Magnetic Resonance Imaging (MRI)

Nuclear magnetic moments

• Hydrogen dipoles
• Normally randomly positioned

Strong magnetic field

• Repositions hydrogen dipoles

Relaxation times

• Takes time for dipoles to re-position after magnetic field turned off

Longitudinal relaxation time (spin lattice, or T1)

• Long axis
• 100 to 2000 ms in biological tissue

Transverse relaxation time (spin-spin, or T2)

• Perpendicular to long axis
• 30 to 300 ms in biological tissue

Relaxation time longer in damaged tissue

Spinal Cord

CNS

Ascending tracts

• Somatosensory information to brain

Descending tracts

• Motor-control information from brain

Central pattern generators

• Interneurons
• Brain influence

Spinal reflexes

• Sensory neuron
• Interneuron
• Motor neuron
• e.g., flexion reflex

  

Subcortical Structures of the Brain

Brainstem

• Cranial nerves

Medulla and pons

• Postural reflexes
  • Balance
• Vital reflexes
  • Breathing, heart rate, etc.

Mid-brain

• Basic movements
• Connections to CPGs in spinal cord

Thalamus

• "Relay station"
• Connects parts of the brain
• Sensory tracts from brainstem terminate here
  • Output then to cerebral cortex

  

Cerebellum and Basal Ganglia

Cerebellum

• Motor control
• Rapid, powerful movement
• Information processor
  • Input from sensory organs
  • Coordinates complex movement

Basal ganglia

• Grey matter
  • Unmyelinated
• Motor control
• Slow, precise movement

Limbic System and Hypothalamus

Limbic system

• Amygdala
  • Scent
  • Drives and emotion
• Hippocampus
  • Memory Hypothalamus
• Regulates internal environment of the body
  • Autonomic nervous system
  • Hormones
  • Drive states

  

Cerebral Cortex

Primary sensory area

• Input from sensory nerves (via thalamus)
  • Visual area
  • Auditory area
  • Somatosensory area
• Back

Primary motor area

• Sends axons to motor neurons in brainstem and spinal cord
• Middle

Associative areas

• Perception, thought, decision making
• Receive input
  • Sensory areas
  • "Lower brain" structures
• Front

Cortex and evolution

Cortical Asymmetry

Right and left hemispheres

Corpus callosum

• Connects hemispheres

Contralateral pathways

• Sensory neurons from right side input to left hemisphere and vise versa
• Motor neuron from left hemisphere to right side of body
• Unified sensation and movement due to corpus callosum

Not all brain function is unified

• Left hemisphere
  • e.g., Speech
• Right hemisphere
  • e.g., Spatial tasks

Split Brain Patients

Corpus callosum is severed

Contralateral pathways

Visual information

• Right visual field to left hemisphere
• Left visual field to right hemisphere
• Corpus callosum would transfer information

Experiment

• Visual picture in left visual field
• Test: touch object with left hand
  • Success!
• Test: name object
  • Failure!

Hormones

Chemical messengers

• Related to neurotransmitters

Slow, distance

Released by:

• Endocrine glands
• Internal organs
• Brain

Carried by bloodstream

Hormone effects

• Long-term
  • e.g., Anatomical sex differences, growth, bone strength
• Short-term
  • e.g., Fight-or-flight response, healing, menstrual cycle

Classes of hormones

• Peptides
  • Pituitary gland
  • Don't pass cell membranes easily
  • Act like neurotransmitters
    • Open/close membrane channels
    • Change ion concentration
• Steroids
  • Adrenal cortex and gonads
  • Pass cell membranes easily
  • Effect in cell nucleus
    • Genes
    • Production/reduction of certain proteins

Brain control of hormones

• Pituitary
  • Posterior
    • Part of the brain
    • Connected to neurosecretory cells in hypothalamus
    • Produces hormone releasing factors
  • Anterior
    • Triggered by releasing factors
    • Produces pituitary hormones
    • Releases hormones to bloodstream

Chapter 6 in Review

Neurons: signaling, information transfer

Soma, axon, terminal, dendrites

Chemical synapses: neurotransmitters

Electrical synapses: ion flow

Resting membrane potential

Action potential: threshold, charged particles

Central pattern generators

Artificial neural networks

PNS

• Skeletal
• Autonomic: sympathetic, parasympathetic

MRI

CNS levels and function

Cortical asymmetry and split brain patients

Hormones

Mental Mastications

In split brain patients, why is it the case that the right hand doesn't know what the left hand is doing?

What effect could a severe blow to the back of the head (resulting in damage to the cerebellum) have?

What is so much better about a human brain than a dog, or even a monkey, brain?

How are hormones and neurotransmitters similar?