Biological Bases of Behavior

Neuron

- Basic elements of brain and spinal cord

3 Types of Neurons

1. Sensory

  • Receive information about the environment from sensory receptors
  • transduction
    •

    • 2. Motor

  • Carry information from brain and spinal cord to muscles, organs, and glands
    •

    3. Interneurons

    Most common

    Connect one neuron with another

     NEURONS

    1. Similar to other cells

    Semipermeable outer membrane

    Cell body

    Nucleus

    Mitochondria

    2. Specialized features

    Excitable membrane

    Axon

    Dendrites

  • Synapses
    •

    Excitable membrane is polarized and selectively permeable

    Keeps A- , K+ inside and Na+, Cl- out

  • ~ - 70 mV difference between the inside and outside of the cell

    Dynamic equilibrium

    Electrostatic force

    Concentration Gradient

    Na+ Moves in Because of diffusion and

    electrostatic force

    ENa = +55 mv

    K+ Moves out mostly because of diffussion

    EK = -75 mv

    not a lot of electrostatic force

    •

    Electricity and Conduction

    Current is the movement of + electrical charges

    Voltage is the energy to move + electrical charges

    Potential is the separation of + and -

    The Nerve Impulse

    1. Current (the movement of + ions) depolarizes
  • the cell

    e.g., electrical energy from sensory receptors

    Threshold

    2. Voltage activated Na channels open

    membrane becomes permeable to Na+

    Potential driven toward ENa = +55 mv

    Positive charge inside increases, +40

    •
    1. Voltage activated K+ channels open
      Potential driven toward EK = -75 mv

      Na channels close

    4. Na K pump restores resting state

    Refractory period

    Action potential is self-propagating

    i.e., does not diminish as it travel down the axon

    All or nothing

    Increased stimulation increases the rate of

    firing not the strength of the impulse

    1. - 120 meters/second
  • Faster if
    Larger diameter

    Myelin sheath

    •

    Spontaneous activity

    cells fire at a base rate without any stimulation

    Communication Between Cells

  • Synaptic Vesicles

    Neurotransmitters

    Excitatory, inhibitory

    Synapse

    •
  • Dendrite of next neuron
  • postsynaptic signal fades as it travels

    toward the cell body

    •

    • Removal of neurotransmitter from receptor sites

    Enzyme breakdown, reuptake

    Neurotransmitters

    1. Acetylcholine

    Excitatory

    Works to cause skeletal muscles to contract

    Depletion of ACh in brain may be responsible for memory loss associated with Alzheimer’s
  •  
    •

    2. Norepinephrine

    Inhibitory in brain and spinal cord

    Excitatory effect of smooth muscles

    Antidepressants block reuptake of NE 

    3. GABA

    Major inhibitory transmitter

    Needed for muscle control

    Degeneration of GABA cell in brain may be involved in Huntington’s Chorea

    4. Dopamine - Movement

    Parkinson’s
    - Degeneration of dopamine neurons

    - Shakiness and difficulty initiating movement

    Schizophrenia

    oversensitivity to dopamine

     5. Serotonin - Sleep and Mood

    Tryptophan from food
  • - Carbohydrates
    •

    Psychoactive Drugs

    - Alter neurotransmission

    1. Alter amount released

    2. Mimic

    Agonist

    3. Block receptors

    Antagonist

    4. Blocking reuptake oe enzymatic breakdown

     

    The Brain

    Three Major Subdivisions

    1. Hindbrain

    - Extension of the spinal cord

    Medulla
    Control of vital functions
  • Pons
    sensations from head and face

    facial movement

    •

    Cerebellum

    - Fine motor movements
  • -Well rehearsed movements
    •

    2. The Midbrain

  • Thalamus
    Relay for information from the eyes, ears, and skin

    Superior Colliculi

    reflexive eye movements

    Inferior Colliculi

    reflexive head movements

     

    •

    Hypothalamus

    Helps regulate eating, drinking

    and sexual behavior

    Hippocampus

    consolidation of memory

    Reticular Formation

    Region brain cells throughout the hindbrain and midbrain responsible

    for the general arousal of the brain

    Cerebral peduncles

    connect midbrain to cortex

     

    3. The Forebrain

    - Most highly developed part of the brain

    Corticle Receiving Areas

    Cerebral Cortex

    - Surface area of 1 to 2 square feet
  • Compact, convolutions
    •

    Divided into four areas by deep fissures or sulci

    1. Parietal Lobe

    - Skin

    Touch, pain, temperature

    sensory hommunculus

    2. Occipital Lobe

    - Visual Information

    blindsight

    3. Temporal Lobe

    Auditory

  • Located near area of cortex involved in understanding language
    •

    The Brain Divided By Function

    1. Sensory and Motor Cortex

    a. Sensory

    Parietal - tactile

    Occipital - vision

    Temporal - auditory

    - language

    b. Somatosensory

    Sensations from neighboring parts of skin are brought to neighboring parts of the somatosensory cortex
  •  
    •

    c. Motor Cortex

  • voluntary movements inspecific body parts
  • frontal lobe important for planing
    •

     

    2. Association Cortex

  • Combine sensory and motor

    information and perform complex cognitive tasks

    - Abstract thinking

     

    Aphasia

    •

    Broca’s - production, frontal lobe

    Wernicke’s - understanding, temporal lobe