Chapter Four

Biology OfBehaviorBy Courtney Graul

Now for the stuff we all know and love… the brain’s components and how they affect us.

The brain has two primary

responsibilities:

1)control of behavior

2)regulation of our body’s physiological functions

In order for us to understand how the brain carries out these to main functions we need to understand how the brain itself works.

Two Important Divisions

The Central Nervous System

Brain and spinal cord

The Peripheral Nervous System

Cranial and spinal nerves

Central Nervous System

Three main structures of the brain:

1) Brain stem

2) Cerebellum

3) Cerebral hemispheres

Cells of the Nervous System Neurons (nerve

cells) - the parts of the nervous system that bring sensory information to the brain, store memories, reach decisions, and control the activities of muscles

Glial cells – found in the CNS and provide support for neurons and supplies them with needed chemicals

Principal Parts of a Neuron

Soma – or cell body, contains mechanisms that controls metabolism and maintenance of the cell. The soma also receives messages from other neurons.

Principal Parts of a Neuron Dendrites – branch

from the soma to receive messages from other neurons and transmit that information to the soma.

Axon – (nerve fiber) carries messages away from the soma toward the cells the neuron is communicating with =action potential

Terminal button – rounded swelling at the end of the axon of a neuron; releases transmitter substance

The Action potentialThe message carried by the axon –

a quick reversal in the electrical charge of the axon, causing the release of transmitter substance.

The outside of the membrane is positively charged (and the inside is negatively charged) because the axon contains ions. When the axon is resting, its ion channels are closed, so ions cannot move in or out of the axon. An action potential is caused by the opening of some ion channels in the membrane at the end of the axon nearest the soma.

Ion – a positively or negatively charged particle; produced when many substances dissolve in water

Ion channel – a special protein molecule located in the membrane of a cell; controls the entry or exit of particular ions.

Communication

Neurons can communicate with the help of synapses.

Synapse – the junction between the terminal button of one neuron and the membrane of a muscle fiber, a gland, or another neuron.

Types of Neurons Presynaptic Neuron-

a neuron whose terminal buttons form synapses with and excite or inhibit another neuron.

Postsynaptic Neuron – a neuron with which the terminal buttons of another neuron form synapses and that is excited or inhibited by that neuron.

Types of Neurons Motor neurons – a

neuron whose terminal buttons form synapses with muscle fibers. When an action potential travels down its axon, the associated muscle fibers will twitch.

Sensory neuron – detects changes in the external or internal environment and sends information about these changes to the central nervous system.

Regions of Primary Sensory and Motor Cortex Three areas of the cerebral cortex

receive information from sensory organs:

1)primary visual cortex – receives visual information and is located in occipital lobes

2)primary auditory cortex – receives auditory information and is located in the temporal lobes

Primary somatosensory cortex – receives information directly from the somatosensory system (touch, pleasure, vibration, pain, and temperature); and is located in the front part of the parietal lobes

The three regions of primary sensory cortex in each hemisphere receive information from the opposite side of the body. These connections between the sensory organs and the cerebral cortex are said to be contralateral.

Various areas of the brain:Primary motor cortex – directly

controls the movements of the body, located in the back part of the frontal lobes.

Frontal lobe – The front portion of the cerebral cortex, including Broca’s speech area and the motor cortex; damage impairs movement, planning and flexibility in behavioral strategies.

Parietal lobe – located in the cerebral cortex behind the frontal lobe and above the temporal lobe; contains the somatosensory cortex; is involved in spatial perception and memory.

Temporal lobe – the portion of the cerebral cortex below the frontal and parietal lobes and containing the auditory cortex.

Occipital lobe – the rearmost portion of the cerebral cortex; contains the primary visual cortex.

Sensory association cortex – receives information from the primary sensory areas.

Motor association cortex – those regions of the cerebral cortex that control the primary motor cortex; involved in planning and executing behaviors.

More vocabularyCorpus callosum – a large bundle of

axons that connects the cortex of the two cerebral hemispheres.

Homeostasis – the process by which important physiological characteristics are regulated so they remain at their optimum level.

The Brain StemThe brain is made up of three main

structures including:

1)medulla – closest to the spinal cord; controls vital functions such as heart rate and blood pressure.

2)Pons – just anterior to the medulla; involved in the control of sleep.

The Brain StemMidbrain – just anterior to the pons;

involved in control of fighting and sexual behavior (and decreased sensitivity to pain during these behaviors).

CerebellumPlays an important role in the control of

movement.Monitors information concerning posture

and balance and produces eye movements that correlate with changes in the position of the head.

Damage to the cerebellum could result in jerky, uncoordinated movements. May also have difficulty speaking because control of speech muscles muscles may have been affected.

Structures within the Cerebral HemispheresThalamus – all sensory information

except olfactory information is sent here and then relayed to the cerebral cortex.

Hypothalamus – located just above the pituitary gland; controls the autonomic nervous system and many behaviors related to regulation and survival, such as eating, drinking, fighting, shivering, and sweating.

Autonomic Nervous System – the portion of the peripheral nervous system that controls the functions of the glands and internal organs.

Sympathetic branch – portion of the ANS that activates functions that accompany arousal and expenditure of energy.

Parasympathetic Nervous System – The portion of the ANS that activates functions that occur during a relaxed state (such as digestion of food).

Limbic system – a set of interconnected structures of the brain important in emotional and species-typical behavior; includes the amygdala, hippocampus, and limbic cortex.

Amygdala – part of the limbic system of the brain located deep in the temporal lobe; damage causes changes in emotional and aggressive behavior.

Hippocampus – also a part of the limbic system, located in the temporal lobe; plays important role in learning.

DRUGSDrugs can affect the release or

production of transmitters substances.Drugs can mimic the effects of

transmitter substances on receptor molecules, block these effects, or interfere with the reuptake of a transmitter substance once it has been released. These changes can alter perceptions, thoughts, and behaviors controlled by certain transmitters substances.

BarbituratesThis is a drug that causes sedation by

depressing the brain’s activity by stimulating a certain category of neuromodulator receptors.

In low doses can have a calming effect, but as the dose increases may produce difficulty in walking, talking, may lead to unconsciousness, coma, and death.

Abused by people searching for something to calm them.

Sometimes prescribed as sleep medications, but they have serious downfalls such as:

-inhibit or suppress dreaming

-produce unrefreshing sleep

-a dose prescribed to allow sleep is not much lower than one causing death – not very safe.

BenzodiazepineMany antianxiety drugs belong to the

benzodiazepine family of drugs Includes Valium and LibriumAre very effective at reducing anxiety

and are sometimes used to treat people who are afflicted by periodic attacks of severe anxiety

Cocaine and Amphetamine Both inhibit the reuptake of dopamine

therefore strengthen the effectiveness of synapses that use this transmitter substance.

The drugs mimic the effects of reinforcing stimuli and cause many to abuse them

If these drugs are taken over a period of several days in large enough doses the result could be symptoms of paranoid schizophrenia.

Those using the drugs regularly may suffer from hallucinations and their thoughts may be confused and difficult to control.

The End