Neurons: resti ng potential, action potential and propagation (copy) (copy)

What are glial cells and their functions

What are glial cells and their functions

Glial cells are non-neuronal cells that support and protect neurons, maintaining homeostasis and forming myelin. Functions include:

• Insulation (myelination): Create myelin sheaths to speed up signals.

• Protection: Shield neurons from injury and infection.

• Nutrition and waste removal: Supply nutrients and remove waste.

• CSF circulation: Maintain the environment around neurons.

Myelinating cells

Myelinating cells are a type of glial cell that insulate neuronal axons, enhancing the speed of electrical signal conduction.

Schwann cells

Found in the Peripheral Nervous System (PNS); myelinate single neuronal axons (about 1mm each).

Oligodendrocyte's

Found in the Central Nervous System (CNS); myelinate multiple sections of different neuronal axons, providing insulation and support.

Support cells

General term for cells that provide structural and functional support within the nervous system.

Microglia

Located in CNS; phagocytic cells that clear extra cellular debris and act as immune responders of glial cells.Have 9 sub-types and are extremely plastic. They divide and multiply at a fast rate.

Astrocyte

Star-shaped cells in CNS; Help provide (3D) structural support and are involved in the physical structuring of the brain. wrap around or surround the connections between neurons, called synapses. End feet contact blood vessels and are thought to be involved in regulation of blood flow.

Ependymal cells

found in ventricles and central canal of spinal cord; produce and regulate CSF form the 'Ependyma' which is the tissue lining the ventricular system and central canal of the spinal cord., The top of the cells have cilia which beat in a coordinated pattern to circulate CSF. Extensions of the basal membrane attach to astrocytes..

How do neurones work

Neurons communicate via neurotransmitters at synapses, where electrical signals are converted to chemical signals and transmitted between cells.

Axon terminals

Release neurotransmitters to communicate with other neurons.

Node of rangier

Gaps in the myelin sheath where ion exchange occurs.

Myelin sheath

Insulating layer surrounding the axon; increases transmission speed.

Axon

Long projection that conducts electrical impulses away from the cell body.

Axon hillock

Area where action potentials are initiated.

Dendrite

Branch-like structures that receive signals from other neurons.

Dendritic spines

Small protrusions on dendrites that form synapses with other neurons.

3 types of neurones based on direction of impulse

1. Sensory / afferent neurons: These carry impulses from sensory organs (like your eyes, skin, or ears) toward the brain and spinal cord (CNS).

2. Motor neurons: These carry impulses from the brain and spinal cord to muscles and glands. They tell your muscles to move or glands to release hormones.

3. Interneurons: These are found between sensory and motor neurons in the brain and spinal cord. They help process and relay signals between the other types of neurons.

Bipolar neuron

Typically found in sensory pathways, having two distinct processes—dendrite and axon. Found in special sense organs, sensory neuron

Unipolar neuron

found in sensory neurones of peripheral nervous system characterized by a single process extending from the cell body, which then splits into two branches (one branch acts like a dendrite, and the other acts like an axon).

Multipolar neuron

Have multiple processes; one axon and many dendrites, , most common neuron, involved in motor and interneuron functions.,

What are cortical cells

Neurons found in cortex

Granular cells

Small, densely packed neurons primarily found in the granular layer of the cerebellum. send signals to other types of cells in the cerebellum. Process info for movement.

Pyramidal cells

Large neurons with a pyramid-shaped cell body in the cortex cortex; send messages between different parts of the brain and control things like movement and thought.

Purkinje cells

Large neurons in the cerebellum with extensive dendritic trees, crucial for motor control.

Neuronal cell membrane

Composition includes phospholipids and proteins crucial for membrane function, forming a semi-permeable barrier vital for ion exchange

Ions

• Neutral particles: Have no net charge.

• Anions: Carry a net negative charge.

• Cations: Carry a net positive charge.

Resting potential voltage

A neuron at rest has a voltage of approximately -70mV due to the uneven distribution of ions across its membrane, primarily maintained by ion pumps and channels

Active ion transport

2 K+ ions are pumped by sodium potassium pumps into the cell while 3 Na+ ions are pumped out, maintaining concentration gradients essential for resting membrane potential.

Depolarisation process

Local currents modify the phospholipid bilayer, triggering the opening of ion channels, leading to K+ outflux and Na+ influx. This process ultimately initiates an action potential via voltage-gated ion channels.

Action potential

A rapid change in membrane potential, triggered when the neuron reaches a threshold level (-55mV). This involves depolarization (Na+ influx) followed by repolarization (K+ efflux).

Key voltages for action potential

• Resting: -70mV

• Threshold for action potential: -55mV

• Peak membrane potential: +40mV

Propagation of action potential

Action potentials travel along axons via two mechanisms: continuous conduction in unmyelinated fibers and saltatory conduction in myelinated fibers, enhancing speed and efficiency

Ligand gated receptors

• Neurotransmitter binds to the receptor on the postsynaptic membrane, initiating signal transduction and resulting in Na+ influx that may lead to depolarization.

Happens in synaptic cleft