The Nervous System: Command & Control Centers

Nervous systems Effector cells~ muscle or gland cells Nerves~ bundles of neurons wrapped in connective tissue Central nervous system (CNS)~ brain and spinal cord Peripheral nervous system (PNS)~ sensory and motor neurons

Structural Unit of Nervous System Neuron~ structural/functional unit (the actual “Nerve Cell”) Cell body~ nucleus and organelles Axon Hillock ~ where impulses generate Dendrites~ impulses from tips to neuron Axons~ impulses toward tips (away!!) Myelin sheath~ supporting, insulating layer, made of…. Schwann cells~PNS support cells Oligodendrocytes ~ the CNS version of Schwann cells Astrocytes ~ form the blood–brain barrier, provision of nutrients, maintenance & repair Synaptic terminals~ neurotransmitter releasers Animation

Simple Nerve Circuit Sensory neuron: convey information to spinal cord Interneurons: information integration Motor neurons: convey signals to effector cell (muscle or gland) Reflex: simple response; sensory to motor neurons Ganglion (ganglia): cluster of nerve cell bodies in the PNS Supporting glial cells: nonconducting cell that provides support, insulation, and protection

Neural signaling: First, in the resting state, there is…. Membrane potential (voltage differences across the plasma membrane) Intracellular/extracellular ionic concentration difference K+ diffuses out (Na+ in); large anions can’t follow….selective permeability of the plasma membrane …and of course the Sodium/Potassium pumps never sleep! Net negative charge of about -70mV

Neural Signaling, continued…. Excitable cells~ cells that can change membrane potentials (neurons, muscle) Gated ion channels (open/close response to stimuli): Examples of stimuli: Photoreceptors; vibrations in air (sound receptors); Chemical (neurotransmitters) Voltage (membrane potential changes) Graded Potentials (depend on strength of stimulus): 1- Hyperpolarization (outflow of K+); increase in electrical gradient; cell becomes more negative 2- Depolarization (inflow of Na+); reduction in electrical gradient; cell becomes less negative.

Neural signaling, continued still… 1-Resting state•both channels closed 2-Threshold •a stimulus opens some Na+ channels 3-Depolarization •action potential generated •Na+ channels open; cell becomes positive (K+ channels closed) 4-Repolarization •Na+ channels close, K+ channels open; K+ leaves •cell becomes negative 5-Undershoot •both gates close, but K+ channel is slow; resting state restored 6-Refractory period~ insensitive to de-polarization due to closing of Na+ gates (region is “hyperpolarized”) Animation

Neural signaling, finale’ “Travel” of the action potential is self-propagating Regeneration of “new” action potentials only after refractory period Forward direction only Action potential speed: 1-Axon diameter (larger = faster; 100m/sec) 2-Nodes of Ranvier (concentration of ion channels); saltatory conduction

Synaptic communication Presynaptic cell: transmitting cell Postsynaptic cell: receiving cell Synaptic cleft: separation gap Synaptic vesicles: neurotransmitter releasers Ca+ influx: caused by action potential; causes vesicles to fuse with presynaptic membrane and release…. Neurotransmitters!! So let’s talk neurotransmitters:

Neurotransmitters: 2 main types Those that relay an: EPSP- Excitatory Post Synaptic Potential Occur when terminal releases a neurotransmitter that opens Na+ channels. And then there are those that relay an: IPSP- Inhibitory Post Synaptic Potential Occur when terminal releases a neurotransmitter that opens either K+ channels or Cl- channels. YouTube!

Neurotransmitters, some examples: Acetylcholine (most common) Might be either EPSP or IPSP. Important for skeletal muscle contraction. Biogenic amines (derived from amino acids) •norepinephrine – excitatory •dopamine- generally excitatory. Too little: Parkinson’s Too much: schizophrenia Cocaine prevents the reuptake/breakdown in cleft. •Serotonin- Usually inhibitory; important for sleep/relaxation

Neurotransmitters, more examples: Single Amino acids: G.A.B.A.- “Gamma AminoButeric Acid” – inhibitory at neuromuscular junction. Aspartate- Excitatory (found in high concentrations in artificial sweeteners) Tryptophan- Inhibitory (Happy Thanksgiving!!) Glutamate- Excitatory (like acetylcholine; important at neuromuscular junction) (Blocked by alcohol) Neuropeptides (short chains of amino acids) Endorphins- generally inhibitory (see why they’re called natural painkillers?) “Substance P”- Excitatory D:\bc_campbell_biology

Vertebrate PNS Sensory division (Afferent) Motor division (Efferent) •Somatic system- Information from voluntary/conscious parts. •Visceral system- senses information from involuntary parts. Motor division (Efferent) •somatic system carries signals to skeletal muscle (mostly voluntary, but some are reflex) •autonomic system √parasympathetic conserve energy (digestion, decrease heart/breathing rates) √sympathetic increase energy consumption

Vertebrate CNS Basically, it’s Brain & Spinal Cord Axons are in well defined bundles White Matter- heavily myelinated Gray Matter- not as myelinated In brain, white is in, gray is out Reversed in Spinal Cord

The Vertebrate Brain Forebrain: Midbrain: •cerebrum~memory, learning, emotion •cerebral cortex~sensory and motor nerve cell bodies •corpus callosum~connects left & right hemispheres •thalamus- sorts info; emotion hypothalamus- hormones, thermostat Midbrain: •inferior (auditory) and superior (visual) colliculi Hindbrain: •cerebellum~coordination of movement & balance Medulla oblongata/pons: homeostatic functions YouTube- Teenage Brain Mike the Headless Chicken!

Ear & Eye Links Ear: Eye: http://www.hhmi.org/biointeractive/cochlea http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter19/animation__effect_of_sound_waves_on_cochlear_structures__quiz_2_.html http://jeffmilner.com/backmasking.htm Can you trust your Ears? Eye: D:\bc_campbell_biology_7\0,7052,3117257-,00.html