THE CENTRAL NERVOUS SYSTEM
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Explore the embryonic development of the brain and the organization of the central nervous system. Learn about brain ventricles, cerebral hemispheres, cortical function, and neuroimaging techniques.
THE CENTRAL NERVOUS SYSTEM
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Presentation Transcript
EMBRYONIC DEVELOPMENT • At three weeks’ gestation, the ectoderm forms the neural plate, which invaginates, forming the neural groove, flanked on either side by neural folds • By the fourth week of pregnancy, the neural groove fuses, giving rise to the neural tube, which rapidly differentiates into the CNS • The neural tube develops constrictions that divide the three primary brain vesicles: • Prosencephalon (forebrain) • Mesencephalon (midbrain) • Rhombencephalon (hindbrain)
REGIONS AND ORGANIZATION • The basic pattern of the CNS consists of a central cavity surrounded by a gray matter core, external to which is white matter • In the brain, the cerebrum and cerebellum have an outer gray matter layer, which is reduced to scattered gray matter nuclei in the spinal cord
VENTRICLES • The ventricles of the brain are continuous with one another, and with the central canal of the spinal cord. • They are lined with ependymal cells, and are filled with cerebrospinal fluid • The paired lateral ventricles lie deep within each cerebral hemisphere, and are separated by the septum pellucidum • The third ventricle lies within the diencephalon, and communities with the lateral ventricles via two interventricular foramina • The fourth ventricle lies in the hindbrain and communicates with the third ventricle via the cerebral aqueduct
CEREBRAL HEMISPHERES • The cerebral hemispheres form the superior part of the brain, and are characterized by ridges and grooves (convolutions) called gyri (elevated ridges of tissue) and sulci (hollow grooves) • Deeper grooves called Fissures separate large regions of the brain • The cerebral hemispheres are separated along the midline by the longitudinal fissure, and are separated from the cerebellum along the transverse cerebral fissure • The five lobes of the brain separated by specific sulci (all but the last named for the cranial bone that overlie them) are: frontal, parietal, temporal, occipital, and insula ( buried deep within the lateral sulcus: equilibrium) • The cerebral cortex is the location of the conscious mind, allowing us to communicate, remember, and understand
CEREBRAL HEMISPHERES • The two hemispheres are largely symmetrical in structure but not entirely equal in function • There is a lateralization (specialization) of cortical function • NO function area of the cortex acts alone and conscious behavior involves the entire cortex in one way or another
NEUROIMAGING • Shows that 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 very large areas of the cortex
NEUROIMAGING • PET scans: • Positron emission tomography • Positron: a particle having the same mass as a negative electron but possessing a positive charge • Shows maximal metabolic activity
NEUROIMAGING • MRI scans: • Magnetic resonance imaging • Reveals blood flow
CEREBRAL HEMISPHERES • The cerebral cortex has several motor areas located in the frontal lobes, which control voluntary movement: • The primary motor cortex allows conscious control of skilled voluntary movement of skeletal muscles • The premotor cortex is the region controlling learned motor skills • Broca’s area is a motor speech area that controls muscles involved in speech production • The frontal eye field controls eye movement
CEREBRAL CORTEX • Primary motor area: conscious control of skilled voluntary movement of skeletal muscles • Premotor cortex: region controlling learned motor behavior (typing, playing musical instrument) • Frontal eye field: eye movement
CEREBRAL CORTEX • Prefrontal cortex: • Most complicated cortical region • Involved with intellect, complex learning abilities (cognition), recall, and personality • Production of abstract ideas, judgment, reasoning, persistence, long-term planning, concern for others, and conscience • In children matures slowly and is heavily dependent on positive and negative feedback • Closely linked to the emotional part of the brain (limbic system) • Plays a role intuitive judgments and mood • Tremendous elaboration of this region sets humans apart from other animals • Language comprehension and word analysis
CEREBRAL CORTEX • Somatic sensation: receives information from the general (somatic) sensory receptors in the skin and skeletal muscle and integrates the different sensory inputs (temperature, pressure, etc.) • Gustatory cortex: taste • General interpretation area: • Found in one hemisphere only (usually left) • Receives input from all incoming signals and focuses into a single thought or understanding of the situation
CEREBRAL CORTEX • Visual association area: recognizes a flower or a person’s face • Auditory association area: memories of sounds
CEREBRAL CORTEXLANGUAGE AREAS:LEFT HEMISPHERE • Broca’s area: • Motor speech area that controls muscles (tongue, lips, throat) involved in speech production • Considered to be present in only one hemisphere (usually the left) • Becomes active as we prepare to speak and even when we think about (plan) many voluntary motor activities other than speech • Wernicke’s area: • Language comprehension and articulation • Believed to be the area responsible for understanding written and spoken language • Involved in sounding out unfamiliar words • Prefrontal cortex: language comprehension and word analysis • Lateral and Ventral parts of temporal lobe: coordinate auditory and visual aspects of language when reading
CORRESPONDING AREARIGHT HEMISPHERE • Non-language dominance • Involved in body language and non-verbal emotional (affective) components of language rather than speech mechanics • Allows the lift and tone of our voice and our gestures to express our emotions when we speak • Permits us to comprehend the emotional content of what we hear ( a soft response to your question conveys quite a different meaning than a sharp reply)
LATERALIZATION • We use both cerebral hemispheres for almost every activity, and the hemispheres appear nearly identical • BUT, there is division of labor, and each hemisphere has unique abilities not shared by its partner (LATERALIZATION) • Although one cerebral hemisphere or the other “dominates” each task, the term cerebral dominance designates the hemisphere that is dominant for language
LATERALIZATION • Right Hemisphere: • 10% of people • Non-language dominant • Visual-spatial skills, intuition, emotion, artistic and musical skills, poetic, creative • Most left-handed • More often males
LATERALIZATION • Left Hemisphere: • 90% of people • Greater control over language abilities, math and logic • Most right handed
LATERALIZATION • BILATERAL: • Ambidextrous • Could be cerebral confusion: Is it your turn or mine? • Learning disabilities (dyslexia, etc.)
CEREBRAL HEMISPHERES • There are several sensory areas of the cerebral cortex that occur in the parietal, temporal, and occipital lobes • The primary somatosensory cortex allows spatial discrimination and the ability to detect the location of stimulation • The somatosensory association cortex integrates sensory information and produces an understanding of the stimulus being felt • The primary visual cortex and visual association area allow reception and interpretation of visual stimuli • The primary auditory cortex and auditory association area allow detection of the properties and contextual recognition of sound • The olfactory cortex allows detection of odors • The gustatory cortex allows perception of taste stimuli • The vestibular cortex is responsible for conscious awareness of balance
CEREBRAL CORTEX • Do not confuse the sensory and motor areas of the cortex with sensory and motor neurons: All neurons in the cortex are interneurons
Motor and Sensory Areas of the Cerebral Cortex • Red: Primary (somatic) motor cortex • Located in the precentral gyrus of the frontal lobe of each hemisphere • Central sulcus: groove between Red/Blue • Blue: Primary somatosensory cortex • Located on the postcentral gyrus of the parietal lobe, just posterior to the premotor cortex
Motor and Sensory Areas of the Cerebral Cortex • The body is typically represented upside down: the head at the inferolateral part of the precentral gyrus, and the toes at the superomedial end
Motor and Sensory Areas of the Cerebral Cortex • PRIMARY MOTOR CORTEX • The motor innervation of the body is contralateral (opposite) • The left primary motor gyrus controls muscles on the right side of the body, and vice versa • Misleading: a given muscle is controlled by multiple spots on the cortex and that individual cortical motor neurons actually send impulses to more than one muscle • In other words: individual motor neurons control muscles that work together in a synergistic way (so that one does not over react)
Motor and Sensory Areas of the Cerebral Cortex • PRIMARY SOMATOSENSORY CORTEX: • Receives information from the general (somatic) sensory receptors located in the skin and from proprioceptors in skeletal muscles (locomotion, posture, and tone) • Right hemisphere receives input from the left side of the body and vice versa
CEREBRAL HEMISPHERES • Several association areas are not connected to any sensory cortices • The prefrontal cortex is involved with intellect, cognition, recall, and personality, and is closely linked to the limbic system • The language areas involved in comprehension and articulation include Wernicke’s area, Broca’s area, the lateral prefrontal cortex, and the lateral and ventral parts of the temporal lobe • The general interpretation area receives input from all sensory areas, integrating signals into a single thought • The visceral association area is involved in conscious visceral sensation
CEREBRAL HEMISPHERES • There is lateralization of cortical functioning, in which each cerebral hemisphere has unique abilities not shared by the other half: • One hemisphere (often the left) dominates language abilities, math, and logic, and the other hemisphere (often the right) dominates visual-spatial skills, intuition, emotion, and artistic and musical skills • Cerebral white matter is responsible for communication between cerebral areas and the cerebral cortex and lower CNS centers • Basal nuclei consist of a group of subcortical nuclei, which play a role in motor control and regulating attention and cognition
BASAL NUCLEI • The precise role of the basal nuclei has been elusive because of their inaccessible location and because their functions overlap to some extent with those of the cerebellum • Role in motor control is complex • Plays a role in regulating attention and in cognition (reasoning/thinking) • Important in starting, stopping, and monitoring movements executed by the cortex • Inhibit unnecessary movements • Disorders result in either too much or too little movement as exemplified by Huntington’s and Parkinson’s disease
DIENCEPHALON • The diencephalon is a set of gray matter areas, and consist of the thalamus, hypothalamus, and epithalamus • The thalamus plays a key role in mediating sensation, motor activities, cortical arousal, learning, and memory • The hypothalamus is the control center of the body, regulating ANS activity such as emotional response, body temperature, food intake, sleep-wake cycles, and endocrine function • The epithalamus includes the pineal gland, which secretes melatonin and regulates the sleep-wake cycle
