Chapter 48: The Nervous System

1. 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 or associative neurons within the CNS relay message Motor response A reaction or behavior resulting in response to a stimulus Effecter- muscle or gland which carries out a response

2. Neurons • Nerve cells • Structure similar in all organisms • Organization of cells varies among organisms • Parts • Dendrites • receive signal • Cell body • contains nucleus & other organelles • Axon • transmits signal • Myelin sheath • encloses axon, insulating signal • aids in speed of action potential • Terminal branches • 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 • regulate ion & neurotransmitter concentration; dilation of blood vessels • Radial glia • act as stem cells • Oligodendrocytes (CNS) & Schwann cells (PNS) • form myelin sheath

3. 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

4. Response of neurons • Graded potentials • Magnitude of depolarization or hyper-polarization varies with stimulus strength • Bigger stimuli= bigger change • Action potentials • 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

5. 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

6. 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

7. 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

8. Cerebellum • Lower, posterior portion of brain • Regulates muscle balance, tone, coordination, & error checking during motor, perceptual, & cognitive functions • Brainstem • 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

9. 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

10. Diseases & Disorders • Schizophrenia • Bipolar disorder/Manic depressive disorder • Major depression • Alzheimer’s disease • Parkinson’s disease