Chapter 12

Dendrites

the receiving or init portions of a neuron, the plasma membranes of dendrites contain numerous receptor sites for binding chemical messengers from other cells

Synapse

the site of communication between a neuron and effector cell

Multipolar Neuron

usually have several dendrites and one axon. Most neurons in the brain and spinal cord are of this type as well as motor neurons

Depolarizing Graded Potential

when the response makes the membrane less polarized, inside is less negative

Hyperpolarizing Graded Potential

when the response makes the membrane more polarized, inside is more negative

Hyperpolarization

An increase in the membrane potential that decreases the possibility of generating a nerve impulse.

integrative

Analyze incoming sensory information, store some aspects, and make decisions regarding appropriate behaviors

Tight Junctions

Connection with little space between plasma membrane and small intercellular space; Prevents leakage of organ to outside tissue; ET has cell junctions

Excitatory Postsynaptic Potential

Depolarizing, results in the opening of ligand gated Na+ channels, postsynaptic cell is more likely to reach threshold

Oligodendrocytes

Form myelin sheath in CNS

Inhibitory Postsynaptic Potential

NT causes hyper polarization of the post synaptic membrane resulting in the opening of ligand gated CL- or K+ channels causing the postsynaptic cell to become more negative (Hyperpolarized)

Saltatory Conduction

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.

Neurolemma

Schwann cell cytoplasm & nucleus for the outermost layer, inner portion being the myelin sheath

Synaptic Cleft

Small gap between the presynaptic and postsynaptic membranes of a synapse.

Graded potential is detrimental

The mode of travel by which graded potentials die out as they spread along the membrane is known as decremental conduction

Motor (Efferent) Neurons

Transmit nerve impulses from the brain and spinal cord to effector sites

Neurotransmitters

a chemical that when released excites or inhibits other neurons, muscle fibers or glands

Summation

if several presynaptic end bulbs release their neurotransmitter at about the same time, the combined effect may generate a nerve impulse

Enteric Nervous System

involuntary, consists of over 100 million neurons in enteric plexuses that extend most of the length of the gastrointestinal tract. Many of these neurons function independently, govern contraction

gap junction

neuron to neuron; chemical and electrical messages; nerve/muscle cell-smooth muscle GI tract, cardiac, neuron; CNS

Ligand Gated Channels

opens and closes in response to the binding of a ligand stimulus

Volted Gated Channels

opens in response to a change in membrane potential, participate in the generation and conduction of action potentials in the axons of all types of neurons

Mechanically Gated Channels

opens or closes in response too mechanical stimulation in the form of vibration, touch, pressure, or tissue stretching. The force distorts the channel from its resting position, opening the gate.

Axon

propagates nerve impulses toward another neuron, a muscle fiber, or a gland cell. Long, thin, cylindrical projection that often jots to the cell body at a cone shaped elevation called the axon hillock

Leak Channels

randomly alternate between open and closed positions.

Action Potential

sequence of rapidly occurring events that decrease and eventually reverse

Graded Potentials

small deviation from the resting membrane potential that makes the membrane either more polarized or less polarized

Astrocytes

star shaped cells that have many processes and are the largest and most numerous of neuroglia. Two types.

Temporal Summation

summation of effect of neurotransmitters released form 2 or more firings of the same end bulb in rapid succession onto a second neuron on the same part of its cell membrane

Spatial Summation

summation of neurotransmitters released from several end bulbs onto one neuron at different locations on its cell membrane

Axon Terminals

the axon and its collaterals end up by divining into many fine processes

Threshold of a Neuron

-55mV

threshold

-55mV

Myelin

A layer of fatty tissue segmentally encasing the fibers of many neurons; enables vastly greater transmission speed of neural impulses as the impulse hops from one node to the next.

Repolarization

A state in which the cell becomes more negative, moving away from equilibrium with the extracellular fluid, this is an active process

Continuous Conduction

Action potential traveling down an unmyelinated fiber

Determination of speed

Amount of myelin=greater=faster; Axon diameter= Larger= Faster; Temperature= Cooler= Slower

All or none principle (with Action Potential)

An action potential occurs completely or does not occur at all (dominos)

Depolarization

An electrical state where the inside of an excitable cell is made less negative compared with the outside; if an axon is depolarized, an impulse is passing

Interneurons

CNS neurons that internally communicate and intervene between the sensory inputs and motor outputs

Membrane Potential

The charge difference between a cell's cytoplasm and the extracellular fluid, due to the differential distribution of ions, affects the activity of excitable cells and the transmembrane movement of all charged substances.

Electrical Excitability

ability to respond to certain stimuli by producing electrical signals

Cell Body

also known as the perikaryon or soma, contains a nucleus surrounded by cytoplasm that includes typical cellular organelles such as lysosomes, mitochondria and a Golgi complex

Axon Hillock

at junction of cell body and axon

desmosomes

attaching to intermediate filaments in cytoskeleton otherwise similar to adherents junction; helps hold skin together; *cardiac-strong connection

adherens junctions

bigger intercellular fluid tight junctions transmembrane glycoprotein; attaches to microfilament in cytoskeleton; holds skin together

Peripheral Nervous System

consists of all nervous tissue outside the CNS, includes nerves, ganglia, enteric plexuses, and sensory receptors

Autonomic Nervous System

consists of sensory neurons that convey information to the CNS from autonomic sensory receptors, located primarily in visceral organs such as the stomach and lungs. Motor neurons that conduct nerve impulses from the CNS to smooth muscle, cardiac muscle and glands. Action is involuntary

Central Nervous System

consists of the brain and spinal cord, processes many different kinds of incoming sensory informing, source of thoughts, emotions, and memories. Most signals that stimulate muscles to contract and glands to secrete originate in this system

Somatic Nervous System

division of the PNS, consists of sensory neurons that convey information to the CNS from somatic receptors in the head, body wall, and limbs and from receptors for the special senses of vision, hearing, taste, and smell. Motor neurons conduct impulses from the CNS to skeletal muscles only. Action is voluntary

Nodes of Ranvier

gaps in the myelin sheath, appear at intervals along the axon

Unipolar Neuron

have dendrites and one axon that are fused together to form a continuous process that emerges from the cell body. More appropriately called pseudo unipolar neurons because they being in the embryo as bipolar neurons and during development the dendrites and axon fuse together and become a single process.

Bipolar Neuron

have one main dendrite and one axon, found in the retina of the eye, the inner ear and the olfactory area of the brain

Neuroglia

make up about half the volume of the CNS, actively participate in the activities of nervous tissue, usually smaller than neurons, do not generate or propagate action potent ions and they can multiply and divide in the mature nervous system.

Schwann Cells

myelin ate axons in the PNS, cell cytoplasm and nucleus forms outermost layer of neurolemma with inner portion being the myelin sheath. Can form a regeneration tube which guides the repair of an axon

Sensory (Afferent) Neurons

nerve cell that carries information from the environment to the central nervous system