Control Systems (PB Lecture 17 – Spring 2008 Althoff Ch. 34) Nervous system

Systems of Control: ENDOCRINE & NERVOUS BOTH “SYNTHESIZE” MESSENGER CHEMICALS THAT ARE RELEASED INTO EXTRACELLULAR SPACES HormonesNerve cells Distance to impact ApproachTarget Duration of impact

Functions Messenger (receive stimuli) Communicator (process stimuli) The critical “network” for maintaining homeostasis…for advanced animals, this means they are “wired” for quick response

Nervous System: CNS = _____________________ (central nervous system) vs. PNS = all nerves & ganglia ________ the CNS (peripheral nervous system)

______

Brain & spinal cord __________ sensory input, __________ response Nerves: carries sensory info to CNS and motor commands from CNS ______ to muscles & glands CNS PNS

Nerves Bundles of nerve fibers outside the CNS, most notably the axon and dendrite(s) portion of neurons.

Cell Types ___________--conducts nerve impulses ___________--supports and services neurons. Supplies nutrients, provides protection, and gets rid of waste

Neuron Structure  CELL BODY  DENDRITE  AXON  AXON ENDINGS (= axon terminals)  MYELIN

Neuron Structure CELL BODY --nucleus & most organelles DENDRITE--receive incoming information (i.e., stimulus) AXON--carry information away from cell body AXON ENDING --makes contact with other neurons, muscles, glands MYELIN--covering on some neurons

3 Types of Neurons  __________ NEURON  __________ NEURON  _________________ (association neurons) Not all neurons look alike Not all neurons carry the same type of information

Types of Neurons…con’t Consider types relative to CNS Collectively, they are the electronic communications network of the body…. …know these types as well as their relationship to one another!

Carry ________ info from periphery to CNS (i.e., PNS  CNS) Both dendrite and axon are myelinated ____________ is in the PNS Examples: pain, pressure, touch, hot, cold, light, sound, blood pressure, blood CO 2, bladder stretch, etc.  SENSORY NEURON

Carry ___________________ from CNS to muscles or glands (i.e., CNS  PNS) Skeletal muscles - causes contraction Smooth muscles - “ “ Adrenal gland - secrete hormone Cell body is in the CNS, therefore, axon is usually ______  MOTOR NEURON

Found _____ inside the CNS Connects ___________ (sensory to motor and vise versa) Typically short dendrites and either long or short axons  INTERNEURONS (association neurons)

PNS CNS Hand moves

Nerve Impulse A small ___________________ that occurs across the plasma membrane of neurons and then conducted along the axon/dendrite of the neuron

RESTING POTENTIAL NEURON AT REST

RESTING POTENTIAL NEURON AT REST +40mV -65mV OUTSIDE INSIDE _________________ __________

RESTING to __________________ During ACTION POTENTIAL, _____ channels open first, Na + rushes in resulting in depolarization…then _____ channels open, K + rushes out. Na + in K + out

Summary RESTING POTENTAIL Maintained at about -65mV by sodium- potassium pump (i.e., Na-K pump) _____ always diffusing back and forth because of ___________________ Na + higher outside an axon, K + higher inside the axon resulting in the axon having a negative charge

ACTION POTENTIAL A rapid change in polarity across the plasma membrane as the nerve impulse occurs It is an “____________” phenomenon If it causes depolarization to a certain level, it is called a ____________ and an “action potential” occurs

ACTION POTENTIAL…con’t Strength of an action potential does ____ change… …but an intense stimulus can cause the axon to fire at a ______________ Requires two types of GATED CHANNELS: one for ____ and one for _____. The Na + channel opens first

ACTION POTENTIAL…con’t During this process, Na + moves to the inside of the axon during the depolarization phase (-65mV  +40mV) K + moves to the outside of the axon during the repolarization phase. (+40mV  -65mV) Review Fig. 34.5, pages 651 in Johnson and Losos

Propagation of an Action Potential As action potential travels down the axon, each successive portion of the axon undergoes depolarization, followed by repolarization Like a _________________ As the action potential moves on, previous portion goes through refractory period--Na + channels are shut, then K + channels are shut

Propagation of an Action Potential…con’t With refractory period (i.e., Na + gate closed), the action potential _________________ ______________….just forwards At “nodes”, the action potentials jump from node-to-node. At nodes, voltage-sensitive Na+ channel gates are numerous. Speeds of _____ meters/second (_____ miles/hour) have been recorded along a motor neuron

Synapse Structure & Function Where “signal” is transmitted from ____ _____________________ Axon bulb  synaptic cleft  postsynaptic neuron ___________________--molecules that transmit the signal across the synaptic cleft

Presynaptic neuron Postsynaptic neuron Synapse (synaptic cleft)

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Neurotransmitters ____+ known substances or suspected to be neurotransmitters Acetylcholine (ACh) and Norephinephrine (NE) best known Acetylcholinestrease (AChE) is an enzyme that breaks down ACh

Neurotransmitters Others include:dopamine serotonin opioids(endorphin) Many drugs either _________________ ________________________________

Integration Neurons handle “excitatory” and “inhibitory” signals Each neuron sums up the two signal types in a process known as INTERGRATION Result: neuron either “fire” signal down axon…or not “fire signal