Neuroscience TB1

Neurons:

Process information, Sense environmental changes, Communicate changes to other neurons, Commands body response

Glia

Insulates, supports, nourishes

Contributes to the regulation of neurons

Neurons communicate using:

Electrical signals

Chemical signals

A typical neuron is composed of:

Soma (cell body)

Dendrites

Axon

The nucleus is responsible for:

Gene expression, translation, RNA processing

Myelin Sheath:

Fatty insulation layer around the axon that offers protection and speeds up signal transmission

Neuronal Membrane:

Barrier that encloses cytoplasm

Approx. 5nm thick

Protein concentration in membrane varies

Structure of discrete membrane regions influences neuronal function

Soma

Contains nucleus

Protein synthesis (ER)

Metabolic center (mitochondria)

Receives Information

Integrates Signals

Axon

Originates in the soma

Long extension

Transmits signals

Transmits Information

Myelination (protection & speed)

Afferent

Carry information towards a certain point

Efferent

Carry information away from a certain point

Postsynaptic Location of the Neuron

Dendrite

Presynaptic Location of the Neuron

Axon

Single Neurite

Unipolar

Two Neurites

Bipolar

More than two neurites

Multipolar

Stellate Cells

Star shaped

Pyramidal Cells

Pyramid Shaped

Motor Neurons

Transmit messages from the brain to the muscles to generate movement

Sensory Neurons

Detect light, sound, odour, taste, heat, pressure and send messages to the brains

Other neurons of the NS:

Control involuntary processes e.g. heartbeat, release of hormones, digestion

Neurons…

Receive information via dendrites

Process information in the cell body (soma)

Transmit it via axons and axon terminals

and overall allow communication and responses to environmental stimulus

Functions of the Plasma Membrane

Flexible yet sturdy semi-permeable regulator

Covers and protects the cell

Controls what goes in and comes out

Links to other cells

Flies ‘flags’ to let other cells know ‘who’ it is

Ion Channel (Integral)

Allows specific ion to move through water-filled pore. Most plasma membranes include specific channels for several common ions.

Carrier (Integral)

Allows specific substances across membrane by changing shape. Carrier proteins are also known as transporters.

Receptor (Integral)

Recognises specific ligands and alters cell’s function in some way.

Enzyme (Integral and Peripheral)

Catalyzes reaction inside or outside the cell (depending on which direction the active site faces)

Linker (Integral and Peripheral)

Anchors filaments inside and outside the plasma membrane, providing structural support and shape to the cell. May also participate in the movement of cell or link two cells together.

Cell-Identity Marker (Glycoprotein)

Distinguishes between your cells and anyone else’s cells. An important class of such markers are the major histocompatibility (MHC) proteins

Diffusion

the passive, random spread of particles

Diffusion Depends On:

Amount of substance

Concentration gradient

Temperature

Surface Area

Diffusion Distance

Ion Channels

Allow passive movement of certain ions down their concentration gradients

Distinguished by their ion selectivity for K⁺, Na⁺, Cl^-, Ca²⁺, etc.

Regulated or ‘gated’ holes through the membrane

Flow through ion channels is at near thermodynamic equilibrium approx. 10⁶ ions/s

Mechanisms of Gating

Voltage

Ligands

Temperature

pH

Mechanical Stress

Transporters (Carriers)

Allow passive movement of solute across membrane.

Concentration-gradient dependant

Exhibits saturation kinetics

Osmosis

the net passive movement of water through a selectively permeable membrane from a region of high water concentration to one of lower water concentration and is opposed by hydrostatic pressure

Hydrostatic pressure

occurs when membrane is permeable to water but not solutes

Tonicity

A measure of a solutions ability to change the volume of a cell by altering its water content.

Since semi-permeable membranes separate fluid compartments, osmosis of water can occur between any fluid space and another.

Primary Active Transport Mechanisms

Required for solutes that need to move against their concentration gradients.

Requires energy from the hydrolysis of ATP

Exhibit saturation kinetics

Crucial for maintaining cell volume and ionic gradients responsible for setting resting membrane potential and generating action potentials

Secondary Active Transport:

Uses energy stored in Na⁺ or H⁺ concentration gradients to drive transport of other solutes against their concentration gradients

These concentration gradients are already established by Primary Active Transport

Secondary Active Transport indirectly uses energy from ATP hydrolysis

Antiporters

carry two substances across the membrane in different directions

Symporters

carry two substances across the membrane in the same direction

Vesicle

A small spherical sac formed by budding off from a membrane

Endocytosis

Materials move into a cell in a vesicle

1). receptor-mediated endocytosis

2). phagocytosis

3). bulk-phase endocytosis

Exocytosis

Vesicles fuse with the plasma membrane, releasing their contents into the extracellular fluid

Transcytosis

a combination of endocytosis and exocytosis