The Nervous System

Functions of the Nervous System Figure 7.1

Functions of the Nervous System Sensory input — gathering information To monitor changes occurring inside and outside the body Changes = stimuli Integration To process and interpret sensory input and decide if action is needed

Functions of the Nervous System Motor output A response to integrated stimuli The response activates muscles or glands

Crash Course: Part 1 https://www.youtube.com/watch?v=qPix_X-9t7E

Organization of the Nervous System Figure 7.2

Structural Classification of the Nervous System Central nervous system (CNS) Brain Spinal cord Peripheral nervous system (PNS) Nerves outside the brain and spinal cord Spinal nerves Cranial nerves

Functional Classification of the Peripheral Nervous System Sensory (afferent) division Nerve fibers that carry information to the central nervous system Motor (efferent) division Nerve fibers that carry impulses away from the central nervous system

Functional Classification of the Peripheral Nervous System Motor (efferent) division (continued) Two subdivisions Somatic nervous system = voluntary Autonomic nervous system = involuntary

Neuron Classification Figure 7.6

Neurons = nerve cells Cells specialized to transmit messages

Figure 7.4

Nervous Tissue: Neurons Figure 7.5

Nervous Tissue: Neurons Cell body Main functional unit of the neuron Contains: Nucleus Large nucleolus Processes outside the cell body Dendrites—conduct impulses toward the cell body Axons—conduct impulses away from the cell body

Dendrite - conduct impulses toward the cell body Nissle substance (bodies) – rough ER Neurofibrils – filaments that help maintain cell shape Axon hillock – the beginning of the axon Axon - conduct impulses away from the cell body Schwann cells – cells that surround the axon Nodes of Ranvier -- gaps in myelin sheath along the axon Myelin sheath -- white, fatty material covering axons (insulates) Axon terminals – ends of the axon

Nervous Tissue: Neurons Axons end in axonal terminals Most cells average about 10,000 axon terminals Axon terminals contain vesicles with neurotransmitters (chemicals that excite or inhibit neurons or effector cells) Axon terminals are separated from the next neuron by a gap Synaptic cleft—gap between adjacent neurons Synapse—junction between nerves

Neuron Cell Body Location Most neuron cell bodies are found in the central nervous system White matter – condensed areas of myelinated fibers Gray matter — areas of unmyelinated fibers Ganglia —collections of cell bodies outside the central nervous system

Structural Classification of Neurons Multipolar neurons—many extensions from the cell body Where found? BRAIN Figure 7.8a

Structural Classification of Neurons Bipolar neurons—one axon and one dendrite Where found? SENSE ORGANS Figure 7.8b

Structural Classification of Neurons Unipolar neurons—have a short single process leaving the cell body Where found? SKIN Figure 7.8c

Crash Course: Part 2 https://www.youtube.com/watch?v=OZG8M_ldA1M

Nerve Impulse The principle way neurons communicate is by generating and propagating ACTION POTENTIALS (AP). Only cells with excitable membranes (like muscle cells and neurons) can generate APs. An AP is a brief reversal of membrane potential. In neurons, an AP is called a NERVE IMPULSE and only axons can generate one. An AP involves the movement of Na+ and K+ ions moving in and out of the neuron, resulting in changes in POLARITY.

All or None Response If the action potential (nerve impulse) starts, it is propagated over the entire axon There are NO partial impulses. The impulse happens completely or not at all. Impulses travel faster when fibers have a myelin sheath. saltatory conduction: impulse jumps from node to node

Action Potential First, remember how DIFFUSION works… http://www.youtube.com/watch?v=OXCKjhE1xco Bozeman

Nerve Impulses Resting neuron Depolarization The plasma membrane at rest is polarized Fewer positive ions are inside the cell than outside the cell Depolarization A stimulus depolarizes the neuron’s membrane A depolarized membrane allows sodium (Na+) to flow inside the membrane The exchange of ions initiates an action potential in the neuron

Nerve Impulses Repolarization Potassium ions rush out of the neuron after sodium ions rush in, which repolarizes the membrane The sodium-potassium pump, using ATP, restores the original configuration

Action Potential video http://www.youtube.com/watch?feature=player_detailpage&v=yQ-wQsEK21E

Nerve Impulses Figure 7.9a–b

Nerve Impulses Figure 7.9c–d

Nerve Impulses Figure 7.9e–f

Action Potential explained https://www.youtube.com/watch?v=SdUUP2pMmQ4

Transmission of a Signal at Synapses Impulses are able to cross the synapse to another nerve Neurotransmitter is released from a nerve’s axon terminal The dendrite of the next neuron has receptors that are stimulated by the neurotransmitter An action potential is started in the dendrite

Transmission of a Signal at Synapses Axon terminal Vesicles Synaptic cleft Action potential arrives Synapse Axon of transmitting neuron Receiving neuron Neurotrans- mitter is re- leased into synaptic cleft Neurotrans- mitter binds to receptor on receiving neuron’s membrane Vesicle fuses with plasma membrane Neurotransmitter molecules Ion channels Transmitting neuron Receptor Neurotransmitter Na+ Neurotransmitter broken down and released Ion channel opens Ion channel closes Transmission of a Signal at Synapses Figure 7.10

Action potential arrives Axon of transmitting neuron Axon terminal Vesicles Synaptic cleft Action potential arrives Synapse Axon of transmitting neuron Receiving neuron Action potential arrives Figure 7.10, step 1

2. Vesicle fuses with plasma membrane Axon terminal Vesicles Synaptic cleft Action potential arrives Synapse Axon of transmitting neuron Receiving neuron Vesicle fuses with plasma membrane Ion channels Transmitting neuron 2. Vesicle fuses with plasma membrane Figure 7.10, step 2

3. Neurotransmitter is released into synaptic cleft Axon terminal Vesicles Synaptic cleft Action potential arrives Synapse Axon of transmitting neuron Receiving neuron Neurotrans- mitter is re- leased into synaptic cleft Vesicle fuses with plasma membrane Neurotransmitter molecules Ion channels Transmitting neuron 3. Neurotransmitter is released into synaptic cleft Figure 7.10, step 3

4. Neurotransmitter binds to receptor on receiving neuron’s membrane Axon terminal Vesicles Synaptic cleft Action potential arrives Synapse Axon of transmitting neuron Receiving neuron Neurotrans- mitter is re- leased into synaptic cleft Neurotrans- mitter binds to receptor on receiving neuron’s membrane Vesicle fuses with plasma membrane Neurotransmitter molecules Ion channels Transmitting neuron Axon terminal Vesicles Synaptic cleft Action potential arrives Synapse Axon of transmitting neuron Receiving neuron Neurotrans- mitter is re- leased into synaptic cleft Neurotrans- mitter binds to receptor on receiving neuron’s membrane Vesicle fuses with plasma membrane Neurotransmitter molecules Ion channels Transmitting neuron 4. Neurotransmitter binds to receptor on receiving neuron’s membrane Figure 7.10, step 4

Axon terminal Vesicles Synaptic cleft Action potential arrives Synapse Axon of transmitting neuron Receiving neuron Neurotrans- mitter is re- leased into synaptic cleft Neurotrans- mitter binds to receptor on receiving neuron’s membrane Vesicle fuses with plasma membrane Neurotransmitter molecules Ion channels Transmitting neuron Receptor Neurotransmitter Na+ Ion channel opens REUPTAKE SYSTEM Once neurotransmitters have stimulated the receiving neuron’s membrane, the excess neurotransmitters are recaptured by the transmitting neuron. Figure 7.10, step 5

Transmission of a Signal at Synapses Axon terminal Vesicles Synaptic cleft Action potential arrives Synapse Axon of transmitting neuron Receiving neuron Neurotrans- mitter is re- leased into synaptic cleft Neurotrans- mitter binds to receptor on receiving neuron’s membrane Vesicle fuses with plasma membrane Neurotransmitter molecules Ion channels Transmitting neuron Receptor Neurotransmitter Na+ Neurotransmitter broken down and released Ion channel opens Ion channel closes Transmission of a Signal at Synapses Figure 7.10, step 6

Figure 7.10, step 7 Axon terminal Vesicles Synaptic cleft Action potential arrives Synapse Axon of transmitting neuron Receiving neuron Neurotrans- mitter is re- leased into synaptic cleft Neurotrans- mitter binds to receptor on receiving neuron’s membrane Vesicle fuses with plasma membrane Neurotransmitter molecules Ion channels Transmitting neuron Receptor Neurotransmitter Na+ Neurotransmitter broken down and released Ion channel opens Ion channel closes Figure 7.10, step 7

Distribution in the Central Nervous System Neurotransmitter Distribution in the Central Nervous System Functions Affected Drugs That Affect It Dopamine Midbrain, Ventral tegmental area (VTA), Cerebral cortex, Hypothalamus Pleasure and reward Movement, Attention, Memory Cocaine, Methamphetamine, Amphetamine. In addition, virtually all drugs of abuse directly or indirectly augment dopamine in the reward pathway Serotonin Midbrain, VTA, Cerebral cortex, Hypothalamus Mood, Sleep, Sexual desire, Appetite MDMA (ecstasy), LSD, Cocaine Norepinephrine Sensory processing, Movement, Sleep, Mood, Memory, Anxiety Cocaine, Methamphetamine, Amphetamine Endogenous opioids (endorphin and enkephalin) Widely distributed in brain but regions vary in type of receptors, Spinal cord Analgesia, Sedation, Rate of bodily functions, Mood Heroin, Morphine, Prescription painkillers (Oxycodone) Acetylcholine Hippocampus, Cerebral cortex, Thalamus, Basal ganglia, Cerebellum Memory, Arousal, Attention, Mood Nicotine Endogenous cannabinoids (anandamide) Cerebral cortex, Hippocampus, Thalamus, Basal ganglia Movement, Cognition and memory Marijuana Glutamate Widely distributed in brain Neuron activity (increased rate), Learning, Cognition, Memory Ketamine, Phencyclidine, Alcohol Gamma-aminobutyric acid (GABA) Neuron activity (slowed), Anxiety, Memory, Anesthesia Sedatives, Tranquilizers, Alcohol

Impact of Drugs on Neurotransmission http://www.drugabuse.gov/news-events/nida-notes/2007/10/impacts-drugs-neurotransmission