BioPsy - Module 2 (Anatomy and Functions of the Nervous System) PDF

BASIC FEATURES OF THE NERVOUS SYSTEM The efferent nerves of the autonomic nervous system are composed of two kinds, the peripheral DIVISIONS OF THE NERVOUS SYSTEM nervous system,...

BASIC FEATURES OF THE NERVOUS SYSTEM The efferent nerves of the autonomic nervous system are composed of two kinds, the peripheral DIVISIONS OF THE NERVOUS SYSTEM nervous system, and the sympathetic nervous system. The nervous system is one of the most These two systems perform opposite functions to important systems of the human body. It is responsible maintain internal balance. for every bodily function and behavior. Specifically, it The peripheral is the fight or flight response serves three main functions: sensory, integration, and system that is activated when a person is confronted motor (Barclay, 2020). by a perceived threat. Thus, this system causes the First, it collects sensory information from the body to be in a state of alertness and excitement. internal and external environment of the body. That is, our ability to hear, see, and taste are MENINGES just some of the sensory functions performed The central nervous system is one of the most by the nervous system. delicate organs of the human body which is protected Second, the nervous system serves an by three membranes/meninges. integrative function by processing the sensory signals in the brain which are then evaluated, and used for making decisions. Lastly, the nervous system is also responsible for our motor functions. For instance, our reflex response after touching a hot surface. The nervous system consists of two main divisions: the central nervous system and the peripheral nervous system. Central nervous system - composed of the brain (located inside the skull/cranium) and First, the outermost layer of meninges is spinal cord (a long tube-like structure that called the dura mater. It is composed of two extends from the end of the brain stem up to layers: namely, the periosteal/endosteal layer the lower part of the vertebral or spinal and the meningeal layer. The dura mater column) serves as a protective function to the brain and Peripheral nervous system - the nerves the spinal cord and limits the rotational connected to the spinal cord (peripheral movement of the brain (Kekere & Alsayouri, nerves) and directly to the brain (cranial 2020). nerves) can be found. It is composed of two Second, the arachnoid mater is the web-like divisions based on the voluntary and meningeal layer underneath the dura mater. involuntary responses: the somatic nervous Lastly, the pia mater is the innermost thin and the autonomic nervous system. The membrane and directly adherent to the surface somatic nervous system controls voluntary of the brain and spinal cord. body movement through the use of skeletal The space between the arachnoid mater and muscles. the pia mater is called the subarachnoid space which is filled with cerebrospinal fluid (CSF) [functions as a AUTONOMIC NERVOUS SYSTEM cushion to the CNS and skull (Heimer, 1983)] The autonomic nervous system controls the involuntary movement of the body. It regulates the THE VENTRICULAR SYSTEM AND internal processes of the body such as internal organs. PRODUCTION OF CEREBROSPINAL FLUID It is also responsible for controlling the vital functions of the body such as heart rate, respiration, breathing, and digestion (ProEdify, 2016). The autonomic nervous system is also composed of the efferent neurons which carry sensory information from the internal organ to the CNS and efferent neurons which transmit motor signals from the CNS down to the internal organ.  BLOOD-BRAIN BARRIER The blood-brain barrier is the barrier between the blood vessels and the brain tissues (Götz, 2017). It is an extremely selective semi-permeable border of endothelial cells. Between these endothelial cells lies the tight conjunctions (TJs) which control the blood-borne substances/ pathogens (e.g. HBV, HCV, HIV) from entering the brain (Sandoval, & Witt, 2008). The cerebrospinal fluid (CSF) serves a The blood-brain barrier serves several protective function by acting as a shock functions; such as: absorber and cushion to the brain (Telano, & 1. it manages the microenvironment (regulates Baker, 2020) to prevent pressures from the the substances and structures around a external environment. particular area), ○ It also provides essential nourishment 2. it regulates the entry of nutrients, and helps in removing waste from the 3. regulates the exit of brain waste, CNS (Telano, & Baker, 2020). 4. it regulates the ion and fluids between the ○ The CSF is a colorless liquid blood and the brain, and contained in the subarachnoid space, 5. helps maintain relatively normal levels of ventricular system, and the central hormones (Dr Matt & Dr Mike, 2020; Götz, canal of the spinal cord. 2017; Daneman & Prat, 2015). The central canal, or sometimes called spinal Thus, the blood-brain barrier prevents the toxins from foramen or ependymal canal, extends entering the brain while allowing the essential throughout the spinal cord. nutrients to be absorbed by the brain. Additionally, The ventricular system is composed of four different pathways or systems transport nutrients into internal chambers in the brain, the two lateral the brain. It includes diffusion, paracellular transport, ventricles, third and fourth ventricles. transport protein, receptor-mediated transcytosis, These three interconnected systems (subarachnoid adsorptive transcytosis, and efflux. space, central canal, & ventricular system) forms a single reservoir that facilitates the production of NEUROANATOMICAL TECHNIQUES cerebrospinal fluid (CSF)in the brain. The brain is made up of more than 100 billion interconnected neurons that communicate with each The production and secretion of most cerebrospinal other through synapses (Hoffman, n.d.). fluid occur in the choroidal plexus of the ventricular These neurons are tightly packed so looking at system. the structures under the microscope may be difficult. It flows from the lateral ventricle to the third Therefore, to be able to study its structure the ventricle via the interventricular foramen researchers use various techniques such as the: (also called the foramen of Monro). Golgi Staining Technique– it was named Then, it goes to the fourth ventricle by after Camillo Golgi, an Italian physician who passing through the cerebral aqueduct (also discovered this technique in the early 1870s. called the aqueduct of Sylvius). This method uses silver nitrate to densely stain It exits the fourth ventricle into the cerebral an entire single neuron including its dendrite subarachnoid space through the median and axon branches. This helps researchers see aperture (also called the foramen of the structure of a single neuron, although in Magendie) and the two lateral apertures (also silhouette form. However, this technique called the foramen of Luschka). cannot provide evidence about the number of single neurons in a particular area. The CSF continues into the spinal NISSL Staining Technique - The technique is subarachnoid space through the central canal named after its discoverer Franz Nissl, a of the spinal cord. (Adigun, & Al-Dhahir, 2019) German psychiatrist. This method uses dyes such as cresyl violet and other Nissl dyes to estimate the number of cell bodies in a  particular part of the brain by counting the Nissl stained dots. These planes are different lines used to divide Electron Microscopy – this technique is used the human brain. It includes the coronal plane (frontal to get information about the detailed structure plane), horizontal plane (also called transverse plane or of neurons. It uses a scanning electron cross-section plane), and the sagittal plane. microscope to obtain an electron micrograph which provides the details of neuron structure. However, due to a detailed picture of the neurons, it becomes difficult to visualize general aspects of neuron structure. NEUROANATOMICAL DIRECTIONS To easily locate the regions or areas of the nervous system, the neuroanatomists often used the three-dimensional system of directional coordinates. The vertebrate nervous system has three axes: anterior/ventral–posterior/dorsal superior/cranial– inferior/ caudal and medial-lateral Anterior/ventral means towards the “front” The coronal plane (frontal plane) is divided and posterior/dorsal means towards the “back”. into anterior and posterior which is created by The term superior/cranial/ rostral means slicing the brain vertically. towards the head end or upper/higher part of the body, The horizontal plane (transverse plane) and inferior/caudal means away from the head or the divides the brain into superior/rostral (towards lower part of the body. the nose) and inferior/caudal (towards the tail-end) directions which are done by slicing the brain horizontally. The sagittal plane is created by slicing the brain in the middle, thus dividing it into right and left cerebral hemispheres. THE CENTRAL NERVOUS SYSTEM The Development of the Central Nervous System After fertilization, the central nervous system starts to develop during the third week of the embryonic stage. The developing central nervous system contains three interconnected chambers that later To understand the medial-lateral axis, imagine become the ventricles. drawing a line in the middle of the body. The medial The tissues that surround the ventricles form means towards the midline of the body, while lateral the three primary vesicles: the prosencephalon means away from the midline. (forebrain), mesencephalon (midbrain), and the The proximal and distal are other directional rhombencephalon (hindbrain) terms, which means toward or near to the point of As the brain continuously develops, the rostral origin of a part and away or far from the point of origin chamber becomes the three separate divisions of of a part, respectively. chambers: the left and right ventricles and the third ventricles. NEUROANATOMICAL PLANES The area surrounding the lateral ventricles In order to easily study the structure of the becomes the telencephalon and the area surrounding central nervous system, the neuroanatomist also used the third ventricle becomes the diencephalon. different neuroanatomical planes. In the final structure, the chamber inside the midbrain (mesencephalon) becomes narrow, forming the cerebral aqueduct, and the two structures develop gyrus/motor cortex) and motor in the hindbrain: the metencephalon and the functions (precentral gyrus). myencephalon. ○ The parietal lobe regulates the body temperature, controls movement, and Three Major Divisions of the Brain processes information related to taste I. FOREBRAIN (PROSENCEPHALON) and touch. Specifically, the The forebrain is the largest division of the postcentral gyrus regulates the sense human brain. It is composed of the telencephalon and of touch and the remaining parts of the diencephalon. parietal lobe are responsible for the a. TELENCEPHALON- The telencephalon perception of our body and objects includes the two hemispheres of the brain that location as well as in directing forms the cerebral cortex. It also contains the attention to a particular stimulus. limbic system and the basal ganglia which are ○ The occipital lobe is responsible for located beneath the cerebral cortex. the vision. ○ The temporal lobe processes memory 1. CEREBRAL CORTEX and information perceived by the The cerebral cortex is the outer layer of the sense of taste, hearing, sight, and neural tissue of the cerebrum. This outermost touch. layer displays the gray matter which is mainly The superior temporal gyrus is responsible for composed of cell bodies (soma). processing information related to hearing and The deeper layer is commonly known as the language, the inferior temporal gyrus deals in white matter which is composed of myelinated identifying complex visual information, and axons. the medial part of the temporal lobe play an The cerebral cortex is highly convoluted which important role in certain kinds of memory forms a folded curved-shape. processes. A long and deep groove between the The cerebral cortex is also composed of two convoluted cortex is called the fissures and the parts: the neocortex and the allocortex. short and small grove is called the sulci ○ The allocortex covers 10% of the (plural: sulcus). The gyri (plural: gyrus) is the cerebral cortex. ridge on the surface of the brain which is ○ The neocortex constitutes 90% or the separated by fissures and sulci. major area of the cerebral cortex The cerebral cortex covers the two portions of which is responsible for an the cerebral hemispheres: the left and right individual's direct attention, thought, hemispheres. perception, and episodic memory It is separated by long and deep fissures, called (Bennett, 2019). the longitudinal fissures. These two It consists of a six-layer of neural tissues that hemispheres are connected by a bundle of can be easily identified using the common nerve fibers underneath the cerebral cortex, staining methods. These layers are: called the cerebral commissures. ○ molecular layer The largest commissure is called the corpus ○ external granular layer callosum which serves as the communicating ○ external pyramidal layer pathway between the two cerebral ○ internal granular layer hemispheres. ○ internal pyramidal layer Two long grooves divide the brain into four ○ fusiform or multiform layer lobes. It includes the lateral fissures and the Furthermore, the neocortex is comprised of central sulcus which divide the cerebral cortex four characteristics. into frontal lobes, parietal lobes, occipital ○ First, the cortical neurons can either be lobes, and the temporal lobes. pyramidal or stellate cells. Each lobe of the brain performs different The pyramidal cells are multipolar functions. pyramid-shaped neurons/cells with ○ The frontal lobe is responsible for huge dendrites (apical dendrites), performing complex cognitive (frontal while the stellate cells are small cortex anterior to the precentral  star-shaped neurons with short or no ability to encode information in long-term axons. memory and process it for later retrieval. ○ Second, cortical neurons in different Fornix layers have different density and sizes. The fornix is a C-shaped bundle of nerve ○ Third, many of the axons and fibers located in the medial aspects of the dendrites in the neocortex are cerebral hemispheres. organized vertically. Damage to fornix may result in deficits in ○ Lastly, the thickness of each layer declarative memories which deal with varies from area to area. autobiographical information. Cingulate Cortex 2. LIMBIC SYSTEM The cingulate cortex is a curved fold covering The limbic system is a set of brain structures the corpus callosum which regulates emotions that is responsible for an individual’s and behavior. emotions, motivated behaviors, regulating If the cingulate cortex is damaged it will result autonomous and endocrine function, and in cognitive, emotional, or behavioral consolidating memories (Stephani, 2014). disorders such as depression, anxiety It is involved in motivated behavior which is disorders, and obsessive-compulsive disorder known for its 5 F’s: (Bailey, 2020). ○ feeding (satiety and hunger), Septum ○ forgetting (memory) The septum is a midline nucleus located in the ○ fighting (emotional response) subcortical area of the brain. ○ family (sexual reproduction, maternal Mammillary Bodies instincts) The mammillary bodies are a pair of small ○ fornicating (sexual arousal) round bodies, located at the end of the anterior It is composed of the amygdala, the part of the fornix. hippocampus, the fornix, the cingulate cortex, the septum/septal area, and the mammillary 3. BASAL GANGLIA bodies. The basal ganglia are a group of the structure located within the subcortical region of the Amygdala brain which is involved in motor control and (has right and left part) is an almond-shaped learning, executive functions, behavior, and structure that can be found within the anterior emotions (Lanciego, Luquin, & Obeso, 2012). portion of the temporal lobes. It has four major parts: the amygdala, caudate, It is involved in regulating emotional putamen, and globus pallidus. responses such as anger, violence, fear, and anxiety Amygdala The amygdala is also responsible for the considered part of the basal ganglia and limbic perception of emotions from other people. system which is responsible for emotion. Hippocampus Caudate A structure located posteriorly to the Thecaudate is a long tail-like structure located amygdala. posterior and anterior to the amygdala. The hippocampus (has right and let portion) is The caudate nucleus is responsible for a small, curved structure embedded within the executing movements, motor learning, temporal lobe which plays an important role in motivation, and reward. learning, memory, and associating emotional Inferior to the head of caudate and anterior to responses to particular situations of events. the tail of caudate, a round-shape structure Hippocampus also helps process and retrieve known as putamen can be found. declarative (i.e., memories related to facts and Putamen events) and spatial relationship memories (i.e., The putamen, together with the caudate forms pathways or routes) (Dresden, 2017). the dorsal striatum which is involved in If this part is damaged, a person may facilitating voluntary movements. experience loss of memory and may lose the Globus Pallidus Lastly, the mammillary bodies are a pair of It is located between the putamen and small round bodies which is involved in thalamus and controls conscious and processing recollective memories (i.e., proprioceptive movements [(e.g., knowing memories related to episodes of past whether feet are on soft grass or hard cement experiences). without looking (even while wearing shoes), However, memory information starts from the balancing on one leg, throwing a ball without hippocampus in which CA3 neurons is having to look at the throwing arm]. activated by the theta waves before transmitting the information via the fornix to the mammillary bodies The diencephalon is composed of two major structures: the thalamus or hypothalamus. II. MIDBRAIN (MESENCEPHALON) a. MESENCEPHALON 1. Thalamus The midbrain or the mesencephalon is a small The thalamus is a two-lobe structure situated region of the brain that is inferior to the forebrain beneath the cerebral cortex and above the (prosencephalon) and superior to the hindbrain brainstem. (rhombencephalon). Although it is small compared to Primarily, the function of the thalamus is to the other two regions, it still plays an important relay the motor and sensory neurons to the function in controlling motor movements, particularly cerebral cortex. the movements of the eye, visual processing, and It is composed of different pairs of nuclei that auditory functions. project to the cortex. One of the most understood is the sensory 1. TECTUM relay nuclei which receive the sensory signal, The tectum receives sensory information then processes, transmit, and project sensory perceived by the eyes and ears. information to areas of the sensory cortex. It is composed of two pairs of bumps called Examples of sensory relay nuclei are lateral colliculi. geniculate nuclei which relay visual The inferior colliculi receive auditory inputs information, medial geniculate nuclei which and superior colliculi receive the visual relay auditory information, and ventral information. posterior nuclei which relay somatosensory These two colliculi formed the corpora information to areas of the sensory cortex. quadrigemina. 2. Hypothalamus 2. TEGMENTUM The hypothalamus is a small structure located Tegmentum is located at the ventral part of below the anterior part of the thalamus and the midbrain. near the pituitary gland. It contains three important structures that are It is also involved in regulating some of the of particular interest to biopsychologists: The motivated behaviors such as sleeping, eating, periaqueductal gray matter, Substantia nigra, and the and sexual behaviors. Red nucleus It also controls the endocrine system by regulating the release of hormones from the Periaqueductal Gray Matter pituitary gland The periaqueductal gray matter is the gray matter that surrounds the cerebral aqueduct. 3. Optic chiasm and mammillary bodies It regulates heart rate and blood pressure, Beneath the hypothalamus lies the other two autonomic processes, production of structure called the optic chiasm and vocalization, and fearful and defensive mammillary bodies. reactions. The optic chiasm is an X-shaped structure It is also a particular interest to formed by the crossing of the optic nerves in biopsychologists because of its important role the brain which allows the visual cortex to in analgesia (inability to feel pain). generate binocular vision. Substantia Nigra b. MYELENCEPHALON The substantia nigra is a highly pigmented The medulla oblongata, or commonly known (neuromelanin) structure within the midbrain as the medulla, is a major structure found in which is responsible for modulating motor myencephalon and makes-up the brainstem. movements and rewarding behaviors. It is in charge of the body’s autonomic It is Latin for black substance. (involuntary) functions such as respiration and It works with basal ganglia through a circulation. connection called dopaminergic nigrostriatal The medulla contains a portion of the reticular pathway (the pathway that travels from formation, a structure located at the center of the substantia nigra to the striatum) which is brainstem which performs an important role in a state believed to influenced behavior (Boie, 2011). of consciousness, emotion processing, visual Additionally, the substantia nigra is divided coordination, cardiovascular control, and posture into two areas: the substantia nigra par compacta and substantia nigra pars reticulata. SPINAL CORD ○ The substantia nigra par compacta The spinal cord is a long, thin, tube- like are darker and highly pigmented structure that extends from the end of the compared to its counterpart as it is brainstem up to the bottom of the spine. densely populated by dopamine It is a communication pathway wherein the neurons. transmission of sensory and motor signals ○ The substantia nigra pars reticulata from the brain to the rest of the body, or vice is slightly bright as it is heavily versa takes place. populated by GABA neurons. It is apparent that the spinal cord consists of Red Nucleus two major areas: the gray and white matter. The red nucleus plays an important part in the The gray matter which is composed largely of coordination of sensorimotor information. soma (cell bodies) and few unmyelinated neurons are located beneath the spinal cord. III. HINDBRAIN (RHOMBENCEPHALON) The white matter forms the outer layer and is a. METENCEPHALON made of myelinated axons. The metencephalon is divided into two areas: the pons and the cerebellum. Pons Pons is a large structure which lies superior to the medulla and inferior to the midbrain. It is the region of the brain with many connected cranial nerves such as the trigeminal nerve, abducens nerve, facial nerve, and vestibulocochlear nerve which are in charge of feeling in the face, eye movements, facial expression, and transmitting of sounds from the ear to brain, respectively. Cerebellum The cerebellum is located posterior to the The two dorsal arms are called dorsal horns, pons. It is covered by the outermost layer of whereas the two ventral arms are called gray matter called cerebellar cortex. ventral horns. The cerebellum is primarily in-charge of Thirty-one pairs of peripheral nerves are performing motor movements.Specifically, it directly connected to the spinal cord. helps a person to maintain balance, and learn Each of these nerves divides and connects to and coordinate motor movements. the spinal cord through one of two roots, the Damage to the cerebellum can also lead to dorsal and ventral root. cerebellar disorders such as ataxia wherein the All dorsal roots are sensory or afferent main presenting signs and symptoms are lack unipolar neurons that contain a group of cell of muscle control and coordination, and walking and mobility difficulties.  bodies outside the cord, thus forming the TWO MAJOR PROBLEMS IN THYROID dorsal root ganglion. On the other hand, the ventral roots are motor HYPERTHYROIDISM or efferent multipolar neurons where their cell Happens when the thyroid gland makes too bodies can be found in the ventral horns. much thyroid hormone HYPOTHYROIDISM ENDOCRINE SYSTEM When the thyroid gland doesn’t make enough thyroid hormones to meet your body’s needs A complex network of glands and organs. It uses hormones to control and coordinate your body’s THYMUS metabolism, energy level, reproduction, growth and Located in the upper part of the chest and development, and response to injury, stress, and mood. produces white blood cells that fight infections and destroy abnormal cells PITUITARY GLAND OR HYPOPHYSIS ADRENAL GLANDS Attached to the hypothalamus at the base of Also known as suprarenal glands the brain Small, triangular-shaped glands located on top Can be divided into posterior pituitary and of both kidneys anterior pituitary Two parts: cortex and medulla HYPOTHALAMUS ADRENAL CORTEX Is the major integrating link between the Is the outer region and also the largest nervous and endocrine system part of an adrenal gland The area of the brain that controls body ADRENAL MEDULLA temperature, hunger and thirst Located inside the adrenal cortex in HYPOTHALAMUS & PITUITARY GLAND the center of an adrenal gland regulate virtually all aspects of growth, ADIPOSE CAPSULE development, metabolism, and homeostasis. Where the adrenal cortex and adrenal medulla PINEAL GLAND are developed that forms a protective layer The main function of the pineal gland is to around a adrenal gland receive and convey information about the current light-dark cycle from the environment HORMONES OF ADRENAL MEDULLA via the production and secretion of melatonin cyclically at night (dark period) EPINEPHRINE (ADRENALINE) & THYROID GLAND NOREPINEPHRINE (NORADRENALINE) Are located in the front of the neck, below the Controls hormones that initiate the flight or larynx. fight response THYROXINE Produced by thyroid in the body KEY HORMONES PRODUCED BY ADRENAL PARATHYROID GLAND CORTEX Play an important role in the regulation of the ZONA FASCICULATA body’s calcium balance Cortisol (Glucocorticoids) CRETINISM ZONA GLOMERULOSA A condition of abnormal mental and physical Aldosterone (Mineralocorticoids) development resulting from a deficiency of ZONA RETICULARIS thyroid hormone in fetal or early life, typically Androgens characterized by intellectual disability, small stature, and thickening of the facial features. MOST COMMON ADRENAL GLANDS There are 12 pairs of it, and each corresponds DISEASE to a roman numeral which is based on the location, from front to back. ADDISON’S DISEASE They are typically categorized as sensory, Happens when your body doesn’t have enough motor, or both. cortisol and aldosterone The sensory nerves are involved with senses, CUSHING’S SYNDROME whereas the motor nerves are in charge of Happens when your body has too much controlling movements. cortisol (hypercortisolism) PANCREAS I. OLFACTORY NERVE (SENSORY) Helps with digestion and releases hormones It is a nerve that transmits sensory information that regulate your body sugar perceived by the person’s sense of smell via Also plays a role in supporting other organs the olfactory bulb. like heart, liver and kidneys II. OPTIC NERVE (SENSORY) OVARIES It is responsible for carrying visual It releases progesterone and estrogen information to the brain. ○ PROGESTERONE is a female sex III. OCULOMOTOR NERVE (MOTOR) hormone which is helpful during This nerve is in charge of controlling muscle pregnancy and menstrual cycle movements of the eye including the movement ○ ESTROGEN is a main female sex of eyeballs and eyelids. hormone responsible for development It also performs involuntary functions such of female reproductive system and that pupil size changes as it responds to light. secondary female sec characteristics The pupil constricts when the light is bright to and feminine physical appearance allow less light to pass through and the pupil TESTES dilates when dark to allow more light to enter. Testes produce androgens IV. Trochlear nerve (motor) ○ ANDROGENS secretes sex hormones This nerve is also involved in movements of and function is for the development of the eye, specifically controls the downward masculine structure and inward movements. ○ TESTOSTERONE at puberty, it V. Trigeminal nerve (sensory & motor) promotes the growth and maturation This largest cranial nerve is responsible for of the reproductive system organs to chewing and clenching teeth (motor prepare the young man for functions), as well as sensations (sensory reproduction function) to three divisions (ophthalmic, maxillary, & mandibular) of the face. VI. Abducens nerve (motor) THE PERIPHERAL NERVOUS SYSTEM This nerve controls the lateral rectus muscle which is also involved in controlling eye a. SPINAL NERVES movements (e.g., outward gaze) A spinal nerve is a nerve directly connected to VII. Facial nerve (sensory & motor) the spinal cord which carries sensory, motor, This is the most complex cranial nerve which and autonomic signals from the body to the consists of four nuclei responsible for brain, or vice versa. controlling muscle movements (used for facial There are 31 pairs in different levels of the expression chewing, swallowing, and jaw spine: 8 cervical, 12 thoracic, 5 lumbar, 5 movements), sense of taste of the major parts sacral, and 1 coccygeal. of the tongue, the sensation from the external Each pair connects the spinal cord with a ear and supply major glands in the head and specific region of the body neck. VIII. VESTIBULOCOCHLEAR NERVE b. CRANIAL NERVES (SENSORY) The cranial nerves are pairs of nerves that It is composed of the vestibular nerve and connect the brain and different parts of the cochlear nerve which are responsible for head, neck, and truck. balance and hearing, respectively. IX. GLOSSOPHARYNGEAL NERVE (SENSORY confronted by stress and emergencies. For & MOTOR) instance, a person’s heart tends to beat faster This 9th cranial nerve is involved in receiving and saliva tends to be overly produced when a sensory information from the throat, inner ear, person is being chased by a king cobra. and back of the tongue (involved in the sensation of taste) (sensory functions). 2. PARASYMPATHETIC NERVOUS SYSTEM It is also involved in controlling the The parasympathetic nervous system is known stylopharyngeus, a muscle that allows the as the rest and digest system, as it controls throat (pharynx) to shorten and widen. bodily processes during ordinary situations. X. VAGUS NERVE (SENSORY & MOTOR) It supports the activities that are involved in It is the longest nerve involved in the sensation the constriction of pupils, decreased heart rate perceived from the outer ear and the internal and blood pressure, constriction of bronchial organs in the neck, chest, and abdomen. muscles, increase digestion, increased It also controls the muscles in the throat and production of saliva and mucus, and increase soft palate which helps the person speak and in urine secretion. swallow. The vagus nerve plays a minor role in taste COMMUNICATION BETWEEN NEURONS sensation. Additionally, it is also involved in the Measuring Electrical Potential Axons sensation to the heart which detects changes in Electrode – electrical conductors that provide blood pressure and oxygen levels in the blood. a path for electricity to enter or leave the XI. ACCESSORY NERVE (MOTOR) medium This cranial nerve controls the neck muscles Microelectrode – a very fine electrode, responsible for rotating, flexing, and extending generally used to record activity of individual the neck and shoulders. neurons It is divided into two parts: the spinal and Oscilloscope – instrument capable of cranial portion. displaying graph of voltage XII. HYPOGLOSSAL NERVE (MOTOR) Membrane potential – the difference in This nerve is responsible for controlling the electric potential between the interior and the movements of the major parts of the tongue exterior of a biological cell. It equals the wherein, damage to this nerve can cause interior potential minus the exterior potential. tongue paralysis. ACTION POTENTIAL The brief electrical impulse that provides the A. AUTONOMIC NERVOUS SYSTEM basis for conduction of information along an axon The autonomic nervous system is the control system of the peripheral nervous system which is responsible for involuntary bodily functions including heart rate, blood pressure, respiration, digestion, and sexual arousal. It is composed of two main subdivisions: the sympathetic and parasympathetic nervous systems. Both of these systems consist of afferent and efferent neurons which facilitate and transmit the sensory and motor signals from the internal organs to the brain, or vice versa. 1. Resting Potential – the membrane potential of 1. SYMPATHETIC NERVOUS SYSTEM a neuron when it is not being altered by The sympathetic nervous system is mostly excitatory or inhibitory postsynaptic potentials involved in the fight or flight response of the (-70 mV) body. 2. Threshold of excitation – voltage level that This means that this division of the autonomic triggers an action potential (-55 mV) nervous system is usually activated when  3. Depolarization – reduction (towards 0) of the The sudden inflow of positively charged ions would membrane potential of a cell from its normal drastically change the membrane potential. resting potential 4. Repolarization - is a stage of an action THE ACTION POTENTIAL potential in which the cell experiences a Ion channel – a specialized protein molecule that decrease of voltage due to the efflux of permit specific ions to enter or leave the cell potassium (K+) ions along its electrochemical Conduction of the Action Potential gradient. Saltatory conduction – conduction of action 5. Hyperpolarization – an increased in the potentials by myelinated axons. The action potential membrane potential of a cell, relative to the jumps from one node of Ranvier to the next normal resting potential. SYNAPTIC TRANSMISSION The Membrane Potential: Balance of Two Forces To describe the ways in which neurons can The Force of Diffusion: Movement of communicate with each other. molecules from regions of high concentration These communications make it possible for to regions of low concentration. circuits of neurons to gather sensory The Force of Electrostatic Pressure: The information, make plans and initiate behaviors. attractive force between atomic particles The primary means of communication charged with opposite signs or the repulsive between neurons is synaptic transmission – force between atomic particles charged with the transmission of messages from one neuron the same sign. Cations (-) Anions (+) to another through a synapse These messages are carried by Intracellular fluid – the fluid contained neurotransmitters, released by terminal within cells buttons. These chemical diffuse across the Extracellular fluid – body fluids located fluid-filled gap between the terminal buttons outside the cells and the membranes of the neurons with which A- ⎯ organic anions (negatively charged they form synapses proteins and intermediate products of the cell’s Neurotransmitters produce postsynaptic metabolic processes are found only in the potentials – alterations in the membrane intracellular fluid) potential of a postsynaptic neuron, produced Chloride ions (Cl-) ⎯ (found predominantly in by release of neurotransmitter at the synapse – extracellular fluid) that increase or decrease the rate of firing of Sodium ions (Na+) ⎯ Natrium (found the axon of the postsynaptic neuron predominantly in extracellular fluid) Potassium ions (K+) ⎯ Kalium (found Ligand - chemical that binds with the binding predominantly in intracellular fluid) site of a receptor. Neurotransmitters are natural ligands, Question: How can Na+ remain in greatest produced and released by neurons concentration in the extracellular fluid, despite the fact that both forces (diffusion and electrostatic pressure) tend to push it inside? The membrane is impermeable to Na+, as it is to A-, the organic anions. Sodium-potassium transporter – a protein found in the membrane of all cells that transports sodium ions out of the cell and transports potassium ions into the cell Question: What would happen if the membrane suddenly became permeable to Na+? Synapses can occur in three places: molecule of a neurotransmitter binds with a postsynaptic receptor – which permits the passage of specific ions to pass through the membrane, changing the local membrane potential. The direct method is simpler, when a molecule of the appropriate neurotransmitter attaches to the binding sites, the ion channel opens. The indirect method is more complicated. Most receptors do not open ion channels directly but instead start a chain of chemical events. 1. Axodendritic synapses – can occur on the Two types of receptors: smooth surface of a dendrite or on dendritic spines – a small bud on the surface of a dendrite, with which a terminal button from other neuron forms a synapse. 2. Axosomatic synapse – occur on somatic membrane 3. Axoaxonic synapse - consists of synapses between two terminal buttons Presynaptic membrane – the membrane of the terminal button that lies adjacent to the post- synaptic membrane POSTSYNAPTIC POTENTIALS Postsynaptic membrane – the cell membrane opposite the terminal button in a synapse; the Major Types Of Neurotransmitter- Dependent Ion membrane of the cell that receives the message. Channels found in the Postsynaptic membrane Synaptic cleft – the space between the presynaptic a. Sodium (Na+) membrane and the postsynaptic membrane Contains b. Potassium (K+) extracellular fluid, through which the neurotransmitter c. Chloride (Cl-) diffuses. Synaptic vesicle – a small hollow, bead like structure TERMINATION OF THE POSTSYNAPTIC found in terminal buttons; contains molecules of a POTENTIAL neurotransmitter. a. Postsynaptic potentials Release zone – a region of the interior of the are brief depolarization or presynaptic membrane to which synaptic vesicles hyperpolarization caused by the attach and release their neurotransmitter into the activation of postsynaptic receptors synaptic cleft with molecules of a neurotransmitter. RELEASE OF A NEUROTRANSMITTER Two mechanisms keep them brief: ACTIVATION OF RECEPTORS a. Reuptake – the reentry of the They do so by diffusing across the fluid that neurotransmitter just release by a fills the synaptic cleft. Once they reach the terminal button back through its other side of the synaptic cleft, they attach to membrane, thus terminating the the binding sites of the postsynaptic receptors postsynaptic potential. – a receptor molecule in the postsynaptic b. Enzymatic deactivation - the membrane that contains a binding site for a destruction of the neurotransmitter by neurotransmitter. an enzyme after it release Once binding occurs, the postsynaptic receptors open neurotransmitter-dependent ion channels – an ion channel that opens when a  Acetylcholine (ACh) – a neurotransmitter AUTORECEPTORS found in the brain, spinal cord, and parts of the A receptor molecule located on a neuron that PNS; responsible for muscle contraction. responds to the neurotransmitter released by that Acetylcholinesterase (AChE) – the enzyme neuron. that destroys acetylcholine soon after it is Postsynaptic receptors detect the presence of a released by the terminal buttons, thus neurotransmitter in the synaptic cleft and initiate terminating the postsynaptic potential. excitatory or inhibitory postsynaptic potentials. But the postsynaptic membrane is not the only location of EFFECTS OF POSTSYNAPTIC POTENTIAL: receptors that respond to neurotransmitters. NEURAL INTEGRATION NEURAL Many neurons also possess receptors that INTEGRATION respond to the neurotransmitter that they release, Excitatory postsynaptic potentials increase the called autoreceptors. likelihood that the postsynaptic neuron will fire; Autoreceptors do not control ion channels. inhibitory postsynaptic potentials decrease this Thus, when stimulated by a molecule of the likelihood. appropriate neurotransmitter, autoreceptors do not Thus, the rate at which an axon fires is produce changes in the membrane potential. Instead, determined by the relative activity of the excitatory they regulate internal processes, including the and inhibitory synapses on the soma and dendrites of synthesis and release of the neurotransmitter. the cell. In most cases, the effects of autoreceptor activation are inhibitory; that is, the presence of the Neural integration – the process by which inhibitory neurotransmitter in the extracellular fluid in the and excitatory potentials summate and control the rate vicinity of the neuron causes a decrease in the rate of of firing of a neuron. the synthesis or release of the neurotransmitter. Autoreceptors are part of a regulatory system NEURAL INTEGRATION that controls the amount of neurotransmitter release. If The interaction of the effects of excitatory and too much is released; if not enough is released, the inhibitory synapses on a particular neuron. rates of production and release go up. Excitatory synapses becomes active The release of the neurotransmitter produces COMMUNICATION AT AXOAXONIC depolarizing EPSPs in the dendrites of a SYNAPSES neuron. Axoaxonic synapses do not contribute directly These EPSPs are then transmitted down the to neural integration. Instead, axoaxonic synapses alter dendrites, across the soma, to the base of the the amount of a neurotransmitter released by the axon. terminal buttons of the postsynaptic axon. If the depolarization is still strong enough The release of a neurotransmitter by a terminal when it reaches this point, the axon will fire. button is initiated by an action potential. Normally, a Inhibitory synapses becomes active particular terminal button releases a fixed amount of inhibitory postsynaptic potentials are neurotransmitter each time an action potential arrives. hyperpolarizing – they bring the membrane potential away from the threshold of COMMUNICATION AT AXOAXONIC excitation. SYNAPSES Thus, they tend to cancel the effects of The release of the neurotransmitter can be excitatory postsynaptic potentials. modulated by the activity of the axoaxonic synapses. They can produce presynaptic modulation: The rate at which a neuron fires is controlled by the relative activity of the excitatory and inhibitory a) Presynaptic inhibition – the action potential of a synapses on its dendrites and soma. If the activity of presynaptic terminal button in an axoaxonic synapse; the excitatory synapses goes up, the rate of firing will reduces the amount of neurotransmitter released by the go up. If the rate of inhibitory synapses goes up, the postsynaptic terminal button. rate of firing will go down b) Presynaptic facilitation – the action of a presynaptic terminal button in an axoaxonic synapse; increases the amount of neurotransmitter released by the postsynaptic terminal button. Nonsynaptic communication: Neuromodulators – a naturally secreted substance that acts like a neurotransmitter except that it is not restricted to the synaptic cleft but diffuses through the extracellular fluid. Hormones – are produced in cells located in the endocrine glands Endocrine gland – a gland that releases its secretions into the extracellular fluid around capillaries and hence into the blood-stream. Target cell – the type of cell that is directly affected by a hormone or nerve fiber Axon Hillock Connects the cell body and the axons and is responsible for firing signals (i.e. action ANATOMY AND FUNCTIONS OF CELLS OF potential) down the axons THE NERVOUS SYSTEM Myelin or myelin sheath Is made up of fatty substances and proteins GLIAL CELLS that form around the axons. Non-neuronal cells and do not transmit It plays three important functions: it protects electrical impulses, plays an important role in and acts as an insulator to the axons, and maintaining equilibrium enhances the speed of transmitting the NEURONS electrical signal Transmit electro-chemical signals to and from Node of Ranvier the brain, muscles, gland cells and the rest of facilitates the rapid transmission of electrical the nervous system. impulses along the axons The bodily processes and functions including thoughts, feelings and behavior would be impossible without neurons and supporting cells within the nervous system. EXTERNAL ANATOMY OF NEURONS Cell body Or the soma supplies protein to other parts of the neurons which is essential for the proper functioning of neurons. It is composed of organelles and nucleus that Terminal buttons are also involved in a variety of cell functions. are small-knob structures located at the end of Dendrites the axons which releases chemicals (called Are tree-like branches designed for receiving neurotransmitters) into the synapse and send electrochemical signals from other neurons signals to other neurons and transmit them to the cell body Synapse Cell membrane is a gap located at the end of the terminal Is a semipermeable membrane that protects the buttons which consist of the presynaptic neuron. membrane, synaptic cleft, and postsynaptic It is a two- layer lipid molecule which consists membrane of embedded signal proteins and channel proteins. Axon Transmits Electrochemical signals away from the cell body INTERNAL ANATOMY OF NEURONS Neurotransmitters are chemicals messengers stored inside the Nucleus synaptic vesicles which are involved in the an oval-shaped structure that contains DNA synaptic transmission (deoxyribonucleic acid) and plays a critical role in the production of protein within the cell TYPES OF NEURONS Cytoplasm A clear jellylike fluid inside the neuron. It is important in supporting and keeping organelles and molecules in place. Mitochondria It is responsible for regulating calcium ions (CA2+) which helps transmit the electrical impulses down to the axon and triggers the presynaptic membrane and synaptic vesicles to release the neurotransmitters into the synapses. Endoplasmic Reticulum (ER) Endoplasmic Reticulum (ER) forms a series of A neuron with more than two processes flattened sacs within the cytoplasm. extending from its cell body is classified as a It consists of two types: the rough endoplasmic multipolar neuron; most neurons are reticulum (RER) and the smooth endoplasmic multipolar. reticulum (SER). A neuron with one process extending from its ○ The rough endoplasmic reticulum cell body is classified as a unipolar neuron (RER) consists of ribosomes and is Unipolar neurons are typically sensory located only in the cell body. neurons with receptors located within the skin, ○ The smooth endoplasmic reticulum joints, muscles, and internal organs. (SER) consists of tubule networks that A neuron with two processes extending from connect the RER and Golgi apparatus its cell body is classified as a bipolar neuron. Neurons with a short axon or no axon at all are Golgi Apparatus called interneurons; their function is to also called Golgi Complex and Golgi Body is integrate neural activity within a single brain a membrane-bound organelle that receives structure, not to conduct signals from one proteins from the rough endoplasmic reticulum structure to another (RER), then sorts and packs them into vesicles before it secretes to the cell membrane THE VISUAL SYSTEM Ribosomes a type of organelle located in the endoplasmic Introduction reticulum (ER) which is involved in producing The visual system constructs a mental proteins necessary for neuronal functions representation of the world around us. This contributes Microtubules to our ability to successfully navigate through physical are abundant in neurons, occupying axons and space and interact with important individuals and dendrites as part axially aligned arrays. objects in our environments. These microtubule arrays provide a structural backbone for axons and dendrites that allows ANATOMY OF THE VISUAL SYSTEM them to acquire and maintain their specialized morphologies. The eye is the major Synaptic Vesicles (SVs) sensory organ are small, electron-lucent vesicles that are involved in vision. clustered at presynaptic terminals. Light waves are They store neurotransmitters and release them transmitted across the by calcium triggered exocytosis. SVs are made cornea and enter the locally at the terminals and are regenerated eye through the pupil. after exocytosis CORNEA CONES The cornea is the transparent covering over The cones are specialized types of the eye. photoreceptors that work best in bright light It serves as a barrier between the inner eye and conditions. the outside world, and it is involved in Cones are very sensitive to acute detail and focusing light waves that enter the eye. provide tremendous spatial resolution. They PUPIL also are directly involved in our ability to The pupil is the small opening in the eye perceive color. through which light passes, and the size of the pupil can change as a function of light levels While cones are concentrated in the fovea, as well as emotional arousal. where images tend to be focused, rods, another type of When light levels are low, the pupil will photoreceptor, are located throughout the remainder of become dilated, or expanded, to allow more the retina. light to enter the eye. When light levels are high, the pupil will RODS constrict, or become smaller, to reduce the Rods are specialized photoreceptors that work amount of light that enters the eye. well in low light conditions, and while they The pupil’s size is controlled by muscles that lack the spatial resolution and color function are connected to the iris, which is the colored of the cones, they are involved in our vision in portion of the eye. dimly lit environments as well as in our perception of movement on the periphery of BASIC STRUCTURE OF THE EYE our visual field. CORNEA - This transparent outer layer protects the Rods and cones are connected (via several eye and helps focus light interneurons) to retinal ganglion cells. Axons from the IRIS- The colored part of the eye that regulates retinal ganglion cells converge and exit through the the size of the pupil, controlling the amount of light back of the eye to form the optic nerve. entering The optic nerve carries visual information LENS - This clear structure behind the iris focuses from the retina to the brain. light onto the retina RETINA - The inner lining of the eye containing There is a point in the visual field called the photoreceptor cells (rods and cones) that convert light blind spot: Even when light from a small object is into electrical signals focused on the blind spot, we do not see it. THE OPTIC NERVE - Transmits visual information We are not consciously aware of our blind spots for from the retina to the brain two reasons: First, each eye gets a slightly different view of After passing through the pupil, light crosses the visual field; therefore, the blind spots do the lens, a curved, transparent structure that serves to not overlap. provide additional focus. Second, our visual system fills in the blind The lens is attached to muscles that can change spot so that although we cannot respond to its shape to aid in focusing light that is reflected from visual information that occurs in that portion near or far objects. of the visual field, we are also not aware that In a normal-sighted individual, the lens will information is missing. focus images perfectly on a small indentation in the back of the eye known as the fovea, which is part of the retina, the light-sensitive FOVEA The fovea contains densely packed specialized photoreceptor cells. These photoreceptor cells, known as cones, are light-detecting cells.  The optic nerve from each eye merges just ASTIGMATISM below the brain at a point called the optic chiasm. Irregular curvature of the cornea or lens causes The optic chiasm is an X-shaped structure that distorted vision at all distances. sits just below the cerebral cortex at the front of the Corrected with cylindrical lenses. brain. CATARACTS At the point of the optic chiasm, information Clouding of the eye's lens, leading to blurry from the right visual field (which comes from both vision. eyes) is sent to the left side of the brain, and Treatable with surgery to replace the cloudy information from the left visual field is sent to the right lens. side of the brain. GLAUCOMA Increased intraocular pressure damages the Once inside the brain, visual information is optic nerve, leading to vision loss. sent via a number of structures to the occipital lobe at Managed with medication or surgery. the back of the brain for processing Visual information might be processed in parallel pathways which can generally be described as the “what pathway” (ventral) and the “where/how” pathway (dorsal), The “what pathway” is involved in object recognition and identification, while the “where/how pathway” is involved with location in space and how one might interact with a particular visual stimulus (Milner & Goodale,2008; Ungerleider & Haxby, 1994) For example, when you see a ball rolling down the street, the “what pathway” identifies what the object is, and the “where/how pathway” identifies its location or movement in space Image showing dorsal stream (green) and ventral stream (purple) in the human brain visual system. COMMON EYE DISORDERS MYOPIA (NEARSIGHTEDNESS) Distant objects appear blurry due to the elongation of the eyeball or excessive curvature of the cornea. Corrected with concave lenses. HYPERMETROPIA (FARSIGHTEDNESS) Close objects appear blurry due to the shortening of the eyeball or flat cornea. Corrected with convex lenses.