudal end

  • occulta

  • meningocele

  • myelomeningocele

Arnold-Chiari Deformity: Abnormal Embryological Development

• Cerebellum & Medulla elongate through foramen magnum into vertebral canal, impacting on medulla and cervical cord

Galvani

• discovered that muscle and nerve cells produced electricity

• He thought “animal electricity” was a fluid secreted by the brain, and that the flow of this fluid through nerves activated muscles

Golgi

• develops method for staining neurons

• silver method for unknown reasons stains a limited number of cells allowing individual neurons to be visualized

• silver method still use today

• Golgi method identified cell bodies and processes

• Golgi believed in the ‘Reticular Theory’ which postulated that the nervous system was a syncytial system of continuous fibers forming an intricate network that the nervous impulse propagated along

Ramon y Cajal

• used Golgi technique for detailed anatomical studies of the nervous system

• demonstrated that nervous tissue was network of discrete cells and not a syncytium

• convincing support for the neuron doctrine - individual neurons are the elementary signaling elements of the nervous system

Bernhard von Gudden

• developed the first commercial microtone for slicing of brain tissue

• allowed for consistency and reproducibility allowing researchers to engage in more sophisticated investigations.

• also found that destroying specific cortical areas lead to pathologies

Paul Broca & Carl Carl Wernicke

• Broca - cortical area necessary for producing speech

• Wernicke - cortical area for understanding speech - gave the young field of neurology and neuroscience the idea of “functional cortical areas”

Herman von Helmholtz

• axons generate electricity as a way of sending a message. His student Julian Bernstein electrical messages result from ions flowing across membrane

Sir Charles Sherrington

1) reflexes utilize excitation and inhibition of neurons and muscles

2) Brain organizes movements and projects this information to neurons in the spinal cord

3) shared Nobel prize in 1932 (with sir Edgar Adrian)

Sir Edgar Adrian

• All APs are identical

• Intensity is coded by discharge frequencies of neurons

• Different modalities are sensed by the activation of different cortical areas

• shared Nobel prize in 1932

Sherrington’s insights

• dominance of the “neuronal Doctrine.” Individual neurons are the “elementary of signaling elements” of the CNS. Termed the gap between neurons a “sunapse”

• reflexes utilize excitation and inhibition of neurons and muscles

• Brain organizes movements and projects this information to neurons in the spinal cord. Coordinated movement requires continuous and ongoing feedback

• Had the insight to understand that some “common point” must be responsible for signaling muscles to contract - the go between cortical activation to muscle contraction - this being the very specialized neuron the “motoneuron”

• Shared Nobel Prize in 1932 (with Sir Edgar Adrian)

Alan Hodgkins (brilliant student of edgar adrian)

• using giant squid axon found that during an AP not all channels open only some do

• proposed channels opened and closed like gates were dependent on voltage changes in the axon “voltage gate hypothesis” of nerve transmission

• They won the Nobel prize in 1963

Neurons

• carry information via electro-chemical conduction

• communicate across specialized intracellular spaces (synapses)

• come in a variety of morphological shapes

Glial cells

• support and maintain neuron functioning

• import for synapse formation, memory, and neural communications

What are the smallest units of the CNS

Neurons

What are the smallest functional units of the CNS

Columns

Cortical columns

• are like small tiny computer processes found throughout the corex

• As we evolved more and more of these columns developed until a point was reached that our brains grew larger, formed ridges and bumps, and began to fold

Afferent (Sensory neurons

carry signals toward nervous system

Efferent (Motor) neurons

carry signals away from nervous system

Interneurons

carry signals within nervous systems

Projection interneurons

carry signals to other regions of nervous system

Local interneurons

carry signals withing a region

Oligodendrocytes

• a type of neuroglia

• wrap axon in CNS with myelin

Astrocytes

• a type of neuroglia

• protect/form part of the astrocytic blood brain barrier

Cell body (soma)

keeps neuron alive

Dendrites

collect inputs from other cells

Axons

carry impulse away from cell body

Terminal Boutons

termination of axon and houses neural transmitters

Myelin

increases impulse conduction speed