Nervous System Notes PDF

NERVOUS SYSTEM Spinal Cord – embedded in the muscles and viscera o Cervical cord OVERVIEW...

NERVOUS SYSTEM Spinal Cord – embedded in the muscles and viscera o Cervical cord OVERVIEW o Thoracic cord With a mass of only 2 kg (4.5 lbs.), about o Lumbar cord 3% of total body weight, the nervous o Sacrococcygeal cord system is one of the smallest and yet the most complex of the 11 body PERIPHERAL NERVOUS SYSTEM systems. Spinal nerves (31 pairs) This intricate network of billions of Cranial Nerves (12 pairs) neurons and even more neuroglia is Peripheral nerves organized into two main subdivisions: Autonomic nerves o Central nervous system o Peripheral nervous system Neurology deals with normal STRUCTURAL CLASSIFICATION OF functioning and disorders of the nervous NEURONS system Neurologist is a physician who diagnoses and treats disorders of the nervous system Central Nervous System (processing center) Peripheral Nervous System (delivery PARTS OF A NEURON network) Cell body/soma o Contains the organelles of a cells including the nucleus o Processes and interprets all the messages that it receives and transmits o They are grouped together in the entire nervous system (Gray matter) Dendrites o Most often receives stimulus or the message and transmit it towards the cell body Axon DIVISIONS OF THE NERVOUS SYSTEM o Often transmit the message CENTRAL NERVOUS SYSTEM away from the body o Axons vary in length and are Brain – encased on the skull and usually a lot longer than vertebral column dendrites o Cerebrum o Covered by a membrane o Brainstem axolemma o Cerebellum  Axon terminal Allows SALTATORY conduction o The most distal end the axon o Impulse jumps from one node to o The specific part of the axon that another along the length of the will transfer the impulse or the axon for faster conduction message to another neuron or an effector organ Axon Hillock o A cone shaped portion of the cell body as it connects into the axon o Attached is the initial segment which is the most excitable part of the axon Nucleus (nuclei) o Within the brain but outside of TYPES OF NEURONS (ACCORDING TO the cerebral cortex STRUCTURE) Ganglion (ganglia) o Outside of the spinal cord Unipolar o Autonomic ganglion o Neuron with single axon ▪ A cluster of neuronal cell Bipolar bodies and their dendrites o Neuro with 1 dendrite and 1 axon and is essentially a Multipolar junction between o Neuron with several dendrites autonomic nerves and 1 axon originating from the CNS Sensory (Afferent) Neurons and autonomic nerves o Conduct impulses from innervating their target receptors to CNS organs in the periphery. Association or Interneurons o Dorsal root/Spinal Ganglion o Not specifically motor or sensory ▪ Nodule on a dorsal root of neurons the spine that contains Motor (efferent) Neurons cell bodies of nerve cells o Convey motor impulses from the that carry signals from CNS to effectors sensory organs toward the NEUROGLIA/GLIAL CELLS appropriate integration center MYELIN SHEATH The lipid-rich insulating material the axon, arranged in multiple concentric layers Produced by the Schwann cells in the PNS and Oligodendrocytes in the CNS ASTROCYTES NODES OF RANVIER A structure and metabolic support Points along the axon NOT myelinated o Satellite cells → Specific to PNS  Regulators of electrolyte balance Axoaxonic – synapses made by one Formation of blood-brain-barrier (BBB) neuron onto the synapse of another Repair of damage neural tissue neuron EPENDYMAL CELLS ORGANIZATION OF THE NERVOUS SYSTEM Lines the ventricles of the brain and spinal cord to form the CSF Central Nervous System o Consists of the brain and spinal MICROGLIA cord. They are the phagocytic cells and o The brain is the part of the CNS macrophages or scavengers of the CNS that is in the skull and contains They form part of the nervous system’s about 85 billion neurons. defense against infection or injury o The spinal cord is connected to the brain through the foramen magnum of the occipital bone COMPOSITION OF THE NEURAL TISSUE and is encircled by the bones of Peripheral nerve the vertebral column. o Covered by Epineurium o The spin cord contains about 100 Fascicles million neurons. o Covered by Perineurium o The CNS processes many kinds Nerve Fibers of incoming sensory o covered by Endoneurium information. It is also the source of thoughts, emotions, and memories. Most signals that stimulate muscles to contract and glands to secrete originate in the CNS Peripheral Nervous System o Consists of all nervous tissue outside the CNS (nerves and SYNAPSES sensory receptors) o A nerve is a bundle of hundreds communication between neurons to thousands of axons plus Usually occurs from the axon terminal associated connective tissue of the transmitting neurons to the and blood vessels that lies receptive region of the receiving neuron outside the brain and spinal TYPES: cord. o Twelve pairs of cranial nerves Axodendritic – connection formed emerge from the brain and thirty- between the axon of one neuron and one pairs of spinal nerves the dendrite of another emerge from the spinal cord. Axosomatic – direct connection o The term sensory receptor between the axon of one neuron to refers to a structure of the the cell body of another neuron nervous system that monitors  changes in the external or ▪ With a few exceptions, effectors interval environment. Examples (motor division) receive innervation of sensory receptors include from both of these parts, and usually touch receptors in the skin, the two divisions have opposing photoreceptors in the eye, and actions. olfactory (smell) receptors in the A third branch of ANS: Enteric plexuses – an nose. extensive network of over 100 million neurons o Divided into 2 divisions: confined to the wall of the digestive canal. A. Sensory of afferent division – o The enteric plexuses help regulate the conveys input into the CNS from activity of the smooth muscle and sensory receptors in the body. This glands of the digestive canal. division provides the CNS with o Although the enteric plexuses can sensory information about the function independently, they somatic senses (tactile, thermal, communicate with and are regulated by pain, and proprioceptive sensations) the other branches of the ANS. and special senses (smell, taste, vision, hearing, and equilibrium) B. Motor or efferent division – conveys output from the CNS to effectors (muscles and glands). This division is further subdivided into a somatic nervous system and an autonomic nervous system a. Somatic nervous system (SNS) – conveys output from the CNS to skeletal muscles only. FUNCTIONS OF THE NERVOUS SYSTEM Because its motor responses can be consciously controlled, the action 1. Sensory function (INPUT) – sensory of this part of the PNS is voluntary. receptors detect internal stimuli, such as an increase in blood pressure, or external stimuli b. Autonomic nervous system (for example, a raindrop landing on your arm). (ANS) – conveys output from the This sensory information is then carried into CNS to smooth muscle, cardiac the brain and spinal cord through cranial and muscle, and glands. Because its spinal nerves. motor responses are not normally under conscious control, the action 2. Integrative function (PROCESS) – the of the ANS is involuntary. nervous system processes sensory information o 2 main branches of ANS: by analyzing it and making decisions for 1. Sympathetic division – helps support appropriate responses—an activity known as exercise or emergency actions—the so- integration. called “fight-or-flight” responses. 2. Parasympathetic division – “rest-and- 3. Motor function (OUTPUT) – once sensory digest” activities information is integrated, the nervous system may elicit an appropriate motor response by activating effectors (muscles and glands) through cranial and spinal nerves. Stimulation of the effectors causes muscles to contract and glands to secrete. BRAIN A. Cerebrum a. Frontal lobe b. Parietal lobe c. Temporal lobe d. Occipital lobe B. Diencephalon BRAIN ORGANIZATION a. Thalamus b. Hypothalamus c. Epithalamus C. Cerebellum D. Brainstem a. Midbrain b. Pons c. Medulla Oblongata PROTECTIVE STRCUTURES 1. First layer of protection for the central nervous system is the hard bony skull and vertebral column. The skull encases the brain, and the vertebral column surrounds the spinal cord, providing strong protective defenses against damaging blows or bumps. 2. The second protective layer is the meninges, three membranes that lie between the bony encasement and the nervous tissue in both the brain and spinal cord. 3. Finally, a space between two of the meningeal membranes contain cerebrospinal fluid, a buoyant liquid that suspends the central nervous tissue in weightless environment while surrounding it o 2. Chemical protection – with a shock-absorbing, hydraulic cushion. CSF provides an optimal chemical environment for accurate neuronal signaling o 3. Circulation – CSF is a medium for minor exchange of nutrients and waste products between the blood and adjacent nervous tissue. Choroid plexus – production of CSF CIRCULATION OF CSF Mnemonics: o Come Let’s Meet Tita Sylvia For Lunch Mamaya sa Aristocrat Choroid plexus > Lateral ventricle > Foramen of Monroe > Third ventricle > MENINGES Sylvian aqueduct > Fourth ventricle > The meninges are three distinct Foramen of Luschka > Foramen of protective, connective tissue covering Magendie > Subarachnoid space that encircle the spinal cord and brain. 1. dura mater – most superficial 2. arachnoid mater 3. pia mater – deep The spinal meninges cover the spinal cord and are continuous with the cranial meninges, which cover the brain The spinal cord is also protected by a cushion of fat and connective tissue located in the epidural space a space between the dura mater and the wall of the vertebral canal. CEREBROSPINAL FLUID Is a clear, colorless liquid composed primarily of water that protects the brain and spinal cord from chemical CEREBRUM and physical injuries. Is the “seat of intelligence”. It provides 4 CSF filled cavities in the brain us with the ability to read, write, and called VENTRICLES speak; to make calculations and FUNCTIONS: compose music; and to remember the o 1. Mechanical protection – past, plan for the future, and imagine CSF serves as a shock- things that have never existed before. absorbing medium  Cerebral cortex – is a region of gray FRONTAL LOBE matter that forms the outer rim of the Occupies area anterior to the CSR and cerebrum. superior to Lateral Sulcus o During embryonic development, Precentral gyrus: Primary motor cortex when brain size increases rapidly, Functions: the gray matter of the cortex o Behavior, judgement and enlarges much faster than the emotion deeper white matter. o Intelligence o As a result, the cortical region o Voluntary movement rolls and folds on itself forming a o Broca’s area: motor aspect of series of elevated ridges speech (CEREBRAL GYRI) and depressions called GROOVES. Cerebral sulci (singular is cerebral sulcus) are grooves that separate neighboring cerebral gyri. Interlobar sulci are grooves that separate the various lobes of the cerebrum. Cerebral fissures are grooves that separate parts of the brain. LOBES OF THE CEREBRAL HEMISPHERES Frontal Parietal PARIETAL LOBE Temporal Occupies are posterior to the CSR Occipital and superior to Lateral Sulcus Post Central Gyrus: Primary sensory cortex Functions: o Receives tactile, proprioceptive, pain and  temperature sensation from the opposite side of the body. OCCIPITAL LOBE Occupies area posterior to Parieto- Occipital Sulcus Primary Visual cortex: receives/ processes visual stimuli Visual Association cortex: process visual stimuli Function: o Vision TEMPORAL LOBE Occupies area inferior to Lateral Sulcus Primary Auditory cortex: auditory stimuli DIENCEPHALON Associative: processes auditory stimuli Wernicke’s: language comprehension THALAMUS Functions: Major relay station for most sensory that o Speech and language reach the primary sensory cortex of the o Hearing (auditory) cerebrum from the spinal cord and brainstem. Contributes to motor functions by transmitting information from the cerebellum and corpus striatum to the primary motor cortex of the cerebrum. Relays nerve impulses between different areas of the cerebrum and  plays a role in the maintenance of LIMBIC SYSTEM consciousness. The limbic system is sometimes called Regulating the body through sleep and the “emotional brain “because it plays a wake cycles. primary role in a range of emotions, HYPOTHALAMUS including pain, pleasure, docility, Inferior to the thalamus that controls affection, and anger. It also is involved in many body activities and is one of the olfaction (smell) and memory. major regulators of homeostasis Secretes hormones that control multiple functions, such as body temperature, sleep, and thirst/hunger. EPITHALAMUS Small region, superior and posterior to the thalamus Contains PINEAL GLAND –secretes melatonin; and HABENULAR NUCLEI – involved in olfaction, especially emotional responses to odors. CRANIAL NERVES CEREBELLUM Second only to the cerebrum in size, occupies the inferior and posterior aspects of the cranial cavity. Posterior to the medulla and pons and inferior to the posterior portion of the cerebrum For movement coordination and balance BRAINSTEM MEDULLA OBLONGATA Continues with the superior part of the spinal cord, forms inferior of the brainstem, begins at foramen magnum PONS Lies directly superior to medulla and anterior to cerebellum MIDBRAIN Eye movements: Extends from pons to diencephalon OCULOMOTOR - medial rectus, superior and inferior rectus, inferior oblique TROCHLEAR unmyelinated axons, axon terminals, and - superior oblique neuroglia. It appears grayish, rather than white, ABDUCENS because the Nissl bodies impart a gray - lateral rectus color and there is little or no myelin in these areas. THE SPINAL CORD AND SPINAL NERVES BRAIN The spinal cord and spinal nerves WHITE MATTER – inner part contribute to homeostasis by providing GRAY MATTER – outer part quick reflexive responses to many stimuli SPINAL CORD The spinal cord is the pathway for WHITE MATTER – outer part sensory input to the brain and motor GRAY MATTER – inner part output from the brain. EXTERNAL ANATOMY OF SPINAL CORD Conus medullaris o A conical structure that is inferior to the lumbar enlargement and where the spinal cord terminates as a tapering, which ends at the level of the intervertebral disc between the first and second lumbar vertebrae (L1-L2) in adults. White matter is composed primarily of Spinal Tap – L3-L4, L4-L5 myelinated axons. The whitish color of myelin Filum Terminale gives white matter its name. o An extension of the pia matter that extends inferiorly, fuses with The gray matter of the nervous system the arachnoid mater and dura contains neuronal cell bodies, dendrites,  mater, and anchors the spinal PERIPHERAL NERVES: CERVICAL PLEXUS cord to the coccyx. Spinar nerves o Are the parts of communication between the spinal cord and specific regions of the body. o 31 pairs of spinal nerves that emerge from the intervertebral foramen. 8 pairs of cervical nerves PERIPHERAL NERVES: BRACHIAL PLEXUS (C1-C8) 12 pairs of thoracic nerves (T1-T12) 5 pairs of lumbar nerves (L1-L5) 5 pairs of sacral nerves (S1-S5) 1 pair of coccygeal nerves (Co1)  PERIPHERAL NERVES: SACRAL PLEXUS PERIPHERAL NERVES: LUMBAR PLEXUS