Brain notes for class for students

BRAIN-NOTES

                                          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 Hemispheres.

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.

Corpus Callosum 

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

Function of Cerebrum 

• 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.

2. Diencephalon 

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.

ii. Limbic System 

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.

ii. Amygdala 

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.

3. Pons 
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.