Nervous System Function Neurons Base unit that has very simple function – “decide” whether to transmit signal or not Organization Billions of Neurons (estimates of 100 billion) Very complex interconnections Create systems/circuits that can function independently (parallel processing) “Simple decisions” passed to “higher” levels for that add additional information to create generate more complex decisions (hierarchical processing) Very expensive - less than 2% of weight but uses 20% of energy

Neuron Structure Cell Body Nucleus – genetic information Dendrites Receive information Axon Carry information “long” distances Myelin (Multiple Sclerosis) Axon Terminals Transmit information

Neuron - Structure

Neuron Function Electrical Activity Used to transmit signal within neuron Chemical Activity Used to transmit signal between neurons Synapse – small gap that physically separates neurons Neurotransmitters – special “chemicals” that neurons use to transmit message across the synapse

Neuron Function Electrical Activity Resting Potential Inside negative (-70 mV) compared to outside Inside has high K + (negativity comes from proteins & other negative ions) Outside has high Na + Forces at work  Electrical  Diffusion

Neuron Function Electrical Activity Graded Potential Depolarization – Inside less negative (e.g., Na + enters) Hyperpolarization – Inside more negative (e.g., Cl - enters) Action Potential When graded reaches approximately -55mV Electrical impulse that travels down cell – axon to axon terminals Axon terminals release neurotransmitter

Neuron Function Electrical Activity Restoring Resting Potential Sodium-Potassium Pump – moves Na + out of cell and K + into cell This requires cell to use energy

Neuron Function Chemical (Neurotransmitter) Activity Leads to graded potentials in neuron Excitatory NTs – causes depolarization in neuron Initiatory NTs – causes hyperpolarization in neuron

Neuron – Excitation & Inhibition

Neuron - Synapse

Synapse Types Multiple ways of connecting Examples Axon to Dendrite – excite or inhibit neuron Axon to Axon Terminal – moderate NT release Axon to Extracellular Space or blood – potential for diffuse effects

Synapse Types

Synapse Function Neurotransmitter cycle in Axon Terminals Synthesis Storage Release Inactivation Reuptake Degradation Neural transmission problems if cycle disrupted (e.g., drugs) at any step

Synapse Function

Neurotransmitter Types Small Molecules Nine – Acetylcholine (ACh), dopamine (DA), norepinephrine (NE), epinephrine (adrenaline), serotonin (5-HT), histamine, GABA, glycine, glutamate Simple (or no) alterations to basic food components Glutamate & glycine are amino acids DA and NE from tyrosine & 5-HT made from tryptophan Manufactured in axon terminals Large quantity and have short duration

Neurotransmitter Types Peptides 50+ and grouped into families depending on function Opoids (enkephalins, dynorphin) – pain Gastrins (gastrin, cholocystokinin) – food digestion 2 or more amino acids and made in cell body (ribosomes) from DNA instruction Slower to manufacture & transport Small concentrations and longer durations Gases At least 2 – nitric oxide (NO) & carbon monoxide (CO) Can work on releasing cell

Neurotransmitter Function No one to one relation between type and function Same NT can be used in different places with very different effects Acetylcholine – contracts muscles, used in autonomic nervous system, and brain

Neurotransmitter Receptor Proteins Channel Proteins NT binding site and channel trough membrane NT opens a channel to allow chemical flow (Na + ) across membrane Second Messengers NT binding site – NT activates a “second messenger” (1 st is the NT) inside the cell Change function of cell (e.g., change protein production to permanently alter cell function for learning)

Neurotransmitter Receptor Proteins

Usually multiple receptors for a given NT Acetylcholine Nicotinic receptor – found a junction between neuron and muscle Muscarinic receptor – more prevalent in brain Acetylcholine affects both Drugs can have more specific effects (or not depending on the drug)  Nicotine & curare –affect nicotinic but not muscarinic

Neurotransmitter Receptor Proteins Usually multiple receptors for a given NT Serotonin (5-HT) 13 known receptors grouped into 6 families People with schizophrenia have an excess of one type  Demonstrates how genetic differences can influence motivational temperaments Dopamine 5 known receptors grouped into 2 families

Psychoactive Drug Overview Two Broad effects on NT function Facilitate or increase function of a specific NT Inhibit or Decrease function of a specific NT 2 Broad effects accomplished by altering any of the 7 synapse functions (previous slide) Acetylcholine

Psychoactive Drug Overview Acetylcohine Example Axon Release Black widow spider venom – released from axon terminals Botulinum toxin (Botox) – blocks release from axon terminals Synapse Stimulation Nicotine – mimics ACh Curare – blocks ACh from getting to terminals Inactivation Physostigmine – blocks effect of enzyme that destroys ACh

Psychoactive Drug Overview

Nervous System adapts drug presence Inhibitory drug – may create more protein receptors to detect smaller amounts of NTs that are getting to postsynaptic cell Excitatory drug – may remove protein receptors NS now requires drug for functioning Inhibitory drug – “normal” signals are too strong Excitatory drug – “normal” signals not strong enough

Nervous System Organization

Central Nervous System (CNS) Spinal Cord – simple decisions & information transmission Brain – “complex” decisions Peripheral Nervous System (PNS) Somatic – sensory information & voluntary movement Autonomic Sympathetic – increases support increased physical activity Parasympathetic – increases support decreased physical activity Enteric – gastrointestinal system

Autonomic Nervous System

Nervous System Organization Neuron Groups Peripheral NS Nerve – collection of axons in PNS Ganglia – collection of cell bodies & dendrites Central NS Tract – collection of axons in CNS (White Matter) Nuclei – collection of cell bodies (Grey Matter) Glial Cells Support and assist neurons (many types) Produce myelin, nourishment, repair, waist disposal, etc.

Spinal Cord 31 segments with pairs (left & right) nerves carrying sensory and efferent information Functions Ascending and descending neural tracts Interneurons responsible for spinal reflexes (relatively simple decisions) Link sensory information (e.g., pain) with motor response (e.g., muscle contraction)

Brain Structure Very Complex Many different ways of describing brain structures (location, function, etc.) General Principles Layered Lateralized

Brain Neural Systems Brain circuits responsible for brain function E.g., - vision, hearing, movement, reward System could be  Localized (vision) or diffuse (arousal)  General (vision) or specific (color vision) Broad Divisions Sensory Motor Association

Brain Complex behaviors (fear/defensive learning) depend on many systems Sensory Learning Memory Output Differences in a function (e.g., motivation) might be due to different reasons (e.g., sensory, learning, etc.)

Studying Brain Function Gross lesions Structural assessments Selective lesions specific neurotoxins transient lesions Local functioning Single-cell recording Neurotransmitter measurement & manipulation Gene expressions Non-invasive measures Functional MRI EEG & ERP