Chapter 5
The Nervous System
Outline
Introduction
Funtional Organization of the Nervous System
How Neurons Work and Influence One Another
Introduction
Why do we study the biological aspects of behavior?
Our body is made up of biological processes.
Everything we feel, think or do has biological components.
Biological processes help us to understand behavior.
Every section of this course is at least indirectly about the nervous system. All of the psychological phenomena covered in this course are a direct product of these biological process. Psychology is the study of what the nervous system does. Therefore an understanding of this system is essential to an understanding of human psychology.
NOTE TO STUDENTS: As you study these notes, try to answer the questions that appear in this column to check your mastery of the material. To see the answers to the questions, highlight the 'invisible' text that is after the word ANSWER.
The Human Brain
Functional Organization of the Nervous System
The nervous system is an electrochemical communication system that does 4 things:
1. It receives sensory messages from the external environment.
2. It organizes information and integrates it with already stored information.
3. It uses integrated information to send out messages to muscles and glands, producing organized movement and secretions.
4. It provides the basis for conscious experience.
The structure of the nervous system
1. The Central Nervous system - spinal cord and brain - consists of tracts tracts are bundles of axons forming a pathway
2. The Peripheral Nervous system - everything else - consists of nerves nerves are bundles of axons of sensory or motor neurons existing outside of the CNS
a. Skeletal (somatic) - voluntary muscle control of skeletal muscles. This system controls the motor neurons and is under voluntary control.
b. Autonomic NS - muscles and gland of internal organs (e.g. heart).
A major difference between skeletal and autonomic NS is that a skeletal muscle is inactive when the motor neuron is not sending it a signal. However, the autonomic motor neuron only modifies the activity of the visceral muscle that it acts on. Visceral muscles have built in, nonneural mechanisms for generating activity.
Example: Heart continues to beat, muscles of intestinal walls continue to contract even if all nerves to these organs are destroyed.
The three types of Neurons
1. Sensory (afferent - inward) neurons - sends information from the sensory organs, through the nerves, into the CNS 2. Motor (efferent - outward) neurons - carry messages from CNS, through nerves, to operate muscles and glands (the most of these - 100 billion at least)
3. Interneurons - exist only within the CNS. They carry messages from 1 set of neurons to the other. They can bring information from different sources together into one location in the CNS.
The structure of the Neuron
1. Cell body (soma) contains the nucleus (containing the genetic info) and other things found in most cells. It also produces neurotransmitter which are stored in synaptic vesicles.
2. Dendrites - receives incoming signals from other neurons. They look like plant roots.
3. Axons - a single tubelike fiber that is thicker and longer than Dendrites. It is used by the neuron to transmit an electrical impulse to other neurons. They may be tiny or up to a meter in length.
4. Myelin sheath - a fatty white substance which grows around the axon. It speeds the neural impulse by insulating the axon (increases conduction). Not all neurons have myelinated axons.
5. Axon terminal - the end of the axon.
6. Synapse - the area between the axon terminal and the dendrites. Neurons do not actually touch each other.
The sympathetic and parasympathetic divisions of the autonomic nervous system.
Most visceral muscles and glands are connected to 2 sets of neuronal systems which produce opposite effects. The Sympathetic division and the Parasympathetic division.
1. Sympathetic - arousal for defensive action (prepares body for fight or flight), increases heart rate and blood pressure, increases blood sugar, dilates arteries to increase blood flow to muscles, relaxes the bladder, stimulates adrenal glands, and cools the body with perspiration. This makes you alert and ready for action
2. Parasympathetic - When the stressor is over, this takes over. Calming, conserves energy, produces the opposite effect (Decreases heart rate, etc)
The spinal cord
The spinal cord serves three important functions:
1. Organizes information to and from the brain.
2. Organizes certain reflexes.
3. Generates rhythmic components of locomotor movements.
Reflexes - involves an automatic response to stimuli.
The sensory Neuron is stimulated by stimuli, send impulse to spinal cord. An interneuron in the spinal cord simultaneously sends impulse to:
1. Motor neuron in the finger
2. to the brain
Consequently, you react before the message reaches the brain. Thus you feel no pain as you react, but feel it afterwards.
The structures of the brain
1. The Central Core
a. Medulla
hooked directly onto spinal cord
controls breathing, digestion, heart rate
b. Cerebellum
looks like a little brain
in control of force and range of movement.
helps initiate and control rapid limb movement (kicking, punching)
plays a role in eye movement
plays a role in body equilibrium when standing
c. Pons
assists cerebellum in controlling movement and posture
d. Midbrain
visual reflexes
auditory reflex
motivation of movement
e. Reticular formation
involved in sleep and arousal, excites cerebral cortex
f. Thalamus
the relay center of the brain
g. Hypothalamus
connected with the limbic system and some consider it to be part of the Limbic system
main purpose is to control the internal environment of the body. It does this by
influences the pituitary gland - which releases hormones
influences drive states such as thirst and hunger
influences activity of the Autonomic NS
involved in emotions
h. Endocrine system
secrete hormones
adrenal gland - secretes epinephrine and norepinephrine - regulates heart rate, blood pressure and blood sugar level
Pituitary gland - responsible for growth, master gland
i. The Limbic system
Hippocampus - memory for new events
plays a role in emotional behavior
2. The Cerebral Cortex - gray matter
newest portion of the brain
covers the rest of the brain.
about 1/8 inch thick, contains billions of neurons
80% of total brain volume
can be divided into 4 regions or lobes (occipital, temporal, parietal, frontal)
Cortical Areas
Primary motor area - located in the frontal lobe
the finer the movement of a body part, the larger the area it takes up on the primary motor area.
Primary sensory areas - the more sensitive a body part is to perception, the larger area it takes up (i.e. the tongue)
Visual area - fibers from the right side of both eyes go to the right side of the brain.
Association areas - all other parts of the brain
receives input from the sensory areas
receives input from lower parts of the brain
involved in perception, thought, decision-making
Cerebral Hemispheres
Left hemisphere - responsible for speech, math computations, processes right visual area
Right hemisphere - spatial tasks, visualizing in 3-D, processes left visual filed
Communicate via Corpus Callosum
Split brain patients (read about in your text)
Other areas of the brain
Wernicke's area - in left temporal lobe in most people language comprehension.
Broca's area - usually on left hemisphere - speach production problems
Aphasia - disorder of language that is often found when people have suffered a stroke or some kind of damage to the brain.
What are the elementary units of the nervous system called?
ANSWER: neurons
The Central Nervous System
Which of the three types of neurons do we have the most of and whose job is the most complex?
ANSWER: interneurons
Which division of the autonomic nervous system prepares the body for "fight or flight?
ANSWER: sympathetic
Which part of the brain is functionally and anatomically similar to the spinal cord?
ANSWER: brainstem
In the textbook, Gray says that, "If I had to give up one cubic millimeter of tissue from some part of my brain [this] is the last place I would want it taken from". What part of the brain was he talking about?
ANSWER: hypothalamus
How Neurons Work and Influence One Another
How do the Neurons communicate?
Action Potential - an electrical charge which is produced by a change in the chemical balance of the fluids inside and surrounding the neurons.
at resting state, the axon contains fluid that is made up of negatively charged ions and is surrounded by fluid that is comprised of positively charged ions (polarization)
polarization is maintained by the cells ability to control whether or not some atoms are allowed in.
when a nerve is stimulated by something (light, pressure, heat) it fires, the gates of the axon begin to open and positively charged ions begin to enter the axon which "depolarize" the cell. This continues until the neuron reaches its threshold and sends an impulse though the axon to the dendrite of the next neuron. Then it returns to its resting state.
The action potential acts on an all-or none principle. It has to reach the threshold before it will fire, and then it fires completely.
This process occurs repeatedly at about 100 times per second.
When the impulse gets to the end of the axon, it reaches the Axon terminal or presynaptic ending.
The impulse is carried across the synapse by a neurotransmitter - when the action potential reaches the terminal, neurotransmitter molecules are released into the synapse...some of which will bind to the postsynapticmembrane.
Neurotransmitter - a chemical substance - over 70 different ones identified
Once it crosses the gap, it binds to receptor sites on the dendrites (causing the gates to open) If the neurotransmitter doesn't fit the receptor, it gets taken back up by the first neuron (reuptake)
Some Neurotransmitters
1. Ach - responsible for muscle communication, affects memory.
2. Serotonin - affects mood, eating behavior. Prozac prevents serotonin from being taken back up by the neurons...keeps more serotonin in the system.
3. Dopamine - too much = Schizophrenic symptoms. Too little = Parkinson symptoms. Drugs treating Schizophrenia can lead to Parkinsonian symptoms
4. Endorphins - natural opiates - released in response to pain and vigorous exercise
(Cartoons by Mark Parisi. Used by special permission. For many more, visit his site.)
What chemical mechanism continuously moves sodium out of the cell and potassium into it?
ANSWER: sodium-potassium pump
So How Do We Know All This About The Brain?
So how do we know all of this about the brain??
Studying animals
Study persons with brain injuries
Brain imaging techniques
PET
MRI
SPECT
MEG