Neurons - specialized for transmitting signals from one location in body to another - cell body includes two structures ...

Dendrites - receives signal - conveys to rest of neuron

Axon - conduct message toward tip

Central Nervous System (CNS) - interprets information from stimulation of sensory receptors and associates with appropriate responses by body

Peripheral Nervous System (PNS) - communicates sensory and motor signals between CNS and rest of body

Sensory neurons - communicate information from receptors to CNS

Interneurons - integrate sensory and motor output - connect only with other neurons

Motor neurons - convey information from CNS to effector cells

Supporting cells (glia) - provide support for nerves

Resting potential - membrane potential of nonconducting excitable cell - normally negative

Action potential - rapid change in membrane potential of excitable cell - caused by opening and closing of sodium and potassium ion gates in membrane - causes changes in concentrations inside and outside of cell

Potassium ions (+ charge) higher inside cell

Proteins & amino acids (- charge) normally higher inside cell

In nonconducting nerve cell, charge at rest negative (-70mV)

Protein "gates" in membrane

Pump sodium ions out of cell and potassium ions into cell (against concentration gradient) - requires energy

Maintains negative charge on inner surface of membrane (resting potential)

Depolarizing phase - sodium gates open - influx of sodium ions causes positive charge to develop on inner side of membrane

Repolarizing phase - potassium gates open - outflux of potassium ions causes negative charge to develop on inner side of membrane

Undershoot - continuing outflux of potassium accentuates negative charge

Depolarization of membrane at initial site spreads to adjacent area of axon - causes depolarization at second area - spreads to third area, etc.

Refractory period at initial site prevents "backward" movement of impulse

Impulse travels in one direction only

Presynaptic cell receives impulse - causes calcium to enter nerve cell

Synaptic vesicles containing neurotransmitter fuse with membrane - neurotransmitter released into synapse

Neurotransmitter binds to receptor(s) in postsynaptic cell - causes response

Neurotransmitter degraded rapidly

Gap junctions between cells allow ion currents of action potential to flow between neurons

Action potential spreads directly from presynaptic cell to postsynaptic cell

Single neuron may receive from numerous synapses - both excitatory and inhibitory

Excitatory postsynaptic potential - gates allow Na⁺ to enter & K⁺ to exit - neurotransmitter depolarizes membrane

Inhibitory postsynaptic potential - gates allow Cl^- to enter & K⁺ to exit- neurotransmitter hyperpolarizes membrane

Single EPSP usually not strong enough to trigger action potential in postsynaptic cell

Summation - addititive effect of EPSPs - may trigger action potential

Temporal summation - chemical transmissions close together in time

Spatial summation - transmissions close together in space

Many types - same neurotransmitter can produce different effects in different types of cells

Acetylcholine - one of most common in vertebrates and invertebrates - degraded by cholinesterase

Nerve net - no centralization - cnidarians

Bilaterally symmetrical - brain with 2 longitudinal nerve cords - flatworms

Brain & ventral nerve cord with ganglia - annelids & arthropods

Central nerve ring w/ radial nerve net - echinoderms

Highly centralized and cephalized - certain molluscs (squids & octupus) & vertebrates

Highly centralized and cephalized

Consists of central nervous system - brain & spinal cord - and the peripheral nervous system - cranial and spinal nerves originating in the brain

Brain provides integrative power underlying complex behavior

Spinal cord integrates simple responses - conveys information to and from brain

Axons within CNS within well-defined bundles

Brain and spinal cord contain cavities filled with cerebrospinal fluid - circulates nutrients & hormones - cushions brain

Consists of paired cranial and spinal nerves -associated ganglia

Divided into sensory (afferent) and motor (efferent) divisions

Sensory division conveys information to CNS from sensory neurons

Motor division conveys signals from CNS to effector cells

Somatic nervous system - carries signals to skeletal muscles in response to external stimuli

Autonomic nervous system - controls smooth and cardiac muscles & organs of gastrointestinal, excretory, cardiovascular and endocrine systems - regulation of internal environment

Parasympathetic division - signals enhance activities that gain and conserve energy - e.g., digestion and slowing heart rate

Sympathetic division - signals generally increase energy consumption and prepare individual for action - e.g., accelerating heart rate

Often have antagonistic or opposite effects

Develops from 3 anterior bulges of spinal cord - forebrain, midbrain & hindbrain

Brainstem - midbrain & hindbrain - medulla oblongata & pons control homeostatic functions - midbrain receives and integrates sensory information

Cerebellum - controls movement and balance

Thalamus & hypothalamus - forebrain - internal regulation & hormone production

Cerebrum - integration center