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Afferent: sensory component (towards)

-conveys information from receptors to the CNS

Efferent (away)

-conveys information from CNS to muscles and glands

Somatic NS-conveys information from the CNS to skeletal muscles

Autonomic NS-conveys information from the CNS to smooth muscles, cardiac muscle, and glands

-Autonomic system is really important for drugs

Sympathetic NS: muscle activity (fight/flight)

-goes off as a full unit w/ all processes at once

-controls catabolic processes (breaking down/using stuff)

Parasympathetic: rest

-operations are independent, not always a unit

-controls anabolic processes (conserving/restoration)

Most organs are controlled by dual input with the two having opposing physiological reactions

• blood vessles dilate
• glucose synthesis
• air passages open to oxygenate blood
• heart rate increases
• BP increase
• release of stress hormone

• Digestion (but sympathetic can stop it to allow more blood availability during fight/flight)
• constricts pupils
• slows heart rate

Starts with the neural tube, which becomes brain at one end and spinal chord at the otehr.

Eventually divides into 4 regions: Forebrain, midbrain, hindbrain, spinal cord

Midbrain (mesencephalon) is least divided of the 3 main brain areas

Neocortex also develops: outer most covering of the brain

AKA Medulla

Lowest part of brain stem: primative functiohns

Controls vital functions

(heart rate, BP, respiration, digestion)

Medulla reflexes: coughing, vomitting (area postrema)

2 main parts:

Cerebellum

Small and undifferentiated structure rostral to pons

• Pariaqueductal gray: analgesia
• lots of narcoctic receptors (where analgesics suppress pain)
• surrounds dorsal canal, which is an aquadut (fluid filled whole) in mesencephalon
• Dorsal canal comments 3rd & 4th ventricle
• Substantia Nigra: movement
• bilatterally symmetrical
• Ventral tegmental area: reward
• between the 2 substantia nigra

Lower portion of Forebrain

• Thalamus-senses, except smell, go here before cortex
• responsible for sensory relay
• Hypothalamus: needed for survivial & reproduction
• 4 Fs: feeding, fighting, fleeing, fucking 
• Controls the sympathetic NS

Highest part of brain

• Cortex: outer cover
• Basal Ganglia: gray matter deep in telencephalon (past cortex & white matter)
• misnomer name (not a collection of cell bodies)
• Limbic system: emotional responses
• primitive responses, primitive
• boundary b/ primitive (emotional) & higher order processes (reasoning) 

Preganglionic Fibers start in spine and synapse on Postganglion fibers that go to organs

-All Primary Afferents synapse and this collection is called a ganglion (PNS)

Sympathetic nerves start in thoracid & lumbar regions

Parasympathetic start in cranial & sacral regions

-Cranial: set of 12 that enter through brain stem

-Cervical

-Thoracic

-Lumbar

-Sacral

• Neuroglia (glial cells): supportive
• astrocytes (maintain BBB)
• oligodendrocytes: make myelin in CNS (one can make myelin for lots of axons)
• Schwann cells: make myelin in PNS (each makes only 1 segment of myelin)
• Neurons: functional unit of the NS
• function of NS is to produce adaptive bx by processing information
• basic unit of information processing

within cell (neuron) communication

-Different from b/ neuron communication (neurotransmission)

-almost all drugs effect transmission (not neuroconduction)

Potential = seperation of charge across space

1. resting potential: static

2. Postsynaptic potential: fluctuation

3.Action potential: fluctuation

-65mV: small neg charge due to seperation of charg b/ extra and intracellular fluid

-causes neg charges to line up on intercellular and pos charges on extracellular

Na+    intra=15    extra=150    Nernst=+62mV

K+      intra=100  extra=5        Nernst=-80mV

Cl-      intra=13    extra=150    Nernst=-65mV

A-       intra=345    

1. Active transport (sodium-potassium pump)
2. force of diffusion
3. electrostatic force
4. membrane resistance (antonym conductance) 

A-, stays in due to membrane resistance (too big)

K+, diffusion pushes out, electrostatic pressure pushes in

Cl-, diffusion pushes in, electrostatic pressure pushes out

Na+, diffusion & electrostatic pressure push in

Na+/K+ pump keeps more Na+ out of cell and more K+ in the cell (pushes out 2 Na+ for each K+ pumped in)

A signal in a neuron is a transient fluctuation in membrane voltage that spreads from one point in the neuron to another

Two types:

1. postsynaptic potential

2. action potential

Changes in membrane voltage in a localized area of the postsynaptic neuron when it gets input from the presynaptic neuron

-EPSP depolarizes, Vm goes towards zero (more positive)

-IPSP hyperpolarizes:Vm away from zero (more negative)

Caused by transmembrane ion currents

e.g. influx of Na+, Ca++ = EPSPs

influx of Cl- = IPSPs

efflux of K+ = IPSPs

Transmembrane currents are caused by increased conductance

Increasing conductance of an ion is accomplished by gating

Ion channels can be gated in 2 ways:

-ligand gated (ligand attaches and it opens)

-voltage gated (change in mV opens channel)

Postsynaptic potentials decrease as they move away from the point of origin

-One reason is the current leakage (current leaving the membrane and decreasign the potential)

Neural Integration

Absolute refractory during the actual action potential

Relative refractory during the aftershoot period (takes moer then normal depolarization to activate)

Resting state: K+ channels are open (steady in & out flow), Na+ are closed

Rising Phase: Na+ channels open and flow in (due to concentration grad & electrostatic press), K+ is open and leaves cell (bc of cell getting more positive)

Falling phase: Na+ close, K+ continues to leave to get back to resting potential

Voltage gated Na+ channels along axon open as the depolarization hits that area, lets in more positive to make up for the positive ions diffusing through membrane

Action Potentials are slow & inefficient

-1 to 100 meters/second (1/3 slower then speed of sound)

-Energy is used to maintain the concentration gradients

1. increase diameter of neuron: decreases internal resistance

2. myelination: increase membrane resistance to potassium and decreases capacitance

-Saltatory Conduction: act pot jumps between the Nodes of Ranvier (between myelin) to increases speed

-not a continuous wave, depolarization at one node is enough to depolarize the next and it jumps around

Parts of a synapse: presynaptic element, post synaptic elemnt, synaptic cleft

Types of synapses: axodendritic, axosomatic, axoaxonic

Occurs through Gap Junction Channells composed of 6 units of Connexon

-Ions and small molecules move through for synapses

pre and postsynaptic cells are much closer together (3.5nm) than chemical synapses

Response is faster, but only works for simple bx

-often bidirectional

1. Action potential is propagated over the presynaptic membrane
2. Depolarization of the presynaptic terminal leads to influx of Ca+
3. Ca+ causes vesicles to fuse w/ presynaptic membrane and release transmitter into synaptic cleft
4. transmitter binds to postsynaptic membrane & opens channels, starting EPSP/IPSP
5. EPSP/IPSP spreads passively across dendrite and cell body to axon hillock on postsynaptic cell
6. Inactivation of extra NT
7. NT binds to autoreceptor in presynaptic membrane

Enzymes and precrursors for NT synthesis of NT and vesicles are continuously transported to axons terminals

NT must be inactivated quickly so the next signal can occur

1) enzyme deactivation breaks down the NT

2) Reuptake by membrane transporter

-transporter is energy dependent and pumps NT back into presynaptic cell

-recycles the NT and reduces demand for production

-Receptor for the same NT that the presynaptic cell produces

-Acts as a feedback mechanism: activation inhibits presynaptic activity and decreases release of NT

Three types:

1. Alters NT synthesis

2. Alters Action Potential impulses

3. Alters NT release

• NT should be synthesized in neuron from which it is released
• NT should be released upon neuronal excitation
• NT should act on a specific receptor
• There should be mechanisms for terminating action of the NT after release 

Two different possible meanings:

1. Neurons release one and the same NT at each synapse

2. Neurons release the same set of NT at all synptes

First meaning is not true

Second may hold sufficiently as a "rule of thumb"

Although there are complications, neurons are often classificied by their principal NT

Lots of chemicals are suspected to be NTs

• release of diff NTs at afferent terminals differentiates input
• allows for more complex communication
• multiple NTs released by a neuron encode diff chemical messages
• postsynaptic can discriminate the source of the input or figure out which presynaptic sent it
• Multiple Nts released by a given neuron are synthesized, metabolized, and released at diff rates
• release NT in sequence, not at the same time
• Different Nts are released from diff parts of neurons