Nervous Tissue

Graded (local) potential

A small change away from the resting membrane potential in a specific region (generally small) of the neuron's plasma membrane

Multipolar Neurons

3 or more processes (numerous dendrites and 1 axon); most common (90%)

Speed of propagation: Temperature

AP's propagate faster at higher temps

Afferent Division

All of the incoming information and is often classified as sensory pathways

Efferent Division

All of the outgoing information and is often classified as motor pathways

Action Potentials

Allow communication over long distances within the body

Axon collaterals

Along the length of the axon are side branches that branch at right angles to the axon.

Enteric Nervous System

Associated with involuntary control of the gastrointestinal tract. Many of the neurons the ENS function independently of the ANS and CNS to some extent although they also communicate with the CNS via sympathetic and parasympathetic neurons.

Synaptic end bulbs

At the tips of some axon terminals there are bulb-shaped swellings

Motor/efferent neurons

Carry impulses away from the CNS to the effector organs (muscles/glands); multipolar; cell bodies located in the CNS

Satellite Cells

Cells that surround cell bodies in the PNS ganglia to support neurons in the PNS ganglia. They surround the cell bodies of neurons of PNS ganglia. They help regulate exchanges of materials between neuronal cell bodies and interstitial fluid.

Leakage (nongated) channels

Channels that randomly alternate between open and closed.

Endocrine System

Communicates by means of chemical messengers (hormones) secreted into the blood

Ependymal Cells

Cuboidal to columnar shaped cells containing microvilli and cilia. They form thin sheets that line fluid-filled cavities in the brain and spinal cord. Their function is to produce, possibly monitor, and assist in the circulation of cerebrospinal fluid.

Axons or Nerve Fibers

Cylindrical and relatively unbranched fibers that conduct the nerve signal to points remote from the cell body.

Interneurons/association neurons

Lie between motor and sensory neurons in neural pathway; both motor and sensory; involved with integration; found almost entirely in the CNS; Make up over 99% of the neurons in the body

Refractory period

During an action potential and for a few milliseconds after, it is difficult or impossible to stimulate that region of a neuron to fire again.

Nervous System

Employs electrical and chemical means to send messages very quickly from cell to cell

Neurons

Excitable cells that conduct the impulses that make possible all nervous system functions. They are the wiring of the body.

Propagation

For neurons to transmit signals, the transient depolarization and repolarization that occur during an action potential must from where they arise at the trigger zone of the axon to the axon terminals.

Microglia

Found only in the central nervous system can evoke an immune response in areas of infection, trauma or stroke. They function as phagocytes by removing cellular debris, microbes, and damaged nervous tissue.

Astrocytes

Found only in the central nervous system wrap themselves around blood capillaries. they contribute to the blood brain barrier. They pick up nutrients from the blood and pass it along to the delicate cells of the brain. They also support neurons due to their considerable strength.

Oligodendrocytes

Hold nerve fibers together and form a wrap of insulation around the fiber called a myelin sheath, a multilayered lipid and protein covering around some axons that insulates them and increases the speed of nerve impulse conduction.

Speed of propagation: amount of myelination

Myelinated axons propagate AP's more rapidly

White Matter

Myelinated fibers have many Schwann cells that form a thick myelin sheath. White in color is due to myelin sheath.

Neuroglia

Nonexcitable supporting cells of nervous tissue

Schwann Cells

Only found in the peripheral nervous system. These cells wrap themselves around a single nerve fiber creating several layers of fatty insulation again called a myelin sheath. The myelin sheath acts to protect the nerve fiber, electrically insulate fibers from one another, and to increase the speed of nerve impulse transmission.

Liquid-gated channels

Open and close in response to a specific chemical stimulus (neurotransmitters, hormones, and particular ions). This can lead to a neuron becoming excitable.

Voltage-gated channels

Open in response to a change in membrane potential (voltage). These are important for generation and conduction of action potentials.

Mechanically gated channels

Open or close in response to mechanical stimulation in the form of vibration (sound waves, touch, pressure, or tissue stretching), which can open the gate.

Neurilemma

Outside layer of the Schwann cells wrap. Is essential to the regeneration of injured nerve fibers. It contains the nucleus cytoplasm, and organelles of Schwann cells.

Sympathetic Division

Produces the "fight-or-flight" responses eg: increase heart rate, increase release of sugar from liver into blood

Parasympathetic Division

Produces the "rest-and-digest" responses eg: stimulate secretion of saliva or digestive enzymes into stomach

Dendrites

Resemble bare branches of tree that extend from the cell body. They are the primary site for receiving signals from the other neurons.

Unipolar Neurons

Single short process with cell body as an appendage off to the side of the axon; dendrites emerge from one of the terminal ends of the axon

Telodendria or Axon Terminals

Small branches located at the distal end of the axon that terminate as a synaptic knob

Continuous Conduction

Step-by-step depolarization and repolarization of each adjacent segment of the plasma membrane. This form of conduction occurs in unmyelinated axons and in muscle fibers

Synaptic Vesicles

Synaptic end bulbs contain many tiny membrane-enclosed sacs. These store chemicals known as neurotransmitters.

Axon Hillock

The axon extends from a tapered portion of the cell body. In most neurons, nerve impulses arise at the junction of the axon hillock and the initial segment known as the trigger zone.

Cell body or soma

The control center of the neuron. It contains a single nucleus and the cytoplasm contains mitochondria, lysosomes, a Golgi complex, rough ER (called Nissl bodies), and a cytoskeleton.

Resting membrane potential

The excessive negative charge in the cytosol of a resting (unstimulated) cell. At rest a neuron has a membrane potential of -70 mV

Nodes of Ranvier

The microscopic gap between each Schwann cell. Here, nerve impulses jump from one node to the next in a process called salutatory conduction due to these areas being uninsulated portions of the axon.

Bipolar Neurons

The most rare neurons (only found as specialized sensory neurons in eye, ear, olfactory organs); Contain 2 processes (1 dendrite and 1 axon)

Synapse

The place where signals are transmitted from one neuron, called the presynaptic neuron, to another neuron/cell, called postsynaptic neuron/cell.

Sensory/ afferent neurons

Transmit impulses from sensory receptors toward or into the CNS; almost all sensory neurons are unipolar; found in the sensory ganglia outside of the CNS

Gray Matter

Unmyelinated fibers contain very little to no myelin sheath. Contains either neuron cell bodies, dendrites, and axon terminals or bundles of unmyelinated axons and neuroglia. Gray in color due to the absence of myelin.

Grades Potentials

Used for short distance communication only

Depolarizing graded potential

When the response makes the membrane less polarized (less negative inside)

Hyperpolarizing graded potential

When the response makes the membrane more polarized (more negative inside)

Saltatory conduction

a special mode of action potential propagation that occurs along myelinated axons. This type of propagation involves an AP "leaping" from a node of Ranvier to the next node of Ranvier. Saltatory conduction propagation is much more rapid than continuous conduction.

Autonomic Nervous System

associated with involuntary control and carries information to the autonomic effectors (cardiac and smooth muscle; glands; adipose and other tissues)

Somatic Nervous System

associated with voluntary control and carries information to and from skeletal muscle

Nerve fiber

general term for any neuronal process that emerges from the cell body of a neuron

Speed of propagation: Axon diameter

larger-diameter axons propagate AP's more rapidly

Absolute refractory period

last from the start of the action potential until the membrane returns to the resting membrane potential (does not include hyperpolarization phase). No stimulus of any strength will trigger a new action potential during this time.

Relative refractory period

lasts until hyperpolarization ends. During this period it is possible to trigger a new action potential, but only with an unusually strong stimulus.