Warm Up for Thurs. 1/8  Please do this on your own paper:  Define passive and active transport. Give at least one example for each.

Human Nervous System Central and Peripheral

A General Sense…

Peripheral Nervous System Central Nervous System -Brain -Spinal Cord Motor Neurons -carry signals away from CNS Sensory Neurons -carry messages towards spinal cord from sensory receptors Somatic System: Voluntary Nerves --neurons control skeletal muscles Autonomic System: Visceral, Involuntary --heart, blood vessels, digestive organs, smooth muscle Sympathetic Division --“fight or flight” --activated by stress Parasympathetic Division: --Routine An Overview of the Nervous System:

Nervous System Cells  Called neurons  Neurons have long axons that enable them to transmit signals. Many neurons together are called a nerve.  Each nerve has a dorsal root (info into the CNS) and a ventral root (info out from CNS to body).

Neuron Anatomy

Anatomy of a Neuron  Cell body – main part, has nucleus  Dendrite – receives action potential (stimulation) from other neurons  Axon – branches from cell body, where the action potential occurs  Axon terminal – end of an axon  Myelin sheath – lipid layer for protection over neurons that allows for increase in speed of signal transmission; made by Schwann cells  Nodes of Ranvier – gaps in myelin sheath along the axon, where most Na+ pumps are located  Synaptic Cleft – gap between neurons; between the axon terminal of one neuron and the dendrite of a second neuron

Anatomy of a Neuron-Draw this!

Central Nervous System (CNS) BRAIN  About 1.4 kg, 2% of body weight  About 100 billion neurons  12 pairs of cranial nerves are connected to the human brain Example: Pupil reflex in response to bright light, to avoid damage to retina. Nerves that control this reflex are connected to the brain.Example: Pupil reflex in response to bright light, to avoid damage to retina. Nerves that control this reflex are connected to the brain. Others: blinking, Hering-Breuer reflexOthers: blinking, Hering-Breuer reflex

Spinal Cord  Starts at the medulla oblongata (in the brain)  Outer area is made up of the axons of the neurons: “white matter”  Inner, rigid core made up of cell bodies: “gray matter”  31 pairs of spinal nerves branch out to the body  Spinal Reflexes: these don’t go to the brain, instead they go to the spinal cord--patellar reflex

The Patellar Reflex

Peripheral Nervous System (Motor and Sensory) Motor Division: signals away from CNS  Somatic nervous system is for voluntary muscle control. These neurons control the skeletal muscles…. Also some spinal reflexes. EX = patellar reflex  Autonomic nervous system is automatic. Control of heart rate, respiration, blood pressure, smooth muscle, etc. This has 2 separate divisions: sympathetic and parasympatheticThis has 2 separate divisions: sympathetic and parasympathetic

Autonomic: Sympathetic Division & Parasympathetic Division  Sympathetic: Shunting of blood from one part of body (ex = stomach to heart) to another. Activated by physical or emotional stress. “Fight or Flight” response.  Parasympathetic: Routine life, conserves energy, heart rate lowers, digestive organs back to normal. “Rest and Ruminate” response.

Autonomic NS: Parasympathetic and Sympathetic Controls

Peripheral Nervous System Sensory Division  Sensory neurons carry messages toward the CNS from sensory receptors all over body.  Sensory receptors act as “energy transducers”. A transducer is a device for converting a non- electrical signal into an electrical one. In this case, the electrical signal produced is the action potential of a nerve.  Sensory receptors are in sense organs, such as eyes, ears, mouth, nose, skin… and different regions of the brain respond to different signals.

Warm Up  Friday 1/9/09 What are the two types of neurons of the Peripheral Nervous System and what do they do?  Answer:

Types of Sensory Receptors Stimulus Type of Sensory Receptor Location LightPhotoreceptorsRetina MechanicalMechanoreceptors Under the skin, inner ear HeatThermoreceptors Hypothalamus, under the skin PressureBaroreceptors Walls of some arteries ChemicalsChemoreceptor Mouth, nose

Transmission of neural signals: How it Works…  In general, the signaling activity of the nervous system is composed of electrical activity within neurons and chemical flow between neurons. Quite a complex network!  200 years ago… found out that a recently dead animal will still contract muscles if an electrical stimulation is sent through.

Within one neuron…  The “resting potential” of a neuron is -70 millivolts. The inside of the cell is relatively more negative than the outside, due to an imbalance of ions and some negatively charged proteins inside.  When a dendrite/cell body is stimulated (pressure, light, air vibrations, etc.), membranes become temporarily permeable to Na + ion at the site of stimulation (triggers these gates to open).  Na+ ions rush into the cell, through gated protein channels, and the inside becomes more positive. This reverse of polarity begins an “action potential.” The action potential starts where the cell body meets the axon. Action potential is about +30 millivolts. Threshold potential is about -50 millivolts.  Gated channels keep opening along the axon, and Na+ continues to enter…. Much like fire burns down a rope. Action potential continues from start of axon to terminal, always in one direction.

And even more… AH!  Shortly after Na + channels open, they close, and the K + channels open, allowing K + ions to leave the cell, and the resting potential returns.  The neuron cannot generate another action potential during this time. Na + gates close, K + flow out returns the neuron to resting potential. This period is called the “refractory period.”  The Na + /K + pump (that we learned about in active transport) pumps away to keep the proper concentrations of ions across the membrane. This requires lots of energy – ATP!

Diagram of action potential through an axon…

Transmitting to another neuron…  When the Action Potential reaches the axon terminal, vesicles which contain neurotransmitters fuse with the pre-synaptic membrane (1 st neuron).  Neurotransmitters are released via exocytosis, and they bind to receptors in the postsynaptic membrane (2 nd neuron).  This signals Na+ ion channels to open in the 2 nd neuron, and Na+ comes rushing in…and if there is enough of a stimulation, and the action potential is created then the electrical signal is continued.  This is all or nothing. Not enough Na+ in, not enough change in polarity, no action potential will happen.  Note: The release of neurotransmitter at the axon terminal is caused by Ca +2 coming into the cell.

Examples of Neurotransmitters  Acetylcholine: in skeletal muscles  Norepinephrine and Epinephrine: respond to stress  Dopamine & Serotonin: in the brain  Enzymes break down neurotransmitters so neurons are not “over stimulated.” Ex. = cholinesterase (breaks down acetylcholine). Ex. = cholinesterase (breaks down acetylcholine).

A Little Quiz…  1. What is the potential for the resting neuron?  2. What is the potential for a neuron that is sending an action potential?  3. When a neuron goes from its resting potential to its action potential… which ion moves? Where does the ion move? How does it move? Active or Passive?  4. When a neuron goes from its action potential to its resting potential… which ions move? Where do they move? How does it move? Active or Passive?

A Few More…  5. Where in the neuron is the presynaptic membrane? (axon, cell body, or dendrite)  6. What happens when the action potential reaches the presynaptic membrane?  7. What happens when the neurotransmitter binds to the receptors on the postsynaptic membrane?