Chapter 2: cells of the nervous system

Soma

• cell body

• contains nucleus, golgi, ribosomes

Dendrities

• branches that serve as the primary input

• many receptors are located here

Axon

• cable like structure

• contains myelin sheath

• acts a highway system for the cell

• transport of ions

Myelin sheath

• is the protective layer

• makes action potential occur faster and more efficiently

• the unmyelinated portions are called nodes of Ranvier

• Myelin sheath is not continuous because it draws current from the ions dissolved in water on the outside of the cell

• MS is a condition for loss of myelin sheath

  • a common symptom is paralysis

Terminal button

• the end of the action potential

• releases neurotransmitters

• contains synaptic vessicles

Synapse

space in which two neurons communicate through chemical and electrical signals

Bipolar neuron

• used in reflexes

• are also located in brain areas that require communication with each other

• relay a signal from one neuron to another

Unipolar neuron

• also known as sensory neurons

• are activated by pressure

Multipolar neurons

• commonly motor neurons responsible for executive movement

• commonly found in muscles

Pyrimidal neurons

• involved in learning

• found in CNS only

• most commonly seen in the hippocampus

Glial cells

• are there to support the neurons

• several types:

  • Microglia: provides immune to neuron

  • Astrocytes: transport nutrients

  • Ogliodendrocytes: provide myelin to the CNS cells

  • Schwann cells: provide myelin to PNS cell. Also involved in healing of the neuron

Blood Brain Barrier

• selectively permeable

• large proteins must be transported through active transport

• is the weakest in the nasal area

• detects toxins in the blood and induces a vomiting response

excitation

• activation of a neuron

• increases the probability of action potential occurring

inhibition

• leads to neuron going in silence

• decreases the probability of action potential occurring

Diffusion

• movement of molecules down their concentration gradient

Electrostatic pressure

• molecules with the same charge repel each other

Action potential

• Takes place in axon

• a ligand needs to bind to a receptor

• the binding of the ligand opens the gates and to the receptor

• sodium goes into the cell (depolarization)

• a minimum threshold needs to be met in order for action potential to happen

• potassium goes out of the cell (repolarization)

• chloride goes into the cell

• eventually the cell will go into refractory period. During this period active transport will move sodium out of the cell and potassium into the cell. No action potential can occur during this period

• you can have multiple action potential happening because there are multiple segments.

• the cell will go into resting period

All or none

• action potential will either happen or it won’t

Rate of law

• rate of firing conveys the signal

• low rate of firing= weaker signal

Calcium

• once action potential reaches the terminal button, Ca2+ channels will open.

• calcium causes the release of neurotransmitters

• calcium acts like an enzyme

• it is important to cellular memory (learning)

• the more calcium in the cell, the more active a cell is

ligand gated ion channels

needs a ligand to bind to the receptor

• many receptors can share ligand

Spatial summation

the excitatory and inhibitory receptor cancel each other out

neurotransmitter reuptake

• neurotransmitters are removed from the synapse

• important for maintaining cell homeostasis

Enzymatic deactivation

• metabolize neurotransmitter

• metabolites are taken up and recycled into new metabolites

Auto receptors

• act as synaptic thermostat

• may control Ca2+ ion channels

• control production of neurotransmitter release.