cells of the nervous system and neuro physiology

what are the 2 types of nervous system cells?

1. neurons

2. neuroglial cells

what are neurons?

specialized cells of the nervous system that send signals along their axons and communicate with other cells

How do neurons communicate with other cells?

By releasing chemicals called neurotransmitters at cell-cell junctions called synapses.

What are neuroglial cells?

Non-neuronal cells that provide support and nutrition in the nervous system as well as electrochemical surroundings of neurons

Approximately how many neurons are in the human brain?

86 billion

What is the primary role of neurons compared with neuroglial cells?

Neurons communicate and transmit signals, while neuroglial cells support neurons and maintain their environment.

What structures are found in grey matter?

Dendrites, cell bodies, and axon terminals (connections between neurons).

What can grey matter areas in the CNS be called?

Nuclei

What is white matter primarily composed of?

Bundles of myelinated axons.

What are the different names used for white matter areas?

Fasciculus, funiculus, lemniscus, peduncle, and tract.

What are the two ways neurons can be classified?

Structural classification and functional classification.

What are the three structural classifications of neurons?

Multipolar, bipolar, and unipolar neurons.

What are multipolar neurons?

motor neurons that make up 90% of the CNS

what are bipolar neurons?

sensory neurons of the retina of eye and nose

what are unipolar neurons?

neurons with a single process that divides into two branches.

In a unipolar neuron, where do the two branches extend?

one to the CNS, and one to the periphery.

Where are unipolar neurons primarily found?

In sensory ganglia neurons

What are the three functional classifications of neurons?

Sensory (afferent), motor (efferent), and interneurons.

What do sensory (afferent) neurons do?

Carry action potentials toward the CNS.

What do motor (efferent) neurons do?

Carry action potentials away from the CNS.

What are interneurons?

Neurons that are located within the CNS and connect one neuron to another.

Approximately what percentage of neurons are interneurons?

99%

What is the easiest way to remember afferent vs. efferent?

Afferent Arrives at the CNS; Efferent Exits the CNS.

What are neurons?

Electrically excitable cells in the nervous system that process and transmit information.

What is the function of dendrites?

Receive signals from other cells.

What is the soma (cell body) responsible for?

Integrating signals received by the neuron.

What is the axon?

The main, long extension of a neuron that sends signals away from the cell body.

Where does the signal in the axon begin?

At the axon hillock.

What is a synapse?

A junction that facilitates transmission of impulses from one neuron to another

What is the myelin sheath?

A myelin covering around the axon that helps facilitate rapid signal transmission.

What are the Nodes of Ranvier?

Gaps between sections of myelin sheath along an axon.

What is the presynaptic neuron/cell?

The cell before the synapse that releases neurotransmitters.

What is the postsynaptic cell?

The cell after the synapse that receives the neurotransmitter signal.

Why is axonal transport necessary?

Because an axon can be 1,000–10,000× the length of the cell body, so materials must be transported along the axon.

What is anterograde transport?

Transport away from the cell body toward the synapse/axon terminals.

What is retrograde transport?

Transport toward the cell body.

What is the easiest way to remember anterograde vs. retrograde transport?

Anterograde = Away from the cell body; Retrograde = Return toward the cell body.

How do viruses and toxins enter the nervous system?

through hijacking the retrograde transport by being taken up at axon terminals in peripheral nerves and transported back toward cell bodies in the CNS.

what are the 2 types of synapses? and give examples of each

1. Chemical synapses = neurotransmitters

2. Electrical synapses = gap junctions in mammals

what are the 2 major locations of neuroglial cells?

1. CNS

2. PNS

what are the 4 types of neuroglial cells in the CNS?

1. astrocytes

2. oligodendrocytes

3. microglia

4. ependymal cells

What are the two types of neuroglial cells in the PNS?

1. schwann cells

2. satellite cells

What are astrocytes?

Star-like neuroglial cells that are the most numerous and diverse type of neuroglial cell.

What are the two major types of astrocytes?

1. Fibrous astrocytes

2. protoplasmic astrocytes

How do astrocytes compare with neurons in terms of diversity?

Astrocytes are highly heterogeneous, similar to neurons.

Do all astrocytes have the same physiological properties?

No. Astrocytes in different regions of the brain may have different physiological properties.

During what stages can astrocytes regulate and remodel synapses?

During development, aging, and disease.

what are the 5 functions of astrocytes?

1. maintaining brain homeostasis

2. blood brain barrier formation

3. CNS blood flow regulation

4. store and distribute energy substrate

5. modulate synaptogenesis and synaptic maintenance

How do astrocytes help maintain brain homeostasis?

They regulate extracellular K⁺ and glutamate levels.

How do astrocytes help form the blood brain barrier?

with their end-feet which helps provide brain defense

How do astrocytes regulate blood flow in the CNS?

They regulate blood flow through functional hyperemia.

What is functional hyperemia?

An increase in blood flow to active areas of the brain to meet increased metabolic demands.

What is an astrocytoma?

A primary brain tumor arising from astrocytes, occurring in both children and adults.

(critical role in neurodevelopment)

What role do astrocytes play in neurodegenerative disease?

They contribute to inflammation associated with neurodegenerative diseases.

(alzheimers and Parkinsons)

What are microglia?

Resident macrophages of the brain and spinal cord.

What do “resting” microglia do?

They continuously scan their environment for signs of injury, infection, or other changes.

What are the 4 functions of microglia?

1. first and main form of active immune defense in the CNS

2. phagocytosis

3. promotion of repair

4. releases active oxygen species when chronically activated

What is the primary function of oligodendrocytes?

To create myelin sheaths around axons in the CNS.

What is the approximate composition of myelin?

Approximately 80% lipid and 20% protein.

How many axons can a single oligodendrocyte extend its processes to?

50

How does an oligodendrocyte differ from a Schwann cell in the number of axons it can myelinate?

An oligodendrocyte can myelinate multiple axons, while a Schwann cell in the PNS wraps around only one axon.

What are the gaps between myelin segments called?

Nodes of Ranvier

What is a demyelinating disease?

A disease in which myelin surrounding axons is damaged or lost, impairing normal nerve signal conduction.

(ex: multiple sclerosis)

What happens to oligodendrocytes and myelin segments in multiple sclerosis?

Groups of oligodendrocytes and their myelin segments degenerate.

What replaces areas of damaged oligodendrocytes and myelin in multiple sclerosis?

Astrocytic plaques

Why does loss of myelin impair nerve function?

Loss of myelin can interrupt the propagation of action potentials down the axon.

Do demyelinated axons immediately die?

NO. demyelinated axons temporarily survive

how does some remyelination occur in multiple sclerosis?

via the myelin-producing oligodendrocyte precursor cells

Where are ependymal cells located?

in the lining of the inner surfaces of the brain ventricles and the central canal of the spinal cord.

what are the 4 functions of ependymal cells?

1. control of CSF production

2. barrier formation between brain tissue and CSF

3. controls brain metabolism

4. waste clearance

where are satellite cells located?

they are found surrounding the cell bodies of neurons in sensory and autonomic ganglia

what do schwann cells do?

ensheath axons in the PNS

whats a schwannoma?

a noncancerous nerve sheath tumor that develops from schwann cells

what is the most common type of schwannoma?

a unilateral vestibular/acoustic schwannoma

what are the 3 examples of electrical properties of neurons?

1. excitability

2. conductivity

3. secretion of neurotransmitters

What two major factors determine a cell's electrical properties?

1. Ion concentration gradients across the plasma membrane

2. membrane permeability.

What is neuronal excitability?

The ability of a neuron to respond to appropriate stimulation.

What types of stimuli can excite a neuron?

Mechanical, thermal, chemical, and electrical stimuli.

what does it mean to say that the “all-or none rule” applies to the excitability level of a neuron?

once the threshold is reached, the size of the action potential is independent of the stimulus — thus a greater stimulus does not give a greater action potential

What is the resting membrane potential of a typical neuron?

−70 mV.

What must happen before an action potential is generated?

The membrane potential must reach the threshold of excitation.

what are the 6 stages of action potential?

1. Na+ channels open, Na+ enters the cell

2. K+ channels open, K+ leaves the cell

3. Na+ channels become refractory, no more Na+ enters

4. K+ that keeps leaving cell return membrane potential to resting level

5. K+ channels close, Na+ channels reset

6. extra K+ outside diffuses away

what is an absolute refractory period?

The period after an action potential where it is not possible to elicit a second action potential.

Why can't a second action potential occur during the absolute refractory period?

Because most of the neuron's sodium (Na⁺) channels are inactivated and cannot be opened.

what is the relative refractory period?

the inactivated channels return to the closed (but ready-to-open) state, and this takes many milliseconds

during the relative refractory period, it is more difficult than normal to do what?

elicit a second action potential

How does an action potential spread along an unmyelinated axon?

the action potential regenerates itself as its electrical current depolarizes the neighboring region of the axon membrane

Why can't an action potential normally travel backward?

Na⁺ channels behind the zone of depolarization are inactivated, preventing that region from immediately generating another action potential.

In what direction do action potentials travel along an axon?

Toward the synaptic terminals (axon terminals).

myelin prevents the movement of what ions through the membrane?

Na+ and K+

Where can Na+ and K+ cross the membrane in a myelinated axon?

through the Na+ and K+ channels that are located in the interruption of myelin (Nodes of Ranvier)

Where do action potentials occur in a myelinated axon?

Only at the Nodes of Ranvier.

how is the neighboring Node of Ranvier activated, creating another action potential?

Current from the previous node depolarizes the membrane at the next node until threshold is reached, triggering another action potential.

what it the name given to the fast, leaping conduction movement of the action potential traveling down a myelinated axon?

saltatory conduction

what is the speed of unmyelinated conduction?

0.5 to 10 m/s

what is the speed of myelinated axon conduction?

up to 150 m/s

what are the 2 types of synapses?

1. electrical

2. chemical

How do electrical synapses transmit signals?

By passive flow of ionic current through gap junctions between presynaptic and postsynaptic cells.

What is a major general purpose of electrical synapses?

To synchronize electrical activity among populations of neurons.

What is an example of neurons connected by electrical synapses?

Certain hormone-secreting neurons in the mammalian hypothalamus