Psych 2210 Communication Within the Nervous System

neuron

a specialized cell of the nervous system that communicates information through electrical and chemical signals

• 86B in the human brain

• ~50% of brain cells

4 morphologically defined regions:

1. cell body

2. dendrites

3. axon

4. axon terminals

dendrites

extensions of the neuron that receive information from other cells

myelin sheath

increases speed of neural signals

axon hillock

generates neural impulse

axon

transfers neural signals

axon terminal

forms junctions with other cells; contains neurotransmitters

cell body (soma)

• most prominent part of the neuron

• filled with cytoplasm

  • salt water + ions, proteins, molecules

• contains numerous organelles

  • nucleus: DNA-containing structure

  • endoplasmic reticulum, Golgi apparatus, ribosomes: protein synthesis

  • mitochondria: ATP production

• cell membrane

cytoplasm

in cell body; salt water + ions, proteins, molecules

nucleus

in cell body; DNA-containing structure

location of protein synthesis

in cell body; endoplasmic reticulum, Golgi apparatus, ribosomes

mitochondria

in cell body; responsible for ATP production

cell membrane

bilipid layer with proteins “floating” within

• lipid molecules = hydrophilic heads + hydrophobic tails

  • allows membrane to hold its shape

    • heads orient toward liquid

    • tail orients away from liquid

      • double-layer membrane

• some small molecules can pass through; larger molecules only pass through protein channels

motor neurons

• carry commands to the muscles and other organs

• brain → body

• found mainly within CNS

  • multipolar

sensory neurons

• carry information from the body and external world

• body → brain

• found mainly within PNS

  • unipolar, bipolar

interneurons

• connect one neuron to another within CNS

• multipolar

• short or no axon

• communicates locally

selective permeability

some small molecules can pass through the cell membrane, larger molecules only pass through protein channels

→ polarization

• positive electrical charge on one side and a negative charge on another side

• difference in electrical charge between the inside and outside of the neuron = voltage

voltage

the difference in electrical charge between the inside and outside of the neuron

resting potential

the difference in charge between inside and outside of a neuron at rest (usually -70 mV)

• as a result of unequal distribution of electrical charges on extracellular (outside cell) and intracellular (inside) fluid

• the cell is “polarized”

• maintained by passive transport (short-term) and active transport (long-term)

ions outside the cell

lots of sodium (Na+) and chloride (Cl-), more positive ions

ions inside the cell

lots of potassium (K+) and anions (A-), more negative ions (negative resting potential)

ion channels

proteins in cell wall; pore in the center allows ions to enter and leave the cell

passive transport

short-term way of maintaining resting potential; can move ions when the voltage-gated channels are not active

• concentration gradient (force of diffusion): high concentration to low

• electrostatic pressure: ions repelled from the side with similar charges; want to move toward the opposite charge

active transport

long-term way of maintaining resting potential

• sodium-potassium pump: uses ATP, pumps 3 Na+ out and 2 K+ in, uses 40% of the cell’s energy to keep the cell negatively charged at rest

concentration gradient (force of diffusion)

passive transport; high concentration to low

electrostatic pressure

passive transport; ions repelled from the side with similar charges; want to move toward the opposite charge

sodium-potassium pump

active transport; uses ATP, pumps 3 Na+ out and 2 K+ in, uses 40% of the cell’s energy to keep the cell negatively charged at rest

action potential

abrupt depolarization of the membrane that allows the neuron to communicate over long distances

• if local threshold (by a stimulus) can reach a certain threshold, it is initiated (all-or-none)

• then, electrical signal travels along axon

• synapses on another neuron or the target

glial cells

nonneural cells that provide a number of supportive functions to neurons

• myelin-producing

  • oligodendrocytes (CNS)

  • Schwann cells (PNS)

• astrocytes

• microglia

myelin-producing glia

• myelin: fatty tissue that wraps around axon to insulate it

• oligodendrocytes (CNS): 1 cell can wrap multiple internodes

• Schwann cells (PNS): 1 cell wraps single internode

• Nodes of Ranvier: gaps in myelin sheath

• saltatory conduction: a form of transmission in which action potentials appear to jump from node to node

myelin

myelin-producing glia, fatty tissue that wraps around axon to insulate it

oligodendrocytes

myelin-producing glia, found in CNS, 1 cell can wrap multiple internodes

Schwann cells

myelin-producing glia, found in PNS, 1 cell wraps single internode

Nodes of Ranvier

myelin-producing glia, gaps in the myelin sheath

saltatory conduction

myelin-producing glia, a form of transmission in which action potentials appear to jump from node to node

astrocytes

type of glial cells

• support/form blood-brain barrier, insulate neurons, structural support etc.

• compose 20-50% of the brain volume

• arise from radial glia

microglia

• mediate immune responses in the nervous system

• engulf damaged tissue and invading organisms

vesicles

membrane-enclosed bubbles at axon terminals which store neurotransmitters

chemical transmission at the synapse

1. action potential arrives at axon terminals

2. opening of Ca2+ channels

3. Ca2+ enters

4. vesicles move to presynaptic membrane

5. fusion of vesicles

6. neurotransmitter release

effect on cellular processes:

• EPSP and IPSP

• neurotransmitter effects on presynaptic and postsynaptic neuron

excitatory postsynaptic potential (EPSP)

postsynaptic cellular process; when receptors open sodium channels to produce a partial depolarization of the dendrites and cell body

• partial depolarization - more likely to produce action potential

inhibitory postsynaptic potential (IPSP)

postsynaptic cellular process; when receptors open potassium channels, chloride channels, or both to produce a hyperpolarization of the dendrites and cell body

• hyperpolarization - less likely to produce action potential

spatial summation

postsynaptic cellular process; combines potentials occurring simultaneously at different locations on the dendrites and cell body

temporal summation

postsynaptic cellular process; combines potentials arriving a short time apart, from either the same or separate inputs

neurotransmitter binding

postsynaptic cellular process

• ionotropic receptors

  • ligand-gated ion channels

  • binding of neurotransmitter to receptor directly opens or closes an ion channel

  • local, fast, short

• metabotropic receptors

  • ligand-activated proteins and enzymes “second messengers”

  • binding to receptors activates g-protein

  • distant, slow, long

ionotropic receptors

neurotransmitter binding process, postsynaptic cellular process

• ligand-gated ion channels

• binding of neurotransmitter to receptor directly opens or closes an ion channel

• local, fast, short

metabotropic receptors

postsynaptic cellular process

• ligand-activated proteins and enzymes “second messengers”

• binding to receptors activates g-protein

• distant, slow, long

reuptake

presynaptic cellular process; process in which transmitters are taken back into the terminals

• controlling this process is used extensively in psychopharmacology (e.g., antidepressants)

autoreceptors

control the amount of transmitter

neurotransmitter release

• reuptake

• excess neurotransmitters:

  • broken down by enzymes

  • absorbed by glial cells

  • diffuse away

neurotransmitters

chemicals the neuron releases to communicate with a muscle, an organ, or the next neuron in a chain

acetylcholine

1. between nerves and muscles (movement)

   1. nerves communicate with muscles by releasing it

   2. release → muscle contraction

   3. inhibition → muscle relaxation

2. involved in learning

   1. memory - death of these neurons in Alzheimer’s disease

GABA

amino acid; main inhibitory neurotransmitter

• anti-anxiety drugs and alcohol act to enhance it

• deficiency can cause epilepsy

glutamate

amino acid; main excitatory neurotransmitter

• involved in learning and memory - lots in cerebral cortex

serotonin

monoamine; involved in mood, sleep and arousal, aggression, depression, OCD, and alcoholism

dopamine

monoamine

• movement (death of these neurons impairs movement, Parkinson’s disease)

• promotes reinforcing effects of food, sex, and abused drugs

  • motivation

• schizophrenia (blocking its receptors improves psychological disturbance)

norepinephrine

monoamine

• released during stress

• increase arousal and promote sleep/waking cycle

• related to depression

epinephrine (adrenaline)

monoamine

• stress hormone from adrenal glands e.g., making heart beat faster

• minor role in brain

endorphins/enkephalins

neuropeptide

• block pain, produce pleasure (heroin, morphine)

• placebo, acupuncture effects

  • placebo can cause increase in its release/transmission

Substance P

neuropeptide; transmission of pain info

Neuropeptide Y

neuropeptide; initiates eating and produces metabolic shifts

ligand

binds to receptor (has affinity)

affinity

similarity, resemblance in structure

direct agonist

binds and mimics effect of transmitter (has affinity and efficacy)

• number of target chemicals increase

efficacy

ability to produce a desired or intended result

indirect agonist

increases neurotransmitters via a mechanism other than receptor interaction - changes could be in synthesis, storage, release, reuptake, or degradation stage as listed above (has efficacy)

• number of target chemicals increase

antagonist

binds and does not have an effect, preventing transmitter action (has affinity)

• blocker