Neuroscience Quiz: Central and Peripheral Systems

Part I - Background

• Chapters 1, 3-5 cover an introduction to neuropsychology and a review of the nervous system's organization and function.

Neuropsychology

• The scientific study of the relationships between brain function and behaviour.
• This interdisciplinary field draws on biology, biophysics, pharmacology, physiology, chemistry, psychology, and other disciplines.

Why study neuropsychology?

• To understand how the brain is organized to produce behaviour, including human behaviour, consciousness, and diversity (sexual, cultural, etc.).
• To treat individuals with brain injuries, diseases, and neurological disorders.

Major divisions of the human nervous system

• Central Nervous System (CNS):
  • Brain
  • Spinal cord (in vertebrates)
  • Retina (included due to developmental process - diencephalon outpocket)
• Peripheral Nervous System (PNS):
  • Nerves that carry signals in and out of the CNS (e.g., spinal nerves, cranial nerves).

Major divisions of the human nervous system (continued)

• Sensory and motor systems are crossed.
• The brain perceives and controls the opposite side of the body.

Organization of the nervous system

• Two major types of organization:
  • Anatomical: The central nervous system (CNS), and the peripheral nervous system (PNS).
  • Functional: The central nervous system (CNS), somatic nervous system (SNS), autonomic nervous system (ANS), and enteric nervous system.

Overview of nervous system function

• Forms a communication network between parts of an animal's body to generate behavior.
• Three primary functions:
  • Sensory input (signals from sensory receptors to the CNS).
  • Integration (analysis and interpretation of sensory signals, and formulating responses within the CNS).
  • Motor output (command to effector cells to carry out the response).

Directional flow of neural information

• Afferent: incoming information (sensory pathways).
• Efferent: outgoing information (motor pathways).

The human nervous system is composed of cells

• Neurons: specialized cells carrying signals between locations in the body/brain
  • The human brain has approximately 86 billion neurons.
• Glial cells (glia): non-neuronal cells supporting neurons, including nutritional support, immune function, and regulation of neuronal signaling.
  • The human nervous system also contains approximately 85 billion glial cells.

Neurons

• Most behaviors are generated by groups of hundreds or thousands of neurons.
• Functional groups of neurons, called neural networks, connect wide areas of the brain and spinal cord.
• Neurons vary greatly in size and shape.

Diversity in neuron morphology

• Neurons come in various shapes and sizes, including bipolar, unipolar, and pyramidal neurons (e.g., Purkinje cells).

Neurons are information processing units

• Underlie plasticity.
• Dendrites are produced and retracted.
• Dendritic spines may be added or pruned.
• Neurons have up to 20 dendrites, each with many branches and up to 30,000 spines.

Neuronal Structures

• Axon hillock: The junction between the cell body and axon; the site of signal integration.
• Axon collateral: A branch of an axon.
• Telodendria: Terminal branches of an axon.
• Terminal button (end foot): Knobs at the tips of axons that convey information to other neurons.
• Synapse: The junction between neurons, where information is transferred.

Synapses form the basis of neuronal communication

• Presynaptic membrane: The output side of a synapse.
• Postsynaptic membrane: The input side of a synapse.

Axon initial segment

• Signal integration center

Anatomy basics

• Brain nomenclature is not consistent.
• Early investigators named structures after objects, mythology, etc.
• Modern terminology uses numbers and letters to reflect location.

Frame of reference: human face

• Structures toward the brain's midline are medial; structures located away from the midline are lateral.
• Structures on top of the brain are dorsal, structures at the bottom are ventral.
• Anterior is in front, posterior is at the back.

Frame of reference: other body parts and body orientation

• Rostral (beak), caudal (tail), dorsal (back), and ventral (stomach)

Spinal cord and nerves

• Spinal cord lies within the spinal column, made up of vertebra.
• Each spinal nerve is associated with a spinal segment.
• Each spinal segment corresponds to a region of body surface (dermatome).

Cross-section of the human spinal cord

• Posterior root carries sensory information; anterior root carries motor information.

Cranial nerves

• Various cranial nerves, numbered 1-12, have different functions.

Brainstem

• Connects spinal cord to the brain.
• Receives afferent signals from the body and sends efferent signals to the spinal cord.
• Responsible for essential life-sustaining behaviors.

Brainstem – Hindbrain (Reticular Formation, Pons, Medulla)

• Reticular formation: netlike mixture of nuclei and fiber pathways.
• Nuclei within the reticular formation are involved in sleep-wake behaviors, and arousal.
• Pons: Part of the brainstem.
  • Plays a role in coordinating some vital body movements.
• Medulla: Contains critical centers controlling essential life functions (e.g., breathing, cardiovascular).

Brainstem – Midbrain (Tectum, Tegmentum)

• Tectum: posterior sensory structure
• Superior and inferior colliculi
• Produces orienting movements (e.g., turning head toward sound/vision)
• Tegmentum: anterior motor structure
• Species-specific behaviors, perception of pain.

Brainstem – Diencephalon (Thalamus, Hypothalamus)

• Thalamus: sorts sensory inputs and relays them to the appropriate region in the cortex.
• Hypothalamus: controls the body's production of hormones via the pituitary gland; controlling functions like temperature regulation, and behaviours such as drinking, eating, and sexual behavior.

Cerebrum (aka Forebrain): Telencephalon

• Cerebral cortex
• Limbic system
• Basal ganglia: plays a role in coordinating voluntary movements.
• Olfactory bulbs: involved in olfaction.

Forebrain – Basal ganglia

• Collection of nuclei below the white matter in the cortex
• Involved in coordinating movement, regulating the force and fluidity of movement, and associative learning (largely unconscious).

Forebrain – Limbic system

• Involved in emotional and motivational behaviours
• Related to certain forms of learning and memory.

Forebrain – Neocortex

• Human neocortex is up to 2500 cm² in area and 1-3 mm thick.
• Includes multiple lobes (frontal, parietal, temporal, and occipital).

Cortical organization

• Sensory information is received by the primary sensory area, then processed by secondary areas and is further analyzed by the posterior tertiary sensory areas before being received by the frontal associative areas, where decisions are made and actions are planned.

Neocortical layers

• 6 Layers of gray matter
• Different layers have different cell types.
• Cell density varies layer to layer.
• Functional differences between layers.

Brodmann's map

• 52 areas in the cortex, characterized by cytoarchitecture.

Cortical connections

• Tracts connect areas within the same hemisphere or opposite hemispheres.

What about myelin?

• Giant axons (e.g., squid) and mammalian axons have differing rates of transmission depending on myelin presence.

Multiple sclerosis (MS)

• Most common autoimmune disease.
• Loss of myelin formation by oligodendroglia.
• Forms hard scars (plaques)
• Disrupts neuron action potential propagation.

Symptoms of MS

• Blurred or double vision, extreme fatigue, loss of balance, muscle stiffness, speech problems, bladder and bowel problems, short-term memory problems.
• Loss of sensation and motor control, often starting in hands or feet.

Communication in the human nervous system

• 86 billion neurons and trillions of synapses.
• Each neuron receives information from hundreds of other neurons.
• Axon initial segment is the site of integration.

Two modes of synaptic communication

• Chemical synapse:
  • Neurotransmitter release.
  • Postsynaptic response (receptor binding).
• Electrical synapse: Direct current flow between cells.

Chemical – Advantages

• Flexibility (strengthening or weakening).

Electrical – Advantages

• Instantaneous signal transfer.

Why are synapses so important?

• Essential for learning and memory.

Anterograde synaptic transmission

• Small molecule class
• Neurotransmitters synthesized from precursor molecules.
• Neurotransmitters are packaged and stored in vesicles.
• Release of neurotransmitters into the synaptic cleft.
• Receptor action.
• Inactivation

Neurotransmitter transmitter release (mediated by Ca2+ ions channels)

• Action potential arrives
• Voltage-gated calcium channels open.
• Calcium ions enter the presynaptic terminal.
• Vesicles fuse to the membrane, releasing neurotransmitters into the cleft.

Neurotransmitter classes

• Small-molecule transmitters.
• Peptide transmitters.
• Lipid transmitters (endocannabinoids).
• Ion transmitters.

Small molecule neurotransmitters.

4 major activating systems

ACh in the CNS

• First neurotransmitter discovered.
• Works primarily at neuromuscular junction.
• Activates skeletal muscles.
• Involved in learning and memory (ACh in the CNS).

DA in the CNS

• Important for movement, attention, learning, motivation, reward.
• Degeneration in brainstem (substantia nigra) related to Parkinson's disease.

5-HT in the CNS

• Regulates waking activity, mood, aggression, appetite, sleep.
• Associated with depression, obsessive-compulsive disorder.

NE in the CNS

• Active in maintaining emotional tone.
• Decreased activity related to depression.
• Increased activity related to mania.
• Associated with hyperactivity and attention-deficit/hyperactivity disorder.

GABA and Glutamate

• Amino acid neurotransmitters. - Workhorses of the brain.
• Glutamate is the main excitatory neurotransmitter in the brain.
• GABA is the primary inhibitory neurotransmitter.

Peptide Transmitters

• Stress hormones (e.g., cortisol).
• Bonding hormones (e.g., oxytocin).
• Regulate eating / drinking (e.g., orexin).
• Modulate pleasure/pain (e.g., endorphins).

Lipid transmitters (Endocannabinoids)

• Synthesized at the postsynaptic membrane.
• Act on presynaptic receptors. Retrograde signaling.

Two classes of neurotransmitter receptors.

• Ionotropic receptor: Embedded membrane protein with a binding site for NT, and a pore that regulates ion flow.
• Metabotropic receptor: Embedded membrane protein linked to a G protein.

lonotropic Receptor.

Metabotropic Receptor.

10 principles of Nervous System Function

2. Sensory and motor divisions.

3. CNS functions on multiple levels.

Multiple hierarchically organized circuits.

The “binding problem”

5 and 6. Localization and lateralization of function.

Lateralization of speech

Wernicke’s aphasia - Wernicke-Geschwind model

8. Object recognition and motor control. (Dorsal and ventral visual processing streams)