INTRODUCTION TO THE BRAIN

Introduction to the BRAIN (Nervous System)

Human brain is responsible for:

·         Judgement

·         Intelligence

·         Memory

Activities of nervous system:

·         Physical

·         Psychological

·         Intellectual

Functions:

·         Controlling and coordinating system of the body.

·         Adjust the body to the surroundings.

·         Regulate all the bodily act may be voluntary or involuntary.

Parts of nervous system:

·         Sensory: Collects the information from the surroundings and gains knowledge.

·         Motor: Responsible for the response of the body to various sensations.

Nervous system is made of:

·         Nerve Cells or neurons

·         Neuroglial cells (neuroglia) forming the supporting (connective) tissues of Central Nervous System.

·         In Peripheral Nervous system: Schwann Cells and loose connective tissues….

*Both types of cells are supplied by abundant blood vessels.

NEURONS

Made up of:

·         Cell body: Forms the grey matter and nuclei in CNS and ganglia in PNS.

·         Numerous cell processes:

o   Axon: Single elongated process. It forms the tracts. White matter in CNS and nerves in PNS.

o   Dendrites: They are many, short, richly branched and varicose (swollen and stretched out).

Functions of Neurons:

·         Sensitivity

·         Conductivity

*Impulses can flow in them with great rapidity; 125 per second.

*Neurons shows dynamic polarity in its polarity.

Ø  Impulse flows towards the cell body in dendrites and away from cell body in axon.

Ø  Site of contact between the nerve cells is known as SYNAPSE. 1 Dendrites can make the synapse with 1000 axon terminals.

Ø  Impulse is transmitted across a synapse through bio-chemical neurotransmitter namly ACETYLCHOLINE

TYPES OF NEURONS

1.      ACCORDING TO NUMBER OF PROCESSESS

o   Multipolar (single axon and many dendrites): Most of neurons in men are multipolar neuron. E.g. all motor and internuncail (connecting medium between 2 neurons) neurons.

o   Bipolar (Two poled nerve cells): Confined to first neuron of retina, ganglia of  eighth cranial nerve olfactory mucosa.

o   Pseudounipolar neuron: They are actually unipolar to begin with but become bipolar functionally. E.g. dorsal nerve root ganglia and sensory ganglia of cranial nerve.

o   Unipolar neurons:  type of neuron in which one protoplasmic process extents from the cell body E.g. mesencephalic nucleus of trigeminal nerve. More common in lower vertebrates.

2.      ACCORDING TO LENGTH OF AXON

o   Golgi type I with long axon

o   Golgi type II with short axon

* Mature nerve cells are incapable of dividing and therefore cannot form tumors.

* Brain tumors arise from neuroglial cells and immature nerve cells.

NEUROGLIAL CELLS

Types of neuroglial cells:

1.      Astrocytes: Are concerned with nutrition of nervous tissue 

2.      Oligodandrocytes: Are counter part of Schwann cells. Myelinate peripheral nerves. Oligodandrocytes myelinates the tracts.

3.      Microglia: Behaves like macrophages (type of WBC that engulfs and digests cellular debris) of CNS.

4.      Ependymal cells: Are columnar cells lining the cavities of CNS

*Gliosis: Non specific reactive change of glial cells in response to damage to CNS. It involves the proliferation or hypertrophy of different types of glial cells.

REFLEX ARC

A Reflex Arc is a neural pathway that controls a reflex. It’s a functional unit of nervous system. Consists of:

·         A receptor e.g. Skin

·         Sensory neuron

·         Effectors e.g. muscles

*Involuntary motor response to sensory stimulus is known as Reflex Action.

*Cortical Responses are voluntary and Non Cortical Responses are involuntary.

PARTS OF NERVOUS SYSTEM

1). Central Nervous System (CNS)

·         Brain: Occupies cranial cavity.

·         Spinal Cord: Occupies upper two thirds of the vertebral canal.

2). Peripheral Nervous System (PNS)

·         Somatic (Cerebrospinal) Nervous System: Made up of 12 pairs of cranial nerves and 31 pairs of spinal nerves. Its efferent fibres reach the effectors without interruption.

·         Autonomic (Splanchnic) Nervous System: Consists of sympathetic and parasympathetic systems. Its efferent fibres first relay in the ganglion and then the postganglionic fibres pass to the effectors.

PARTS OF THE BRAIN (Forebrain, midbrain and hindbrain)

PARTS	SUBDIVISIONS	CAVITY
1). Forebrain (Prosencephalon)	A). Telencephalon (Cerebrum), made up of 2 cerebral hemispheres and the median part in front of the interventricular foramen. B). Diencephalon (Thalamencephalon), consists of : ·         Thalamus ·         Hypothalamus ·         Metathalamus including medial and lateral geniculate bodies ·         Epithalamus, including the pineal body, habenular trigone and posterior commissure ·         Subthalamus	Lateral cavity Third ventricle
2). Midbrain (Mesencephalon)	Crus cerebri, Substantia Nigra, Tegmentum and Tectum, from before backwards.	Cerebral Aqueduct
3). Hindbrain (Rhombencephalon)	A). Metencephalon, made up of pons and cerebellum B). Myelencephalon, or Medulla Oblongata	Forth ventricle

* Brainstem includes:        

o   Midbrain

o   Pons

o   Cerebellum

*Hindbrain includes:

o    Pons

o    Medulla Oblongata

o    Cerebellum

*The dilated part of the central canal of Spinal Cord within the Conus Medullaris is known as the Terminal Ventricle.

*The cavity of Septum Pellucidum is called as Fifth Ventricle.