The Nervous System

 

Summary
Central Nervous System (CNS)

Peripheral Nervous System
Somatic
Autonomic

The Neuron
Structure
Functions

The Endocrine System

The evolution of the Brain & Comparison Across species

Methods for Brain Research

Brain Structure and it's Functions

The Mysteries of our Two Brains

The Mind-Body Problem
 
 

 


 

The Nervous System

 

Central Nervous System - the portion of the nervous system consisting of the brain and spinal chord.

Spinal Chord - A collection of neurons and supportive tissue running from the base of the brain down to the centre of the back. video

Reflex: An automatic response to a stimulus, requiring no conscious efforts (that often only requires the spinal chord). video

 Two Systems. 

Peripheral Nervous System - All nerves outside the CNS, includes sensory & motor nerves. video

Somatic Nervous System - The subdivision of the peripheral NS that connects to sensory receptors and to skeletal muscles.


Autonomic Nervous System - The subdivision of the PNS that regulates the internal organs and glands (bladder, stomach, heart, blood vessels)
Sympathetic N S - that mobilizes bodily resources and increases the output of energy during emotion & stress (fight or flight - accelerator)
Parasympathetic N S - operates during relaxed states and conserves energy (digest food - brake)

Biofeedback (Miller, 1969, 1978) - monitoring devices track the bodily processes in question and deliver a signal (light or tone) whenever a person makes the desired response - e.g., blood pressure, heart rate, brain waves, (new tech CBC (muse))

Basic Units of the Nervous System

Neurons: Cells that conduct electrochemical signals, the basic unit of the nervous system. Also called a nerve cell.  Arborization. 

Cell Assemblies are collections of cells that work together in neural pathways or circuits.

Glial Cells: cells that hold neurons in place, insulate neurons, and provide neurons with nutrients.

Nerve - a bundle of nerve fibres (axons and dendrites) in the peripheral nervous system.

The Structure of the Neuron 

Dendrites - a neuron's branches that receive information from other neurones and transmit it toward the cell body.

Cell Body - The part of the neuron that keeps it alive and determines whether or not it will fire.

Axon - a neuron's extending fibre that conducts impulses away from the cell body and transmits them to other neurons.

Myelin sheath - A fatty insulation (oligodendrocytes) that may surround the axon of some neurons, also called white matter. After birth develops in sensory and then motor areas, and in adolescence through to pre-frontal cortex.

Synapse - place where transmission of nerve impulses go from one neuron to the next.  alt fig
- Includes the axon terminal, the synaptic cleft, and receptor sites in membrane of the next cell.

Action potential -Electrical impulses or current travelling down nerve cell. Two types of action. video, AP2

unmyelinated smooth flow of current or potential

myelinated jumping skipping flow of potential hopping down nodes fig

Synaptic end bulb - synaptic vesicles - little sacs that release neurotransmitters. video

Neurotransmitter - a chemical substance that is released by a transmitting neuron at the synapses and that alters the activity of a receiving neuron.eg.,

acetylcholine - transmits between nerves and muscles and
        in Pons (REMSleep)
; also memory & learning

      dopamine - important in "reward" system, important in
        schizophrenia & Parkinson's syndrome
;
         also learning, movement and emotion


      serotonin - involved in sleep, dreaming, mood, 
         arousal & emotions
(SS)

      GABA  - involved in inhibition and regulation of anxiety

Receptor sites - lock and key only certain ones fit.

excitatory - increase potential of receptor firing

inhibitory - decrease probability of receptor firing

Neuromodulators - chemical messengers in the NS that increase or decrease the action of specific neurotransmitters. Drugs will affect action of neurotransmitters: release, re-uptake, block, ...
E.g., Cocaine blocks re-uptake of dopamine leading to longer effects then lowered levels

Endorphins - chemical substances in the nervous system that are similar in structure and action to opiates; they are involved in pain reduction, pleasure, and memory and are AKA endogenous opioid peptides.

 

The Endocrine System

 

Hormones - chemical substances secreted by glands that affect the functioning of other distal organs.

Endocrine Glands - Internal Organs that produce hormones and release them into the bloodstream.

-e.g., Melatonin - A hormone, secreted by the pineal gland that is involved in the regulation of daily biological rhythms -sleep cycles & jet lag)

-e.g., Sexual Hormones (testosterone, estrogen)

Evolution of the brain & Comparison across species
The Older parts of the brain are the "lower" ones, evolutionarily speaking.  Paul McLean (1973) suggested that we have a "triune" brain. This three part brain is comprised of:
 

 

Brain Stem
Limbic System
Cortex
Automatic -Ritual
Emotional
Mamalian 
Territoriality
   

 

Elsewhere comparisons have been made between language areas across species and other areas.
 
 

 


 

Methods for Brain Research

Invasive Techniques:
Lesion method (extirpation) - involves the removal or cutting of parts of the brain to see what effects it has on psychological function.

 

Electrode method - inserting an electrode (small needle or wiring) into parts of the brain to either record or stimulate brain activity.

This is used to probe the brain prior to surgery, as pioneered by Dr. Wilder Penfield.


-microelectrodes can be inserted into single cells to measure their activity

Non-invasive techniques
Surface electrodes - disks taped to the head to record activity in that part of the brain, usually measuring 'brainwaves' or cyclical patterns of neuro-electrical activity of millions of neurons.

EEG electroencephalogram - a device for recording neural activity detected by electrodes. Contemporary EEG helmet

Evoked potentials - patterns of brain activity produced in response to specific events.

PET scan (positron-emission tomography) - a method for analysing biochemical activity in the brain, using injections of a glucose-like substance containing a radioactive element.

People with special abilities may not have different overall structures, but rather fewer circuits to do the task, or more efficient operations.

MRI (magnetic resonance imaging) - a method for studying body and brain tissue, using magnetic fields and special radio receivers.

- a computer analyses the signals and blood flow and activity in 'fast' or functional MRI (f-MRI) MRI Basics


 

Structures of the Brain and Their Functions

Localisation of Function- specialization of particular brain structures or areas for particular functions. 3D brain site

Brain stemthe part of the brain at the top of the spinal chord, consisting of the medulla and pons and midbrain. Medulla - a structure in the brainstem responsible for certain automatic functions, such as breathing and heart-rate.

Pons - rostral (anterior) to medulla, is involved in sleeping, waking, and dreaming, and relays information from the cerebrum to cerebellum.

 

Reticular Activating System (RAS) - a dense network of neurons found in the core of the brainstem; it arouses the cortex and screens incoming information.

Midbrain - rostral (anterior) to pons, involved in control of eye movement
         relays to auditory and motor movement

Structures: Tectum (superior colliculus, inferior colliculus, substantia nigra)

 

Cerebellum - 'lesser brain' - a structure that regulates movement and balance, and timing that is involved in the learning of simple kinds of responses.

Forebrain: Emotions, Memory & Thought

 

Thalamus - A brain structure that relays sensory messages to the cerebral cortex, involved in the tracking of visual and auditory information and the execution of movements

Hypothalamus - A brain structure involved in emotions and drives vital to survival (eg., fear, hunger, thirst, & reproduction) it regulates the ANS through pituitary secretions.

 

Pituitary Gland - a small endocrine gland at the base of the brain which releases many hormones and regulates other endocrine glands

Limbic System - A group of brain areas involved in emotional reactions and motivated behaviour.

-emotions and 'pleasure centre' (septal area) of rat brains as seen in repeated bar pressing in a study by Olds & Milner, 1954)

Amygdala - a brain structure involved in the arousal and regulation of emotion and the initial emotional response to sensory information (Appraisal) connects with Olfaction (smell), Prefrontal & Temporal Cortex (planning), Hypothalamus & Brain Stem).
-evaluating sensory information; anxiety and depression.Capgras' Syndrome

Hippocampus - a brain structure involved in the storage of new information in memory - Gateway to memory.

"HM" - man with no memory for new events, although he could learn new tasks or skills (e.g., learned to play tennis, problem solve) but didn't have recall for these events.

Eric Kandel's work on memory

Cerebrum - the largest part of the brain consisting of upper parts of forebrain, it is in charge of most sensory, motor, and cognitive processes. Cerebral Hemispheres- two halves of the cerebrum - latin for brain

Corpus Callosum - the bundle of nerve fibres connecting the two hemispheres

 

Cerebral Cortex - several thin layers of cells covering the cerebrum, "grey-matter" cell bodies of the cortex "white-matter" is myelinated (covered) axons elsewhere in the brain 

Occipital Lobes - lower back part of the brain AKA visual cortex

Parietal Lobes - top and side walls - somatosensory areas with more sensory function have larger areas (i.e., face and hands)

Ramachandran's Peggy E1-4 E1-5

Temporal Lobes - sides of brain (temples) involved in memory, perception, emotion and language, including the auditory cortex.

 Experience God             Prosopagnosia -Facial Recognition disability

Frontal Lobes - Front - forehead - contain motor cortex for voluntary movement, and ability to make plans, think creatively and take initiative.

Prefrontal Cortex - most anterior parts of frontal cortex mice & rats -3.5% in cats, 7% in dogs, 17% in chimps, 29% in humans. > personality
Case of -Phineas Gage - tamping rod through pf cortex - "was able to speak, think, & remember but he changed his personality from 'mild-mannered', friendly, efficient work into a foul-mouthed, ill-tempered, undependable lout who could not hold a steady job or a plan." This is an area that controls other areas (i.e. limbic system) and implies "free-will"

 

Our Two Cortical Hemispheres
  Split brain: Two minds in one head

1953 Myers & Sperry - severed the corpus callosum in cats. Blindfolded one eye - learn to push bar to get treat. Changed eyes and it acted as though it had learned nothing. 

Spilt-Brain Surgery
Most people have language in left brain
- Temporal Wernicke's area comprehension and meaning
- Frontal Broca's area for production
 
  Presented "split images" - Faces cut in half to each visual field - brief exposure

-say what you saw (left brain) - Right side image>>verbal -right visual field
-point with left hand (right brain) - Left side image

Split brain - Chicken claw to left hemisphere & snow to right then have point to related pictures chicken & shovel each pointed to each object & explained claw went with chicken and shovel was for cleaning the coup (no verbal awareness of the snow). Gazzaniga
 

The special abilites of the Right &  Left Brains

Language is typically in the left hemisphere for nearly all right handers and most left handers.

Left side is also more active for some logical tasks (i.e, math problems & technical understanding)

Right side mental skill vastly inferior to cog level of a chimpanzee and that left side tries to explain actions or emotions from non-verbal side (Gazzaniga, 1983)
 

Right side - superior in problem requiring spatial - visual facial recognition, music, art, non-verbal sounds (dog bark) & some language ability including metaphors (Sperry, 1982).

Rational analytic vs. intuitive, holistic

Jill Bolte Taylor's report on her stroke and right hemisphere

 

Lateralisation -challenges: Lefthanders  in a  Righthanded world.


 

The problem of localization: Where are our thoughts and memories stored?

Lashley (1950) searching for the "n-gram" maze learning in rats - systematically extirpated various areas and amounts of rat's brain tissue.

 The Mind- Body problem revisited

Plasticity: Recent cases of hemispherectomies suggests that the right can pick up a great deal of what the left had done for maturing children after age six or seven.
 

The brain that changed itself (Doidge, 2010) thinking and other "brain activity" changes the brain. Brain exercises to change your brain.

Cochlear implants and tongue stimulators that enable blind people to see have build on these principles. (More later during sensation C2, ... )

 Are there 'his' and 'her' brains?
slight anatomical differences - women less lateralized than men & huge variation within genders more so than between  them!!

See Doreen Kimura's work on gender brains and cognition

Gender &, Hormones The varieties of gender & Sexuality Gender Bread Person