FINAL study guide

What are the two divisions of the nervous system?

CNS (central nervous system) and PNS (peripheral nervous system)

What does the CNS include?

The brain and spinal cord

What does the PNS include?

Everything in the body other than the brain and spinal cord, including sensory and motor divisions

Is the autonomic nervous system part of the sensory or motor division and why?

The autonomic nervous system is part of the motor division because autonomic responses are being sent from the brain to other muscles, organs, and glands.

What cells make up nervous tissue?

Neurons and supporting cells (glial cells)

Why are neurons amitotic?

Neurons cannot undergo cell division because they lack centrioles.

From which cells do primary brain tumors originate?

Supporting cells (neuroglial cells), not neurons, since supporting cells can divide

What is the biosynthetic center of a neuron?

The cell body because neurotransmitters are synthesized there

What is the receptive center of a neuron?

Dendrites because they receive messages/electrical impulses and send them towards the cell body.

What is the conducting region of a neuron?

The axon because it transmits action potentials away from the cell body.

How many axons can each neuron have?

Each neuron can have only one axon.

What is the secretory region of a neuron?

Axon terminals because they store and release neurotransmitters.

What is a Nissl body?

The well-developed rough ER in the cell body of a neuron

What is the nuceli?

A cluster of neuron cell bodies in the CNS

What is a ganglion?

A cluster of neuron cell bodies in the PNS

What is a tract?

Bundles of axons in the CNS.

What is a nerve?

Bundles of axons in the PNS.

What is neurilemma?

The cytoplasm and nucleus of Schwann cells squeezed outside the myelin sheath in the PNS.

What are nodes of Ranvier?

The spaces between adjacent myelin sheaths.

What wraps each axon in a nerve/tract?

Endoneurium

What is a fascicle?

Groups of axons (wrapped in endoneurium)

What covers a fascicle?

Perineurium

What covers bundles of fascicles to form a nerve/tract?

Epineurium

What are the 4 types of supporting cells in the CNS?

Microglia, ependymal cells, oligodendrocytes, astrocytes

What are the 2 supporting cells in the PNS?

Satellite cells and schwann cells

What are the functions of microglia?

Act as phagocytes to engulf/destroy pathogens and cell debris, since the immune system does not have access to the CNS

What do ependymal cells do?

Line the ventricles in the brain to circulate CSF by beating cilia

What is the function of oligodendrocytes?

Their extensions myelinate axons of neurons in the CNS.

What is the role of astrocytes?

Form the blood-brain barrier to regulate the chemical environment of the brain and brain function

What do satellite cells do?

Surround cell bodies of neurons to control their chemical environment.

What do Schwann cells do?

Myelinate axons of neurons in the PNS.

Where is the neurilemma present?

The PNS only since it is outside schwann cells

What supporting cells are involve in forming the BBB?

Astrocytes

What is the function of the BBB?

Act as a selective barrier to regulate chemical environments of the brain

What cells in the PNS are similar to oligodendrocytes and why?

Schwann cells because they both myelinate axons

Why do myelinated axons in the CNS not regenerate?

Poor cleanup by microglia, no neurilemma to form a regeneration tube, and presence of growth-inhibiting proteins that inhibit regeneration.

Why can myelinated axons in the PNS regenerate?

The neurilemma (of schwann cells) forms a regeneration tube that guides regeneration and immune cells clean up the damaged area.

Function of myelin sheath

Protect against physical damage, electrical insulation, prevent interference from neighboring axons, increase rate of impulse transmission

What two ions are responsible for establishing the resting membrane potential?

Sodium and potassium.

What is the RMP?

-70mV to -90mV

What causes the depolarization phase of an action potential?

An increase of sodium ions into the axon (sodium influx) that makes the membrane potential more positive

When does an action potential develop?

When the threshold is reached, -55mV

What happens during the repolarization phase of an action potential?

Sodium channels close and potassium channels open, causing potassium to rush out of the axon (=potassium efflux), making the membrane more negative

What causes hyperpolarization during an action potential?

More potassium efflux occurs, driving the membrane potential below the resting membrane potential and more negative

What restores the resting membrane potential?

The Na+/K+ pump.

How is action potential generation affected by a Na+ channel blocker?

If Na+ channels can’t open, depolarization cannot occur, threshold cannot be reached, and action potential cannot be generated (since it requires a Na+ influx)

What is the all-or-none phenomenon of action potentials?

An action potential will be generated if and only when depolarization reaches a threshold potential.

What is a nerve impulse?

A propagated action potential down the axon to the axon terminals.

What is the difference in frequency of action potentials between stronger and weaker stimuli?

A stronger stimulus generates impulses at a higher frequency than a weaker stimulus.

What is the absolute refractory period of an action potential?

The time from the opening of the Na+ activation gates until the closing of inactivation gates when a neuron cannot respond to another stimulus.

What phase of the action potential coincides with the absolute refractory period?

The depolarization phase.

What is the relative refractory period of an action potential?

Follows the absolute refractory period; only a strong stimulus can generate an action potential.

What phase of the action potential coincides with the relative refractory period?

The repolarization phase.

How can you differentiate between a strong and weak stimulus in terms of action potentials?

By the frequency of action potentials; a stronger stimulus results in a higher frequency.

What factors affect the rate of impulse transmission (conducting velocity)?

Diameter of the axon and degree of myelination.

How does the diameter of the axon affect impulse transmission?

Larger axons transmit impulses faster than smaller axons due to less resistance.

How does myelination affect impulse transmission?

Myelinated axons transmit impulses faster than unmyelinated axons.

What is saltatory conduction and what axons use it?

A process where action potentials are generated only at the nodes of Ranvier, allowing impulses to 'jump' from node to node. Used my myelinated axons.

What is continuous conduction and what axons use it?

A process where action potentials develop stepwise across the entire axolemma. Used in unmyelinated axons.

What are the three structural classes of neurons?

Pseudounipolar, bipolar, and multipolar.

What are neurons?

Conducting cells that generate electrical signals

What are supporting cells (neuroglia)?

Non-conducting cells that do not generate electrical signals, but support neurons

What are the structural classes of neurons based on?

The number of processes that extend from the cell body

Which structural class of neurons is most abundant?

Multipolar neurons.

What are the characteristics of pseudounipolar neurons?

Only one short process extends from the cell body, splitting into a central and peripheral process.

Where are pseudounipolar neurons primarily found?

They are most of the body's sensory neurons.

What are the characteristics of bipolar neurons?

Two processes extend from the cell body (one axon and one dendrite)

What structural neurons are rare in the body?

Bipolar neurons

Where are bipolar neurons found?

Only in sensory epithelia like the ear and eye.

What are the characteristics of multipolar neurons?

At least three processes extend from the cell body; one axon and at least two dendrites.

What are multipolar neurons found as?

Motor and interneurons

What are the three functional classes of neurons?

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

What do sensory (afferent) neurons do?

Take messages/impulses from sensory receptors towards the CNS

What do motor (efferent) neurons do?

Take impulses away from the CNS to effector organs (glands, organs, muscles)

Where are interneurons located?

Within the CNS.

What are the functional classes of neurons based on?

Where the neurons are sending information

Which functional class of neurons is most abundant?

Interneurons.

What are the three types of nerve fibers?

Group A, Group B, and Group C fibers.

What are the three types of nerve fibers based on?

Diameter and degree of myelination

What are the characteristics of Group A fibers?

Largest diameter, heavily myelinated, transmit impulses at 150 m/s.

Motor neurons that innervate skeletal muscles are an example of what group of nerve fibers?

Group A

What are the characteristics of Group B fibers?

Intermediate diameter, lightly myelinated with wider gaps of nodes of ranvier, transmit impulses at 15 m/s.

What are the characteristics of Group C fibers?

Smallest diameter, unmyelinated, transmit impulses at 1 m/s.

Which type of nerve fiber has the fastest conduction velocity?

Group A fibers because they have the largest diameter and heavy myelination.

Which type of nerve fiber has the slowest conduction velocity?

Group C fibers because they have the smallest diameter and are not myelinated.

Why is the conduction velocity faster in a large, heavily myelinated axon vs. a smaller axon?

Myelinated axons use saltory conduction where impulses can jump from node to node, and larger axons have larger diameter which means less resistance

What happens to conduction velocity when myelinated axons become demyelinated?

Conduction velocity slows, and saltatory conduction is replaced by slow continuous conduction which results in slow impulse transmission

What are the four structures protecting the brain?

Blood-brain barrier, cranium, cerebrospinal fluid (CSF), and meninges.

What is the significance of the blood-brain barrier?

It is a selective chemical barrier that prevents harmful substances in the blood from crossing to the neurons in the brain.

What supporting cells are involved in the formation of the blood-brain barrier?

Astrocytes (CNS)

What are the three types of meninges?

Pia mater, arachnoid mater, and dura mater.

List the 3 meninges in order from deep to superficial

Pia mater, subarachnoid mater, dura mater

Which meninx is double-layered?

Dura mater. Made of the meningeal layer and superficial periosteal layer

Where is cerebrospinal fluid (CSF) located outside the brain?

In the subarachnoid space.

Where is CSF located inside the brain?

In the 2 lateral ventricles, third ventricle, and fourth ventricle.

Where is the subarachnoid space located?

Between the arachnoid mater and the underlying pia mater

What connects the two lateral ventricles to the third ventricle?

The interventricular foramen.

What connects the 2 lateral ventricles to each other?

The septum pellucidum

Where is the third ventricle located?

In the diencephalon.

What connects the third ventricle (above) to the fourth ventricle (below)?

The cerebral aqueduct.