Physiology Of Neurons
Physiology Of Neurons
1.1. Classification of neurons
1.2. Neurochemistry
1.3. Neuroglia
1.4. The reflex
2. The nervous system
2.1. Divisions of the nervous system
2.2. Spinal cord
Medulla
2.3. Midbrain structures
2.4. Hindbrain structures
2.5. Integrative and behavioral functions
2.6. Forebrain structures
2.7. The autonomic nervous system
1. Cellular neuroscience
1.1. Classification of neurons
Because the size, shape, and functional properties of neurons vary tremendously, several overlapping systems of classification are employed.
1. The number of neurites (processes) is used to classify three basic types of neuron :
- Unipolar neurons have a single neurite (e.g., primary sensory neurons with the cell body located in the dorsal root ganglia of spinal nerves).
- Bipolar neurons have two neurites (e.g., a retinal bipolar cell).
- Multipolar neurons have three or more neurites. This is the most common type of neuron (e.g., spinal motor neuron).
The neuron consist of: dendrites, the cell body, axon hillock, axon (it may have collateral branches) and the terminal bouton, which has many vesicles containing neurotransmitter.
The functions of cell body are: the synthesis of the neurotransmitter, perception, integration, storage and reproduction of information. Perception of information is possible also in dendrites. The axon hillosk (initial segment of axon) lacks myelin and is the site of action potential generation. The function of axon is action potential propagation. The function of the axon terminal is signal transmission (from the neuron to another excitable cell).
2. The organization of dendrites:
- Pyramidal neurons. Pyramidal neurons are the primary neural cell type in the corticospinal tract (mainly motor tract).
- Stellate neurons are any cells that have a star-like shape formed by dendritic processes radiating from the cell body (mainly interneurons).
3. Functional classification :
5. The type of neurotransmitter (about 200)
1.2. Neurochemistry
There is a pattern to the distribution of neurons that use a particular neurotransmitter and, as a result, the neurotransmitter assumes a prominent role in a given function (e.g., dopaminergic neurons are important in the control of movement).
1.3. Neuroglia
Three major types of glia:
1. Astrocytes are highly branched cells that envelope neurons and brain capillaries. Several functions have been ascribed to astrocytes, including:
- To surround neurons and hold them in place
- To supply nutrients and oxygen to neurons
- To maintain a stable [K+] in the brain extracellular fluid.
- To remove neurotransmitters from brain extracellular fluid in the region of synapses.
- To synthesize neurotransmitter precursors for neurons.
2. Microglia are highly reactive cells that are activated by injury or infection, which causes them to proliferate and become phagocytic.
3. Oligodendrocytes produce and maintain the myelin sheaths around neurons in the CNS by wrapping around the axons many times. Schwann cells are the equivalent of oligodendrocytes in the peripheral nervous system .
White matter refers to axon tracts and commissures. White matter is named for its relatively light appearance resulting from the lipid content of myelin. It’s function is conduction.
The other main component of the brain is grey matter , which is composed of neurons soma. It’s function is perception, integration, storage and reproduction of information (reflex function).
1.4. The reflex
A reflex is an involuntary response to a stimulus, which is carried by the nervous system.
The morphological base of reflex is the reflex arch which represents a set of morphologically associated formations that support perception, transmission, and conversion of signals as well as realization of response.
Reflex arch includes the following elements and links:
- sensory receptors perceiving stimuli of external and internal environment;
- afferent (sensory) nerve conductors;
- nerve center – afferent, intercalary and efferent nerve cells;
- efferent (motor) nerve conductors;
- effector (executive) organ.
For sufficient regulation it is necessary to have information about a state of effector as well as its response, i.e. parameter. This information is sent to the nerve center and is called as feedback.
The example of reflex – a withdrawal of limb at pain stimulation. The reflex arch of this reflex includes
skin receptors (1),
afferent (sensory) nerve conductors (2),
sensory neurons (with the bodies locating in spinal ganglia (3),
intercalary neurons (4),
motoneurons of spinal cord (5),
efferent (motor) nerve conductors (6),
and effectors (flexor muscles) (7).
2. The autonomic nervous system
