Question

Draw a tree/flowchart that shows how the nervous system is divided and where branches originate. (Begin with CNS and PNS and go down to the somatic nervous system and the ANS, etc.) This will help you understand connections and signal directions.

Discuss the four basic types of cell configurations, how they work, and where they can be found.

4. Describe how neurons generate and conduct electrical and chemical impulses.

5. Identify the specific mechanisms that could be targeted by a drug that would block the transmission of impulses across a synapse.

Answer 1

Nervous system detects and responds to changes inside and outside the body.

The nervous system consists of the brain, spinal cord and peripheral nerves. The structure and organization of the tissues that form these components enables rapid communication between different parts of the body

Peripheral nervous system		Central nervous system	Peripheral nervous system
Sensory division		Brain and spinal cord	Motor division
Sensory or afferent neurone		Cranial nerves Spinal nerves	Motor or efferent neurone
Sensory receptors			Effector organs
			Somatic (voluntary) Skeletal muscle	Autonomic (involuntary) A cardiac muscle Smooth muscle Glands
Senses Sight Hearing Smell Taste Touch	Internal environment (autonomic) Chemoreceptor Baro receptors Osmoreceptors Gustatory receptors			Sympathetic division	Parasympathetic division

Question no:2

The neurons of CNS are supported by 4 types of non- excited glial cells that make up a quarter to a half of the volume of brain tissue.

Unlike nerve cells, these continue to replicate throughout life.

S.no	Cells	Description
1.	Astrocytes	Main supporting tissue of the central nervous system Star shaped with fine branching processes and they lie in a mucopolysaccharide ground substance At the free ends of some of the processes there are small swellings called foot processes Found in large numbers adjacent to blood vessels with their foot processes Constitute blood brain barrier Functions are analogous to those of fibroblasts elsewhere in the body.
2.	Oligodendrocytes	Smaller than astrocytes They are found in clusters round nerve cell bodies in grey matter Supportive function Form and maintain myelin, having same function as Schwann cells in peripheral nerves
3	Microglia	Derived from monocytes that migrate from the blood into the nervous system before birth Found mainly in area of blood vessels Main function is enlargement and phagocytic, removing microbes and damaged tissue, in areas of inflammation and cell destruction.
4.	Ependymal cells	Form the epithelial lining of the ventricles of the brain and the central canal of spinal cord Form the choroid plexuses of the ventricles secrete CSF.

Question no:3

Neurons have the characteristics of irritability and conductivity

Irritability	Conductivity
Is the ability to initiate nerve impulses in response to stimuli from: Outside the body Inside the body e.g., a change in concentration of carbon dioxide in the blood alters respiration; a thought may result in voluntary movement. This stimulation may be described as partly electrical and partly chemical- electrical	Conductivity means the ability to transmit an impulse

1. An impulse is initiated by stimulation of sensory nerve endings or by the passage of an impulse from another nerve.
2. Transmission of the impulse, or action potential, is due to movement of ions across the nerve cell membrane.
3. In the resting state the nerve cell membrane is polarized due to differences in the concentrations of ions across the plasma membrane
4. Resting membrane potential- different electrical charge on each side of the membrane
5. At rest the charge on the outside is positive and inside it is negative. The principal ions involved are:
   1. sodium- main extracellular cation
   2. Potassium- the main intracellular cation.
6. When stimulated, the permeability of the nerve cell membrane to these ions changes.
7. Initially sodium floods into the neuron from the ECF causing depolarization, creating a nerve impulse or action potential.
8. Depolarization is very rapid, enabling the conduction of a nerve impulse along the entire length of a neuron in a few milliseconds.
9. One- way direction of transmission is ensured because following depolarization it takes time for repolarization to occur.
10. During this process potassium floods out of the neuron and movement of these ions returns the membrane potential to its resting state.
11. Refractory period, which restimulation is not possible.
12. In myelinated neuron, the insulating properties of the myelin sheath prevent the movement of ions.
13. Electrical changes across the membrane can only occur at the gaps in the myelin sheath, i.e., at the nodes of Ranvier.
14. When an impulse occurs at one node, depolarization passes along the myelin sheath to the next node so that the flow of current appears to leap from one node to the next- salutatory conduction.
15. The speed of conduction depends on the diameter of the neuron:
    1. Larger- faster conduction
    2. Myelinated fibres- faster
    3. Unmyelnated fibres- slower

Question no:4

They are 4 steps:

Step 1: synthesized and storage

Neurotransmitter must be synthesized and stored in vesicles so that when an action potential arrives at the nerve ending, the cell is ready to pass it along to the next neuron.

Step 2: neurotransmitter release:

When an action potential does arrive at the terminal, the neurotransmitter must be quickly and efficiently released from the terminal and into the synaptic cleft.

Step 3: neurotransmitter postsynaptic receptors:

Neurotransmitter must then be recognized by selective receptors on the postsynaptic cell so that it can pass along the signal and initiate another action potential.

Step 4: inactivation of neurotransmitter:

It avoids constant stimulation of the postsynaptic cell, while at the same time freeing up the receptor sites so that they can receive additional neurotransmitter molecules.