- Nervous System is a group of tissues composed of highly specialized cells possessing the characteristics of excitability and conductivity
MORPHOLOGICAL DIVISIONS: A. CENTRAL NERVOUS SYSTEM 1. Brain 2. Spinal cord B. PERIPHERAL NERVOUS SYSTEM 1. Cranial Nerves (12 pairs) 2. Spinal Nerves ( 31 pairs) 3. Autonomic Nervous System
FUNCTIONAL DIVISIONS:A. SOMATIC EFFERENT - innervating somatic structures like skeletal muscles and skin.B. VISCERAL EFFERENT - innervating visceral or involuntary structures like smooth muscles, cardiac muscles and glands. This is the autonomic nervous system
TYPES OF CELLS IN THE NERVOUS SYSTEM- The nervous system is composed of a special tissue containing two major types of cells: 1. Neurons - the active conducting elements 2. Neuroglia - the supporting elements
NEURON- basic unit of the nervous system which conducts electrical impulses from one partof the body to another-consists of a cell body (perikaryon),containing a single nucleus, and processestransmitting impulses to and from the body
TWO TYPES OFPROCESSES A. DENDRITES – group of short, unsheathed processes arranged like branches of a tree that transmit impulses toward the cell body B. AXONS – a single, elongated sheathed process conducting impulses away from the cell body. ACCESSORY CELLS – the non nervous elements consist of blood vessels, connective tissue, and supporting cells known collectively as neuroglia
SYNAPSE- point of connection between neurons.The axon of oneneuron makes functional contact with dendrites of anotherneuron.Main neurotransmitters :1. epinephrine (adrenalin)2. norepinephrine (nor adrenaline)3. acetylcholine NERVE IMPULSEA. MYELIN SHEATH – insulating material covering axons in central andperipheral nervous system- the thicher the myelin sheath is, the faster the passage of nerveimpulse will be.- the electril impulse jumps from node to node in myelin sheath insteadof traveling continuously along the nerve fiber. (SALTATORYCONDUCTION OF IMPULSES)
CENTRAL NERVOUS SYSTEM- Central nervous system includes the brain and spinal cord.- It is divided grossly into gray and white matter: A. Gray matter - so called because of its appearance and preponderance of nerve cell bodies and true dendrites. B. White matter - composed chiefly of myelinated nerve fibers - white in gross appearance - and few, if any, nerve cell bodies. - In the spinal cord an H-shaped central region of gray matter is surrounded by white matter
BRAIN- part of the central nervous systemcontained within the skull.- most complex and largest mass of nervoustissue in the body and contains literallybillions of nerve cells.- The average weight of the human brain inthe adult is approximately 1380gms in themale and 1250 grams in the females.
EMBRYOLOGICAL DIVISIONS OF THE BRAIN1. Forebrain (Prosencephalon) a. Telencephalon (cerebrum) b. Diencephalon ( thalamus, hypothalamus, epithalamus, subthalamus)2. Midbrain (Mesencephalon) a. Corpora quadrigemina (tectum) - 2 superior colliculi 2 inferior colliculi b. Cerebral peduncles c. Cerebral Aqueduct of Sylvius (iter)3. Hindbrain (Rhombencephalon) a. metencephalon (cerebellum, pons) b. myelencephalon (medulla oblongata)
1. PROSENCEPHALONA. TELENCEPHALON (CEREBRUM) - represents seven-eights of weight ofbrain - responsible for discriminatoryidentification of and integration ofsensory information, memoryreasoning, - for use of language - for emotional behavior - for initiation of movement
FISSURES OF CEREBRUM1. Longitudinal Fissure - runs from the posterior to the anterior aspects almost completely dividing it into 2 hemispheres. - each hemisphere has a full set of centers for sensory and motor activities of the body, and each associated with one side of the body. - the hemispheres are connected in themidline by the corpus callosum
2. Lateral Sylvian fissure- between the frontal and parietal lobes above and temporal lobe below.- associated with centers for speech and hearing.
3. Central Sulcus (RolandicFissure) - between frontal and parietal lobes- associated with centers for both motor and sensory functions.
4. Transverse fissure - between the cerebellum and the cerebrum5. Parieto - occipital fissure - between the occipital and parietal lobes.6. Calcarine fissure - found in the occipital lobe perpendicular to parieto occipital fissure around which is the visual center.
LOBES OF THE CEREBRAL CORTEX1. Frontal Lobe - includes all the cortex lying anterior to the central sulcus of Rolando and above the lateral sulcus Sylvius - center for motor functions and personality
2. Parietal Lobe- lies posterior tocentral sulcus ofRolando and abovelateral Sylvianfissure.- center for sensoryfunctions
3. Temporal Lobe- lies beneath thelateral sulcus ofSylvian- center for hearingand olfaction
4. Occipital Lobe- occupies theposterior extremityof the cerebralhemisphere behindparieto-occipitalfissure- visual center
5. Insula ( Island of Reil)- exposed when thelips of lateralSylvian fissure areseparated
FUNCTIONS OF THE CEREBRUM 1. seat of advanced intellectual functions like memory storage, recall, learning and reasoning for comprehension and execution of language. 2. perception of all sensations and sites where one modality of sensation can be integrated with others. 3. initiation of movements
FUNCTIONAL AREAS OF THE CEREBRUM2. Primary Motor Area or Pre-central gyrus - lies in the frontal lobe immediately anterior to the central sulcus - controls voluntary movements in the opposite side of body. - the body is represented with head down and lower extremities up and medially in the cerebrum. - Brodmanns area 4
2. Pre-motor Area- in front of themotor area- exerts acontrolling influenceover the motorarea, ensuring anorderly series ofmovementsnecessary forspeech.
4. Primary sensory/Somesthetic Area or Post-central gyrus - lies behind the central sulcus of Rolando in parietal lobe - sensations of pain, temperature, pressure and touch, position and movement sensation from opposite side of body are received and interpreted here. - Brodmanns area 3,1,2
5. Motor speech area- lies in inferiorfrontal gyrus ofdominanthemisphere- Brocas area(Brodmanns area45, 44)
6. Sensory speech area:- lies in temporal lobes posterior to auditory area of dominant hemisphere- Wernickes area (Brodmanns area 22)
7. Auditory or Hearing Area(transverse gyri of Heschl) - lies below lateral sulcus within the temporal lobe - center for hearing - Brodmanns area 41 & 42
8. Visual area:- around the calcarine fissure, including greater part of the occipital lobe- Brodmanns area 17
9. Olfactory or smell area- within the temporallobe
10. Taste Area- above lateral sulcus into the deep layers of the sensory area
BASAL GANGLIAmasses of gray matter embedded in the white matter of the cerebral hemispheres- include the caudate nucleus (medial portion) and the putamen and globus pallidus called lentiform nucleus.- constitute the corpus striatum- Basal ganglia play a role in the control of motor function, and injury produces unilateral or bilateral tremor, rigidity and uncontrolled aimless movements.
B. DIENCEPHALON1. Thalamus - paired mass of gray matter situated below corpus callosum. - subcortical sensory integrating cortex- relay center for sensory impulses (except olfactory) from peripheral receptors to cerebral cortex; responsible for crude awareness of sensation- processes and relays coordinating motor impulses from the basal ganglia and cerebellum to the cerebral motor cortex.- relay and integration center for emotional behavior
2. Hypothalamus- involved in the regulation of body temperature, feeding activities,concentration and volume of extracellular fluid, autonomic nervous system responses, endocrine functions.
2. MESENCEPHALON- connects the forebrain and hindbrain- concerned with motor coordination- connects the pons and the cerebellum with the cerebrum consists of:
a. Cerebral Peduncles (found anteriorly) - pair of cylindrical bodies made up of nerve fiber tracts which connect the forebrain with the hindbrain.b. Corpora Quadrigemina ( found posteriorly) - 4 rounded nuclear masses 1. superior colliculi - upper 2; for visual reflexes 2. inferior colliculi - lower 2; for auditory reflexes
3. RHOMBENCEPHALON CEREBELLUM ( Part of metencephalon )- oval in shape with a central constriction and lateral expanded portions.- the constricted central portion is called the vermis (Latin of worm) and the lateral expanded portions the hemispheres
- divided into lobes by deep and distinct fissures, these lobes include the:a. anterior concerned with the function ofb. posterior / movementsc. flocculonocular lobes - concerned with the function of equilibrium
PONS ( Part of metencephalon )- lies anterior to the cerebellum and between the midbrain and medulla.- bridge-like structure, consisting almost entirely of white matter linking the various parts of the brain
MEDULLA OBLONGATA ( myelencephalon )- continuous with the spinal cord inferiorly and with the pons superiorly- lies ventral to the cerebellum- has a number of vital regulatory and reflex centers, including those controlling the circulatory system, breathing, swallowing, vomiting, coughing, sneezing.
VENTRICLES OF THE BRAIN- spaces inside brain filled with cerebrospinal fluid.- the Ventricular System includes: 1. lateral ventricle - found inside the cerebral hemispheres - each lateral ventricle communicates with the third ventricle by way of an interventricular foramen (foramen of Monroe) 2. third ventricle - small, slitlike cavity in the center of the diencephalon in between the 2 thalamic continuous with the cerebral aqueduct of Sylvius, a canal which passes through the midbrain. 3. fourth ventricle - lies between the cerebellum on the posteriorly side and the pons and medulla on the anteriorly side. - communicates with subarachnoid space through Foramen of Luschka and Magendie
MENINGES-Three membranes collectively known as the meninges provide protection to the brain and spinal cord- from outside in, these are the: A. Dura mater B. Arachnoid mater C. Pia mater
A. DURA MATER- the dura mater (latin for hard mother), the outer meninx, is made of dense, fibrous tissue.- There are 2 portions of the dura mater 1. cranial 2. spinal
B. ARACHNOID MATER- delicate serous membrane located between the dura and pia.- As the name implies, it has the microscopic appearance of a spider web- the cranial portion invests the brain loosely and, with the exception of the longitudinal fissure, it passes over the various convolutions and sulci and does not dip down into them
C. PIA MATER- The pia mater (gentle mother) is a vascular membrane consisting a plexus of fine blood vessels held together by areolar connective tissue.- The cranial portion invests the surface of the brain and dips down into the sulci.
CEREBROSPINAL FLUID- the cerebrospinal fluid circulating within the ventricles, the central canal of the spinal cord and also within the subarachnoid space.- colorless, with a composition similar to that of lymph
SPINAL CORD- the elongated and almost cylindrical part of the CNS, which lies within the vertebral canal.- is continuous with the medulla oblongata above and extends from the level of foramen magnum to the lower border of 1st lumbar vertebra in adult and level of L3 vertebra in children.- average length: 45 cm
- 2 enlargements: 1. cervical enlargement (where nerve supply of arms arises from) - level of 4th cervical to 2nd thoracic vertebrae 2. lumbar enlargement (where nerve supply of legs arises from) - level of 10th thoracic vertebra; widest at the 12th thoracic vertebra - it narrows down as a conus medullaris, where it gives rise to the thread-like filum terminale that terminates in the first coccygeal vertebra. - the lumbar and sacral spinal nerves descend along the filum terminale in a bundle known as the cauda equina
PERIPHERAL NERVOUS SYSTEM:SPINAL AND CRANIAL NERVES I . SPINAL NERVES - a bundle of nerve fibers attached to spinal cord - 31 pairs of nerves called spinal nerves arise from the spinal cord along almost its entire length and emerge from the vertebral canal through the intervertebral foramina
1. dorsal root - containing fibers of sensory neurons2. ventral root - containing fibers of motor neurons - these 2 roots join together to form spinal nerve
- There are eight pairs of cervical spinal nerves, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal
PLEXUSES- group of nerve fibers from ventral rami of cervical , lumbar and sacral spinalnerves. Posterior rami never form plexuses.1. Cervical Plexus - formed by the first 4 cervical nerves (C1C2C3C4) - this supplies the back and sides of the head and the front of the neck - gives off the phrenic nerve to the diaphragm2. Brachial Plexus - lower 4 cervical (C5C6C7C8) nerves and 1st thoracic (T1) supplies the skin and muscles of the upper limb - gives off large nerves: circumflex, radial. median ulnar and musculocutaneous nerves.
3. Lumbar Plexus- from L1 -L4 spinal nerves a. Obturator Nerve - arising from anterior division of L2L3L4 spinal nerves - supplies the muscles and skin on medial aspect of thigh b. Femoral nerve - arising from the posterior divisions of L2L3L4 spinal nerves - supplies muscles and skin on anterior aspect of the thigh
4. Sacral Plexus- from L4L5S1S2S3 spinal nerves- the largest branch of which is the sciatic nerve (the largest nerve in the body)
The thoracic spinal nerves do not form plexuses.T1 - T11 spinal nerves - INTERCOSTAL NERVEST 12 spinal nerves - SUBCOSTAL NERVE Sciatic Nerve divides into: a. tibial nerve - supplies most of the posterior thigh muscles, posterior leg and sole by dividing into medial and lateral plantar nerves b. common peroneal nerve - supplies short head of biceps femoris and anterolateral leg and dorsum of the foot.
II. CRANIAL NERVES- The cranial nerves are 12 pairs of symmetrically arrangednerves attached to the brain.- The cranial nerve includes the following: 1. Olfactory (I) 2. Optic (II) 3. Oculomotor (III) 4. Trochlear (IV) 5. Trigeminal ( V) 6. Abducens (VI) 7. Facial ( VII) 8. Vestibulocochlear (acoustic) (VIII) 9. Glossopharyngeal (IX) 10. Vagus (X) 11. Accessory (XI) 12. Hypoglossal (XII)
CLASSIFICATION OF CRANIAL NERVES SENSORY NERVES - carry impulses towards brain. Also called afferent fibers - cranial nerves I (olfactory), II (optic) and VIII (vestibulocochlear) however carry only sensory fibers ( from the nose, eye, and ear, respectively)
MOTOR NERVES - carry impulses away from the brain.Also called efferent fibers - cranial nerves III (oculomotor), IV(trochlear) and VI (abducens), which supply the eye muscles, XI(accessory) and XII (hypoglossal), which innervates the tongue, have beendescribed as purely motor nerves.
MIXED NERVES- carry both sensory and motor nerve fibers- cranial nerves V, VII, IX, X are mixed nerves
AUTONOMIC SYSTEM- The autonomic nervous system may be divided, both functionally and structurally into sympathetic and parasympathetic nervous divisions.1. Sympathetic or Thoracolumbar Divisions of the autonomic nervous system arises from all the thoracic and the first three lumbar segments of the spinal cord.2.Parasympathetic or Craniosacral Divisions of the autonomic nervous system arises from the third, seventh, ninth, and tenth cranial nerves and from the second, third, and fourth sacral segments of the spinal cord.
FUNCTIONS OF THE ANSORGAN SYMPATHETIC PARASYMPATHETICHEARTSA NODE Increased rate Decreased rateMUSCLE Increased force of contractionLUNGSBronchi Dilation ConstrictionStomach Dec. motility and Increased motilityWall tone; Stimulates secretion ofGlands alkaline juice with low Stimulates secretion enzyme activity of acid with high enzyme
FUNCTIONS OF THE ANSORGAN SYMPATHETIC PARASYMPATHETICSUPRARENALGLAND Secretion of NoneMedulla epinephrineURINARYBLADDERWall Inhibition ExcitationSphincter Excitation InhibitionPENIS EJACULATION ERECTION
FUNCTIONS OF THE ANSORGAN SYMPATHETIC PARASYMPATHETICARRECTOR PILIMUSCLES OF HAIR CONTRACTION NoneFOLLICLESARTERIOLESSplanchnic CONSTRICTION DILATATIONregion and skin