Biological Bases Lecture Notes

I THE NERVOUS SYSTEM: Its Major Divisions

The Central Nervous System (CNS)

  • Composed of the Brain and Spinal Cord 
  • Spinal Cord
    • Consists of 31 pairs of spinal nerves that exit at various points along the spinal cord
    • 12 cranial nerves that leave the brain directly
  • Functions 
1. Relay System 
    • Acts as the relay cable between the Brain and all other parts of the body
    • Carries information from the brain (MOTOR OR EFFECTOR NEURON) to various muscles and glands
    • Carries information from tissue and sense organs of the body to the brain (SENSORY OR AFFERENT NEURON)


    2. Reflexes 

    • seemingly automatic action that is evoked rapidly by particular stimuli

The Peripheral Nervous System

1. Somatic Nervous System
    • carries information to and from the 
    • sense organs (i.e., touch, smell, sight) and 
    • skeletal muscles (muscles under voluntary control)


    2. Autonomic Nervous System

    • Connects the CNS to internal organs, glands, and involuntary muscles (i.e., muscles in the digestive system)

      • i) Sympathetic Division
      • Prepares the body for using energy
ii) Parasympathetic Division
      • Stimulates the body to restore or conserve energy
      • Works in opposite manner than the Sympathetic division

II THE NEURON

  • or NERVE CELL
  • held together by GLIAL CELLS
  • specialized cells for receiving, moving, and processing information
  • Vary in size, shape, and chemical composition
  • 100 billion compose the brain alone

1. Basic Structure of a Neuron

i) Dendrites
    • specialized in RECEIVING information from other neurons
    • Sends the information to the CELL BODY


    ii) Cell Body 

    • contains the nucleus
    • Combines and averages input from all the dendrites
    • Transmits the combined and average information to the AXON


    iii) Axon 

    • Single fibre with an uniformed diameter 
    • Passes information to another neuron
    • Covered in a MYELIN SHEATH
      • Insulates neuron from adjacent neurons
      • Helps to speed the information passed along the axon
      • NODES OF RANVIER
    iv) Terminal (Axon) Buttons 
    • End point of the AXON
    • Axon divides into several small branches
    • SYNAPTIC GAP or SYNAPTIC CLEFT

2. The Nerve Impulse

  • Neurons contain Ions (electrically charged molecules)
  • THRESHOLDS
  • Minimum level of stimulation required before a neuron can become activated
  • ACTION POTENTIAL - This is what is used to send information between neurons
  • All-or-None Response: The nerve impulse either occurs in full strength or it does not occur at all
  • Speed and Size constant. Signal does not decrease along the axon (2 to 200 miles per hour)

3. Synaptic Transmission

  • SYNAPSE = microscopic space between 2 neurons 
  • Space between the terminal buttons (on the axon) of one neuron and the dendrite of a second neuron
  • The number of synapses changes with development and learning experiences - PLASTICITY

4. Synaptic Structures

  • 300 trillion synapses believed to exists in the CNS
  • Presynaptic membrane 
  • located on the terminal button of the axon
  • Synaptic Vesicles 
    • tiny vesicles located in the terminal buttons containing the neurotransmitter substances
  • Synaptic Gap 
  • Narrow space (20 nanometres wide) btw. Pre and Postsynaptic membranes
  • Nanometer = one billionth of a meter
  • Postsynaptic Membrane 
  • Located on the dendrite of a second neuron
  • contains the receptors for the neurotransmitters

5. Neurotransmitters (NT)

  • chemical messengers that carry information between the neurons
  • Lock-and-key
  • Amount released is directly related to the strength of the signal
  • NTs have 2 effects on the receiving neuron
    • EXCITATORY 
      • Increases the likelihood that the neuron will fire
    • INHIBITORY
      • Decreases the likelihood that the neuron will fire

III NEUROCEHMICAL MESSENGERS

NEUROTRANSMITTERS

    1. Serotonin
    • Involved in transmission of information in neurons involved in 
      • Sleep
      • Sensory perception
      • Temperature regulation
      • Pain suppression
      • Mood
    2. Dopamine 
    • Transmitted between neurons involved in
      • Voluntary movement
      • Learning
      • Memory
      • Emotion
    3. Acetylcholine
    • Transmitted between neurons involved in
      • Muscle action
      • Cognitive functioning
      • Memory
      • Emotion
    4. Norepinephrine
    • Increasing the sympathetic division of the ANS
    • Learning
    • Memory
    • Dreaming
    • Arousal from sleep
    • Emotion
    5. Gamma-aminobutyric acid (GABA) 
    • Serves to inhibit brain function

ENDORPHINS

  • Effects similar to natural opiates
  • Reduce pain and promote pleasure
  • Believed to act as neuromodulators
  • Alter the effects of neurotransmitters
    • Increase or decrease the effects of NTs
  • Levels increase under stressful or fearful situations
  • Acts to energize the body for survival

HORMONES

  • Hormones originate in the endocrine glands
  • Released directly into the blood stream
  • Involved in
    • Promoting growth
    • Assisting in digestion
    • Regulating metabolism


    1. Melatonin

    • Secreted by the pineal gland
    • Regulates our biological clock
    2. Adrenal hormones 
    • Secreted by the adrenal glands
    • Cortisol, Epinephrine, Norepinephrine
    • Involved in emotion and stress
    • Moderate levels enhance memory formation


    3. Sex hormones 

    • Secreted by the gonads
      • Testes in males
      • Ovaries in females
    • ANDROGENS
      • Masculinizing hormones
      • Results in the secondary sexual characteristics observed in males and females
      • Involved in sexual arousal in both males and females
    • ESTROGEN
      • Feminizing hormones
      • Involved in the development of secondary sexual characteristics in females
    • PROGESTERONE
      • Produced by the ovaries
      • Involved in the growth and maintenance of the uterine
  • Hormones and Cognitive Functioning
    • Play a role in memory development and cognitive functioning
    • Particularly spatial abilities
      • Increase performance on spatial abilities in males is associated with levels of circulating testosterone
      • Women with higher levels of circulating testosterone also do better on spatial tasks
      • Moreover, during menses woman perform better on spatial tasks
      • Percentage of testosterone is higher during menses because of the lowering on normal levels of estrogen

IV THE BRAIN

1. Basic Survival: THE BRAIN STEM

  • Oldest section of the brain
  • Involved in the control of basic life processes 
    i) MEDULLA 
    • Plays a crucial role in many autonomic, involuntary activities 
    ii) PONS 
    • Between the Medulla and Spinal cord
    • Involved in sleeping, waking, and dreaming
    • Reticular Activating System (of Reticular Formation) 
      • Major component of the brain stem involving components of the Medulla and Pons 
      • Also contains part of the THALAMUS
      • Plays a crucial arousal/attention and sleep
      • Automatically processing all incoming information
    iii) CEREBELLUM
    • Located behind the medulla and pons
    • Coordination of VOLUNTARY muscle activity and 
    • Regulation of physical balance
    • ATAXIA 
      • jerky, drunken-like movements, severe tremors, lack of balance

2. Emotion & Motivation: THALAMUS, HYPOTHALAMUS, & LIMBIC SYSTEM 

    i) THALAMUS
    • Great Relay Station of the Brain
    • Receives input from the various different sense organs (eyes, ears, touch...) and relays it to the correct part of the upper brain
    • Also receives cortical input and transmits this information to the cerebellum and medulla
    ii) HYPOTHALAMUS
    • Basic motivation: hunger/thirst
    • Basic Emotions: fight/flight
    • Physical Homeostasis: temperature, metabolism
    • Control centre for the Endocrine System
    • Through its connects with the PITUITARY GLAND
      • Secretes hormones that modify endocrine activity
    iii) LIMBIC SYSTEM
    • Comprised of the Thalamus, Hypothalamus, Amygdala, and Hippocampus
    • Involved in motivation, memory, and ESPECIALLY EMOTION
    • Stimulation = RAGE, FEAR, SEXUAL RESPONSE
    • PLEASURE CENTER
    • Amygdala associated with AGGRESSION
      • Evaluates sensory input for emotional importance
      • Contributes to the fight/flight response
      • Also involved in mediating anxiety and depression
      • Damage = sharp reduction of aggression
      • Stimulation = rage and violent attacks
    • Hippocampus
      • Heavily involved in memory formation
      • Damaged = unable to form new memories

3. Information Processing: CEREBRAL CORTEX

    CEREBRAL HEMISPHERES
    • Area that we normally refer to as the brain
    • 80% of the adult brain's weight
    • 2 halves
    • Structurally are mirror images of each other
    • Differ functionally 
    • Halves connected by CORPUS CALLOSUM
    • Wide band of AXONS 
    • White = highly myelinated
    • IMPORTANT: the 2 halves control OPPOSITE sides of the body
    • Therefore damage to the left hemisphere will affect the right side of the body
    CEREBRAL CORTEX
    • Grey matter (i.e., cell bodies of neurons) that covers the 2 cerebral hemispheres
      • 3 millimetres thick
    • Folded into grooves and fissures
      • CENTRAL FISSURE
      • LATERAL FISSURE
    LOBES that contain specific cortical functions
    i) OCCIPITAL LOBES 
    • Contains the VISUAL CORTEX
    • Reception and analysis of visual information
    ii) PARIETAL LOBES 
    • Contains the SOMTASENSORY CORTEX
    • Receives information about TOUCH, TEMPERATURE, PRESSURE, and other BODILY OR SOMATIC sensations
    • Face and Hands have highest portion of cortex 
    iii) TEMPORAL LOBES 
    • Spatial perception (Right hemisphere only)
    • Memory formation and Dreaming in both hemispheres
    • Contains the PRIMARY AUDITORY AREA
    • Wernicke's Area 
    • Auditory input is received in this area (Left hemisphere only)
    iv) FRONTAL LOBES
    • Contains the MOTOR CORTEX
    • Sends out information via motor (or efferent) neurons to all body parts under voluntary control
    • Broca's Area
      • front of the motor cortex 
      • involved in speech production
    • Prefrontal Area
      • front of the motor cortex
      • 29% of the human cortex
      • Believed to play a role in personality
      • Also involved in PLANNING; DECISION MAKING; GOAL SETTING; FUTURE DIRECTED BEHAVIOR

4. Lateralization of the Cerebral Cortex

    Split-Brain Research
    • corpus callosum does not exist
    • Could be due to genetics, disease, or surgery 
    • Hemispheres cannot communicate with each other 
    • Must function independently
    • Test of abilities
    Left Hemisphere
    • Language
    • Speech
    • Writing
    • Problem solving
    • Calculations
    • Time sense
    • Rhythm
    • Ordering of complex movements
    Right Hemisphere
    • Nonverbal
    • Perceptual skills
    • Visualizations
    • Recognition of patterns, faces, melodies
    • Recognition & expression of emotions
    • Spatial skills
    • Simple language comprehension