Cell Signals and Nervous System PMCY 4020

In the PNS, neuroglia is made of __. These cells cover the surface of neuron cell bodies, provide support and might control their microenvironment

Satellite cells.

Match.

1.Neuron

2. Microglia

3. Astrocyte

4. Ependymal cell

5. Ooligodendrocyte

An adult male has difficulty moving his hand after a head injury that resulted in damage to neurons in his brain. The damage is likely permanent because __________.

A. He is an adult, and CNS neurons can only regenerate in childhood

B. Inhibitory proteins in the PNS will prevent axons in his hand from ever regenerating

C. Neurons in the CNS lack Schwann cells, which play a major role in axon regeneration

D. Astrocytes that surround the CNS axons do not have enough myelin for regeneration

C

If astrocytes were damaged or lost, how would this impact CNS function?

A. An individual may experience difficulty initiating movement, or slowness in movement

B. The composition of the CSF would be very similar to blood plasma

C. Production of CSF would be diminished

D. Toxic substances could easily build up in the brain

B. & D.

In the CNS, neuroglia is made of __. Produce myelin sheaths around axons

Oligodendrocytes.

Myelin sheaths give a white color:

White matter

__ __: cell bodies and dendrites of neurons in the CNS

Grey matter

In the PNS, __ cells support nerve degeneration; When an axon is cut, the severed portion degenerates and is phagocytosed by __ cells

Shwann

Schwann cells form a __ __. These structure is a guidance track for the regenerating axon

Regeneration trube

Schwann cells seem to secrete __: promote axon regeneration

Neurotrophins

In the CNS, neurons die upon injury or die later via:

Apoptosis

Regeneration in the CNS is __ by inhibitory proteins at the surface of myelin sheaths (ie. Nogo)

Prevented

A __ __ rapidly forms, further preventing axon repair

Glial scar

In the CNS, neuroglia is made of __. Main form of immune defense in the CNS. Able to detect sites of infection or damage

Microglia.

Microglia are also involved in __ __

Synaptic pruning

An altered state of the extracellular environment can lead to microglial activation:

Cells become ameboid and become phagocytic cells. They can detect ATP released from damaged cells thanks to ATP receptors found on their surface

Microglia have the capacity to realse __ ___, ending ___ responses and contributing to neuroprotection

Anti-inflammatory; inflammatory

In the CNS, neuroglia is made of __, they help to regulate the external environment of neurons

Astrocytes

__ are the most abundant microglia in the CNS

Astrocytes

Astrocytes encircle the endothelial cells of blood capillaries with projections named:

End-feet. They are also adjacent to the space between the axon terminal and another neuron

Astrocytes seem to perform many different functions:

• K+ uptake. Astrocytes might soak up the K+ exiting from the neuron during an action potential

• Glucose take up from the blood and releasing lactate for neurons to use

• Neurotransmitter take up

• Synapse maintenance, formation and maturation

• GDNF secretion (promotes neuron survival)

Astrocytic dysfunction is linked to __

Neurodevelopmental disorders such as Alexander’s disease (point mutation)

Astrocytes induce the formation of the ___ __

Blood-brain barrier

Astrocytes release signaling molecules that regulate neuron function:

Gliotransmitters

Capillaries across the body are __. They have pores. Non-specific filtering can happen

Fenestrated

All endothelial cells in the blood-brain barrier are joined by tight junctions and surrounded by __.

Astrocytes

Molecules in the blood can only move through the endothelial cells either by __, __, __.

Diffusion, active transport, or endocytosis.

*O2, CO2, and nonpolar molecules can cross

*Ions and polar molecules require channels and carriers

Astrocytes secrete __ to increase the production of transporters and tight junction proteins; Endothelial cells __ promoting astrocyte growth and differentiation

Regulatory molecules; secrete regulators

__ cells are ciliated epithelial cells lining the entire ventricular surface of the CNS and the central canal of the spinal cord

Ependymal

Ependymal cells also produce __ __ . Using their cilia, they ensure that the _ circulates in the ventricles. It transports nutrients signaling molecules and remove waste products

Cerebrospinal fluid (CSF)

Transmission in synapses occurs in one direction: from the __ neuron to the _ neuron or effector cell

Presynaptic; postsynaptic

Explain Otto Leowi experiment

• Used two frog hearts to demonstrate existence of neurotransmitters

• The neurotransmitter discovered was acetylcholine

• Can either be chemical or electrical

1. Stimulate vagus nerve

2. Heart rate slows

3. Add fluid to recipient heart

To be electrically coupled, cells must be almost what? Why?

• Must be almost the same size and joined by areas of contact with low electrical resistance

• Allows the impulses to be regenerated without interruption

Two electrically coupled cells are joined together by:

Gap junctions

Gap junctions are made of proteins called:

Connexins

__ connexins form a _, then two _ from opposing cells come together to form a complete gap junction

six; hemichannel; hemichannels

The _ muscle has gap junctions that allow the whole organ to be contracted as a unit

Cardiac

_ synapses are the most abundant type of synapse. Occurs when the presynaptic axon releases neurotransmitters

Chemical

The axon endings of the presynaptic neuron are called:

Terminal boutons

The space between the presynaptic and the postsynaptic cell is the:

Synaptic cleft

_ _ are located in the terminal bouton. They contain neurotransmitters awaiting to be released

Synaptic vesicles

Describe neurotransmitter release:

1. Action potentials reach axon terminals

2. Voltage-gated Ca2+ channels respond to the action potentials and open. Ca2+ enters the cell

3. Ca2+ binds to synaptotagmin, triggering the fusion of the synaptic vesicle to the plasma membrane leading to exocytosis of neurotransmitter.

4. Once released, the neurotransmitters reach the postsynaptic membrane where they bind to specific receptors

5. Binding causes the opening of ion channels in the postsynaptic membrane: chemically regulated channels

When chemically regulated channels open, they produce a:

Graded potential

If Na+ and Ca2+ channels open, they produce a postsynaptic membrane becomes less negative: graded depolarization called:

excitatory postsynaptic potential (EPSP)

If Cl- channels open, the postsynaptic membrane becomes more negative: graded hyperpolarization called

Inhibitory postsynaptic potential (IPSP)

EPSPs and IPSPs are produced in the __, and must propagate from the cell body to the _ _ of the axon to influence action potential production

Dendrites; initial segment

The initial segment has a high Na+ and K+ channel density and is where _ _ and the first action potential occurs

Synaptic integration

One neuron can make synapses with many others: there is a ; Many axons can converge into one neuron: __

Divergence of neural pathways; convergence of neural pathways

What is spatial summation? (Add photo)

Release of neurotransmitters from neurons 1 and 2

Temporal summation:

Successive release of neurotransmitters from one neuron only

__and __ hyperpolarize the postsynaptic membrane: post-synaptic inhibition

Glycine; GABA

What is paracrine signaling?

Happens in cells within an organ. Happens when a cell targets a nearby cell. Local

Cells that are adjacent to each other can communicate through _ junctions

gap

What is synaptic signaling?

happens only between neurons and their target cell. The neuron releases neurotransmitters

What is endocrine signaling?

happens when cells from endocrine glands release hormones into the blood. The hormones can then reach their cells

Second messengers are _ _ upon binding of the regulatory molecule to its receptor

indirectly produced

Explain the G-protein cycle

All cells have a membrane potential:

the resting membrane potential

Only a few cells can change their membrane potential upon stimulation:

excitable cells

After stimulation, if positive charges enter the cell →

depolarization

If negative charges inter the cell →

hyperpolarization

Return to the rpm →

repolarization

In neurons, depolarization is __and hyperpolarization is __

excitatory; inhibitory

In general, Na+ channels are all _

voltage gated

2 types of K+ channels:

voltage gated and not voltage gated (leakage channels)

Na+ channels can be also blocked by different molecules:

sodium channel blockers

Describe action potential

• The voltage-gated Na+ channels open: Na+ rushes into the cell

• The Na+ channels close, then the voltage-gated K+ channels open: K+ rushes out of the cell

• The K+ channels close, bringing the membrane potential back to rpm

When the gated Na+ channels open, _

a positive feedback loop occurs

When the gated K+ channels open, a _

negative feedback loop

The length of time that the Na+ and K+ channels remains open is _ of the depolarization stimulus

independent

If the threshold is not reached: no action potential is produced. If the threshold is reached: and action potential is reached

all or none

a stronger stimulus does not produce an action potential with greater amplitude

stimulus strength is not amplitude modulated

stronger stimuli on a neuron triggers more action potentials:

strength is frequency modulated

When a neuron generates an action potential, it is incapable to respond to further stimulation

The neuron is refractory to further stimulation

The refractory period is caused by:

the inactivation of the voltage-gated Na+ channels

Explain the absolute refractory period

When a region of the axon is producing an action potential, it is incapable of responding to further stimulation

Explain the relative refractory period

When the membrane is repolarizing, only a very strong depolarization will trigger a new action potential

Action potential conduction is _ due to the refractory period

unidirectional

Action potentials are produced along the entire length of the _

axon

What is myelin?

Insulating layer of phospholipids and proteins found wrapped around axons

Myelin prevents …

any ion movements except in zones of the axon where it is not present: nodes of Ranvier

Action potentials are propagated through _ _ A new action potential is produced at every node and not at every region of the axon’s membrane

saltatory conduction

True or false: action potentials are propagated faster in a myelinated axon

true (100m per second!)

The nervous system can be divided into two:

• Central nervous system

• Peripheral nervous system

Neurons have three principal regions:

• Cell body. Contains the nucleus of the neuron

• Dendrites.

• Axon

A cluster of cell bodies in the CNS:

nucleus

A cluster of cell bodies in the PNS:

ganglion

_ _ conduct impulses out of the CNS to effector organs

Motor (or efferent) neurons

_ _ conduct impulses from sensory receptors into the CNS

sensory (or afferent)

_ relay signals between two other neurons. Located only in the CNS

interneurons

_ _ are the most abundant neurontype, possess several dendrites and one axon

multipolar neurons

_ _ one branch received stimuli, while the other relays the signal into the CNS

pseudounipolar neurons

_ _ neurons with two extensions, one at either side of the cell body

bipolar neurons

In the PNS, multiple axons together form a . _In the CNS, they form a _

nerve; tract

In the PNS, neuroglia is made of _ cells. Produce myelin sheaths around axons and surround all PNS axons to form the neurilemmal sheath

Schwann

There are two inhibitory neurotransmitters in the CNS:

• GABA. 1/3 of the brain uses this

• Glycine. Used by the spinal cord, brain stem and retina

GABA and glycine receptors are — gated. Binding to their receptors opens Cl- channels, leading to — and —.

ligand;hyperpolarization;IPSPs

GABA is involved in — control: a deficiency of GABA-releasing neurons is linked to Huntington’s disease

motor

— is used as an excitatory neurotransmitter by somatic motor neurons at the neuromuscular junction.

Acetylcholine

At autonomic nerve endings it can be excitatory or inhibitory due to the presence of different types of Ach receptors:

• Nicotinic Ach receptors (nicotine can bind them)

• Muscarinic Ach receptors (muscarine (mushroom) can bind to them)