Ch.48 Nervous System

I. Functions –A. Sensory input –B. Integration – interpretation of input –C. Motor output- involves effector cells like the muscles and endocrine glands

II. Parts of the nervous system –A. Central (CNS) – Brain and spinal cord –B. Peripheral (PNS) – Network of nerves that carry input from the body to the CNS and motor output away from CNS. –C. Neurons 1. Specialized for transmitting chemical and electrical signals 2. Large cell body –i. Contains most of the cytoplasm and nucleus of cell –ii. Usually in CNS or ganglia 3. Dendrites – convey signal to cell body (large surface area) 4. Axons – conduct impulses away from cell body –i. In vertebrate PNS they are wrapped into Schwann cells which form an insulating myelin sheath –ii. Synapse- gap between terminal and target cell –iii. Neurotransmitters – chemical that cross the synapse to relay impulse to next cell.

5. Classes of neurons –i. Sensory – convey info about environment from receptors to CNS –ii. Interneurons –integrate sensory input and motor output –iii. Motor –convey impulses from CNS to effector cells 6. Neurons are arranged in groups –i. Simple circuit – synapse between sensory and motor (reflex). –ii. Convergent – Info from several neurons come together at one neuron. –iii. Divergent – Info from a single neuron spreads to several neurons –iv. Reverberating – Circular (memory) –v. Nucleus – cluster of nerve cell bodies in the brain –vi. Ganglion – Cluster in the PNS –vii. Glia – cells which reinforce, insulate and protect neurons

III. Neural signals –A. Membrane potentials 1. –50 to –100mV in animal cells 2. Outside cell is zero, cytoplasm is negatively charged compared to outside 3. –70mV = resting neuron 4. Inside cell = K+, outside Na+ 5. Amino acids, phosphates (-) inside, Cl- outside –B. Creation of the membrane potential 1. K+ diffuse out (+ moves outside) 2. Negative molecules are too big to leave 3. Negative charge inside attracts K+ back and Na+ also. 4. This creates a slight + charge inside 5. Na+ is pumped out by Na/K pump

C. Action potential – only neurons –1. Due to the presence of gated ion channels –2. Stimuli that open K channels hyperpolarize the neuron (interior -) –3. Stimuli that open Na channels depolarize the cell (interior +) –4. When the cell reaches a threshold an action potential is triggered. Hyperpolarization makes the cell less likely to reach the threshold

5. Four phases of an action potential –i. Resting state – no channels open –ii. Large depolarization ( inside +, outside -), Na travels in –iii. Repolarization – Na gates closed, K open –iv. Undershoot – hyperpolarization – refractory period 6. Self – propagating 7. Electrical synapses – impulses travel from one cell to another ( less common than chemical) 8. Chemical synapses – involves release of Ca+ ions which stimulate the release of neurotransmitters which bind to receptors and open ion gates

9. Types of neurotransmitters –i. Acetylcholine – functions between motor neuron and muscle cell and CNS –ii. Biogenic amines – derived from amino acids. Epinephrine, norepinephrine and dopamine from tyrosine and serotonin from tryptophan (imbalances of dopamine and serotonin are associated with mental illness) –iii. Amino acids –iv. Neuropeptides – endorphins –v. Gaseous transmitters – NO and CO

IV. Organization of the nervous system –A. Correlates to body symmetry 1. Cnidaria have a nerve net ( no central control) 2. Cephalization in bilateral organisms –i. Flatworms – simple brain –ii. Annelids and arthropods have ventral nerve cord and brain

B. Vertebrate nervous system –1. CNS- spinal cord and brain covered with meninges (connective tissue) –2. In brain white matter is interior, gray is outer, opposite in spinal cord –3. Cerebrospinal fluid – circulates hormones,nutrients and white blood cells, also absorbes shock. –4. PNS – 12 pairs of cranial nerves and 31 pairs of spinal nerves i. Sensory division – to CNS ii. Motor division – CNS to effector cells iii. Control responses to environment and maintain homeostasis iv. Somatic system - voluntary skeletal muscle v. Autonomic – involuntary (parasympathetic-conserve energy, sympathetic – increases energy use.