Transcript Document
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. – A. • • • • • – B. • • • • • Neural signals 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 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. ii. iii. iv. Resting state – no channels open Large depolarization ( inside +, outside -), Na travels in Repolarization – Na gates closed, K open 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. – A. • • Organization of the nervous system 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.