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

Hormones Nerve cells

Distance to impact

Approach Target

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 BODYDENDRITEAXONAXON 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 CO2, 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 PNSCNS

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+

inK+

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

neuronPostsynaptic

neuron

Synapse

(synaptic cleft)

Put graphic from text here

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:dopamineserotoninopioids (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