Neurons: Structure and Function

Neurons

• Neurons are individual cells responsible for receiving, integrating, and transmitting information within the nervous system, which contains 80-90 billion neurons.

Neuron Divisions

• Neuron divisions consist of:
  • Cell body (soma): contains the cell nucleus
  • Mitochondria: provides metabolic energy
  • Golgi apparatus: packages cellular materials into vesicles for transport
  • Ribosomes: translates genetic information to produce protein

Neuron Zones

• Functional zones include:
  • Input zone: collects information from other neurons or sensory structures
  • Dendrites are extensions of the cell body that receive synaptic inputs
  • Integration zone: initiates neural electrical activity, located at the cell body
  • Conduction zone: the axon transmits electrical signals away from the cell body, with axon collaterals forming branches
  • Output zone: axon terminals or synaptic boutons transmit the neuron's activity across synapses to other neurons

Neuron Categories

• Neurons classified by function:
  • Motor neurons: trigger movements via long axons synapsing on muscles
  • Sensory neurons: carry messages from peripheral tissue to the spinal cord
  • Interneurons: receive input from and send input to other neurons

Neuron Shapes

• Neuron categories include:
  • Multipolar neurons: have one axon and multiple dendrites
  • Bipolar neurons: have one axon and one dendrite
  • Unipolar/monopolar neurons: have a single branch extending in two directions from the cell body, one side being the input and the other the output zone

Dendrites

• Dendritic arborization determines the complexity of a neuron's information processing
• Neural plasticity: the configuration of synapses on dendrites and the cell body changes with experience
• Dendritic spines increase the surface area for synapses and can rapidly change

Neuron Doctrine

• Neuron doctrine states that the brain is composed of cells that are distinct structurally, metabolically, and functionally, and it is composed of independent cells.
• Synapses are tiny gaps between neurons where information passes from one to another
• Presynaptic neuron (output): the region of a synapse that releases neurotransmitters
• Neurotransmitters: chemicals released from the presynaptic axon terminal for communication between neurons
• Postsynaptic neuron (input): the region of a synapse that receives and responds to neurotransmitters -Synaptic cleft: separates the pre- and postsynaptic membranes

Axons

• Axons are single nerve fibers that carry action potentials from the cell body
• Axonal transport:
  • Anterograde transport moves material toward the axon terminals; retrograde transport moves materials back to the cell body using motor proteins
• Axons function in:
  • Rapid transmission of electrical signals
  • Slower transportation of substances

Glial Cells

• Glia provides neurons with information and affects neuronal function
• Glial cell composition:
  • 75% oligodendrocytes
  • 17% astrocytes
  • 7% microglia
• Astrocytes swell in response to injury and cause edema, which damages neurons

Types of Glial Cells

• Astrocyte: regulates local blood flow, maintains the blood-brain barrier, attaches to the neuron's soma, and monitors neuronal synapses
  • It may participate in transmitting information between neurons, contribute to new synapse formation and the shortening of surplus synapses, and influence local brain chemistry
• Microglia: changes shape/size, forms a containment zone when there is damage
  • It removes debris and is involved in pain perception and neuronal remodeling
• Oligodendrocytes: create myelination in the brain and spinal cord
  • Nodes of Ranvier are small uninsulated patches between the beads.

Schwann Cells

• Schwann cells are glial cells that form myelin in the PNS
• Myelin: fatty insulation around an axon that increases the speed of nerve impulses
• Myelination: ensheathing axons in myelin, and increases the speed of electrical signals that jump from node to node.

Vascular System

• The internal carotid artery supplies 80% of the brain's blood and supplies blood to the anterior and middle cerebral arteries
  • Anterior cerebral arteries supply the medial frontal and parietal lobes and are interconnected by the anterior communicating artery
  • Middle cerebral arteries supply most of the lateral surface of the cerebral hemispheres
• Vertebral arteries supply remaining 20% that join to form the basilar artery, supplying blood to the brainstem and posterior cerebral arteries
  • Posterior cerebral arteries arise from the basilar artery and supply blood to the posterior aspects of the cerebral hemispheres, cerebellum, and brainstem
• Circle of Willis: a vascular structure at the base of the brain formed by communicating arteries

Blood Brain Barrier

• The blood-brain barrier makes the movement of substances from blood vessels into brain cells more difficult

Ventricular System

• Cerebrospinal fluid acts as a shock absorber, a medium for material exchange, and removes toxins
• Ventricular system: fluid-filled cavities that produce and distribute cerebrospinal fluid(CSF)
• Lateral ventricle: lateral portion of the ventricular system within each hemisphere
• Choroid plexus: vascular portion of the ventricles lining that secretes cerebrospinal fluid
• Third ventricle: conducts cerebrospinal fluid from the lateral ventricle to the fourth ventricle
• Fourth ventricle: receives cerebrospinal fluid from the third ventricle and surrounds cerebellum and brainstem

Glymphatic System

• Glymphatic system: a lymphatic system in the brain that removes wastes, and nutrients and signaling compounds

Early Development

• Epigenetics: factors affecting gene expression
• Ontogeny: process when individual grows
• Mature brain: Over 80 billion neurons and quadrillion synapses
• Zygote: fertilized egg
• Embryo: earliest developmental stage (10 weeks)
• Fetus: developing stage after embryo
• Genotype: all inherited genetic information
• Phenotype: physical traits change
• Gene expression: cells transcribe particular genes to make proteins
• Cell differentiation: cells acquire characteristics Cell-cell interactions: cells development affect neighboring ones

Radial Glial Cells

• Radial glial cells: guide migration in development in the emerging cerebral hemispheres.
• CAM: cell adhesion molecule found on the surface of cells for migration and pathfinding.

Neural Development - Ectoderm

• Zygote divides after 12 hours after fertilisation.
• Neural crest: forms the PNS
• Layers of the embryo after 18 days thicken to form the neural plate which folds inward, forming the neural groove
• Neural tube becomes ventricles (fluid filled)
• Head of the neural tube forms:
  • Prosencephalon (forebrain): which then forms cerebrum (telencephalon and diencephalon)
  • Mesencephalon: midbrain
  • Rhombencephalon (hindbrain: metencephalon (pons and cerebellum) & myelencephalon (medulla) → cerebellum and brainstem
  • Spinal cord: transmits signals between Brian and rest of body

Nervous System Development - Stages

• 1. Neurogenesis: non-neural cells divide.
• 2. Cell migration: Cells move to establish distinct nerve cell populations and radial glial cells guide migrating neurons
• 3. Differentiation: transformation of precursors
• 4. Synaptogeniesis: forming Synaptic connections
• 5. Neuronal cell deals: Many nerve cells die
• 6. Synapse rearrangement: Some synapses are lost, so development to refine synapses.
• Synaptic pruning is due to experience - for Flexibility in the brain.

Terms

• Neurogenesis: production/growth of nerve cells
• Ventricular zone: region lining cerebral ventricles. displays mitosis = glials and neurons
• Adult neurogenesis: production of new neurons in the adult brain
• Apoptosis: "surplus" cells die
• Sensitive period: permanently altered during development due to experience/treatment
• Epigenetics: effects of gene expressions - no nucleotide sequence change
• Cell migration: cells move from origin to final spot
• Synaptogenesis: establish Synaptic connections = growth

Degeneration & Factors

• Retrograde degeneration: destruction of the nerve
• Anterograde degeneration/Wallerian: Loss of part of axon from injury
• Neurotrophic factor: Target-derived chemical that "feeds" to help survive. Nerve growth (NGF) A substance affects growth of neurons
• Brain-derived: that keep some classes of neurons alive.

The Role of Experience

• Experience-expectant development: input for development to unfold + time windows
• Caregiving: newborns require support and caregiving, which assists the developing immature infant. Is predictable, and sensitive
• Perceptual Discrimination: Fx. specific discrimination tuned to environment
• Neural plasticity: permits developmental perturbations that produce vulnerability
• Experience-dependent: Unique to individuals. Eg. a language

Prenatal Abilities & Newborn Abilities

• 3 Months: Basic physical reflex
• 4 Months: Reacts to light and sounds
• 5 Months: Movements being more controlled
• 6 Months: Learning can be observed
• 7 Months: Electrical activity was detected
• The last trimester: gyrification takes Place.
• Newborn preferable - prefers response to maternal stimuli.
• Infancy – dramatic brain changes, the elimination of unused Synapses. They Are born with Small brains, that reached half size of adult after the first year
• Myelination: Early growth = white matter growth.

Subcortical Mechanisms

• • Fetal/newborn cognition is helped by mechanisms Face detection mechanisms are low sensitive = development to bias
• Central Nervous System - Brian and Spinal cord
• Meninges - DAP

Cerebrum

• Cerebrum: largest part with high cognitive function. cortex = divided into 2 hemispheres and the 4 lobes
• Pyramidal cell is the most prominent cell
• White matter has axons with myelin/ Grey matter: cell bodies (dendrites) with/out myelin
• Corpus callosum: band of axons links 2 hemispheres.

Frontal Lobe

• Frontal Lobe - Anterior portion and responsible for: complex cognitive functions / plan / behaviour , motor.
• Precentral gyrus (motor cortex): motor functions
• Brocas Area – language left
• Prefrontal cortex: and impulse control
• orbitofrontal cortex-centre: and motivation/reward, regulating Here

Parietal Lobe

• Parietal Lobe - Cortex between Frontal and Occipital lobes on Each Hemisphere: register yd re input like pressure and Muscle
• Postcentral gyrus Supratnarginal gyrus + Angle gyrus Area
• Temporal lobe – learning / auditory
  • Olfactory bulb (smell)

Occipital Lobe and Major Features

• Occipital Lobe - Cortex on posterior
• (eye functions) : visual information + impulses
• Postcentral Gyrus and front the cortex on central with sensory body, and sulcus,
• precentral = Front for the Movernent.
• Sylvian Sulcus is fold divides Tempora and is Frontal
• Central Sulcus divides/ Frontal. Telencephalon frontal Subdivision = hemispheres

Nucleus, Putamen and Globus Pallidus

• Caudate Nucleus within the voluntary
• Putamen: structure in basal ganglia coordinates the movement
• Globus Pallidus: for decision making functions + motivation

Diencephalon

• Diencephalon: in the forebrain: information + functions thalamus consists = Nuclei relay sensory information except

Hypothalamic functions + is part of brainstem:

• nuclei (regulation , mm)
• regulates autonomous (hormonal)

Mesencephalon

• brainstem Midbrain is sensory and motor _ Tectum: part of system Process both audity visual . _ Tegmentur main body – motor is

Metaencephalon Cerebellum

• Responsible For movement and pons motor

Medullo Oblongata is part of brain stem

• cardiovasvular/ respiratory functions and reflexes
• Subcortical- for the cortex. Basal Ganglia: of structures in movements Receives information Thalamus cortex to

Limbric System

• The Limbric system – for emotion: located above brainstem
• hypothalamus - for endrocine system
• Stria terminalis a band connects others
• Olfactory bulb for smell
• The septum (regulating-emotion) nucleus: structures in that Are part of

Peripheral Nervous System

• Peripheral nervous system (Outside of Skull - Column) for transmits information + sensory, motor nerves
• Somatics nervous known as voulntarly _ 12 Cranial nerves for Muscle and neck _ Spinal Nerves group from Spinal cord for
  • Cervical: necks , shoulder
  • Thoracic: / Upper chest
  • Lumbar : in legs
  • the sacral at base -genitals
  • ventral side: Motor and front
  • Dorsal side ; sensory

Nervous System

• Autonomic : internal and involuntary
• Autonomic Ganglia : outside the CNS
• Sympathetic: Actions to PREPARE and Flight.

Other Terms

• Parasympathetic: to digest/ rest
• Enteric: to help gut controlled BY CNS
• NEUROLINGO brain
• Three = of 3 VIEWS brain. to see

The 3 Planes

• divisions
• Horizontal Plane : lower
• : Vertical halves
• _ Coronal Plane: + backwards

Neurotransmission

• Neurotransmission- transformation. Neurotransmitters Are The - basis . Criterion Is: -axon The contains Enzymes. _ That receptor The Application / activity

Terms

• K+(Potassium)Na sodium CI-Chloride. Ca+ ( Calcium): -Receptor
• Molecules transmitter. the, agonist Binds = antagonist. the.

Non-Competitive

_Modulator, that - without ligand's. = At the molecule cell. Is - In/Exogenous = study = An Gated ion channel - channel. channel The Channel . Membrane /Exocytosis. to: To AID that into

Neurotransmitter (Systems) and Brain Stem

• Brain –Acetylcholine with , attention+ Memory for (skeletal ) alzheimer
• Main from raphe nuclei. have - for Alertness from 1,2 Beta serotonin ( 5HT) _ Memory
• Multiple DA (dopamine VTA) -reward : cognition. is for movement. -the ( and is has(↓), (
• Inhibitory: GLUTAMATA with nervous Excitatory, Plasticity GABA _ In Anxiety Dendrites Synthesis.

• Electrical by+ more - A"s

Effects

• Pre -Drug: Effects - synthesis/Blockade of. Release _Channel/Release.

Physiologic

Post- synaptic processes :Receptors/ Modulation ,4, . (Neurophysiology – function)

Charged Paticles

• Particles 1 by K++Sodium _ C1+ ( Calcium); An of gain -A A +ve –(cation, charge
• fluid. membrane/ Electrical

Soduim Pump

• _ Pump/ the/ + the is: It + 2 K++/Cycle:
• to: At Resting potentials; membrane
• (balance) In is. more.

Signals & Release

• • Transmillter unidireclinal, Common . Sumatiom an. in: It release - flow is"

The Action & Propagation

-: Increase of In + - Until40 mV + to

• -increase+ K+ The, - to and is ~150. km is

EPSP /IPSP

• Excitatory: Glutamate, Noradrenaline, Dopamine results in:
• De-polarization of neurons (+):
• ↑ neural transmission and produces
• Alertness, focus, etc
• Inhibitory: GABA, Serotonin, Taurine results in:
• Hyper-polarisation of neurons (-):
• ↓ neural transmission and produces
• Relaxation, sleep, etc

Neuro-Imaging

• information for: Fx: basis + brain/Visual cell/ Golgi
• -isotope /label for
• immunes /antibodies. tissue -: nucleic _ tracer inject Brain + study

Structural Imaging & Tomography

• : to see , Monitor
• Scanning: an an overall stroke / lesion
• Resonance and MRI, waves
• By- . . + For Model

DTI STRUCTURAL IMAGING

to =>Measures fibre in of there

Functional imaging Dynamic

• the different, like : MEC _ non electrical are -to over

• signal for close surface sleep PET -gamma scanner and -detailed Exposure is/

• Hormones :Messengers AND Produced

Hormones are chemical messengers and systems.

Peptides & Action

They Are for , (ACH/ are action Hormone :with for = Portal : with system. Hormone and ( insulin).

Gland: The -

The + A:Feedback  to, - with or is + balance with and stress

hormones the and