Nervous System What allows you to perceive the world around you, to recognize the incoming stimuli and to react to the environment Sensory systems Motor.

Nervous System What allows you to perceive the world around you, to recognize the incoming stimuli and to react to the environment Sensory systems Motor systems Memory/learning

Nervous System Central Nervous System (CNS)
Brain and Spinal Cord Peripheral Nervous System (PNS) All nervous tissue outside the CNS Somatic Nervous System (SNS)---voluntary Sensory and motor neurons to skeletal muscle Autonomic Nervous System (ANS)---Involuntary Sensory and motor neurons to viscera Sympathetic Division (increase heart rate) Parasympathetic Division (decrease heart rate)

Neurons (=nerve cells) general characteristics:
Nervous System Neurons (=nerve cells) general characteristics: - can be very long---6 feet or more - conduct nervous impulses---communication - long lived---entire life span - high metabolic rate; high O2 and glucose needs---brain accounts for less than 10% of body mass, yet gets over 25% of body’s energy

Types of Neurons (functional classification)
Motor Neurons--- carry info from brain to body Sensory Neurons--- carry info from body to brain Interneurons--- carry info within the Central Nervous System (CNS). These account for 90% of the neurons in the body Neuroglia---support cells Oligodendrocytes---CNS Schwann cells---PNS

Types of Neurons (structural classification)
Multipolar---many processes located in CNS Bipolar---2 processes located in sensory organs (eye, ear & nose) Unipolar--1 process these are sensory neurons. The axon and dendrite fuse into one process. Interneurons---Named based on looks or after the person who first described them (fig. 12.5) Purkinje cells, Pyramidal cells

Anatomy of a `typical’ motor neuron
nucleus

nucleus cell body = soma = perikaryon

nucleus Nissl bodies = rough endoplamic reticulum cell body = soma = perikaryon

nucleus Nissl bodies cell body = soma = perikaryon Golgi apparatus

other organelles: mitochondria lysosomes neurofilaments nucleus Nissl bodies cell body = soma = perikaryon Golgi apparatus

neural processes: axon = nerve fiber dendrites

Flow of Information: axon dendrites

axon hillock (trigger zone) axon dendrites

terminal branches= telodendria axon hillock axon dendrites

terminal branches axon hillock axon axonal terminals = synaptic knobs = synaptic boutons dendrites

axonal terminals = synaptic knobs = synaptic boutons

synaptic vesicles with neurotransmitters

Myelin Sheath Some Axons are myelinated
Myelin Sheath (schwann cell in PNS and oligodendrocyte in CNS) axon Multiple layers wrapped around = myelin Cell body and cytoplasm (outer most layer) = Neurolemma

myelination:

myelination: Special Glial cells -- make up the myelin sheath

Anatomy of a ‘typical’ motor neuron
Myelin

nodes of Ranvier

Resting Membrane Potential
Voltage across the membrane Electric potential energy Due to separation of ions All cells have a resting membrane potential

+ - - + + + + - + - - + + - - -

+ - + - + - - - - + + +

Amplifier Electrode Oscilloscope 0 mV

Amplifier Electrode Oscilloscope -70 mV

Resting Membrane Key Players
Sodium-Potassium (Na+/K+) Pump Moves Sodium and Potassium against their concentration gradients Moves 3 Na+ out of the cell and 2 K+ into the cell

Resting Membrane Potential Key Players:
Na+/ K+ Pump: 3 Na+ out Cell exterior cell membrane ATP NA/K pump establishes and maintains resting membrane potential Cell interior 2 K+ in

Na+ K+ Resting Membrane Potential Key Players: Leaky Channels K+ Na+
Cell exterior cell membrane Cell interior K+ Na+ Many K+ “leak” channels Few Na+ “leak” channels

Together creates -70 mV Resting Membrane Potential
K+ 2 K+ K+ ATP K+ 2 K+ Pumps 3 Na+ K+ Leak Channels 2 K+ K+ _ + K+ 3 Na+ Na+ Together creates -70 mV Resting Membrane Potential 3 Na+ 2 K+ Na+ Leak Channels Na+

Voltage across the membrane Electric potential energy Due to separation of ions All cells have a resting membrane potential

Electrical Signaling Through Changes in Membrane Potential
Describing Changes in Membrane Potential Graded Potentials Action Potentials Propagation of Action Potentials

Two Types of Change: Depolarizing Hyperpolarizing
-70 mV 0 mV -90 mV Depolarizing reduce membrane potential make inside less negative Na+ move into cell -70 mV 0 mV -90 mV Hyperpolarizing increase membrane potential make inside more negative K+ move out of cell

Signals produced by a change in membrane potential
Graded potentials Short lived Local Signaling Either depolarizing or hyperpolarizing

Graded Potentials are the first step in neuronal communication
are essential in initiating action potentials typical of dendrites and cell body (NOT axons)

Graded Potentials “graded” because - magnitude of the potential change varies directly with the strength of the stimulus Can be hyperpolarizing or depolarizing -70 +70 weak hyperpolarized strong depolarized

Graded Potentials Cause current flow that decreases in magnitude with distance (Signal dies out with distance) due to leaky membrane Distance (mm) Membrane Potential (mV) Site of stimulus -70

Graded Potentials Cause current flow that decreases in magnitude with distance (Signal dies out with distance) due to leaky membrane

How are graded potentials produced?
Changing the membrane’s permeability to different ions by opening/closing ion channels

Na+ How are graded potentials produced?
Changing the membrane’s permeability to different ions by opening/closing ion channels Triggering a depolarizing graded potential Na+ cell membrane + + + - - - Resting Depolarized - - - -70 mV e.g., +30 mV Na+ Open chemically-gated or voltage gated channels for cation (Na+) flow INTO cell  depolarization

Cl– How are graded potentials produced?  hyperpolarization
Changing the membrane’s permeability to different ions by opening/closing ion channels Triggering a hyperpolarizing graded potential Open channels for cation (K+) flow OUT of cell Open channels for anion (Cl-) flow INTO cell K+ Cl– e.g., -90 mV -70 mV + + + - - - Resting Hyperpolarized  hyperpolarization

Signals produced by a change in membrane potential
Graded potentials Action potentials All or None Self Propagating Long distance communication

Action Potential Key Players:
Voltage gated ion channels Channel is blocked by one or more ‘gates’ Membrane Potential hits a threshold voltage and ‘gate’ opens

Concept of Threshold Graded potentials that are not large enough to depolarize a large area of the axon hillock, fade away and never reach threshold A stimulus that is large enough to depolarize a large enough section of the axon hillock hit threshold ( -55mV), causes an ACTION POTENTIAL Threshold Stimulus Stimulus Strength Sub-threshold Stimuli Supra-Threshold -70 Membrane Potential (mV) -55 30 threshold

Why? Many Voltage gated Na+ channels located at trigger zone
If graded potential is strong enough to hit threshold when it reaches the axon hillock, it will trigger an Action Potential Why? Many Voltage gated Na+ channels located at trigger zone On soma & dendrite : / um2 membrane At trigger zone : / um2 membrane

Action Potential Key Players:
Voltage gated ion channels Voltage gated Na+ activation gate closed at resting inactivation gate open at resting Voltage gated K+ Single gate closed at resting

Action Potentials + + + + + + + + + + + + + + + + + + + + + + + + + +
Remember that due to Resting Membrane Potential: there is a large diffusional gradient inward for Na+ as well as a large electrical gradient inward for Na+ There is a large diffusional gradient outward for K+

Depolarization that reaches threshold opens the Na+ activation gates and Na+ RUSHES into the cell

Action Potentials and the membrane potential Depolarizes ... Amplifier
Electrode -70 mV Oscilloscope and the membrane potential Depolarizes ...

As membrane potential peaks at about 30 mV, the Na+ inactivation gates close and Na+ can no longer enter the cell K+ channels open and K+ RUSHES out of the cell

Action Potentials Return to resting membrane potential Amplifier
Electrode +30 mV -70 mV Oscilloscope Return to resting membrane potential

+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
Action Potentials + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + As membrane potential approaches resting potential the Na+ activation gate closes and the inactivation gate opens K+ gate closes

Stages of the action potential
1) Depolarization +30 2) Repolarization Membrane Potential (mV) 3) Hyperpolarization -70 1 2 3 Time (msec) Notice the Time scale……

1) Depolarization Initially, depolarization is a local current until it reaches threshold (-55 to -50 mV) Na+ activation & inactivation gates are opened; K+ gates are closed Na+ rushes into cell Membrane Potential (mV) -70 1 2 3 Time (msec)

2) Repolarization Sodium inactivation gates close Membrane permeability to Na+ declines to resting levels Voltage-gated K+ channels open K+ exits the cell and internal negativity of the resting neuron is restored Membrane Potential (mV) -70 1 2 3 Time (msec)

3) Hyperpolarization Potassium gates are slow to close, causing an excessive outflow of K+ This outflow causes hyperpolarization of the membrane (undershoot) Na+ Activation gates close Na+ inactivation gates open Membrane Potential (mV) -70 1 2 3 Time (msec)

Refractory Periods Absolute RP Relative RP Na+ channels open
Na+ channels inactivated No new action potential possible Relative RP Some Na+ channels still inactivated New action potential possible, but it requires a stronger than normal stimulus Membrane Potential (mV) -70 Time (msec)

Action Potentials are ALL-or None
Once we hit threshold the voltage gated channels are ‘popped’ and the Na+ rushes in We have an Action Potential Threshold Stimulus Stimulus Strength Sub-threshold Stimuli Supra-Threshold -70 Membrane Potential (mV) -55 30 threshold (Its like firing a gun)

Action Potentials are Self-Propagating
+ + + + + + + + + + + + + + + + + + + + + +

+ + + + + + + + + + + + + + + + + + + + + + +

+ + + + + + + + + + + + + + + + + + + + + +

Continuous Conduction: the action potential moves down the entire length of the axon Trigger Zone Graded Potentials Action Potentials

What about myelinated axons?

Myelinated Axons Myelin Sheath (each made by a Schwann cell) Nodes of Ranvier

Myelinated Axons

Myelinated Axons Action Potentials are Self-Propagating Myelinated Axons

Myelinated Axons

Myelinated Axons Saltatory conduction: action potential jumps from one node of Ranvier to another -- speeds up conduction in Vertebrates WOW! APs in unmyelinated = 1m/sec in myelinated = 150m/sec

An Action Potential is an Action Potential……
If there are no BIG Action Potentials for BIG stimuli…… how do we tell the difference?

Frequency Coding for Stimulus Intensity

Graded Potentials vs Action Potentials
“the magnitude of the potential varies directly with the intensity of the stimulus” magnitude decreases with distance from the source Action Potentials All-or None do not decrease in magnitude with distance

Graded Potentials vs Action Potentials
Are generated in Dendrites and cell body in response to stimuli Travel toward the axon hillock Action Potentials Are generated at Axon hillock when depolarization reaches threshold Are Propagated down the axon Continuous conduction Saltatory conduction Refractory Period Absolute Relative

Chemical Synaptic Transmission

[239]

Synaptic Cleft [239]

Synaptic Cleft [239] Ca++ Chemical Synaptic Transmission
calcium channels open Ca++ Synaptic Cleft [239]

Synaptic Cleft [239] Ca++ Chemical Synaptic Transmission
calcium channels open calcium moves into presynaptic cell Ca++ Synaptic Cleft [239]

[239] Ca++ Chemical Synaptic Transmission calcium channels open
calcium moves into presynaptic cell synaptic vesicles fuse with membrane Ca++ [239]

calcium moves into presynaptic cell synaptic vesicles fuse with membrane exocytosis of neurotransmitter Ca++ [239]

calcium moves into presynaptic cell synaptic vesicles fuse with membrane exocytosis of neurotransmitter neurotransmitter diffuses across cleft Ca++ [239]

calcium moves into presynaptic cell synaptic vesicles fuse with membrane exocytosis of neurotransmitter neurotransmitter diffuses across cleft Ca++ neurotransmitter - receptor interaction [239]

[240] Ca++ Excitatory Postsynaptic Potential =EPSP EPSP Na+ Na+
neurotransmitter - receptor interaction opening of post-synaptic ion channels [240]

K+ K+ [240] Ca++ Inhibitory Postsynaptic Potential =IPSP IPSP
neurotransmitter - receptor interaction opening of post-synaptic ion channels [240]

calcium moves into presynaptic cell synaptic vesicles fuse with membrane exocytosis of neurotransmitter neurotransmitter diffuses across cleft Ca++ neurotransmitter - receptor interaction opening of post-synaptic ion channels [239] degradation of neurotransmitter

Temporal Summation threshold [241]

Spatial Summation threshold [242]

Spatial Summation threshold [243]

Spatial Summation (+) threshold (+) (-) [243]

Nervous System What allows you to perceive the world around you, to recognize the incoming stimuli and to react to the environment Sensory systems Motor.

Similar presentations

Presentation on theme: "Nervous System What allows you to perceive the world around you, to recognize the incoming stimuli and to react to the environment Sensory systems Motor."— Presentation transcript:

Similar presentations

About project

Feedback

Log in

Auth with social network:

Nervous System What allows you to perceive the world around you, to recognize the incoming stimuli and to react to the environment Sensory systems Motor.

Similar presentations

Presentation on theme: "Nervous System What allows you to perceive the world around you, to recognize the incoming stimuli and to react to the environment Sensory systems Motor."— Presentation transcript:

Similar presentations

About project

Feedback