The nervous system of man is the most advanced, highly developed. It controls all functions of the body. It consists of two parts
1. Central Nervous System (CNS)
2. Peripheral Nervous System (PNS)
1. Central Nervous System (CNS)
Definition
The nervous system consists of brain and spinal cord (hollow nerve cord) and also consists of upto 100 billion inter neurons is called Central Nervous System (CNS).
Components of Central Nervous System
The central nervous system consists of
Brain
Spinal Cord
Protection of Central Nervous System
Brain and spinal cord both are protected in three ways
i. Cranium
ii. The Vertebral Column
iii. Meninges
iv. Cerebrospinal Fluid (CSF)
i. Cranium
Cranium, which is part of skill, protects the brain.
ii. Vertebral Column
Neural arches of vertebrate of vertebral column protect the spinal cord.
iii. Meninges
Beneath the cranium, the brain and spinal cord are protected by triple layers of tough connective tissues called meninges.
iv. Cerebrospinal Fluid (CSF)
Between the layers of meninges, there is a plasma like fluid which bathes the neurons of brain and spinal cord is called Cerebrospinal Fluid (CSF).
It cushions against the bumps and jolts.
2. Peripheral Nervous System (PNS)
Definition
The nerves arises from brain and spinal cord that are spread in various part of body which transmits the signals between CNS and body parts make a nervous system called Peripheral Nervous System.
The peripheral nervous system consists of two types of nerves.
i. Cranial Nerves
ii. Spinal Nerves
i. Cranial Nerves
In humans, there are 12 pairs of nerves which arise from the brain or lead to the brain these nerves are called cerebral or cranial nerves.
ii. Spinal Nerves
In humans, there are 31 pairs of nerves which arise from the spinal cord or lead to the spinal cord are called spinal nerves.
Types of Peripheral Nervous System
The peripheral nervous system is divided into two types according to their functions.
1. Somatic Nervous System
2. Autonomic Nervous System
1. Somatic Nervous System
The peripheral nervous system which controls all the voluntary activities of the body such as contraction of skeletal muscles and movement of joint is called Somatic Nervous System.
2. Autonomic Nervous System
The autonomic nervous system which controls involuntary activities of the body such as smooth muscles, glands, muscles of heart and other internal organs is called Autonomic Nervous System.
Types of Autonomic Nervous System
Autonomic nervous system divided into two types
i. Para Sympathetic Nervous System
ii. Sympathetic Nervous System
i. Para Sympathetic Nervous System
The autonomic nervous system formed by some cranial nerves, vagus nerves and the spinal nerves that are arising from the sacral vertabrate are called Para Sympathetic Nervous System.
ii. Sympathetic Nervous System
The autonomic nervous system whose nerves arise from the thoracic and lumber regions of spinal nerves is called Sympathetic Nervous System.
Functions
This system is important during emergency situation and is associated with “flight or fight”. It increases the heart beat, breathing rate, slows digestion, dilates pupil etc.
Brain
Definition
The most important part of Central Nervous System develops from dorsal, hollow nerve cord well protected in the cranium of skull and composed of inter neurons and is the seat of our intelligence, learning and memory is called Brain.
Part of Brain
The brain consists of three parts
1. Fore Brain
2. Mid Brain
3. Hind Brain
1. Fore Brain
Fore brain can be divided into two regions
i. Telencephalon
ii. Diencephalon
i. Telencephalon
The largest part of fore-brain which is differentiated into two cerebral hemisphere or cerebrum is called Telencephalon.
Cerebrum
Cerebrum is the largest part of the brain and is divided into two halves called Cerebral Hemisphes.
Cerebral Hemisphere
Each hemisphere consist of an outer grey matter or cerebral cortex and an inner white matter.
Cerebral Cortex
- Cerebral cortex is the largest and the most complex part of human brain.
- It is highly convulated to occupy the greater number of inter neurons.
The two cerebral hemisphere communicate with each other by means of large band of axons called Corpus Callosum.
Part of Cerebrum
Functionally, the cerebrum is differentiated into four lobes.
- Anterior Frontal Lobe
- Lower Central Temporal Lobe Parietal Lobe
- Dorsal Occipital Lobe
- Cerebrum is concerned with intelligence memory, learning, resoning and overall control of all voluntary actions.
- It involved in all conscious activities.
- It co-ordinated different senses together.
The diencephalons consists of two parts
i. Thalamus
ii. Limbic System
i. Thalamus
The clearing house for sensory impulses is called Thalamus.
Functions
- It receives them from different parts of brain and relays them to the appropriate part of the motor cortex.
- It also involves in the perception of pleasure and pain.
The limbic system is located in an are between the thalamus and cerebrum.
Parts of Limbic System
The limbic system consists of
i. Hypothalamus
ii. Amygdala
iii. Hippocampus
i. Hypothalamus
Hypothalamus is the part of limbic system which is called Thermostal of the body.
Functions
- The hypothalamus is important in regulation of homeostasis.
- It regulates pituitary gland.
- It also regulate body temperature, blood pressure, hunger, thirst, aggression, pleasure and pain.
The amygdala produces sensation of pleasure, punishment or sexual arousal stimulation.
It also involve in the feelings of fear.
iii. Hippoc Ampus
Hippocampus is involved in long term memory.
Mid Brain
In mammals mid brain is relatively very small. It consists of the optic lobes which are represented by four small bodies.
Functions
It receives sensory information like vision, odour etc. It receives sensory information from spinal cord and sends them to the fore brain.
Hind Brain
Hind brain consists of
1. Medulla Oblongata
2. Cerebellum
3. Pons
4. Reticular Formation
1. Medulla Oblongata
Medulla oblongata lies on the top of spinal cord.
Function
It controls involuntary actions like blood pressure, heart beat, sneezing, coughing, breathing rate, hicupping, swallowing etc.
2. Cerebellum
The cerebellum lies dorsally behind the optic lobes. It is highly convoluted. It is large in mammals than other animal.
Functions
- The cerebellum plays an important part in controlling muscular co-ordination.
- It specially maintains balance and also position of the body in space.
Pons regulates activities like muscular co-ordination, facial expressions, breathing and sleeping.
4. Reticular Formation
Reticular formation lies in pons, medulla and mid brain.
Functions
It monitors the messages to the brain which should be ignored or should be realized.
Brain Stem
The oldest tissues formed by the combination of medulla oblongata, pons and mid brain is called as Brain Stem.
Functions
It involved in the control of sleep and wakening.
Spiral Cord
Definition
A thick whitish nerve cord that lies below the medulla oblongata and extends down through the neural canal of vertebrate upto the hips is called Spinal Cord.
Cross Section of Spinal Cord
In cross section, the spinal cord is differentiated into two areas.
White Matter
Gray Matter
Unlike brain, spinal cord has grey matter inside surrounded by white matter on the outside. They grey matter has the shape of an “H”. The first synapse of each sensory neuron is located in the grey matter.
Central Canal
The narrow central containing cerebrospinal fluid runs through the middle of the spinal cord. This fluid brings nutrients to the spinal cord.
Spinal Nerves
The nerve arises from spinal cord is called Spinal Nerves.
Each spinal nerve divides into two roots just before it joins spinal cord.
1. Dorsal Root
2. Ventral Root
1. Dorsal Root
The dorsal root joints the dorsal part of the spinal cord and it contains axons of sensory neurons.
Dorsal Root Ganglion
The cell bodies of these neurons aggregate in a small swelling known as the dorsal root ganglion.
2. Ventral Root
The ventral root which is attached to the ventral part of the spinal cord carrying axons of motors neurons, arised from the spinal cord.
Functions of Spinal Cord
Spinal cord serves as an express way for signals between autonomic nervous system.
It is also the control centre for many reflexes.
Receptors
Definition
The single or group of either modified neurons or epithelial cells which receive stimuli either from external environments and relaying them in the form of impulses to the CNS are called Receptors.
Receptionists
The receptors are acts as receptionist of nervous system because they receive any kind of change, which is then transferred to the brain and spinal cord.
Sensation
Receptor converts stimuli into nerve impulses, this stage awareness of stimulus is called Sensation.
Perception
In the control centre of the nervous system, the impulses are converted into perception.
Types of Receptors
Receptors are classified according to type of stimulus which they can detect and give response. Following are some types of receptor.
1. Thermoreceptor
The receptors which detect and respond to temperature fluctuations (heat and cold) are called Thermoreceptor.
2. Chemoreceptor
The receptors which can detect and respond to presence of certain chemicals in their surrounding are called Chemoreceptor.
3. Mechanoreceptor
The receptors which can detect the stimuli of sound, motion, touch, pressure gravity and movement are called Mechanoreceptor.
4. Photoreceptor
The receptors which respond to the stimulus of light and ultraviolet rays are called Photoreceptor.
5. Pain Receptor
The receptors which produced sensation of pain or damage tissues are called the Pain Receptor.
Working of Sensory Receptors in Skin
In human, the receptors in skin are concerned with at least five different senses i.e., touch, pressure, cold, warm and pain.
Types of Sensory Receptor in Skin
There are two types of sensory receptors in the skin.
i. Free Nerve Ending Receptors
ii. Encapsulated Receptors
i. Free Nerve Ending Receptors
The simplest types of receptor which contain free end without any protective capsule and are located just beneath the epidermis are called Free Nerve Ending Receptors.
Functions
Free nerve ending receptors adapt very slowly to stimulation.
Types
They are of different types
a. Mechanoreceptors Receive touch and pressure.
b. Nociceptors Feel pain
c. Thermoreceptors Feel change in temperature
ii. Encapsulated Receptors
The type of receptor contain a protective capsule of connective tissues at their ends and lie in skin are called Encapsulated Receptors.
Types
Encapsulated receptor are of following two types
i. Meissner’s Corpuscles
ii. Pacinian Corpuscles
i. Meissner’s Corpuscles
The encapsulated receptors that are found in those parts which do not have hairs such as finger tips, eyelids, lips palms, soles, nipples etc are called Meissner’s Corpuscles.
Structure of Capsule
Their capsules consists of thick collagen fibers with spiral and highly coiled nerve endings.
Function
There are touch receptors means very sensitive to touch.
ii. Pacinian Corpuscles
The encapsulated receptors which are found in dermis layer and also in some internal organs and moveable joints are called Pacinian Corpuscles.
Structure
Their nerve endings are surrounded by an onion like capsule made of concentric layers of membrane. Between the membranes fluid filled spaces are present.
Functions
They are pressure receptor and detect rapid and deep pressure changes produced by vibration and touch.
Sensory Receptors with Reference to Arteries
The aortic arch and the carotid artery contain many receptor which are
Mechanoreceptor
They detect the pressure changes in arteries.
Baroreceptor
They detect the pulse pressure
Function
These receptors transfer these changes to the medulla oblongata which controls blood pressure.
Aortic Body and Carotid Body
The aortic arch and the carotid sinus also contain chemoreceptor called Aortic body and carotid body.
Function
They are sensitive to CO2 concentration and hydrogen ion concentration of the blood.
Effects of Drugs on Co-Ordination
Drugs
A chemical substance that causes the specific physiological response in the body are called drugs.
Importance
- Many drugs are useful medically to treat emotional stress or certain illness.
- Drugs which people take to alter the mood or emotional state affect body functional interfering with the working of neurotransmitters.
- Therefore their abuse often causes harmful effects.
- It is a drug found in tobacco.
- It acts as a stimulant and is widely used as a neurological agent.
- Nicotine affects post synaptic membrane in CNS and PNS.
- It minimize the action of acetylcholine on nicotine receptors. So it is stimulant to nerve impulse.
- It increase the heart beat, rate, blood pressure and digestive tract mobility.
- Nicotine may induce vomiting and diarrhea.
- It may cause water retention relation by kidneys.
- It stimulate the nervous system thereby reducing fatigue, increasing, alertness and improving the concentration.
The abnormalities appear in brain, spinal cord, central nervous system and peripheral nervous system causes diseases called Nervous Disorders.
Some common disorders of nervous system are as follows
1. Parkinson’s Disease
2. Alzheimer’s Disease
3. Epilepsy
1. Parkinson’s Disease
It is a brain disorder.
Causes
It either caused by degeneration or damage of nerve tissues within the basal ganglia of the brain.
Symptoms
It is characterized by involuntary tremors, diminishing motor power and rigidity. It causes stiffness, weakness and trembling of the muscles. The mental faculties are not affected.
Treatment
Leopoda is the effective medicine which is helpful in minimizing the symptoms by can not halt the degeneration of neurons of brain.
2. Alzheimer’s Disease
It is the progressive degeneration of neurons of brain, especially cortex and hippocampus.
Causes
There is a genetic pre-disposition to the disease in some people, so it tends to run in families.
Stages of Diseases
The disease progresses in three broad stages.
First Stage
At first, the patient notices his forgetfulness.
Second Stage
In second phase, there is a severe loss of memory particularly for recent events. Anxiety increases with sudden changes in mood.
Third Stage
In the third and last stage the disease become severe. He losses memory, hears voices or see faces in the absence of any person. This disease is called Hallucination. He does not share his ideas and does not accept ideas of other persons, such disease is called paranoid delusions.
Symptoms
The main symptom of the disease is the loss of memory called dementia.
Treatment
- Effective medicines should be used.
- Psychological treatment is better to control the disease.
- Personal care of patient is necessary otherwise he may get any harm.
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