Diagram of neurons

Parts of neuron:

• Dendrite: The function of the dendrite is to receive the stimulus and carry impulses to the cell body.
• Cell body: The cell body contains a nucleus and most of the cytoplasm.
• Axon: The axon is the fiber that carries the impulses far from the cell body.
• Schwann cells: These cells produce myelin or fat layer in the PNS.
• Myelin sheath: It is a dense lipid layer that insulates the axon and makes it gray.
• Node of Ranvier: the nodes present on the myelin sheath.

Three types of Neurons

Sensory neurons: the sensory neurons bring messages to the CNS

Motor neurons: these neurons carry messages from CNS

Interneurons: the neurons present between the sensory & the motor neurons in the CNS

Impulses:

Stimulus: The stimulus is the change in the environment with a sufficient strength for initiating response.

Excitability: the ability of a neuron to respond to the stimulus and then convert it into nerve impulse.

All of Nothing Rule: it states that the stimulus is either strong enough to start and impulse or nothing happens.

• The impulses always have the same strength along a neuron and they are self-propagated, once it starts it continues in only one direction from dendrite to the cell body

• There is a movement of ions across the cell membrane of nerve cell caused by the nerve impulse

Synapse: the synapse is the gap or space between the axon of one neuron and the dendrite of the next. It is the junction between the neurons. These neurons use the transmitters to start the impulse in the next neuron. The synapse is only responsible for one way transmission of impulse.

Neurotransmitters: the neurotransmitters are the chemicals in the junction by which the impulse started in the next neuron

Reflex Arc: the sudden reaction or response given by the spinal nerves is called as the reflex arc

Components of Reflex Arc:

• Receptor: the receptor reacts to a stimulus
• Afferent pathway (sensory neuron): it connects impulses to the CNS
• Interneuron: the interneuron consists of one or more synapses in the CNS
• Efferent pathway (motor neuron): it conducts the impulses from CNS to the effector.
• Effector: the effector is contains the muscle fibers or a gland that responds by contracting or secreting a product.

Spinal reflexes: these are initiated and completed at the spinal cord level. They occur without the involvement of the higher brain.

Central Nervous System

Brain: the brain is the main organ of the Central Nervous System. The brain consist of brain stem cerebellum, cerebrum.

The Brain stem contains the medulla, pons, and midbrain

Diencephalon contains the thalamus & hypothalamus

Cerebellum

Cerebrum

Spine: contain the spinal Cord

Meninges: there are the three main coverings around the brain and the spine called meninges, function of meninges is to give protection and nourishment to the brain and the spinal cord.

Dura mater: The Dura mater is the most outer layer of the brain it is the toughest layer.

Arachnoid mater: Arachnoid mater is the middle layer of the brain and it adheres to the dura mater and has web like attachments to the innermost layer i.e. the pia mater.

Pia mater: The pia mater is thin and transparent and hard and it covers the entire brain it is tough also.

Cerebrospinal fluid (CSF): the cerebrospinal fluid provides nourishment to the brain and spinal cord; it also detoxifies the brain and the spinal cord. The CSF flows between the arachnoid mater and the pia mater.

Regions of the Brain

Cerebellum: movement coordination with the help of motor nerves

Cerebrum: is responsible for conscious activities including perception, emotion, thought, and planning

Thalamus: the thalamus is the Brain’s switchboard: it filters the information then relays it to various brain regions

Medulla: the medulla is responsible for the vital reflexes such as heart beat and respiration

Brainstem: the medulla, pons, and midbrain (involuntary responses) and relays data/information from spine to upper brain

Hypothalamus: the hypothalamus is involved in regulating activities of the internal organs by monitoring information from the autonomic nervous system. The hypothalamus controls the pituitary gland and hormones secreted by it. It also regulates sleep and appetite.

Cerebrum: the cerebrum is the largest part of the brain; it covers around two-third part of the brain mass

The cerebrum consists of two hemispheres divided by a fissure called corpus callosum

It also includes the cerebral cortex, the medullary body, and basal ganglia.

Cerebral cortex: the cerebral cortex is that layer of the brain that resembles to the gray matter of the brain because it has cell bodies synapses but there is myelin is absent.

The cortex is the thin layer and it is gray because of the absence of myelin sheath or lack of insulation. Myelin sheath makes the most of the parts of the brain to appear white.

The cortex covers the outer part (1.5mm to 5mm) of the cerebrum and cerebellum.

There is the folded bulge present in the cortex known as gyri, this gyri create deep fissures called as sulci.

These folds in the brain increase the amount of gray matter and also increase the quantity of the information to be processed.

Medullary body: the medullary body is the white matter of the cerebrum and it contains the myelinated axons.

Commisural fibers: these fibers conduct impulses between the hemispheres of the brain and form corpus callosum

Projection fibers: the projection fibers conduct impulse in and out of the cerebral hemispheres

Association fibers: the association fibers conduct impulses within the hemispheres

Basal ganglia: the masses of the gray matter in each hemisphere which are involved in the control of voluntary muscle movements are called as basal ganglia.

Lobes of the Cerebrum: there are four lobes in the cerebrum

• Frontal lobe: the frontal lobe is the motor area; it is involved in movement and in planning & coordinating the behavior

• Parietal lobe: the parietal lobe is responsible for the sensory processing, attention, and language

• Temporal lobe: the temporal lobe is responsible for auditory perception, speech, and complex visual perceptions

• Occipital lobe: the occipital lobe is the visual center it plays a role in processing visual information.

Image of lobes

Some Special regions of brain:

• Broca’s area: it is located in the frontal lobe, it is important for the speech production.

• Wernicke’s area: helps in comprehension of language and the production of meaningful speech

• Limbic System: it is a group of brain structures (aamygdala, hippocampus, septum, basal ganglia, and others) that helps in regulating the expression of emotions and emotional memory

Brain Waves: the brain waves are rhythmic fluctuation of electric potential between parts of the brain. The brain waves can be seen on an electroencephalogram (EEG).

Electroencephalogram: it is a procedure that measures the brain waves by placing electrodes on the scalp.

There are four types of brainwaves:

• Beta
• Alpha
• Theta
• Delta

Peripheral Nervous System: the peripheral nervous system contains all the nerves of the brain and the spinal cord.

Cranial nerves: the cranial nerves are present in 12 pairs. The cranial nerves attached to the undersurface of the brain.

Spinal nerves: there are 31 pairs of the spinal nerves attached to the spinal cord.

Somatic Nervous System (voluntary): it takes the information from skin, sense organs & skeletal muscles give it to CNS. It also brings responses back to skeletal muscles for voluntary responses.

Autonomic Nervous System (involuntary): it regulates body’s involuntary responses, relays information to internal organs

There are two divisions of the autonomic nervous system

1. Sympathetic nervous system
2. Parasympathetic nervous system

Major Sense Organs

•Eye: Vision

•Ear: Hearing

•Taste receptors: Taste

•Olfactory system: Smell

• Skin: Hot, cold, pressure, pain

Disorders of the Nervous System:

Epilepsy: Epilepsy is a disorder characterized by recurring seizure; also known as the seizure disorders. A seizure is a brief temporary disturbance in electrical activity of the brain.

The brain is the source of epilepsy. All brain functions including feeling, seeing, thinking, moving muscles depend on the electrical signal passed between nerve cells of the brain.

A seizure occurs when too many nerve cells in the brain fire too quickly causing an electric storm.

Symptoms:

1. Periods of blackout or confused memory.
2. Occasional fainting spells
3. Episodes of blank starring in children
4. Sudden fall for no apparent region
5. A convulsion with without fear
6. Clusters of sniff jerking movements in babies.

Management:

1. Stay calm and track time
2. Do not restrain the person, but help them to avoid hazards: protect head, remove glasses, and loosen tight neck wear.
3. If seizure occurs last than 5 minutes call for medical help.