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Neurophysiological Basis of Movement World III: Structures Lecture 13: Brain Anatomy A B F F F C F P T E C T T P P O O E O Typical placement of EEG electrodes at the top of the head (A) and at the side of the head (B). Areas of interest: central (C), frontal (F), occipital (O), parietal (P), temporal (T), and ear (E). Major EEG Waveforms Beta Alpha Theta Delta 1s Typical EEG waves include beta waves (13 to 25 Hz), alpha waves (10 to 12 Hz), theta waves (5 to 8 Hz), and delta waves (1 to 5 Hz). Alpha Rhythm Disappears With Eye Opening Evoked Potentials Evoked potential A B Time Stim Evoked brain potentials to peripheral stimuli (e.g., to an electrical stimulus) are frequently obscured by background activity (A). However, averaging a large number of trials may reveal an evoked potential (B). Evoked Potentials in the Spinal Cord Evoked potential A L1 T1 B L1 T1 Stim Evoked potentials in the spinal cord can be recorded from the back in response to an electrical stimulation of a peripheral nerve. In A, stimulation of the tibial nerve leads to evoked potentials over the L1 and T1 vertebrae. In B, there is a potential over L1 but not over T1. Most likely, transmission along the spinal cord is damaged in B. Radiography (X-Ray Absorption) Identifies objects with different X-ray absorption Typically correlates with density Inexpensive High spatial resolution Computer Tomography (CT) Receiver Emitter Computer tomography involves making a series of X-ray images while rotating the emitter and the receiver of X-rays. Computer Tomography (CT) Creates a 3-D image based on radiography Low cost Short examination time Relatively high resolution Positron Emission Tomography (PET) g-ray detectors g-ray g-ray detectors g Positron + Electron − Bang! g Positron emission tomography (PET) uses radioactive isotopes of lowmolecular-weight elements that emit positrons. Positrons collide with electrons and emit X-rays (gamma rays), which are detected by an array of gamma ray detectors surrounding the head. Positron Emission Tomography (PET) Measures the concentration of radioactive tracers Selective sensitivity to different substances and processes Costly Poor time resolution Magnetic Resonance Imaging (MRI) N Magnetic field S MRI signal Frequency Magnetic resonance imaging (MRI) is based on the ability of elements with an odd atomic weight to align their spins along an external magnetic field. If the field is perturbed, spin alignment is violated. When the perturbation is turned off, the spins return to the previous alignment and emit radio waves in the process. The frequency of the waves and the time it takes the nuclei to come to a lower-energy state are specific to the element. We can use a magnetic field that changes in space to identify the location of certain elements. Magnetic Resonance Imaging (MRI) Radio-frequency pulse perturbs protons, which release energy that can be analyzed Very high degree of contrast of different matter; no bone artifact Requires high degree of cooperation from the patient Problems with metal objects High cost Functional Magnetic Resonance Imaging (fMRI) Comparing MRI measurements obtained before and after performing a task Can show changes in the signal in different brain structures during natural tasks Very poor time resolution Questionable interpretation of the BOLD response Angiography Injection of contrast into major blood vessels; making X-ray shots High spatial resolution Low cost Shows only major blood vessels Transcranial Magnetic Stimulation (TMS) Transcranial Magnetic Stimulation (TMS) Transcranial Magnetic Stimulation (TMS) Stimulation of deep structures inside the body (brain structures) using a quickly changing magnetic field Informs on interactions among brain structures and between these structures and the spinal cord Noninvasive; can be used for basic research and in clinics Interpretation is ambiguous; can stimulate many structures A General Scheme of the CNS Brain Ventricles Meninges Central canal Spinal cord The central nervous system (CNS) consists of the spinal cord and the brain. Both are bathed in cerebrospinal fluid and are surrounded by meninges. The Medulla Pons Nuclei Cerebellum Medulla Fourth ventricle Reticular formation Spinal cord At its rostral end, the spinal cord borders with the medulla. The medulla contains a number of important nuclei, the caudal portion of the reticular formation, and the fourth ventricle. At its rostral end, the medulla borders with the pons. The Pons Midbrain Aqueduct Pons Cerebellum Medulla Reticular formation The pons is located between the medulla and the midbrain. It contains white fiber tracts (both ascending and descending) and several nuclei, including those of cranial nerves V to VIII. The Cerebellum Cerebellum Pons Peduncles Medulla Left hemisphere Vermis Right hemisphere The cerebellum lies just behind the medulla and the pons. It consists of two hemispheres and a central area (vermis). The cerebellum is supported by three pairs of peduncles (bundles of neural fibers). The Midbrain Midbrain Red nucleus Colliculi Substantia nigra Sylvius aqueduct Pons Medulla Cerebellum The midbrain (mesencephalon) contains four elevations called colliculi, which are divided into two superior colliculi and two inferior colliculi. The midbrain also contains two major nuclei—the red nucleus and the substantia nigra—as well as the Sylvius aqueduct. The Diencephalon Diencephalon Thalamus Hypothalamus Third ventricle Epiphysis Hypophysis Mammilary body Midbrain Cerebellum The diencephalon is almost completely surrounded by cerebral hemispheres. It contains the thalamus, the hypothalamus, the hypophysis, and the epiphysis (the pineal gland). Inside the diencephalon is the third ventricle. The Limbic System Cingulate gyrus Fornix Olfactory bulb Hypothalamus Amygdaloid nucleus Hippocampus Cerebellum The limbic system includes the hypothalamus, the fornix, the hippocampus, the amygdaloid nucleus, and the cingulate gyrus of the cerebral cortex. The Cerebrum Central sulcus Frontal lobe Lateral sulcus Parietal lobe Temporal lobe Occipital lobe The cerebrum consists of two hemispheres connected by the corpus callosum and the anterior commissure. Each hemisphere is divided by fissures into five lobes: the frontal lobe, the parietal lobe, the occipital lobe, the temporal lobe, and the insula. The Basal Ganglia The basal ganglia represent pairs structures that include the globus pallidus, the putamen, the caudate nucleus, the subthalamic nucleus, and the substantia nigra. Summary of Brain Structures Nuclei of cranial nerves: control of neck and face Reticular formation: stimulation can induce locomotion Cerebellum: piece of magic (Synergy formation? Timing? Memory? Learning?) Red nucleus: source of a major descending pathway Thalamus: sensorimotor integration Limbic circle: emotions Basal ganglia: motor control, movement initiation Cortex of large hemispheres: “higher” functions, motor control