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The whole nervous system can be divided into two main systems- central nervous system and peripheral nervous system.
Nervous system is absolutely necessary for the reception, storage and release of different information for regulating or initiating particular behavior of individual ranging from cellular to the gross animal being.
The chief functions of CNS are to enable the individual to response in a coordinated manner to changes of environment.
This system operates through two main systems- central nervous system and autonomic nervous system (reflex control) which again consists of the sympathetic and parasympathetic systems.
The central nervous system consists of brain and spinal cord whereas the peripheral nervous system consists of cranio spinal nerves having 12 pairs of cranial nerves and 31 pairs of spinal nerves; and visceral nervous system comprising sympathetic and parasympathetic system
The central nervous system is symmetrically arranged into two lateral halves. It consists of brain -inside the cranial cavity, and spinal cord inside the vertebral column.
Development
The forebrain anterior part differentiates to corpus striatum, amygdala, hippocampus, neocortex and its cavity- 1st and 2nd ventricle.
The forebrain posterior part differentiates to sub thalamus, hypothalamus, thalamus, pituitary glands, geniculate body, epithalamus (pineal body, habenular nucleus) and its cavity-3rd ventricle.
The midbrain differentiate to tectum (dorsal part -colliculus), cerebral peduncle (tegmentum, substantia nigria, pedunculi base) and it cavity – cerebral aqueduct.
BRAIN ANATOMY
Frontal lobe
This is the most recent evolutionary addition to the brain.
The functions of the frontal lobe include reasoning, attention, creative thoughts, reflection, inhibition, problem solving, judgment, impulse control, behavior, higher emotions such as empathy and altruism, motor control,memory, coordination of movements, sense of smell, and libido.
Broca’s area is concerned with speech production and understanding language.
Parietal lobe
Temporal lobe
Occipital lobe
LIMBIC SYSTEM
Hippocampus is concerned with formation, classification and storage of memories.
Amygdale is related with fear and emotionally charged memories.
Cingulate gyrus: It is concerned with sensory input with emotions.
Olfactory cortex is involved with identification odors.
Hypothalamus
It controls daily rhythmical daily activities, bodily urges, appetite, thirst, autonomic functions, hormonal system, temperature regulation, sexual maturation, homeostasis, mood and motivation.
Thalamus
It is relay station of all sensory signals. It is concerned with identification of odor and motor functions.
BRAIN STEM
HIND BRAIN
Pons
Medulla oblongata
Cerebellum
The spinal cord carries signals to the brain and instruction back down
Physiology
Nervous tissue consists of two elements Neuron and Neuroglia.
Neuron consists of cell body and two types process-axon (which carries impulses away from it) and dendron (which carries towards the cell body).
Neuroglia is a special type of interstitial tissue and is present both in the grey matter and white matter.
Types of neuroglia
Astrocytes (star like supporting cells -ectodermal origin)
Oligodendrocytes
Microglia
Brain substance consists of grey matter and white matter.
Generally nerve fibers consists of three components namely axons, myelin sheath and nucleated sheath of Schwann. This outer sheath is absent in central nerve system.
Nervous system has three functions
Sensory nerves gather information from the environment, and send to spinal cord and brain. The brain makes sense of that message and fire off a response.
Motor neurons deliver the instruction from the brain to the rest of the body. Each motor fiber has about 150 branches and each of which end in separate muscle fiber.
Spinal and cerebellar connections are under homo lateral control.
Pyramidal tracts
Functions
Paralysis of upper motor neuron shows loss of volitional movement, spasticity, increased deep reflexes, loss of superficial reflexes and positive Babinski sign (plantar extension of great toe).
Paralysis of lower motor neuron shows loss of deep reflexes and voluntary movement, and loss of muscle tone.
Extra pyramidal system
Extra pyramidal tracts act as alternative pathway for volitional impulses and also a platform on which pyramidal system works skillfully. Cerebral cortex exerts inhibitory control over the lower centers through these tracts. Dyskinesia or involuntary movement is common symptom in extrapyramidal diseases. These include Parkinsonism, chorea, athetosis, dystonia, and hemiballismus.
BASAL GANGLIA
Movements are mainly pyramidal in origin in mammals, and extrapyramidal nuclei modulate it through reflex mechanism.
Basal ganglia maintain motor activities, automatic movements, locomotion, feeding and postural adjustments.
Positive movements (tremor and chorea) are due to excess of neural activity (releasing phenomenon).
Various Neurotransmitters present in nervous system are acetylcholine (present in caudate nucleus, thalamus, cerebral cortex and retina), nor adrenaline (hypothalamus), dopamine (striatum, substantia nigra, hypothalamus, retina), histamine (hypothalamus), serotonin (basal ganglia, hypothalamus. spinal cord), amino acids like glutamic acid (central neurons) and gamma amino butyric acid (spinal cord and cerebral cortex- inhibition), glycine (spinal cord- inhibition), peptides (hypothalamus, substantia nigria and retina), and prostoglandins (cerebellum, spinal cord and cerebral cortex).
Dopamine is stored in axons of neurons which cell body may be located in distant area. Dopamine content in substantia nigria and globus pallidus is become low parkinsonism. Increased level of Ach can cause degradation of dopamine which promotes abnormal involuntary movements, alterations in muscle tone and disturbance in bodily posture.
Hyper activity of dopaminergic fiber in caudate nucleus and putamen can cause reflexly low secretion of serotonin which can promote depression in beginning.
Further depletion of dopamine results in bradykinesia, and reflexively increases serotonin (5 HT) and acetylcholine (Ach) which cause delusion and tremor respectively.
Chemical changes predominate than morphological changes. Normally acetylcholine and related enzymes; dopamine and norepinephrine are high in these nucleus.
There is a balance between acetylcholine, dopamine and nor adrenaline in brain.
When cholinergic predominate than dopamine tremor can result.
Hypo activity of dopaminergic fibres in substantia nigria can cause bradykinesia.
Neuron-degeneration
Vascular defect
Degeneration, subsequent necrosis and softening in basal ganglia result in cystic formation. These spaces are filled with astrocytes which may either undergo proliferation (glial proliferation) or hypersensitivity tendency (interstitial inflammation can cause irritable nerve discharge).
Involvements of interstitial tissues lesions are common more than neuron lesions. So individual symptoms developed are less in diseases with glial proliferation. The symptoms developed here are mainly due to local pressure.
Toxins
Nutritional factors include errors of carbohydrate, protein and fat metabolism, hypoglycemia, liver cirrhosis, deficiencies of choline, casein, methionine, inositol, enzymes, vitamin B1and B12.
Infections
Nervous system is absolutely necessary for the reception, storage and release of different information for regulating or initiating particular behavior of individual ranging from cellular to the gross animal being.
The chief functions of CNS are to enable the individual to response in a coordinated manner to changes of environment.
This system operates through two main systems- central nervous system and autonomic nervous system (reflex control) which again consists of the sympathetic and parasympathetic systems.
The central nervous system consists of brain and spinal cord whereas the peripheral nervous system consists of cranio spinal nerves having 12 pairs of cranial nerves and 31 pairs of spinal nerves; and visceral nervous system comprising sympathetic and parasympathetic system
The central nervous system is symmetrically arranged into two lateral halves. It consists of brain -inside the cranial cavity, and spinal cord inside the vertebral column.
The brain and spinal cord remain covered by three membranes which from outside inwards are known as dura mater, arachnoid mater and pia mater.
Main blood vessels lie in between pia and arachnoid mater.
arachnoid membrane is continuous with those of spinal cord.
Blood vessels of pia matter ensure a rich blood supply to grey matter.
There is subarachnoid space under the arachnoid containing cerebrospinal fluid. There is about 150 ml of CSF in ventricular system. Choroid plexuses produce cerebrospinal fluid.
Main blood vessels lie in between pia and arachnoid mater.
arachnoid membrane is continuous with those of spinal cord.
Blood vessels of pia matter ensure a rich blood supply to grey matter.
There is subarachnoid space under the arachnoid containing cerebrospinal fluid. There is about 150 ml of CSF in ventricular system. Choroid plexuses produce cerebrospinal fluid.
Development
Nervous system is ectodermal in origin.
The brain develops from 3 swelling at the anterior end of neural tube. From front to back these develop into forebrain, midbrain and hindbrain by 6 weeks in the embryo. As the embryo grows they differentiate further.
The forebrain anterior part differentiates to corpus striatum, amygdala, hippocampus, neocortex and its cavity- 1st and 2nd ventricle.
The forebrain posterior part differentiates to sub thalamus, hypothalamus, thalamus, pituitary glands, geniculate body, epithalamus (pineal body, habenular nucleus) and its cavity-3rd ventricle.
The midbrain differentiate to tectum (dorsal part -colliculus), cerebral peduncle (tegmentum, substantia nigria, pedunculi base) and it cavity – cerebral aqueduct.
Hindbrain differentiate to cerebellum, pons, medulla oblongata and it cavity-4th ventricle.
BRAIN ANATOMY
CEREBRUM
It is largest part of the brain. A deep furrow divides the cerebrum into two halves known as right and left hemispheres.
The corpus callosum is a bundle of axons which connects these two halves.
The right side of the brain controls the left side of body and vice verse. The right hemisphere is related with analysis of nonverbal information, emotion, communication, the art, spatial and music.
The left hemisphere is concerned with linear, rational, and verbal aspects.
The corpus callosum is a bundle of axons which connects these two halves.
The right side of the brain controls the left side of body and vice verse. The right hemisphere is related with analysis of nonverbal information, emotion, communication, the art, spatial and music.
The left hemisphere is concerned with linear, rational, and verbal aspects.
It is divided into four lobes; the frontal, occipital, temporal and parietal lobe.
The neo cortex is a six layered structure of cerebral cortex and is associated with higher information processing in humans.
The outer surface has about 1.5 mm to 5mm thickness.
The neo cortex is a six layered structure of cerebral cortex and is associated with higher information processing in humans.
The outer surface has about 1.5 mm to 5mm thickness.
Frontal lobe
This is the most recent evolutionary addition to the brain.
The functions of the frontal lobe include reasoning, attention, creative thoughts, reflection, inhibition, problem solving, judgment, impulse control, behavior, higher emotions such as empathy and altruism, motor control,memory, coordination of movements, sense of smell, and libido.
Broca’s area is concerned with speech production and understanding language.
Parietal lobe
The Parietal lobe is concerned with pain and touch sensation, movement, orientation, cognition about location and speed of objects, some language and reading functions.
Temporal lobe
Temporal lobe is concerned with hearing, speech, language understanding, music, visual and auditory memories, emotion, fear, sense of identity, and behavior.
Occipital lobe
Occipital lobe is concerned with visual processing and color recognition.
LIMBIC SYSTEM
Limbic systems concerned with emotional reaction, motivation, biological rhythms and olfaction. It lies within the cerebrum.
These include limbic lobe, thalamus hypothalamus, amygdale, epithalmus; part of basal ganglia, reticular formation and hippocampus.
These include limbic lobe, thalamus hypothalamus, amygdale, epithalmus; part of basal ganglia, reticular formation and hippocampus.
Hippocampus is concerned with formation, classification and storage of memories.
Amygdale is related with fear and emotionally charged memories.
Cingulate gyrus: It is concerned with sensory input with emotions.
Olfactory cortex is involved with identification odors.
Hypothalamus
It controls daily rhythmical daily activities, bodily urges, appetite, thirst, autonomic functions, hormonal system, temperature regulation, sexual maturation, homeostasis, mood and motivation.
Thalamus
It is relay station of all sensory signals. It is concerned with identification of odor and motor functions.
BRAIN STEM
Underneath the limbic system is brain stem.
The midbrain and hindbrain together make up the brain stem.
Midbrain is concerned with auditory and visual responses as well as motor function.
The midbrain and hindbrain together make up the brain stem.
Midbrain is concerned with auditory and visual responses as well as motor function.
HIND BRAIN
It extends from the spinal cord and is composed of pons and medulla oblongata at ventral part and cerebellum at posterior part.
Pons
It involved in autonomic functions, sleep and consciousness.
It relays sensory information between cerebrum and cerebellum.
It relays sensory information between cerebrum and cerebellum.
Medulla oblongata
It controls basic functions like primary instincts, digestion, breathing and heartbeat.
It relays signals of brain and spinal cord.
It relays signals of brain and spinal cord.
Cerebellum
It has two hemisphere and highly folded cortex.
It is the oldest part of the brain.
It is related with learning movements, motor coordination, posture and balance.
It is the oldest part of the brain.
It is related with learning movements, motor coordination, posture and balance.
The spinal cord carries signals to the brain and instruction back down
Physiology
The brain is the most complex organ in the body.
Average weight of brain is about 1460 gm in male and 1250 gm in female.
It consumes glucose and O2 about 70 mg/minute and 45 ml/minute respectively.
The blood flow is about 750 ml/minute.
1/5 of total oxygen of body is taken by brain.
1/5 of total oxygen of body is taken by brain.
Nervous tissue consists of two elements Neuron and Neuroglia.
Neuron consists of cell body and two types process-axon (which carries impulses away from it) and dendron (which carries towards the cell body).
Neuroglia is a special type of interstitial tissue and is present both in the grey matter and white matter.
Types of neuroglia
Astrocytes (star like supporting cells -ectodermal origin)
It found in cerebellum and cerebrum. The sheath of astrocytes covers the blood vessel and act as blood brain barrier which does not allow dyes and certain toxins.
Oligodendrocytes
It takes part in the formation of myelin sheath which is cholesterol free lipid layer. But the cholesterol content is increased due to degeneration of this layer.
Microglia
It is mesodermal in origin and has phagocyte properties.
Brain substance consists of grey matter and white matter.
Former contains with cluster of nerve cells while later contains the cluster of nerve fibers.
Grey matter remains on surface of the brain but it remains in centre in the spinal cord.
Grey matter remains on surface of the brain but it remains in centre in the spinal cord.
Generally nerve fibers consists of three components namely axons, myelin sheath and nucleated sheath of Schwann. This outer sheath is absent in central nerve system.
Nervous system has three functions
Sensory (afferent-consciousness or unconsciousness), motor (efferent- voluntary and reflex or involuntary-conditioned and unconditioned) and associative functions (idea, memory and intelligence).
Sensory nerves gather information from the environment, and send to spinal cord and brain. The brain makes sense of that message and fire off a response.
Motor neurons deliver the instruction from the brain to the rest of the body. Each motor fiber has about 150 branches and each of which end in separate muscle fiber.
Spinal and cerebellar connections are under homo lateral control.
Pyramidal tracts
Pyramidal cells and their axons are known as upper motor neuron, and spinal cord with their neurons are known as lower motor neurons.
Pyramidal tract fibers originate from betz cells (about 35000; 4% of total pyramidal cells) in the precentral gyrus (area 4, 6).
The fibers are arranged upside down; those for toes are at top, those for the trunk in the middle and those for head, below. They also arise from frontal and parietal lobe cells (area 1, 2, 5, 7).
55% of pyramidal fibers end in the cervical, 20% end in the thoracic, and 25% end in lumbosacral region.
Pyramidal tract fibers originate from betz cells (about 35000; 4% of total pyramidal cells) in the precentral gyrus (area 4, 6).
The fibers are arranged upside down; those for toes are at top, those for the trunk in the middle and those for head, below. They also arise from frontal and parietal lobe cells (area 1, 2, 5, 7).
55% of pyramidal fibers end in the cervical, 20% end in the thoracic, and 25% end in lumbosacral region.
Functions
Pyramidal tracts convey motor impulse to the spinal cord for controlling voluntary movement especially skilled movement.
Paralysis of upper motor neuron shows loss of volitional movement, spasticity, increased deep reflexes, loss of superficial reflexes and positive Babinski sign (plantar extension of great toe).
Paralysis of lower motor neuron shows loss of deep reflexes and voluntary movement, and loss of muscle tone.
Extra pyramidal system
Extra pyramidal system mainly consists of group of nuclear mass in the forebrain and its neural connection at mid brain (reticular formation), cerebrum and cerebellum.
This system with cerebral cortex involves for production of automatic movement and postural adjustment.
It is highly developed and but not dominated by cerebral cortex in lower animal. The cortical regions controlling extra pyramidal tract are (area 6 and 8) from premotor area of frontal lobe.
It is responsible for tone, posture and equilibrium, touch, movements of eyeball, automatic associated movements, and coordination movement of limbs.
It is highly developed and but not dominated by cerebral cortex in lower animal. The cortical regions controlling extra pyramidal tract are (area 6 and 8) from premotor area of frontal lobe.
It is responsible for tone, posture and equilibrium, touch, movements of eyeball, automatic associated movements, and coordination movement of limbs.
Extra pyramidal tracts act as alternative pathway for volitional impulses and also a platform on which pyramidal system works skillfully. Cerebral cortex exerts inhibitory control over the lower centers through these tracts. Dyskinesia or involuntary movement is common symptom in extrapyramidal diseases. These include Parkinsonism, chorea, athetosis, dystonia, and hemiballismus.
1 Putman | 7 Thalamus | 13 Amygdaloid |
2 Caudate nucleus | 8 Corpus callosum | 14 Hippocampus |
3 Globus pallidus | 9 Vestibular nucleus | 15 Hypophysis |
4 Substantia nigra | 10 Lateral geniculate body | 16 Cerebral cortex |
5 Sub thalamic nucleus of Luysi | 11 Optic nerve | 17 Pineal body (Epiphysis) |
6 Superior colliculus | 12 Red nucleus |
BASAL GANGLIA
These are group of nuclear masses in the forebrain. These include Striatum (caudate nucleus and putman have similar in morphological structure and collectively called striatum), Globus pallidus, Substantia nigria, Subthalamic nucleus, and Red nucleus.
Movements are mainly pyramidal in origin in mammals, and extrapyramidal nuclei modulate it through reflex mechanism.
Basal ganglia maintain motor activities, automatic movements, locomotion, feeding and postural adjustments.
Positive movements (tremor and chorea) are due to excess of neural activity (releasing phenomenon).
Various Neurotransmitters present in nervous system are acetylcholine (present in caudate nucleus, thalamus, cerebral cortex and retina), nor adrenaline (hypothalamus), dopamine (striatum, substantia nigra, hypothalamus, retina), histamine (hypothalamus), serotonin (basal ganglia, hypothalamus. spinal cord), amino acids like glutamic acid (central neurons) and gamma amino butyric acid (spinal cord and cerebral cortex- inhibition), glycine (spinal cord- inhibition), peptides (hypothalamus, substantia nigria and retina), and prostoglandins (cerebellum, spinal cord and cerebral cortex).
Dopamine is stored in axons of neurons which cell body may be located in distant area. Dopamine content in substantia nigria and globus pallidus is become low parkinsonism. Increased level of Ach can cause degradation of dopamine which promotes abnormal involuntary movements, alterations in muscle tone and disturbance in bodily posture.
Hyper activity of dopaminergic fiber in caudate nucleus and putamen can cause reflexly low secretion of serotonin which can promote depression in beginning.
Further depletion of dopamine results in bradykinesia, and reflexively increases serotonin (5 HT) and acetylcholine (Ach) which cause delusion and tremor respectively.
Chemical changes predominate than morphological changes. Normally acetylcholine and related enzymes; dopamine and norepinephrine are high in these nucleus.
There is a balance between acetylcholine, dopamine and nor adrenaline in brain.
When cholinergic predominate than dopamine tremor can result.
The increased level acetylcholine in caudate nucleus and putamen can cause hypo activity of dopamine or vice versa. Destruction of caudate nucleus and putamen can cause hyperactivity of substantia nigria fibers.
Hypo activity of dopaminergic fibres in substantia nigria can cause bradykinesia.
Stress can promote secretion of adrenaline; hyper activity of both peripheral dopamine and adrenaline. This may result the depletion of central dopamine. (This also favors transient rebound activity of Ach and resultant tremor). Chronic stress can reduce the dopamine reserve. This can result to rigidity and bradykinesia. Vomiting can develop by the effects of peripheral dopamine.
Neuron-degeneration
Common causes are age process, radiation, vascular defects, toxicity, under nutrition, infections and neoplasm.
Vascular defect
Common causes of atheromatous changes are heredity, disturbance of cholesterol metabolism (hypothyroidism, diabetes mellitus, old age, dietary habits; polyarteritis nodosa (due to hypersensitivity to toxin, bacteria, virus; rheumatoid arthritis), and disturbance of circulation (bradycardia, constitutional hypotension, sudden hypotension in hypertensive) etc.
Hypoxia or anoxia can be developed from arteriosclerosis, obstruction, intra cranial aneurysms (familial); vegetative embolism originating from mitral stenosis, hypertension, spasm, thrombosis and hemorrhage.
Hypoxia or anoxia can be developed from arteriosclerosis, obstruction, intra cranial aneurysms (familial); vegetative embolism originating from mitral stenosis, hypertension, spasm, thrombosis and hemorrhage.
Thrombosis and fibrosis in middle cerebral artery proximal to basal ganglia can cause degeneration of basal ganglia but distal to basal ganglia do not affect cerebral cortex because of collateral circulation through anterior cerebral arteries.
Degeneration, subsequent necrosis and softening in basal ganglia result in cystic formation. These spaces are filled with astrocytes which may either undergo proliferation (glial proliferation) or hypersensitivity tendency (interstitial inflammation can cause irritable nerve discharge).
Involvements of interstitial tissues lesions are common more than neuron lesions. So individual symptoms developed are less in diseases with glial proliferation. The symptoms developed here are mainly due to local pressure.
Toxins
toxicity from Phosphorus, Mercury, Arsenic, Lead, Carbon monoxide (from chronic cigarette smoking, in garage worker- pink skin), Manganese, large quantity of alcohol or alcoholic extract (Juniper), toxic acids and drugs.
Nutritional factors include errors of carbohydrate, protein and fat metabolism, hypoglycemia, liver cirrhosis, deficiencies of choline, casein, methionine, inositol, enzymes, vitamin B1and B12.
Infections
Viral infections include encephalitis lethargica, encephalitis influenza, toxoplasmosis, coxsackie group B infections (Encephalitis), Coxsackie group A infections (Herpes, Pleurodynia, and Meningitis) and ECHO virus infections (from fish and shellfish-rubella like lesions).
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