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Unit 3 - Biological Bases of Behavior. Why study biology in a psychology class?. “Everything psychological is simultaneously biological.” Every thought, behavior, emotion, perception, etc. is rooted in our biology, particularly our brain

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why study biology in a psychology class
Why study biology in a psychology class?
  • “Everything psychological is simultaneously biological.”
    • Every thought, behavior, emotion, perception, etc. is rooted in our biology, particularly our brain
    • The brain is a “psychological organ” as well as a biological one
  • Biological psychology: studies the link between our biology and our behaviors and mental processes
    • a.k.a. biopsychology, neuroscience
starting small the neuron
Starting small: The Neuron
  • neuron: a nerve cell; receives signals from other neurons or sensory organs, processes these signals, and sends signals to other neurons, muscles, or bodily organs
    • the basic unit of the nervous system
the neuron
The Neuron
  • 3 types of neurons:
    • 1. sensory neurons: respond to input from sensory organs (skin, eyes, etc.)
    • 2. motor neurons: send signals to muscles to control movement
    • 3. interneurons: connect the sensory neurons and motor neurons
      • most of the neurons in the brain = interneurons
  • average human brain  100 billion neurons
    • plus 10x as many glial cells
    • glial cell: a cell that fills the gaps between neurons, facilitate communication between neurons, and help in the care and upkeep of neurons
structure of the neuron1
Structure of the Neuron
  • cell body (soma): the central part of the neuron, contains the nucleus
    • regulates cell functioning
  • dendrites: the branching part of the neuron that receives messages from other neurons and relays them to the cell body
structure of the neuron2
Structure of the Neuron
  • axon: the long, cable-like extension that delivers messages to other neurons
  • myelin sheath: layer of fatty tissue that insulates the axon and helps speed up message transmission
    • multiple sclerosis: deterioration of myelin leads to slowed communication with muscles and impaired sensation in limbs
  • terminal button: structure at the end of one of the axon’s branches that releases chemicals into the space between neurons, when the neuron is fired
the neuron in action
The Neuron in Action
  • resting potential: the negative charge maintained within neurons that are at rest
    • due to more sodium ions outside neuron than inside, and more potassium inside neuron than outside
  • messages from other neurons are either excitatory (like pushing the neuron’s accelerator) or inhibitory (like pushing the neuron’s brakes)
    • threshold: the level of stimulation required to trigger a neural impulse
the neuron in action1
The Neuron in Action
  • When the threshold is reached, channels in the cell membrane open and allow transfer of sodium and potassium ions
  • action potential: a neural impulse; the shifting change in charge that moves down the axon to terminal buttons
    • all-or-none law
from neuron to neuron
From Neuron to Neuron
  • ≈100 billion neurons in a human brain, connected to an average of 10,000 others; some up to 100,000 (Shepherd, 1999)
  • synapse: the place where an axon of one neuron meets with the dendrite/cell body of another neuron
from neuron to neuron2
From Neuron to Neuron
  • synaptic cleft: the gap between the axon and the dendrite/cell body across which neural transmission occurs
  • neurotransmitters: a chemical that sends signals from one neuron to another over the synaptic cleft
from neuron to neuron3
From Neuron to Neuron
  • Neurotransmitters are stored in vescicles in the terminal buttons, and bind to receptors on the cell membrane of the next neuron.
    • Each receptor can only bind with one kind of neurotransmitter.
  • Some of the neurotransmitter remains in the synaptic cleft, needs a special chemical reaction to reuptake (reabsorb) to vescicles
neurotransmitters at work an example
Neurotransmitters at Work:An Example
  • Low levels of the neurotransmitter serotonin have been associated with clinical depression.
  • depression treated with selective serotonin-reuptake inhibitors (SSRIs)
    • e.g. Prozac, Zoloft, Paxil
the nervous system
The Nervous System
  • comprised of the central nervous system and the peripheral nervous system
  • central nervous system: brain and spinal cord
    • 31 pairs of spinal nerves radiate from the spinal cord
    • reflex: an automatic response to an event
      • e.g. sensory neuron detects pain, send signal to spinal cord  signal to interneurons  signal to motor neurons
    • Why the middle man of interneurons? To allow brain to prevent reflex responses when appropriate
the nervous system1
The Nervous System
  • Peripheral Nervous System: links central nervous system to organs
    • comprised of the skeletal nervous system and the autonomic nervous system
    • skeletal nervous system: controls voluntary movements of our skeletal muscles
the nervous system2
The Nervous System
  • autonomic nervous system: controls many of the self-regulatory functions of the body (e.g. digestion, circulation)
    • comprised of the sympathetic and parasympathetic nervous systems
    • sympathetic: prepares us for defensive actions against threats (e.g. faster heartrate, increased breathing rate, inhibits digestion, dilates pupils to allow greater light sensitivity)
    • parasympathetic: counteracts effects of sympathetic nervous system, calms us down
structure of the brain
Structure of the Brain
  • The human brain is comprised of “older” and “newer” parts.
    • “older”: lower level structures, responsible for basic survival mechanisms
    • “newer”: higher level structures, responsible for more advanced human faculties
structure of the brain1
Structure of the Brain
  • brainstem: the set of neural structures at the base of the brain, including the medulla, the reticular formation, and the pons
    • facilitates communication between the brain and spinal cord
the brainstem
The Brainstem
  • medulla: controls heartbeat, breathing, and swallowing
  • reticular formation: regulates alertness and autonomic nervous system activity
  • pons: bridge from brainstem to cerebellum; controls a variety of functions, including sleep and control of facial muscles
the cerebellum
The Cerebellum
  • “little brain” extending from rear of brainstem
    • coordinates physical movement
    • contributes to estimating time and paying attention
  • cerebellum + other lower level brain structures occur without conscious effort
    • Much of our brain’s activity occurs outside of our awareness
the brainstem1
The Brainstem
  • thalamus: the brain’s sensory switchboard; receives signals from the sensory and motor systems, and relays them to the appropriate parts of the brain
    • also receives signals from higher brain structures, relays them to medulla and cerebellum
the limbic system
The Limbic System
  • limbic system: doughnut-shaped system of neural structures at the border of the brainstem and cerebral hemispheres
    • involved in the basics of emotion and motivation: fighting, fleeing, feeding, and sex
    • comprised primarily of the hypothalamus, the hippocampus, and the amygdala
the limbic system1
The Limbic System
  • hypothalamus: brain structure that sits under the thalamus and plays a central role in controlling eating and drinking, and in regulating the body’s temperature, blood pressure, and heart rate
    • “pleasure center”? (Olds & Milner, 1954)
the limbic system2
The Limbic System
  • hippocampus: brain structure that plays a key role in allowing new information to be stored in memory
    • patient H.M.
    • hippocampus does not contain memories itself, but does trigger processes that store memories elsewhere in the brain
the limbic system3
The Limbic System
  • amygdala: almond-shaped structure that plays a critical role in anger and fear
    • Lesioning the amygdala of the rhesus monkey turns the animal into a mellow, “unangerable” creature (Kluver & Bucy, 1939).
    • Electrically stimulating one part of the amygdala leads to anger response in cats; another spot leads to fear response.
the visible brain
The Visible Brain
  • cerebral cortex: the convoluted pinkish-gray surface of the brain, where most mental processes take place
  • The brain is divided into two halves (cerebral hemispheres), separated by a deep fissure
    • hemispheres control opposite side of body (e.g. right-handers’ writing is controlled by the left hemisphere)
our divided brains
Our Divided Brains
  • cerebral hemispheres connected by the corpus callosum, a large band of neural fibers that transmits messages between hemispheres
    • contains more than 200 million nerve fibers, can transfer more than 1 billion bits of information per second
our divided brains1
Our Divided Brains
  • evidence of hemispheric specialization?
    • left brain: written language, spoken language, number skills, reasoning (analytical and verbal)
    • right brain: insight, art awareness, imagination/creativity, music awareness (intuitive and perceptual)
  • But it’s not as simple as simply “left-brained” and “right-brained”... The two hemispheres continually work together on most tasks.
our divided brains2
Our Divided Brains
  • How do we know about hemispheric specialization?
    • split-brain patients: people whose corpus callosum has been severed for medical purposes, so that neuronal impulses no longer pass from one hemisphere to the other
      • used to treat epilepsy: a disease that results in massive amounts of uncontrolled neuronal firing that leads to seizures
      • prevents spasm from engaging both hemispheres, thus limiting its severity
    • split-brain patients typically function well; personality and intelligence intact
split brains
Split Brains
  • left half of both eyes’ field of vision sent to the right hemisphere; right half sent to left hemisphere
    • corpus callosum allows hemispheres to share information
  • in split brains, information is confined to the hemisphere that receives it
    • Objects in the left half of the visual field can be difficult or impossible to see and name. But they are still seen...
the visible brain1
The Visible Brain
  • The brain has “wrinkles” to increase surface area, while keeping the brain compact.
    • sulcus (plural = sulci): a crease in the brain
    • gyrus (plural = gyri): a bulge between sulci in the cerebral cortex
  • cerebral cortex alone contains roughly 30 billion neurons and 300 trillion synaptic connections
structure of the cortex
Structure of the Cortex
  • cerebral cortex divided into lobes, or regions of the brain
    • Each lobe is (roughly) responsible for different higher-level functions, but remember that they do not work merely in isolation.
structure of the cortex1
Structure of the Cortex
  • occipital lobe: brain lobe at the back of the head
    • responsible primarily for vision; separate areas specify visual properties such as shape, color, and motion
structure of the cortex2
Structure of the Cortex
  • temporal lobe: the brain lobe under the temples, in front of the ears
    • many functions, including processing sounds, committing information to memory, and comprehending language
structure of the cortex3
Structure of the Cortex
  • parietal lobe: brain lobe at the top and center/rear of the head
    • involved in registering spatial location, attention, and motor control
    • also involved in arithmetic
      • Einstein’s parietal lobes were found to be about 15% bigger than average (Witelson et al.,1999)
structure of the cortex4
Structure of the Cortex
  • sensory cortex (a.k.a. somatosensory strip): the gyrus immediately behind the central sulcus
    • registers sensation on the body, and is organized by body part
structure of the cortex5
Structure of the Cortex
  • sensory cortex (a.k.a. somatosensory strip): the gyrus immediately behind the central sulcus
    • registers sensation on the body, and is organized by body part
structure of the cortex6
Structure of the Cortex
  • frontal lobe: the brain lobe located behind the forehead
    • the seat of planning, memory search, motor control, reasoning, emotions, and many other functions
    • In many ways, the frontal lobe is what makes us uniquely human.
structure of the cortex7
Structure of the Cortex
  • motor cortex: the gyrus immediately in front of the central sulcus
    • controls fine movements and is organized by body part (just like the sensory cortex)
mapping brain functions
Mapping Brain Functions
  • How do we know that different lobes of the brain are responsible for distinct functions?
    • brain damage patients
      • e.g. Phineas Gage
        • marked personality differences, and trouble with social interactions after frontal lobe damage
      • e.g. stroke victims
mapping brain functions1
Mapping Brain Functions
  • electroencephalograph (EEG): an amplified recording of the pulses of electrical activity (“brainwaves”) that sweep across the brain’s surface
    • advantages:
      • tracks electrical activity either in response to a specific stimulus or over time (high temporal resolution; 1 msec)
      • non-invasive
    • drawback: electrodes on scalp do not demonstrate precise location of the electrical current
neuroimaging techniques
Neuroimaging Techniques
  • brain scanning techniques that produce a picture of the structure or functioning of neurons
  • computer-assisted tomography (CT scan): the oldest neuroimaging technique (1971 prototype), produces a 3D image of brain structure using X-rays
    • advantages:
      • allows direct view of level of interest
      • high-contrast resolution
    • disadvantage: potential for damage due to high levels of radiation
neuroimaging techniques1
Neuroimaging Techniques
  • positron emission tomography (PET scan): a neuroimaging technique that uses small amounts of radioactive glucose to track energy consumption in the brain (functionality)
    • neurons use more glucose when active; radioactive injection delivered to most active areas of brain
    • as the radioactive isotope decays, it shoots off protons, which then give off a small burst of light when they meet with the scanner
    • advantage: provides an estimate of amount of glucose consumption in each part of the brain
    • drawbacks:
      • radiation exposure
      • lengthy process (up to 40 seconds of brain activity to build an image)
      • expensive equipment necessary to create radioactive isotopes
pet scans
PET Scans

Dementia patient’s brain

Normal human brain

neuroimaging techniques2
Neuroimaging Techniques
  • magnetic resonance imaging (MRI): a technique that uses magnetic properties of atoms to take sharp pictures of the structure of the brain (and other soft tissue)
    • different atoms resonate to different frequencies of magnetic fields
    • background magnetic field aligns all the atoms in the brain
    • second magnetic field turned on/off repeatedly many times per second
    • atoms align with second field at proper frequency, then swing back to background when second field is turned off
neuroimaging techniques3
Neuroimaging Techniques
  • functionalmagnetic resonance imaging (fMRI): a type of MRI that detects the amount of bloodflow in different regions of the brain
    • bloodflow = proxy for oxygen delivery
    • MRI = structure, fMRI = function
    • advantages:
      • indicates specific regions of activity (high spatial resolution, 3-6 millimeters)
      • non-invasive, does not require radiation or X-rays
      • quick process (only a few seconds)
    • disadvantages:
      • brain is never “off”, consistently consuming oxygen
        • fMRI compares brain function while doing a task vs. at rest (but what’s going on in rest?)
      • can be uncomfortable for participant (lie very still in a small, noisy tube)
the brain s flexibility
The Brain’s Flexibility
  • plasticity: the brain’s capacity for modification, as evident in brain reorganization following damage (brain most plastic in childhood)
    • After finger amputation, the sensory cortex reassigns that finger’s section to receive information from adjacent fingers, making them more sensitive. (Fox, 1984)
    • Blind: sensory cortex for blind people’s Braille finger expands as sense of touch invades visual cortex (Barinaga, 1992; Sadato et al., 1996)
      • temporarily “knocking out” visual cortex with magnetic stimulation leads blind people to make more errors on a language task (Amedi et al., 2004)
plasticity cont
Plasticity cont.
  • Deaf: temporal lobe gets no auditory signal, eventually seeks out signal from other systems (vision)
    • deaf people often have enhanced peripheral vision (Bosworth & Dolkins, 1999)
  • typically reorganization, though there is now also evidence for regeneration of nerve cells too (Kempermann & Gage, 1999; Van Praag et al., 2002)
brain organization and handedness
Brain Organization and Handedness
  • close to 90% of people are right-handed (Medland et al., 2004)
    • close to 10% are left-handed
    • a small number are ambidextrous
  • 95% of right-handers process speech primarily in the left hemisphere
    • left-handers: 50% in left hemisphere, 25% in right hemisphere, 25% in both
is handedness inherited
Is Handedness Inherited?
  • human bias for right-handedness has been around a long time and is pervasive
    • studies of prehistoric cave drawings, tools, and arm/hand bones (Corballis, 1989; Steele, 2000)
    • right-handedness prevalent in all human cultures
      • before effects of culture: more than 9 of 10 fetuses suck the right hand’s thumb in the womb (Hepper et al., 1990, 2004)
  • chimpanzees and gorillas (closely related to humans) = 65% right-handed (Hopkins et al., 2005)
    • other, more distant primates are more evenly split
lefties vs righties
Lefties vs. Righties
  • Lefties are more likely than righties to experience reading disabilities, allergies, and migraine headaches (Geschwind & Behan, 1984).
  • Iranian university students report handedness on entrance exam; lefties consistently outperform righties in all subjects (Noroozian et al., 2003)
    • left-handedness more common among musicians, mathematicians, professional baseball and cricket players, architects, and artists
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