Lesson 2 Chapter 3 – The Central Nervous System

Lesson 2 Chapter 3 – The Central Nervous System 1 Unit 6 Study Guide Excluded Pages 128 Sleep: an active process up to 131 left column The Organization of the Central Nervous System The nervous system is organized into the CNS, consisting of the brain and spinal cord, and the peripheral nervous system (PNS), consisting of nerve fibers that carry info between CNS and other parts of the body (periphery). The PNS is further divided into afferent and efferent division. The afferent carries info to the CNS informing it of changes in the external (eg. Ambient temperature) and internal (eg. Hunger) environments. Instructions from the CNS are communicated via efferent division to effector organs. The somatic nervous system consists of the nerve fibers of the motor neurons that supply the skeletal muscles. The ANS consists of nerve fibers that innervate smooth muscle, cardiac muscle, and glands. The ANS is further divided into SNS and PNS, both of which innervate most of the organs supplied by the autonomic system. Lesson 2 Chapter 3 – The Central Nervous System 2 Lesson 2 Chapter 3 – The Central Nervous System 3 The cerebral cortex, also known as the cerebrum, is divided into three functional areas: 1) Sensory areas 2) Motor areas 3) Association areas The sensory areas receive and interpret sensory impulses. The motor areas control muscular movement. The association areas are involved in integrative functions such as memory, emotions, reasoning, will, judgment, personality traits, and intelligence. There are functional areas of cerebral cortex that help in information processing. Frontal Lobe The frontal lobe function involves problem solving, planning and making decision. It frontal lobe location is anterior to the parietal lobe of the cerebral cortex. Other functions include motor functions, judgment, controlling impulse, memory and other high order functions. Parietal Lobe The parietal lobe function includes reception of sensory information from the body and processing this information to carry out appropriate action. The parietal lobe location is superior to the occipital lobes. It's present posterior to the central sulcus and frontal lobe. Other functions include spatial orientation, speech, visual perception, cognition as well as sensation of pain and touch. Occipital Lobe The occipital lobe function includes helping one see, that is, vision. It is located at the tail end part of the cerebral cortex and helps in controlling vision as well as recognizing color. Temporal Lobe The temporal lobe function includes helping one hear, understand and express emotions, memory and language processing. The temporal lobe is located anterior to the occipital lobe and lateral to the Fissure of Sylvius. The other functional areas include the following:      Auditory Association Area: This the region where complex processing of auditory information takes place. Auditory Cortex: This region is involved in detection of sound quality like the loudness, tone, etc. Broca's Area: This the region of speech production and articulation. Motor Association Cortex: This functional area helps in coordination of complex movements. Prefrontal Cortex: The region for problem Solving, emotion, complex thoughts, etc. is the prefrontal cortex. Lesson 2 Chapter 3 – The Central Nervous System      4 Primary Motor Cortex: This area helps in initiation of voluntary movements of the body. Primary Somatosensory Cortex: This is where the tactile information from the body is received. Sensory Association Area: The process of multisensory information occurs in this area. Visual Association Area: This region helps in complex processing of visual information. Visual Cortex: Simple visual stimuli is located in this area. The primary somatosensory cortex sends axons from posterior to anterior. The precentral gyrus is all motor while the postcentral gyrus is all sensory. It’s easy to remember the postcentral gyrus is posterior to the precentral gyrus because it’s in the name: postcentral. Association Areas of the Cortex The prefrontal association area is located in the frontal lobe and is involved in such activities as controlling social behavior, making decisions, personality, and more. Parietal-temporal-occipital association cortex: emotional feeling attached to sensory functions, some thinking related to what you hear (ex: the songs you heard as a child) The limbic association area is located on the medial side of the frontal lobe. This is what helps form memories and translates that to motor responses and processes emotions and guides emotional responses. It’s very important for social interactions and expressions of the personality. Lesson 2 Chapter 3 – The Central Nervous System Cerebral Hemispheres • Left side is most commonly the dominant hemisphere for fine motor control, so most people are right-handed – Left side excels in logical, analytic, sequential, and verbal tasks – Right side excels in non-language skills such as spatial perception and arts and music talents 5 Lesson 2 Chapter 3 – The Central Nervous System 6 Language Areas Broca’s area is found in the left inferior frontal gyrus and Wernicke’s area is located in the left posterior superior temporal gyrus. - Broca’s area (motor) o Left frontal lobe o Controls the muscles necessary for articulation o Eg: Speaking Receptive Aphasia Individuals with Broca's aphasia may become mute or may be able to use single-word statements or full sentences, although it may require great effort. - Wernick’s area (sensory) o Left parietal-temporal-occipital lobe o Concerned with understanding both spoken and written language o Formulating coherent patterns of speech Expressive Aphasia People with Wenick’s aphasia speak in long, uninterrupted sentences, but the words used are often unnecessary and unintelligible. Diencephalon Very deep inside the brain, surrounded by the cerebral hemispheres is where we find the diencephalon. This structure surrounds the third ventricle and is primarily made of brain nuclei (gray matter). It functions as a relay system between sensory input neurons and other parts of the brain, as an interactive site for the central nervous and endocrine systems, and works in tandem with the limbic system. It is composed of three paired structures: Thalamus: It is composed mainly of gray substance and translates impulses from appropriate receptors into crude sensations of pain, temperature, and touch. It also participates in associating sensory impulses with pleasant and unpleasant feelings, in the arousal mechanisms of the body, and in the mechanisms that produce complex reflex movements. Hypothalamus: It activates, controls, and integrates the peripheral autonomic nervous system, endocrine processes, and many somatic functions, such as body temperature, sleep, and appetite. Lesson 2 Chapter 3 – The Central Nervous System Epithalamus: 7 poster inferior to thalamus and is mostly the single pineal gland (which secretes melatonin for sleep) Cerebral White Matter and Gray Matter and Basal Ganglia (basal nuclei) The basal ganglia are a collection of nuclei found on both sides of the thalamus, outside and above the limbic system, but below the cingulate gyrus and within the temporal lobes. Although glutamate is the most common neurotransmitter here as everywhere in the brain, the inhibitory neurotransmitter GABA plays the most important role in the basal ganglia. - Controls cognition; especially intensity of movements Movement coordination Voluntary Movement Association fibers are the ones in red connecting different parts of same hemisphere. Commissural fibers are in green. They run horizontal and are what create the corpus callosum. They connect corresponding gray areas of right and left hemispheres. Lesson 2 Chapter 3 – The Central Nervous System 8 Projection fibers in blue run vertically, ascending and descending to and from spinal cord. Where they connect is the decussation of pyramids. Decussation in biology means an intersection or crossing of two tracts that form the letter X. Limbic System and Reticular Activating System Includes portions of the hypothalamus and other forebrain structures that encircle the brain stem. It is responsible for - Emotion Mood (happiness, anger, fear...) Plays important role in motivation and learning Neurotransmitters in pathways for Emotions and Behaviour - Norepinephrine Dopamine Serotonin Depression is associated with defects in limbic system neurotransmitters The limbic system and reticular formation are networks of neurons that function together even though they are widely separated. - Receives and integrates all synaptic input Promotes cortical awareness Helps direct attention toward specific events The limbic system is the “emotional brain” made of deep gray matter structures linked together by the fornix. The fiber tracts have the appearance of oval fibers and looks like the corpus callosum but it’s not the same. The limbic system also includes certain structures of the diencephalon: the anterior thalamus and hypothalamus. The Reticular Formation runs through the central core of the brainstem with connections throughout cerebral hemispheres. It is made up of ascending and descending fibers. It plays a big role in filtering incoming stimuli to discriminate irrelevant background stimuli. The Reticular Activating System (RAS) is made up of the reticular formation and its Lesson 2 Chapter 3 – The Central Nervous System widespread connections. It maintains consciousness and alertness and functions during sleep and arousal from sleep. Putamen stores “subconscious” memories, such as motor skills gained by repetition. Amygdala recalls powerful emotions associated with memorable events, such as fear Hippocampus establishes long-term memories and knowledge linked with spatial awareness Memory • Memory trace – • Neural change responsible for retention or storage of knowledge Consolidation – Process of transferring and fixing short-term memory traces into long-term memory stores 9 Lesson 2 Chapter 3 – The Central Nervous System 10 • Reflexive memory (automatic – implicit memory, like learning to play music or driving; won’t require conscious attention) • Declarative memory (explicit memory, higher-level thinking like planning for a meeting, step-by-step process) • Working memory (higher order functions, problem solving and organizational skills) Cerebellum This area is important for balance and in planning and executing voluntary movements. There are three different parts: - Vestibulocerebellum o Important in maintain balance and controls eye movements Spinocerebellum o Enhances muscle tone and coordinate skilled, voluntary movements Cerebrocerebellum o Plays role in planning and initiating voluntary activity by providing input to cortical motor areas o Stores procedural memories Lesson 2 Chapter 3 – The Central Nervous System The Brain Stem • origin of cranial nerves • cardiovascular, respiratory and digestive system control centers • regulation of muscle reflexes involved in equilibrium and posture • reception and integration of all synaptic input from spinal cord • reticular formation runs through the brain stem The Spinal Cord • 31 pairs of spinal nerves emerge from spinal cord through spaces formed between arches of adjacent vertebrae [starts at the foramen magnum and ends at L1.] – Named for region of vertebral column from which they emerge • 8 pairs cervical (neck) nerves • 12 pairs thoracic (chest) nerves • 5 pairs lumbar (abdominal) nerves • 5 pairs sacral (pelvic) nerves • 1 pair coccygeal (tailbone) nerves 11 Lesson 2 Chapter 3 – The Central Nervous System 12 Lesson 2 Chapter 3 – The Central Nervous System 13 Spinal nerves are composed of: sensory neurons, motor neurons, and (IF it is between T1 and L2 sympathetic nerve fibers) Interneurons are in between neurons. Spinal Tracts The white matter of the spinal cord contains tracts which travel up and down the cord. Many of these tracts travel to and from the brain to provide sensory input to the brain, or bring motor stimuli from the brain to control effectors. Ascending tracts, those which travel toward the brain are sensory, descending tracts are motor. For most the name will indicate if it is a motor or sensory tract. Most sensory tracts names begin with spino, indicating origin in the spinal cord, and their name will end with the part of the brain where the tract leads. For example the spinothalamic tract travels from the spinal cord to the thalamus. Tracts whose names begin with a part of the brain are motor. For example the corticospinal tract begins with fibers leaving the cerebral cortex and travels down toward motor neurons in the cord. Lesson 2 Chapter 3 – The Central Nervous System 14 The Spinal Cord and Peripheral System The spinal cord is the connection center for the reflexes as well as the afferent (sensory) and efferent (motor) pathways for most of the body below the head and neck. The spinal cord begins at the brainstem and ends at about the second lumbar vertebra. The sensory, motor, and interneurons discussed previously are found in specific parts of the spinal cord and nearby structures. Sensory neurons have their cell bodies in the spinal (dorsal root) ganglion. Their axons travel through the dorsal root into the gray matter of the cord. Within the gray matter are interneurons with which the sensory neurons may connect. Also located in the gray matter are the motor neurons whose axons travel out of the cord through the ventral root. The white matter surrounds the gray matter. It contains the spinal tracts which ascend and descend the spinal cord. Surrounding both the spinal cord and the brain are the meninges, a three layered covering of connective tissue. The dura mater is the tough outer layer. Beneath the dura is the arachnoid which is like a spider web in consistency. The arachnoid has abundant space within and beneath it (the subarachnoid space) which contains cerebrospinal fluid, as does the space beneath the dura mater (subdural space). This cerebrospinal fluid supplies buoyancy for the spinal cord and brain to help provide shock absorption. The pia mater is a very thin layer which adheres tightly to the surface of the brain and spinal cord. It follows all contours and fissures (sulci) of the brain and cord. Reflex Arc - Reflexes, are involuntary, almost instantaneous movements in response to a specific stimulus. Reflex arcs which contain two neurons, a sensory and a motor neuron, are considered monosynaptic. (petaller reflex and Achilles reflex) Most reflexes are polysynaptic, meaning multiple neurons (also called relay neurons) intereface between the sensory and motor neuron n the reflex pathway. Lesson 2 Chapter 3 – The Central Nervous System 5 components: - Receptor Afferent pathway Integrating center Efferent pathway Effector Autonomic reflex: unconscious (blood pressure, pH levels, body chemicals….) Spinal reflex: conscious perception - aware (you know its painful/hot) Cerebrovascular Accidents A stroke is the sudden death of brain cells in a localized area due to inadequate blood flow. Classification of Stroke: 1) Ischemic stroke a. Due to thrombosis [blood clot in blood vessel] and/or embolism [part of thrombus or air bubble] 2) Hemorrhagic stroke a. Intracerebral hemorrhage b. Subarachnoid hemorrhage 15 Lesson 2 Chapter 3 – The Central Nervous System 16 Two main types of strokes (Brain Attack) • Ischemic strokes – • Caused by an interruption of blood flow in a cerebral vessel and are the most common type of stroke, accounting for 70–80% of all strokes. Hemorrhagic strokes – Caused by bleeding into brain tissue, usually from a blood vessel rupture caused by hypertension, aneurysms, arteriovenous malformations, head injury, or blood dyscrasias Etiology (Risk factors) • Age, Gender, Race, High cholesterol levels, Cigarette smoking, Diabetes mellitus, Other risk factors – Heart diseases – Blood diseases – Alcohol, cocaine and illicit drug use (Chlamydia pneumoniae) – Sedentary life style Lesson 2 Chapter 3 – The Central Nervous System 17