Presentation on theme: "THE NERVOUS SYSTEM NERVOUS SYSTEM: Receives & relays info. About activities w/in the body & monitors & responds to internal & external changes. NEURONS:"— Presentation transcript:
THE NERVOUS SYSTEM NERVOUS SYSTEM: Receives & relays info. About activities w/in the body & monitors & responds to internal & external changes. NEURONS: Cells that carry messages throughout the NS. Impulses- Messages taking the form of electrical signals Sensory- from sense organs to brain & spinal cord Motor- from brain & spinal cord to muscles or glands Interneurons- connect sensory & motor neurons Parts: Cell body-Lgst. Part w/ nucleus & cytoplasm; ATP Dendrites-Short branched extensions carrying impulses from environment or other neurons toward cell body. Axon- Long fiber carrying impulses away from cell body Axon terminals- series of small swellings at the end of the axon; located some distance from cell body. (fig. 37-3)
THE NERVE IMPULSE-1 Luigi Galvani: Found that nerves work with electrical charges along the cell membrane due to mov’t of ions across membranes. RESTING POTENTIAL (Figure 37-4) Nerve cells have an electrical potential of 70 mV. Due to the difference of + & - charged ions on each side of the cell mem. Na + -K + pumps move Na + ions out of cell and actively pump K + ions into the cell. This Active transport causes the cytoplasm to have more K + ions and fewer Na + ions than the surrounding medium. The cytoplasm has negatively charged protein molecules & ions. The K + ions leak back out more easily than Na + ions leak in, and the – charged molecules don’t leak in or out. The net result is a – charge on the inside of the cell membrane. This is known as resting potential. Causing it to be polarized. (fig. 37-4) (- chgd. On the inside & + chgd. On the outside)
THE NERVE IMPULSE 2 The moving impulse (like the mov’t. of water rippling in a pond) Cell membrane has “gates” that allow Na & K to go through At impulse, gates open so Na + flow inside the membrane causing the cell membrane to be depolarized. As impulse passes, K + gates open allowing + chgd. K + ions to flow out. (repolarized) Action Potential: The depolarization and repolarization of a membrane. Several impt. Facts: Not an electric current; it’s a wave of depolarization and repolarization passing along a neuron. Much slower than an electric current. (10cm to 1m/sec.) The strength of an impulse is always the same.
THE SYNAPSE Receptor: Sensory neurons in sense organs that receive stimuli from their external environment. Effector: Muscles or glands that bring about a response. Synapse: Points of contact at which impulses are passed from one cell to another. Neurotransmitters: substance used by neurons to signal each other located within tiny vesicles at axon terminals. Impulse moves down axon & vesicles discharge the neurotransmitters into gap between which diffuse into special receptors on next neuron. Permeability of the membrane changes, Na + ions diffuse through membrane which can depolarize the neuron. Threshold is reached and an impulse begins in 2 nd cell. Neurotransmitter detaches, is remove or destroyed halting the effect.
THE NERVE IMPULSE-3 Propagation of the impulse An impulse at one point of the membrane causes the impulse at the next point of the membrane Unlike dominoes, it can restore itself. The mov’t. is only in one direction because Na gates will not open. The Role of Myelin Made of lipids & proteins, it forms an insulated sheath, wrapping around the the axon. Myelin has small nodes, gaps, between adjacent sheaths along axons. This allows the impulse to jump from node to node greatly increasing the speed of the impulse. The Threshold: Minimal level of a stimulus that is required to activate a neuron. (All or none; dominos) Not restricted to impulses as they travel along neurons. It also occurs when they move from one neuron to another.