Korean, Edit

Chapter 3. Neurophysiology

Highter category : 【Brain Science】 Brain Science Index

1. The characteristics of the brain

⑴ 2 % of the body weight (1200 ~ 1400 g)

⑵ 20 % of the total oxygen consumption

⑶ 20 % of the total blood current

2. Neuron

⑴ There are 100 billion neurons in an adult body.

⑵ Neurons are bigger than other cells ordinarily.

⑶ The structure of neuron

① The nerve cell body(soma)

○ It has nucleus, ribosome, endoplasmic reticulum, Golgi body, mitochondria, etc.

○ There is nucleus in the center of the cell body, and at the center of the cell body exists clear “nucleolus”.

○ Nissl body : The structure that looks like leopard pattern when dying “rough endoplasmic reticulum” in which proteins are actively synthesized with many “rER”s.

② Dendrite : The nerve protuberance that looks like branch

○ Unmyelinated.

○ It receives information from other neurons. (postsynaptic)

○ Dendrite spine : It enlarges the surface area.

○ Excitory neurons are connected to the spine of the dendrite and inhibitory neurons are connected to the stem of the dendrite.

③ Axon : It is also called “nerve fiber”.

○ Myelinated.

○ Length : 1 ~ 1.5 m at most.

○ It transfers information to other neurons. (presynaptic)

○ Axon collateral

④ Nerve terminal(bouton)

⑷ The class of the neuron

① Unipolar neuron

○ It has a dendrite and an axon in one direction.

○ It can be found in invertebrates.

② Pseudo unipolar neuron

○ It has an axon which splits into a dendrite and an axon.

○ Example : Spinal ganglion cells, etc.

③ Bipolar neuron

○ It has a dendrite in one direction and an axon in the opposite direction.

○ Example : Retinal cells, olfactory cells, etc.

④ Multipolar neuron

○ It has many dendrites in one direction and an axon in the opposite direction.

○ Example : Most neurons, etc.

⑸ The functional classification of the neuron

① Afferent neuron(sensory neuron) : It transfers information through the spinal cord in the back(dorsal) direction.

② Efferent neuron(motor neuron) : It transfers information through the spinal cord in the front(ventral) direction.

③ Interneuron : It connects the afferent neuron and the efferent neuron. 

⑹ The class of the cerebral neural fiber

① Association fiber

○ It connects two parts in the same cerebral hemisphere. 

○ Short association fiber : It connects the adjacent gyri.

○ Superior longitudinal fasciculus : It connects the frontal lobe and the occipital lobe.

○ Example : Short association (U) fiber, neighborhood association fiber, superior longitudinal (arcuate) fasciculus, middle longitudinal fasciculus, inferior longitudinal fasciculus, superior occipitofrontal fasciculus, inferior occipitofrontal fasciculus, superior fronto-occipital (subcallosal) fasciculus, inferior fronto-occipital fasciculus, uncinate fasciculus, cingulum, extreme capsule, etc.

② Commissural fiber

○ It connects one hemisphere and the other hemisphere.

○ Example : Anterior commissure, posterior commissure, habenular commissure, corpus callosum, hippocampal commissure, tectal commissure, etc.

③ Projection fiber

○ It ranges from cerebrum to the lower partes such as middle brain.

○ Example : Crus cerebri, Muratoff bundle(subcallosal fasciculus of Muratoff), external capsule, internal capsule, corona radiata, optic radiation, thalamocortical radiation, thalamic peduncle, acoustic radiation, fornix, thalamic bundle, pyramidal tract, pontine bundle, etc.

3. Glia

⑴ There are  1 trillion cells in an adult body.

① The etymology of “glia” is “glue”.

② It plays a role like connective tissue.

③ Although all the roles aren’t discovered, the glia is regarded as the principal cells in the nerve system.

⑵ Astrocyte

① It is largest among glias.

② Class : Protoplasmic astrocyte, fibrous astrocyte

③ Location : It contacts the vascular tube in a direction and the neuron, the “pia meter”, the neural fiber in the opposite direction.

④ Function

○ It braces other neurons.

○ It contributes to the mass transfer between the neuron and the vascular tube.

○ It covers the nodes of Ranvier so that the axon isn’t exposed to the environment.

○ It maintains the microscopic environment by cleaning out the reaction products and reducing increased potassium ion concentration around the neuron.

○ It helps maintain BBB(blood brain barrier) in the vascular tube.

⑶ Oligodendrocyte : It creates the myelin of the neuron in CNS(central nerve system).

⑷ Schwann cell : It creates the myelin of the neuron in PNS(peripheral nerve system).

⑸ Microglia

① Phagocytosis : It is included in “mononuclear phagocytic system”.

○ Macrophage is also included in “mononuclear phagocytic system”.

② It plays immune function in the nerve system.

⑹ Ependymal cell : As epithelial cell, it covers inner surface of the central canal and ventricles.

4. Restion membrane potential

⑴ Membrane potential is the inner-membrane electrical potential relative to the outer-membrane electrical potential. (unit : ㎷)

⑵ The equilibrium states of restion membrane potential is -70 ㎷.

① The nonhomogenous distribution of ions around the cell membrane.

② The selective transparency of the cell membrane (Na⁺ < K⁺)

③ Na⁺/ K⁺ pump : It moves 3 molecules of Na⁺ outside the cell and moves 2 molecules of K⁺ inside the cell.

④ The attractive force by the negative-charged proteins in the cell

⑶ Nernst equation

5. The generation of the active potential

⑴ It follows the law of “all or none”.

⑵ Resting state

① Sodium channel : Activation gate is closed and inactivation gate is open at this step.

⑶ Depolarization

① Threshold potential : -40 ~ -50 ㎷, Depolarization should make the membrane potential exceed the threshold potential in order to generate the active potential.

② Sodium channel : Activation gate is open and inactivation gate is closed at this step.

③ Potassium channel : It is closed at this step.

⑷ Repolarization

① Sodium channel : Activation gate is open and inactivation gate is closed (right after the membrane potential hits 30 ㎷)

② Potassium channel : When the membrane potential hits 30 ㎷, repolarization begins by the leakage of the potassium ion.

③ Astrocyte begins to lower the concentration of the potassium ion.

⑸ Hyperpolarization

① Sodium channel : Activation gate is closed and inactivation gate is open at this step.

② Potassium channel : It is closing at this step.

③ By the mechanism of restion membrane potential, the membrane potential returns to -70 ㎷ slowly.

⑹ Refractory period

① The period from the potassium ion moves outside the axon and the membrane potential returns to -70 ㎷

② Absolute refractory period : In this period, it is impossible to regenerate the active potential no matter how big the stimulus is. It is related to the inactivation gate.

③ Relative refractory period : In this period, it is possible to regenerate the active potential. It is related to the activation gate.

6. The conduction of the active potential

⑴ Regenerative conduction : It generates the active potential by depolarizing the adjacent position.

⑵ Because the position in which the active potential already passes is in refractory period, the active potential conducts in one way.

⑶ Saltatory conduction

① Myelination

○ Myelin is slowly formed for a year after birth.

○ Oligodendrocyte : It makes encompassing myelin around the neuron by extending its protuberance.

○ Schwann cell : It makes encompassing myelin by rolling itself up around the neuron.

○ Myelin is made from the double-layer membrane and the main component of myelin is lipid which is also abundant in the membrane.

○ The boundaries of the oligodendrocytes or Schwann cells is also the boundaries of myelin and this boundary is called “node of Ranvier”.

② Myelination is insulation. Thus the active potential is generated at nodes of Ranvier and the conduction speeds considerably improved.

○ The period to generate the active potential is the period to diffuse the sodium ion and the potassium ion locally.

○ Not to generate the active potential all axon long, most position of axon should be insulated.

③ Saltatory conduction : It means that the active potential jumps to the next node of Ranvier at all steps.

⑷ The bigger the diameter of the nerve is, the faster the conduction is.

7. Chemical synapse

⑴ The principle of the chemical synapse

① Neurotransmitter

⑵ The synthesis and storage of neurotransmitter : They are stored in synaptic vesicles.

⑶ The release of neurotransmitter 

① Ca²⁺ promotes the fusion of the synaptic vesicle and the presynaptic membrane.

② Neurotransmitters are poured into the “synaptic cleft”.

⑷ EPSP/IPSP

① EPSP(excitatory postsynaptic potential)

② IPSP(inhibitory postsynaptic potential)

⑸ Synaptic integration

① Spatial summation, temporal summation

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② Shunting inhibition

⑹ The kind of neurotransmitter

① Ach

○ The life cycle of Ach

○ nAchR(Nicotinic Acetylcholine Receptor)

○ mAchR(Muscarinic Acetylcholine Receptor)

② GABA

③ Glu (excitatory)

④ Gly (inhibitory)

○ Africa native’s poisoned needle : Inhibition of Gly receptors → over-excitation of the circuit of the spinal cord → paralysis

⑤ NE

○ Influence to the heart beat

⑥ P substance

8. The histology of the cerebrum and the cerebellum

⑴ In the nerve system, the cell bodies are clustered functionally.

Example : Basal ganglion, thalamus, various nuclei of nerve, gray matter, ganglion, etc.

⑵ The histology of the cerebrum

① The cerebrum has the gray matter at its cortex, the white matter at its medulla and can be segmented with 6 layers.

② Molecular layer

○ It is the outer layer of the cerebral cortex.

○ There are few neurons.

○ There are neural fibers parallel to the cerebral cortex.

③ External granular layer : There are granule cells, glias, etc.

○ Granular layer cells receives information from the outside.

④ External pyramidal layer : There are pyramidal cells.

○ Pyramidal layer cells transmits information to the outside.

⑤ Internal granular layer : Small granule cells are located densely.

⑥ Internal pyramidal layer : There are the largest pyramidal cell at this layer.

⑦ Multiform layer : There are various forms of cells.

⑶ The histology of the cerebellum

① The cerebellum has the gray matter at its cortex, the white matter at its medulla and can be segmented with 3 layers.

② Molecular layer    

○ It is the outer layer of the cerebellar cortex.

○ Cells are distributed sparsely.

③ Purkinje cell layer : Very big purkinje cells are aligned between the molecular layer and the granular layer.

④ Granular layer : Neurons are distributed densely.

9. Learning and memory

⑴ LTP(long-term potentiation) : It takes place at the hippocampus.

① Molecular mechanism(see below)

② The change of synapse

⑵ LTD(long-term depression) : It takes place at the cerebellum.

① Molecular mechanism

② The change of synapse

③ The learning and memory in the cerebellum

○ The cerebellum is one-tenth of the cerebrum in size but is equal in the number of neurons.

○ Input : PF(parallel fiber), CF(climbing fiber); It represents address.

○ Output : PC(purkinje cell); There is the change of synaptic strength.

Input: 2018.09.17 23:53