Download 1. 2. a) Explain the compositions of white matter and gray matter

Tfy-99.2710 Introduction to the Structure and Operation of the Human Brain, fall 2015
Exercise 1
1.
2. a) Explain the compositions of white matter and gray matter.
White matter consists of glial cells and myelinated axons. It does not contain the cell bodies of
neurons and acts as a signal pathway for the gray matter regions of the central nervous system. Gray
matter consists of glial cells and unmyelinated axons. It contains neuronal cell bodies.
b) Explain shortly the structure of a neuron.
Neurons can be divided into three main parts: the cell body or the soma, the dendrites and the axon.
The dendrites act as neuronal antennas in that they receive incoming signals. The cell body
functions as the information processing unit of the neuron, and is responsible for sending signals
forward. The axon is the signal pathway of the neuron; the signals sent by the cell body are
transmitted along the axon to the axon terminals located away from the cell body. Signal transfer is
along the axon is aided by the myelin sheath that covers the axon.
c) Explain:
Tfy-99.2710 Introduction to the Structure and Operation of the Human Brain, fall 2015
Exercise 1
i) myelin
Membrane that wraps around axons. Formed from glial support cells: oligodendrogolia in the
central nervous system and Schwann cells in the peripheral nervous system. Myelin facilitates
signal transfer along axons by allowing action potentials to skip between the nodes of Ranvier
(saltatory conduction).
ii) receptor
Molecule specialized in receiving a chemical signal by binding a specific neurotransmitter.
iii) interneuron
Neuron that is not a sensory or a motor neuron. The terms is also used to refer to a neuron whose
axon does not extend beyond the structure the neuron is contained in, i.e a neuron that does not
receive or send information beyond the containing structure but rather exchanges signals with
nearby neurons..
iv) pyramidal cell
A name given to dendritic trees with a pyramidal shape (wide base, narrow top). This dendrite class
along with stellate cells (star shaped) are common in the cerebral cortex. Shapes of the dendrite
trees are shown in the figure below.
Tfy-99.2710 Introduction to the Structure and Operation of the Human Brain, fall 2015
Exercise 1
d) what would happen without glial cells
Glial cells contribute to brain function by insulating, supporting and nourishing their nearby
neurons. If the glia were absent, the neurons – and hence the brain – could not function properly.
3.
Roger Sperry received the Nobel Prize in physiology and medicine in 1981 for his experiments on
split brain patients that provided strong evidence for lateralization of speech processing in the brain.
Sperry's experiments showed, that the left hemisphere is responsible for the formation of speech
while the right hemisphere is essentially mute. Furthermore, his work showed that while only the
left hemisphere is able to verbalize the information carried by visual stimuli, both hemispheres are
able to process and comprehend the information.
In what are now known as the split brain experiments, Sperry recruited a group of subjects who had
undergone a surgical procedure where the nerve fibers connecting the two hemispheres (corpus
callosum) had been severed. The procedure known as corpus callosotomy was an early treatment of
severe epilepsy that effectively disconnected the two sides of the brain from one another and thus
restricted the exchange of information between them. Knowing that the nerves of the two eyes
crossed at the optic chiasm and were connected to the hemisphere opposing the location of the eye,
Sperry could present visual stimuli to either hemisphere of split brain patients in isolation.
Information presented to the left visual field was directed to the right hemisphere and vice versa; the
severed corpus callosum restricted the hemispheres from sharing the incoming information. When
the stimuli was routed to the left hemisphere, the subjects could describe the stimuli verbally. In
trials where the right hemisphere received the stimulus, subjects were unable to verbalize their
observations, but could communicate the received information in other ways e.g., by drawing or
pointing to a corresponding image.
Split brain experiments provided evidence for the lateralization of specific brain functions to either
of the two hemispheres and led to further research on the lateralization of various other brain
functions. Although performing split brain experiments is becoming more and more unfeasible due
to the lack of subjects who have undergone corpus callosotomy, the development of brain imaging
methods such as fMRI has enabled more detailed investigations into the location of various brain
functions.