Chapter 12 Nervous Tissue

Neuron

a nerve cell; a specialized cell transmitting nerve impulses.

Cell body (soma/ perikaryon)

houses the nucleus with nucleoli surrounded by cytoplasm

Nucleoplasm

viscous fluid inside the nucleus; enclosed by the nuclear envelope

Neuroplasm

cytoplasm of neuron

Neurolemma (neurilemma, Schwann's Sheath)

The outermost nucleated cytoplasmic layer of Schwann cells that forms the outermost layer of the nerve fiber in the PNS.

Nissl bodies

RER in neurons; site of protein synthesis, give a gray color to neuron cell bodies; accounts for the gray color in gray matter

axoplasm

cytoplasm of axon

Axolemma

plasma membrane of axon

Dendrites

Branchlike parts of a neuron that are specialized to receive information.

Axons

a part of a neuron that carries impulses away from the cell body

Nerve fiber

axon of a neuron

Tracts

bundles of axons in the CNS

Axon collateral

a branch of an axon from a single neuron

Terminal branches

The branched end of the axon that contains neurotransmitters.

Conducting region

Plasma membrane exhibits voltage-gated Na+ and K+ channels; the axon of the neuron

Secretory region

Axon terminals release neurotransmitters.

Sensory input

Information gathered by sensory receptors about internal and external changes; any electrical impulse sent from the sensory organs to the central nervous system

Integration

nervous system function that combines sensory perceptions and higher cognitive functions (memories, learning, emotion, etc.) to produce a response

Motor output

Activation of effector organs (muscles and glands) produces a response

Central Nervous System (CNS)

brain and spinal cord

Peripheral Nervous system (PNS)

the sensory and motor neurons that connect the central nervous system (CNS) to the rest of the body.

Sensory (afferent) division

Division of the PNS that carries impulses/information to the CNS; consists of both somatic and visceral sensory nerve fibers that conducts impulses from sensory receptors to the CNS

Motor (efferent) division

-motor nerve fibers
-conducts impulses from the CNS to effectors (muscles and glands)

Somatic nervous system

the division of the peripheral nervous system that controls the body's skeletal muscles

Autonomic nervous system

A subdivision of the peripheral nervous system. Controls involuntary activity of visceral muscles and internal organs and glands.

Sympathetic division

The part of the autonomic nervous system that sends messages to internal organs and glands that help us respond to stressful and emergency situations. Fight of Flight division of the nervous system.

Parasympathetic division

Part of the ANS that restores the body to normal functioning after arousal and is responsible for the day-to-day functioning of the organs and glands. Rest and Digest division of the nervous system.

Neuroglia (in CNS)

astrocytes, oligodendrocytes, microglia, ependymal cells

Astrocytes

Provide structural and metabolic support for neurons. Form blood brain barrier.

Microglial cells

extremely small glial cells that remove (phagocytose) cellular debris from injured or dead cells as well remove bacterial or other foreign cells.

Ependymal cells

produce and circulate cerebrospinal fluid

Oligodendrocytes

Type of glial cell in the CNS that wrap axons in a myelin sheath.

Neuroglia (in PNS)

Schwann cells and satellite cells

Satellite cells

surround neuron cell bodies in PNS

Schwann cells

Type of glia in the PNS, Supporting cells of the peripheral nervous system responsible for the formation of myelin.

Nuclei (CNS- cluster of cell body)

Clusters of neuronal cell bodies inside the CNS

Ganglia (PNS)

Clusters of neuronal cell bodies outside CNS

Anterograde movement

movement along the axon away from the cell body

Retrograde movement

movement along the axon toward the cell body

Myelin Sheath

covers the axon of some neurons and helps speed neural impulses

Myelinated fibers

segmented sheath surrounds most long or large-diameter axons

Unmyelinated fibers

axon with myelin that conduct nerve impulses slowly

Dynein

motor proteins involved in retrograde transport using ATP

Kinesin

motor proteins in anterograde transport using ATP

Nodes of Ranvier

Gaps in the myelin sheath between adjacent Schwann cells, to which voltage-gated sodium channels are confined.

saltatory conduction (propagation)

Rapid transmission of a nerve impulse along an axon, resulting from the action potential jumping from one node of Ranvier to another, skipping the myelin-sheathed regions of membrane.

Multipolar Neurons

neuron with one axon and many dendrites; most common type of neuron

Bipolar neurons

A neuron that has only two projections (one axon/one dendrite) from the cell body

Unipolar neurons

neurons with just one process extending from the cell body; are always sensory neurons

Peripheral process

Axon "before" sensory neuron's cell body; myelinated or unmyelinated; axon branch that has dendritic branches at tip

Central process

Sensory neuron axon branch that extends into CNS, ends in synaptic end bulbs

Sensory or afferent neurons

neurons that carry incoming information from the sense receptors to the central nervous system

Motor or efferent neurons

neurons that carry messages from the spinal cord or brain to the muscles and glands

Interneurons/ association neurons

found in neural pathways in the CNS, connect sensory and motor neurons

Protein channels

a protein that allows the transport of specific substances across a cell membrane

Leakage channels

channels that are always open

Chemically gated channels/ ligand-gated channels

open when a ligand binds to a receptor on the channel to allow ions to move down their concentration gradients

Voltage-gated channels

open and close in response to changes in membrane potential

Mechanically gated channels

Open and close in response to physical deformation of receptors; Found in sensory receptors (touch, pressure, vibration)

Electrochemical gradient

The diffusion gradient of an ion, which is affected by both the concentration difference of an ion across a membrane (a chemical force) and the ion's tendency to move relative to the membrane potential (an electrical force).

Concentration gradient

A difference in the concentration of a substance across a membrane.

Electrical gradient

difference in electrical charges between the inside and outside of the cell

Resting membrane potential

An electrical potential established across the plasma membrane of all cells by the Na+/K+ ATPase and the K+ leak channels. In most cells, the resting membrane potential is approximately -70 mV with respect to the outside of the cell.

Graded potentials

small changes in membrane potential that by themselves are insufficient to trigger an action potential

Receptor Potential

An initial response of a receptor cell to a stimulus, consisting of a change in voltage across the receptor membrane proportional to the stimulus strength. These receptor potentials are graded potentials and occur in a receptor cell that is not a neuron. The receptor cell releases chemical transmitters to stimulate a sensory neuron.

Generator Potential

A local change in the resting potential of a receptor cell in response to stimuli, which may initiate an action potential

Postsynaptic potential

the change in the membrane potential of a neuron that has received stimulation from a neuron

Action potentials

the change in electrical potential associated with the passage of an impulse along the membrane of a muscle cell or nerve cell.

Nerve impulse

el

Sodium-potassium Pump

a carrier protein that uses ATP to actively transport 3 sodium ions out of a cell and 2 potassium ions into the cell

Resting state

the state in which a neuron is not being stimulated and there is a negative electrical charge of about -70 millivolts within a neuron

Depolarization

The process during the action potential when sodium is rushing into the cell causing the interior to become more positive.

Threshold

the level of stimulation required to trigger a neural impulse

Repolarization

Period during which potassium ions diffuse out of the neuron

Hyperpolarization

membrane potential becomes more negative than resting potential due to potassium ions leaving the cell prior to re-establishing resting membrane potential

Refractory period

the time following an action potential during which a new action potential cannot be initiated

Absolute refractory period

time during which another action potential is impossible; limits maximal firing rate

Relative refractory period

A period after firing when a neuron is returning to its normal polarized state and will fire again only if the incoming message is much stronger than usual

Conduction Velocity

the speed at which an action potential is propagated along the length of an axon

Axon diameter

Larger-diameter fibers have less resistance to local current flow, so have faster impulse conduction

Degree of myelination

continuous conduction in nonmyelinated axons is slower than saltatory conduction in myelinated axons

Continuous Conduction

the step-by-step depolarization and repolarization of each adjacent segment of the plasma membrane

Synapse

gap between two neurons or between a neuron and the effector cell

Presynaptic neuron

conducts impulses toward the synapse

Postsynaptic neuron

the cell that receives the signal

Axodendritic synapses

synapses between the axon endings of one neuron and the dendrites of other neurons

Axosomatic synapses

synapses between axon endings of one neuron and cell bodies of other neurons

Synaptic delay

the brief delay between the arrival of an action potential at the axon terminal and the creation of a postsynaptic potential

Electrical synapses

gap junctions that allow an ionic current to flow between adjacent cells

Chemical synapses

Synapses that transmit information via the secretion of chemical signals (neurotransmitters).

Neurotransmitters

chemicals that transmit information across the synapse to a receiving neuron's dendrites

Excitatory Postsynaptic potentials (EPSPs)

depolarizations that bring the membrane potential toward threshold

Inhibitory Synapses (IPSPs)

Neurotransmitter binds to and opens channels for K+ or Cl-
Causes a hyperpolarization (the inner surface of membrane becomes more negative)
Reduces the postsynaptic neuron's ability to produce an action potential

Neural integration

the process by which inhibitory and excitatory postsynaptic potentials summate and control the rate of firing of a neuron

No summation

2 stimuli separated in time cause EPSPs that do not add together

Temporal Summation

A phenomenon of neural integration in which the membrane potential of the postsynaptic cell in a chemical synapse is determined by the combined effect of EPSPs or IPSPs produced in rapid succession.

Spatial Summation

Integration by a postsynaptic neuron of inputs (EPSPs and IPSPs) from multiple sources.

Synaptic potentiation

Repeated use of synapse increases ability of presynaptic cell to excite postsynaptic neuron

Long-term potentiation

an increase in a synapse's firing potential after brief, rapid stimulation. Believed to be a neural basis for learning and memory.

Acetylcholine

neurotransmitter chemical released at the ends of nerve cells