summary-the-central-nervous-system-ch12.pdf -...

This preview shows page 1 out of 26 pages.

Unformatted text preview: lOMoARcPSD|3704854 Summary - The Central Nervous System (Ch12) Introduction to Anatomy and Physiology I (University of Wollongong) StuDocu is not sponsored or endorsed by any college or university Downloaded by Lauren Myburgh ([email protected]) lOMoARcPSD|3704854 CH 12 THE CENTRAL NERVOUS SYSTEM The Brain Regions and organization • Adult brain regions: -­‐ Cerebral hemispheres -­‐ Diencephalon -­‐ Brain stem (midbrain, pons, medulla oblongata) -­‐ Cerebellum • Spinal cord -­‐ Central cavity surrounded by a gray matter core -­‐ External white matter composed of myelinated fiber tracts Ventricles • Arise from the expansions of the lumen (cavity) of the embryonic neural tube • connected to one another and with the central canal of the spinal cord • lined with ependymal cells (a type of neuroglia) • hollow chambers filled with cerebrospinal fluid Include: • paired lateral ventricles (one deep within each cerebral hemisphere) -­‐ large C-­‐shaped chambers that reflect the pattern of cerebral growth -­‐ anteriorly: lateral ventricles lie close together, separated only by a thin median membrane called the septum pellucidum -­‐ each lateral ventricle communicates with the third ventricles via a channel called an interventricular foramen • third ventricle (in the diencephalon) -­‐ continuous with fourth ventricle via the canal-­‐like cerebral aqueduct that runs through the midbrain • fourth ventricle (in the hindbrain) -­‐ continuous with the central canal of the spinal cord inferiorly -­‐ three openings mark the walls of the fourth ventricle: the paired lateral apertures in the side walls and the median aperture in its roof (these apertures connect the ventricles to the subarachnoid space, a fluid-­‐filled space surrounding the brain) SHS111 Anatomy & Physiology I -­‐ 1 Downloaded by Lauren Myburgh ([email protected]) lOMoARcPSD|3704854 Cerebral hemispheres • form the superior part of the brain – account for about 83% of total brain mass • surface markings: -­‐ gyri: elevated ridges of tissue (singular: gyrus) -­‐ sulci: shallow grooves between gyri (singular: sulcus) -­‐ fissures: deep grooves that separate large regions of the brain • longitudinal fissure – separates the cerebral hemispheres • transverse cerebral fissure – separates the cerebral hemispheres from the cerebellum below • Lobes: -­‐ frontal -­‐ parietal -­‐ temporal -­‐ occipital -­‐ insula (buried deep within the lateral sulcus and covered by portions of all other lobes) • Sucli: -­‐ central sulcus: lies in the frontal plane and separates the frontal lobe from the parietal lobe -­‐ precentral sulcus: anteriorly borders the central sulcus -­‐ postcentral sulcus: posteriorly borders the central sulcus -­‐ parieto-­‐occipital sulcus: separates the occipital lobe from the parietal lobe -­‐ lateral sulcus: outlines the flaplike temporal lobe and separates it from the parietal and frontal lobes • anterior cranial fossa: houses the frontal lobes • middle cranial fossa: houses the anterior parts of the temporal lobes • posterior cranial fossa: houses the brain stem and cerebellum SHS111 Anatomy & Physiology I -­‐ 2 Downloaded by Lauren Myburgh ([email protected]) lOMoARcPSD|3704854 • Each cerebral hemisphere has three basic regions: -­‐ A superficial cortex of gray matter -­‐ An internal white matter -­‐ The basal nuclei (islands of gray matter situated deep within the white matter) 1. Cerebral Cortex: • • • • • thin superficial layer of grey matter (neuron cell bodies, dendrites, associated glia and blood vessels) 40% of total brain mass site of conscious mind: enables us to be aware of ourselves and our sensations, to communicate, remember and understand, and to initiate voluntary movements functional regions of the cortex – specific motor and sensory functions are localized in discrete cortical areas called domains (many higher mental functions, such as memory and language, appear to have overlapping domains and are spread over large areas of the cortex) Remember: 1. contains three kinds of functional areas: motor areas, sensory areas, and association areas -­‐ motor areas: control voluntary movement -­‐ sensory areas: conscious awareness of sensation -­‐ association areas: integrate diverse information 2. each hemisphere is mainly concerned with the sensory and motor functions of the opposite (contralateral) side of the body 3. although largely symmetrical in structure, the two hemispheres are not entirely equal in function à there is lateralization (specialization) of cortical functions 4. no functional area of the cortex acts alone è Motor areas Ø Primary motor cortex, premotor cortex, Broca’s area and the frontal eye field – lie in the posterior part of the frontal lobes and control voluntary movement 1. Primary (somatic) motor cortex – -­‐ Located in the precentral gyrus of each hemisphere -­‐ Large neurons, called pyramidal cells¸ in these gyri allow us to consciously control the precise or skilled voluntary movements of our skeletal muscles -­‐ Their long axons form the massive voluntary motor tracts called the pyramidal tracts (or corticospinal tracts) -­‐ Most of the neurons in these gyri control muscles in body areas having the most precise motor control (eg. face, tongue, hands) -­‐ Motor innervations of the body is contralateral: the left primary motor gyrus controls muscles on the right side of the body, and vice versa -­‐ Individual pyramidal motor neurons control muscles that work together in a synergistic way to perform a given movement 2. Premotor cortex – -­‐ Located in the frontal lobe just anterior to the precentral gyrus -­‐ Controls learned motor skills of a repetitious or patterned nature (such as playing a musical instrument or typing) -­‐ Coordinates the movement of several muscle groups either simultaneously or sequentially, mainly by sending activating impulses to the primary motor cortex -­‐ Also influences the motor activity more directly by supplying about 15% of pyramidal tract fibers -­‐ Also appears to be involved in planning movements – uses sensory information received from other cortical areas, it can control voluntary actions that depend on sensory feedback 3. Broca’s area – -­‐ Located anterior to the inferior region of the premotor cortex -­‐ Present in one hemisphere only -­‐ A special motor speech area that directs the muscles involved in speech production -­‐ Also becomes active as we prepare to speak and think about (plan) many voluntary motor activites other than speech 4. Frontal eye field -­‐ SHS111 Anatomy & Physiology I -­‐ 3 Downloaded by Lauren Myburgh ([email protected]) lOMoARcPSD|3704854 -­‐ -­‐ Located partially in and anterior to the premotor cortex and superior to Broca’s area controls voluntary movement of the eyes è Sensory Areas Ø Areas concerned with conscious awareness of sensation Ø Occur in the parietal, insular, temporal and occipital lobes 1. Primary somatosensory cortex Located in the postcentral gyrus of the parietal lobe Neurons in this gyrus receive information from the general (somatic) sensory receptors in the skin and from proprioceptors (positions sense receptors) in skeletal muscles, joints and tendons -­‐ The neurons then identify the body region being stimulated – an ability called spatial discrimination -­‐ The amount of sensory cortex devoted to a particular body region is related to that region’s sensitivity (that is, how many receptors it has), not to the size of the body region -­‐ -­‐ 2. Somatosensory association cortex Located just posterior to the primary somatosensory cortex and has many connections with it Integrates sensory inputs (temperature, pressure etc) relayed to it via the primary somatosensory cortex to produce an understanding of an object being felt: its size, texture, and the relationship of its parts -­‐ Eg. when you reach into your pocket, your somatosensory association cortex draws upon stored memories of past sensory experiences to perceive the objects you feel -­‐ -­‐ 3. Visual areas Primary visual (striate) cortex – located on the extreme posterior tip of the occipital lobe (but most of it is buried in a deep sulcus). The largest of all cortical sensory areas, the primary visual cortex receives visual information that originates in the retina of the eye -­‐ Visual association area – surrounds the primary visual cortex and covers much of the occipital lobe. The visual association area uses past visual experiences to interpret visual stimuli (colour, form, and movement), enabling us to recognize objects or faces. -­‐ 4. Auditory areas Primary auditory cortex – located in the superior margin of the temporal lobe abutting the lateral sulcus. Sound energy exciting the hearing receptors in the inner ear causes impulses to be transmitted to the primary auditory cortex, where they are interpreted as pitch, loudness, and location. -­‐ Auditory association area – located posterior to the primary auditory cortex. Permits the perception of the sound stimulus (which we ‘hear’ as speech, a scream, music, thunder etc). Wernicke’s area includes parts of the auditory cortex. -­‐ 5. Olfactory cortex Primary olfactory (smell) cortex – located on the medial aspect of the temporal lobe in a small region called the piriform lobe. Afferent fibers from smell receptors in the superior nasal cavities send impulses along the olfactory tracts that are ultimately relayed to the olfactory cortices. The outcome is conscious awareness of different smells -­‐ The olfactory cortex is part of the primitive rhinencephalon, which includes all parts of the cerebrum that receive olfactory signals. The only portions of the human rhinencephalon still devoted to smell are the olfactory bulbs and tracts and the greatly reduced olfactory cortices. During the course of evolution, parts of the rhinencephalon took on new functions concerned chiefly with emotions and memory. -­‐ 6. -­‐ -­‐ Gustatory cortex Gustatory (taste) cortex – involved in the perception of taste stimuli Located in the insula just deep to the temporal lobe 7. -­‐ Visceral sensory areas The cortex of the insula just posterior to the gustatory cortex is involved in conscious perception of visceral sensations SHS111 Anatomy & Physiology I -­‐ 4 Downloaded by Lauren Myburgh ([email protected]) lOMoARcPSD|3704854 -­‐ Include upset stomach, full bladder, and the feeling that your lungs will burst when you hold your breath for too long 8. Vestibular (equilibrium) cortex -­‐ Posterior part of the insula and adjacent parietal cortex -­‐ Responsible for conscious awareness of balance è Multimodal association areas Ø Most of the cortex is complexly connected, receiving inputs from multiple senses and sending outputs to multiple areas – these areas are called multimodal association areas Ø Information flow: -­‐ Sensory receptors -­‐ To the appropriate primary sensory cortex -­‐ To a sensory association cortex -­‐ To the multimodal association cortex Ø Multimodal association cortex allows us to give meaning to the information that we receive, store it in memory if needed, tie it to previous experience and knowledge, and decide what action to take. Ø Once the course of action has been decided, those decisions are relayed to the premotor cortex, which in turn communicates with the motor cortex Ø The multimodal association areas can be divided into three parts: 1. Anterior association area: -­‐ In the frontal lobe -­‐ Most complicated cortical region -­‐ Involved with intellect, complex learning abilities (called cognition), recall and personality -­‐ Contains working memory – necessary for the production of abstract ideas, judgement, reasoning, persistence, and planning 2. Posterior association area: -­‐ Large region encompassing parts of the temporal, parietal and occipital lobes -­‐ Plays a role in recognising patterns and faces, localizing us and our surroundings in space and in binding different sensory inputs into a coherent whole -­‐ Also involved in understanding written and spoken language 3. Limbic association area: -­‐ Includes the cingulated gyrus, the parahippocampal gyrus and the hippocampus -­‐ Part of the limbic system -­‐ Provides the emotion impact that makes a scene important to us -­‐ The hippocampus establishes memories that allow us to remember particular incidents è Lateralization of cortical functioning Ø We use both cerebral hemispheres for almost every activity Ø But each hemisphere has unique abilities not shared by the other – called lateralization Ø Cerebral dominance: designates the hemisphere that is dominant for language In most people (90%): -­‐ the left hemisphere has greater control over language abilities, maths and logic -­‐ The right hemisphere is more free-­‐spirited, involved in visual-­‐spatial skills, intuition, emotion, and artistic and musical skills -­‐ In the remaining 10% of people, the roles of the hemispheres are reversed or the hemispheres share their functions equally SHS111 Anatomy & Physiology I -­‐ 5 Downloaded by Lauren Myburgh ([email protected]) lOMoARcPSD|3704854 SHS111 Anatomy & Physiology I -­‐ 6 Downloaded by Lauren Myburgh ([email protected]) lOMoARcPSD|3704854 2. Cerebral White Matter: • • • • • • Deep to the cortical gray matter Responsible for communication between cerebral areas and between the cerebral cortex and lower CNS centre Consists largely of myelinated fibers bundled into large tracts which are classified according to the direction in which they run: -­‐ Commissural -­‐ Association -­‐ Projection Commissures (run horizontally) -­‐ composed of commissural fibers, connect corresponding gray areas of the two hemispheres, enabling them to function as a coordinated whole. -­‐ The largest commissure is the corpus callosum, which lies superior to the lateral ventricles, deep within the longitudinal fissure. Association fibers (run horizontally) – connect different parts of the same hemisphere. -­‐ Short association fibers connect adjacent gyri -­‐ Long association fibers are bundled into tracts and connect different cortical lobes Projection fibers (run vertically) – these fibers either enter the cerebral cortex from the lower brain or cord centres, or descend from the cortex to lower areas. -­‐ Sensory information reaches the cerebral cortex and motor output leaves it through these fibers -­‐ They tie the cortex to the rest of the nervous system and to the body’s receptors and effectors -­‐ Internal capsule: the compact band of projection fibers at the top of the brain stem -­‐ Corona radiate: the fanlike arrangement of projection tract fibers that go through the cerebral white matter to the cortex 3. Basal Nuclei • • • • • • • • LOCATION: Deep within the cerebral white matter Receive input from the entire cerebral cortex, as well as form other subcortical nuclei and each other The output nucleus of the basal nuclei (globus pallidus) and the substantia nigra project to the premotor and prefrontal cortices – so they influence muscle movements directed by the primary motor cortex FUNCTION: important in starting, stopping and monitoring the intensity of movements executed by the cortex. They inhibit antagonistic and unnecessary movements The caudate nucleus, putamen, and globus pallidus constitute most of the mass of each group of basal nuclei Lentiform nucleus: the putamen and globus pallidus together -­‐ flanks the internal capsule laterally Corpus striatum: Lentiform and caudate nuclei together Functionally associated with the subthalamic nuclei (located in the lateral part of the diencephalon) and the substantia nigra (of the midbrain) SHS111 Anatomy & Physiology I -­‐ 7 Downloaded by Lauren Myburgh ([email protected]) lOMoARcPSD|3704854 Dienchaphalon: • Forms the central core of the forebrain • Consists largely of three paired structures: -­‐ thalamus -­‐ Hypothalamus -­‐ Epithalamus • These gray matter areas collectively enclose the third ventricle Thalamus: • FUNCTION: the relay station for information coming into the cerebral cortex • contains a large number of nuclei – each nuclei has a functional specialty • and each projects fibers to and receives fibers from a specific region of the cerebral cortex • impulses having to do with similar functions are relayed as a group via the internal capsule to the appropriate area of the sensory cortex as well as t specific cortical areas Hypothalamus: • LOCATION: below the thalamus • FUNCTION: the main visceral control centre of the body (vitally important to overall homeostasis) • Contain mamillary bodies: (paired pealike nuclei that bulge anteriorly from the hypothalamus) relay stations in the olfactory pathways • Infundibulum: a stalk of hypothalamic tissue that connects the pituitary gland to the base of the hypothalamus • Its chief homeostatic roles are: 1. Autonomic control centre – regulates ANS activity by controlling the activity of centres in the brain stem and spinal cord 2. Centre for emotional response – lies at the centre of the limbic system (the emotional part of the brain). The hypothalamus acts through ANS pathways to initiate most physical expressions of emotion. 3. Body temperature regulation – contains the body’s thermostat and initiates sweating and shivering to maintain a constant body temperature. Neurons monitor blood temperature and receive input from other temperature receptors in the brain and body. 4. Regulation of food intake – responds to changing blood levels of certain nutrients or hormones, and regulates feelings of hunger and satiety 5. Regulation of water balance and thirst – when body fluids become too concentrated, hypothalamic nuclei become excited and trigger the release of antidiuretic hormone (ADH) from the posterior pituitary (ADH causes kidneys to retain water). The same conditions also stimulate hypothalamic neurons in the thirst centre. 6. Regulation of sleep-­‐wake cycles – sets the timing of the sleep cycle in response to daylight-­‐darkness cues received from the visual pathways 7. Control of endocrine system functioning – acts as the helmsman of the endocrine system in two ways àits releasing and inhibiting hormones control the secretion of hormones by the anterior pituitary gland and its supraoptic and paraventricular nuclei produce the hormones ADH and oxytocins. Epithalamus: • LOCATION: The most dorsal portion of the diencephalon • Forms the roof of the third ventricle • Pineal gland (extends from its posterior border) – secretes the hormone melatonin (a sleep-­‐inducing signal and antioxidant) • FUNCTION: helps regulate the sleep-­‐wake cycle SHS111 Anatomy & Physiology I -­‐ 8 Downloaded by Lauren Myburgh ([email protected]) lOMoARcPSD|3704854 Brain stem • Three main regions: -­‐ Midbrain -­‐ Pons -­‐ Medulla oblongata • Organization is similar to that of the spinal cord – deep gray matter surrounded by white matter fiber tracts (but the brain stem has nuclei of gay matter embedded in the white matter) • FUNCTION: -­‐ produce the rigidly programmed, automatic behaviours necessary for survival -­‐ provides a pathway for fiber tracts running between higher and lower neural centres -­‐ heavily involved in the innervations of the head (brain stem nuclei are associated with 10 of the 12 pairs of cranial nerves Midbrain: • LOCATION: between the diencephalon and the pons • Cerebral peduncles: vertical pillars that hold up the cerebrum -­‐ Each peduncle contains a large pyramidal motor tract descending toward the spinal cord • Cerebral aquaduct: a hollow opening which connects the thirds and fourth ventricles • Superior colliculi: visual reflex centres that coordinate head and eye movements when we visually follow a moving object • Inferior colliculi: part of the auditory relay from the hearing receptors of the ear to the sensory cortex Pons: • LOCATION: The bulging brain stem region wedged between the midbrain and the medulla oblongata • Forms part of the anterior wall of the fourth ventricle • Pons = bridge • Chiefly composed of condu...
View Full Document

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture