Neurophysiological Basis of Movement World III: Structures

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). B F C T P O A F C PP O O F F EE TT Lecture 13: Brain Anatomy

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). Major EEG Waveforms 1 s Beta Alpha Theta Delta

Alpha Rhythm Disappears With Eye Opening

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 Time A B Evoked potential 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. Evoked Potentials in the Spinal Cord Evoked potential A B L1 T1 L1 T1 Stim

 Identifies objects with different X-ray absorption  Typically correlates with density  Inexpensive  High spatial resolution Radiography (X-Ray Absorption)

Computer tomography involves making a series of X-ray images while rotating the emitter and the receiver of X-rays. Computer Tomography (CT) Emitter Receiver

 Creates a 3-D image based on radiography  Low cost  Short examination time  Relatively high resolution Computer Tomography (CT)

Positron emission tomography (PET) uses radioactive isotopes of low- molecular-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) Bang!   + − Positron Electron  -ray detectors  -ray detectors  -ray

 Measures the concentration of radioactive tracers  Selective sensitivity to different substances and processes  Costly  Poor time resolution Positron Emission Tomography (PET)

Magnetic Resonance Imaging (MRI) 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. S N Magnetic field MRI signal Frequency

 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 Magnetic Resonance Imaging (MRI)

 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 Functional Magnetic Resonance Imaging (fMRI)

 Injection of contrast into major blood vessels; making X-ray shots  High spatial resolution  Low cost  Shows only major blood vessels Angiography

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 Transcranial Magnetic Stimulation (TMS)

The central nervous system (CNS) consists of the spinal cord and the brain. Both are bathed in cerebrospinal fluid and are surrounded by meninges. A General Scheme of the CNS Brain Spinal cord MeningesVentricles Central canal

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 Medulla Pons Spinal cord Medulla Cerebellum Fourth ventricle Nuclei 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 Pons Pons Medulla Cerebellum Reticular formation Midbrain Aqueduct

The Cerebellum 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). Pons Medulla Cerebellum Peduncles Vermis Left hemisphere Right hemisphere

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 Midbrain Pons Medulla Cerebellum Midbrain Sylvius aqueduct Red nucleus Substantia nigra Colliculi

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 Diencephalon Midbrain Diencephalon Cerebellum Thalamus Hypothalamus Hypophysis Epiphysis Mammilary body Third ventricle

The Limbic System The limbic system includes the hypothalamus, the fornix, the hippocampus, the amygdaloid nucleus, and the cingulate gyrus of the cerebral cortex. Cerebellum Hypothalamus Hippocampus Amygdaloid nucleus Fornix Cingulate gyrus Olfactory bulb

The Cerebrum 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. Parietal lobe Central sulcus Frontal lobe Occipital lobe Temporal lobe Lateral sulcus

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