Transcript F - Journals

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