1. Central Nervous System (CNS) – It includes the Brain and spinal cord.
2. Peripheral nervous System (PNS) – Spinal and Cranial nerves
3. Autonomic Nervous System (ANS) – It includes Parasympathetic and Sympathetic nervous systems.
· Nervous system is derived from ectoderm: except 2M: Microglia and meninges which are derived from mesoderm.
A. CNS (Central Nervous System)
1. BRAIN· Brain is ectodermal in origin.
· The brain is protected in the cranium or brain box and covered by Meninges.
· Meninges are the coverings of the brain which consists of 3 layers.
i) Dura mater: It is the toughest thick outermost layer that is attached to the cranium.
ii) Arachnoid mater: It is the middle, delicate, thin and vascular layer.
iii) Pia mater: It is the innermost or immediate covering of the brain & spinal cord.
· Meninges are the coverings of the brain which consists of 3 layers.
i) Dura mater: It is the toughest thick outermost layer that is attached to the cranium.
ii) Arachnoid mater: It is the middle, delicate, thin and vascular layer.
iii) Pia mater: It is the innermost or immediate covering of the brain & spinal cord.
· It is a thin, soft and vascular layer.
· Brain consists of:
- Forebrain or Prosencephalon
- Midbrain or Mesencephalon
- Hindbrain or Rhomboncephalon
A) Forebrain or Prosencephalon:
· It consists of the olfactory lobes anteriorly, the middle diencephalon and the cerebral hemisphere posteriorly.
a. Olfactory lobe or Rhinencephalon:
· It is the anteriormost part of the brain which has 2 cubed shaped olfactory bulbs and olfactory tracts.
· They are attached to the hippocampal lobe of the cerebrum by olfactory tracts.
· Its internal cavity is called 1st ventricle or rhinocoel which opens posteriorly into the cerebral hemispheres of their sides.
· Function- it controls the sense of smell.
· It is the anteriormost part of the brain which has 2 cubed shaped olfactory bulbs and olfactory tracts.
· They are attached to the hippocampal lobe of the cerebrum by olfactory tracts.
· Its internal cavity is called 1st ventricle or rhinocoel which opens posteriorly into the cerebral hemispheres of their sides.
· Function- it controls the sense of smell.
b. Cerebrum:
· It is the largest part of the brain which consists of two cerebral hemispheres.
· It is the largest part of the brain which consists of two cerebral hemispheres.
· These are separated by a groove called Median fissure.
· Sylvian fissure is the lateral somewhat oblique fissure that divides the cerebral hemisphere into a larger anteriomedian frontal lobe and small posterolateral temporal lobe.
· Sylvian fissure is the lateral somewhat oblique fissure that divides the cerebral hemisphere into a larger anteriomedian frontal lobe and small posterolateral temporal lobe.
· A ventral rhinal fissure demarcates the olfactory lobes and hippocampal sulcus or fissure demarcates the hippocampal lobe.
· Corpus callosum is the internal broad transverse nerve band of nervous tissue which connects the two cerebral hemispheres internally to convey the impulse in to and for ways.
· Inner cavity of each hemisphere is called 2nd or lateral ventricle or paracoel.
· These two paracoels are internally connected to each other and dioecoel through foramen of Monro.
· The roof of this cavity is formed by the corpus callosum whereas the lateral walls and floor are formed by the corpus striatum.
· Two corpora striata are connected by transverse anterior commissure.
· These two paracoels are internally connected to each other and dioecoel through foramen of Monro.
· The roof of this cavity is formed by the corpus callosum whereas the lateral walls and floor are formed by the corpus striatum.
· Two corpora striata are connected by transverse anterior commissure.
c. Diencephalon
· It is small and depressed which is covered by a backward extension of cerebral hemispheres.
· Its narrow cavity is called the 3rd ventricle or dioecoel.
· Roof of the dioecoel is called the epithalamus, lateral walls are called optic thalami and the floor is the hypothalamus.
· Two optic thalami are connected by middle commissure which contains only nerve cells but no nerve fibres.
· Middle part is the Thalamus which is the relay station for all sorts of general and special sensations.
· It is often considered as the the Thermoregulatory centre of the body.
· Roof of the diencephalon bears pineal body as endocrine function and the rest of the part is vascular called the anterior choroid plexus which secretes cerebrospinal fluid.
· Lower end of the hypothalamus has an oval Rathke, pouch or hypophysis behind which attached a small rounded body called Corpus Albicans.
· In front of the infundibulum, optic chiasma is present.
· It is small and depressed which is covered by a backward extension of cerebral hemispheres.
· Its narrow cavity is called the 3rd ventricle or dioecoel.
· Roof of the dioecoel is called the epithalamus, lateral walls are called optic thalami and the floor is the hypothalamus.
· Two optic thalami are connected by middle commissure which contains only nerve cells but no nerve fibres.
· Middle part is the Thalamus which is the relay station for all sorts of general and special sensations.
· It is often considered as the the Thermoregulatory centre of the body.
· Roof of the diencephalon bears pineal body as endocrine function and the rest of the part is vascular called the anterior choroid plexus which secretes cerebrospinal fluid.
· Lower end of the hypothalamus has an oval Rathke, pouch or hypophysis behind which attached a small rounded body called Corpus Albicans.
· In front of the infundibulum, optic chiasma is present.
B) Midbrain or Mesencephalon
· It acts as connecting stalk between Forebrain and Hindbrain.
· It differentiates into corpora quadrigemina (four dorsal rounded lobes) and crura cerebri.
· Anterior two optic lobes are called superior colliculi which are concerned with vision and posterior two larger lobes are called inferior colliculi are related to acute hearing.
· Crura cerebri is the thick tract of fibres that connects the forebrain with the hindbrain.
· The internal cavity of the midbrain is called Sylvius aqueduct or Iter.
· Each cerebral hemisphere is subdivided superficially into a number of lobes by fissures.
· The surface of the cerebrum is throne into elevations called Gyri and depression called Sulci.
· Crura cerebri is the thick tract of fibres that connects the forebrain with the hindbrain.
· The internal cavity of the midbrain is called Sylvius aqueduct or Iter.
· Each cerebral hemisphere is subdivided superficially into a number of lobes by fissures.
· The surface of the cerebrum is throne into elevations called Gyri and depression called Sulci.
C) Hindbrain or Rhombencephalon
· It consists of Pons, Cerebellum and Medulla oblongata.
· Midbrain, pons and medulla comprise the brain stem.
a. Cerebellum
· It is the second-largest part of the brain which is differentiated into a middle lobe vermis and two lateral lobes called cerebellar hemispheres.
· Each hemisphere has a ventrolateral extension called flocculus.
· Cerebellum helps to maintain equilibrium, control tone, posture and co-ordinates voluntary muscle movement.
· It is the second-largest part of the brain which is differentiated into a middle lobe vermis and two lateral lobes called cerebellar hemispheres.
· Each hemisphere has a ventrolateral extension called flocculus.
· Cerebellum helps to maintain equilibrium, control tone, posture and co-ordinates voluntary muscle movement.
b. Pons Varolii
· It is a pair of stout transverse bands of fibres that are connected with the cerebellar hemispheres.
· It is a pair of stout transverse bands of fibres that are connected with the cerebellar hemispheres.
c. Medulla oblongata
· It is the last part of the brain which is broad anteriorly and tapers posteriorly to connect with the spinal cord.
· It is the last part of the brain which is broad anteriorly and tapers posteriorly to connect with the spinal cord.
· Its internal cavity is called the 4th ventricle or metacoel of the brain that communicates with the spinal canal.
· Roof of the metacoel is non- nervous but vascular called posterior choroid plexus which secretes cerebrospinal fluid.
· It is the vital centre for controlling circulation, digestion, respiration and excretion
· Medulla regulates vomiting, coughing & sneezing.
· Roof of the metacoel is non- nervous but vascular called posterior choroid plexus which secretes cerebrospinal fluid.
· It is the vital centre for controlling circulation, digestion, respiration and excretion
· Medulla regulates vomiting, coughing & sneezing.
Ventricles of Brain:
· Ventricles are the cavities within the brain lined by ependymal cells.
· Olfactory lobes are solid, so no olfactory ventricles.
· Cavities of two cerebral hemispheres are known as lateral (first and second) ventricles.
· Two lateral ventricles communicate posteriorly to the 3rd ventricle by the Foramen of Monro.
· 3rd ventricle is present in Diencephalon.
· 3rd ventricle communicates with 4th ventricle through the narrow Iter or aqueduct of Sylvius.
· 4th ventricle is present in the Medulla oblongata.
· Ventricles are the cavities within the brain lined by ependymal cells.
· Olfactory lobes are solid, so no olfactory ventricles.
· Cavities of two cerebral hemispheres are known as lateral (first and second) ventricles.
· Two lateral ventricles communicate posteriorly to the 3rd ventricle by the Foramen of Monro.
· 3rd ventricle is present in Diencephalon.
· 3rd ventricle communicates with 4th ventricle through the narrow Iter or aqueduct of Sylvius.
· 4th ventricle is present in the Medulla oblongata.
Histology of Brain:
· Briain is formed by two types of nervous tissues– white matter and grey matter.
· Outer layer of the brain is called the cortex which is formed by grey matter.
· It consists of nerve cells, neuroglia and blood vessels.
· Inner part of the brain is called the medulla which is formed by white matter.
· White matter has only nerve fibres and neuroglia.
· Neuron is the structural and functional unit of the nervous system.
· Basic properties of neurons are excitability or irritability and conductivity.
· Inner part of the brain is called the medulla which is formed by white matter.
· White matter has only nerve fibres and neuroglia.
· Neuron is the structural and functional unit of the nervous system.
· Basic properties of neurons are excitability or irritability and conductivity.
SPINAL CORD OR MYELON
· Extends from the medulla of the brain almost to the end of the vertebral column or up to the 4th lumbar vertebra.
· It passes through the vertebral or neural canal.
· At the hinder end, the spinal cord narrows forming Conus terminals from which filum terminale arises.
· Spinal cord has some white flattened surfaces due to the presence of two mid-longitudinal grooves– deeper mid ventral fissure and broader mid- dorsal fissure.
· Central canal runs along the length of the spinal cord at its centre.
· It shows 2 slight enlargements– brachial swelling at the level of forelimbs and sciatic swelling at the level of hindlimbs.
· Histologically, its inner surface has grey matter (made up from nerve cells) and outer white matter (made up from nerve fibres)
· Grey matter has 2 dorsal horns and 2 ventral horns.
· Dorsal horn acts as a sensory branch and the ventral horn acts as a motor branch.
· At the hinder end, the spinal cord narrows forming Conus terminals from which filum terminale arises.
· Spinal cord has some white flattened surfaces due to the presence of two mid-longitudinal grooves– deeper mid ventral fissure and broader mid- dorsal fissure.
· Central canal runs along the length of the spinal cord at its centre.
· It shows 2 slight enlargements– brachial swelling at the level of forelimbs and sciatic swelling at the level of hindlimbs.
· Histologically, its inner surface has grey matter (made up from nerve cells) and outer white matter (made up from nerve fibres)
· Grey matter has 2 dorsal horns and 2 ventral horns.
· Dorsal horn acts as a sensory branch and the ventral horn acts as a motor branch.
Function:
· It is the centre of reflex action.
· It is the centre of reflex action.
· It also conducts impulses to and fro the brain.
Peripheral Nervous System (PNS)
· This system consists of 12 pairs of cranial and 37 pairs of spinal nerves.1. Cranial Nerves are:
i) Olfactory nerve – Purely Sensory
ii) Optic – Sensory
iii) Occulomotor – Motor
iv) Trochlear – Somatic Motor
v) Trigeminal – Both or mixed = Sensory + Motor
vi) Abducens – Motor
vii) Facial nerve – Both or mixed
viii) Auditory nerve – Sensory
ix) Glossopharyngeal nerve – Both
x) Vagus – Both or mixed
xi) Spinal accessory – Motor
xii) Hypoglossal – Motor
· Note: @ Some say marry money but my brother says bad boy marry money.
i) Olfactory nerve – Purely Sensory
ii) Optic – Sensory
iii) Occulomotor – Motor
iv) Trochlear – Somatic Motor
v) Trigeminal – Both or mixed = Sensory + Motor
vi) Abducens – Motor
vii) Facial nerve – Both or mixed
viii) Auditory nerve – Sensory
ix) Glossopharyngeal nerve – Both
x) Vagus – Both or mixed
xi) Spinal accessory – Motor
xii) Hypoglossal – Motor
· Note: @ Some say marry money but my brother says bad boy marry money.
B. Spinal nerves are:
· In rabbits, 37 pairs of spinal nerves. (8 cervical, 12 thoracics, 7 lumbar, 4 sacral and 6 caudal nerves)
· All are mixed nerves.
· All are aroused from dorsal and ventral horns of spinal cord
· Dorsal horn has only sensory nerves which bear dorsal root ganglia. These ganglia are located within the neural canal except that of the second cervical.
· Ventral root develops from ventral horn and has no ganglion but only motor nerves are present.
· Both roots unite as a single nerve in the neural canal to form the spinal nerve.
· Spinal nerves exit from the intervertebral foramen of the vertebral column and divide into three branches or Rami.
· Dorsal ramus- it supplies to the skin, muscles of the back.
· Ventral ramus- it supplies to latero-ventral parts of the body.
· Visceral ramus or Ramus communicans- it joins the sympathetic system to supply visceral organs.
Autonomic Nervous System (ANS)
· It is also known as Self-governing Nervous System which can be divided physiologically into two systems: 1. Sympathetic nervous system
2. Parasympathetic nervous system
2. Parasympathetic nervous system
1. Sympathetic system:
· It includes a pair of long sympathetic cords, trunks or nerves.
· This cord bears in all 24 ganglia in which 3 cervical, 10 thoracic, 6 lumbar, 4 sacral and 1 caudal ganglion.
· These ganglia are connected with corresponding spinal nerves through ramus communicans.
· It enters in visceral organs, heart and glands.
· Its overall effect is excitatory.
· It includes a pair of long sympathetic cords, trunks or nerves.
· This cord bears in all 24 ganglia in which 3 cervical, 10 thoracic, 6 lumbar, 4 sacral and 1 caudal ganglion.
· These ganglia are connected with corresponding spinal nerves through ramus communicans.
· It enters in visceral organs, heart and glands.
· Its overall effect is excitatory.
· It increases heartbeat, dilates the iris or bronchi.
· So the Sympathetic nervous system plays important role in danger or during an emergency or stressful condition.
2. Parasympathetic nervous system or Cranio-sacral portion or system
· It is formed by the nerve fibres of III, IV, IX, X cranial nerves as well as II, III, and IV sacral nerves.
· They supply the nerve fibres in all organs where the sympathetic nervous system supplies.
· The parasympathetic system opposes the action of the sympathetic nervous system.
· So, Its overall effect is inhibitory for example stimulation of the parasympathetic system slows down heartbeat, B.P., constrict pupil or bronchi and speed up peristalsis etc
· Sympathetic and parasympathetic systems have antagonistic (opposite) effects.
· So, Its overall effect is inhibitory for example stimulation of the parasympathetic system slows down heartbeat, B.P., constrict pupil or bronchi and speed up peristalsis etc
· Sympathetic and parasympathetic systems have antagonistic (opposite) effects.
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