AP Bio – 3/19/13 The Nervous System, Chp.48 Body Systems Test Thursday (Chp.40, 43 (Immune), 45 (Endocrine), & 48 (Nervous) 1

2 Animals have nervous systems that detect external and internal signals, transmit and integrate information, and produce responses. The Nervous System

What trends do you notice?

Noteworthy Trends In Development Increase in ganglia Increase in sensory reception Increase in cephalization – Cephalization is the concentration of nervous tissue in the anterior region of the organism. 4

Human Nervous System 5

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Neuron = nerve cells The neuron is the basic structure of the nervous system that reflects function. Neuron structure allows for the detection, generation, transmission, and integration of signal information. 8

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Neuron Anatomy A typical neuron has a cell body, axon and dendrites. 10

Myelin Sheath  Axon coated with Schwann cells  insulates axon  speeds signal  signal hops from node to node  saltatory conduction 11

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

dendrites cell body axon synaptic terminal  Structure fits function  many entry points for signal  one path out  transmits signal signal direction signal direction synapse myelin sheath dendrite  cell body  axon

Evolutionary Adaptations of Axon Structure The speed of an action potential increases with the axon’s diameter In vertebrates, axons are insulated by a myelin sheath, which causes an action potential’s speed to increase

Axon Myelin sheath Schwann cell Nodes of Ranvier Node of Ranvier Layers of myelin Axon Schwann cell Nucleus of Schwann cell 0.1  m

Cell body Schwann cell Depolarized region (node of Ranvier) Myelin sheath Axon Saltatory Conduction Saltatory conduction. Notice that the conduction along a myelinated axon can occur quickly as large spaces can be skipped and impulse propagation occurs only at the nodes of Ranvier.

Describe a Resting Potential: Membranes of neurons are polarized by the establishment of electrical potentials across the membranes 17 What is the charge inside the neuron at rest?

Source of Charge Differences: 18

Action Potential Action potentials propagate impulses along neurons. – In response to a stimulus, Na + and K + gated channels sequentially open and cause the membrane to become locally depolarized. – Na + /K + pumps, powered by ATP, work to maintain membrane potential. 19

Figure 48.11a Action potential Threshold Resting potential Time Membrane potential (mV)  50  100 

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

OUTSIDE OF CELL INSIDE OF CELL Inactivation loop Sodium channel Potassium channel Threshold Resting potential Time Membrane potential (mV)  50  100  50 0 Na  KK Key 1 1 Resting state At resting potential 1.Most voltage-gated sodium (Na + ) channels are closed; most of the voltage- gated potassium (K + ) channels are also closed

OUTSIDE OF CELL INSIDE OF CELL Inactivation loop Sodium channel Potassium channel Threshold Resting potential Time Membrane potential (mV)  50  100  Resting state Depolarization When an action potential is generated 2.Voltage-gated Na + channels open first and Na + flows into the cell

OUTSIDE OF CELL INSIDE OF CELL Inactivation loop Sodium channel Potassium channel Action potential Time Membrane potential (mV)  50  100  50 0 Na  KK Key Resting state Depolarization Rising phase of the action potential 3.During the rising phase, the threshold is crossed, and the membrane potential increases to and past zero

OUTSIDE OF CELL INSIDE OF CELL Inactivation loop Sodium channel Potassium channel Action potential Threshold Resting potential Time Membrane potential (mV)  50  100  50 0 Na  KK Key Resting state Depolarization Rising phase of the action potential Falling phase of the action potential 4. During the falling phase, voltage-gated Na + channels become inactivated; voltage-gated K + channels open, and K + flows out of the cell

5. During the undershoot, membrane permeability to K + is at first higher than at rest, then voltage-gated K + channels close and resting potential is restored ***Action potentials travel in only one direction: toward the synaptic terminals

OUTSIDE OF CELL INSIDE OF CELL Inactivation loop Sodium channel Potassium channel Action potential Threshold Resting potential Time Membrane potential (mV)  50  100  50 0 Na  KK Key Resting state Undershoot Depolarization Rising phase of the action potential Falling phase of the action potential

Sequence the following in order of occurrence Depolarization Resting state Repolarization Hyperpolarization

Sequenced in order of occurrence Resting state Depolarization Hyperpolarization Repolarization Resting state

Depolarization Hyperpolarization Repolarization Resting state ? ? ? Time Membrane potential (mV)  50  100 

a. the resting membrane potential to drop to 0 mV. b. the inside of the neuron to become more negative relative to the outside. c. the inside of the neuron to become positively charged relative to the outside. d. sodium to diffuse out of the cell and potassium to diffuse into the cell. Adding a poison that specifically disables the Na + /K + pumps to a culture of neurons will cause

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

Name three specific adaptions of the neuron membrane that allow it to specialize in conduction 33

What happens when the impulse reaches the end of the axon? 34

Synapses Transmission of information between neurons occurs across synapses. A chemical synapse is a junction between two nerve cells consisting of a narrow gap across which impulses pass by means of a neurotransmitter 35

Cell To Cell Communication Events 1.Action potential depolarized the membrane of synaptic terminal, this triggers an influx of Ca That causes synaptic vesicles to fuse with the membrane of the pre-synaptic neuron. 3.Vesicles release neurotransmitter molecules into the synaptic cleft. 4.Neurotransmitters bind to the receptors of ion channels embedded in the postsynaptic membrane. 36

Note the structural features that allow the cell to cell communication to occur in the synaptic region: Calcium gated channels in the synaptic knob Sodium channels in the post-synaptic membrane Fluidity of the lipid bi-layer allows for exocytosis of the neurotransmitter

Exocytosis Neurotransmitter release is a form of exocytosis. In exocytosis, internal vesicles fuse with the plasma membrane to secrete macromolecules out of the cell. 39

Neuron Transmitter Binds With A Receptor On The Postsynaptic Membrane

The neurotransmitter will then be released from the postsynaptic membrane and degraded. 41

Response Transmission of information along neurons and synapses results in a response. The response can be stimulatory or inhibitory. 42

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Acetylcholine – transmit signal to skeletal muscle Epinephrine (adrenaline) & norepinephrine – fight-or-flight response Dopamine – widespread in brain – affects sleep, mood, attention & learning – lack of dopamine in brain associated with Parkinson’s disease – excessive dopamine linked to schizophrenia Serotonin – widespread in brain – affects sleep, mood, attention & learning ***There are more than 100 neurotransmitters 1 neurotransmitter may have more than a dozen different receptors

Neurotransmitters Weak point of nervous system – any substance that affects neurotransmitters or mimics them affects nerve function gases: nitrous oxide, carbon monoxide mood altering drugs: – stimulants » amphetamines, caffeine, nicotine – depressants » quaaludes, barbiturates hallucinogenic drugs: LSD, peyote SSRIs: Prozac, Zoloft, Paxil poisons

Injecting ethylene glycol tetraacetic acid (EGTA), a chelating agent that prevents calcium ions from moving across membranes, to a synaptic region would likely a. increase the release of neurotransmitters by the presynaptic neuron. b. decrease the release of neurotransmitters by the presynaptic neuron. c. result in neurotransmitters being released, but could not bind to its receptors on the post synaptic neuron. d. result in the lack of calcium ions keeping the ligand-gated ion channels open on the post synaptic neurons.

The contraction of a muscle is a typical response generated by the nervous system. Muscle contraction demonstrates the interdependence of the nervous and muscle systems. Ex - Nervous and muscular

Motor cortex (control of skeletal muscles) Frontal lobe Prefrontal cortex (decision making, planning) Broca’s area (forming speech) Temporal lobe Auditory cortex (hearing) Wernicke’s area (comprehending language) Somatosensory cortex (sense of touch) Parietal lobe Sensory association cortex (integration of sensory information) Visual association cortex (combining images and object recognition) Occipital lobe Cerebellum Visual cortex (processing visual stimuli and pattern recognition)