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Chapter 48: The Nervous System The nervous system & endocrine system work to regulate the organism & maintain homeostasis. Nervous system Involves: Sensory reception Stimulus (change in environment) triggers a response concentrated in sense organs Sensitivity determined by density of receptors Integration Interneurons Motor A or associative neurons within the CNS relay message response reaction or behavior resulting in response to a stimulus Effecter- muscle or gland which carries out a response Neurons Nerve cells Structure similar in all organisms Organization of cells varies among organisms Parts Dendrites Cell body Axon transmits signal encloses axon, insulating signal aids in speed of action potential Terminal branches contains nucleus & other organelles Myelin sheath receive signal may contain neurotransmitters Synaptic gap site of communication between 2 neurons via neurotransmitters *Impulse enters via dendrites & exits via terminal branches Glia= supporting cells Types Astrocytes Radial glia regulate ion & neurotransmitter concentration; dilation of blood vessels act as stem cells Oligodendrocytes (CNS) & Schwann cells (PNS) form myelin sheath Reflexes Automatic, inborn, unlearned Protective responses to stimulation Examples: blinking, sneezing, coughing Reflex arc Stimulus (receptors on sense organ) sensory neuron interneuron within CNS (analyze & interpret) motor neuron effectors at neuromuscular junction Instincts- automatic & inborn like reflexes but not necessarily protective in function Habits Automatic, learned behaviors Examples: smoking, tying shoe laces, using profanity, writing Response of neurons Graded potentials Magnitude of depolarization or hyper-polarization varies with stimulus strength Action potentials Bigger stimuli= bigger change All or none depolarization Same strength regardless of stimulus Nerve impulse Electrochemical signal; speeds of 100 meters/second Resting state both Na+ & K+ activation gate channels are closed Resting potential- membrane more permeable to K+ so more K+ moves out than Na+ moves in. Ion permeability must change to send an impulse Threshold must be achieved to depolarize neuron membrane & produce an action potential Depolarization: Na+ channels open & Na+ flows into neuron reversing polarity Re-polarization: K+ ions allowed into neuron as Na+ is blocked Refractory: brief period of time when cell can not be stimulated to carry an impulse The Synapse Types Electrical synapses Gap junctions allow action potential to travel cell to cell Chemical synapses Neurotransmitters released from synaptic vesicles & bind to dendrites of next neuron to start a new action potential **Majority of synapses Neurotransmitters Chemicals released into synaptic gap that diffuse & bind to next neuron Ca+2 required for release Excitatory neurotransmitters Transmit impulses Examples: acetylcholine (to skeletal muscle), norepinephrine, dopamine, glutamate, aspartate Inhibitory neurotransmitters Block impulse transmission Examples: acetylcholine (to cardiac muscle), serotonin, epinephrine, glycine, GABA, endorphins Regulation in invertebrates Protists Sensitive to light, chemicals, temperature Cnideria (hydra) Nerve net Whole organism responds to stimulus Annelida (earthworm) Ventral nerve cord Fused ganglia (clusters of neurons) acting as brain Arthropoda (insects) Ventral nerve cord Sensory organs Antennae Tympanum Compound eyes Mammalian Nervous System Central Nervous System Cerebrospinal fluid helps supply nutrients & hormones to brain & removes waste cushions brain & spinal cord Meninges- protective layers surrounding brain & spinal cord Brain Cerebrum Largest, upper portion of brain thinking, memory, body awareness, social behavior, language EEG (electroencephalogram) detects brain wave activity Convolutions- folds in brain Limbic system- lower part of brain that interacts with cerebral cortex to produce emotions, complex reasoning, & personality Includes: Amygdala- emotional memories Hippocampus- emotional events, long term memories Olfactory bulb Corpus callosum- axons that enable communication between hemispheres of cerebrum Lobes: Frontal- speech, motor function Temporal- smell, hearing, auditory association Occipital- vision Parietal- reading, somatosensory association, speech, taste Cerebellum Brainstem Lower, posterior portion of brain Regulates muscle balance, tone, coordination, & error checking during motor, perceptual, & cognitive functions Primitive brain controlling involuntary activities includes: Midbrain Pons- heart beat, swallowing, vomiting, digestion Medulla oblongata- breathing Reticular formation network of neurons in the brainstem which selects information being sent to cerebral cortex affects alertness Diencephalon Includes Epithalamus- pineal gland & choroid plexus Thalamus- input center for sensory info & output center for motor info & emotions Hypothalamus- homeostatic regulation; connection between nervous & endocrine systems; regulates circadian rhythms Spinal cord- connects the brain to the peripheral nervous system Peripheral nervous system System of branching nerves linking CNS to body tissues & organs Consists of: Somatic nervous system Voluntary control or awareness of muscles, sense organs, & skin Allows for conscious control in response to external stimulation Autonomic nervous system Automatic, unconscious or involuntary regulation Regulates internal environment by controlling smooth & cardiac muscle & organs Includes Sympathetic nervous system- increased heart beat, blood vessel constriction, bronchi open, pupils dilate, peristalsis slows, bladder relaxes Parasympatheic nervous system- reverse reactions of sympathetic nervous system Enteric nervous system- network of neurons to control organ secretions & smooth muscles; regulated through the sympathetic & parasympatheic nervous systems Diseases & Disorders Schizophrenia Bipolar disorder/Manic depressive disorder Major depression Alzheimer’s disease Parkinson’s disease