RDP_UPDATED_HAP-II_NERVOUS SYSTEM_ BRAIN.pdf
- 1. HAP-II_NERVOUS SYTEM PREPARED BY: Mrs. Rishita Patel_ IICP 1. NERVOUS SYSTEM (CNS - BRAIN & CIRCULATION) DIVISIONS OF NERVOUS SYSTEM Nervous system controls all the activities of the body. It is quicker than other control system in the body, namely endocrine system. Primarily, nervous system is divided into two parts: 1. Central nervous system 2. Peripheral nervous system.
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- 3. HAP-II_NERVOUS SYTEM PREPARED BY: Mrs. Rishita Patel_ IICP Parts of Brain Brain consists of three major divisions: 1. Prosencephalon 2. Mesencephalon 3. Rhombencephalon INTRODUCTION Neuron or nerve cell is defined as the structural and functional unit of nervous system. Neuron is similar to any other cell in the body, having nucleus and all the organelles in cytoplasm. However, it is different from other cells by two ways: 1. Neuron has branches or processes called axon and dendrites 2. Neuron does not have centrosome. So, it cannot undergo division. „ CLASSIFICATION OF NEURON Neurons are classified by three different methods. A. Depending upon the number of poles B. Depending upon the function C. Depending upon the length of axon. „ DEPENDING UPON THE NUMBER OF POLES Based on the number of poles from which the nerve fibers arise, neurons are divided into three types: 1. Unipolar neurons 2. Bipolar neurons 3. Multipolar neurons.
- 4. HAP-II_NERVOUS SYTEM PREPARED BY: Mrs. Rishita Patel_ IICP 1. Unipolar Neurons Unipolar neurons are the neurons that have only one pole. From a single pole, both axon and dendrite arise. This type of nerve cells is present only in embryonic stage in human beings. 2. Bipolar Neurons Neurons with two poles are known as bipolar neurons. Axon arises from one pole and dendrites arise from the other pole. 3. Multipolar Neurons Multipolar neurons are the neurons which have many poles. One of the poles gives rise to axon and all other poles give rise to dendrites. DEPENDING UPON THE FUNCTION On the basis of function, nerve cells are classified into two types: 1. Motor or efferent neurons 2. Sensory or afferent neurons. 1. Motor or Efferent Neurons: Motor or efferent neurons are the neurons which carry the motor impulses from central nervous system to peripheral effector organs like muscles, glands, blood vessels, etc. Generally, each motor neuron has a long axon and short dendrites. 2. Sensory or Afferent Neurons: Sensory or afferent neurons are the neurons which carry the sensory impulses from periphery to central nervous system. Generally, each sensory neuron has a short axon and long dendrites.
- 5. HAP-II_NERVOUS SYTEM PREPARED BY: Mrs. Rishita Patel_ IICP DEPENDING UPON THE LENGTH OF AXON Depending upon the length of axon, neurons are divided into two types: 1. Golgi type I neurons 2. Golgi type II neurons. 1. Golgi Type I Neurons Golgi type I neurons have long axons. Cell body of these neurons is in different parts of central nervous system and their axons reach the remote peripheral organs. 2. Golgi Type II Neurons Neurons of this type have short axons. These neurons are present in cerebral cortex and spinal cord. STRUCTURE OF NEURON Neuron is made up of three parts: 1. Nerve cell body 2. Dendrite 3. Axon. Dendrite and axon form the processes of neuron. Dendrites are short processes and the axons are long processes. Dendrites and axons are usually called nerve fibers. „ NERVE CELL BODY Nerve cell body is also known as soma or perikaryon. It is irregular in shape. Like any other cell, it is constituted by a mass of cytoplasm called neuroplasm, which is covered by a cell membrane. The cytoplasm contains a large nucleus, Nissl bodies, neurofibrils, mitochondria and Golgi apparatus. Nissl bodies and neurofibrils are found only in nerve cell and not in other cells. Nucleus Each neuron has one nucleus, which is centrally placed in the nerve cell body. Nucleus has one or two prominent nucleoli. Nucleus does not contain centrosome. So, the nerve cell cannot multiply like other cells.
- 6. HAP-II_NERVOUS SYTEM PREPARED BY: Mrs. Rishita Patel_ IICP Nissl Bodies Nissl bodies or Nissl granules are small basophilic granules found in cytoplasm of neurons and are named after the discoverer. These bodies are present in soma and dendrite but not in axon and axon hillock. Nissl bodies are called tigroid substances, since these bodies are responsible for tigroid or spotted appearance of soma after suitable staining. Dendrites are distinguished from axons by the presence of Nissl granules under microscope. Nissl bodies are membranous organelles containing ribosomes. So, these bodies are concerned with synthesis of proteins in the neurons. Proteins formed in soma are transported to the axon by axonal flow. Number of Nissl bodies varies with the condition of the nerve. During fatigue or injury of the neuron, these bodies fragment and disappear by a process called chromatolysis. Granules reappear after recovery from fatigue or after regeneration of nerve fibers. Neurofibrils Neurofibrils are thread-like structures present in the form of network in the soma and the nerve processes. Presence of neurofibrils is another characteristic feature of the neurons. The neurofibrils consist of microfilaments and microtubules. Mitochondria Mitochondria are present in soma and in axon. As in other cells, here also mitochondria form the powerhouse of the nerve cell, where ATP is produced.
- 7. HAP-II_NERVOUS SYTEM PREPARED BY: Mrs. Rishita Patel_ IICP Golgi Apparatus Golgi apparatus of nerve cell body is similar to that of other cells. It is concerned with processing and packing of proteins into granules. DENDRITE Dendrite is the branched process of neuron and it is branched repeatedly. Dendrite may be present or absent. If present, it may be one or many in number. Dendrite has Nissl granules and neurofibrils. Dendrite transmits impulses towards the nerve cell body. Usually, the dendrite is shorter than axon. AXON Axon is the longer process of nerve cell. Each neuron has only one axon. Axon arises from axon hillock of the nerve cell body and it is devoid of Nissl granules. Axon extends for a long distance away from the nerve cell body. Length of longest axon is about 1 meter. Axon transmits impulses away from the nerve cell body. Organization of Nerve: Each nerve is formed by many bundles or groups of nerve fibers. Each bundle of nerve fibers is called a fasciculus. Coverings of Nerve The whole nerve is covered by tubular sheath, which is formed by a areolar membrane. This sheath is called epineurium. Each fasciculus is covered by perineurium and each nerve fiber (axon) is covered by endoneurium.
- 8. HAP-II_NERVOUS SYTEM PREPARED BY: Mrs. Rishita Patel_ IICP Internal Structure of Axon – Axis Cylinder Axon has a long central core of cytoplasm called axoplasm. Axoplasm is covered by the tubular sheath like membrane called axolemma. Axolemma is the continuation of the cell membrane of nerve cell body. Axoplasm along with axolemma is called the axis cylinder of the nerve fiber. Axoplasm contains mitochondria, neurofibrils and axoplasmic vesicles. Because of the absence of Nissl bodies in the axon, proteins necessary for the nerve fibers are synthesized in the soma and not in axoplasm. After synthesis, the protein molecules are transported from soma to axon, by means of axonal flow. Some neurotransmitter substances are also transported by axonal flow from soma to axon. Axis cylinder of the nerve fiber is covered by a membrane called neurilemma. Non-myelinated Nerve Fiber Nerve fiber described above is the non-myelinated nerve fiber, which is not covered by myelin sheath FIGURE: A. Myelinated nerve fiber; B. Non-myelinated nerve fiber.
- 9. HAP-II_NERVOUS SYTEM PREPARED BY: Mrs. Rishita Patel_ IICP Myelinated Nerve Fiber Nerve fiber which is insulated by myelin sheath is called myelinated nerve fibers. „ MYELIN SHEATH Myelin sheath is a thick lipoprotein sheath that insulates the myelinated nerve fiber. Myelin sheath is not a continuous sheath. It is absent at regular intervals. The area where myelin sheath is absent is called node of Ranvier. Segment of the nerve fiber between two nodes is called internode. Myelin sheath is responsible for white color of nerve fibers. Chemistry of Myelin Sheath Myelin sheath is formed by concentric layers of proteins, alternating with lipids. The lipids are cholesterol, lecithin and cerebroside (sphingomyelin). Formation of Myelin Sheath – Myelinogenesis Formation of myelin sheath around the axon is called the myelinogenesis. It is formed by Schwann cells in neurilemma. In the peripheral nerve, the myelinogenesis starts at 4th month of intrauterine life. It is completed only in the second year after birth. Functions of Myelin Sheath 1. Faster conduction Myelin sheath is responsible for faster conduction of impulse through the nerve fibers. In myelinated nerve fibers, the impulses jump from one node to another node. This type of transmission of impulses is called saltatory conduction. 2. Insulating capacity Myelin sheath has a high insulating capacity. Because of this quality, myelin sheath restricts the nerve impulse within single nerve fiber and prevents the stimulation of neighboring nerve fibers. „ NEURILEMMA Neurilemma is a thin membrane, which surrounds the axis cylinder. It is also called neurilemmal sheath or sheath of Schwann. It contains Schwann cells, which have flattened and elongated nuclei. Cytoplasm is thin and modified to form the thin sheath of neurilemma. One nucleus is present in each internode of the axon. Nucleus is situated between myelin sheath and neurilemma. In non-myelinated nerve fiber, the neurilemma surrounds axolemma continuously. In myelinated nerve fiber, it covers the myelin
- 10. HAP-II_NERVOUS SYTEM PREPARED BY: Mrs. Rishita Patel_ IICP sheath. At the node of Ranvier (where myelin sheath is absent), neurilemma invaginates and runs up to axolemma in the form of a finger-like process. Functions of Neurilemma In non-myelinated nerve fiber, the neurilemma serves as a covering membrane. In myelinated nerve fiber, it is necessary for the formation of myelin sheath (myelinogenesis). Neurilemma is absent in central nervous system. So, the neuroglial cells called oligodendroglia are responsible for myelinogenesis in central nervous system. Classification of Nerve Fibers BASIS OF CLASSIFICATION Nerve fibers are classified by six different methods. The basis of classification differs in each method. Different methods of classification are listed in. Different methods to classify nerve fibers Classification of nerve fibers 1. Depending upon structure 2. Depending upon distribution 3. Depending upon origin 4. Depending upon function 5. Depending upon secretion of neurotransmitter 6. Depending upon diameter and conduction of impulse (Erlanger Gasser classification) 1. DEPENDING UPON STRUCTURE Based on structure, nerve fibers are classified into two types: i. Myelinated Nerve Fibers Myelinated nerve fibers are the nerve fibers that are covered by myelin sheath. ii. Non-myelinated Nerve Fibers Nonmyelinated nerve fibers are the nerve fibers which are not covered by myelin sheath. 2.DEPENDING UPON DISTRIBUTION Nerve fibers are classified into two types, on the basis of distribution: i. Somatic Nerve Fibers Somatic nerve fibers supply the skeletal muscles of the body. ii. Visceral or Autonomic Nerve Fibers Autonomic nerve fibers supply the various internal organs of the body. 3. DEPENDING UPON ORIGIN On the basis of origin, nerve fibers are divided into two types: i. Cranial Nerve Fibers Nerve fibers arising from brain are called cranial nerve fibers.
- 11. HAP-II_NERVOUS SYTEM PREPARED BY: Mrs. Rishita Patel_ IICP ii. Spinal Nerve Fibers Nerve fibers arising from spinal cord are called spinal nerve fibers. 4.DEPENDING UPON FUNCTION Functionally, nerve fibers are classified into two types: I: Sensory Nerve Fibers Sensory nerve fibers carry sensory impulses from different parts of the body to the central nervous system. These nerve fibers are also known as afferent nerve fibers. II: Motor Nerve Fibers Motor nerve fibers carry motor impulses from central nervous system to different parts of the body. These nerve fibers are also called efferent nerve fibers. 5.DEPENDING UPON SECRETION OF NEUROTRANSMITTER Depending upon the neurotransmitter substance secreted, nerve fibers are divided into two types: I: Adrenergic Nerve Fibers Adrenergic nerve fibers secrete noradrenaline. II: Cholinergic Nerve Fibers Cholinergic nerve fibers secrete acetylcholine. 6. DEPENDING UPON DIAMETER AND CONDUCTION OF IMPULSE (ERLANGER- GASSER CLASSIFICATION) Erlanger and Gasser classified the nerve fibers into three major types, on the basis of diameter (thickness) of the fibers and velocity of conduction of impulses: i. Type A nerve fibers ii. Type B nerve fibers iii. Type C nerve fibers. Among these fibers, type A nerve fibers are the thickest fibers and type C nerve fibers are the thinnest fibers. Type C fibers are also known as Type IV fibers. Except type C fibers, all the nerve fibers are myelinated. Type A nerve fibers are divided into four types: a. Type A alpha or Type I nerve fibers b. Type A beta or Type II nerve fibers c. Type A gamma nerve fibers d. Type A delta or Type III nerve fibers. Velocity of Impulse Velocity of impulse through a nerve fiber is directly proportional to the thickness of the fiber.
- 12. HAP-II_NERVOUS SYTEM PREPARED BY: Mrs. Rishita Patel_ IICP PROPERTIES OF NERVE FIBERS EXCITABILITY Excitability is defined as the physiochemical change that occurs in a tissue when stimulus is applied. Stimulus is defined as an external agent, which produces excitability in the tissues. Chronaxie is an important parameter to determine the condition of nerve fiber. Clinically, the damage of nerve fiber is determined by measuring the chronaxie. It is measured by chronaxie meter. Nerve fibers have a low threshold for excitation than the other cells. Response Due to Stimulation of Nerve Fiber When a nerve fiber is stimulated, based on the strength of stimulus, two types of response develop: 1. Action potential or nerve impulse Action potential develops in a nerve fiber when it is stimulated by a stimulus with adequate strength. Adequate strength of stimulus, necessary for producing the action potential in a nerve fiber is known as threshold or minimal stimulus. Action potential is propagated. 2. Electrotonic potential or local potential When the stimulus with subliminal strength is applied, only electrotonic potential develops and the action potential does not develop. Electrotonic potential is non propagated. Cathelectrotonic and Anelectrotonic Potentials While recording electrical potential in a nerve fiber, two electrodes, namely cathode and anode are used. The potential change that is produced at cathode is called cathelectrotonic potential. The potential that is developed at anode is known as anelectrotonic potential. Only the cathelectrotonic potential can be transformed into electrotonic potential or action potential. Properties of Action Potential Properties of action potential are given. „ ELECTROTONIC POTENTIAL OR LOCAL POTENTIAL Electrotonic potential or local potential is a non-propagated local response that develops in the nerve fiber when a subliminal stimulus is applied. Subliminal or subthreshold stimulus does not produce action potential. But, it alters the resting membrane potential and produces slight depolarization for about 7 mV. This slight depolarized state is called electrotonic potential. Firing level is reached only if depolarization occurs up to 15 mV. Then only action potential can develop. Electrotonic potential is a graded potential Properties of Electrotonic Potential 1. Electrotonic potential is non-propagated 2. It does not obey all-or-none law. If the intensity of the stimulus is increased gradually every time, there is increase in the amplitude till the firing level is reached, i.e. at 15 mV.
- 13. HAP-II_NERVOUS SYTEM PREPARED BY: Mrs. Rishita Patel_ IICP GENERATION OF ACTION POTENTIAL An action potential (AP) or impulse is a sequence of rapidly occurring events that decrease and reverse the membrane potential and then eventually restore it to the resting state. An action potential has two main phases: a depolarizing phase and a repolarizing phase. During the depolarizing phase, the negative membrane potential becomes less negative, reaches zero, and then becomes positive. During the repolarizing phase, the membrane potential is restored to the resting state of -70 mV. Following the repolarizing phase there may be an after-hyperpolarizing phase, during which the membrane potential temporarily become more negative than the resting level. The period of time after an action potential begins during which an excitable cell cannot generate another action potential in response to a normal threshold stimulus is called the refractory period. During the absolute refractory period, even a very strong stimulus cannot initiate a second action potential. This period coincides with the period of Na+ channel activation and inactivation. The relative refractory period is the period of time during which a second action potential can be initiated, but only by a larger-than-normal stimulus. It coincides with the period when the voltage-gated K+ channels are still open after inactivated Na+ channels have returned to their resting state.
- 14. HAP-II_NERVOUS SYTEM PREPARED BY: Mrs. Rishita Patel_ IICP AP GENERATION: Depolarizing Phase When a depolarizing graded potential or some other stimulus causes the membrane of the axon to depolarize to threshold, voltage-gated Na+ channels open rapidly. Both the electrical and the chemical gradients favor inward movement of Na+, and the resulting in rush of Na+ causes the depolarizing phase of the action potential. The inflow of Na+ changes the membrane potential from -55 mV to +30 mV. At the peak of the action potential, the inside of the membrane is 30 mV more positive than the outside. Repolarizing Phase Shortly after the activation gates of the voltage-gated Na+ channels open, the inactivation gates close. Now the voltage-gated Na+ channel is in an inactivated state. In addition to opening voltage-gated Na+ channels, a threshold level depolarization also opens voltage-gated K+ channels. Because the voltage-gated K+ channels open more slowly, their opening occurs at about the same time the voltage-gated Na+ channels are closing. The slower opening of voltage- gated K+ channels and the closing of previously open voltage-gated Na+ channels produce the repolarizing phase of the action potential. After-hyperpolarizing Phase While the voltage-gated K+ channels are open, outflow of K+ may be large enough to cause an after-hyperpolarizing phase of the action potential. During this phase, the voltage-gated K+ channels remain open and the membrane potential becomes even more negative (about -90 mV). As the voltage-gated K+ channels close, the membrane potential returns to the resting level of -70 mV. Unlike voltage-gated Na+ channels, most voltage-gated K+ channels do not exhibit an inactivated state. Instead, they alternate between closed (resting) and open (activated) states.
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- 16. HAP-II_NERVOUS SYTEM PREPARED BY: Mrs. Rishita Patel_ IICP CONDUCTIVITY Conductivity is the ability of nerve fibers to transmit the impulse from the area of stimulation to the other areas. Action potential is transmitted through the nerve fiber as nerve impulse. Normally in the body, the action potential is transmitted through the nerve fiber in only one direction. However, in experimental conditions when, the nerve is stimulated, the action potential travels through the nerve fiber in either direction. MECHANISM OF CONDUCTION OF ACTION POTENTIAL Depolarization occurs first at the site of stimulation in the nerve fiber. It causes depolarization of the neighboring areas. Like this, depolarization travels throughout the nerve fiber. Depolarization is followed by repolarization. CONDUCTION THROUGH MYELINATED NERVE FIBER – SALTATORY CONDUCTION Saltatory conduction is the form of conduction of nerve impulse in which, the impulse jumps from one node to another. Conduction of impulse through a myelinated nerve fiber is about 50 times faster than through a non-myelinated fiber. It is because the action potential jumps from one node to another node of Ranvier instead of travelling through the entire nerve fiber. Mechanism of Saltatory Conduction Myelin sheath is not permeable to ions. So, the entry of sodium from extracellular fluid into nerve fiber occurs only in the node of Ranvier, where the myelin sheath is absent. It causes depolarization in the node and not in the internode. Thus, depolarization occurs at successive nodes. So, the action potential jumps from one node to another. Hence, it is called saltatory conduction (saltare = jumping).
- 17. HAP-II_NERVOUS SYTEM PREPARED BY: Mrs. Rishita Patel_ IICP Mode of conduction through nerve fibers A. Non-myelinated nerve fiber: continuous conduction. B. Myelinated nerve fiber: saltatory conduction (impulse jumps from node to node). AP = Action potential. ADAPTATION While stimulating a nerve fiber continuously, the excitability of the nerve fiber is greater in the beginning. Later the response decreases slowly and finally the nerve fiber does not show any response at all. This phenomenon is known as adaptation or accommodation. Cause for Adaptation
- 18. HAP-II_NERVOUS SYTEM PREPARED BY: Mrs. Rishita Patel_ IICP When a nerve fiber is stimulated continuously, depolarization occurs continuously. Continuous depolarization inactivates the sodium pump and increases the efflux of potassium ions. INFATIGABILITY Nerve fiber cannot be fatigued, even if it is stimulated continuously for a long time. The reason is that nerve fiber can conduct only one action potential at a time. At that time, it is completely refractory and does not conduct another action potential. ALL-OR-NONE LAW All-or-none law states that when a nerve is stimulated by a stimulus it gives maximum response or does not give response at all. Refer Chapter 90 for more details on all-or-none law. PROTECTION OF THE CNS The brain and spinal cord are protected (surrounded) by bones, membranes, and fluid. A. Bones 1. The brain is encased by eight skull bones 2. The spinal cord is encased by 26 bones that make up the vertebral column B. Meninges Three membranes around the brain and spinal cord are called "meninges" a. Dura mater = "tough mother" outermost covering b. Arachnoid Mater = "spider mother" due to spider- web-like appearance; subarachnoid space = contains cerebrospinal fluid c. Pia Mater = "tender mother" innermost covering
- 19. HAP-II_NERVOUS SYTEM PREPARED BY: Mrs. Rishita Patel_ IICP The Central Nervous System (BRAIN) A. The brain is the largest and most complex portion of the nervous system. It occupies the cranial cavity and is composed of one hundred billion multipolar neurons. B. Cerebrum = the largest portion of the brain, which is divided into two cerebral hemispheres 1. Anatomy of Cerebrum a. Conscious thought, memory storage and processing, sensory processing, and the regulation of skeletal muscle contractions. b. The surface of the cerebrum is highly folded and covered with a superficial layer of gray matter called the cerebral cortex. a. Fissures = deep grooves 1. longitudinal fissure separates the two cerebral hemispheres. 2. transverse fissure (separates cerebrum from cerebellum) b. Sulci (sulcus) = shallow depressions that separate the folds or wrinkles 1. central sulcus (separates frontal lobe from parietal lobe) 2. lateral sulcus (separates frontal and parietal lobes from temporal lobe) c. Gyri (gyrus) = elevated regions that increase surface area 1. precentral gyrus (motor cortex) 2. postcentral gyrus (somatosensory cortex) c. Each cerebral hemisphere is further subdivided into lobes. There are five lobes: the frontal, parietal, occipital, temporal, and insula (deep). d. The gyrus immediately anterior to the central sulcus is called the precentral gyrus while the gyrus immediately posterior the central sulcus is called the postcentral gyrus. e. Gray matter = neuron cell bodies and unmyelinated axons. f. White matter = myelinated axons. For example the corpus callosum provides the major pathway for communication between the two
- 20. HAP-II_NERVOUS SYTEM PREPARED BY: Mrs. Rishita Patel_ IICP hemispheres of the cerebral cortex 2. Important features of cerebrum a. Cerebrum functions include conscious thought, memory storage and processing, sensory processing, and the regulation of skeletal muscle contractions. b. The two hemispheres are not equal in function. i. Right brain = analyzes sensory information and relates the body to the sensory environment; interpretive centers in this hemisphere enable you to identify familiar objects by touch, sight, smell, taste, or feel. Right brained individuals are often more artistic, musically inclined, or attuned to their emotions. ii. Left brain = possesses the general interpretive and speech centers and is important in language-based skills; important in reading, writing, speaking, math, and logic. c. The cerebral cortex was analyzed microscopically and divided into 52 areas called Brodmann’s areas which align with the functional differences within the cortex.
- 21. HAP-II_NERVOUS SYTEM PREPARED BY: Mrs. Rishita Patel_ IICP Lateral view of the cerebral cortex showing the principal gyri and sulci. d. Motor areas of Cerebral Cortex i. Primary Motor Cortex (Area 4) = precentral gyrus of the frontal lobe 1. Possesses large neurons called pyramidal cells 2. Conscious control of skilled voluntary movements of skeletal muscles. 3. Motor areas of the precentral gyrus have been spatially mapped = somatotopic organization. ii. Premotor Cortex 1. Regions that control learned motor skills that are repeated/patterned (such as playing an instrument). Sometimes called called muscle memory. iii. Broca’s Area (area 44/45) = motor speech center 1. Production of language, or controlling muscles responsible for speech 2. Present in only one hemisphere (typically the left) iv. Frontal Eye Field 1. Controls the voluntary movements of the eye 2. Has no role in the interpretation of visual stimuli. e. Sensory areas of Cerebral Cortex i. Somatosensory Cortex = located within the parietal lobe 1. Primary somatosensory cortex = postcentral gyrus of parietal lobe a. Neurons receive touch information (i.e. temperature, pressure, vibration, pain, etc.) from the somatic sensory receptors of the skin and from proprioceptors in skeletal muscle. b. Allow you to interpret what body region is being stimulated. 2. Somatosensory association area a. Integrates and analyzes the somatic sensory inputs form the primary somatosensory cortex and memories of previous experience to produce an understanding about what is being felt. b. Allows you to recognize the cold, flat, round thing in your pocket is a quarter. ii. Visual Cortex = located within the occipital lobe
- 22. HAP-II_NERVOUS SYTEM PREPARED BY: Mrs. Rishita Patel_ IICP 1. Primary visual cortex receives light information from the retina of the eye such as color, form, texture, and movement. 2. Visual association area integrates and analyzes the visual information coming from the primary visual cortex and past experiences to interpret what the image is or means (a face, a flower, a car, a stop sign). iii. Auditory Cortex = located within the temporal lobes 1. Primary auditory cortex (areas 22) receives sound information from the ear such as pitch, rhythm, and volume. 2. Auditory association area integrates and analyzes the information from the primary auditory cortex and past experiences to interpret what the sound stimulus is or means (a scream, music, a fire alarm, thunder, etc.) iv. Other sensory areas: 1. Olfactory cortex = perception of odors or smells. 2. Gustatory cortex = perception of taste. 3. Visceral sensory cortex = visceral sensations (upset stomach, full bladder, urge to defecate, etc.)
- 23. HAP-II_NERVOUS SYTEM PREPARED BY: Mrs. Rishita Patel_ IICP f. Interpretive areas of Cerebral Cortex i. Prefrontal Cortex = also called the anterior association area 1. Involved with intellect, complex learning abilities, recall, and personality 2. Necessary for abstract ideas, judgment, reasoning, planning, concern for others and a conscience. Tumors in this area frequently lead to personality disorders. ii. General Interpretive Areas = also called the posterior association area 1. Parts of the temporal, occipital, and parietal lobes of one hemisphere (usually the left) 2. Seamlessly integrates sensory and motor information with emotions. 3. Wernicke’s area = understanding written and spoken language g. Basal Nuclei = There are islands of gray matter located deep within the white matter of the cerebrum. i. The function of these islands of gray matter is to subconsciously control large automatic skeletal muscle contractions (arm swinging when walking), play in a role in maintaining attention, and to produce dopamine. ii. Disorder of the basal nuclei result in too much or too little movements as exemplified by Huntington’s (too much) and Parkinson’s (too little). h. Limbic System i. The limbic system is our emotional brain. 1. The amygdala (amygdaloid body) recognizes angry and fear, assesses danger, and elicits fear responses associated with “fight or flight”. 2. The cingulate gyrus plays a role in expressing our emotions through gestures and in resolving mental conflicts when frustrated. ii. The limbic system also holds the hippocampus region which (along with the amygdala) plays a role in formation of memories. C. Diencephalon = serves as the structural and functional link between the cerebral hemispheres and the rest of the central nervous system.
- 24. HAP-II_NERVOUS SYTEM PREPARED BY: Mrs. Rishita Patel_ IICP 1. The diencephalon is covered by the cerebrum and is not visible by external examination. 2. The diencephalon is further subdivided into the: a. Thalamus i. Contains important relay and processing centers for sensory information. Sometimes called the gatekeeper or relay station. b. Hypothalamus i. Its homeostatic roles include: 1. Autonomic control center=influences BP, HR, GI motility 2. Body temperature regulation and initiates sweating and shivering 3. Regulates food intake 4. Regulates water balance through the thirst mechanism c. Epithalamus i. pineal gland secretes melatonin and regulates the sleep-wake cycles. D. Cerebellum 1. The cerebellum functions in the coordinates subconsciously skilled muscle movements, posture, equilibrium (i.e. balance) 2. The cerebellum is separated from the cerebrum by the transverse fissure. 3. The cerebellum also possesses fold-like “leaf-like” wrinkles called folia 4. The two cerebellar hemispheres are separated by the vermis 5. The white matter of the cerebellum is called the arbor vitae and is surrounded by gray matter fold-like “leaf-like” wrinkles called folia of the cerebellar cortex.
- 25. HAP-II_NERVOUS SYTEM PREPARED BY: Mrs. Rishita Patel_ IICP E. Brain stem 1. Subdivided into: a. Midbrain i. Corpora quadrigemina – “four twin bodies” 1. Superior colliculi – visual reflexes; head-eye coordination 2. Inferior colliculi – auditory reflexes and startle reflex centers ii. Substantia nigra – produces dopamine, and regulates the activity of the basal nuclei of the brain, lack of dopamine has been linked to Parkinson’s disease b. Pons i. “bridge” ii. contains respiratory centers that help to maintain the normal rhythm of breathing (pneumotaxic area) c. Medulla oblongata i. Cardiac center = Controls the force and rate of heart contraction ii. Vasomotor center = Regulates blood pressure by regulating the smooth muscle of blood vessels (vasoconstriction = BP increase; vasodilation = BP decrease) iii. Respiratory center = Regulates the rate and depth of breathing iv. Regulates visceral reflexes such as vomiting, hiccupping, swallowing, coughing, and sneezing.
- 26. HAP-II_NERVOUS SYTEM PREPARED BY: Mrs. Rishita Patel_ IICP 2. Reticular Activating System (RAS) - Reticular Formation = extends through the medulla oblongata, pons and midbrain. a. Maintains cerebral cortical awareness, regulates consciousness b. Controls brains alertness; inhibited = sleep, alcohol, tranquilizers c. Filters out repetitive or weak stimuli 13.2 Circulation and the Central Nervous System A. Meninges 1. The meninges are specialized membranes surrounding the brain and spinal cord and provide physical support and shock absorption. 2. The spinal meninges consist of three layers: - The tough fibrous dura mater “tough mother” is the outermost covering - The arachnoid mater “spider mother” is the middle meningeal layer. The subarachnoid space extends between the arachnoid mater and the pia mater is filled with cerebro-spinal fluid (CSF). CSF acts as a shock absorber and a diffusion medium for dissolved gases, nutrients, chemical messengers, and waste products - The pia mater “delicate mother” is the innermost layer and firmly bound to the underlying neural tissue. B. The brain possesses four, fluid-filled chambers called ventricles. 1. The ventricles contain CSF. CSF is formed by the choroid plexus, an intricate network of capillaries, and CSF is absorbed by the arachnoid villi (granulations, trabeculae). 2. The ventricles are lined with ependymal cells which whip their cilia to circulate the CSF. 3. There are four ventricles: a. There are two lateral ventricles (right and left) each within one of the cerebral hemispheres. b. The third ventricle is located in the diencephalon. c. The fourth ventricle begins in the metencephalon and extends into the superior portion of the medulla oblongata. It then narrows and is continuous with the central canal of the spinal cord. 4. The third ventricle communicates with the fourth ventricle via the cerebral aqueduct.
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