Cerebellum

Location and Functions

• Located at the posterior cranial fossa

• Functions:

  • Control balance and posture coordination of skilled voluntary movements

  • Movement planning

  • Command to move

• Overlies the posterior side of the pons & medulla

• Shallow anterior cerebellar incisure superiorly

• Deeper incisure inferiorly

• Superficial layer: gray matter

• Inner layer: white matter called the arbor vitae

• Symmetrical hemispheres connected by vermis

• Furrows called fissures: anterior and posterolateral

Functional Division

• Longitudinal Division:

  • Lateral zone

  • Intermediate zone

  • Vermis

• Nuclei:

  1. Fastigeal nucleus: most medial; contains small & large multipolar neurons

  2. Globose nucleus: contains small & large multipolar neurons

  3. Emboliform nucleus: wedge-shaped mass composed of large multiform nucleus with dendrites

  4. Dentate nucleus: largest & most lateral; appears as convoluted mass resembling the olivary nucleus

Lobes and Fissures

• Lobes:

  • Anterior lobe: control posture, locomotion & fine motor coordination

  • Posterior lobe: control posture, locomotion & fine motor coordination

  • Flocculonodular lobe: control balance & eye movement

• Fissures:

  • Primary fissure

  • Posterolateral fissure

  • Horizontal fissure

Phylogenetic Subdivision

1. Archicerebellum: oldest; regulation of equilibrium and posture; receives input from the vestibular nerve and medial vestibular nuclei

2. Paleocerebellum: associated with proprioceptive & exteroceptive inputs from head and body; regulates muscle tone

3. Neocerebellum: largest and newest; associated with neocortex of cerebrum, pontine nuclei, & inferior olivary nucleus of medulla; muscle coordination of phasic movements

Cerebellar Peduncles

• Superior cerebellar peduncle (Brachium conjunctivum): connects cerebellum to midbrain; forms the largest cerebellar efferent bundle; fibers arise from dentate, emboliform & globose nuclei

• Middle cerebellar peduncle (brachium pontis): connects cerebellum to pons; fibers arise from pons thru ponto-cerebellar tract; consist of afferent fibers

• Inferior cerebellar peduncle (brachium restiformins): connects the cerebellum with the medulla; conveys unconscious proprioceptive & exteroceptive information to the cerebellum

Cerebellum, CSF & Meninges

• Cerebellum found below the occipital lobe of the cerebrum & behind the medulla & pons of the brain stem & within the posterior cranial fossa

• Separated from these lobes by the tentorium cerebelli, a tough layer of dura mater

• 50% of the total number of neurons in the brain

• Considered a motor structure, because cerebellar damage leads to impairments in motor control & posture

• Cerebellum modifies the motor commands of the descending pathways to make movements more adaptive & accurate

Functions of the Cerebellum

• Maintenance of balance & posture

• Coordination of voluntary movements

• Motor learning

• Cognitive functions such as language

Ventricular System of the Brain

• Ventricles are a communicating network of cavities

• Choroid plexus produces cerebrospinal fluid (CSF)

• Ventricles are lined with specialized connective tissue called ependyma

• Ventricles are connected by tight junctions forming the blood-CSF barrier

Ventricles of the Brain

1. Lateral ventricle: found inside the cerebral hemispheres; divided into central portion and lateral extensions or horns

2. Third ventricle: small, slit-like cavity in the center of the diencephalon between the two thalami; continuous with the cerebral aqueduct of Sylvius

3. Fourth ventricle: diamond-shaped cavity located between the pons and the cerebellum

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• The meninges are membranous coverings of the brain and spinal cord.

  • Layers of the meninges:

    • Pachymeninx (dura mater)

      • Composed of dense, fibrous tissues

      • Contains periosteal layer and meningeal layer

      • Dural venous sinuses located between the two layers

    • Leptomeninges

      • Arachnoid mater

        • Located between the dura and pia mater

        • Has a microscopic appearance of spider web

        • Contains arachnoid granulations that allow CSF to re-enter circulation

      • Pia mater

        • Located underneath the sub-arachnoid space

        • Tightly adhered to the surface of the brain and spinal cord

• The dura mater is the outermost layer of the meninges.

  • Composed of dense, fibrous tissues

  • Contains periosteal layer and meningeal layer

  • Dural venous sinuses located between the two layers

  • Dural reflections or dural folds help hold the brain in place within the skull.

    • Falx cerebri is the largest dural fold, lies in the longitudinal fissure.

    • Tentorium cerebelli is oriented horizontally between the cerebrum and cerebellum.

• The arachnoid mater is located between the dura and pia mater.

  • Has a microscopic appearance of spider web

  • Contains arachnoid granulations that allow CSF to re-enter circulation.

• The pia mater is located underneath the sub-arachnoid space.

  • Tightly adhered to the surface of the brain and spinal cord

  • The only covering to follow the contours of the brain (the gyri and fissures)

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• The subarachnoid space is located between the arachnoid and pia mater.

  • Occupied by thin, connective tissue trabeculae

  • Contains cerebrospinal fluid (CSF)

• The arachnoid granulations allow CSF to re-enter circulation via the dural venous sinuses.

• The pia mater is tightly adhered to the surface of the brain and spinal cord.

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• Cerebrospinal fluid (CSF) is a colorless fluid that circulates within the ventricles, central canal of the spinal cord, and subarachnoid space.

  • Acts as a cushion for the brain and spinal cord

  • Formed in the ventricles from the capillaries of the choroid plexus

  • CSF is absorbed from the subarachnoid space into the venous blood by the arachnoid villi and arachnoid granulations.

  • Functions of CSF include supporting brain growth, protecting against external trauma, removing metabolites, and transporting biological substances.

• Lumbar puncture is a clinical application for CSF analysis.

• Hydrocephalus is a pathological accumulation of CSF within brain spaces.

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• The brain is supplied with blood by the internal carotid artery and vertebral artery.

• The anterior cerebral artery supplies the medial and superolateral surfaces of the cerebral hemisphere.

• The middle cerebral artery supplies the entire lateral surface of the cerebral hemisphere except along the superolateral margin and occipital pole.

• The posterior cerebral artery supplies the inferior portion of the temporal lobe and occipital lobe.

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• The meninges are protective coverings of the central nervous system.

• The dura mater is the dense outermost fibrous covering of the brain.

• The dura mater has two layers: outer endosteal and inner meningeal.

• The dural reflections or dural folds include falx cerebri, falx cerebelli, tentorium cerebelli, and diaphragma sella.

• The dural venous sinuses are located between the two layers of the dura mater.

• The superior sagittal sinus is located at the attached border of the superior sagittal sinus.

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• Terminates into transverse sinus

  • Communicates with foramen cecum with the veins of the frontal air sinus & veins of the nose

• Inferior Saggital Sinus

  • Located at the posterior free border of falx cerebri

  • Joins the great cerebral vein of Galen to form the straight sinus

• Straight Sinus

  • Usually opens into the left transverse sinus

• Transverse Sinus

  • Paired sinus & the widest, begins at the internal occipital protuberance

  • Lies in the transverse groove of the skull & attached to the margin of the tentorium cerebelli

  • Terminates by becoming sigmoid sinus

  • Tributaries of transverse sinus:

    • Veins from cerebrum & cerebellum

    • Occipital diploic vein

    • Superior petrosal sinus

    • Superior sagittal sinus

    • Straight sinus

• Superior Petrosal Sinus

  • Very narrow sinus which begins in the posterior end of cavernous sinus

  • Runs along the upper border of petrous temporal bone

  • Attached to the margin of tentorium

  • Ends in the transverse sinus at the point where it continuous with sigmoid sinus

• Cavernous Sinus

  • Short wide channel that lies on the side of the body of sphenoid, extending from medial end of superior orbital fissure to apex of the petrous temporal bone

  • Tributaries:

    • Anterior: receives ophthalmic veins & spheno-parietal sinus

    • Posterior: receives one or more cerebral veins and a large superficial middle cerebral vein

    • Inferior: communicates with venous plexuses outside the skull through emissary veins

• Structures traversing the cavernous sinus:

  • Cranial Nerves III, IV, VI

  • Ophthalmic & maxillary divisions of trigeminal nerve

  • Internal carotid artery

• Cranial Arachnoid

  • Forms a fold between the cerebellum & medulla

  • At base of brain, enshrouds the olfactory bulbs & tracts, while outer surface stretches as continuous sheet from one temporal lobe to another

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• The sheet serves as a bridge over interpeduncular fossa & stems of lateral fissure

• Space in between arachnoid & pia is called subarachnoid space

• Cisterns:

  • Cisterna basalis:

    • Lies between the cerebrum divided by optic chiasm into two parts

    • Cisterna chiasmatis

    • Cisterna interpeduncularis

  • Cisterna magna:

    • Lies between splenium of corpus callosum & superior surfaces of the cerebellum & mesencephalon

• Cranial Pia Mater:

  • Closely applied on the external surface of the brain dipping in all fissures & sulci

  • Inner surface receives numerous attachments from processes of neuroglia resulting in pia-glial membrane

  • Sends strong vascular duplication into great transverse fissures of the encephalon

  • Transverse cerebellar fissure: between the cerebellum & medulla

  • Transverse cerebral fissure: between cerebellum, mesencephalon, diencephalon & overhanging cerebral hemispheres

  • Duplications spread over the 3rd & 4th ventricles and known as choroid plexus of these ventricles

• CSF Circulation

• Emissary Veins: veins that connect the veins outside the skull with dural venous sinuses

  • Parietal emissary vein

  • Emissary vein that passes through the foramen cecum

  • Mastoid emissary vein

  • Posterior condylar emissary vein

  • Emissary vein that passes the carotid canal

  • Ophthalmic vein

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• Cranial Nerves:

  • Olfactory

  • Optic

  • Oculomotor

  • Trochlear

  • Trigeminal

  • Abducens

  • Facial

  • Acoustic

  • Glossopharyngeal

  • Vagus

  • Accessory

  • Hypoglossal

• Classification of CN:

  • Purely sensory: afferent fibers, carry impulses towards the brain (CN I, II, VIII)

  • Purely motor: efferent fibers, carry impulses away from brain (CN III, IV, VI, XI, XII)

  • Mixed: both sensory & motor fibers (CN V, VII, IX, X)

• Summary of Cranial Nerves and their functions

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• Summary of Cranial Nerves and their functions (continued)

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• Spinal Nerves & Autonomics

• Spinal Nerve:

  • Union of dorsal roots and ventral roots of the spinal cord

  • Mixed nerves containing axons of both sensory and somatic motor neurons

  • 31 Nerves connecting the spinal cord and various body regions

• Plexuses:

  • Cervical plexus: originate from C1 to C4, innervate muscles attached to hyoid bone

  • Brachial plexus: from C5 to T1, supplies upper limb and shoulder

    • 5 major nerves derived from brachial plexus:

      • Musculocutaneous nerve

      • Axillary nerve

      • Radial nerve

      • Median nerve

      • Ulnar nerve

  • Lumbosacral plexus: from T12-L5, supply the lower limb

    • Branches:

      • Obturator nerve

      • Femoral nerve

      • Ischiatic or sciatic or tibial nerve

      • Common fibular nerve

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• Lumbosacral plexus (continued)

• Branches:

  • Obturator nerve

  • Femoral nerve

  • Tibial nerve

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• Common Fibular nerve:

  • Innervates lateral thigh and leg and some intrinsic muscles of the foot.

• Sciatic nerve:

  • Tibial and common fibular nerves are bounded by connective sheath, forming the sciatic nerve.

• Autonomic Nervous System:

  • Parasympathetic Division:

    • Preganglionic neurons come from the brain or sacral region of the spinal cord.

    • Synapse on ganglia located near or in effector organs.

  • Sympathetic Division:

    • Thoraco-lumbar region.

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• General Senses:

  • Light touch, pressure, touch, pain, temperature, awareness of limb position and motion.

• Receptors:

  • Specialized cells that recognize general senses.

  • Part of neurons that send signals.

• Five functional types of receptors:

  1. Mechanoreceptors: Mechanical deformation.

  2. Thermoreceptors: Temperature changes.

  3. Nociceptors: Stimuli that cause damage to tissues.

  4. Electromagnetic receptors: Changes in light intensity and wavelength.

  5. Chemoreceptors: Chemical changes associated with taste, smell, O2 and CO2 concentration in the blood.

• Classification of receptors according to origin or location of stimulus:

  1. Exteroceptors: Stimuli from outside the body.

  2. Interoceptors/Visceroceptors: Stimuli arising within the body.

  3. Proprioceptors: Respond to muscle or tendon stretch and help monitor body position.

• Types of receptors according to structure:

  • Non-encapsulated: Free nerve endings, Merkel's tactile receptors, hair root plexus.

  • Encapsulated: Meissner's corpuscles, Pacinian corpuscles, Kraus end-bulb receptor, Ruffini's receptors, muscle spindles.

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• Meissner's corpuscles:

  • Location: Papillary of the dermis, may be present in skin of nipples and genitalia.

  • Ovoid shape, consist of Schwann cells arranged transversely across the long axis of corpuscle.

  • Very sensitive to touch and rapidly adapting mechanoreceptors.

  • Distinguish two-point structures.

• Pacinian Corpuscle:

  • Pressure and vibration receptors.

  • Location: Deep dermis, joint capsule, internal organs.

  • Capsule consists of concentric lamellae of flattened cells.

  • Golgi mazzoni corpuscles (genital corpuscle) are similar to pacinian corpuscles but smaller in size.

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• Kraus end bulb:

  • Cold receptors.

  • Location: Dermis of the skin, conjunctiva, mucosa of the tongue, external genitalia (glans penis and clitoris).

• Golgi tendon organ:

  • For proprioception.

• Muscle Spindles:

  • For proprioception.

• General Sense Pathway:

  • First order neuron: N1 (Sensory neuron).

  • Second order neuron: N2 (Association neuron).

  • Third order neuron: N3 (Motor neuron).

• Functional classification of fibers:

  • Afferent fibers (sensory):

    • General Somatic Fibers (GSA): Carry exteroceptive and proprioceptive information.

    • General Visceral Afferent Fibers (GVA): Carry interoceptive information from receptors in visceral structures.

    • Special Somatic Afferent Fibers (SSA): Convey sensory information from special senses (eye, ear).

    • Special Visceral Afferent Fibers (SVA): Carry impulses from olfactory and gustatory receptors.

  • Motor fibers (efferent):

    • General Somatic Efferent Fibers (GSE): Innervate striated skeletal muscles.

    • General Visceral Efferent Fibers (GVE): Innervate smooth muscle, cardiac muscles, and regulate glandular secretion.

    • Special Efferent Fibers: Innervate musculature of branchiomeric origin.

    • Special Visceral Efferent Fibers (SVE): Innervate striated muscles derived from pharyngeal arches.

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• Afferent Fibers:

  • Motor Fibers with cell origin from the spinal cord, brainstem, and autonomic ganglia are referred to as General Efferent Fibers.

• Anterolateral system:

  • Lateral Spinothalamic tract: For pain and temperature except the head region.

  • Anterior Spinothalamic tract: For crude touch, light touch, and light pressure except the head region.

• General Senses:

  • Includes pain, temperature, touch, pressure, vibration, and proprioception.

  • Receptors for these sensations are distributed throughout the body.

• Specificity:

  • Allows each receptor to respond to a particular stimulus.

  • Simplest receptors are free nerve endings.

• General Sense Receptors:

  • Three basic types: Exteroceptors, proprioceptors, interoceptors.

  • Four specific types: Nociceptors, thermoreceptors, mechanoreceptors, chemoreceptors.

• Nociceptors (pain receptors):

  • Found in superficial portions of the skin, joint capsules, periostea of bone, around walls of blood vessels.

  • Free nerve endings with large receptive fields.

• Thermoreceptors (temperature sensors):

  • Free nerve endings located in the dermis of the skin, skeletal muscles, liver, hypothalamus.

  • Cold receptors are more numerous than warm receptors.

Page 24: Sensory Receptors

• No difference between warm or cold receptors structurally

• Krause end bulbs detect cold

• Ruffini endings detect warmth

• Mechanoreceptors are sensitive to stimuli that distort the cell membrane

• Three classes of mechanoreceptors: tactile receptors, baroreceptors, and proprioceptors

• Tactile receptors provide the sensation of touch, pressure, and vibration

• Baroreceptors detect pressure changes in blood vessels and digestive, reproductive, and urinary tracts

• Proprioceptors monitor the position of joints

• Various types of tactile receptors include free nerve endings, root hair plexus, Merkel discs, Meissner's corpuscles, Pacinian corpuscles, and Ruffini corpuscles

• Chemoreceptors can detect small changes in the concentration of specific chemicals or compounds

• They respond to water soluble and lipid soluble substances dissolved in surrounding fluid

• Chemoreceptors play a major role in the senses of taste and smell

Page 25: Cardiovascular

• The heart is a hollow muscular organ shaped like an inverted cone

• It is located between the lungs in the middle mediastinum

• The heart has two closed circuits: the pulmonary circuit and the systemic circuit

• The systemic circuit includes arteries, arterioles, capillaries, venules, and veins

• The heart is bounded by the sternum anteriorly and vertebrae posteriorly

• The pericardium is the connective tissue covering of the heart and base of the great vessels

• It has two layers: fibrous pericardium and serous pericardium

• The fibrous pericardium is tough and non-elastic, preventing overstretching of the heart

• The serous pericardium is a thinner, more delicate membrane with a parietal layer and a visceral layer

• The walls of the heart consist of the epicardium, myocardium, and endocardium

• The heart has four chambers: right atrium, left atrium, right ventricle, and left ventricle

• The chambers are separated by internal structures called septa

• The heart has valves, including atrioventricular valves and semilunar valves

Page 26: Heart Anatomy

• The right atrium receives blood from various sources and is divided into a right auricle and a posterior principal cavity or sinus venarum

• The wall of the right atrium contains musculi pectinati and a crista terminalis

• The left atrium receives blood from the pulmonary veins and has a smooth wall except for the auricular portion

• The ventricles are the actual pumps of the heart and have thicker walls than the atria

• The fibrous skeleton of the heart provides support and attachment for muscles and valves

• Coronary arteries supply blood to the heart, including the left coronary artery and the right coronary artery

• Coronary veins drain blood from the heart, including the coronary sinus and its tributaries

• The heart has major types of blood vessels: arteries, veins, and capillaries

Page 28: Major Types of Blood Vessels

• Arteries have a smaller lumen and thicker walls compared to veins

• Arteries stretch and recoil to increase pressure, while veins distend but do not have high-pressure blood flow

• Arteries transport oxygenated blood, except for the pulmonary artery, while veins transport deoxygenated blood, except for the pulmonary vein

• Capillaries are the smallest blood vessels and are involved in the exchange of nutrients and waste materials between blood and tissue cells

Page 29: Major Arteries of Systemic Circulation

• The aorta is the largest artery of the body and has four parts: ascending aorta, arch of the aorta, thoracic/descending aorta, and abdominal aorta

• The ascending aorta arises from the left ventricle and gives rise to the right and left coronary arteries

• The arch of the aorta continues from the ascending aorta and branches into the brachiocephalic artery, left common carotid artery, and left subclavian artery

• Common carotid arteries supply blood to the head and neck, with the right common carotid artery arising from the brachiocephalic artery and the left common carotid artery arising from the arch of the aorta

• Subclavian arteries supply blood to the upper extremities

• Various arteries supply blood to different parts of the body, including the axillary artery, brachial artery, radial artery, and ulnar artery

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• Thoracic or descending aorta

  • Begins from the end of the arch of the aorta at the level of T4

  • Descends to the diaphragm to become abdominal aorta

• Abdominal or ascending aorta

  • Continuation of the thoracic portion

  • Passes through the diaphragmatic opening at the level of T12 into the abdominal cavity

• Branches of thoracic aorta

  • Visceral branches

    • Bronchial, esophageal, pericardial & mediastinal arteries

  • Parietal branches

    • Posterior intercostal, subcostal & superior phrenic arteries

• Branches of abdominal aorta

  • Visceral

    • Paired: middle suprarenal, renal & testicular or ovarian

    • Single: coeliac, superior mesenteric, inferior mesenteric

  • Parietal

    • Paired: inf. Phrenic, lumbar & common iliac

    • Single: median sacral

  • Terminal branches

    • Right & left common iliac arteries

    • Median sacral arteries

• Divisions:

  • Internal iliac / hypogastric – supplies pelvic organs

  • External iliac – continues as femoral artery

• Blood Supply of the Brain

  • Main sources:

    • Internal carotid artery

    • Vertebral artery

• Blood Supply of the Lower Extremities

  • The common iliac artery at the level of the sacroiliac joint divides into:

    • Internal iliac artery

    • External iliac artery

  • Internal iliac artery supplies the pelvic organs

  • External iliac artery continues in the thigh as femoral artery, then at the back of the knee becomes popliteal artery, which divides into anterior & posterior tibial arteries

• Major Veins of Systemic Circulation

  • Superior vena cava

    • Drains deoxygenated blood from the head, neck, upper limb & thorax into the right atrium

  • Inferior vena cava

    • Drains deoxygenated blood from the lower parts of the body into the right atrium

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• Azygous System

  • Located on either side of the vertebral column

  • Drains the viscera within the mediastinum, as well as the back and thoracoabdominal walls

  • Consists of the azygos vein and its two main tributaries: the hemiazygos vein and the accessory hemiazygos vein

  • Azygous vein

    • Formed by the union of right ascending lumbar & right subcostal vein

    • Passes the diaphragm and opens into the back of SVC

  • Hemizygous vein

    • Formed by the union of left ascending lumbar & left subcostal vein

    • Opens into azygous vein at T7 level

  • Join the SVC & IVC

  • Responsible for draining the thoracic wall and upper lumbar region

  • Provides important collateral circulation between the superior and inferior venae cavae should they become obstructed

• Portal Circulation

  • A system of blood vessels that begins and ends in capillaries

  • Connecting veins between arterial and venous circulation

  • Veins between the connected capillaries are called portal veins

  • Blood draining from the capillary bed of one structure flows through larger vessels to supply the capillary bed of another structure, before returning to the heart

  • Hepatic portal carries nutrients from digestion to the liver to store and metabolize, after a meal

  • Blood from the intestines goes through portal circulation to the liver

  • From intestinal veins, it goes through superior mesenteric veins, joins splenic vein, then portal vein, and finally reaches the liver

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• Cardiovascular system

  • Composed of:

    • A. heart

    • B. blood vessels

• Heart

  • Main pumping organ and propels blood to different areas of the body

  • Location: middle mediastinum, between the lungs and on its posterior boundary is the vertebral column

  • Size: as big as the fist

  • Generates blood pressure

    • Contraction generates blood pressure required for blood flow through blood vessels

  • Routes blood

    • The heart separates the pulmonary & systemic circulations to ensure the flow of oxygenated blood to tissues

  • Ensures one-way blood flow

    • The valves of the heart ensure one-way flow of blood through the heart to the blood vessels

  • Regulates blood supply

    • Changes in heart rate and force of heart contraction match blood flow to changing metabolic needs of the tissues during rest, exercise, and changes in body position

  • Cone shape, apex directing on the 5th ICS MCL

  • Base directed posterior, superiorly to the right

  • Anteriorly lies below the 2nd rib and relatively fixed because of the great blood vessels

  • Apex is freely movable

• Pericardium

  • A. fibrous pericardium

  • B. serous pericardium

• Fibrous pericardium

  • Dense inelastic connective tissue

  • Anchors the heart within the mediastinum

  • Protects the heart and prevents overstretching

• Serous pericardium

  • Forms double layers

    • A. parietal layer

      • Outer layer fused with the fibrous pericardium

    • B. visceral layer

      • Inner layer, tightly adhering on the surface of the heart (superior)

      • Also called epicardium

• Pericardial cavity

  • Space between the parietal & visceral layer

  • Filled with slippery pericardial fluid to reduce friction during heart movement

  • Inflammation: pericarditis

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• External features of the heart

  • The right & the left atria are located at the base of the heart

  • The right & left ventricles extend from the base of the heart towards the apex

• Blood supply

  • A. right & left coronary arteries

    • Direct branch of the aorta

  • B. coronary sinus

• Chambers of the heart

  • A. atrium

    • Right and left atrium

  • B. ventricles

    • Right & left ventricles

• Septa

  • A. interatrial septum

    • Between two atrium

  • B. interventricular septum

    • Between two ventricles

• Heart valves

  • Called cusps

  • A. atrioventricular valves

    • Between atrium and ventricles

    • A.1. tricuspid valve (RA/RV)

    • A.2. mitral valve or bicuspid valve (LA/LV)

  • B. semilunar valves

    • B.1. pulmonic valve (RV/PT)

    • B.2. aortic valve (LA/AA)

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• Features of the right atrium and left atrium

  • Size: wider (right atrium), narrower (left atrium)

  • Auricle-ear-like structure outside the atrium: present in bigger size (right atrium), present in smaller size (left atrium)

  • Pectinate muscles-parallel muscle bundles: found in right atrium auricle & anterior wall of the right atrium, present in left atrium

  • Fossa ovalis-remnant of fetal foramen ovale (oval depression seen at the septal wall): none (right atrium), present (left atrium)

• Openings of blood vessels

  • Superior vena cava, inferior vena cava, coronary sinus (right atrium)

  • 4 pulmonary veins (left atrium)

• Features of the right ventricle and left ventricle

  • Lumen (space): crescent shape (right ventricle), circular (left ventricle)

  • Thickness of wall: thin (right ventricle), thicker (left ventricle)

  • Chorda tendineae-tendon-like chords attached to the cusp valves: present (right ventricle), present (left ventricle)

  • Papillary muscles-nipple-like attached to chorda tendineae: present (right ventricle), present (left ventricle)

  • Trabeculae carnae-coarse cardio muscle fiber ridges along the cardiac wall: present (right ventricle), present (left ventricle)

  • Moderator band-specialized muscle column at the septal wall- it prevents overdistention of right ventricle: present (right ventricle), none (left ventricle)

  • Pulmonic valve: present (right ventricle), none (left ventricle)

• Conduction system of the heart

  • SA node or the sino-atrial node: pacemaker or site where the rhythm of electrical excitation causes the heart to contract

  • Atrioventricular node or the AV node: lies at the base of the right atrium near the interatrial septum

  • Atr

Page 35:

Cardiac Cycle

• One heartbeat consists of the contraction and relaxation of atria and ventricles

• The purpose is to force blood from areas of higher pressure to lower pressure

• Systole phase: contraction phase following depolarization

• Diastole phase: relaxation phase following repolarization

Blood Vessels

Arteries

• Elastic arteries: also known as conducting arteries, carry large volumes of blood away from the heart

• The walls of elastic arteries are resilient due to a high density of elastic fibers and few smooth muscle cells

• Muscular arteries: medium-sized arteries that distribute blood to various organs

• Arterioles: smaller branches of arteries that can constrict to control blood flow

Veins

• Collect blood from all tissues and organs and return it to the heart

• Classified according to size: venules, medium-sized veins, and large veins

• Medium-sized veins have thin tunica media and few smooth muscle cells

• Large veins have all three tunica layers and a thick tunica externa

Page 36:

Difference Between Arteries and Veins

• Arteries carry blood away from the heart, while veins carry blood toward the heart

• Arteries have thick walls and carry blood under high pressure, while veins have thin walls and carry blood under low pressure

• Arteries have a pulse flow, while veins have a smooth flow

• Arteries have a narrow lumen diameter, while veins have a large lumen diameter

• Arteries do not have valves, while veins have valves

• Arteries carry oxygen-rich blood (except pulmonary artery), while veins carry oxygen-poor blood (except pulmonary veins)

Capillaries

• Function: material exchange with tissues

• Capillaries have low pressure and extremely narrow lumen diameter

• Capillaries have a single tunica intima layer and lack smooth muscle and elastic fibers

Page 37:

Lymphatics

• Function of the Lymphatic System:

  • Returns leaked fluids from the blood vascular system back to the blood

  • Removes foreign material from the lymph stream

  • Provides a site for immune surveillance

  • Transports absorbed lipids from meals

• Consists of three parts: lymphatic vessels, lymphatic organs, and lymph nodes

Lymphatic Vessels

• Lymph capillaries: blind-ended tubes where the transport system begins, permeable and found in almost all organs except CNS, bone, teeth, and bone marrow

• Lymphatic collecting vessels: similar in structure to veins but with thinner walls, collect lymph from lymphatic capillaries

• Lymphatic trunks: formed by the union of the largest collecting vessels, drain large areas of the body

• Lymphatic ducts: right lymphatic duct and thoracic duct, empty into the internal jugular vein and subclavian vein

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Lymph Transport

• Lymphatic system lacks an organ that acts as a pump

• Lymphatic system is maintained by the milking action of active skeletal muscles, pressure changes in the thorax, valves to prevent backflow, and pulsation of nearby arteries

• Pathogens and cancer cells can spread through the lymphatic capillaries

Similarities and Differences between Lymph Vessels and Blood Vessels

• Similarities:

  • Lined with a simple squamous endothelium

  • Have fibrous connective tissue adventitia wrapping their outer surfaces

  • Transmit fluid in a single direction with little or no backflow permitted

• Differences:

  • Lymph vessels are delicate and thin-walled, lack a tunica media with smooth muscle

  • Lymph vessels transmit lymph, while blood vessels transmit blood

  • Lymph vessels have valves, while only some veins and no arteries have valves

  • Lymph vessels form an open system, while blood vessels form a closed system

Lymphatic Organs

• Lymph nodes: filter lymph and add antibodies, contain macrophages and play a role in immune response

• Thymus gland: important during early years of life, produces immunocompetent cells

• Spleen: largest lymphoid organ, involved in lymphocyte proliferation, immune surveillance and response, and blood cleansing

• Mucosa Associated Lymphoid Tissues (MALT): tonsils and Peyer's patches

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Lymph Nodes

• Distributed along lymphatic vessels, filter lymph and add antibodies

• Macrophages within lymph nodes engulf and destroy bacteria, cancer cells, and foreign materials

• Structure: fibrous capsule, cortex with primary follicles of lymphocytes, medulla with medullary cords and sinuses

Thymus Gland

• Found in the neck and thorax, prominent in newborns and atrophies after puberty

• Continues to produce immunocompetent cells even after atrophy

Spleen

• Soft, blood-rich organ located in the abdomen

• Functions: lymphocyte proliferation, immune surveillance and response, blood cleansing

• Structure: surrounded by a fibrous capsule, contains lymphocytes, macrophages, and erythrocytes

Page 40: Lymphoid Tissues and Mucosa-Associated Lymphoid Tissues (MALT)

• Red pulp and white pulp are two components of the spleen.

  • Red pulp is where worn-out red blood cells (RBCs) and blood-borne pathogens are destroyed.

    • Composed of macrophages and erythrocytes.

  • White pulp is where immune functions take place.

    • Composed mainly of lymphocytes.

Mucosa-Associated Lymphoid Tissues (MALT)

• MALT is a set of lymphoid tissues located in mucous membranes of the body.

• It helps protect against pathogens entering the body.

• Includes:

  • Tonsils

  • Peyer's patches

  • Appendix

Tonsils

• Tonsils are a ring of lymphoid tissues around the entrance of the pharynx (Waldeyer's Ring).

• Types of tonsils:

  • Palatine tonsils: Located on either side at the posterior end of the oral cavity.

  • Pharyngeal tonsil (adenoids): Located on the posterior wall of the nasopharynx.

  • Lingual tonsil: Located at the base of the tongue.

• Tonsils are not fully encapsulated.

• They have invaginations forming blind-ended structures called crypts, which trap bacteria and particulate matters.

Peyer's Patches (GALT)

• Peyer's patches are large clusters of lymph nodules found in the ileum.

• They consist of macrophages that capture and destroy bacteria, preventing them from reaching the intestinal wall.

Appendix

• The appendix is a tubular offshoot of the first portion of the large intestine.

• It contains a high concentration of lymphoid tissues.

• The appendix generates many memory lymphocytes for long-term immunity.