Neuron & Glial cells
- 1. Neuron & Glial cells (Paper-2 Unit-4) Asst Prof. Abhijeet Bhattacharya KSD’s Model College
- 2. Neuron Introduction ➢A neuron ( also known as nerve cell) is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. ➢ Neurons are the core components of the nervous system, which includes the brain, spinal cord, and peripheral ganglia. ➢ Human brain comprises tens of billions of neurons, each linked to thousands of other neurons via the chemical channels called synapse.
- 4. Parts of a Neuron ➢There are many types of neuron but a typical neuron has some common structural and functional characteristics. ➢A neuron consists of three main parts ➢The Cell body or Perikaryon or Soma, ➢Dendrites, the receiving processes. ➢Axons, the transmitting fiber.
- 5. SOMA
- 6. SOMA or CELL BODY ➢The cell body is the central region which is the most important part of the neuron containing the nucleus of the cell. ➢The soma is, the site of major metabolic activity in the neuron. ➢ The size of neuronal somas range widely from 0.005 mm to 0.1 mm in mammals. ➢Collections of cell bodies (somas) give the greyish appearance to the gray matter of the brain.
- 7. SOMA or CELL BODY contd… ➢The protoplasm of cell body contains peculiar angular granules, which stain deeply with basic dyes, such as methylene blue; these are known as Nissl’s granules. ➢These granules disappear (chromatolysis) during fatigue or after prolonged stimulation of the nerve fibers connected with the cells. ➢ Thought to be involved in the synthesis of neurotransmitters such as acetylcholine
- 8. Dendrites ➢Dendrites are extensions that carry impulses toward the cell body and are referred to as being afferent fibers. ➢ They increase the surface area of a neuron by the presence of rough structure on their surface called dendritic spines, to increase its ability to communicate with other neurons.
- 9. Axon ➢An axon is a type of protoplasmic protrusions that extrude from the cell body of a neuron . ➢Unlike dendrites axons are long, slender projection of a neuron, that conducts electrical impulses away from the neuron's cell body or soma. ➢Axons are distinguished from dendrites by several features, including shape, length , and function. ➢The point where the axon arises from a cell body is termed as Axon Hillock. ➢Axoplasm is the cytoplasm within the axon.
- 10. Axon diagram
- 11. Axon contd….. ➢The axolemma is the cell membrane surrounding an axon. ➢It is responsible for maintaining the membrane potential of the neuron, and it contains ion channels through which ions can flow. ➢The axons of many neurons are sheathed in myelin, which is formed by either of two types of glial cells: Schwann cells myelinate peripheral neurons and oligodendrocytes myelinate the central nervous system ➢ The Myelin sheath functions to: – Protects the axon and increases the rate of Action Potential transmission (saltation) ➢Along myelinated nerve fibers, gaps at intervals in the sheath known as Nodes of Ranvier.
- 12. Axon contd…. ➢Terminally the Axon forms synaptic knob, which contains synaptic vesicles, containing Neurotransmitter. ➢Axons contact with other cells via the synaptic knob on dendrites of other neurons but sometimes muscle or gland cells—at junctions called synapses. ➢The region between the two connecting neurons is known as the Synaptic gap or Snaptic cleft or neural junction.
- 13. Classification of neurons BASED ON POLARITY ➢ Unipolar : type of neuron in which only one protoplasmic process (neurite) extends from the cell body. – Found mostly in inverterbrate – In humans mostly found in dorsal root ganglia ➢Bipolar: An axon and a single dendrite on opposite ends of the Soma are abundant in sensory pathways for smell, sight, taste, hearing and vestibular functions. ➢Multipolar: An Axon along with more than two dendrites –Includes motor neurons and interneurons.
- 14. Classification of Neuron Based on Polarity
- 15. Classification of neurons BASED ON CONDUCTION DIRECTION ➢Afferent neurons also called sensory neurons. Convey information from tissues and organs into the central nervous system. ➢Efferent neurons also called as motor neurons. Carry nerve impulses away from the central nervous system to effectors such as muscles or glands. ➢ Interneuron also called as relay neuron or local circuit neuron connects afferent neurons and efferent neurons in neural pathways
- 16. Classification of neurons BASED ON NEUROTRANSMITTER PRODUCTION ➢Cholinergic neurons —secreting acetylcholine ➢GABAergic neurons — secreting gamma aminobutyric acid. ➢Glutamatergic neuron — secreting glutamate ➢Dopaminergic neurons — secreting dopamine . ➢ Serotonergic neurons — secreting serotonin.
- 17. Classification of neurons BASED ON UNIQUE SHAPE AND FUNCTION ➢Betz cells – Large motor neurons located within the fifth layer of the grey matter in the primary motor cortex. ➢Purkinje cells - Some of the largest neurons in the human brain, found within the Purkinje layer in the cerebellum. ➢Renshaw cells - Neurons with both ends linked to alpha motor neurons. ➢Pyramidal cells- Type of neurons with triangular soma found in areas of the brain including cerebral cortex, the hippocampus, and in the amygdala. ➢Basket cells - Inhibitory GABAergic interneurons found in several brain regions: the molecular layer of the cerebellum, the hippocampus, and the cortex.
- 18. Glial Cells. ➢Glia, also called glial cells or neuroglia, are non- neuronal cells in the central nervous system (brain and spinal cord) and the peripheral nervous system. ➢Do not produce electrical impulses. ➢They maintain homeostasis ➢Produces myelin ➢ Provide support and protection for neurons. ➢In CNS Glial cells outnumber neurons 10:01
- 19. Types of Glial Cells & Radial Glial Cells
- 20. Neuroglia in the CNS There are four types of neuroglia found within the central nervous system: ➢Astrocytes – maintain the blood brain barrier and preserve the chemical environment by recycling ions and neurotransmitters ➢Oligodendrocytes – myelinate axons in the central nervous system and provide an overall structural framework ➢Ependymal cells – line ventricles (brain) and central canal (spine) and are involved in the production of cerebrospinal fluid ➢Microglia – remove cell debris, wastes and pathogens via phagocytosis
- 21. Neuroglia in the PNS There are two types of neuroglia found within the peripheral nervous system: ➢Schwann cells – myelinate axons in the peripheral nervous system ➢Satellite cells – regulate nutrient and neurotransmitter levels around neurons in ganglia