Anatomical & Function of CNS PDF

Introduction: The vast complexity of body function controlled by the nervous system is unique. These function ranges from the somatic motor & sensory function to highly integrated functions such as memory learning , emotion & perception.  The nervous system respond to changes in the external & i...

Introduction: The vast complexity of body function controlled by the nervous system is unique. These function ranges from the somatic motor & sensory function to highly integrated functions such as memory learning , emotion & perception.  The nervous system respond to changes in the external & internal environment. Anatomic divisions of the NS :
 Central Nervous System(CNS):  The CNS comprises brain & spinal cord.  The brain lying with the cranium of the skull & the spinal cord lying within the vertebral column. Peripheral Nervous System (PNS); consists of 43 pairs of nerves which enter & leave the CNS. include the cranial nerves 12 & the spinal nerves 31. physiological divisions of the NS :
 Somatic Nervous System: (SNS)  Mainly deals with voluntary movement such as skeletal muscle movement & the various somatic sensory function.  Autonomic Nervous System :(ANS) oWhich deals with involuntary control mechanism , such as regulation of the heart rate , blood pressure ,visceral function …. Brain:  The brain can be divided into four subdivisions:  Cerebrum (telencephalon).  Brain stem (mesencephalon). Midbrain , Pons & Medulla oblongata.  Cerebellum.  Diencephalon. Thalamus & hypothalamus  Cerebrum:( forebrain)  The largest part of the brain. Consists of the right & left cerebral hemisphere.  connected in the midline , by a bundle of fibers C shaped called the corpus callosum. That transmits messages from one side to another.  Each hemisphere controls opposite side of the body. Not all function of the hemisphere are shared.  In general , the left hemisphere controls : speech, comprehension , writing & arithmetic. Also is dominant in hand use & language in about 92% of people.  right hemisphere controls creativity , spatial ability, artistic & musical skills.  The superficial layer of hemisphere is composed of grey matter (the cerebral cortex) means (bark).  Grey matter contains bodies of nerve cells.  This encloses a larger of white matter , contains axonal extension of neurons & their myelin sheath , inside which lie , a number of nuclei, known as the basal ganglia.  basal ganglia plays a very important role in the planning & control of movement.  The cerebral cortex has (elevations) folds is called a gyrus & (depressions) grooves between folds is called a sulcus.  Which greatly increase surface area , allowing more neurons to fit inside the skull & enabling higher functions.  There are names for the grooves & folds that help define specific brain regions Eg: - postcentral & precentral gyrus , central & lateral sulcus.  Each hemisphere is divided into four lobes :- 1- Frontal lobe 2- Parietal lobe 3- Temporal lobe 4- Occipital lobe It is important to understand that each lobe of the brain does not function alone there are very complex relationships between the lobes of the brain &  also between right & left hemisphere. Frontal lobe:  The central sulcus forms borderline between the frontal lobe anteriorly & the parietal lobe posteriorly. Function:  Body movement (motor strip).  Personality , behavior, emotions.  Judgment, planning , problem solving.  Intelligence , concentration ,  self awareness. This is due to dopamine o The frontal lobe contains most of Dopamine delicate neuron in the cerebral cortex.  Speech: speaking, writing (broca’s area/ premotor cortex ). If Broca’s area is damaged , one may have difficulty moving the tongue or facial muscles to produce the sounds of speech (difficulty in speaking & writing). Parietal lobe:  Is positioned behind the central sulcus functions:  Interprets language ,words.  Sense of touch, pain , temperature (sensory strip).  Interprets signals from vision, hearing motor, sensory & memory.  Spatial & visual perception. Temporal lobe :  Lies on the lateral surface of the hemisphere below the lateral fissure (deep groove) that separates it from the frontal & parietal lobes above. It contains  the primary auditory area, which is the center of hearing.  Sequencing & organization.  New memory. (Wernicke’s area )  The parietal , temporal , occipital lobes meet in the angular gyrus. Just in front of this gyrus is an area of cortex called Wernicke’s area.  It often called the general knowing area interpretative area or gnostic are a , plays a crucial role in higher functions of the brain , such as thinking ,speech & language. oDamage to Wernicke’s area causes Wernicke’s aphasia. The individual may speak in long sentences that have no meaning. Occipital lobe:  The occipital lobe lies most posterior in the cerebral hemisphere.  In it is located the primary visual cortex the center for vision V1. ( color, light, movement). Note :  The postcentral lies immediately behind the central sulcus & form the primary sensory area , which perceive sensory information arriving from ski n , muscle, joints , the viscera …..  The precentral gyrus lies immediately in front of the central sulcus ,& this forms the primary motor area, which controls muscular movements… Brainstem :  The brainstem plays a vital role in the many essential functions.  It also a passage way to sensory & motor pathway & pain control center.  It represents the emergence area of most cranial nerve. Consists of the  Midbrain.  Pons.  Medulla oblongata. The midbrain :  Is continuous with the pons below & the diencephalon above. This small but  important structure plays crucial role in processing visual & auditory signals.  It is channel for spinal cord transmitting stimuli from head & body to the brain.  It divided into three portions : Tectem , Tegmentum & Cerebral peduncle.  It contains nuclei of cranial nerves III & IV which mediate pupillary reflexes eye movement. Facilitate various functions from hearing & movement to calculating responses & environmental change. The midbrain also contains the substantia nigra, an area affected in Parkinson's disease which enable movement & coordination.(Dopamine↓)  The pons :  Is continuous with the medulla & contains control centers for respiratory & cardiovascular systems.  The pons named for the Latin word for “bridge” so it is the connection between the midbrain & the medulla.  It is the origin for four cranial nerves, V ,VI, VII, VIII ,which  which enable a range of activities such as tear production, chewing , blinking & focusing vision , balance , hearing & facial expression.  It also contains nuclei that relay signals from the forebrain to the cerebellum ,  It deal with sleep , bladder control, hearing equilibrium ,tastes, swallowing , facial sensation & posture. The medulla oblongata:  It is cone-shaped neural mass, forms the lower part of the brainstem.  The word bulbar refer to nerve & tract connected to the medulla.  The medulla is essential to survival.  It contains motor & sensory nuclei of the throat , mouth & neck ,  nuclei for cardiovascular (regulate heart rhythm , blood flow) ,  respiratory control centers (breathing , oxygen & carbon dioxide levels )  it contains the olive & a pair of pyramids that contain the corticospinal fibers of the pyramidal tract, it ends at the bottom by the pyramidal decussation. a crossing region of the corticospinal tract. also contains gracilus & cuneate nuclei & the nuclei of cranial nerves IX,X , XI &XII.  Reticular formation of the brainstem extends from the medulla through the pons to the midbrain.  It is composed mainly of ascending & descending tracts & some nuclei.  Recticular formation plays an important role in the control of muscle tone & in arousal or alerting mechanism. o Muscle tone: State of maintained partial contraction(resistance to stretch) The spinal cord:  The spinal cord is a long ,thin ,tubular structure ,made up of nervous tissue that extend from the medulla oblongata in the brainstem & through a large opening in the bottom of the skull to the lumbar region of the vertebral column.  The center of it is hollow & contains a structure called central canal , which contains cerebrospinal fluid(CSF).  It supported by the vertebrae. The spinal cord protection is by vertebrae bone, meninges & CSF.  The spinal cord , like the brain is surrounded & protected by the three layers of membranes (the meninges ) :  The Pia mater , The arachnoid mater & The dura mater.  Grey &white matter are two different  In the brain ,grey matter refers to the darker, outer portion, while  white matter describes the lighter , inner section underneath  In the spinal cord this order is reversed. Grey matter forms the core of the spinal cord & appear like letter H in cross section ,  Grey matter , is primarily composed  While white matter surrounds the grey matter, is mostly made of axons.  It is made of ascending (sensory ) & descending (motor) tracts. consists of segments & divides into four region cervical ,thoracic, lumber & sacral.  These regions are broken down into 31 segments. with 31 pairs of spinal nerves  8 cervical segments forming 8 pairs of cervical nerves ( C8 between C 7 & T1)  12 thoracic segments forming 12 pairs of thoracic nerves.  5 lumbar segments forming 5 pairs of lumbar nerves.  5 sacral segment forming 5 pairs of sacral nerves.  each of which has a pair of nerve roots on each side,  The dorsal roots( posterior) carry impulses from peripheral receptors into the spinal cord (sensory).  While ,the ventral roots (anterior) carry impulses to periphery (motor) (i.e. muscle).  These two nerve root unite to form a spinal nerve in each side.  The spinal cord functions include:- 1-transmission of sensory (afferent) impulses coming from peripheral receptors to the brain & 2-of motor (efferent) impulses from the brain to motor neurons , which supply effector organs (i.e.muscle & glands ). 3-Serving as a center for some reflexes some of which are the basis of movement & posture ,e.g. stretch reflex.