PSYC 273 Chapter 2 Notes PDF

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Chapter 2 The nervous system is composed of cells All organs and muscles are in communication with the nervous system which is made up of cells Neurons: also called nerve cell. The basic unit of the nervous system, each composed of receptive extensions called dendrites, an integrating Cell body, a conducting axon, and a transmitting axon terminal Each neuron receives inputs from many other neurons integrates those inputs, and then distributes the processed information to other neurons. Your brain contains 100 billion of these. And a similar number of (glial cells: also called glia. Nonneuronal brain cells that provide structural, nutritional, and other types of support to the brain) are found in the brain. We know more about neurons because they are large and produce readily measured electrical signals Santiago Ramon y Cajal (1852-1934): showed 1) neurons and other cells of the brain are structurally, metabolically, and functionally independent, and 2) information is transmitted from neuron to neuron across tiny gaps later named (synapses: the cellular location at which information is transmitted from a neuron to another cell) we have a football field full of sand that represent the vast network of connections that are responsible for humanity’s achievements The neuron has 4 principal divisions A neuron contains DNA inside the cell nucleus, as well as an assortment of organelles (aka other cells of the body) like mitochondria produces energy and ribosomes manufacture protein under control of DNA in the nucleus. But neuron also has some unique, highly specialized features…. 1. Input zone: part of a neuron that receives information from other neurons or from specialized sensory structures. At cellular extensions called (dendrites: an extension of the cell body that receives information from other neurons), neurons receive info from other neurons. Dendrites may be elaborately branched out, to accommodate synapses from many other neurons. 2. Integration zone: part of a neuron that initiates electrical activity. Then the neurons (cell body: also called soma: the region of a neuron that is defined by the presence of the cell nucleus) integrates (combines) the info that has been received to determine whether or not to send a signal of its own 3. Conduction zone: part of a neuron -typically the axon- over which the action potential is actively propagated. The (axon: aka nerve fiber. A single extension from the nerve cell that carries action potentials from the cell body toward the axon terminals) conducts the neuron’s output information, in the form of electrical impulses, away from the cell body. 4. Output zone: part of neuron at which the cell sends info to another cell. Specialized swellings at the ends of the axon, called (axon terminals: aka synaptic bouton. The end of an axon or axon collateral, which forms a synapse with a neuron or other target cell There are hundred of different forms of neurons with shapes to reflect their specialized functions. Motoneurons: aka motor neurons, that transmits neural messages to muscles (or glands). Large and have long axons reaching out to synapse on muscles, causing muscular contractions. Sensory neurons: nerve cell that is directly affected by changes in the environment, such as light, odor, or touch. Diverse shapes depending on whether they detect light, or sound, or touch.

Interneurons: nerve cell that is neither a sensory neuron nor a motoneuron; interneurons receive input from and send output to other neurons. These are most of neurons in the brain, which analyze info gathered from one set of neurons and communicate with others. Axons of interneurons measure a few micro meters while moto and sensory neurons axons are a meter or more getting info from the most distant parts of body. In general, larger neurons tend to have more complex inputs and outputs, cover greater distances, and/or convey info more rapidly than smaller in addition to size, anatomist classify neurons according to 3 general shapes, each specialized for a particular kind of info processing: 1. Multipolar neurons: nerve cell that has many dendrites and a single axon. Most common type 2. Bipolar neurons: nerve cell that has a single dendrite at one end and a single axon at the other end. Especially common in sensory system, such as vision 3. Unipolar neurons: also called monopolar neurons, with a single branch that leaves the cell body and then extends in two directions; one end is the input zone and the other end is the output zone. Transmits touch info from body into spinal cord *these 3 neurons all go through the four stages, in all 3 neurons the dendrites comprise the input zone. In multi and bipolar neurons the cell body also receives synaptic inputs so it’s a part of the input zone. Info is received through synapses A neuron’s dendrites reflect the complexity of inputs that are received. At each synapse, info is transmitted from an axon terminal of a presynaptic (located on the “transmitting” side of a synapse) neuron to the postsynaptic ( region of a synapse that receives and responds to neurotransmitter) neuron. Synapse composed of following elements 1. The specialized presynaptic membrane (specialized membrane on the axon terminal of a nerve cell that transmits info by releasing neurotransmitter) of the axon terminal of the presynaptic neuron 2. Specialized postsynaptic membrane (specialized membrane on the surface of a neuron that receives info by responding to neurotransmitter form a presynaptic neuron) on the dendrite or cell body of the postsynaptic neuron 3. Synaptic cleft (space between the presynaptic and postsynaptic neurons at a synapse) which is tiny, measuring 20-40 nanometers Presynaptic axon terminals contains synaptic vesicles (small, spherical structure that contains molecules of neurotransmitter) Neurotransmitter (aka synaptic, chemical, or simply transmitter. The chemical released from the presynaptic axon terminal that serves as the basis of communication between neurons. Neurotransmitter are how presynaptic neuron communicates with postsynaptic cells. To signal the post synaptic cell, the presynaptic neuron fuses may synaptic vesicles to its presynaptic membrane, realizing their contents into the synaptic cleft. After crossing the cleft the released neurotransmitter interacts with matching neurotransmitter receptors (aka receptor, specialized protein often embedded in the cell membrane, that selectively senses and reacts to molecules of a corresponding neurotransmitter or hormone) these receptors capture and react to molecules of the neurotransmitter, altering the level of excitation of the postsynaptic neuron and thus affecting the likelihood that he postsynaptic

neuron will in turn release its own neurotransmitter from its axon terminals. Molecules of neurotransmitter generally do not enter the postsynaptic neuron; they simply bind to the receptors momentarily and then disengage. The configuration of synapses on and around dendrites and cell body is constantly changingsynapses come and go, and dendrites change their shape- in response to new patterns of synaptic activity and the formation of new neural circuits or Neuroplasticity (ability of the nervous system to change in response to experience or the environment. The axon integrates and then transits information (axon hillock comes before the axon) Axon hillock: cone shaped area on the cell body form which the axon originates. From which the neuron’s axon projects. Has unique properties that allow it to gather and integrate incoming info form the synapse on the dendrites and cell body, converting those inputs into a code of electrical impulses. These electrical signals race down the axon toward the targets that the neuron is said to innervate (to provide neural input to) The axon itself is narrow tube that may divide near the end into branches called axon collaterals (a branch of an axon). Various substances such as enzymes and structural proteins, are conveyed inside the axon from the cell body, where they are produced, to the axon terminals where they are used. Axon transports (transportation of materials from the neuronal cell body toward the axon terminals and from the axon terminals back toward the cell body for recycling) thus the axon has two quite different functions: the rapid transportation of electrical signals along the outer membrane, and the much slower transportation of substances within the axon, to and from the axon terminals. Glial cells protect and assist neurons Early neuroscientists thought they were mostly filler, holding nervous system together but know we know they directly affect neuronal processes by providing neurons with raw materials, chemical signals, and specialized structural components. 4 types of glial cells. myelin ((fatty insulation around an axon, formed by glial cells. This sheath boosts the speed at which nerve impulses are conducted))in the central nervous system) Oligodendrocytes (glial cell that forms myelin in the central nervous system) and Schwann cells (glial cell that forms myelin in the peripheral nervous system) – wrap around successive segments of axons to insulate them with myelin. Myelin sheaths give an axon the appearance of a string of elongated slender beads. Nodes of Ranvier (the gap between successive segments of the myelin sheath where the axon membrane is exposed) remain exposed. With the brain and spinal cord, myelination is provided by Oligodendrocytes, each cell typically supplying myelin beads to several nearby axons. In the rest of the body it’s supplied by Schwann cells which wraps itself around a segment of one axon to provide a single bead of myelin. Astrocytes (star shaped glial cell with numerous processes (extensions) that run in all directions) weave in between neurons with tentacle-like extensions some stretch between

neurons and fine blood vessels, controlling local blood flow to increase the amount of blood reaching more-active regions. Help form the tough outer membranes that swaddle the brain and also secrete chemicals that modulate neural activity and the formation of synapses. In contrast microglial cells (aka microglial, extremely small motile glial cells that remove cellular debris from injured or dead cells) are tiny and mobile. Primary job appears to be to contain and clean up sites of injury, and additional roles like maintenance of synapses and contribution to pain perception. Although glial cells are beneficial they are also problems, bc they continue to divide in adulthood (unlike neurons) glial cells can give rise to deadly brain tumors. Some glial cells, especially astrocytes, respond to brain injury by changing size- or swelling. This edema (swelling of tissue in response to injury) damages neurons and is responsible for many symptoms of brain injury. The Nervous System Extends throughout the Body Gross neuroanatomy: anatomical features of nervous system that are apparent to naked eye Central nervous system (CNS): portion of the nervous system that includes the brain and spinal cord Peripheral nervous system: portion of the nervous system that includes all of the nerves and neurons outside the brain and spinal cord and has two divisions. It consists of nerves (collection of axons bundled together outside of the central nervous system) that extend throughout the body. Some nerves are.. Motor nerves (transmits information from the CNS to the muscles and glands) and sensory nerves (conveys info from the body to the CNS) 1. Somatic nervous system: supplies neural connections mostly to the skeletal muscles and sensory systems of the body. It consists of cranial nerves and spinal nerves 2. Autonomic nervous system: provides the main neuron connections to glands and to smooth muscles of internal organs Somatic Nervous System ● Main pathway through which the brain controls movement and receives sensory information from the body and from the sensory organs of the head ● Nerves making up SNS form two anatomical groups 1. Cranial nerves: nerve that is connected directly to the brain a. We each have 12 pairs of them that arise from the brain and innervate the head, neck, and visceral organs directly, without every joining the spinal cord ----- figure 2.7 on page 31 is helpful b. Some are exclusively sensory: olfactory, optic vision, & vestibulocochlear c. Exclusively motor pathways from the brain: oculomotor, trochlear, abducens, spinal accessory, and hypoglossal d. Remain have both: trigeminal, facial, glossopharyngeal, and vagus 2. Spinal nerves: nerve that emerges from the spinal cord through regularly spaced openings along both sides of the backbone a. We have 31 pairs of spinal nerves and one member of each pair serves each side of the body. Each nerve is made up of group of motor fibers, projecting from the ventral (front) part of the spinal cord to the organs and muscles, and a group of sensory fibers that enter the dorsal (rear) part of the spinal cord

b. Cervical: referring to the topmost 8 segments of the spinal cord, i the neck region c. Thoracic: referring to the 12 spinal segments below the cervical portion of the spinal cord, corresponding to the chest d. Lumbar: referring to the 5 spinal segments that make up the upper part of the lower back e. Sacral: referring to the 5 spinal segments that make up the lower part of the lower back f. Coccygeal: referring to the lowest spinal vertebra (the coccyx, aka the “tailbone”) Autonomic nervous system ● We have little conscious, voluntary control over its actions. It’s the brain’s main system for controlling the organs of the body. Control functions are performed by two divisions 1. Sympathetic nervous system: part of ANS that acts as the “fight or flight” system, generally activating the body for action a. Axons from it exit form the middle parts of the spinal cord, travel a short distance and the innervate the sympathetic ganglia (small cluster of neurons found outside the CNS), which run two chains along the the spinal cord, one along each side. Axons from the sympathetic ganglia then course throughout the body innervating all the major organ systems preparing body for immediate action: blood pressure increases, pupil widen, and heart quickens 2. Parasympathetic nervous system: part of ANS that generally prepares the body to relax and recuperate a. Aka “rest and digest” response, in brain and spinal cord, parasympathetic axons travel a longer distance before terminating in parasympathetic ganglia, usually located close to the organs they serve. b. The two opposing systems release different neurotransmitters and the balance between them determines the state of the internal organs at any given moment CNS consists of the brain and spinal cord ● Spinal cord funnels sensory info from the body up to the brain and converys the brain’s motor commands out ot the body. The outer surface of the brain: ● Cerebral hemispheres: one of the two haves -- right or left -- of the forebrain, about the size of your two fist together ● The lumpy brain is result of elaborate folding of thick sheet of tissue, mostly dendrites cell bodies, and axonal projections of neurons called Cerebral cortex (or cortex, the outer covering of the cerebral hemispheres, which consist of largely nerve cell bodies and their branches). Resultant ridges of tissue called gyri ((gyrus for singular) ridged or raised portion of a convolved brain surface) are separated from each other by crevies called sulci ((sulcus for singular)crevice or valley of a convoluted brain surface) ● Neuroscientists rely on a combination of landmarks and functions to distinguish among 4 major cortical regions of the cerebral hemisphere: frontal (most anterior portion of

cerebral cortex), parietal (large region of cortex lying between the frontal and occipital lobes in each cerebral hemisphere), temporal (large lateral region of cortex in each cerebral hemisphere. It is continuous with the parietal lobe posteriorly and separated from the frontal lobe by the sylvian fissure), and occipital lobes (large region of cortex that covers much of the posterior part of each cerebral hemisphere) ● In some cases boundaries between adjacent lobes are very clear, sylvian fissure (or lateral sulcus. A deep fissure that divides the temporal lobe from other regions) and the central sulcus (fissure that divides the frontal lobe from the parietal lobe ● The cortex is the seat of complex cognition, depending on specific regions affected, cortical damage can cause symptoms ranging from impairments of movement or body sensations; through speech errors, memory problems, and personality changes, to many kinds of visual impairments ● Corpus callosum: main band of axons that connects the two cerebral hemispheres -allowing the brain to act as a single entity during complex processing ● Postcentral gyrus: strip of parietal cortex, just behind the central sulcus that receives somatosensory information from the entire body ● Precentral gyrus: strip of frontal cortex, just in front of the central sulcus that is crucial for motor control ● Occipital lobes crucial for vision and temporal for auditory inputs and help in memory formation. But each lobe also performs a wide variety of other high level functions ● Gray matter: areas of the brain that are dominated by cell bodies and are devoid of myelin. It mostly receives and processes information -- outer layer of cortex that’s grayish, they contain a preponderance of neuronal cell bodies and dendrites ● White matter: light-colored layer of tissue, consisting mostly of myelin sheathed axons, that lies underneath the gray matter of cortex, mostly transmits information Subdivisions within the brain -Neural tube: an embryonic structure with subdivisions that correspond to the future forebrain, midbrain, and hindbrain -- made of cells and filled with fluid -- a few weeks after conception the human neural tube begins to show 3 seperate swellings at head end 1. Forebrain: frontal division of the neural tube containing the cerebral hemispheres, the thalamus, and the hypothalamus -- by about 50 days the fetal forebrain develops two subdivisions a. Telencephalon: the anterior part of the fetal forebrain, which will become the cerebral hemispheres in the adult brain b. Diencephalon: the posterior part of the fetal forebrain, which will become the thalamus and hypothalamus in the adult brain 2. Midbrain: middle division of the brain a. Brainstem: region of brain that consists of the midbrain, the pons, and medulla 3. Hindbrain: rear division of the brain, which the mature vertebrate further develops into several large structures the cerebellum, pons, and medulla -within and between the major brain regions are collections of neurons called nuclei ((singular nucleus) collection of neuronal cell bodies within the central nervous system (eg caudate nucleus)) and bundles of axons called tracts (bundle of axons found within the CNS) The Brain is Described in Terms of Both Structure and Function

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Our body is bilaterally symmetrical, including our brain… except the right side of our brain controls and receives sensory info from the left side of the body and so on The Cerebral Cortex Performs Complex Cognitive Processing ● The cortex is made up of 6 different layers -- each unique in appearance bc it consists of either a band of similar neurons, or a particular pattern of dendrites or axons ● Pyramidal cell:type of large nerve cell that has a roughly pyramid-shaped cell body and is found in the cerebral cortex -- the most prominent kind of neuron in the cerebral cortex ● Cortical columns: one of the vertical columns that constitute the basic organization of the cerebral cortex -- extend through entire thickness of the cortex, from the white matter to surface Important Nuclei are Hidden Beneath the Cerebral Cortex ● Basal ganglia: group of forebrain nuclei, including the caudate nucleus, globus pallidus, and putamen, found deep within the cerebral hemisphere -- critical in movement ● Caudate nucleus, putamen, and globus pallidus: one of basal ganglia ● Limbic system: loosely defined widespread group of brain nuclei that innervate each other and form a network -- emotions mostly but also learning, its overlapping and curled around the basal ganglia ○ Amygdala: group of nuclei in the medial anterior part of the temporal lobe several subdivisions...