Chapter 3 – Biological Bases of Behavior
Neuroanatomy
- Neuroanatomy refers to the study of the parts and function of neurons.
o Where neurons are individual nerve cells.
o Neurons make up entire nervous system.
§ Each made up of discrete parts.
- Dendrites are the root like parts of the cell that stretch out from the cell body.
o Grows to make synaptic connections with other neurons.
- Cell body (aka soma) contains the nucleus and the other parts of the cell needed to sustain its life.
- Axon, the wirelike structure ending in the terminal buttons that extends from the cell body.
o Myelin sheath is a fatty covering around the axon that speeds neural impulses
- Terminal buttons (aka end buttons, terminal branches of axon, and synaptic knobs) – the branched end of the axon that contains neurotransmitters
o Where neurotransmitters are chemicals contained in terminal buttons that enable neurons to communicate
o They fit into receptor sites on the dendrites of neurons like a key fits into a lock.
- Synapse is the space between the terminal buttons of one neuron and the dendrites of the next neuron.
How a Neuron “Fires”
- Different parts of a neuron work in sequence when a neuron transmits a message.
o In its resting state, a neuron has an overall slightly negative charge.
§ Mostly negative ions within the cell and positive ions surrounding it.
o Cell membrane slightly permeable and prevents these ions from mixing.
- A reaction process
o Reaction begins when terminal buttons of neuron A are stimulated and release neurotransmitters into the synapse.
§ Neurotransmitters fit into receptor sites on the dendrites of neuron B.
o If enough neurotransmitters are received (this level is called a threshold), the cell membrane of neuron B becomes permeable and positive ions rush into the cell.
§ Change in charge spreads down the length of neuron B like a bullet from a gun.
· Electric message firing = action potential at 120ms-1
o When charge reaches the terminal buttons of neuron B, the buttons release their neurotransmitters into the synapse.
§ Goes from terminal end to dendrite to terminal end.
§ Process may begin again if enough neurotransmitters are received by that next cell to pass the threshold
- Note that a neuron either fires completely or it does not fire
o Called the all-or-none principle
o If dendrites of a neuron receive enough neurotransmitters to push the neuron past its threshold, the neuron will fire completely every time.
§ A neuron cannot fire a little or lot
§ The impulse is the same every time.
- Note: Neural firing is an electrochemical process
o Electricity travels within the cell (from dendrites to the terminal buttons)
o Chemicals (neurotransmitters) travel between the cells via the synapse.
§ Electricity does not jump between neurons.
Neurotransmitters
- Different types of neurotransmitters exist
o Some are excitatory, exciting the next cell into firing
o Others are inhibitory, preventing the next cell from firing.
- Amount and type of neurotransmitters received on the receptor sites of the neuron determine whether it will pass the threshold and fire.
o Acetylcholine is an important neurotransmitter involved in motor movement
§ Lack of acetylcholine is associated with Alzheimer’s disease
o Dopamine is an important neurotransmitter involved in motor movement and alertness.
§ Lack of dopamine is associated with Parkinson’s disease, an overabundance is associated with schizophrenia.
o Endorphins deals with pain control, and involved in additions.
o Serotonin controls mood and lack of serotonin is associated with clinical depression.
Nervous System
- Since neurons only fire in one direction, body needs two sets of wires: one to take information to brain, and the other from brain to muscles.
- Afferent neurons take information from the senses to the brain.
o One way to think of it is that afferent nerves take information in at the brain
- Once information reaches the brain or the spinal cord, interneurons take the messages and send them elsewhere into the brain or to efferent neurons.
- Efferent neurons take information from the brain to the rest of the body
o Think of efferent nerves as carring information that exits the brain.
Organization of the Nervous System
- The nervous system is divided into different categories based on function:
- Nervous system
o Central Nervous system
- Brain
- Spinal Cord
o Peripheral Nervous System
- Autonomic
· Sympathetic
· Parasympathetic
- Somatic
The Central Nervous System
- Central nervous system (CNS) consists of our brain and spinal cord – or all the nerves within bone (nerves in the skull and vertebrae)
o Where the spinal cord is a bundle of nerves that run through the center of the spine.
§ Transmits information from the rest of the body to the brain
The Peripheral Nervous System
- The peripheral nervous system (PNS) consists of all other nerves in your body that are not encased in bone.
o Divided into two categories, the somatic and autonomic nervous systems.
o Somatic nervous system
§ Controls voluntary muscle movement, primarily controlled by the motor cortex of our brain
o Autonomic Nervous System
§ Controls the autonomic functions of the body, including the heart, lungs, internal organs, glands, etc.
- Sympathetic nervous system
o Mobilizes body response to stress
o Carries messages to the control systems of the organs, glands, and muscle that direct our body’s response to stress.
o The alert system of the body
o Accelerates some functions (heart rate, blood pressure, respiration), but also conserves resources needed for a quick response by slowing down other functions (i.e. digestion)
- Parasympathetic nervous system
o Responsible for slowing down body after stress response.
o Carries messages to the sympathetic nervous system that causes our body to slow down.
§ The brake pedal that slows down the body’s autonomic nervous system.
The Normal Peripheral Nervous System Transmission
- The process: When you stub your toe, sensor neurons in toe are activated and the message is transmitted up a neuron that runs from your toe to the base of your spine (afferent nerves). Message continues up the spinal cord on more afferent nerves until it enters your brain through the brain stem and is transmitted to the brain’s sensory cortex (see below) and from there you know you have stubbed your toe. Motor cortex sends impulses down the spinal cord to the muscles controlling your leg and foot (efferent nerves), causing you to hop up and down in pain.
Reflexes: An Important Exception
- Most sensory information and muscle movements controlled by process above.
o HV humans have few reflexes that work differently.
o These reactions occur the moment sensory impulses reach the spinal cord.
§ Include the knee cap – sensor information processed by spine, which tells your leg to move.
§ By the time the information reaches the brain, reflex would have already occurred.
o Another important reflex is response to heat or cold.
§ Spine sends the signal for a person to jerk back from fire.
Brain
- Brain is hard to study as a brain thinking looks exactly like a brain not thinking.
Ways of Studying the Brain
- First challenge of brain research is creating a way to detect brain function.
- Accidents
o 1848 railroad worker Phineas Gage was involved in any accident that damaged the front part of his brain
§ Gage’s doctor documented how his behavior changed after > he became highly emotional and impulsive.
- Lesions
o Lesioning is the removal or destruction of part of the brain.
§ Of course never done purely for experimental purposes.
§ Sometimes doctors decide that best treatment of certain conditions involves surgery removing part of the brain (i.e. brain tumor)
o After surgeries, would closely examine patient behavior.
o Frontal lobotomy often performed on mentally ill patients.
§ Where researchers knew that lesioning part of the frontal lobe would make patients calm and relieve some serious symptoms.
- Drug treatments now replaced frontal lobotomies.
- Electroencephalogram
o An electroencephalogram (EEG) detects brain waves.
§ Can examine type of waves the brain produces during different stages of consciousness and use this information to generalize brain function.
o Widely used in sleep research to identify different stages of sleeping/dreaming.
- Computerized Axial Topography
o A CAT scan is a sophisticated X ray
o Can only show the structure of the brain and not the functions.
- Magnetic Resonance Imaging
o A MRI is similar to a CAT scan in that it gives a detailed picture of the brain only.
o HV uses magnetic fields to measure the density and location of brain material.
§ Does not use X rays
§ Patient is not exposed to carcinogenic radiation.
- Position Emission Tomography
o A PET scan lets researchers see what areas of the brain are most active during certain tasks.
§ Measures how much of a certain chemical (i.e. glucose) parts of the brain are using.
o More used = more activity.
- Functional MRI (fMRI)
o A new technology that combines elements of MRI and PET scansU
o Can show structure of the brain with information about blood flow, tying brain structures to brain activity during cognitive tasks.
Brain Structure and Function
- Brain is most complicated organi in the body
- TF organized into three separate major categories
o Hindbrain, midbrain, and forebrain.
- The hindbrain consists of structures in the top part of the spinal cord.
o Is the LIFE SUPPORT system
§ Controls basic biological functions that keep us alive.
§ Important parts are medulla, pons, and cerebullum.
o Where the medulla is involved in control of blood pressure, heart rate and breathing.
§ Aka the medulla oblongata located above the spinal cord.
o Where the pons (located just above the medulla and toward the front) connects the hindbrain with the midbrain and forebrain.
§ Also involved in the control of facial expression.
o Cerebullum (located on the bottom rear of the brain) is like a smaller version of our brain stuk onto the underside of our brain
§ Cerebellum = “little brain”
§ Coordinates fine muscle movements such as typing.
- Midbrain located just above the spinal cord but still below areas categorized as “forebrain”
o Very small in humans.
o Coordinates simple movements with sensory information.
§ If you turn your head right now, your midbrain coordinates your muscles to keep your eyes on the text.
o For AP test, should know that area is b/w hindbrain and forebrain and integrates some types of sensory information and muscle movements.
§ Reticular formation is a netlike collection of cells throughout hindbrain that controls general body arousal and ability to focus our attention.
o If reticular formation does not function, we fall into coma.
- Areas of the forebrain control what we think of as thought and reason.
o Large in comparison with other areas.
o Most psychological researchers focus here.
o Thalamus is located on top of the brain stem
§ Receives sensory signals coming up spinal cord and sends them to appropriate areas in forebrain. (see specific areas in section about cerebal cortex later)
o Hypothalamus is a small structure right in “front” of thalamus.
§ Controls metabolic functions including body temperature, sexual arousal (libido), hunger, thirst, and the endocrine system.
§ If one considers themselves a morning person or a night person, hypothalamus might be involved as it controls biological rhythms.
o Amygdala and Hippocampus
§ Hippocampus are two arms surrounding the thalamus.
§ Structures near the end of each hippocampal arm are the amygdala.
§ Areas important in how we process and perceive memory and emotion.
· Memories are not permanently stored in this area of the brain.
· Are processed here and sent to other locations in the cerebal cortex for permanent storage.
§ Memories must pass through this area first in order to be encoded.
o Where these parts of the brain, the midbrain (thalamus, hypothalamus, amaygdala and hippocampus are grouped together and called the limbic system b/c they deal with aspects of emotion and memory).
Cerebral Cortex
- When most people think of the brain, they picture the cerebral cortex, the gray wrinkled surface of the brain.
o Thin layer (1 mm) covers the rest of the brain, including most structures above so far.
- When born, cerebral cortex is full of neurons waiting to be connected.
o Would eventually form the complex neural web we have now, where the wrinkles in the cerebral cortex are fissures.
§ More wrinkles = more surface area.
Hemispheres
- Cerebral cortex divided into two hemispheres: left and right.
o Two hemispheres look like mirror images of one another.
- Left hemisphere get sensory images and controls the motor function of the right half of the body, and vice versa for the right hemisphere.
o Possibility that left hemisphere more active during logic and sequential tasks and right hemisphere more active for spatial and creative tasks
- Where specialization in each hemisphere is brain lateralization or hemispheric specialization.
o Most of differences between hemispheres done by examining split-brain patients, patients whose corpus callosum (the nerve bundle that connects two hemispheres) has been cut off to treat severe epilepsy.
§ Where split brain patients cannot orally report information only presented to the right hemisphere, since spoken language centers of brain are usually in left hemisphere.
Areas of the Cerebral Cortex
- When one studies the cerebral cortex, think of it as a collection of different areas and specific cortices.
- Think of cerebral cortex as 8 different lobes, four in each hemisphere: frontal, parietal, temporal, and occupital.
o Where any area of the cerebral cortex not associated with receiving sensory information/controlling muscles is labeled as an association area.
§ Though specific actions not known for association areas, areas are very active in various human thoughts and behaviors incl judgement and humor (complex, sophisticated thoughts)
- Frontal lobes are large areas of the cerebral cortex located in the top front of the brain behind the eyes.
o Responsible for abstract thought and emotional control.
§ In Phineas Gage’s example, his limbic system (midbrain) was separated from his frontal lobes in an accident.
· Reported to have lost control of emotions and became animalistic.
- In most people, frontal lobe in the left hemisphere contain one of two special areas responsible for language processing (some left-handed people’s languaged centers are in the right hemisphere)
o Broca’s area is in the frontal lobe and responsible for controlling the muscles involved in producing speech.
§ Other area, Wernicke’s area located in the temporal lobe [below]
o Thin vertical strip at the back of the frontal lobe (farthest from eyes) is called the motor cortex.
§ Sends signals to our muscles, and control voluntary movements.
§ Top of body is controlled by neurons at the bottom of the cortex (by the eras) and vice versa.
· Top of motor cortex controls the feet and toes.
- Parietal lobes located behind the frontal lobe but still on the top of the brain.
o Contain the sensory cortex (aka somato-sensory cortex) located right behind the motor cortex in the frontal lobe.
o Is a thin vertical stripe that receives incoming touch sensations from the rest of the body.
§ Organized similarly with the motor cortex.
- Occipital Lobes are at the very back of the brain, farthest from the eyes.
o Interpret messages from our eyes in our visual cortex (Study hint: term occipital looks like optical)
o Impulses from the right half of each retina are processed in the visual cortex in the right occipital lobe, and vice versa.
- Temporal lobes process sound sensed by ears.
o Sound waves are processed by the ears, turned into neural impulses, and interpreted by our auditory cortices.
o Auditory cortex not lateralized like the visual cortices.
§ Where sound received in the left air are processed in both hemispheres.
o Second language area located in the temporal lobe (first was Broca’s area in frontal lobe).
§ Wernicke’s area interprets written and spoken speech.
§ Damage to area affects ability to understand ability, and impairs proper syntax and grammer.
Brain Plasticity
- Researchers discovered that the brain is somewhat plastic or flexible.
o With cortices and lobes performing functions already mentioned, other parts of brain can adapt themselves to perform other functions if needed.
- Since cerebral cortex is made up of a complex network of neurons connected by dendrites that grow to make new connections, and grow throughout our lives.
o If damaged, dendrites can grow to make new connections in another part of the brain that would be able to take over the functions.
- Dendrites grow most quickly in younger children.
Endocrine System
- Endocrine system is a system of glands that secrete hormones that affect many different biological processes in our bodies.
o Controlled by hypothalamus.
o Adrenal glands produce adrenaline which signals rest of body to prepare for fight or flight.
§ Response in connection w/ autonomic nervous system
o Ovaries and testes are women and men’s (respectively) sex hormone production glands.
§ Estrogen for women and testosterone for men.
§ Where these hormones partially explain gender differences physically and mental/socially.
Genetics
- Besides brain and nervous system, genetics affect human thought and behavior.
o Most human traits (body shape, introversion, temper) result from combined effects of nature (our genetic code) and nurture (the environment where we grow up and live).
- Every human cell contains 46 chromosomes in 23 pairs.
o Genetic material that makes up chromosomes is DNA (deoxyribonucleic acid)
o Where certain segments (genes) of DNA control the production of specific proteins that control some human traits.
§ Genes can be dominant or recessive.
§ If one inherits two recessive genes for a particular trait, the trait will be expressed.
- Any other combinations, the dominant trait is expressed.
- Identical twins (aka monozygotic twins as they come from the same fertilized egg called a zygote) share same genetic material.
o In one famous study, Thomas Bouchard found more than 100 identical twins and compared hundreds of traits and concluded about relative influences of genetics and (i.e. IQ).
§ Higher correlation for IQ between twins who lived together than those who didn’t.
o HV criticized as living together would create the same effective psychological environment for both twins.
§ This might be a factor in explaining the correlations that Bouchard attributed to genetic influence.
Chromosomal Abnormalities
- Gender determined by 23rd pair of chromosomes.
o Men have X and Y chromosome, women have X and X chromosome.
o Usually man will contribute X chromosome (for girl) or Y chromosome (for boy)
§ HV chromosomes may combine (or fail to) in an unusual way, resulting in a chromosomal abnormality.
o Babies with Turner’s syndrome are born with a single X chromosome in 23rd pair.
§ Causes some physical characteristics like shortness, webbed necks, and differences in physical sexual development.
o Babies with Klinefelter’s syndrome have an extra X chromosome, resulting in an XXY in the 3rd chromosome.
§ Effects vary wildly, but cause minimal sexual development and personal traits like extreme introversion.
o Other chromosomal abnormalities may cause mental retardation
§ Most common is Down’s syndrome.
· Born w/ extra chromosome on 21st pair.
§ Rounded face, shorter fingers and toes, slanted eyes, and different extents of mental retardation.
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