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NEURONS AND IMPULSES

Dr. Steinmetz 1

OVERVIEW ¢ Structure of neuron ¢ Glia ¢ Neurophysiology � Axonal membrane � Resting potential � Action potential

¢ Saltatory conduction

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OVERVIEW ¢ Structure of neuron ¢ Glia ¢ Neurophysiology � Axonal membrane � Resting potential � Action potential

¢ Saltatory conduction

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STRUCTURE OF A NEURON

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FUNCTION OF A NEURON ¢ Reception - take info

from neighboring neurons

¢ Conduction

(integrate signals) ¢ Transmission (pass

on to other neurons) 5

ANATOMY OF A NEURON ¢ Cell body: (Gray)

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ANATOMY OF A NEURON ¢ Dendrites

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ANATOMY OF A NEURON ¢ Axon (White)

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ANATOMY OF A NEURON ¢ Myelin

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ANATOMY OF A NEURON ¢ Nodes of Ranvier ¢ Salutatory Action

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http://www.youtube.com/watch?v=pnB_Hc-Qfs0&feature=related 12

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ANATOMY OF A NEURON ¢ Cell body: (Gray) ¢ Axon (White) ¢ Dendrite ¢ Axon terminals ¢ Myelin ¢ Nodes of Ranvier

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MEMBRANE

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WHERE ARE NEURONS BESIDES THE BRAIN?

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DIFFERENT TYPES OF NEURONS ¢ What is the relationship between

morphology (shape) and function of a neuron? �  What would be the purpose of

multiple dendrites? �  Long vs. short axons? �  Other variations?

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PURKINJE CELL - CEREBELLUM

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PYRAMIDAL CELLS – CEREBRAL CORTEX

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TYPES OF NEURONS

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TYPES OF NEURONS: MOTOR NEURON

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REFLEX

2. What kind of neuron?

1. What kind of neuron?

Spinal Cord

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TYPES OF NEURONS: SENSORY NEURONS

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HOW FAST IS AN ACTION POTENTIAL?

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WHAT IS THE SPEED OF AXONAL CONDUCTION?

• Highly variable, depending on the diameter of the neuron

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• Approximately 1-100 m/sec

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OVERVIEW ¢ Structure of neuron ¢ Glia ¢ Neurophysiology � Axonal membrane � Resting potential � Action potential

¢ Saltatory conduction

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OTHER CELLS OF THE BRAIN Glia ¢ Build myelin ¢ Remove waste materials ¢ Guide migration of

neurons ¢ Exchange chemicals

with adjacent neurons � Reuptake of

neurochemicals 26

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TYPES OF GLIA CELLS ¢ Myelin insulates the neurons •  Schwann Cells - PNS myelin •  Oligodendrocytes - CNS myelin

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TYPES OF GLIAL CELLS CONT. ¢ Astrocytes - different

variants have functions ranging from developmental to structural to removal of waste

•  Microglia – respond to brain damage – removal of waste – scarring in CNS 28

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OVERVIEW ¢ Structure of neuron ¢ Glia ¢ Neurophysiology � Axonal membrane � Resting potential � Action potential

¢ Saltatory conduction

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CAN YOU LABEL THIS NEURON?

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NEURAL SIGNALING ¢ All neurons perform the following tasks:

¢ Input – from sensory receptors or other neurons

¢ Processing – input signal is processed in the soma and the decision of whether or not to send an output is made

¢ Signal Conduction – action potential ¢ Output – release of neurotransmitters

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OVERVIEW ¢ Structure of neuron ¢ Glia ¢ Neurophysiology � Axonal membrane � Resting potential � Action potential

¢ Saltatory conduction

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AXON Nodes of Ranvier

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AXONAL MEMBRANE ¢ Phospholipid bilayer ¢ Phosphoric acid head

is attracted to water ¢ Lipid tail avoids water ¢ Consistency is labile

(moveable, squishy)

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STRUCTURE OF THE AXON ¢ Semi-permeable cell

membrane: 10nm thick

¢ Ion channels are selectively permeable

¢ Ions inside and outside

membrane

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STRUCTURE OF THE AXON

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OVERVIEW ¢ Structure of neuron ¢ Glia ¢ Neurophysiology � Axonal membrane � Resting potential � Action potential

¢ Saltatory conduction

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RESTING POTENTIAL ¢  -70mV ¢ Outside positive (+)

relative to inside ¢ Primary ions involved � Na+

� K+

� Cl - � Ca++ (axon

terminals) 39

RESTING POTENTIAL

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FORCES ACTING ON IONS

¢ Diffusion/concentration gradient

¢ Electrical gradient

¢ Sodium/potassium pumps

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RESTING POTENTIAL

http://www.youtube.com/watch?v=YP_P6bYvEjE

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FACTORS THAT PRODUCE THE RESTING POTENTIAL

¢ Sodium-Potassium pump (ATPase)

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SODIUM-POTASSIUM PUMP ¢ Pumps out Na+; Pumps in K+ ¢ Pump requires energy ¢ Pump is an enzyme: ATPase

�  Complex of 2 unequally sized proteins �  Folded enzyme partially in/out of membrane �  Enzyme reacts with ATP and becomes phosphorylated �  Relaxes pump and shifts position �  3 Na+ ions out; 2 K+ ions in

¢ Cyanide blocks formation of ATP (source of brain’s energy)

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SODIUM-POTASSIUM PUMP ANIMATIONS

http://www.brookscole.com/chemistry_d/templates/student_resources/shared_resources/animations/ion_pump/ionpump.html

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.html

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SODIUM-POTASSIUM PUMP

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FACTORS THAT PRODUCE THE RESTING POTENTIAL

¢ Negatively charged proteins inside membrane

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FACTORS THAT PRODUCE THE RESTING POTENTIAL

¢ Electrostatic pressures

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FACTORS THAT PRODUCE THE RESTING POTENTIAL

¢ Diffusion/concentration gradient

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FACTORS THAT PRODUCE THE RESTING POTENTIAL

¢ Ion channels with voltage-sensitive gates

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RESTING POTENTIAL IS A DYNAMIC PROCESS

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OVERVIEW ¢ Structure of neuron ¢ Glia ¢ Neurophysiology � Axonal membrane � Resting potential � Action potential

¢ Saltatory conduction

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NEURAL SIGNALING ¢ All neurons perform the following tasks:

¢ Input – from sensory receptors or other neurons

¢ Processing – input signal is processed in the soma and the decision of whether or not to send an output is made

¢ Signal Conduction – action potential ¢ Output – release of neurotransmitters

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ACTION POTENTIAL: ALL OR NONE SELF-PROPAGATING

Nodes of Ranvier 54

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ACTION POTENTIAL

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¢ Sodium channels open ¢ Threshold passed? ¢ Depolarization: Moves from –70mV to +50 mV ¢ Potassium channels open ¢ Sodium channels close ¢ Potassium channels close

Threshold -55 mV

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ION FLOW DURING THE ACTION POTENTIAL

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ACTION POTENTIAL

http://www.youtube.com/watch?v=ifD1YG07fB8&NR=1 63

http://www.youtube.com/watch?v=ifD1YG07fB8&NR=1

ACTION POTENTIAL: ALL OR NONE SELF-PROPAGATING

Nodes of Ranvier 64

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ION FLOW DURING THE ACTION POTENTIAL

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ION WORKSHEET

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OVERVIEW ¢ Structure of neuron ¢ Glia ¢ Neurophysiology � Axonal membrane � Resting potential � Action potential

¢ Saltatory conduction

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SALTATORY CONDUCTION

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CROSS SECTION OF SIATIC NERVE MYELIN

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SALTATORY CONDUCTION

Multiple sclerosis destroys myelin sheath 70

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THINGS YOU SHOULD BE ABLE TO DO:

¢ Label parts of a neuron ¢ Describe the factors that produce the resting potential

¢ Describe an action potential in detail

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NEURAL SIGNALING ¢ All neurons perform the following tasks:

¢ Input – from sensory receptors or other neurons

¢ Processing – input signal is processed in the soma and the decision of whether or not to send an output is made

¢ Signal Conduction – action potential ¢ Output – release of neurotransmitters

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SYNAPSE

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FOR NEXT TIME… ¢ Review Ch. 3 Section on the action potential 3.1

¢ Work on Week 2 Neuroanatomy Lab (Midline Structures) for lab practical

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FOR NEXT TIME… ¢ Review Chapter 3.2 and read 4.1

¢ Work on Week 3 Neuroanatomy Lab (Internal Structures) for lab practical tomorrow

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REVIEW: WHAT PRODUCES THE RESTING POTENTIAL?

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REVIEW: WHAT PRODUCES THE RESTING POTENTIAL?

¢ Diffusion/concentration gradient ¢ Electrical gradient ¢ Sodium/potassium pumps ¢ Ion channels with voltage

sensitive gates ¢ Negative proteins inside

membrane 77