Ch39 Neurons

Neural Signaling

(the process by which an animal responds appropriately to a stimulus) has four components: reception, transmission, integration, and response

Reception

detection of a stimulus (performed by neurons and by specialized sensory receptors

Neurons

a nerve cell; the basic building block of the nervous system

transmission

sending of a message along a neuron to another neuron or to a muscle or gland

integration

sorting and interpretation of neural messages and determination of the appropriate response

response

the "output" or action resulting from the integration of neural messages

afferent neurons

(sensory neurons) transmit stimuli from their sensory receptors to interneurons

sensory neurons

neurons that carry incoming information from the sensory receptors to the brain and spinal cord

efferent neurons

carry signals indicating a response away from the interneuron to the effectors (muscles and glands)

effectors

muscles and glands

motor neurons

efferent neurons that carry signals to skeletal muscle

cell body

contains nucleus and most organelles

dendrites

receive signals and transmit them toward cell body

axons

conducts signals away from cell body to another neuron or an effector; may be from -1mm to more than 1m long

axon hillock

site of origin of axon

axon terminal

connects neuron functionally with adjacent neuron or effector

neural circuit

group of interconnected neurons that are responsible for neural processing; contains afferent neuron, one or more interneurons and an efferent neuron

peripheral nervous system

the sensory and motor neurons that connect the central nervous system to the rest of the body

central nervous system

consists of the brain and spinal cord

ganglion

group of neurons lying outside the CNS

nucleus

concentration of cells within the CNS

glial cells

neuron support cells; contain astrocytes and oligodendrocytes

astrocytes

(in the vertebrate CNS) closely cover the surfaces of blood vessels, providing physical support and maintaining concentration of ions in the interstitial fluid

oligodendrocytes

in the CNS and Schwann cells in the PNS wrap around axons to form insulating myelin sheaths

Schwann cells

Supporting cells of the peripheral nervous system responsible for the formation of myelin.

nodes of Ranvier

Gaps in the myelin sheath to which voltage-gated sodium channels are confined; speed signal transmission

synapse

A junction where information is transmitted from one neuron or with an effector to the next.

presynaptic cell

The transmitting neuron in a synapse.

postsynaptic cell

the cell that receives the signal

electrical synapses

plasma membranes of presynaptic and postsynaptic cells are in direct contact

chemical synapses

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

synaptic cleft

The narrow gap that separates the presynaptic neuron from the postsynaptic cell.

neurotransmitter

chemical messengers that cross the synaptic gaps between neurons

synaptic vesicles

Membrane-bounded compartments in which synthesized neurotransmitters are kept.

membrane potential

separation of positive and negative charges across a plasma membrane that produces an electrical potential

voltage

electrical potential

Na+/K+ pump

Active transporter that moves three Na+ out of a cell and two K+ into the cell against their respective concentration gradients.

resting membrane potential

The charge of a neuron when it is not being stimulated. Rangers from -40 to -90 millivolts (mV); average about -70 mV

equilibrium potential

the membrane potential at which chemical and electrical forces are balanced for a single ion.

Nernst equation

Ecell= E°cell - (RT/nF) (lnQ)

depolarize

in the nervous system, to lose the charge that normally exists across the neuronal membrane; making cytoplasmic side less negative

action potential

When a neuron transmits an electrical impulse, an abrupt change in the membrane potential occurs called the

threshold potential

The minimum membrane potential that must be reached in order for an action potential to be generated. Typically 10-20 mV more positive than resting potential

hyper polarized

About -80 mV; More Polarized, more difference between the inside and the outside of a cell.

all-or-nothing principle

The principle that once the electrical impulse reaches a certain level of intensity (its threshold), it fires and moves all the way down the axon without losing any intensity.

refractory period

the time following an action potential during which a new action potential cannot be initiated' consists of two phases; in the initial phase, the cell cannot be restimulated; in the second phase, the threshold required for generation of an action potential is much higher than normal

voltage-gated ion channels

Channels that open or close in response to a change in the membrane potential. Found mainly on the axon and the axon hillock

patch-clamp technique

A method that allows researchers to study the ion channels of a tiny patch of membrane by tightly sealing a micropipette to the patch and measuring the flow of ions through the channels.

saltatory conduction

allows action potential to "hop" rapidly along myelin coated axons

ionotropic neurotransmitter receptors

A receptor in the postsynaptic membrane to which a neurotransmitter binds directly, causing an associated ion channel gate to open or close thereby altering the flow of a specific ion or ions in the postsynaptic cell. Binding site + channel combines, second messenger-independent, short latency action, rapid responses (10-50ms), postsynaptic

ligand-gated ion channel

Type of membrane receptor that has a region that can act as a "gate" when the receptor changes shape.

metabotropic neurotransmitter receptors

A receptor in the postsynaptic membrane, typically of the G-protein-coupled receptor type, to which a neurotransmitter binds as a first messenger, activating the receptor and triggering generation of a second messenger that brings about changes in ion-conducting channels in the membrane. longer latency, slow responses, pre and postsynaptic, binding site not associated with channel

acetylcholine

Between some neurons of CNS and at neuromuscular junctions in PNS; mostly excitatory; inhibitory at some sites

EPSP (excitatory postsynaptic potential)

a change in membrane potential that pushed the neuron closer to threshold; occurs when a ligand-gated Na+ channel opens and Na+ enters the cell, causing depolarization

IPSP (inhibitory postsynaptic potential)

A change in membrane potential that pushes the neuron farther from threshold; occurs when a ligand gated ion channel opens that allows Cl-to flow in and K+ to flow out (hyper polarization)

graded potentials

membrane potential increases/decreases without necessarily trigger an action potential