Summary

This document provides a detailed overview of the central nervous system (CNS), including its components, structure, and functions. It discusses the brain, spinal cord, and associated structures. It also outlines various methods used for visualizing the brain, such as CT, PET, and MRI scans.

Full Transcript

Consists of: – Brain. – Spinal cord. Receives input from sensory neurons. Directs activity of motor neurons.  CNS is composed of gray and white matter. ◦ Gray matter consists of neuron cell bodies and dendrites. ◦ White matter (myelin) consists of a...

Consists of: – Brain. – Spinal cord. Receives input from sensory neurons. Directs activity of motor neurons.  CNS is composed of gray and white matter. ◦ Gray matter consists of neuron cell bodies and dendrites. ◦ White matter (myelin) consists of axon tracts. Ventricles and central canal are filled with cerebral spinal fluid (CSF). Made up of: Grey matter – neuronal cell bodies White matter – dendrites and axons There are three layers of membrane, cerebrospinal fluid, as well as numerous ventricles. These serve to cushion and support the CNS. Three meninges: Dura mater (tough mother): outer membrane, closest to the skull Arachnoid (spider-web like): middle membrane immediately beneath dura mater Below it is the subarachnoid space: consisting of CSF and blood vessels Pia mater (pious mother): third membrane delicate, adheres to surface of CNS Cerebral Ventricles: The four large internal chambers in the brain filled with CSF. Two lateral ventricles - show up clearly on most scans. Third and fourth ventricles are connected by the cerebral aqueduct, a narrow channel Cerebrospinal Fluid (CSF) A colourless fluid that fills the subarachnoid space, the central canal in the spine, and the cerebral ventricles It is continuously produced by the choroid plexuses - networks of capillaries that protrude from the pia mater into the ventricles. CSF serves a number of functions including bathing and removal of wastes, but its most important is the protecting and cushioning of the brain.  Largest portion of brain (80% mass).  Responsible for higher mental functions.  Corpus callosum: ◦ A ajor tract of axons that functionally interconnects right and left cerebral hemispheres.  Characterized by numerous convolutions.  Elevated folds: gyri.  Depressed groves: sulci.  Frontal lobe:  Anterior portion of each cerebral hemisphere.  Contains upper motor neurons.  Involved in motor control.  Body regions with the greatest number of motor innervation are represented by largest areas of motor cortex.  Parietal lobe: ◦ Primary area responsible for perception of somatesthetic sensation. ◦ Body regions with highest densities of receptors are represented by largest areas of sensory cortex.  Temporal lobe: ◦ Contain auditory centers that receive sensory fibers from cochlea. ◦ Interpretation and association of auditory and visual information. Occipital Lobe: – Primary area responsible for vision and coordination of eye movements.  X-ray computed tomography (CT): ◦ Computer manipulations of data obtained from x-ray absorption by tissues of different densities.  Soft tissue.  Positron-emission tomography (PET): ◦ Radioisotopes that emit positrons are injected into blood stream.  Collision of positron and electron result in emission of gamma rays.  Pinpoint brain cells that are most active.  Brain metabolism, drug distribution.  Magnetic resonance imaging (MRI): ◦ Protons (H+) respond to magnetic field.  Emit a radio-wave signal when stimulated.  Brain function.  Measures synaptic potentials produced at cell bodies and dendrites. ◦ Create electrical currents.  Used clinically to diagnose epilepsy and brain death.  Alpha:  Recorded from parietal and occipital regions.  Person is awake, relaxed, with eyes closed.  10-12 cycles/sec.  Beta:  Strongest from frontal lobes near precentral gyrus.  Produced by visual stimuli and mental activity.  Evoked activity.  13-25 cycles/sec.  Theta:  Emitted from temporal and occipital lobes.  Common in newborn.  Adult indicates severe emotional stress.  5-8 cycles/sec.  Delta:  Emitted in a general pattern.  Common during sleep and awake infant.  In awake adult indicate brain damage.  1-5 cycles/sec.  2 types of EEG patterns during sleep: ◦ REM (rapid eye movement):  Dreams occur.  Low-amplitude, high-frequency oscillations.  Similar to wakefulness (beta waves). ◦ Non-Rem (resting):  High-amplitude, low-frequency waves (delta waves).  Superimposed on these are sleep spindles:  Waxing and waning bursts of 7-14 cycles/sec.  Last for 1-3 sec.  Cerebral dominance:  Specialization of one hemisphere.  Left hemisphere:  More adept in language and analytical abilities.  Damage:  Severe speech problems.  Right hemisphere:  Most adept at visuospatial tasks.  Damage:  Difficulty finding way around house.  Broca’s area:  Involves articulation of speech.  In damage, comprehension of speech is unimpaired.  Wernicke’s area:  Involves language comprehension.  In damage, language comprehension is destroyed, but speech is rapid without any meaning.  Angular gyrus:  Center of integration of auditory, visual, and somatesthetic information.  Damage produces aphasias.  Arcuate fasciculus:  To speak intelligibly, words originating in Wernicke’s area must be sent to Broca’s area.  Broca’s area sends fibers to the motor cortex which directly controls the musculature of speech.  Important in the neural basis of emotional states are hypothalamus and limbic system.  Limbic system: ◦ Group of forebrain nuclei and fiber tracts that form a ring around the brain stem.  Center for basic emotional drives.  Closed circuit (Papez circuit): ◦ Fornix connects hippocampus to hypothalamus, which projects to the thalamus which sends fibers back to limbic system. – Areas or the hypothalamus and limbic system are involved in feelings and behaviors. – Aggression: Amygdala and hypothalamus. – Fear: Amygdala and hypothalamus. – Feeding: Hypothalamus (feeding and satiety centers). – Sexual drive and behavior: Hypothalamus and limbic system. – Goal directed behavior (reward and punishment): Hypothalamus and frontal cortex.  Short-term: ◦ Memory of recent events.  Medial temporal lobe: ◦ Consolidates short term into long term memory.  Hippocampus is critical component of memory.  Acquisition of new information, facts and events requires both the medial temporal lobe and hippocampus.  Consolidation of short-term memory into long-term memory. ◦ Requires activation of genes, leading to protein synthesis and formation of new synaptic connections.  Altered postsynaptic growth of dendritic spines in area of contact.  Cerebral cortex stores factual information: ◦ Visual memories lateralized to left hemisphere. ◦ Visuospatial information lateralized to right hemisphere.  Prefrontal lobes: ◦ Involved in performing exact mathematical calculations.  Complex, problem-solving and planning activities.  Thalamus: ◦ Forms most of the walls of the 3rd ventricle. ◦ Acts as relay center through which all sensory information (except olfactory) passes to the cerebrum.  Lateral geniculate nuclei:  Relay visual information.  Medial geniculate nuclei:  Relay auditory information.  Intralaminar nuclei:  Activated by many sensory modalities.  Projects to many areas.  Promotes alertness and arousal from sleep.  Epitheliums contains: ◦ Choroid plexus where CSF is formed. ◦ Pineal gland which secretes melatonin.  Contains neural centers for hunger, thirst, and body temperature.  Contributes to the regulation of sleep, wakefulness, emotions, sexual arousal, anger, fear, pain, and pleasure.  Stimulates hormonal release from anterior pituitary.  Produces ADH and oxytocin.  Coordinates sympathetic and parasympathetic reflexes.  Contains: ◦ Corpora quadrigemina:  Superior colliculi:  Involved in visual reflexes.  Inferior colliculi:  Relay centers for auditory information. ◦ Cerebral peduncles:  Composed of ascending and descending fiber tracts. ◦ Substantia nigra:  Required for motor coordination. ◦ Red nucleus:  Maintains connections with cerebrum and cerebellum.  Involved in motor coordination. Pons  Surface fibers connect to cerebellum, and deeper fibers are part of motor and sensory tracts.  Contains several nuclei associated with cranial nerves V, VI, VII.  Contains the apneustic and pneumotaxic respiratory centers. Cerebellum  Receives input from proprioceptors.  Participates in coordination of movement.  Necessary for motor learning, coordinating different joints during movement, and limb movements. Medulla Oblongata ◦ All descending and ascending fiber tracts between spinal cord and brain must pass through the medulla.  Nuclei contained within the medulla include VIII, IX, X, XI, XII.  Pyramids:  Fiber tracts cross to contralateral side. ◦ Vasomotor center:  Controls autonomic innervation of blood vessels. ◦ Cardiac control center:  Regulates autonomic nerve control of heart. ◦ Regulates respiration with the pons.  Unconscious motor response to a sensory stimulus.  Stimulation of sensory receptors evokes APs that are conducted into spinal cord. ◦ Synapses with association neuron, which synapses with somatic motor neuron.  Conducts impulses to muscle and stimulates a reflex contraction. ◦ Brain is not directly involved.

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