Nervous System: Neurons

Nervous System: Neurons

I). Function

A). Sensory input 
B). Integration:
C). Response  

II). Division of the Nervous System

A). Central Nervous System: (CNS)

Brain and Spinal Cord only

B). Peripheral Nervous System

Outside CNS

1). Sensory or afferent division:

Carries impulses to CNS

2). Motor or efferent division

Carries impulses from the CNS.

i). Somatic Nervous System

voluntary

ii). Autonomic Nervous System

involuntary

a.  Parasympathetic
b.  Sympathetic

III). Types of cells

A). Non nervous or glial cells.

1). Astrocytes
2). Microglia
3). Ependymal
4). Oliodendrocytes
5). Satellite cells
6). Schwann cells form myelin sheaths 

B). Neurons

1). Structure

i). cell body or soma

endoplasmic reticulum called the nissl body.

ii). Processes or tracts (nerves)

a). Dendrites: input region
b). Axon: Carries information away
c). Synaptic knobs or Axonal terminals Releases neurotransmitters.

2). Axons

a). myelin sheath  

	protects and electrically insulates fibers
	conduct nerve impulses faster than nonmylenated fibers.

b). nodes of Ranvier:  

spaces between the sheaths

The action potential skips to the nodes

IV). Nerve Impulse

A). Terms

1). Resting membrane Potential: 

Polarized

2). Depolarization: 

Change in ion concentration

3). Hyperpolarization

Change in ion concentration inside becomes more negative

4). Graded Potential

Localized change in ion; subthreshold

5). Action Potential  

Change in ion concentration that does not decrease over distance.

B). Action Potential

Stages  of an Action Potential

polarized resting potential		depolarizes
repolarizes		undershoot phase

Undershoot : the K+ channels stay open once resting potential is reached;

hyperpolarizing the cell.

C). Propagation

	Cannot be depolarized again until the membrane has reached resting potential.
	The action potential moves at a constant velocity

D). All or none phenomenon

	Not all depolarizations result in action potentials
	The depolarization must reach the threshold point

E). Refractory period

absolute refractory period cannot respond to another stimuli.

relative refractory period  The threshold is higher

F). Impulse Velocity

	Strong stimuli result in more nerve impulses
	Not stronger impulses or faster

V). Synapse

junction that carries information between neurons.

A). Types

1). Electrical synapse: ions to cross junction
2). Chemical synapse

neurotransmitters

Impulse		releases Ca++ (in neuron)
±  neurotransmitter released ± binds to receptors±			ion channels open on postsynaptic membrane

B). Termination of neurotransmitter

1). Degradation enzymes
2). Neurotransmitter reabsorbed
3). Diffusion of the neurotransmitter 

VI). Types of Neurotransmitters

A). Excitatory Synapses

	neurotransmitters results in the depolarization of postsynaptic membrane.
	Creating localized graded response.

(dendrites do not have action potentials)

IF THE GRADED RESPONSE IS STRONG ENOUGH TO BE CARRIED TO THE AXON A FULL ACTION POTENTIAL WILL RESULT

B). Inhibitory Synapses

	Binding neurotransmitters reduces the postsynaptic membranes ability to create an action potential.
	Induces hyperpolarization.

C). Integration or Summation of Synaptic Events

It takes more than one synaptic event to create an action potential.

Presynaptic inhibition =

excitatory neurotransmitter by one neuron +

inhibitory neurotransmitter of another neuron

VII) Neurotransmitters

A). Acetylcholine (ACh)
B). Biogenic Amines

1). Dopamine
2). Norepinephrine
3). Epinephrine
4). Serotonin

C). Amino Acids
D). Peptides

1). endorphins

E). Novel or Miscellaneous