Neurons and the Brain

3/21-23/05

Next Test:Neurons, Emotions and Beyond

• Jansen’s lecture notes

• Bedell’s notes and handout

• Jacobson’s lecture notes

• Reading on emotions

• Clark Reading

• TEST: 4/12

• Presentations: 4/14; 4/19; 4/21; 4/26

Individualism

• And its consequences:

• Discussion: Why isn’t a memory just in your head?

• The nervous system is the information highway of the body. It consists of the central and peripheral nervous systems. The central nervous system is composed of the brain and the spinal cord. The peripheral nervous system is made up of neurons and nerve endings. The neuron is the basic unit and messenger of the peripheral nervous system. It is composed of dendrites, a cell body, an axon and axon terminals. When a nerve signal is sent by the nervous system, the dendrites receive the signal. The axon then transmits the nerve signal to the axon terminals which synapse with dendrites or other tissues such as a muscle.

•There are two types of axons, myelinated and unmyelinated. Unlike unmyelinated axons, myelinated axons have a sheath of fatty tissue called myelin wrapped around them. There are breaks in the myelin called Nodes of Ranviers which allow the nerve signal to jump from node to node. This causes the nerve signal to be transmitted faster.

•

• The Nerve Action Potential•

Nerve action potentials are the electrical signals sent out by the body to control bodily processes such as muscular movement. They are controlled by ions and their concentrations around the nerve cell. They propagate uniformly along the nerve cell and are governed by the all-or-none phenomena. This means that a nerve action potential will not occur unless the depolarization threshold is met. The depolarization threshold is the potential that must be reached before depolarization of the nerve cell will occur. As a nerve action potential propagates along a neuron it goes through several phases which are shown in the graph below.

 

•

• where

(A) Resting state = the membrane potential at rest(before the nerve action potential occurs)(B) Depolarization = occurs when there is a drastic reversal in membrane potential(C) Repolarization = occurs when the membrane potential is returning to the resting state(D) Undershoot = occurs because the potassium gate stays open too long

The Role of Ions

•   The concentration of ions around the nerve cell controls the action potential. There are two ions that are essential to a normal action potential. These ions are Sodium (Na+) and Potassium (K+). The Depolarization phase is controlled by Sodium. An external stimulus causes an influx of Sodium in the nerve cell. This depolarization, or action potential continues down the neural pathway, until it reaches its destination. After the cell depolarizes, it must repolarize to its resting potential before it can depolarize again. This repolarization phase is controlled by Potassium. An efflux of Potassium causes the potential to return to its resting state. 

The influx of Sodium ions and the efflux of Potassium ions are controlled by protein gates in the plasma membrane. The influx and efflux of these ions occurs by diffusion. Diffusion is the process by which ions move from an area of higher concentration to lower concentration. For example, after the nerve cell has been stimulated by an external stimulus, an influx of Sodium occurs because the extracellular concentration is higher than that of the intracellular.

The Sodium-Potassium Pump is a separate protein channel that replenishes the extracellular environment with Sodium, and the intracellular environment with Potassium. This protects the extracellular environment from becoming saturated with Potassium and the intracellular with sodium.

signals

Camillo Golgi• Biographical Sketch and Scientific Work• Camillo Golgi was born in July 1843 in Corteno, a village in the mountains near Brescia in

northern Italy, where his father was working as a district medical officer. He studied medicine at the University of Pavia, where he attended as an 'intern student' the Institute of Psychiatry directed by Cesare Lombroso (1835-1909). Golgi also worked in the laboratory of experimental pathology directed by Giulio Bizzozero (1846-1901), a brilliant young professor of histology and pathology (among his several contributions, Bizzozero discovered the hemopoietic properties of bone marrow). Bizzozero introduced Golgi to experimental research and histological techniques, and established with him a lifelong friendship. Golgi graduated in 1865 and was, therefore, a student during the last years of the fights for the independence of Italy (Italy became a united nation in 1870). Seated left to right: Perroncito, Kölliker, Fusari

In 1872, due to financial problems, Golgi had to interrupt his academic commitment, and accepted the post of Chief Medical Officer at the Hospital of Chronically Ill (Pio Luogo degli lncurabili) in Abbiategrasso (close to Pavia and Milan). In the seclusion of this hospital, he transformed a little kitchen into a rudimentary laboratory, and continued his search for a new staining technique for the nervous tissue. In 1873 he published a short note ('On the structure of the brain grey matter') in the Gazzetta Medica Italiana, in which he described that he could observe the elements of the nervous tissue "studying metallic impregnations... after a long series of attempts". This was the discovery of the 'black reaction' (reazione nera), based on nervous tissue hardening in potassium bichromate and impregnation with silver nitrate. Such revolutionary staining, which is still in use nowadays and is named after him (Golgi staining or Golgi impregnation) impregnates a limited number of neurons at random (for reasons that are still mysterious), and permitted for the first time a clear visualization of a nerve cell body with all its processes in its entirety.

Golgi

Hippocampus

Hippocampus

• hippocampus: means "sea horse", and is named for its shape. It is one of the oldest parts of the brain, and is buried deep inside, within the limbic lobe. The hippocampus is important for the forming, and perhaps long-term storage, of associative and episodic memories. Specifically, the hippocampus has been implicated in (among other things) the encoding of face-name associations, the retrieval of face-name associations, the encoding of events, the recall of personal memories in response to smells. It may also be involved in the processes by which memories are consolidated during sleep. 

Santiago Ramon y Cajal

• Cajal turned all his efforts to improving the silver nitrate technique. As Golgi had developed it, the staining involved including soaking the tissue in various substances. Cajal added several levels of preparation and made other refinements as the debate over the true structure of the central nervous system was intensifying. While no one had yet seen an entire nerve cell, or could tell whether it was independent or just part of a larger structure, some scientists already questioned the old "single network" theory. Fridtjof Nansen, better known today for his Arctic explorations, had joine several others in theorizing that nerve cells were independent, basic structures. Still, almost everyone else, including Golgi and Cajal, believed in the network structure.

• In 1887, Cajal became chair of Normal and Pathological Histology at the university in Barcelona. His most consuming work, however, was slicing, soaking, staining and affixing to glass slides, slivers of the cerebellum of the embryo of a small bird. Then he carefully drew what he saw under the microscope. He became an ardent convert to the independent-cell camp. In 1889, he was invited to show his drawings to the Congress of the German Anatomical Society at the University of Berlin. It could easily have been a disaster.

• The "short, powerfully built Spaniard with penetrating black eyes set up a small exhibit of drawings done on paper with colored inks," Everdell writes, reconstructing the scene. Cajal had explanatory papers delivered to the German scientists in advance, but few who tried to read them knew any Spanish. Cajal delivered his speech in fractured French, but still won his case on the strength of his drawings and slides.

• "Each stained cell stood out perfectly against a background of staggering complexity," writes Everdell, "and no matter how many times the tiny fibers of one nerve cell met those of another, there was clearly no physical connection between them. The basic unit of the brain–the neuron–had been isolated." To this day, Cajal’s meticulous drawings are a defining fixture in neuroscience texts.

The Nobel and Beyond • In 1906, Cajal and Golgi shared a Nobel Prize for medicine. The two

met for the first time in Stockholm, and while Cajal was tactful about sharing the prize, the two still disagreed about the structure of the brain. Golgi’s speech attacked Cajal’s concept of the independent neuron, while Cajal’s speech the next day defended it.

• Cajal continued his research, introducing four major new hypotheses, three of which are now accepted by neuroscientists. He died in Madrid in 1934

The Nervous SytemsStructure of the Nervous system

• 1. Central Nervous system (red)1. Brain2. Spinal Cord

• 2. Peripheral Nervous System (blue)1. Somatic

1. sensory-afferents from skin/muscle2. motor-efferents controlling

movement2. Autonomic

1. sympathetic- Active in emergency "fight or flight" reactions

2.  Parasympathetic-dominant in functions related to life maintenance (eating, storage of fuels)

Medial Saggital View

Coronal SectionMid-Brain/MRI

• The brain is surrounded and protected by the rigid, bony skull and three membranes, or meninges. The tough, fibrous outer membrane is the dura mater. The intermediate membrane, named the arachnoid, is thin and weblike. The pia mater is the innermost covering and is the most delicate. It is molded to the shape of the brain. The cerebrospinal fluid (CSF) surrounds the brain and spinal cord and flows through open chambers in the brain, known as ventricles, and out an opening to the spinal cord. The brain actually floats in the shock-absorbing CSF, and is thus protected from trauma. The CSF also brings nutrients to the brain and removes wastes.

Gyrus and Sulcus

• gyrus: a fold or convolution in the cerebrum• Sulcus: a cleft or fissure in the cerebrum

Central Sulcus

Brain Development• The brain develops, in utero, in three

separate portions, reflecting evolutionary history: the hindbrain, the midbrain, and the forebrain.

• The bottom-most part of the brain is the brain stem. The brain stem is attached to the spinal cord. It relays information between parts of the brain or between the brain and body and regulates basic body function. It is made up of the midbrain, medulla and the pons.

• Midbrain: The midbrain contains the major motor supply to the muscles controlling eye movements and relays information for some visual and auditory reflexes.

• Pons: The pons is a mass of nerve fibers that serves as a bridge between the medulla and midbrain above it. The pons is associated with face sensation and movement.

• Medulla: The medulla (also known as the medulla oblongata) is located at the base of the brain stem and controls many of the mechanisms necessary for life, such as heartbeat, blood pressure and breathing.

Hindbrain

• The hindbrain (the oldest part of the brain) develops into the cerebellum, the pons and the medulla.

• The outermost and top layer of the brain is the cerebral cortex. The cerebral cortex is the most recently evolved and most complex part of the brain. As one moves lower into the brain, the parts have increasingly primitive and basic functions and are less likely to require conscious control.

Cerebellum

• At the back of the head, in between the brain stem and cerebral cortex, is the cerebellum. The cerebellum controls balance and coordination and is where learned movements are stored. Purkinje neurons that control the refinement of motor movements are found in the cerebellum. The cerebellum receives input from many parts of the brain regarding pressure on the limbs, limb movement, and the position of the limbs in space. The dentate nucleus, located within the cerebellum, coordinates skilled movement. Damage to this region, as a result of HD, causes movements that were once smooth and refined to become jerky. Movements must also be constantly relearned.

Lobes

Frontal lobe• Frontal Lobe - Front part of the brain;

involved in planning, organizing, problem solving, selective attention, personality and a variety of "higher cognitive functions" including behavior and emotions.

• The anterior (front) portion of the frontal lobe is called the prefrontal cortex. It is very important for the "higher cognitive functions" and the determination of the personality.

• The posterior (back) of the frontal lobe consists of the premotor and motor areas. Nerve cells that produce movement are located in the motor areas. The premotor areas serve to modify movements.

• The frontal lobe is divided from the parietal lobe by the central culcus.

Others• Occipital Lobe - Region in the back of the brain which processes visual information. Not only is

the occipital lobe mainly responsible for visual reception, it also contains association areas that help in the visual recognition of shapes and colors. Damage to this lobe can cause visual deficits.

•  • Parietal Lobe - One of the two parietal lobes of the brain located behind the frontal lobe at the

top of the brain.• Parietal Lobe, Right - Damage to this area can cause visuo-spatial deficits (e.g., the patient may

have difficulty finding their way around new, or even familiar, places).• Parietal Lobe, Left - Damage to this area may disrupt a patient's ability to understand spoken

and/or written language.• The parietal lobes contain the primary sensory cortex which controls sensation (touch, pressure).

Behind the primary sensory cortex is a large association area that controls fine sensation (judgment of texture, weight, size, shape).  

• Temporal Lobe - There are two temporal lobes, one on each side of the brain located at about the level of the ears. These lobes allow a person to tell one smell from another and one sound from another. They also help in sorting new information and are believed to be responsible for short-term memory.

• Right Lobe - Mainly involved in visual memory (i.e., memory for pictures and faces).• Left Lobe - Mainly involved in verbal memory (i.e., memory for words and names).

• Brodmann’s Areas

Studies done by Brodmann in the early part of the twentieth century generated a map of the cortex covering the lobes of each hemisphere. These studies involved electrical probing of the cortices of epileptic patients during surgery. Brodmann numbered the areas that he studies in each lobe and recorded the psychological and behavioral events that accompanied their stimulation.

The Frontal Lobe contains areas that Brodmann identified as involved in cognitive functioning and in speech and language.

Area 4 corresponds to the precentral gyrus or primary motor area. Area 6 is the premotor or supplemental motor area. Area 8 is anterior of the premotor cortex. It facilitates eye movements and

is involved in visual reflexes as well as pupil dilation and constriction. Areas 9, 10, and 11 are anterior to area 8. They are involved in cognitive

processes like reasoning and judgement which may be collectively called biological intelligence.

Area 44 is Broca's area.Areas in the Parietal Lobe play a role in somatosensory processes. Areas 3, 2, and 1 are located on the primary sensory strip, with area 3

being superior to the other two. These are somastosthetic areas, meaning that they are the primary sensory areas for touch and kinesthesia.

Areas 5, 7, and 40 are found posterior to the primary sensory strip and correspond to the presensory to sensory association areas.

Area 39 is the angular gyrus.Areas involved in the processing of auditory information and semantics as

well as the appreciation of smell are found in the Temporal Lobe. Area 41 is Heschl's gyrus, or the primary auditory area. Area 42 immediately inferior to area 41 and is also involved in the detection

and recognition of speech. The processing done in this area of the cortex provides a more detailed analysis than that done in area 41.

Areas 21 and 22 are the auditory association areas. Both areas are divided into two parts; one half of each area lies on either side of area 42.

Area 37 is found on the posterior-inferior part of the temporal lobe. Lesions here will cause anomia.

The Occipital Lobe contains areas that process visual stimuli. Area 17 is the primary visual area. Areas 18 and 19 are the secondary visual areas.

Limbic System

http://www2.umdnj.edu/~neuro/studyaid/Practical2000/practical2000.htm

Rods and Cones

• two kinds of photoreceptors of vertebrate eyes

• rods very light sensitive, and sensitive to wider range of wavelengths, useful at night and under low light conditions, incapable of wavelength discrimination

• in moderate light, both rods and cones contribute to vision, at high light levels, rods saturate

• cones useful in higher light conditions, populations with differing wavelength sensitivity form basis for color vision

The LGN

• Optic nerve fibres from the eyes terminate at two bodies in the thalamus (a structure in the middle of the brain) known as the Lateral Geniculate Nuclei (or LGN for short). One LGN lies in the left hemisphere and the other lies in the right hemisphere.

Visual System

Areas of the Visual Cortex

Macque Monkey VS

The binding problem

• Visual information processing takes place in parallel with different areas processing different image attributes. How does brain keep track of how these attributes relate to one another? Our phenomenal experience is of a singular unitary visual world, how does this relate to the multiple visual maps of our brain?

LOLA