The Nervous System

The Nervous System Master controlling and communicating system of the body Has the same function as what other body system? Endocrine system How did these two systems differ? Endocrine: widespread, slow-acting Nervous: specific, fast-acting

Functions Gathers information and monitors changes sensory input Processes and interprets the input and makes decisions Integration Effects a response Motor output

Organization Structural Central Nervous System (CNS) Brain and spinal cord Peripheral Nervous System (PNS) All of the nerves outside of the CNS

Organization Functional—only relevant to PNS Sensory division AKA afferent division Conveys impulses to the CNS Associated with the sensory input Motor division AKA efferent division Carries impulse from the CNS to effector organs Muscles and glands

Organization Motor-2 divisions Somatic Autonomic nervous system Will communicate with skeletal muscle Voluntary control Autonomic nervous system Will communicate with heart, digestive system, and endocrine glands Involuntary control Sympathetic nervous system Fight for flight Parasympathetic nervous system Rest and digest

Let’s Draw a Tree! The Nervous System CNS PNS Sensory/Afferent Division Motor/Efferent Division Somatic Voluntary Autonomic Involuntary Sympathetic Cardiac/smooth muscle, glands Parasympathetic Skeletal muscle

Cells Neurons Supporting Cells

Neurons Characteristic shape that is specialized to transmit messages (nerve impulses) from one part of the body to another Major regions Cell body Contains the usual organelles and the nucleus Processes Fibers that extend from the cell body Dendrites axons

Neurons-Processes Processes Dendrites: conduct impulses toward the cell body Axon: conduct impulses away from the cell body End at axon terminals Contain vesicles with neurotransmitters Often wrapped in a myelin sheath Nodes of Ranvier = sausage links

Axon terminals are separated from the next neuron by a gap Synaptic cleft Gap between adjacent neurons Synapse Junction between nerves

Supporting Cells-CNS CNS Astrocytes Microglia Star-shaped Help nourish the neurons Deliver nutrients Protection Control chemical environment Microglia Spider-like cells Clean up debris and bacteria “Garbage man”

Supporting Cells-CNS Oligodendrocytes Create the myelin sheath around CNS neurons Multiple sclerosis: these cells are destroyed so the cells in the CNS are not myelinated

Supporting Cells-PNS PNS Schwann cells Satellite cells Form myelin sheath around cells in the PNS Satellite cells Protective, cushioning cells

Physiology 2 main function of neurons Irritability Conductivity Ability to respond to stimuli Conductivity Ability to transmit an impulse

The plasma membrane at rest is polarized This means that fewer positive ions are inside the cell than outside the cell There is a high concentration of sodium (Na+) OUTSIDE the cell and a high concentration of potassium (K+) INSIDE the cell

Let’s draw a picture! Question: According to diffusion, what direction does sodium want to move? Question: What direction does potassium want to move?

Sodium and potassium are blocked from going in/out of the cell by a series of gatekeepers Protein channels To open the gate, they need to be unlocked by the correct neurotransmitter Remember the lock and key model!

Let’s say that the neuron’s dendrite receives a signal It touches a neurotransmitter The gates will open and allow sodium to rush into the cell This causes the membrane to undergo depolarization Inside=positive, outside=negative

If the signal is strong enough (aka a lot of neurotransmitters open a lot of gates), it will cause an action potential (impulse) to travel along the length of the axon The myelin sheath helps this go faster

However, the potassium gates open Almost immediately after the sodium ions rush into the neuron, the sodium gatekeepers close However, the potassium gates open Where will the potassium flow? OUTSIDE the cell This reestablishes the electrical conditions within the cell Called repolarization

After the impulse has traveled along the length of the axon, tiny vesicles containing neurotransmitters will fuse with the neurotransmitter membrane They will diffuse across the synapse, bind the receptors, and the process is repeated! The signal travels on As the neuron undergoes more action potentials, the ions will continue to move down their concentration gradient. In order to COMPLETELY restore the neuron to its initial conditions (both with charge and ion concentration), the sodium-potassium pump (a protein) will send sodium OUT and potassium IN This is an ACTIVE process

Let’s List the Steps A neurotransmitter is released by the pre-synaptic neuron The neurotransmitter touches a gated Na+ channel Na+ rushes into the cell Cell membrane depolarization (gets more positive internally) K+ gates open Na+ gates close K+ rushes out of the cell Cell membrane repolarization (reestablishes electrical equilibrium) Neurotransmitters released Na+/K+ pump reestablishes chemical equilibrium

Let’s Look at a Graph

Let’s Watch a Video http://www.youtube.com/watch?v=7EyhsOewnH4