Exam 2 prep; Ch 39; 40, 41, 43

What is Neural signaling

process by which an animal responds appropriately to a stimulus

Name the four components of neural signaling

Reception, Transmission, Integration, Response

What is Reception

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

What is Transmission

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

What is Integration

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

What is the Response in Neural signaling

the “output” or action resulting from the integration of neural messages

What are three functional classes of neurons

Afferent, Interneurons, and Efferent Neurons

Define Afferent neurons

Sensory neurons transmit stimuli from their sensory receptors to interneurons

Define Interneurons

Integrates the information to formulate an appropriate response

Define Efferent neurons

Carry signals indicating a response away from the interneurons to the effectors (muscle and glands)

Define motor neurons

efferent neurons that carry signals to skeletal muscle

Parts of a Neuron; Cell body

Contains nucleus and most organelles

Parts of a Neuron; Dendrites

receive signals and transmit them toward the cell body

Parts of a Neuron; Axon

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

Parts of a Neuron; Axon hillock

site of origin of axon

Parts of a Neuron; Axon terminal

connects neuron functionally with adjacent neuron or effector

What are Glial Cells

neuron support cells, includes several types of non-neuronal cells that provide nutrition and support to neurons

Astrocytes

In the vertebrate CNS
closely cover the surface of blood vessels, providing physical support and maintaining concentrations of ions in the interstitial fluid

Oligodendrocytes (CNS) and Schwann cells (PNS)

Function: wrap around axons to form insulating myelin sheaths gaps between Schwann cells (nodes of Ranvier) speed signal transmission

Interneurons form the___

central nervous system (CNS), consisting of the brain and spinal cord

In vertebrates, afferent and efferent neurons form the___

peripheral nervous system (PNS)

A typical neural circuit contains an

afferent (sensory) neuron, one or more interneurons, and an efferent neuron

Ganglia and nuclei are?

clusters of nerve cells typically having related functions

A ganglion

is a group of neurons lying outside the CNS

A nucleus

is a concentration of cells within the CNS

ganglia forms___ and occurs in the __

the plexuses, PNS

Nuclei occurs in the___ and ____

CNS, gray matter of the brain

Nuclei refers to

the structure that contain a number of cell bodies of the central nervous system

Ganglia refers to

the structure that contain a number of cell bodies of the peripheral nervous system

Membrane potential

A separation of positive and negative charges across themplasma membrane that produces an

electrical potential (voltage)

Resting potential

When a neuron is not being stimulated, it maintains a resting potential

 Ranges from –40 to –90 millivolts (mV)

 Average about –70 mV

How is the Resting Potential Created?

The inside of the cell is more negatively charged than the outside

1. Sodium–potassium pump

 Brings two K+ into cell for every three Na+ it pumps out

2. Ion leak channels

 Allow more K+ to diffuse out than Na+ to diffuse in

action potential

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

depolarization

An action potential begins when a stimulus causes positive charges outside the membrane to flow inward, making the cytoplasmic side less negative

threshold potential

Depolarization proceeds slowly until it reaches this point

Propagation of Action Potentials; An action potential is initiated at

the dendrite end of the neuron, then travels away from the stimulation point as a wave of

depolarization along the surface of the cell

Propagation of Action Potentials; In the axon, local current flow between the area

undergoing

an action potential and the adjacent inactive areas depolarizes the downstream membrane

to threshold

Propagation of Action Potentials; The refractory period keeps an action potential from

reversing direction along an

axon – only downstream voltage-gated ion channels are able to open, ensuring one-way movement

In an unmyelinated axon

the rate of conduction increases with the diameter of the axon

Meyelin increases the rate of ___ in smaller axons

conduction

Saltatory Conduction allows

action potentials to “hop” rapidly along myelin-coated axons

 Uncoated nodes of Ranvier expose the axon membrane to extracellular

fluids at regular intervals

 Voltage-gated Na+ and K+ channels at the nodes allow action potentials

to develop only at these positions

 Na+ ions diffuse rapidly to the next node where they cause depolarization,

inducing an action potential at that node

Chemical Synapses; Action potentials ____

can’t jump across the cleft in a chemical synapse

Chemical Synapses; The arrival of an action potential causes neurotransmitter

molecules to be released

by the plasma membrane of the axon terminal (presynaptic membrane)

Chemical Synapses; The neurotransmitter diffuses across the cleft and alters

ion conduction by activating ligand-gated ion channels in the

postsynaptic membrane

Synapse

where a neuron makes a communicating connection with

another neuron, or with an effector

On one side of the synapse is an axon terminal of the presynaptic cell

the neuron that transmits the signal

the postsynaptic cell

the other side of the synapse is the dendrite or effector cell that receives

the signal

Communication across a synapse may occur by

direct electrical flow, or through a chemical neurotransmitter

Electrical synapses

the plasma membranes of the presynaptic and postsynaptic cells are in direct contact

When an electrical impulse arrives at the axon terminal,______ allow ions to flow directly between the two cells

gap junctions

Electrical synapses allow

rapid signal conduction, but are essentially on/off and are unregulated

Electrical synapses are found in

cardiac muscle, the retina of the eye, and the pulp of a tooth

In Chemical synapses, the presynaptic and postsynaptic cells are separated by a narrow

synaptic cleft

When an electrical impulse arrives at an axon terminal

a neurotransmitter is released into the synaptic cleft

In chemical synapses; The neurotransmitter diffuses across

the synaptic cleft and binds to a receptor in the postsynaptic cell membrane

Neurotransmitters are stored in

synaptic vesicles in the cytoplasm of an axon terminal

Arrival of an action potential at the terminal releases the neurotransmitters by

exocytosis

Release of synaptic vesicles depends on

voltage-gated Ca2+ channels in the plasma membrane

ECa is strongly positive

an action potential opens Ca2+ channel gates, allowing Ca2+ to flow back into the cytoplasm

Rise in Ca2+ concentrations in the axon triggers

a protein in the membrane of the synaptic vesicle that allows exocytosis

When action potentials stop arriving at the axon terminal

voltage-gated Ca2+ channels close, and Ca2+ in the axon cytoplasm is

pumped to the outside

The drop in cytoplasmic Ca2+ stops

vesicles from fusing with the presynaptic membrane, and no further neurotransmitter molecules

are released

Neurotransmitters open or close

ligand-gated ion channels that conduct Na+,K+, or Cl– across the postsynaptic

membrane

Altered ion flow in the postsynaptic membrane may stimulate or inhibit the

generation of action potentials by that cell

Excitatory postsynaptic potential (EPSP)

• A change in membrane potential that pushes the

neuron closer to threshold

• Occurs when a ligand-gated Na+ channel opens

and Na+ enters the cell, causing depolarization

Inhibitory postsynaptic potential (IPSP)

• 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

(hyperpolarization)

EPSPs and IPSPs are…

EPSPs and IPSPs are graded potentials in which membrane potential increases or

decreases without necessarily triggering an action potential

The postsynaptic neuron receives

inputs from many chemical synapses with presynaptic neurons

What are nerve nets

loose meshes of neurons organized within their radial symmetry

Cnidarians and Echinoderms

Both have nerve nets, and their neurons lack clearly differentiated structures

dendrites and axons, impulses are conducted through the nerve net in all

directions from the point of stimulation

In echinoderms (e.g., sea stars), some neurons are organized into nerves

bundles of axons enclosed in connective tissue and following the same pathway

A nerve ring surrounds the ____ located mouth and a radial nerve

branches ____ each arm

centrally, throughout

Ganglia

Neurons are concentrated into functional clusters 

Cephalization

the formation of a distinct head region containing a control center

(ganglia or brain) and major sensory structures – are a key evolutionary

development

One or more solid nerve cords extend from the_____

central ganglia to the rest of the body – connected to smaller nerves

In flatworms, a small brain (consisting of a pair of ganglia at the anterior end) is connected

by

two or more longitudinal nerve cords to nerve nets in the rest of the body

Flatworms: The brain integrates inputs from sensory receptors including a pair of anterior___

eyespots with receptors that respond to light

Flatworms: The brain and longitudinal nerve cords constitute a simple

central nervous system CNS

Flatworms: Nerves from the CNS to the rest of the body constitute the

Peripheral nervous system PNS

Arthropods: such as insects, have a head region that contains a brain and ventral pairs of ganglia

and major sensory structures usually eyes and antennae

A ventral nerve cord ____

enlarges into a pair of ganglia in each body segment

In arthropods with a fused body segments, as in the thorax of insects..

ganglia are fused into larger masses forming secondary control centers

Mollusks (clams, snails, octopuses) also have

neurons clustered into paired ganglia and connected by major nerves

Cephalopods have the most pronounced

cephalization of any invertebrate group

The vertebrate CNS consists of

the brain and spinal cord

the PNS consists of all the

nerves and ganglia that connect the brain and spinal cord to the rest of the body

The vertebrate brain and nerve cord are hollow,

fluid-filled structures located

dorsally

The embryonic nervous system begins as a hollow

neural tube

neural tube

The anterior end develops into the brain, and the rest

develops into the spinal cord

The cavity of the neural tube becomes the fluid-filled

ventricles of the brain and the central canal through the

spinal cord

Early in embryonic development, the anterior part of the neural tube

enlarges into three distinct regions:

hindbrain, midbrain, and forebrain

The hindbrain gives rise to the

medulla oblongata, cerebellum, and pons

medulla oblongata

controls vital involuntary tasks such as respiration and blood circulation

cerebellum

integrates sensory signals from eyes, ears, and muscles with motor signals from the telencephalon and pons

pons

A major traffic center for information passing between the cerebellum and the higher integrating centers of the adult telencephalon

The midbrain gives rise to the adult midbrain which with the pons and medulla…

constitutes the brain stem

The midbrain has centers for coordinating reflex responses (involuntary reactions) to

visual and auditory input and relays signals to the telencephalon

The forebrain develops into the

cerebrum (telencephalon)

The forebrain is the

largest part of the brain
controls thought, memory, language, emotions, and voluntary movements

The forebrain also forms

thalamus and hypothalmus