Chapter 10

The Central Nervous System (CNS)

the nervous system is divided into a CNS that includes the brain and spinal cord

Nerve Impulse

this occurs as a sequence of depolarization that continues from the beginning of the axon to the end

Repolarization

voltage regulated sodium channels will open when depolarization of the membrane brings the membranes potential to -55 mb. They will stay open until membrane potential reaches +30mv

Then the sodium channels

will close and the voltage regulated potassium channels will open, allowing the outflow of potassium ions which will help to re-polarize the membrane.

Chemically regulated ion channels

will open and close due to binding of specific chemicals called neurotransmitters

Voltage regulated ion channels

will open and close due to changes in the voltage at the membrane. The distribution of ions at the membrane.

Third

After processing the information, an action may be taken by the motor division.

Nerve Fiber Regeneration

An injury to the cell body of a neuron usually causes death to the entire fiber, and no regeneration will occur, but an injured nerve fiber may regenerate.

refractory period

For a very short period of time, a threshold stimulus will not trigger another action potential.

Two other important neurotransmitters that have the structure form of amino acids

GABA (gamma-aminobutyric acid), and Glutamate. GABA has an inhibitory effect in the CNS and glutamate has an excitatory effect in the CNS.

Classification of Neurons by Function

Motor neurons, Sensory Neurons, Interneurons.

Neurotransmitters

Neurotransmitters are chemicals that are secreted from the axon terminal into the synaptic cleft.

Ion Channels

allow specific ions to move from one side of a membrane to the other. There are two main types of ion channels that allow action potentials to occur in neurons.

Acetylcholine

also acts in the sympathetic and parasympathetic divisions of the autonomic nervous system.

Second

an information processing part decides what to do with the information.

Peripheral Nervous System (PNS)

and a PNS includes the cranial and spinal nerves. The PNS has a sensory division and a motor division.

Some Sodium Channels

are chemically regulated and some are voltage regulated

Interneurons

are found within the central nervous system. Interneurons are classified structurally as multipolar neurons.

The cell bodies of some unipolar neurons

are localized in collections of nervous tissue called ganglia; ganglia. They are located outside the brain and spinal cord. Outside the central nervous system.

Neurons

are specialized to react to changes in their environment. There are three main parts of the neuron.

Graded potentials

are temporary and variable. Graded potentials may lead to action potentials, if they are big enough but the membrane must first reach threshold potential.

Sodium ions

are the major extracellular positive ions.

Potassium ions

are the major intracellular positive ions.

Neural Tissue

consists of two cell types Neurons, and Neuroglia

The central process of a unipolar neuron

contains the axon terminals

The peripheral process of a unipolar neuron

contains the dendrites

An inhibitory postsynaptic potential (IPSP)

is a graded potential that hyperpolarizes the membrane and makes it less likely that the membrane will be depolarized to threshold, leading to an action potential. This is called inhibition.

Astrocyte

neuroglial cell that connects neurons to blood vessels and maintains the blood-brain barrier

Oligodendrocyte

neuroglial cell that forms myelin in the CNS

Ependymal cell

neuroglial cell that lines the ventricles of the brain and cover the capillaries of the choroid plexus, aiding in the formation of cerebrospinal fluid

Satellite Cell

neuroglial cell that supports functioning of neuron cell bodies in ganglia

Microglial cell

neuroglial cell that supports neurons and is phagocytic

Schwann Cell

neuroglial cell that surrounds a fiber of a peripheral nerve, forming the neurilemma and myelin

Temporal summation

occurs when the cumulative effect of multiple action potentials, arriving one after another, change the membrane potential.

Spatial summation

occurs when the cumulative effect of multiple actions potentials arriving at different locations at the same time change the membrane potential to threshold.

the processing

or decision-making part takes place at the synapse

as the voltage regulated sodium ion open

other voltage regulated ion channels farther down the axon will open due to depolarization of the adjacent membrane

The remaining Schwann cells

proliferate and surround the new axon with myelin. If a sprout grows into the remaining basement membranes of the original tract, the new fiber may rejoin with its original connection.

Convergence

results from more than one neuron bringing nervous impulses to a single neuron, the result being summation of impulses.

Divergence

results from one neuron bringing a nervous impulse to more than one postsynaptic neuron, the result being amplification of the single impulse to many effectors.

facilitation

EPSP is due to a decrease in the net positive charge on the outside of the postsynaptic cell in comparison to the inside (facilitation)

The Nervous System Has 3 Basic Functions

First, the sensory part collects information.

a neural pool

Groups of neurons that synapse with each other to perform a particular task are part of what is called a neural pool.

hyperpolarized

If the resting potential becomes more negative, such as -85 mV, the cell membrane potential is said to be hyperpolarized. This is due to an increase in the net positive charge on the outside of the cell in comparison to the inside.

Postsynaptic Potentials

If the stimulus at a synapse causes the resting potential of the postsynaptic cell to become less negative, the cell is said to be depolarizing.

hyperpolarizing

If the stimulus at a synapse causes the resting potential of the postsynaptic cell to become more negative. This is due to an increase in the net positive charge on the outside of the postsynaptic cell in comparison to the inside.

depolarizing

If the stimulus causes the resting potential to become less negative, the cell is said to be depolarizing. The cell membrane depolarizes when a neurotransmitter binds to the chemically regulated ion channel and causes it to open, allowing sodium ions to move into the cell.

membrane resting potential

It is measured by a voltmeter at -70 mv

Neuroglia

Neuroglia are support cells within the nervous system. There are four main types of neuroglia found in the CN

There are two main types of neuroglia found in the PNS

Satellite Cells, and Schwann Cells

Two main types of positively charged ions

Sodium Ions, and Potassium Ions

Membrane Potential

The resting potential, is the difference between the charge inside and the charge outside of the cell's membrane.

Threshold Potential

Threshold potential (usually about -55mV) is the level of membrane potential where an action potential will occur in the trigger zone of an axon.

Dopamine and serotonin

are two other important biogenic amines.

All potassium channels

are voltage regulated

The other cell may

be another neuron or a muscle fiber (neuromuscular junction) or a glandular cell (neuroglandular junction).

Norepinephrine

belongs to an important class of neurotransmitters called biogenic amines. These chemicals are derived from amino acids.

Sensory Neurons

bring nerve impulses from peripheral parts of the body to the brain and spinal cord, the central nervous system. Most sensory neurons are unipolar, some specialized ones, found in the ears, eyes, and nose are bipolar.

Motor neurons

carry nerve impulses away from the central nervous system to the effectors. The effectors are muscles and glands. Motor neurons are multipolar neurons.

grades potentials

caused by the binding of a neurotransmitters to ion channels and to the subsequent temporary opening of the chemically regulated gates may hangs the voltage across the membrane enough to trigger the action potential

Opening the chemically regulated sodium ion channels

causes a localized depolarization of the membrane, where the voltage potential may move from -70mV to -65mV. These localized changes in the membrane potential are not an action potential. Instead, they are called graded potentials.

Sensory information

comes in for processing

An ATP driven ion pump

establishes an ion gradient, where the concentration of sodium ion is higher outside the cell, and the concentration of potassium ions is higher inside the cell. This ion gradient creates what is called a membrane potential, and it is measured in millivolts.

Motor Information

goes out to initiate actions to be taken

The outside of the membrane

has a net positive charge and the interior has a net negative charge.

Serotonin

has many functions. It helps induce sleepiness, and some antidepressant drugs work by increasing its concentration in synapses.

Multipolar neurons

have one axon, and many dendrites connected to the cell body, hence the name multipolar. Most neurons within the central nervous system are multipolar neurons.

Bipolar Neurons

have one process that is an axon and one process that is a dendrite.

Unipolar neurons

have the cell body connected by a single process to a long axon that is divided into a peripheral process and a central process.

action potential

in response to a threshold potential an action potential will occur at a specific site at the beginning of the axon

Bipolar neurons are found

in specialized parts of the eyes, nose, and ears.

Neurons and neural pools

interact in ways that use both excitatory and inhibitory post synaptic potentials to process information and make decisions.

Summation

involves the combined effects of more than one postsynaptic potential.

excitatory postsynaptic potential (EPSP)

is a graded potential that depolarizes the membrane and makes it more likely that the membrane will be depolarized further, eventually to threshold leading to an action potential

a nerve pulse

is an action potential in a neuron cell membrane

the action potential, or nerve impulse

is an all-or-none response, and it does not vary in strength. the information coming from a single neuron is only an "on" or "off" signal.

The Motor Division

is divided into the Somatic Motor System and the Autonomic Nervous system. Information flows in only one direction in each system.

The trigger zone

is found in the axon hillock

Dopamine

is linked with a sense of well-being. Its deficiency is also linked with Parkinson's disease.

The resting membrane potential

is maintained by active transport of sodium ions out of the cell and potassium ions into the cell

Norepinephrine

is neurotransmitter that also acts in the autonomic nervous system, but it only acts in part of the sympathetic division of the autonomic nervous system.

If the axon of a peripheral nerve

is severed from the cell body, the distal portion will deteriorate and the fragments will be removed by macrophages. The proximal end will then develop new sprouts, and nerve growth factors from surrounding neuroglia cause the sprouts to grow.

acetylcholine

is the best known neurotransmitter, and this is the same neurotransmitter released at the neuromuscular junction, causing the muscle impulse that leads to contraction of skeletal muscle tissue

A presynaptic neuron

is the first of two neurons in a series, and it is the one that is transmitting an impulse. It is located before the synapse.

Axon

is the part of the neuron that carries out-going nerve impulses

Cell Body

is the part of the neuron that contains the nucleus

Dendrites

is the part of the neuron that receives in-coming signals

A postsynaptic neuron

is the second of two neurons and it is the one that is transmitting an impulse. It is located after the synapse.

Synapses

is the site of communication between a nerve and another cell.

Regeneration in the CNS

is unlikely due to the presence of a more complicated structure involving more neurons, the formation of scar tissue, and the release of inhibitory chemicals produced by the astrocytes.

when at action potential occurs at the trigger zone of an axon

it depolarizers the adjacent membrane

The binding of the neurotransmitter to the receptor

may cause a nerve impulse in another neuron, or may cause a muscle impulse that stimulates a muscle fiber to contract.

the action potential

moves like a wave of spreading depolarization farther and farther down the axon away from the cell body and toward the axon terminal