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.