NERVOUS SYSTEMNERVOUS SYSTEM

The nervous system is composed of The nervous system is composed of specialized cells called neuron, which specialized cells called neuron, which exercise control by sending electrical exercise control by sending electrical signals called nerve impulses. Nerve signals called nerve impulses. Nerve cells are the structural and functional cells are the structural and functional unit of nervous systemunit of nervous system..

STRUCTURE OF NEURONSTRUCTURE OF NEURON

A neuron consists of three prominent parts-A neuron consists of three prominent parts-

1.Cell body- The cell body of neuron is also 1.Cell body- The cell body of neuron is also called cyton or soma. It receives nerve called cyton or soma. It receives nerve impulses from dendrites and transmit them to impulses from dendrites and transmit them to axon.axon.

2.Dendrites- dendrites are the parts of neuron 2.Dendrites- dendrites are the parts of neuron where sensation acquired. The information where sensation acquired. The information then travels as an electric impulse towards the then travels as an electric impulse towards the cell body.cell body.

Axon:-It is a single, cylindrical Axon:-It is a single, cylindrical protoplasmic nerve fibre. At its protoplasmic nerve fibre. At its terminal axon is highly branched. The terminal axon is highly branched. The axon conducts nerve impulses away axon conducts nerve impulses away from the cell body.from the cell body.

The neurons lie end to end in chains to transmit The neurons lie end to end in chains to transmit nerve impulses in the animal body. The neurons nerve impulses in the animal body. The neurons are not connected. There occurs a very minute are not connected. There occurs a very minute gap between terminal portion of axon of one gap between terminal portion of axon of one neuron and the dendron of other neuron. This neuron and the dendron of other neuron. This minute gap is called synapse. minute gap is called synapse.

Axon terminal expand to form presynaptic knob Axon terminal expand to form presynaptic knob and dendrite forms post synaptic depression. In and dendrite forms post synaptic depression. In between the two lies a fluid filled space called between the two lies a fluid filled space called synaptic cleft. synaptic cleft.

ARRANGEMENT OF NEURONARRANGEMENT OF NEURON

As the nerve impulses reaches the pre-synaptic As the nerve impulses reaches the pre-synaptic knob, the synaptic vesicles get stimulated to knob, the synaptic vesicles get stimulated to release a chemical called neurotransmitter in release a chemical called neurotransmitter in the synaptic cleft. The neurotransmitter the synaptic cleft. The neurotransmitter molecules diffuse across the gap to come in molecules diffuse across the gap to come in contact with the chemoreceptor site in the contact with the chemoreceptor site in the nerve impulses passes from one neuron to nerve impulses passes from one neuron to other.other.

REFLEX ACTIONSREFLEX ACTIONS

A Reflex actions may be defined as a A Reflex actions may be defined as a spontaneous, automatic and mechanical spontaneous, automatic and mechanical response to a stimulus , acting on a specific response to a stimulus , acting on a specific receptor , without the will of an animal . In receptor , without the will of an animal . In certain situation , sensation requires immediate certain situation , sensation requires immediate response as time used for processing may cause response as time used for processing may cause harm to the body. In such situation reflex action harm to the body. In such situation reflex action occur.occur.

Example:-blinking of eyes ,withdraw of hand Example:-blinking of eyes ,withdraw of hand suddenly pinched or touched by a hot object.suddenly pinched or touched by a hot object.

HUMAN NERVOUS SYSTEMHUMAN NERVOUS SYSTEM

Human nervous system is the most complex. Human nervous system is the most complex. It is divided into two main parts-It is divided into two main parts-

i)i) Central nervous systemCentral nervous system

ii)ii) Peripheral nervous system Peripheral nervous system

It is hollow and lies on the mid-dorsal It is hollow and lies on the mid-dorsal part along the main axis of the body. It is part along the main axis of the body. It is covered by a part of axial skeleton. The covered by a part of axial skeleton. The CNS in turn consists of two parts-CNS in turn consists of two parts-

1. Brain or Encephalon situated in the head.1. Brain or Encephalon situated in the head.

2. Spinal cord or Myelon located in the neck 2. Spinal cord or Myelon located in the neck and trunk.and trunk.

CENTRAL NERVOUS CENTRAL NERVOUS SYSTEMSYSTEM

BRAINBRAIN

The The brain brain is the widest and the uppermost part of is the widest and the uppermost part of the central nervous system . It is the highest the central nervous system . It is the highest coordinating centre in the body. Brain is situated coordinating centre in the body. Brain is situated in the cranial cavity of the skull. The brain is soft, in the cranial cavity of the skull. The brain is soft, whitish organ. It weighs 1.2 to 1.4 kg and forms whitish organ. It weighs 1.2 to 1.4 kg and forms about 98% of the weight of the whole nervous about 98% of the weight of the whole nervous system. It has about 100 bilion neurons. Brain is system. It has about 100 bilion neurons. Brain is surrounded by three membranes called meninges surrounded by three membranes called meninges which provide protection to it. The space between which provide protection to it. The space between the meninges is filled with the cerebro- spinal the meninges is filled with the cerebro- spinal fluid . fluid .

Brain is divisible into three main region –Brain is divisible into three main region –

1.1. FOREBRAINFOREBRAIN- It forms the greater part of - It forms the greater part of the brain. It consists of three parts: olfactory the brain. It consists of three parts: olfactory lobes, cerebral hemisphere and diencephalon.lobes, cerebral hemisphere and diencephalon.

i) i) Olfactory lobes-Olfactory lobes- A pair of widely A pair of widely separated club- shaped small structure . Each separated club- shaped small structure . Each olfactory lobe consist of an anterior olfactory olfactory lobe consist of an anterior olfactory bulb and a posterior narrow olfactory stalk. bulb and a posterior narrow olfactory stalk. These lobes receive impulses from These lobes receive impulses from olfactoreceptors and relay sense of smell to olfactoreceptors and relay sense of smell to the temporal region of the cerebrum. the temporal region of the cerebrum.

(ii) (ii) Cerebral hemisphere-Cerebral hemisphere- It is the largest part of the It is the largest part of the brain . The two cerebral hemisphere lie side by side brain . The two cerebral hemisphere lie side by side separated by deep cerebral fissure. The cerebral separated by deep cerebral fissure. The cerebral hemisphere divided into four lobes – hemisphere divided into four lobes –

a. a. Frontal lobeFrontal lobe is the region for speech ,facial, is the region for speech ,facial, muscular activities and mental activities. muscular activities and mental activities.

b. b. Temporal lobeTemporal lobe is the region for auditory reception is the region for auditory reception (hearing ) .(hearing ) .

c. c. Occipital lobeOccipital lobe is the region for visual reception is the region for visual reception (sight ) (sight )

d. d. Parietal lobeParietal lobe is the region for touch ,taste ,smell, is the region for touch ,taste ,smell, temperature and conscious association.temperature and conscious association.

(iii) (iii) DiencephalonDiencephalon:-It lies on the side of cerebrum It :-It lies on the side of cerebrum It roof is called epithalamus, sides are called thalami roof is called epithalamus, sides are called thalami and its floor is called hypothalamus. Diencephalon and its floor is called hypothalamus. Diencephalon has a narrow cavity called third ventricle. has a narrow cavity called third ventricle.

2. 2. MID BRAINMID BRAIN:-It is significantly small region. It :-It is significantly small region. It consists of two fibre tracts called crura cerebri and consists of two fibre tracts called crura cerebri and a pair of two swellings called superior and infeior a pair of two swellings called superior and infeior colliculi on each side. the two superior colliculi colliculi on each side. the two superior colliculi have centres for sight reflexes and the two inferior have centres for sight reflexes and the two inferior colliculi have centre for sight reflexes. It controls colliculi have centre for sight reflexes. It controls the movement of head, neck, eye muscles ;changes the movement of head, neck, eye muscles ;changes in pupil size as well as shape of eye lens.in pupil size as well as shape of eye lens.

3. 3. HIND BRAINHIND BRAIN:- The hind brain consists of :- The hind brain consists of three parts- three parts- cerebellum, pons varolii andcerebellum, pons varolii and medulla oblongatamedulla oblongata. The cerbellum is the second . The cerbellum is the second largest part of the brain , constituting nearly largest part of the brain , constituting nearly 12% of it. It has two large, lateral cerebellar 12% of it. It has two large, lateral cerebellar hemispheres and a central vermis. Cerebellum hemispheres and a central vermis. Cerebellum maintains the posture, equilibrium and muscles maintains the posture, equilibrium and muscles tone. Pons varolii controls some aspects of tone. Pons varolii controls some aspects of respiration. Medulla oblongata is the posterior respiration. Medulla oblongata is the posterior part of the brain. It controls rate of heartbeat, part of the brain. It controls rate of heartbeat, breathing movements etc. breathing movements etc.

SPINAL CORDSPINAL CORD

Spinal cordSpinal cord is a cylindrical structure and is about is a cylindrical structure and is about 45cm long . It begins in continuation with the 45cm long . It begins in continuation with the medulla oblongata of brain extend downward up medulla oblongata of brain extend downward up to early part of the lumber region . It then extend to to early part of the lumber region . It then extend to the end of vertebral column as fibrous connective the end of vertebral column as fibrous connective called filum terminale. Internally the spinal cord called filum terminale. Internally the spinal cord possess a narrow, fluid filled cavity called central possess a narrow, fluid filled cavity called central canal. Spinal cord is enclosed in the vertebral canal. Spinal cord is enclosed in the vertebral column or backbone which protect it. It conducts column or backbone which protect it. It conducts sensory and motor impulses to and from the brain. sensory and motor impulses to and from the brain. It act as center for the reflex action It act as center for the reflex action

PERIPHERAL NERVOUS SYSTEMPERIPHERAL NERVOUS SYSTEM

It connects CNS with different part of the It connects CNS with different part of the body . It has two component, voluntary and body . It has two component, voluntary and Autonomic nervous system. These are-Autonomic nervous system. These are-

1. 1. Voluntary peripheral nervousVoluntary peripheral nervous system is system is under the control of will. It consist of nerves under the control of will. It consist of nerves that arise directly from CNS connecting that arise directly from CNS connecting different body parts for voluntary control of different body parts for voluntary control of the brain. the brain.

2. 2. Autonomic nervous systemAutonomic nervous system (involuntary (involuntary nervous system), on other hand, is not under nervous system), on other hand, is not under the control of human will. It developed the control of human will. It developed branches of some cranial and some spinal branches of some cranial and some spinal nerves called visceral nerves. It is subdivided nerves called visceral nerves. It is subdivided into two parts:into two parts:

(i) sympathetic nervous system(i) sympathetic nervous system

(ii) parasympathetic nervous system(ii) parasympathetic nervous system

The Organization of the The Organization of the Sympathetic Division of the ANSSympathetic Division of the ANS

Sympathetic chain ganglia (paravertebral Sympathetic chain ganglia (paravertebral ganglia) – preganglionic fibers of the ganglia) – preganglionic fibers of the sympathetic NS that carry motor impulses to the sympathetic NS that carry motor impulses to the body wall or thoracic cavity synapses in chain body wall or thoracic cavity synapses in chain gangliaganglia

Collateral ganglia (prevertebral ganglia) – Collateral ganglia (prevertebral ganglia) – group of second order neurons that innervate group of second order neurons that innervate organs in the abdominopelvic regionorgans in the abdominopelvic region

Sympathetic ganglia Sympathetic ganglia

Sympathetic PathwaysSympathetic Pathways

Sympathetic PathwaysSympathetic Pathways

Sympathetic PathwaysSympathetic Pathways

Animation: The sympathetic division (see tutorial)

The Distribution of Sympathetic The Distribution of Sympathetic InnervationInnervation

Rejoin spinal nerves and reach their destination Rejoin spinal nerves and reach their destination by way of the dorsal and ventral ramiby way of the dorsal and ventral rami

Those targeting structures in the thoracic cavity Those targeting structures in the thoracic cavity form sympathetic nervesform sympathetic nerves Go directly to their destinationGo directly to their destination

Postganglionic fibersPostganglionic fibers

Sympathetic innervation via preganglionic fibers Sympathetic innervation via preganglionic fibers that synapse within collateral gangliathat synapse within collateral ganglia Splanchic nerves – carry fibers that synapse in Splanchic nerves – carry fibers that synapse in

collatheral gangliacollatheral ganglia

Abdominopelvic visceraAbdominopelvic viscera

Celiac ganglionCeliac ganglion Innervates stomach, liver, gall bladder, pancreas, Innervates stomach, liver, gall bladder, pancreas,

spleenspleen Superior mesenteric ganglionSuperior mesenteric ganglion

Innervates small intestine and initial portion of large Innervates small intestine and initial portion of large intestineintestine

Inferior mesenteric ganglionInferior mesenteric ganglion Innervates kidney, urinary bladder, sex organs, and Innervates kidney, urinary bladder, sex organs, and

final portion of large intestinefinal portion of large intestine

Abdominopelvic visceraAbdominopelvic viscera

Sympathetic activation is controlled by Sympathetic activation is controlled by sypathetic centers in the hypothalamus.sypathetic centers in the hypothalamus.

In crises, the entire sympathetic division In crises, the entire sympathetic division respondsresponds Sympathetic activationSympathetic activation Affects include increased alertness, energy and Affects include increased alertness, energy and

euphoria, increased cardiovascular and respiratory euphoria, increased cardiovascular and respiratory activities, elevation in muscle tone, mobilization of activities, elevation in muscle tone, mobilization of energy resourcesenergy resources

Sympathetic activationSympathetic activation

Stimulation of sympathetic division has two Stimulation of sympathetic division has two distinct resultsdistinct results Release of ACh or NE at specific locationsRelease of ACh or NE at specific locations Secretion of E and NE into general circulationSecretion of E and NE into general circulation

Most postganglionic fibers are adrenergic, a few Most postganglionic fibers are adrenergic, a few are cholinergic or nitroxidergicare cholinergic or nitroxidergic

Neurotransmitters and Neurotransmitters and sympathetic functionsympathetic function

Sympathetic VariositiesSympathetic Variosities

Preganglionic neurons in the brainstem and sacral segments of Preganglionic neurons in the brainstem and sacral segments of spinal cordspinal cord

Ganglionic neurons in peripheral ganglia located within or near Ganglionic neurons in peripheral ganglia located within or near target organstarget organs

Parasympathetic divisionParasympathetic division

The Organization of the The Organization of the Parasympathetic Division of the Parasympathetic Division of the

ANSANS

Preganglionic fibers of parasympathetic neurons Preganglionic fibers of parasympathetic neurons can be found in cranial nerves III, VI, IX, Xcan be found in cranial nerves III, VI, IX, X

Sacral neurons form the pelvic nervesSacral neurons form the pelvic nerves Almost 75% of all parasympathetic outflow Almost 75% of all parasympathetic outflow

travels along the vagus nerve (cranial nerve X)travels along the vagus nerve (cranial nerve X)

Organization and anatomy of the Organization and anatomy of the parasympathetic divisionparasympathetic division

The Distribution of The Distribution of Parasympathetic InnervationParasympathetic Innervation

Effects produced by the parasympathetic division Effects produced by the parasympathetic division relaxationrelaxation food processingfood processing energy absorptionenergy absorption

Parasympathetic activationParasympathetic activation

All parasympathetic fibers release AChAll parasympathetic fibers release ACh Short-lived response as ACH is broken down by Short-lived response as ACH is broken down by

AChE and tissue cholinesteraseAChE and tissue cholinesterase

Neurotransmitters and Neurotransmitters and parasympathetic functionsparasympathetic functions

SympatheticSympathetic Widespread influence on visceral and somatic Widespread influence on visceral and somatic

structuresstructures ParasympatheticParasympathetic

Innervates only visceral structures serviced by cranial Innervates only visceral structures serviced by cranial nerves or lying within the abdominopelvic cavitynerves or lying within the abdominopelvic cavity

Effects produced by the parasympathetic branch Effects produced by the parasympathetic branch include increased secretion by digestive glandsinclude increased secretion by digestive glands

• Dual innervation = organs that receive input Dual innervation = organs that receive input from both systemsfrom both systems

Sympathetic and Sympathetic and parasympathetic divisionsparasympathetic divisions

Sympathetic and parasympathetic systems Sympathetic and parasympathetic systems intermingle to form autonomic plexusesintermingle to form autonomic plexuses Cardiac plexus – sympathetic and parasympathetic Cardiac plexus – sympathetic and parasympathetic

fibers bound for the heart and kungs pass through the fibers bound for the heart and kungs pass through the cardiac plexuscardiac plexus

Pulmonary plexusPulmonary plexus Esophageal plexusEsophageal plexus Celiac plexusCeliac plexus Inferior mesenteric plexusInferior mesenteric plexus Hypogastric plexus Hypogastric plexus

Anatomy of dual innervationAnatomy of dual innervation

The Autonomic PlexusesThe Autonomic Plexuses

Important physiological and functional Important physiological and functional differences existdifferences exist

Comparison of the two divisionsComparison of the two divisions

Summary: The Anatomical Summary: The Anatomical Differences between the Differences between the

Sympathetic and Parasympathetic Sympathetic and Parasympathetic DivisionsDivisions

A Comparison of Somatic and A Comparison of Somatic and Autonomic FunctionAutonomic Function

Activity in the ANS is controlled by centers in Activity in the ANS is controlled by centers in the brainstem that deal with visceral functioningthe brainstem that deal with visceral functioning

Higher levels of autonomic Higher levels of autonomic controlcontrol

Levels of Autonomic ControlLevels of Autonomic Control

Example of higher-level of autonomic function would be increased heart rate when you see a person that you dislike.

Are performed by the cerebral cortex and involve complex Are performed by the cerebral cortex and involve complex interactions interactions

Involve conscious and unconscious information processingInvolve conscious and unconscious information processing Are subject to modification and adjustment over timeAre subject to modification and adjustment over time

Higher order functionsHigher order functions

Short term or long termShort term or long term Memory consolidation is moving from short term to long termMemory consolidation is moving from short term to long term

Hippocampus is essential for memory consolidationHippocampus is essential for memory consolidation Mechanisms involved in memory formation and storage are:Mechanisms involved in memory formation and storage are:

Increased release of neurotransmitterIncreased release of neurotransmitter Formation of additional synaptic connectionFormation of additional synaptic connection Formation of memory engrams (single circuit that Formation of memory engrams (single circuit that

correspond to single memory)correspond to single memory) Amnesia is the loss of memory due to disease or traumaAmnesia is the loss of memory due to disease or trauma

MemoryMemory

Memory that can be voluntarily retrieved and Memory that can be voluntarily retrieved and verbally expressed are called declarative verbally expressed are called declarative memoriesmemories

Conversion of a short term memory to a long Conversion of a short term memory to a long term memory is called memory consolidationterm memory is called memory consolidation

MemoryMemory

Memory StorageMemory Storage

Deep sleep, the body relaxes and cerebral cortex activity is lowDeep sleep, the body relaxes and cerebral cortex activity is low The reticular activating system (RAS) is important to arousal The reticular activating system (RAS) is important to arousal

and maintenance of consciousnessand maintenance of consciousness RAS is located in the mesencephalonRAS is located in the mesencephalon

ConsciousnessConsciousness

The Reticular Activating SystemThe Reticular Activating System

Reduction in brain size and weightReduction in brain size and weight Reduction in the number of neuronsReduction in the number of neurons Decrease in blood flow to the brainDecrease in blood flow to the brain Changes in synaptic organization of the brainChanges in synaptic organization of the brain Intracellular and extracellular changes in CNS neuronsIntracellular and extracellular changes in CNS neurons

Age-related changesAge-related changes

You should now be familiar with:You should now be familiar with: The organization of the autonomic nervous system.The organization of the autonomic nervous system. The structures and functions of the sympathetic and The structures and functions of the sympathetic and

parasympathetic divisions of the ANS.parasympathetic divisions of the ANS. The mechanisms of neurotransmitter release in the The mechanisms of neurotransmitter release in the

sympathetic and parasympathetic divisions.sympathetic and parasympathetic divisions. The effects of sympathetic and parasympathetic The effects of sympathetic and parasympathetic

neurotransmitters on target organs and tissues.neurotransmitters on target organs and tissues. The hierarchy of interacting levels of control in the ANS.The hierarchy of interacting levels of control in the ANS. How memories are created, stored and recalled.How memories are created, stored and recalled. The effects of aging on the nervous system.The effects of aging on the nervous system.