Zoology 101: Animal Biology Last Lecture Outline Lecture 23 1. Lungs/gas exchange in the lungs2. Circulatory system3. Blood Current Lecture 1. Neuroscience• Dendrites • Nervous systems 2. How does a neuron transmit a signal?Neuroscience • Nervous systems provide a rapid response by integrating internal and external information• made up of neurons and supporting cells• The more complex you get in animal body plans, the more complex the nervous system◦ Sponges do not have a nervous system◦ Vertebrae have several hundred thousand neurons, a spinal cord, and sensory ganglia ◦ Cephalization: cluster of interneurons and sensory neurons at the front end (brain) • Neuron◦ Dendrites receive the signal◦ cell body maintains the neuron ◦ axon hillock generates the signal (point of summation) ◦ The axon sends signals to terminal branches (myelin sheath coats the terminal)◦ Synaptic terminal sends signal to other cell• Vertebrae nervous system has a central nervous system (brain, spinal cord) and a peripheral nervous system • Peripheral nerves are outside of CNS◦ Comprised of 3 components (2 efferent, 1 afferent)◦ Efferent: Motor system- Signals skeletal movement ▪ Autonomic: involuntary, controls smooth muscles ◦ Afferent: sensory system (external cue) • Subdivisions ◦ Afferent take to the brain (internal/external stimuli) → CNS◦ CNS will send out to the PNS ▪ Autonomic splits into sympathetic, parasympathetic, enteric (involuntary) and motor system (control of skeletal muscle..voluntary) • Sympathetic: regulates arousal and energy generation (fight or flight), secretes epinephrine, inhibits digestion, increases heart rate• Parasympathetic: promotes calming and a return to rest/digestion functions, decreases heart rate, increases digestion • Enteric: controls activity of digestive tract, pancreas and gall bladder, regulates secretions and peristalsis • Complex animals CNS interacts with PNS (see figure 49.3 in book) ◦ Class example: a hyena and a dead zebra ▪ sensory neurons/ input (PNS → CNS) ▪ Interneurons and integration ▪ Motor (effector) neurons/ output (CNS → PNS) • Form of neurons match function ◦ Sensory and motor neurons: long, few connections ◦ Interneurons: short, many connections • Brain has supporting cells called glial cells; several types and they out number neurons ◦ Oligodendrites (CNS) and Schwann cells (PNS) myelnate axons to increase signal speed ◦ Astrocytes provide metabolic support to neurons and form the blood-brain barrier (helps filter toxins from the brain, allows Oxygen to pass through, alcohol can pass through) How does a neuron transmit a signal?• Every cell has membrane potential: electrical potential difference (voltage) across plasma membrane (-70mV)• Inside of a cell is more negative relative to the outside ◦ Outside: high [Na+] [Cl-] ◦ Inside: High [K+] A- (anions found in macromolecules) • Resting potential: membrane potential of a neuron not transmitting a signal • Active transport of ions helps maintain resting potential • Na+ and K+ channels are selectively permeable • Sodium potassium pump: pushes Na+ ions out of cell and K+ into cell • Ion channels closed in a neuron at rest • Hyperpolarization: cell becomes more negative on inside relative to outside◦ These responses are graded potentials: amplitude depends on strength stimulus • Depolarization: cell becomes less negative on inside relative to outside◦ sodium enters ◦ graded potentials: depend on strength of stimulus • Threshold: point at which something will happen (just enough to occur) • When graded potential is large enough/reaches threshold → stimulates action potential◦ action potential: nerve impulse that carries electrical signal along axon ◦ All or none principle: It either fires or it waits till it has enough to fire completely (will not half fire) Threshold is -55 mV• Resting state: most voltage, gated channels are closed • Depolarizing: stimulus opens some Na+ channels, Na moves into cells • Rising phase of action potential: most Na+ channels are open, inside of cell mostly positive • Falling phase of action potential: Na+ gates close, K+ channels open, K+ rushes out of the cell, inside of the cell is now negative • Undershoot: Na pump is still closed, few K+ channels are open, cell becomes more negativethan initial state , K+ leaving is
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