Nervous System

Nervous System

Functions

Neurons Receptors: Interpret: Response:

Afferent

Efferent

Organization of Nervous System

Central Nervous System Peripheral Nervous System

Sensory(Afferent) Motor (Efferent)

ANS Somatic

Sympathetic

“Fight or Flight”

Parasympathetic

“Resting and Digesting”

Cellular Organization: 2 types of Cells

Neurons Responsible for

conducting electrical impulses

Characterisitics Long Life Span Amitotic High Metabolic Rate

Dendrite, Cell Body and Axon

Dendrites: Receive stimuli from receptorsCell Body: Contains nucleus and organelles; lacks

centriolesAxon: Generate and transmit nerve impulses

Input

conducting

Secreting output

Sensory Neurons (Afferent)

Exteroceptors Provide information of about

external environment I.e.

Proprioceptors Monitor the position of

skeletal muscles and joints

Interoceptors Monitor the activities of

internal systems and organs I.e.

Motor Neurons (Efferent)

Carry Instructions from CNS to muscles, tissues and organs

Called Effectors because they cause a response

Interneurons

Located in brain and spinal cord

Analyze sensory input (afferent) and coordinate motor output (efferent)

Neuroglia/Glial Cells

Supporting cells to neurons

Act as phagocytes

Outnumber Neurons

Mitotic

Astrocytes

Secretes chemicals important for the maintenance of the Blood Brain Barrier

o Feeds neuronso Repairs damaged

neural tissues

                                                                 

Ependymal Cells

Produce CSF (cerebrospinal fluid)

Line central cavities of brain and spinal cord

These ciliated cells circulate CSF

Microglia

Phagocytic cells

Produced by leukocytes (WBCs)

Fight infection

Schwann Cells/OligodendrocytesProduce myelin sheath-increases the speed of impulses, insulator

Myelin=lipid componentsNodes of Ranvier-gaps in myelin sheath,

axon contacts its external environmentSchwann cells-glial cells in PNS that

produce myelin sheathMylenated vs. Unmyelinated axonsDemylinated (multiple sclerosis)

Unmyleninated vs. Myleninated Axon

Ion transport occurs along the length of the axon in an unmyleninated axon.

Ion transport occurs only where the Nodes of Ranvier are located in a myleninated axon.

Na+-K+ PumpActive Transport – requires ATP

Resting Membrane Potential

Measured as voltage difference across the membrane

Inside of membrane is -70 mV (.07 V) C battery = 1.5 V

Maintained by Na+K+ pump 3 Na ions are pumped out for every 2 K ions that are pumped in Requires ATP; maintaining a concentration

gradient

More Na+ leave the cell than K+ enter.

Charge difference of -70mv across membrane

Inside of axon is negative compared to the outside.

Na ions and K ions are actively pumped out and in the cell. Maintain a concentration gradient (difference) Ions do not reach equilibrium.

Depolarization

Axon hillock is where impulse will begin

Na diffuses into axon

Reach -55mV = threshold

At threshold Na gates open; Na ions diffuse into axon

Reach +30 mV; Na gates close

Graded Potential – depolarization occurs but you never reach threshold.Not enough Na+ moves into cell, impulse is not sent.

Action Potential/Impulse

Enough neurons fire so red neuron reaches threshold

Impulse is sent to next neuron (green)

Enough Na+ diffuses into the cell reaching thresholdNa+ continues to diffuse into cell until voltage rises to +30 mV.

Repolarization – Na gates close, K gates open. K+ diffuse out of cell

Repolarization

K+ ions diffuse out of the cell

Returning the inside of the cell to its negative charge.

Charge inside the axon goes below -70mV.

Caused by K+ leaving the cell and Na+ not able to enter the cell.

Increase in negative charge since + ions are leaving axon with no + ions being able to enter the neuron.

Change in Ion permeability with Impulse.

Why would Na+ enter the cell before K+?

What is happening whenNa+ enter the cell?

What is happening when K+ leave the cell?

Absolute Refractory Period •time needed to return the neuron’s membrane to Resting Membrane Potential•Limits the number of impulses that can be sent

Intensity of Impulse

Number of times impulse is sent More impulses;

higher intensity

Speed of Impulse

Presence of Myelin Sheath

Size of Neuron Large neurons =

less resistance; impulse travels faster through neurons larger in diameter

Axon Bud

-Responsible for sending chemical messengers (neurotransmitter) across the synapse.

-Synaptic vesicles release NT by exocytosis

-Receptor cells on the dendrites receive the NT.

Axon Bud

Exocytosis requires ATP

Axon Bud AnimationImpulse travels to axon bud

Ca ions enter through gated channels of axon bud.

Ca attaches to vesicles; NT released by exocytosis.

NT attaches to receptor cells on dendrite

Na gates open in dendrite and Na ions begin to enter the dendrite. Reach Threshold = Action Potential

How is the impulse stopped?

As long as the NT remains attached to a receptor, it will continue to send impulses.

NT is stopped by: Reuptake of NT into vesicles; begin as soon as

impulse begins in postsynaptic neuron NT diffuses away from postsynaptic synapse Enzymes break down NT.

I.e. neurotransmitter acetylcholine is broken down by acetylcholinerase

Acetylcholine → acetate + choline

What happens at the Axon Bud!

Antidepressants