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1. Classification of Nervous System

The nervous system is classified into the Central Nervous System (CNS) (brain and spinal cord) and the Peripheral Nervous System (PNS) (nerves outside the CNS). Functionally, the PNS further divides into the Somatic Nervous System (voluntary control of muscles) and the Autonomic Nervous System (ANS), which regulates involuntary functions and splits into the Sympathetic (fight-or-flight) and Parasympathetic (rest-and-digest) systems.

2. Autonomic Nervous System

It Controls involuntary bodily functions like heart rate, breathing, digestion, and blood pressure, operating automatically without conscious thought to maintain homeostasis (internal balance). It's part of the peripheral nervous system, divided into the sympathetic (fight-or-flight) system, which prepares the body for action, and the parasympathetic (rest-and-digest) system, which conserves energy, with both working in balance

3. N.S. Classification

Central Nervous System (CNS): The body's command center, interpreting information and making decisions. Brain: Processes thoughts, memories, emotions, and controls motor skills. Spinal Cord: Relays messages between the brain and the rest of the body, protected by vertebrae. Peripheral Nervous System (PNS): Connects the CNS to limbs, organs, and skin. Cranial Nerves: Emerge from the brain. Spinal Nerves: Emerge from the spinal cord.

4. Organization of Nervous System

Somatic Nervous System (Voluntary): Controls skeletal muscles. Autonomic Nervous System (Involuntary): Controls internal organs, glands, and smooth muscles. Sympathetic Nervous System: Prepares the body for stress (e.g., increases heart rate). Parasympathetic Nervous System: Promotes relaxation and energy conservation (e.g., slows heart rate).

5. Autonomic Nervous System

Heart Rate & Blood Pressure: Regulates how fast your heart beats and your blood pressure. Respiration: Adjusts your breathing rate. Digestion: Manages digestion, nutrient absorption, and waste elimination. Metabolism: Controls metabolic processes and energy use. Temperature Regulation: Manages sweating and blood flow to cool or warm the body. Pupil Response: Controls pupil dilation and constriction. Sexual Arousal: Involved in sexual function

7. Somatic and ANS

Controls voluntary body movements by connecting the brain and spinal cord (CNS) to skeletal muscles, allowing conscious actions like walking or talking, and also manages voluntary sensory input from skin, muscles, and senses. It operates via sensory (afferent) nerves bringing info to the CNS and motor (efferent) nerves sending commands to muscles, handling both intentional actions and rapid reflex arcs (like pulling your hand from heat

9. A.N.S.

Sympathetic Nervous System (Accelerator): Prepares the body for stress or emergencies ("fight-or-flight") by increasing heart rate, diverting blood to muscles, and boosting alertness. Parasympathetic Nervous System (Brake): Calms the body down, conserving energy and promoting "rest-and-digest" functions, slowing heart rate and increasing digestion

10. Neurons Types

Neurons are categorized by function (Sensory, Motor, Interneurons) and structure (Unipolar, Bipolar, Multipolar), working together to process information: Sensory neurons detect stimuli, Motor neurons control muscles/glands, and Interneurons connect them within the CNS, while structural types describe axon/dendrite count, like Multipolar (most common, many dendrites, one axon) and Bipolar (one dendrite, one axon).

Multipolar Neuron Structure

Most common type of nerve cell, defined by having one axon and multiple dendrites branching from its cell body, allowing it to receive and integrate vast amounts of information, forming the backbone of the central nervous system (brain, spinal cord) and autonomic nervous system

Neuron Types

Bipolar: One axon and one dendrite, found in special senses (eyes, ears). Unipolar (Pseudounipolar): Single extension from the cell body splits into axon and dendrite; typically sensory neurons

Neuron Structure HD

Cell body (soma), which contains the nucleus; multiple branching dendrites that receive signals; and a single long axon that transmits signals away, ending in terminal buttons that form synapses with other cells, allowing communication via neurotransmitters.

Myelinated Neuron

The myelin sheath is a fatty, protein-rich insulating layer that wraps around certain neuron axons, speeding up electrical impulse transmission by allowing signals to "jump" between gaps called Nodes of Ranvier (saltatory conduction). Formed by glial cells (Schwann cells in PNS, oligodendrocytes in CNS), this lipid-packed sheath acts like electrical wire insulation, preventing signal loss and enabling rapid, efficient nerve communication.-pkk

Classification of Neuron 3

Anaxonic: No distinct axon; only dendrites, can't produce action potentials (e.g., in brain, retina) Multipolar: Most common; many dendrites, one axon (e.g., motor neurons, interneurons

Purkinje Cell -Brain

Purkinje cells are large, unique neurons in the cerebellum, famous for their massive, flat, branched dendritic trees that integrate vast amounts of sensory-motor information, acting as the sole output of the cerebellar cortex to control coordinated movement, motor learning, cognition, and emotion, primarily through inhibitory signals (GABA).

Neuron Cytoskeleton

A dynamic network of microtubules, neurofilaments (intermediate filaments), and actin filaments (microfilaments) that provides structural support, maintains cell shape, and enables crucial functions like axonal growth, intracellular transport (moving organelles/vesicles), and synaptic transmission, allowing neurons to form complex connections.-PKK

Cytoskeleton Neuron 2

Microtubules (MTs): Made of tubulin, these are hollow tubes (25nm) acting as tracks for motor proteins, essential for transporting materials (organelles, vesicles) from the cell body to axon terminals (axonal transport) and for neurite extension

Alzheimer's Neuron 1

In Alzheimer's, neurons (brain cells) die due to the buildup of abnormal proteins, forming amyloid plaques outside cells and tau tangles inside, disrupting communication and function, leading to progressive memory loss, cognitive decline, and eventually, widespread brain shrinkage and death of nerve cells, starting in memory centers like the hippocampus-PKK

Alzheimer's Neuron 2

Amyloid-beta: Normally cleared, but in AD, it forms sticky plaques outside neurons. Tau: Stabilizes microtubules; in AD, it becomes abnormal, forms tangles, and disrupts cell transport

Neuronal Synapse 1

A Crucial junction where one neuron communicates with another neuron or a target cell (like muscle/gland), allowing nerve impulses to pass via electrical or chemical signals, forming the basis for brain function, learning, and memory, with chemical synapses using neurotransmitters and electrical ones using direction flow.

Neuronal Synapse 2

Presynaptic Neuron: The neuron sending the signal, containing neurotransmitters in vesicles. Postsynaptic Neuron: The receiving neuron, with receptors on its surface (often a dendrite). Synaptic Cleft: The tiny gap between them

2. Parts of Brain- Lobes

Parts, Lobes and Sulcus of Brain-PKK

1. Parts of Brain- Medial Surface

The medial surface of the brain, seen in a midsagittal view, features major structures like the C-shaped Corpus Callosum, the surrounding Cingulate Gyrus (part of the limbic system), the Cerebellum, and the Brainstem, with key sulci (grooves) like the Cingulate Sulcus, Parieto-Occipital Sulcus, and Calcarine Sulcus defining lobes and areas crucial for memory (hippocampus), vision,and Emotion-pkk

3. Fifth Lobe - Insula of Brain

The insular region (insula) is a crucial, deep-seated brain structure, often called the "fifth lobe," hidden beneath the frontal, temporal, and parietal lobes, vital for integrating sensory, emotional, and cognitive information, especially relating to body states (interoception), emotions (like fear, empathy), risk-reward, taste, pain, and autonomic functions, acting as a key hub for linking feelings with decision-making and awareness-PKK

4. Inner Structures of Brain

The inner parts of the brain include the deep structures within the cerebrum (like the thalamus, hypothalamus, basal ganglia, hippocampus, amygdala), the cerebellum (coordination/balance), and the brainstem (midbrain, pons, medulla) controlling vital functions, all connected by white matter and protected by cerebrospinal fluid within ventricles, crucial for relaying signals and managing complex processes. -PKK

5. Brain- Parts in Saggital View

A sagittal view cuts the brain vertically, revealing major structures like the cerebrum, cerebellum, and brainstem, plus internal components such as the corpus callosum, thalamus, hypothalamus, and the ventricular system (including the 3rd and 4th ventricles), showing deep grooves (sulci) and folds (gyri) like the central sulcus, and lobes (frontal, parietal, occipital) on the medial surface-PKK

6. Lobes of Brain

Four main lobes—Frontal, Parietal, Temporal, and Occipital—each responsible for specific functions like reasoning, sensation, hearing, and vision, though they work together complexly. Some models also identify the Insular (deep within) and Limbic lobes, expanding the functional divisions-PKK

8. Brain Anatomy- Medial Surface

The C-shaped corpus callosum (connecting hemispheres), the curved cingulate gyrus (part of the limbic system), and the deep grooves (sulci) separating lobes, such as the callosal, cingulate, and parieto-occipital sulci, revealing parts of the frontal, parietal (like the paracentral lobule), and occipital lobes, along with the diencephalon (thalamus, hypothalamus) and brainstem-PKK

9. Base Of Brain- Interpeduncular Fossa

The base of the brain primarily consists of the Brainstem, which connects the brain to the spinal cord and includes the Midbrain, Pons, and Medulla Oblongata, controlling vital functions like breathing, heart rate, and relaying signals; the Cerebellum, located at the back, handles coordination and balance; and structures like the Thalamus, Hypothalamus, and pituitary gland are also deep at the base, managing sensory relay, homeostasis, and hormones-PKK

10. Interpeduncular Fossa

The interpeduncular fossa is a crucial depression at the base of the brain, located on the midbrain between the two large cerebral peduncles (crura cerebri). Its floor contains important structures like the mamillary bodies, tuber cinereum, infundibulum, and the posterior perforated substance, while the optic chiasma forms its front, and it's where the oculomotor nerve (CN III) emerges-PKK

10. Interpeduncular Fossa Boundaries

A key depression at the brain's base, is bounded anteriorly by the optic chiasma, posteriorly by the pons, and laterally by the diverging cerebral peduncles, containing vital structures like the Circle of Willis and the origin of the oculomotor nerve (CN III), forming part of the midbrain's floor.

11. Structures of Base of Brain

The base of the brain is dominated by the brainstem, a crucial relay connecting to the spinal cord, comprising the Midbrain, Pons, and Medulla Oblongata (controlling vital functions like breathing, heart rate). Also at the base are the Cerebellum (coordinating movement/balance) and deep structures like the Thalamus (sensory relay) and Hypothalamus (hormones, hunger, thirst, temperature), forming the brain's survival and connection center-PKK

Brainstem

The crucial, stalk-like part of the brain connecting the cerebrum to the spinal cord, controlling essential involuntary functions like breathing, heart rate, consciousness, and relaying motor/sensory signals, comprising the midbrain, pons, and medulla oblongata. It's vital for life, acting as a pathway for nerves and regulating fundamental bodily processes-PKK

1. Spinal Cord Structure

Extends from upper border of posterior arch of first cervical vertebrae (C1) to lower border of first lumbar vertebra L1 in adults

2. Spinal Cord, Nerve, Meninges

Covered by spinal meninges: Outer dura mater, middle arachnoid mater, and innermost pia mater

3. Extent of Meninges of Spinal Cord

Dura mater: Extends from foramen magnum to lower border of second sacral vertebra Arachnoid mater (cobweb-like in Latin) Thin transparent membrane loosely surrounds spinal cord Also extends up to lower border of S2 vertebra Pia mater : Thin vascular membrane closely invests spinal cord

4. Spinal Nerves Origin

Thirty-one pairs of spinal nerves – attached to spinal cord Include 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal pairs of nerves Each spinal nerve– attached to spinal cord by 2 roots: Ventral and dorsal nerve roots Ventral or anterior motor root carries motor or efferent fibers from spinal cord

5. Spinal Meninges

Dura mater: Extends from foramen magnum to lower border of second sacral vertebra Arachnoid mater- Thin transparent membrane loosely surrounds spinal cord Also extends up to lower border of S2 vertebra Pia mater : Thin vascular membrane closely invests spinal cord

6. Cauda Equina

Horsetail-like structure formed by bunch of lower spinal nerves surround conus medullaris and filum terminale Components (10 Pair of Nerves) Ventral and dorsal roots of lower four lumbar segments (L2–L5), five sacral (S1 to S5), and one coccygeal segments Filum terminale

6. Structure of Spinal Cord

Anterior median fissure Posterior median sulcus Ventrolateral (anterolateral) sulcus Dorsolateral (posterolateral) sulcus Dorsointermediate (posterointermediate) sulcus

9. Origin of Spinal Nerve

Roots: Nerves start as two distinct roots: the dorsal (posterior) root, carrying sensory info to the spinal cord, and the ventral (anterior) root, carrying motor commands from the spinal cord. Emergence: These roots join to form a spinal nerve just outside the spinal cord. Exit Point: Each nerve exits the vertebral column through an opening called the intervertebral foramen, located between adjacent vertebrae (except the first cervical nerve).

10. Lumbar Puncture

A Needle is inserted into the lower back's spinal canal to collect cerebrospinal fluid (CSF) for testing or to inject/remove substances, diagnosing neurological conditions like meningitis, multiple sclerosis, or bleeding-pkk

11. Ligamentum Denticulatum

extend from pia mater to dura mater stabilize side-to-side movement Each ligamentum denticulatum lies in between anterior and posterior roots of adjacent spinal nerves First ligamentum denticulatum lies at level of foramen magnum while last one lies between T12 and L1 spinal nerves

12. Ligamentum Denticulatum Location

Are 21 pairs of teeth-like projections of pia mater Extend from lateral surface of spinal cord and pierce arachnoid mater to get attached to inner surface of dura mater

13. Parts and Enlargement of Spinal Cord

Two thickened regions—the cervical (neck) and lumbar (lower back)—where the cord bulges to provide extra neurons and connections for the arms (cervical) and legs (lumbar), forming the brachial and lumbosacral nerve plexuses, respectively, allowing complex limb movements

14. Spinal Segment

Portion of spinal cord to which pair of spinal nerve is attached Consists of 31 spinal segments as follows: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal

15. Filum Terminale

Piamater Extension- Thin fibrous filament extends from tip of conus medullaris to first coccygeal vertebra Emerges from vertebral canal through sacral hiatus About 20 cm long

16. Tracts of Spinal Cord

Descending Tracts -- Pyramidal tracts • Lateral corticospinal • Anterior corticospinal Extrapyramidal tracts • Rubrospinal • Medial and lateral reticulospinal • Olivospinal • Lateral vestibulospinal • Tectospinal

19. Tracts of Spinal Cord

Ascending and descending tracts

22. Fissures and Sulci of Spinal Cord

A spinal cord fissure, primarily the deep Anterior Median Fissure (AMF), is a normal anatomical groove on the front (ventral) surface of the cord, dividing the white matter into symmetrical halves and housing the anterior spinal artery and pia mater,

24. CSF Circulation

The continuous flow of fluid through the brain's ventricles and the surrounding subarachnoid space, starting from the lateral ventricles, moving to the third, then fourth ventricle, exiting into the subarachnoid space (around brain and spinal cord) via small openings, and finally being reabsorbed into the bloodstream, primarily through arachnoid villi, providing cushioning, nutrient transport, and waste removal for the CNS

37. Medulla -External Features

Include prominent ridges and grooves on its anterior (ventral) and posterior (dorsal) surfaces, such as the anterior median fissure, paired pyramids (containing corticospinal tracts), and oval olives, with cranial nerves emerging from sulci between them, while the dorsal side shows the posterior median sulcus, gracile and cuneate tubercles, and inferior cerebellar peduncles, all connecting to the spinal cord and cerebellum.

38. Medulla External Features2

Pyramids: Two vertical bulges on either side of the fissure, housing the corticospinal (motor) fibers. Olive: An oval swelling lateral to the pyramids, containing the olivary nucleus, important for movement Posterolateral Sulcus (Post-olivary): Lateral to the olive, where the Glossopharyngeal (CN IX), Vagus (CN X), and Accessory (CN XI) nerves emerge

39. Brainstem -Anterior View

The brainstem's anterior parts, from top to bottom, are the Midbrain, Pons, and Medulla Oblongata, with the anterior surface featuring key motor tracts (like the crus cerebri in the midbrain and pyramids in the medulla) and nuclei for cranial nerves, all vital for connecting the brain to the spinal cord and controlling essential functions like breathing, heart rate, and consciousness

40. Brainstem -Posterior View

The posterior parts of the brainstem include the tectum (midbrain's roof with superior/inferior colliculi), the tegmentum, and crucial white matter tracts like the cerebellar peduncles, forming the dorsal surface alongside the fourth ventricle, while deeper structures like nuclei for cranial nerves (V-XII) and sensory pathways (gracile/cuneate fasciculi) reside within the pons and medulla, connecting to the cerebellum and spinal cord for vital functions.

41. T.S. Medulla -Pyramidal Decussation

shows the crucial crossing (decussation) of most corticospinal motor fibers, forming the lateral corticospinal tract, while dorsal sensory nuclei (gracile and cuneate) are prominent posteriorly, with internal arcuate fibers from them beginning to form the medial lemniscus, marking the transition from brainstem to spinal cord.

42. T.S. Medulla -Sensory Decussation

The crucial crossing point where second-order sensory neurons (internal arcuate fibers) from the gracile and cuneate nuclei cross the midline to form the medial lemniscus, transmitting fine touch, vibration, and proprioception from the body to the opposite side of the brain, ensuring contralateral sensory processing. This crossing happens at the upper part of the closed medulla, anterior to the central gray matter.

43. T.S. Medulla- Sensory Decussation2

First-order neurons enter the spinal cord via the dorsal columns (fasciculus gracilis/cuneatus). They synapse in the gracile or cuneate nuclei in the medulla. The second-order neurons (internal arcuate fibers) then arc around the central gray matter, crossing the midline (decussate). After crossing, they form the medial lemniscus, a major ascending sensory tract.

44. T.S. Medulla -Open Part , At Level of Olive

"open part" (upper medulla) reveals the floor of the fourth ventricle with characteristic features like the median sulcus, hypoglossal and vagal triangles, vestibular area, and area postrema (a chemoreceptor zone). Internally, it shows nuclei for cranial nerves IX-XII, sensory tracts, and the inferior olivary nuclei, with the central canal expanding into the ventricle, contrasting with the "closed" lower medulla.

45. Lateral and Medial Medullary Syndrome

LMS- Sensory and motor deficits: Decreased sensation for pain and temperature on the same side of the face as the stroke, but on the opposite side of the body. Coordination and balance: Vertigo, nausea, vomiting, and loss of balance (ataxia). Speech and swallowing: Hoarseness, difficulty swallowing (dysphagia), and a decreased gag reflex. Other symptoms: Nystagmus (involuntary eye movements), and Horner's syndrome (ptosis, miosis, and anhidrosis).

47. Circle of Willis

he Circle of Willis is a ring of arteries at the base of the brain that connects the internal carotid arteries and the vertebrobasilar system, ensuring continuous blood flow to the brain. It acts as a "fail-safe" system, allowing blood to be rerouted to bypass blockages in one of the major arteries supplying the brain. This collateral circulation reduces the risk of ischemic events, such as stroke. Anterior Circulation: Internal carotid arteries, anterior cerebral arteries, and the anterior communicating artery. Posterior Circulation: Vertebral arteries, basilar artery, posterior cerebral arteries, and the posterior communicating arteries.

PPT File

SECTIONS OF BRAIN

Well labelled Dissected Sectioned Brain- Different Sections of Brain-PKK

49. Pons in Brainstem

Acting as a bridge that connects the cerebral cortex with the medulla and cerebellum. It plays a vital role in regulating essential functions, including breathing, sleep cycles, balance, and facial sensations. It is also responsible for controlling eye movements and chewing.

50. T.S. Lower Part of Pons

Ventral (Basilar) Part: Contains massive transverse pontine fibers, pontine nuclei, and the descending corticospinal and corticonuclear tracts. Dorsal Part (Tegmentum): Abducens Nucleus (CN VI): Located medially beneath the facial colliculus. Facial Nerve (CN VII) Fibers: The motor root of the facial nerve hooks around the abducens nucleus, forming the facial colliculus. Vestibular Nuclei: Located in the lateral area of the floor of the fourth ventricle. Medial Lemniscus: Situated at the junction of the ventral and dorsal parts, arranged horizontally (different from the vertical orientation in the medulla). Spinal Tract and Nucleus of Trigeminal Nerve (CN V): Positioned laterally. Trapezoid Body: Fibers related to the auditory pathway

51. T.S. Upper part of Pons

Ventral (Basilar) Part: Bulky area containing pontine nuclei, transverse fibers, and descending corticospinal/corticopontine tracts. Dorsal Part (Tegmentum): Superior Cerebellar Peduncles (SCP): Prominent, located in the dorsolateral aspect of the tegmentum. Locus Coeruleus: Pigmented nucleus situated in the upper dorsal pons. Medial Longitudinal Fasciculus (MLF): Located paramedially near the floor of the fourth ventricle. Lemnisci (Lateral to Medial): Lateral lemniscus, spinal lemniscus, trigeminal lemniscus, and medial lemniscus.

52. T.S. Pons Lower Part

Medial Lemniscus: Situated at the junction of the ventral and dorsal parts, arranged horizontally (different from the vertical orientation in the medulla). Spinal Tract and Nucleus of Trigeminal Nerve (CN V): Positioned laterally. Trapezoid Body: Fibers related to the auditory pathway

54. Millard Gubler Syndrome-Pons

Ipsilateral facial paralysis: Weakness or paralysis of the facial muscles on the same side as the lesion. This can affect the upper and lower face. Ipsilateral abducens nerve palsy: Difficulty moving the eye on the same side as the lesion, leading to crossed eyes (diplopia). Contralateral hemiparesis: Weakness or paralysis of the limbs on the opposite side of the lesion.