NEUROSCI | MOD 1 | INTRO TO NEUROSCI

Neuroscience

is a multidisciplinary science that is concerned with the study of the structure and function of the nervous system
It is concerned with the development, chemistry, ....

Neuroanatomy

• it is the study of the relationship between structure and function in the nervous system

• it includes the study of macroscopic and microscopic structures

Neurophysiology

• is the subspecialty of neuroscience and physiology that focuses on the physiology and functioning of the nervous system, often using electrophysiological or molecular biological tools.

Cell

Basic living unit of the body

Cell membrane

Organelles

Protoplasm

3 basic composition of cell?

Water

what is the most abundant substance of the cell?

Protein

What is the 2nd most abundant substance of the cell?

Lipids

The fat storage of cells is made up of?

Carbohydrate

What is the nutrition of the cells?

Cell Membrane

• Outer boundary of the cell

• Double phospholipid layer with embedded proteins “selective”

• Also plasma membrane/plasmalemma

• Membrane transport: selectively permeable membrane

Small noon-lipid-soluble molecules

• diffuse between the phospholipid molecules of the plasma membrane.
  

Large non-lipid-soluble molecules

• ions that cannot diffuse across the phospholipid bilayer may move across the plasma membrane with the help of transport proteins.

Cytosol

• clear fluid portion where the particles are dispersed
  

Nucleus

• control center of the cell
  

Mitochondria

• Power house of the cell

• Produces most of the ATP

Ribosomes

• produces proteins
  

Lysosome

• intracellular digestive system (immune

  system of the cell)

• Vesicular organelles that may be formed by RER and Golgi bodies
  

Cytoskeleton

• supports and hold the cell in place

Cilia

• Short and hair-like structures.

• Move materials across cell surface

Flagella

• Long and tail-like structure.

• Propels cell through a medium

• Wave-like movement

Microvilli

• increase surface area of the cell

148

amount of potassium in ICF?

142

Amoung of sodium in ECF?

Diffusion

• Random movement of molecules results in net movement from areas of higher to lower concentration

• Lipid-soluble molecules dissolve in the lipid bilayer and diffuse through it; ions and small molecules diffuse through membrane channels.

Osmosis

• Water diffuses across a selectively

  permeable membrane

Facilitated Diffusion

• Carrier proteins combine with substances and move them across the plasma membrane; no ATP is used; substances are always moved from areas of higher to lower concentration; it exhibits the characteristics of specificity, saturation, and competition.

• Some substances too large to pass through membrane channels and too polar to dissolve in the lipid bilayer are transported.

Active Transport

• ATP powered pumps combine with substances and move them across the plasma membrane; ATP is used; substances can be moved from areas of lower to higher concentration; it exhibits the characteristics of specificity, saturation, and competition.

• Substances too large to pass through channels and too polar to dissolve in the lipid bilayer are transported; substances that are accumulated
  in concentrations higher on one side of the membrane than on the other are transported.

Secondary Active Transport

• Ions are moved across the plasma membrane by active transport, which establishes an ion concentration gradient; ATP is required; ions then move back down their concentration gradient by facilitated diffusion, and another ion or molecule moves with diffusion ion (symport) or in the opposite direction (antiport).

• Some sugars, amino acids, and ions are transported.

Endocytosis

• The plasma membrane forms a vesicle around the substances to be transported, and the vesicle is taken into the cell; this requires ATP; in receptor- mediated endocytosis, specific substances are ingested.

Phagocytosis

• takes in cells and solid particles (solid/large particles)

Pinocytosis

• take in molecules dissolved in liquid (liquid/fine particles)

Exocytosis

• Materials manufactured by the cell are packaged in secretory vesicles that fuse with the plasma membrane and release their contents to the outside of the cell; this requires ATP.

• water-soluble molecules are transported out of cells e.g. mucus, ear wax, sweat, etc.

Transcytosis

• is the process where a cell takes something in on one side, carries it through, and releases it on the other side.

Neurons

• are the fundamental unit of function in the CNS Possess all cellular and metabolic machinery common to all other somatic/body cells

• They are distinguished from most other somatic cells by their:

  o rich diversity in morphology (shape)
  o bioelectrical properties (they generate electrical

  signals)
  o specializations for intercellular communication

Necleus

• Control center

• Contains the neuron’s genetic material Directs the metabolic activity of the neuron

Golgi Apparatus

• Packages neurotransmitter

Mitochondria

• Convert nutrients into an energy source the neuron can use (e.g., synthesizes adenosine triphosphate)

Rough Endoplasmic Reticulum

• aka Nissl bodies or substance

• synthesizes and transports proteins

Smooth Endoplasmic Reticulum

• releases Ca2+ for signaling, and synthesizes and transports lipids

Ribosomes

• Protein synthesis: free ribosomes synthesize proteins for the neuron’s use

• Ribosomes attached to RER synthesize neurotransmitters

Neurons (Nerve Cells)

• receive stimuli and transmit action potentials to other neurons or to effector organs

Cell Body (soma)

• contains nucleus, nucleic acids, and the usual organelles

• very active metabolically

• maintain the intricate protoplasmic processes that arise from neuronal somata

Dendrites

• short protoplasmic extensions that arise from somata

• primarily involved in receiving neural signals from other neurons

Dendritic Spines

• primarily the sites where dendrites receive excitatory signals from the axon terminals of other neurons

• (-) spines – called smooth dendrites, inhibit their synaptic partners

Axon

• long protoplasmic extension that arises from somata

• Can range from very short (<100 μm) to very long (> 1 meter)

• involved in the transmission or sending of neural signals away from the cell body and toward other neurons or effector cells

Cell Body (soma)

Dendrites

Axon

What are the 3 parts of the Neuron?

Nodes of Ranvier (neurofibril nodes)

• Area where myelin sheaths of adjacent cells dip toward the axon but do not cover it

• no covering; not insulated

Nissl Bodies

• The neurofilaments separate abundant rough ER which are located primarily in the cell body and dendrites.

  o Primary site of protein synthesis in neurons, which flows along the dendrites and the axon

  o Replaces the proteins that are broken down during cellular activity

Axon Hillock

• A cone-shaped area of the neuron cell body where a single axon arises from

  o (-) Nissl bodies

Axolemma

• The plasma membrane bounding or covering the axon
  

Axoplasm

• The cytoplasm of the axon

Axo (Axoplasmic) Transport

• The cellular mechanism that transports substances along an axon. Axon transport can be fast or slow.

Anterograde Transport

• most; materials are transported from the cell body to the axon terminals

Retrograde Transport

• moves substances from the synapse back to the soma.

Sensory ( Afferent ) Neurons

• what conduct signals toward the CNS?

• feeling or the 5 senses

• sensation
  

Motor ( Efferent ) Neurons

• conduct signals away from the CNS; moving/movement
  

Interneuron

• conduct action potentials from one neuron to another within the CNS

o Combination of sensory and motor
o Many are excitatory, but most are inhibitory

Multipolar

• several dendrites coming off cell body and a single axon. Most common

  o One dendrite and one axon

  o Found in motor neurons and interneurons
  

Bipolar

• one dendritic root that divides into branches and one axon

  o Can only be found in the ear and eye

  o Found in sensory neurons
  

Unipolar (Pseudounipolar)

• appear to have a single projection from the cell body that divides into two axonal roots.

  o Pseudounipolar cells have two axons and no true dendrites (fake dendrites bc not from cell body)

  o Found in sensory neurons
  o From receptors straight to the sensory neurons

Neuroglia

• major supporting cells of CNS. They support the metabolic and signaling functions of neurons and participates in neuron circuit formation and synaptic plasticity
  

Astrocytes

• Star shaped

• Cover the surfaces of neurons, blood

  vessels, and the pia mater structural support = gliosis or replacement gliosis

• When damaged part in the brain is replaced, function is lessened/not the same with the original

• Forms part of blood brain barrier

• Help maintain ionic balance of

• Extracellular fluids

Oligodendrocytes

• Oligo = few; only a portion

• Form part of the myelin sheaths of

  several axons within the CNS

Ependymal Cell

• Lining the ventricles of the brain and the central canal of the spinal cord

cerebrospinal fluid (CSF)

• gives nutrition to the nervous system, provides cushioning, provides antibacterial properties

Microglia

• Phagocytic cells within the CNS

• WBC converted into neuroglia for the

  CNS

Blood Brain Barrier

• Specialized permeability barrier between the capillary endothelium (inner lining of the blood vessel) and the extracellular space in neural tissue

• Formed by tight junctions between capillary endothelial cells, which are surrounded by “end-feet” processes of astrocytes

o Forming a “glia limitans”, or limiting glial border

• Protects the vessels that pass through brain from the toxins or excess substances from the blood that are not needed

Schwann Cells

• are neuroglia in the PNS that wrap around axons. It forms a myelin sheath

Satellite Cells

• surround neuron cell bodies in sensory and autonomic ganglia

Myelin Sheath

• protects and electrically insulates

  axons from one another
  

Gray Matter

• consists of groups of neuron cell bodies and their dendrites, where there is very little myelin.

  o Collection of cell bodies or axons with very little myelin sheath

White Matter

• Consists of bundles of parallel axons with their myelin sheaths, which are whitish in color.

  o Collection of myelinated axons

  o CNS forms nerve tracts
  o PNS forms nerves.

Resting Membrane Potential

• charge difference across the plasma membrane of an unstimulated cell

Three factors of resting membrane potential

• Membrane is at rest if K is higher inside

• Na is higher outside

• The plasma membrane is more permeable to K+ than

  to Na+.

-70 mv

What is the typical resting membrane potential of a nerve?

-90 mv

What is the typical resting membrane potential of a mucle?

Action Potential

• The inside of the plasma membrane becomes positively charged compared with the outside

• Ion channels open when a cell is stimulated. The diffusion of ions (Na+ and K+) through these channels changes the charge across the plasma membrane

Depolarization

Repolarization

2 phases of action potential?

Depolarization

• The inside of the cell becomes positively charged brought by the inflowing positively charged sodium ions

• Once threshold is reached (-65 to -55 mv), an action potential is triggered; only 5-15 mv is needed to stimulate ap

Repolarization

• Rapid diffusion of potassium ions to the exterior re- establishes RMP

• K opens, Na close = outflow of + charge ions

Hyperpolarization

• Membrane potential becomes more negative and is the movement of the membrane potential further away from zero

• Needs sodium potassium pump to re-establish RMP (- 70)

o pump 2 K+ IN against its concentration gradient and keep it in high concentration inside the cell

o pump 3 Na+ OUT against its concentration gradient and keep it in high concentration outside the cell

• The sodium-potassium pump uses ATP to:

o pump ________ against its concentration gradient and keep it in high concentration inside the cell

o pump ______ against its concentration gradient and keep it in high concentration outside the cell

All-or-None Principle

• If a stimulus produces a depolarizing graded potential that is large enough to reach threshold (-65 to -55mv) → action potential proceed without stopping and are constant in magnitude

• If a stimulus is so weak that the depolarizing graded potential does not reach threshold → returns to its resting level after a brief period without producing an action potential

Refractory Period

• Once an action potential is produced at a given point on the plasma membrane, the sensitivity of that area to further stimulation decreases for a time

Absolute Refractory Period

• The first part of the refractory period, during which

  complete insensitivity exists to another stimulus

• No other signals can be entertained

Relative Refractory Period

• The second part of the refractory period. A stronger

  than threshold stimulus can initiate another action

  potential

• Neuron can entertain another AP as long as it reaches

  threshold

Unmyelinated axon

Which axon?

• Slower; needs the whole axon to be polarized = needing more ATP/energy

Myelinated axon

• Faster

• Requires lesser ATP/energy

Saltatory conduction

Jumps from one node to another

Synapse

• Junction point from one neuron to other neuron

• Functional interneuronal communication occurs

• Impulse reaches axon terminals

• Triggers neurotransmitter release into synaptic cleft

Terminal buttons

End of the axon

Axoaxonic

• Axon to axon

Axosomatic

• Axon to soma

Axodendritic

• Axon to dendrite

Postsynaptic potentials

• _________ are local changes in ion concentration across the postsynaptic membrane

• The effect may be local depolarization or hyperpolarization.

Excitatory Postsynaptic Potential (EPSP)

• Local depolarization (less negative)

• Can lead to generation of an action potential

Inhibitory Postsynaptic Potential (IPSP)

• Local hyperpolarization (more negative)

• Inhibit the generation of an action potential in the postsynaptic cell

Chemical Synapses

• Almost all the synapses used for signal transmission in the CNS

• Neuron secretes at its nerve endings a chemical substance called neurotransmitter

• Neurotransmitter acts on → Receptor protein that will either EXCITE (EPSP) or INHIBIT (IPSP)

• Transmission is slower

• Mediating agent is a chemical messenger

• One way transmission/conduction

• Significant synaptic delay (0.3 ms-0.5 ms)

Electrical Synapses

• Characterized by direct open fluid channels that conduct electricity from one cell to another

• Consists of gap junction – allows free movement of ions from interior of one cell to the next

• Have bridges that interconnect the cytoplasm of pre and post membrane

• Transmission is rapid

• Mediating agent is an ionic current

• Bidirectional

• Little or no synaptic delay

Neurotransmitters

• Any specific chemical agents released by a presynaptic cell on excitation that cross the synaptic cleft and stimulate or inhibit the postsynaptic cell.

• ____________ may affect the postsynaptic neuron directly, by activating ion channels (ionotropic), or indirectly, by activating proteins inside the postsynaptic neuron (metabotropic).