Ch. 43 Review Warm-Up Contrast the functions of B cells and T cells. What are memory cells? How do vaccines work? How does HIV affect the immune system?

Warm-Up Draw and label the parts of a neuron. Describe saltatory conduction. Explain how a nerve impulse is transmitted across a neuron.

Warm-Up What happens at the synapse? Choose 1 neurotransmitter. Describe its action. What is the role of the following structures in the human brain? Brainstem Cerebellum Cerebrum Corpus callosum

Chapters 48 & 49 Campbell Biology – 9th ed. Nervous Systems Chapters 48 & 49 Campbell Biology – 9th ed.

You must know The anatomy of a neuron. The mechanisms of impulse transmission in a neuron. The process that leads to release of neurotransmitters, and what happens at the synapse. How the vertebrate brain integrates information, which leads to an appropriate response. Different regions of the brain have different functions.

Organization of the Nervous System Central nervous system (CNS) = brain + spinal cord Peripheral nervous system (PNS) = nerves throughout body Sensory receptors: collect info Sensory neurons: body  CNS Motor neurons: CNS  body (muscles, glands) Interneurons: connect sensory & motor neurons Nerves = bundles of neurons Contains motor neurons +/or sensory neurons

Neuron Functional Differences Integrates and coordinates info from afferent, sends out response to efferent

Peripheral Nervous System Somatic nervous system Autonomic nervous system Sympathetic division Parasympathetic division Enteric division

Neuron = dendrite + cell body + axon

Neuron cell body: contains nucleus & organelles dendrites: receive incoming messages axons: transmit messages away to other cells myelin sheath: fatty insulation covering axon, speeds up nerve impulses synapse: junction between 2 neurons neurotransmitter: chemical messengers sent across synapse Glia: cells that support neurons Eg. Schwann cells (forms myelin sheath)

Schwann cells and the myelin sheath

Myelin sheath Axon coated with Schwann cells Insulation material (lipid) speeds up signal saltatory conduction Signal “jumps” between gaps in myelin sheath 150 m/sec vs. 5 m/sec (330 mph vs. 11 mph) signal direction myelin sheath

Multiple Sclerosis action potential saltatory conduction Na+ myelin + – axon + + + + – Na+ Multiple Sclerosis immune system (T cells) attack myelin sheath loss of signal

BioFlix: How Neurons Work

Membrane Potential: difference in electrical charge across cell membrane Microelectrode –70 mV Voltage recorder Reference electrode

Neuron at Resting Potential Opposite charges on opposite sides of cell membrane membrane is polarized negative inside; positive outside charge gradient (-70mv) 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). – – +

What makes it polarized? Cells live in a sea of charged ions anions (negative) more concentrated within the cell Cl-, charged amino acids (aa-) cations (positive) Na+ more concentrated in the extracellular fluid Salty Banana! channel leaks K+ K+ Na+ K+ Cl- aa- + – K+

The Na+/K+ pump (using ATP) maintains a negative potential inside the neuron.

Action potentials (nerve impulses) are the signals conducted by axons Resting potential: membrane potential at rest; polarized Na+ outside, K+ inside cell Voltage-gated Na+ channel = CLOSED Nerve impulse: stimulus causes a change in membrane potential Action potential: neuron membrane depolarizes All-or-nothing response Na+ channels open K+ channels open Na+ enters cell K+ leaves cell

How does a nerve impulse travel? Stimulus: nerve is stimulated reaches threshold potential open Na+ channels in cell membrane Na+ ions diffuse into cell charges reverse at that point on neuron positive inside; negative outside cell becomes depolarized The 1st domino goes down! – + Na+

Depolarization Wave: nerve impulse travels down neuron – + change in charge opens next Na+ gates down the line “voltage-gated” channels Na+ continues to diffuse down neuron “wave” moves down neuron = action potential Gate + – channel closed channel open The rest of the dominoes fall! – + Na+ wave 

Voltage-gated channels Ion channels open & close in response to changes in charge across membrane Structure & function! Na+ channel closed when nerve isn’t doing anything.

Repolarization Re-set: 2nd wave travels down neuron + – K+ channels open K+ channels open up more slowly than Na+ channels K+ ions diffuse out of cell charges reverse back at that point negative inside; positive outside Set dominoes back up quickly! + – Na+ K+ wave  Opening gates in succession = - same strength - same speed - same duration

How does a nerve impulse travel? wave of opening ion channels moves down neuron flow of K+ out of cell stops activation of Na+ channels in wrong direction Animation Ready for next time! + – Na+ wave  K+

How does the nerve re-set itself? Sodium-Potassium pump active transport protein in membrane requires ATP 3 Na+ pumped out 2 K+ pumped in re-sets charge across membrane ATP 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!

Conduction of an action potential

Action potential graph Resting potential Stimulus reaches threshold potential Depolarization Na+ channels open; K+ channels closed Na+ channels close; K+ channels open Repolarization reset charge gradient Undershoot K+ channels close slowly 40 mV 4 30 mV 20 mV Depolarization Na+ flows in Repolarization K+ flows out 10 mV 0 mV –10 mV 3 5 Membrane potential –20 mV –30 mV –40 mV Hyperpolarization (undershoot) –50 mV Threshold –60 mV 2 –70 mV 1 Resting potential 6 Resting –80 mV

All or nothing response Once first one is opened, the rest open in succession a “wave” action travels along neuron have to re-set channels so neuron can react again How is a nerve impulse similar to playing with dominoes?

Nerve Impulse Animation

Saltatory conduction speed: 120 m/sec Saltatory conduction: nerve impulse jumps between nodes of Ranvier (unmyelinated gaps)  speeds up impulse Saltatory conduction speed: 120 m/sec

BioFlix: How Synapses Work

Cell communication: neurotransmitter released at synapses Axon (presynaptic cell)  Dendrite (postsynaptic cell)

The Synapse ion-gated channels open Action potential depolarizes membrane Opens Ca++ channels Neurotransmitter vesicles fuse with membrane Release neurotransmitter to synapse  diffusion Neurotransmitter binds with protein receptor ion-gated channels open Neurotransmitter degraded or reabsorbed axon terminal action potential synaptic vesicles synapse Ca++ Calcium is a very important ion throughout your body. It will come up again and again involved in many processes. neurotransmitter acetylcholine (ACh) receptor protein muscle cell (fiber) We switched… from an electrical signal to a chemical signal

Neurotransmitters Chemicals released from vesicles by exocytosis into synaptic cleft Diffuse across synapse Bind to receptors on neurons, muscle cells, or gland cells Broken down by enzymes or taken back up into surrounding cells Types of neurotransmitters: Excitatory: speed up impulses by causing depolarization of postsynaptic membrane Inhibitory: slow impulses by causing hyperpolarization of postsynaptic membrane

Examples of Neurotransmitters Acetylcholine (ACh): stimulates muscles, memory formation, learning Epinephrine: (adrenaline) fight-or-flight Norepinephrine: fight-or-flight Dopamine: reward, pleasure (“high”) Loss of dopamine  Parkinson’s Disease Serotonin: well-being, happiness Low levels  Depression GABA: inhibitory NT Affected by alcohol

Weak point of nervous system Any substance that affects neurotransmitters or mimics them affects nerve function Ex: Gases, drugs, poisons Acetylcholinesterase inhibitors = neurotoxins! Ex: snake venom, insecticides Selective serotonin reuptake inhibitor Snake toxin blocking acetylcholinesterase active site

Mouse Party

Reflexes Simple, automatic response to a stimulus Conscious thought not required Reflex arc: Stimulus detected by receptor Sensory neuron Interneuron (spinal cord or brain stem) Motor neuron Response by effector organ (muscles, glands)

Knee-jerk reflex

Vertebrate Brains Evolutionary trends towards “Cephalization” Central region for integrating and coordinating information. Different regions have different functions:

Forebrain  cerebrum Midbrain  brainstem Hindbrain  cerebellum

Human Brain Structure Function Cerebrum Brainstem Cerebellum Information processing (learning, emotion, memory, perception, voluntary movement) Right & Left cerebral hemispheres Corpus callosum: connect hemispheres Brainstem *Oldest evolutionary part* Basic, autonomic survival behaviors Medulla oblongata –breathing, heart & blood vessel activity, digestion, swallowing, vomiting Transfer info between PNS & CNS Cerebellum Coordinate movement & balance Motor skill learning

Human Brain Structure Function Cerebrum Brainstem Cerebellum Information processing (learning, emotion, memory, perception, voluntary movement) Right & Left cerebral hemispheres Corpus callosum: connect hemispheres Brainstem *Oldest evolutionary part* Basic, autonomic survival behaviors Medulla oblongata –breathing, heart & blood vessel activity, digestion, swallowing, vomiting Transfer info between PNS & CNS Cerebellum Coordinate movement & balance Motor skill learning

Human Brain Structure Function Cerebrum Brainstem Cerebellum Information processing (learning, emotion, memory, perception, voluntary movement) Right & Left cerebral hemispheres Corpus callosum: connect hemispheres Brainstem *Oldest evolutionary part* Basic, autonomic survival behaviors Medulla oblongata –breathing, heart & blood vessel activity, digestion, swallowing, vomiting Transfer info between PNS & CNS Cerebellum Coordinate movement & balance Motor skill learning

Human Brain Structure Function Cerebrum Brainstem Cerebellum Information processing (learning, emotion, memory, perception, voluntary movement) Right & Left cerebral hemispheres Corpus callosum: connect hemispheres Brainstem *Oldest evolutionary part* Basic, autonomic survival behaviors Medulla oblongata –breathing, heart & blood vessel activity, digestion, swallowing, vomiting Transfer info between PNS & CNS Cerebellum Coordinate movement & balance Motor skill learning

Grey matter: neuron cell bodies, unmyelinated axons White matter: fatty, myelinated axons

Discovery Video: Teen Brains