Human A&P 2 Unit I: Fundamentals of the Nervous System and Nervous Tissue

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What does the nervous system do?

The nervous system, along with the endocrine system, helps control and integrate all body activities.

What are the three basic functions of the nervous system?

1. Sensing changes (Sensory)
2. Interpreting those changes (Integrative)
3. Reacting to those changes (motor)

What is neurology?

The branch of the medical science that deals with the normal functioning and disorders of the nervous system.

What are the two divisions of the nervous system?

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

What does the central nervous system consist of?

The brain and spinal cord.

What does the peripheral nervous system consist of?

The cranial and spinal nerves.

What are the two componenets of the peripheral nervous system?

The sensory (afferent) system and the motor (efferent) system.

What is the sensory (afferent) system? And what does it do?

A variety of different receptors as well as sensory neurons.
It conducts nerve impulses to the central nervous system

What is the motor (efferent) system? And what does it do?

Conducts nerve impulses from the Central Nervous System to muscles and glands.

What are the two subdivisions of the Peripheral Nervous System?

Somatic and Autonomic

Is the somatic division of the PNS voluntary or involuntary?

Voluntary.

Is the autonomic division of the PNS voluntary or involuntary?

Involuntary.

What is the somatic division of the PNS?

Consists of neurons that conduct impulses from cutaneous (skin) and special sense receptors to the CNS, and motor neurons that conduct impulses from the CNS to skeletal muscle tissue.

What is the autonomic divison of the PNS?

Contains sensory neurons from visceral organs and motor neurons that convey impulses from the CNS to smooth muscle tisse, cardiac muscle tissue, and glands.

What is a neuroglia?

Specialized cells that assist the neurons.

Also called glia

What do neuroglia include?

1. Astrocytes
2. Oligodendrocytes
3. Microglia
4. Ependymal cells
5. Schwann cells
6. Satellite cells

Where are astrocytes located?

In the Central Nervous System

What do astrocytes do?

-They anchor neurons to capillaries
-Help control blood component exchange between the capillaries and the neurons
-Help to recapture neurotransmitters

What types of neuroglia make up the blood brain barrier?

Astrocytes

What do oligodendrocytes do?

-Wrap their cytoplasmic extensions around nerve processes

What are the cytoplasmic extensions of oligodendrocytes called?

Myelin Sheaths

What are microglia?

Macrophages that engluf microorganisms and dead neural tissue.

What do ependymal cells do?

Form a permeable region for exchange between the neurons and the cerebral spinal fluid.

Where are ependymal cells located?

The line the ventricles of the brain and the central canal of the spinal cord.

What is on the surface of ependymal cells?

Cilia to circulate the cerbral spinal fluid.

What do Schwann cells do?

Wrap their cytoplasmic extensions around nerve cell processes and act as phagocytes that engulf microorganisms and dead neural tissue.

What is another name for Schwann cells?

Neurolemmocytes

What do satellite cells do?

Play a role in controlling the chemical environment of the neurons.

Are neurons mitotic or amitotic?

Amitotic- no cell division

Do neurons have a high or low metabolic rate?

High metabolic rate.

What are the three parts of a neuron?

1. Soma (cell body)
2. Dendrite(s)
3. An axon

What do the dendrites do?

They conduct impulses from receptors or other neurons to the cell body.

What does an axon do?

They conduct nerve impulses from the neuron to the dendrites or cell body or another neuron or to an effector organ of the body (muscle or gland).

What is a nerve fiber?

A general term for any neuronal process like the dendrite or axon.

Where does the action potential start?

In the dendrites.

Where does an action potential end?

The axon.

What is the bundles of neurons called in the Peripheral Nervous System?

Nerves

What is the bundles of neurons called in the Central Nervous System?

Tracts.

What are ganglia?

Nerve cell bodies in the Peripheral Nervous System that form encapsulated clusters.

What are Nissl bodies?

Ribosomes. They are involved in polypeptide (protein) synthesis.

What are the three different structures of a neuron?

1. Multipolar
2. Bipolar
3. Unipolar

What is a multipolar nueron?

Many dendrites and one axon

What is a bipolar neuron?

One dendrite and one axon

What is a unipolar neuron?

One fused process with the cell body off to the side of this one process.

What is the benefit of a unipolar neuron?

By not going through the cell body it speeds up the impulse.

How can neurons be classified on the basis of function?

1. Afferent (sensory)
2. Association (interneurons or connecting)
3. Efferent (motor)

What do afferent neurons do?

Conduct impulses from receptors to the Central Nervous System.

What type of neurons are afferent neurons?

Unipolar.

What do association neurons do?

Conduct impulses to other neurons.

What type of neurons are association neurons?

Multipolar

What do efferent neurons do?

Conduct impulses to effectors (mulscles or glands)

What type of neurons are efferent neurons?

Multipolar

What is white matter?

Aggregations of myelinated processes.

What is gray matter?

Nerve cell bodies, dendrites, and axon terminals or bundles of unmyleinated axons and neuroglia.

What are axon terminals?

Axon endings.

What is the shape of gray matter in the spinal cord?

H-shaped inner core surrounded by white matter.

What is the shape of gray matter in the brain?

A thin cortex (outer shell) of gray matter covers the cerebral hemispheres.

What is a nucleus?

A mass of nerve cell bodies and dendrites inside the Central Nervous System.

What is a ganglion?

A mass of nerve cell bodies inside the Peripheral Nervous System.

What are the two types of ion channels?

1. Leakage (nongated)
2. Gated

What type of ion channel always open?

Linkage (nongated) channels.

What type of ion channel opens and closes in response to a stimulus?

Gated channels

What are the four types of gated channels?

1. Voltage gated
2. Chemically gated
3. Mechanically gated
4. Light gated

What type of gated channel gives the cell excitability and causes an action potential?

Voltage-gated ion channels.

What types of gated channel causes a graded potential which may or may not lead to an action potential?

1. Chemically-gated
2. Mechanically-gated
3. Light-gated

When is a neuron more positive outside and more negative inside?

When the neuron is resting (nonconducting).

What are three reasons why there is more positive outside and more negative inside?

1. The distribution of different ions across the membrane.
2. The outside of the neuron at rest has more positive sodium ions present.
3. The inside of the neuron at rest has more negative ions and large negatively charged proteins.

What is an electrochemical gradiant?

Distribution of different ions.

What is on the outside of a resting neuron?

Positive sodium (Na+) ions

What is inside a resting neuron?

1. Negative ions
2. Negative sulphate (SO4-)
3. Large negatively charged proteins.

What is the value of a typical resting neuron?

-70mV

Is a resting neuron polarized or unpolarized?

Polarized.

What does the sodium-potassium pump do?

Compensates for slow leakage of Na+ into the cell by pumping it back out.

What are graded potentials?

Where different amounts of Na+ enter the neuron in response to different stimuli.

What are graded potentials produced by?

The opening and closing of gated channels in response to chemicals (including neurotransmitters) or physical changes.

What is depolarization?

Loss of polarization

What is hyperpolarization?

More polarized.

What is an action potential?

voltage-gated Na+ and K+ channels open in sequence once the membrane has reached the threshold voltage.

What is another name for action potential?

Nerve impulse

What is threshold voltage?

Achieved when a sufficient amount of positive sodium ions has been allowed to enter the dendrite(s) by the various gated channels.

How does the action potential travel?

In a wave. As sodium enters, this triggers the adjacent sodium gates to open.

What happens after an action potential?

-Depolarization then the reversal of the membrane polarization at the current area of the membrane (-70 mV to 0 to +30mV)

-Repolarization, the recovery of the resting membrane potential ( +30mV to -70mV) occurs due to sodium-potassium pumps.

What is the absolute refractory period?

Another impulse cannot be generated at all

What is the relative refractory period?

Can be triggered only by a suprothreshold stimulus.

What is the all-or-none proncipal?

If a stimulus is strong enough to generate an action potential, the impulse travels at a constant and maximum strength for the existing conditions.

Can a stronger stimulus cause a larger impulse?

No, a stronger stimulus will NOT cause a larger impulse.

Is the propogation speed of a nerve impulse related to the stimulus strength?

No the propogation speed is NOT related to the stimulus strength.

Which conduct impulses faster, large-diameter fibers or small-diamter fibers?

Large-diameter fibers conduct impulses faster than those with small diameters.

Which conduct impulses faster, myelinated fibers or unmylinated fibers?

Myelinated fibers conduct impulses faster than unmyelinated fibers.

Why do myelinated fibers conduct impulses faster?

The action potential jumps between areas of myelin.

What are the areas of seperated myelin called?

Nodes.

What is saltatory conduction?

When the action potential jumps from node to node.

How is the intensity of a stimulus coded?

In the rate of impulse production.
-The frequency (number per second) of action potentials traveling along the neuron.

How does transfer information at a chemical synapse?

From a presynaptic neuron to a postsynaptic neuron.

What is an excitatory neurotransmitter?

A nuerotransmitter that can depolarize the postsynaptic neuron's membrane, bringing the membrane potential closer to threshold.

What an excitatory postsynpatic potential (EPSP)?

A depolarizing postsynaptic potential.

Can a single excitatory postsynpatic potential (EPSP) initiate a nerve impulse?

No but the postsynpatic neuron does become more excitable.

What is summation?

The effect when one excitatory postsynaptic potential causes the neuron to become more excitable so when the next EPSP occurs the neuron is more likely to reach threshold.

What does an inhibitory neurotransmitter do?

Hyperpolarizes the membrane of the postsynaptic neuron (making the inside more negative) and generation of a nerve impulse more difficult.

What is an inhibitory postsynaptic potential (IPSP)?

A hyperpolarizing postsynpatic potential that is inhibitory.

What happens to the threshold when the inhibitory postsynpatic potential (IPSP) occurs?

The membrane potential becomes further away from the threshold voltage.

What are the three ways that a neurotransmitter is removed from the synaptic cleft?

1. Diffusion
2. Enzymatic degradation
3. Uptake into cells (nuerons and glia)

Can the quantity of neurotransmitter released by modified? If so, by what?

Yes, certain synapses can modify the quantity of neurotransmitter released at other synapses.

What is presynaptic facilitation?

Increases the amount of neurotransmitter released by a presynaptic neuron.

What is presynaptic inhibition?

Decreases the amount of neurotransmitter released by a presynaptic neuron.

What may be important in learning and memory?

Presynaptic facilitation and inhibition.

What happens if several presynaptic end bulbs release their neurotransmitter at about the same time?

The combined effect may generate a nerve impulse due to summation.

What are the two different types of summation?

1. Spatial
2. Temporal

What is spatial summation?

How many excitatory vs. inhibitory neurons are present

What is temporal summation?

How frequently are the neurons conducting action potentials and releasing neurotransmitters

What is special about a postsynaptic neuron?

It is an integrator.
-It receives and integrates signals and then responds by conducting an action potential or not.

What type of neurotransmitters are present in both the Central Nervous System and the Peripheral Nervous System?

Excitatory and inhibitory neurotransmitters.

Does the same neurotransmitter have the same effect in the Central Nervous System and the Peripheral Nervous System?

No, the neurotransmitter can be excitatory in some locations and inhibitroy in others.

What determines whether or not a neurotransmitter is excitatory or inhibitory?

The gate at which the neurtransmitter binds determines whether or not the neurtransmitter is excitatory or inhibitory.

What are the four types of neurotransmitters?

1. Acetylcholine
2. Biogenic amines
3. Amino acids
4. Peptides

What does a neuron's chemical and physical environment influence?

It influences both the impulse conduction and synaptic transmission.

What are neuronal pools?

Neurons in the Central Nervous System that are organized into dendrite patterns.

Are all neuronal pools the same?

No, each pool differs from all others and has its own role in regulating homeostasis.

How many neurons can a single neuronal pool contain?

Thousands to millions of neurons.

How are neuronal pools organized?

Into circuits.

After how long does the neuronal cell body lose its mitotic apparatus?

Around 6 months of age

After the neuronal cell body loses its mitotic apparatus, can it divide?

No, after the neuronal cell body loses its mitotic apparatus it is no longer able to divide.

What happens if a neuron is damaged?

It is either permanently lost or in some types of neurons it can be repaired.

In what nervous system is a myelinated axon or dendrite more likely to be repaired in?

In the Peripheral Nervous System

What needs to be intact in order for the myelinated neuron to be repaired?

The cell body.
-Damage to myelinated axons and dendrites may be repaired if the cell body remains intact.

What is the cell that must remain active during the repair of damaged myelinated axons or dendrites

The Schwann cells that perform the myelination must remain active in order to help repair the damaged neuron.

What is Wallerian degeneration?

Degeneration of the distal portion of the neuronal process and myelin sheath.

In what nervous system is damage to a neuron usually permanent?

In the Central Nervous System damage to a neuron is usually permanent.

What are the steps to repair a damage neuron?

1. Wallerian Degeneration
-Degeneration of the distal portion of the neuronal
process and myelin sheath
2. Macrophages phagocytize the remains
3. The Schwann cells for a tube that appears to aid regeneration by directing the regrowing nerve fiber.

What does the Schwann cells do in order to aid in repair of damaged neurons?

Schwann cells make a tube that appears to aid in regeneration by directing the regrowing nerve fiber.

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