Nervous System AP Biology Chapter 48 https://www.youtube.com/watch?v=jubBNWbx3hM Nervous System AP Biology Chapter 48 Watch BioFlix on Nervous System ***Adapted from Kim Foglia’s powerpoint-Ch 48

Parts of a Neuron Cell Body Dendrites Receive stimuli Axon Transmits the nerve impulse Myelin sheath Made of Schwann cells insulation Nodes of Ranvier

The Neuron

Myelin Sheath

Nerve Impulse Direction The nerve impulse always travels FROM the dendrites TO the ends of the axon.

Basic Vertebrate Nervous System Controls mental/physical activity and homeostasis process information in 3 stages Sensory input, integration, motor output

Rapid involuntary stimulus Reflex Arc Rapid involuntary stimulus Bypasses the brain Involves Sensory and motor neuron Maybe neurons in spinal cord, but not brain

The Transmission of the Nerve Impulse Transmission occurs as a result of polarization across a neuron’s membrane Polarization difference in electrical charge which exists between the inside and outside of a membrane Cell Membrane of Axon +++++++ ------------

Cells: surrounded by charged ions (+ and -) Cells live in a aqueous solution of charged ions anions (negative ions ) more concentrated within the cell Cl-, charged amino acids, large marcromolecules cations (positive ions) more concentrated in the extracellular fluid OUTSIDE cell (or think “out” t for +) K+, Na+ channel leaks K+ K+ Na+ K+ Cl- aa- + K+ –

Cells have Voltage! Opposite charges on opposite sides of cell membrane membrane is polarized (polar = 2 different charges on each side) negative inside; positive outside charge gradient stored energy (like a battery) + This is an imbalanced condition. The positively + charged ions repel each other as do the negatively - charged ions. They “want” to flow down their electrical gradient and mix together evenly. This means that there is energy stored here, like a dammed up river. Voltage is a measurement of stored electrical energy. Like “Danger High Voltage” = lots of energy (lethal). – – + https://www.youtube.com/watch?v=YP_P6bYvEjE

Transmission of Nerve Impulse An unstimulated (resting) neuron is said to be polarized The inside of the membrane is negative (-) The outside of the membrane is positive (+) Voltage (difference in charges) measured across a membrane = membrane potential unstimulated neuron = has a resting potential of -70mV

How is polarization maintained across the neuron’s membrane? Some Na+ and K+ are always “leaking” through cell Na/K Pumps are embedded in membrane and actively restoring ions to the appropriate side Na+ K+ Cl- aa-

STEP #1: How does a nerve impulse travel? Stimulus: nerve is stimulated open Na+ channels in cell membrane reached threshold potential membrane becomes very permeable to Na+ Na+ ions diffuse into cell (from High  Low [ ]) charges reverse at that point on neuron positive inside; negative outside cell becomes depolarized – + Na+ Think: “in” is a 2 letters and so it “Na+”

STEP #2: How does a nerve impulse travel? Wave occurs: impulse travels down neuron change in charge opens other Na+ gates in next section of cell “voltage-gated” ion channels Na+ ions continue to move into cell “wave” moves down neuron = action potential – + Na+ wave (action potential) 

STEP #3: How does a nerve impulse travel? Re-set: 2nd wave travels down neuron K+ channels open up slowly K+ ions diffuse out of cell charges reverse back at that point negative inside; positive outside + – Na+ K+ wave (action potential)  Opening gates in succession = - same strength - same speed - same duration

Nerve Impulse Travels One Direction Combined waves travel down neuron wave of opening ion channels moves down neuron signal moves in one direction    flow of K+ out of cell stops activation of Na+ channels in wrong direction + – Na+ wave (action potential)  K+

How does the nerve re-set itself? After firing a neuron has to re-set itself Na+ needs to move back out K+ needs to move back in both are moving against concentration gradients need a pump for active transport!! + – Na+ K+ wave (action potential) 

How does the nerve re-set itself? Na+ / K+ pump active transport protein in membrane requires ATP 3 Na+ pumped out 2 K+ pumped in re-sets charge across membrane Dominoes set back up again. Na/K pumps are one of the main drains on ATP production in your body. Your brain is a very expensive organ to run! That’s a lot of ATP! Feed me some sugar quick!

Neuron is ready to fire again Na+ K+ Amino acids- aa- resting potential + –

Events of the Nerve Impulse

Note: action potential is an ALL or NOTHING http://bcs.whfreeman.com/WebPub/Biology/hillis1e/Animated%20Tutorials/at3402/at_3402_action_potential.html Note: action potential is an ALL or NOTHING If stimulus fails to produce depolarization that exceeds threshold value, then NO action potential results If the threshold value is met, then complete depolarization occurs

ALL Gates closed! hyperpolarization K+ gate opens; Na+ gates remain open Na+ gate opens Hyperpolarization is called an “Undershoot” When more K+ has moved out of the cell than is actually needed to repolarize it K+ gate remain open; Na+ gates close hyperpolarization ALL Gates closed!

Ending the Nerve Impulse Refractory Period When membrane is polarized but Na+/ K+ are on wrong sides of membrane neuron will NOT fire How to restore Na+ and K+ to proper positions? Na/K pumps Once the Na+ and K+ are restored, the refractory period is over and the neuron may respond to another stimulus

Speed of a Neuron Signal Transmission http://highered.mcgraw-hill.com/olc/dl/120107/bio_d.swf http://highered.mcgraw-hill.com/olc/dl/120107/anim0013.swf Extra Animations http://www.classzone.com/cz/books/bio_07/get_chapter_group.htm? cin=9&rg=animated_biology&at=animated_biology&var=animated_bi ology http://learn.genetics.utah.edu/content/begin/cells/cellcom/

Multiple Sclerosis (MS) immune system (T cells) attack myelin sheath 2005-2006 Multiple Sclerosis (MS) immune system (T cells) attack myelin sheath loss of signal

What happens at the end of the axon? Impulse has to jump the synapse! junction between neurons has to jump quickly from one cell to next How does the wave jump the gap? Synapse

from an electrical signal Synaptic terminal Chemicals stored in vesicles release neurotransmitters (LIGANDS) diffusion of chemical across synapse conducts the chemical signal across connecting neurons stimulus for receptors on dendrites of next neuron synaptic terminal We switched… from an electrical signal to a chemical signal neurotransmitter chemicals

http://highered.mcgraw-hill.com/olc/dl/120107/anim0015.swf

Many different types of molecules. 2005-2006 Many different types of molecules. Mostly small molecules — must diffuse across synapse.

Neurotransmitters Weak point of nervous system any substance that affects neurotransmitters or mimics them affects nerve function  gases: nitric oxide (NO), carbon monoxide (CO) mood altering drugs: stimulants amphetamines, caffeine, nicotine depressants hallucinogenic drugs Prozac Poisons, venom Since acetylcholinesterase has an essential function, it is a potential weak point in our nervous system. Poisons and toxins that attack the enzyme cause acetylcholine to accumulate in the nerve synapse, paralyzing the muscle. Over the years, acetylcholinesterase has been attacked in many ways by natural enemies. For instance, some snake toxins attack acetylcholinesterase.

The Nervous System: 2 Divisions Central Nervous System (CNS) Brain and Spinal Cord Peripheral Nervous System (PNS) Nerves **All animals except sponges Have some type of nervous system

Motor Neuron System Two main parts Somatic nervous system Directions contraction of skeletal muscles Autonomic nervous system Controls activities of organs and various involuntary muscles

Brainstem The “lower brain” Functions medulla oblongata pons midbrain Homeostasis (ex: breathing) coordination of movement conduction of impulses to higher brain centers

Medulla oblongata & Pons Controls autonomic homeostatic functions breathing heart & blood vessel activity swallowing vomiting digestion Relays information to & from higher brain centers

Midbrain Involved in the integration of sensory information regulation of visual reflexes regulation of auditory reflexes

Lateralization of Brain Function Left hemisphere language, math, logic operations, processing of serial sequences of information, visual & auditory details detailed activities required for motor control Right hemisphere pattern recognition, spatial relationships, non-verbal ideation, emotional processing, parallel processing of information

http://outreach.mcb.harvard.edu/animations/a ctionpotential_short.swf