Introduction to the Nervous System PDF

Introduction to the Nervous System Part 1  CENTRAL NERVOUS NERVOUS SYSTEM (CNS) SYSTEM Brain Stem PERIPHERAL NERVOUS SYSTEM (PNS)  How is the NS functionally organized?...

Introduction to the Nervous System Part 1  CENTRAL NERVOUS NERVOUS SYSTEM (CNS) SYSTEM Brain Stem PERIPHERAL NERVOUS SYSTEM (PNS)  How is the NS functionally organized? FROM:SKIN, MUSCLE, JOINTS, SPECIAL SENSES SOMATIC SENSORY (CONSCIOUS eg pain, temp, touch) SOMATIC SPECIAL SENSORY (CONSCIOUS vision, hearing, etc) NERVOUS SYSTEM* SOMATIC MOTOR (voluntary, muscle) NERVOUS SYSTEM SYMPATHETIC SYSTEM AUTONOMIC Heart, muscle NERVOUS of organs, SYSTEM* blood vessels, PARASYMPATHETIC glands SYSTEM [NB *The two systems are closely interwoven]  CELLULAR ARCHITECHTURE Nerve cells = neurons (>1bn) Connective tissue cells = neuroglial cells(neuroglia) Structures found in the Nervous system = aa, vv, capillaries, Blood vessels venous sinuses Ventricular System = spaces with CSF Coverings = meninges: 3 layers: dura mater, arachnoid mater, pia mater  Neurons and types DENDRITES CELL BODY/SOMA AXON has one axon that projects from the cell body for relatively a very short distance, before splitting into two branches —have no dendrites, MYELIN SHEATH has two extensions (one axon and one dendrite). transmission of sense.. AXON TERMINALS a type of neuron that possesses a single axon and many dendrites (and dendritic branches) NB.DIRECTION OF IMPULSE = dendrite->cell body-> axon. (D-> N-> A) Functional Classification of neurons Sensory Motor Autonomic motor Interneuron  Simplest/Functional Classification of Neurons CNS Interneurons 99% Motor Neurons Sensory Neurons (EFFERENT) (AFFARENT) Receptor stimuli Effector stimuli eg muscle, gland eg heat, pain  Simplest Classification of Neurons CORTEX CNS BRAIN PNS FIBRE TRACTS SC NERVE eg heat, pain eg muscle, gland  How do neurons communicate with neurons? Synapses Impulse is transmitted Neurotransmitters eg Adr, A Ch, DOPA across a synapse via a neurotansmitter  How do neurons send their impulses to skeletal muscle ? NEUROMUSCULAR JUNCTION SENSORY NEURON MOTORNEURON SENSORY RECEPTORS “Neuroglial” (glial cells) MULTIPOLAR NEURON PROTOPLASMIC ASTROCYTE OLIGODENDROCYTE MICROGLIAL CELL FIBROUS ASTROCYTE  Classify neuroglial CNS - glial cells eg. Astrocytes, ependymal (formation of CSF), oligodendrocytes (Formation of myelin around the tract), microglial PNS - Schwann cells (formation of myelin sheaths- axons of nerves) Reflex arc : defined as an involuntary, unlearned, repeatable, automatic reaction to a specific stimulus which does not require input from the brain. A reflex arc is a neural pathway that controls a reflex. Most sensory neurones have a synapse within the spinal cord, allowing for reflexes to take place without the involvement of the central nervous system (CNS) – speeding up the process. The pathway can be described as a ‘reflex arc’ which is made up of 5 components: A receptor An afferent fibre An integration centre – at the spinal cord An efferent fibre An effector  Monosynaptic Stretch Reflex The muscle stretch reflex is the most basic reflex pathway in the body. The monosynaptic reflex and relevant clinical issues. A monosynaptic reflex, such as the knee jerk reflex, is a simple reflex involving only one synapse between the sensory and motor neurone. If the reflex is not present it could be due to a problem with the receptor, the spinal cord, the motor neurone, the neuromuscular junction or the muscles. Reflex Biceps reflex Brachioradialis reflex Extensor digitorum reflex Triceps reflex Patellar reflex Achilles reflex  How is the NS structurallyorganized? CEREBRUM BRAIN CEREBELLUM CENTRAL BRAIN STEM Midbrain NERVOUS Pons Medulla SYSTEM SPINAL CORD NERVOUS SYSTEM CRANIAL NERVES PERIPHERAL NERVOUS SYSTEM SPINAL NERVES  BRAIN CNS Cerebrum Cerebellum Brain stem Midbrain SPINAL Pons Medulla CORD with with 31 SPINAL NERVE PAIRS PNS 12 CRANIAL Sensory Sensory NERVE & & OR PAIRS Motor Motor & AUTONOMIC  Grey Matter and White Matter in the NS Within the CNS: The cell bodies of neurons in the brain are found in the grey matter of the brain in the cerebral cortex or nuclei (notganglia) The axons of neurons in the brain (millions of them) are seen as white matter, and are arranged as fibre tracts that run in bundles or fascicles Outside the CNS: The cell bodies of neurons are found as collections called ganglia The axons of many neurons in the PNS are seen as NERVES, which consist of many axons running together. A nerve may be both motor and sensory if they are spinal nerves, but motor and sensory ± autonomic in cranial nerves Where is grey matter HORIZONTAL SECTION found in the cerebrum? cerebral cortex basal nuclei Where is white matter found in the cerebrum? tracts CORONAL SECTION  Where is grey and white matter found in the SPINAL CORD? grey white A FIBRE TRACT  Grey matter and white matter in the spinal cord In the spinal cord grey and white matter are easily separated In the “H” shaped grey matter there are sensory neurons (dorsal) interneurons motor neurons (ventral) In the white columns there are: ascending tracts descending tracts  Where is grey and white matter found in the BRAIN STEM? N N U U C C = DISCRETE COLLECTIONS L L OF GREY MATTER E E I I In the cerebrum, cerebellum and brain stem, the white and grey matter are not absolutely separate. A tract of “white” ascending or descending fibres sometimes passes through or between areas of grey matter on its ascent or descent Revise Name all the parts of the NS  The Spinal Cord CERVICAL= 8 SPINAL CORD SEGMENTS THORACIC = 12 ‘’ ‘ ‘ Spinal cord ends here LUMBAR = 5 + SACRAL = 5 (L1-2 /3) COCCYGEAL = 1-3 CONUS MEDULLARIS CAUDA EQUINA Vertebra Column ends here (Coccyx 5) Spinal Cord and Spinal nerves The Spinal Cord VERTEBRA The superior and inferior aspects of the vertebral body are lined with hyaline cartilage. Adjacent vertebral bodies are separated by a fibrocartilaginous intervertebral disc. Different types of vertebra AUTONOMIC NERVOUS SYSTEM SYMPATHETIC VS. PARASYMPATHETIC NERVOUS SYSTEM CRANIOSACRAL OUTFLOW THORACOLUMBAR OUTFLOW AUTONOMIC NERVOUS SYSTEM & SPINAL NERVES The Nervous System Introduction Part 2 THE SKULL 22 BONES, EXCLUDING OSSICLES OF EAR Except for mandible, which is joined to skull by a synovial joint, most skull bones are flat bones joined by interlocking joints called sutures DIVISION OF STRUCTURE NUMBER OF SKELETON BONES AXIAL SKELETON SKULL Cranium 8 Face 14 NUMBER OF INDIVIDUAL BONES 8 CRANIAL BONES Frontal 2 Parietal 2 temporal Occipital Sphenoid Ethmoid 14 FACIAL BONES 2 Nasal 2 Maxillae 2 Zygomatic Mandible 2 Lacrimal 2 Palatine 2 Inferior nasal conchae Vomer  FUNCTIONS Form framework of face Contain cavities for special sense organs Provide openings for air & food passage Secure teeth Anchor muscles eg. muscles of facial expression & mastication SKULL Divided into: Neurocranium or cranium: Consist of the cranial roof and cranial base Viscerocranium: bones of the face (facial skeleton)  NEUROCRANIUM OR CRANIUM Anatomically, the cranium can be subdivided into a roof and a base: Cranial roof – comprised of the frontal, occipital and two parietal bones. It is also known as the calvarium. Cranial base – comprised of six bones: frontal, sphenoid, ethmoid, occipital, parietal and temporal.  CALVARIA Frontal bone, parietal bones, & occipital bone are seen in a superior view of skull Unpaired frontal bone articulates with paired parietal bones at coronal suture Two parietal bones articulate with each other in midline at sagittal suture Parietal bones articulate with unpaired occipital bone at lambdoid suture CALVARIA Four largest sutures of skull are located where parietal bones articulate with other bones: coronal, sagittal, lambdoid sutures  CALVARIA Junction of sagittal & coronal sutures is bregma Junction of sagittal & lambdoid sutures is lambda LATERAL VIEW OF SKULL Junction where frontal, parietal, sphenoid, temporal bones meet = PTERION Bone in this area is particularly thin & overlies anterior division of middle meningeal artery, - can be torn by a skull fracture in this area - extradural hematoma CRANIAL BASE Anterior, middle, & posterior cranial fossae NEWBORN SKULL At birth flat bones of skull separated by narrow seams of connective tissue (sutures) - At points where more than two bones meet, sutures are wide = fontanelles NEWBORN SKULL Most prominent = anterior fontanelle Sutures & fontanelles allow bones of skull to overlap during birth NEWBORN SKULL Closure of fontanelles Anterior closes by 18 months Posterior closes by 1-2 months  CRANIAL MENINGES Comprises: ❑ Tough dura mater Arachnoid mater Pia mater ❑ 3 PROTECTIVE COVERS ❑ THE DURA MATER -DURABLE LINES THE BRAIN & SKULL ❑ ARACHNOID MATER INTERVENES BETWEEN THE PIA AND DURA MATER ❑ PIA MATER ADHERENT TO THE BRAIN DURA MATER is a DOUBLE LAYER : ARACHNOID MATER ❑ Gr. Spidery ❑ Thin fibrocellular layer ❑ Between pia and arachnoid mater- subarachnoid space ❑ This is a “real space” it contains CSF  VENTRICLES The ventricular system is a set of communicating cavities within the brain. These structures are responsible for the production, transport and removal of cerebrospinal fluid, which bathes the central nervous system.  CEREBROSPINAL FLUID The ventricles are structures that Cerebrospinal fluid surrounds the brain and produce cerebrospinal fluid, and spinal cord. transport it around the cranial cavity. It serves three main functions: They are lined by ependymal cells, which form a structure called the Protection – acts as a cushion for the brain, choroid plexus. It is within limiting neural damage in cranial injuries. the choroid plexus that CSF is Buoyancy – by being immersed in CSF, the produced. net weight of the brain is reduced to approximately 25 grams. This prevents excessive pressure on the base of the brain. Chemical stability – the CSF creates an environment to allow for proper functioning of the brain THE BRAIN  THE CEREBRUM Cortex is not uniform in thickness, being thickest in motor area & thinnest at occipital pole In order to increase the cortical area, the surfaces of the hemispheres show numerous convolutions (gyri) and these are separated by fissures (sulci) of varying depth White matter consists of nerve fibres which transmit impulses to and from the cortical nerve cells and from one cortical area to another It encloses some larger and smaller masses of grey matter such as basal nuclei/ganglia/corpus striatum  THE CEREBRUM ▪ Constitutes largest part of the brain ▪ contains two hemispheres separated by ▪ median cleft = longitudinal fissure ▪ Each hemisphere contains an irregular ▪ cavity containing CSF = lateral ventricle Longitudinal fissure  ▪ the two hemispheres are connected to each other by large commissure = Corpus callosum ▪ Composed of: ▪ Grey matter (cortex- externally) ▪ White matter (internally)  THE CEREBRUM Central sulcus Parieto- On superolateral surface- occipital Central sulcus sulcus Which passes downwards to the lateral sulcus Parieto-occipital sulcus towards the back but is better seen on the medial surface Lateral sulcus Joining these the cerebrum divided into 4 lobes  THE CEREBRUM Frontal lobe Parietal lobe Consists of 4 lobes viz: ❑ Frontal ❑ Parietal ❑ Occipital ❑ Temporal Temporal lobe Occipital lobe  FUNCTIONS Frontal: higher intellect, personality, mood, speech, motor cortex Parietal: Sensory cortex Temporal: memory and language, hearing Occipital: visual cortex SULCI AND GYRI The gyri assist in location of certain functional areas of the brain eg,. Motor cortex at the precentral gyrus  THALAMUS & HYPOTHALAMUS The thalamus forms most of the diencephalon. The thalamus relays messages to the appropriate areas of the cerebral cortex. The hypothalamus, regulates the endocrine system. It translates nervous system signals into activating or inhibiting hormones that it sends to the pituitary gland  CEREBELLUM The cerebellum is located at the Function: coordinating voluntary back of the brain, immediately movements. Maintenance of Balance and inferior to posture. the occipital and temporal lobes, and within the posterior cranial fossa.  BRAINSTEM The brainstem is a stalk-like projection extending caudally from the base of the cerebrum. It facilitates communication between the cerebrum, cerebellum, and spinal cord. Consists of: the midbrain, pons, and medulla oblongata Together, they help to regulate breathing, heart rate, blood pressure