Communication & Regulation;

Brain sends message to target organ which elicits a response, and then both afferent and efferent pathways send feedback to and from brain.

Communication in the form of ion flow;

1. NA+ channels open-depolarization of membrane

2. K+ channels open- repolarization/hyperpolarization

3. AP is propagated along nerve cell

Continuous Conduction- propagation in unmyelinated nerve cells (ex: skeletal muscle).

Saltatory Conduction- propagation in myelinated nerve cells; jumping conduction- nodes of ranvier (areas of no myelin) contain voltage-gated channels; APs are generated here; ion travels rapidly between nodes.

In either myelinated or unmyelinated nerves, the AP travels from beginning to end of nerve; Graded potentials start at dendrites; AP start at axon hillock.

Junction between nerve and effector cell; permits & preserves communication between cells; Skeletal muscle synapse=neuromuscular junction; In nerve system, synapse is between 2 nerves.

- Pre-synaptic neurons: submits AP to synapse

- Post Synaptic neurons: receive AP from synapse

1. Axo-dendritic (axo-somatic): synapse nerve on left is synapsing with nerve on right.

2. Axo-axonal: goes 2 different directions when it reaches next nerve

3. Dendro-dedritic: dendrite synapsing another dendrite.

4. Dendro-somatic: dendrite synapsing with cell body.

Electrical Synapses: found in brain; ion flow from on cell to another by gap junctions (connexons); fast & uniform.

Chemical Synapses: synaptic cleft; no physical contact or ion flow between cells; allows discreet control for fine motor movements or blocking out extraneous stimuli (ex: conversing in a noisy room); can inhibit some synapses and excite others;

1. Pre-synaptic nerve synthesizes/stores neurotransmitter in vesicles; Plasma membrane of terminal bouton contains Ca2+ voltage-gated channels.

2. Extracellular Ca2+ is higher than intracellular Ca2+.

3. AP arrives, opening channels causing Ca2+ to difffuse into terminal boutons.

4. Ca2+ causes synaptic vesicles with neurotransmitter to migrate & fuse with pre-synaptic membrane.

5. Neurotransmitter diffuses into synaptic cleft.

6. Neurotransmitter binds ith receptors on post-synaptic neuron membrane.

7. Initiates a graded potential, followed by an AP.

Found in skeletal neuromuscular junction/cerebral cortex, brain stem, & hippocampus.

Function: Memory

Biogenic amine: Catecholamine; Deficiency: Parkinson's; Excess: Schizophrenia;

Function: Feel good & coordination of body movements

Biogenic amine: Catecholamine;

Function: Sleep/wake, attention, and feel good

Biogenic amine: Indolamine;

Function: Sleep/wake, appetite, & mood regulation

Biogenic amine: Indolamine;

Function: Alertness/wakefulness, appetite, & learning/memory

Amino acid; inhibits pre-synaptic nerve from sending AP;

Function: Inhibitory

Amino Acid; Inhibits pre-synaptic nerve from sending AP;

Function: Inhibitory

Amino acid; causes AP to occur at post-synaptic neuron;

Function: excitatory

Peptide; natural opiate; responsible for "runner's high";

Function: Block pain (inhibit Substance P)

Peptide; Important mediator of pain transmission in PNS;

Function: Pain

Gas;

Function: Learning/Memory & Strengthening synapses

Purine; Both an energy currency molecule and neurotransmitter; in PNS & CNS; Adenosine, the nitrogen base of ATP, is inhibitory on brain & induces sleep. Caffeine blocks adenosine receptors.

Function: Excitatory or Inhibitory & pain modulation

Excitatory: Causes AP on post-synaptic neuron.

Inhibitory: Suppresses AP on post-synaptic neuron.

Direct: Open ion channels directly after binding of neurotransmitter; good for rapid action; Ex: Ach in channel-linked receptors.

Indirect: use 2nd messengers to open ion channels & initiate other intracellular effects; slower- often seen in hormone release; Ex: g-protein-linked receptors.

Excitatory Post-Synaptic Potentials (EPSP):often located on dendrites; Na+ channels often involved; Na+ enters cell causing depolarization; promotes AP.

Inhibitory Post-Synaptic Potentials (IPSP): often located at cell body; Cl- channels involved; CL- enters cell causing further hyperpolarization; inhibits AP.

Summation:

-Temporal: multiple impulses sent rapidly to post-synaptic neuron.

-Spatial: several pre-synaptic neurons send impulses to post-synaptic neuron; important in chemical synapses.

Pools of neurons communicate/Circuitry- 3 types:

1. Divergent: amplifying; 1 input creates several outputs.

2. Convergent: concentrating; multiple inputs creates ususally one output.

3. Oscillating: reverberating; circuits go around & around; ex: sleep/wake cycles.

Processing- 2 types:

1. Serial: Sensation pathways & reflex arcs.

2. Parallel: higher level mental functions.

Serial sensation pathways; rapid, automatic response to stimuli; 2 types: Visceral- involves glands (ex: salivation) & Somatic- involves skeletal muscles & includes several spinal reflexes.

Components:

Stimulus: Without stimulus, no response.
Receptor: Translates stimulus into AP; without receptor, cannot know whether stimulus exists.
Sensory Neuron: Carries AP to CNS.
Integration Center: Located in CNS.
Motor Neuron: Carries AP to effector (muscle).
Effector: Executes appropriate response.

Somatic Reflex; occurs in skeletal muscle; small sensory organs imbedded in skeletal muscle called muscle spindles (made of modified skeletal muscle fibers called intrafusal fibers); extrafusal fibers=general skeletal muscle contractile fibers; sensory fibers are in non-contractile center; Y-motor fibers synapse at contractile ends.

-When skeletal muscle is stretched, spindle is also stretched, causing irritation to sensory nerve fibers; This fires an AP to spinal cord.

-At spinal cord, synapse with a-motor neurons supplying skeletal muscle and antagonist muscle; stimulated (stretched) skeletal muscle contracts & antagonist muscle relaxes.

-Spindle tension maintained by APs from Gamma Motor Neurons at ends; if spindle too loose, no mechanical irritation of sensory nerves will occur (no AP).

Somatic Reflex; involves Golgi Tendon Organ (imbedded in tendons of skeletal muscle); Protection.

-In response to stretch of a tendon, GTO is stimulated and an AP fires off along sensory nerve.

-Nerve synapses with a-motor neurons of both stretched muscle & antagonist muscle; Causes relaxation of stretched muscle & contraction of antagonist muscle. -Prevents tearing of stretched muscle.

Somatic Reflexes; 2 types:

Plantar: tests integrity of L4-S2 nerve roots; normal=downward flexion of toes; abnormal=dorsiflexion of foot (babinski sign)- common in non-walking infants;

Abdominal: tests integrity of T8-T12 nerve roots; normal=umbilicus moves to stimulated side due to abdominal muscle contraction; abnormal=doesn't move.