CENTRAL NERVOUS SYSTEM

TABLE OF CONTENTS

• Introduction

• Electrochemical impulse generation

• Synaptic transmission

• How is a reflex arc formed

FUNCTION

• Maintain homeostasis

• Control automatic functions

• React to stimuli

SET UP

• Central nervous system

• Periphiral nervous system

• Sensory pathways

• Motor pathways

• Autonomic nervous system

• Somatic nervous system

PERIPHIRAL NERVOUS SYSTEM

• Named because its located around the central nervous system

• Divided into sensory neurons and motor neurons

• Motor neurons can be divided into the automatic and somatic nervous systems

AUTONOMIC NERVOUS SYSTEM

• Responsible for involuntary body functions.

• Heartbeat

• Breathing

• Digestion

• Etc

• Divided further into sympathetic and parasympathetic nervous systems

• Sympathetic

• Controls fight or flight response

• Bladder relaxaion

• Parasympathetic

• Maintain normal body function

• Controls pupil dilation

• conserves physical energy

• Slows heart rate

CENTRAL NERVOUS SYSTEM

• Consists of the brain and spine

• Recieves information

• Controls the body’s response

STRUCTURE OF NERVOUS SYSTEM

• Made up of neurons

• Runs through the entire body

• Sends signals to muscles and to glands

NEURONS AND GLIAL CELLS

• Nervous system cells

• Three structural types of neurons

• Bipolar

• Unipolar

• Multipolar

• Three functional types of neurons

• Sensory input

• Integration

• Motor output

UNIPOLAR

• A single process that extends from the cell body

• Dendrite and axon are fused

• Found in the peripheral nervous system

• Created by the fusion of two polar processes during development.

MULTIPOLAR

• Has several dendrites

• Has a single axon

• Found in the brain and spinal cord.

BIPOLAR

• Has a single main dendrite

• Has a single axon

• Found in the inner ear, retina of the eye, and the olfactory center of the brain.

SENSORY NEURONS

• Sensory receptor, such as those in the skin

• Recieves input as a nerve impulse

• Part of the central nervous system

INTEGRATION NEURONS

• Known as interneurons

• Found in the central nervous system

• Act as a link between the sensory and motor neurons

MOTOR NEURONS

• Transmit information from the central nervous system

• Transmits to effectors, effectors include muscles glands, and other organs.

ELECTROCHEMICAL IMPULSE

AKA: AN ACTION POTENTIALBY: RITA KUMAR

DISCOVERY OF ELECTROCHEMICAL IMPULSES

Luigi Galvani (1737 – 1798) Julius Bernstein (1839-1917) K.S. Cole and H.J. Curtis

• experimented with frogs at University of Bologna in a solution of saltwater

• Proposed the membrane hypothesis (1902)

Cole and Curtis decided to test this theory

• accidentally touched two different metals together

• Neurons have selectively permeable cell membranes. These membranes allow for the transport of K+ and Na+ ions

Extracted neuron from a squid

• results indicated electrical stimulation

• At rest, the neuron has a potential difference across its membrane

tested with an electrode spanning the cell membrane

• K+ flow out of the cell, resulting in a decrease of potential difference

They proved Bernstein’s hypothesis

Luigi GalvaniK.S. Cole

Julius Bernstein

WHAT DOES IT DO FOR THE BODY?

• The purpose of electrochemical impulse is to pass a stimulus-generated impulse down the neural axon to a receptor, be it another neuron or a muscle.

• The passing of electrochemical impulses allows for organisms to recall, feel, think, emote, hear, see, etc.

• Without proper nerve conduction, diseases such as multiple sclerosis may occur.

SODIUM POTASSIUM PUMP• Since like charges repel, the highly positive

Na+ ions repel each other, and want in the cell membrane.

• The sodium-potassium pump allows these ions to cross an otherwise impermeable membrane.

• 3 Na+ ions move out of the membrane using the pump

• 2 K+ move in the membrane using the same pump

• The net effect, since there are more Na+ ions outside than K+ ions inside, the cell membrane has a strong positive charge outside. The difference from the inside to the outside is -70 mV, or the resting potential.

STEPS IN AN ELECTROTONIC POTENTIAL

• There are voltage gated ion channels for sodium and channels for potassium ions.

• A stimulus forces a Na+ channel open.

• Sodium ions flow into the cell

• The voltage across the membrane will increase

• When the voltage reaches its threshold potential, other voltage gated ion channels are stimulated, and they open as well

• Electrotonic potentials faster than action potentials.

• The effect of electrotonic potential diminishes the further down the cell you go.

STEPS IN AN ACTION POTENTIAL

• The threshold potential for an action potential is -55 mV.

• The Na+ channel is forced open.

• Sodium ions flow into the cell, increasing the potential across the cell greatly.

• The sodium ion channels close at +40 mV

• Now, the inside of the cell is more positively charged than the outside.

• The potassium gate opens at +40 mV

• Potassium ions flow out of the cell due to repulsive forces, decreasing the voltage

• The voltage overshoots since it went lower than the resting potential.

• The potassium gate closes at -80 mV.

• The sodium channel is reactivated to bring the voltage back up to 70 mV.

• Action potentials are “all-or-none”, that is, the voltage must reach -55 mV before it can take place.

• This is an endergonic process, and is slower than the electrotonic potential, but this works better over longer axons.

STRUCTURE OF A NEURON

WORKS CITED LIST

SIGNAL TRANSMISSION ACROSS A SYNAPSE

• -Impulse.... Origin of stimulus--> Sensory Neurons --> Brain --> Motor Neurons --> Muscles or Glands

• synapse: connection between 2 neurons or neuron & effectorExample of effector: Muscle Fibres

SIGNAL TRANSMISSION ACROSS A SYNAPSE

• Neurotransmitter: carry signal fom neuron to neuron or effector

• Pre-BeforePost-After

SIGNAL TRANSMISSION ACROSS A SYNAPSE

• 1) Action potential (A.P) arrives at end of presynaptic neuron, the impulse causes intracellular sacs (synaptic vesicles) which contain neurotransmitters to fuse to the axons membrane. Synaptic vesicles release neurotransmitter into synaptic cleft: (space between neurons) by exocytosis

SIGNAL TRANSMISSION ACROSS A SYNAPSE

• exocytosis: transport method in which vacuole fuses with cell membrane & releases contents outside cell

SIGNAL TRANSMISSION ACROSS A SYNAPSE

• 2) Released neurotransmitter diffuses across synapse taking 0.5-1 ms to reach the dendrites of post synaptic neuron or cell membrane of effector

SIGNAL TRANSMISSION ACROSS A SYNAPSE

• 3) Contents released (the neurotransmitters) and bind to receptor proteins which polarize the post synaptic membrane and allow for Na + ions to flow through the ion channel protein into the postsynaptic channel

• When the postsynaptic membrane is polarized, the threshold potential could be reached which initiates an action potential. The impulse will travel along postsynaptic neuron to its terminal and to the next neuron or effector.

SIGNAL TRANSMISSION ACROSS A SYNAPSE

• 4) Enzyme will break up the neurotransmitters in the postsynaptic neuron and its components will be reabsorbed by the presynaptic neuron.

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HOW IS A REFLEX ARC A FORM OF FEEDBACK?JUDY ZHONG

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OVERVIEW

• Definitions

• The main sections of the Nervous System that are involved in the Reflex Arc

• Feedback System Vs. Reflex Arc

• Video

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DEFINITIONS

• Reflexes:

• An involuntary response to a certain stimulus

• Reflex Arc:

• A simple connection of neurons that results in a reflex action

• Feedback systems:

• A cycle of events in which a variable is monitored, assessed and adjusted (used to maintain homeostasis)

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STRUCTURE OF NERVOUS SYSTEMNervous System

(NS)

Central Nervous System (CNS) Peripheral Nervous

System (PNS)

Sensory Pathways Motor Pathways

Somatic Nervous System (voluntary)

Autonomic Nervous System (involuntary)

Sympathetic Nervous System

Parasympathetic Nervous System

BrainSpinal Cord

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COMPARISON

Negative Feedback System

Reflex Arc

MHR Biology 12Fig.8.3,pg 346 (Negative Feedback System)

Fig.8.11, pg 353 (Reflex Arc)

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VIDEO

• http://www.youtube.com/watch?v=9uBjz5JpRAU