General Anatomy (Nervous Tissue) Flashcards
What are the basic properties of nervous tissues?
- To receive stimuli from within and outside the body
- To conduct stimuli from Receptor to CNS (afferent)
- To transmit impulses from CNS to (efferent)
i) muscles for contraction
ii) glands for secretion
What are the subdivisions of the nervous tissues?
- CNS - Central nervous system
Brain and Spinal cord - PNS - Peripheral nervous system
i) Cranial nerves (12 pairs) from brain
ii) Spinal nerves (31 pairs) from spinal cord - ANS – Autonomic nervous system
i) Sympathetic and
ii) Parasympathetic
What are the two types of cells in the nervous tissue?
- Neurons (or ) Nerve cells
- Nervous connective tissue – Neuroglial cells
What are neurons?
• Neurons are structural and functional units of nervous tissue.
• Adult neurons do not undergo mitosis
Nerve cells or neurons are responsible for the reception, transmission, and processing of stimuli, the triggering of
certain cell activities, and release of neurotransmitters.
What are the three parts of the neurons?
- Cell body or perikaryon - which is the trophic center for the whole cell and also receptive to stimuli.
- Dendrites - Multiple elongated processes specialized in receiving stimuli from environment, sensory epithelial cells, or other neurons. They possess Nissl granules
- Axons - Single process specialized in conducting nerve impulse to other cells (nerve, muscle and glands).
Axon hillock- initial segment of an axon, devoid of Nissl granules.
What are the three types of neurons?
- Bipolar neuron – One dendrite and one axon emerging from the cell body at opposite ends. Found in special sense organs example retina, olfactory neuron.
- Pseudo unipolar or unipolar neuron – single process dividing into two. One goes to peripheral ending and the other to the CNS. Found in posterior root ganglion.
- Multipolar neuron – more than one dendrite and single axon . Most neurons of the brain and spinal cord.
What are motor neurons?
Send motor impulses to muscles and glands and bring about movements of muscles and secretion of glands.
Found in:
i)Brain –Cranialmotornuclei
ii) Spinal cord – Ventral horn of the grey matter
What are sensory neurons?
receive impulses from peripheral receptors
Found in:
i) Brain – Cranial sensory nuclei
ii) Spinal cord- 1. Posterior root ganglia
2. Dorsal horn grey matter
What are connector neuron?
connect and integrate the motor and sensory
neurons
i)- gray mater of spinal cord
What are the types of neurons according to the size of the axon found in the CNS?
- golgi type 1 neurons
- golgi type 2 neutons
What are golgi type 1 neurons?
Have long axon. Axons form long fiber tracts (ascending and descending) of the brain and spinal cord and nerve fibers of peripheral nervous system.
Examples are
i) Pyramidal cells of the cerebral cortex
ii) Purkinje cells of cerebellar cortex and
iii) Motor cells of the spinal cord.
What are golgi type 2 neurons?
have a short axon that terminates near the cell body.
They are more numerous than the Golgi type I neurons. They are numerous in the
i) cerebral cortex
ii) cerebellar cortex and are often inhibitory in function.
What are synapses?
• Site of functional contact between two neurons at which nerve impulses pass from one neuron to another.
• There is no anatomical continuity.
• The function of the synapse is to convert an electrical impulse from the presynaptic cell into a chemical signal that acts on the post synaptic cell.
• This is done by releasing neurotransmitters.
What are neurotransmitters?
Neurotransmitters are chemicals that when combined with a receptor protein initiate second–messenger cascades.
How are synapses formed?
• The synapse is formed by an axon terminal(presynaptic terminal) that delivers the signal.
• A region of another cell where a new signal is generated is postsynaptic terminal.
•The thin intercellular space between them is the synaptic cleft.
What is the presynaptic terminal?
• The presynaptic terminal always contain synaptic vesicles with neurotransmitters and numerous mitochondria.
• Neurotransmitters are synthesized in the cell body and then stored in vesicles in the presynaptic region.
• During transmission they are released into the synaptic cleft by exocytosis.
If an axon forms a synapse
• With a cell body it is called an –
Axosomatic.
• With a Dendrite – Axodendritic
• With an axon - Axoaxonic
What are the two types of synapses?
1 Chemical synapses (use chemical messengers)- commonest
2 Electrical synapses (transmits ionic signals through gap junctions).
The two types differ in structure and in the mechanism of impulse transmission.
Impulse transmission is faster at electrical synapses. Eg: CNS
What are neuroglial cells or glial cells?
Non-neuronal nervous connective tissue cells
• Consists of cell and processes
• Their number is more than the neurons
• They provide a microenvironment suitable for the neuronal activity.
What are the types of neuroglial cells?
- Astrocytes
- Microglia
- Oligodendrocytes
What are Astrocytes?
Astrocytes are star shaped cells with multiple radiating processes. There are 2 types of astrocytes
What are the two types of Astrocytes?
- Fibrous astrocytes located in the white matter
- Protoplasmic astrocytes with many short branched
processes found in the grey matter.
What are the functions of astrocytes?
- Structural support- hold blood vessels and neurons in place
- Metabolic exchanges- increases blood supply when need arises
- Blood brain barrier- perivascular feet
- Repair processes – scar tissue
can form
What are microglial cells?
• Are small elongated cells with short irregular processes and dense elongated nuclei.
• Found in the CNS.
• Phagocytic cells of the mononuclear
phagocytic system in the nerve tissue.
• They are involved in inflammation and
repair in the adult CNS.
What happens microglial cells are activated?
- Microglia retract their processes and become macrophages which are phagocytic
- Act as antigen presenting cell
- Dispose off unwanted cellular debris caused by CNS lesions.