Nervous System - CNS

What are some emergent properties of neural networks?

• Affective behaviors: Related to feeling and emotion (affecting someone)

• Cognitive behaviors: Related to thinking

• Plasticity: The restructuring of the brain networks in response to sensory input and experience

What does dorsal and ventral mean?

• Dorsal: back

• Ventral: abdominal

What does rostral and caudal mean?

• Rostral: nose/front

• Caudal: tail

Explain the different directions in neuroanatomy

**In the brain, dorsal = up and ventral = down. rostral = pointing outward (from the front) and caudral = pointing outward (from the back)

Directions in neuroanatomy

What is the difference between gray and white matter?

• Gray matter:

  • Unmyelinated nerve cell bodies

  • Dendrites

  • Axon terminals

  • Layers of cell bodies

  • Clusters of cell bodies in the CNS are nuclei

• White matter:

  • Myelinated axons

  • Axon bundles connecting CNS regions are tracts

How is the CNS protected?

• Bone

• Connective tissue

• Fluid

What components of the CNS are made of bone?

• Brain: Encased in bony skull, or cranium

• Spinal Cord: Runs through vertebral column

What is the connective tissue in the CNS?

• Meninges lie between bone and tissues to stabilize neural tissue and protect from bruising (3 layers)

• 3 layers:

  • Dura matter

  • Arachnoid membrane

  • Pia matter

What is the cerebrospinal fluid?

• The brain floats in it

• Physical and chemical protection

  • Reduces pressure in CNS and protects your brain/head after you hit your head

• Fills ventricles, subarachnoid space to surround and protect the CNS
  Produced by choroid plexus in ventricles

What is the blood-brain barrier?

• Highly selective permeability (less leaky) of brain capillaries

• Astrocytes helps promote tight junctions between endothelial cells

• Protects brain from toxic water-soluble compounds and pathogens

• Water, gases, and small lipid-soluble molecules can diffuse across the blood-brain barrier

• Larger molecules can only cross if there is a transporter in the capillary endothelium

1) What is L-DOPA?

2) What is its relationship to the blood-brain barrier (BBB) and pharmacology?

1)

• L-DOPA: Primary Parkinson’s disease treatment

2)

• L-DOPA leads to dopamine production

• Dopamine can’t cross the BBB but L-DOPA can

• L-DOPA is converted to dopamine (DA) in the CNS and peripherally

• Too much peripheral DA leads to many side effects

• Carbidopa prevents conversion to DA and does not cross BBB

What are the metabolic requirements of the CNS?

• Brain receives 15% of blood pumped by heart

• Oxygen

  • Brain uses about 20% of body’s oxygen supply

  • Passes freely across BBB

  • Only a few minutes w/o oxygen causes brain damage (when blood flow stops)

• Glucose

  • Brain is responsible for about half of body’s glucose consumption

  • Membrane transporters move glucose from plasma into CSF

  • Progressive hypoglycemia leads to confusion, unconsciousness, and death

How is the spinal cord organized?

• 4 regions: cervical, thoracic, lumbar, sacral

• Each region is divided into segments

• Spinal nerves enter these segments

How is the spinal cord organized?

PNS contains fibers that enter/exit the spinal cord

What are the structural grey matter components of the spinal cord?

• Spinal nerves split into 2 roots (branches) before entering the spinal cord

  • Dorsal root neurons carry sensory info into the CNS
    The cell bodies of these afferent neurons are located in the dorsal root ganglia, outside the spinal cord

  • Afferent neurons connect with interneurons in the dorsal horns

• Ventral roots carry info out from the CNS to muscles and glands

  • Ventral horns contain cell bodies of efferent neurons

What are the structural white matter components of the spinal cord?

• Ascending tracts take sensory info to the brain

• Descending tracts carry signals from the brain

• Propriospinal tracts stay in the cord

  • Spinal reflexes

What is the spinal cord made of?

• Afferent neurons (sensory)

• Sensory cell body

• Interneurons

• Motor cell body

• Efferent neurons (motors)

What is an example of a spinal reflex?

• Propriospinal: Circuits that are only located in the spinal cord

• Spinal reflexes are controlled by propriospinal pathways → initiates a response without input from the brain

  • Brain can increase or decrease brain strength

  • Stretch reflexes (myotatic reflex): Causes a muscle to contract in response to being stretched, helping maintain muscle tone and posture.

  • Withdrawal reflex: Automatically pulls a body part away from a painful stimulus, without needing the brain to initiate it.

• Reflex arc layout (left diagram)

  • Stimulus → sensory neuron → interneuron → motor neuron → response

    • Integrating center → spinal cord

• Stretch (myotatic) reflex example (right diagram)

  • Muscle stretches

  • Muscle spindle detects the stretch

  • Afferent neuron carries sensory info to the spinal cord

  • Sensory neuron synapses in the spinal cord (release neurotransmitters → basically passing signal to next neuron)

  • Alpha motor neuron to the same muscle is activated

  • Response: Muscle contracts/knee-jerk

What is the brainstem?

• Oldest region of the brain

• Contains midbrain, pons, and medulla

  • Midbrain is made of tegmentum and tectum

• All connections between brain and body

• Regulation of consciousness and critical functions like heart rate and breathing

• Has 12 cranial nerves (most start in the brainstem → except I and II)

What is reticular formation (brainstem)?

Network brain stem nuclei that control wakefulness, sleep, muscle tone, pain modulation, coordination of breathing, blood pressure regulation

What is the medulla (medulla oblongata)?

• Controls involuntary functions

• White matter

  • Somatosensory (ascending) and corticospinal (descending) tracts

  • Pyramidal tracts: Paired white matter tracts of corticospinal and corticobulbar tracts

    • 90% of corticospinal tracts cross in this region

• Grey matter

  • Nuclei control involuntary functions: blood pressure, breathing, swallowing, vomiting

What are the pons?

• Relay station (bridge) between cerebellum and cerebrum

• Coordinates control of breathing

What is the midbrain (mesencephalon)?

• Eye movement

• Relays signals for hearing and seeing reflexs

• Substantia nigra → produces dopamine

What is the cerebellum?

• Movement coordination

• Equilibrium and balance

What are the components of the diencephalon?

• Thalamus: Relay station and integration of sensory and motor info

• Hypothalamus: Control of homeostasis, hunger, thirst, and influences endocrine function and the autonomic division

• Pituitary gland: Hormones

• Pineal gland: Melatonin production

What is the cerebrum?

• Consists of different structures + two hemispheres

• Responsible for conscious thought, voluntary movement, sensation, memory, and language

• Corpus callosum connects two hemispheres

• 4 lobes: frontal, parietal, occipital, temporal

• Grey matter:

  • Cerebral cortex: Thinking, perception, decision-making

  • Basal ganglia: Control of movement

  • Limbic system: Link between cognitive functions and emotions

    • Amygdala:

      • Emotion (especially fear-related emotions) nand memory

    • Hippocampus:

      • Critical region for learning and memory

      • Affected in Alzhemier’s disease

• White matter: Communication between brain regions

What is the basal ganglia, and what are its components?

• Group of subcortical nuclei:

  • Striatum (caudate and putamen)

  • Subthalamic nuclei (STN)

  • Globus pallidus external and globus pallidus internal

  • Connected with substantia nigra (midbrain)

• Control of voluntary movement via thalamic output to motor cortex

• Disrupted in Parkinson’s disease and Huntington’s disease

What are the simple and complex pathways in the brain?

What are some functions of the brain?

• Perception

• Motor output

• Behavioral state

• Sleep

• Circadian rhythms

• Emotions, motivation, and moods

• Learning and memory

• Language

• Personality

• Movement

What are some examples of brain imaging techniques (and their functions)?

• Electroencephalography (EEG): Brain electrical activity from how many neurons is measured by electrodes placed on the scalp

• Positive emission tomography (PET): Glucose is tagged with a radioactive substance that emits positively charged particles. Metabolically active cells using glucose light up more

• Functional magnetic resonance imaging (fMRI): Active brain tissue has increased blood flow and uses more oxygen. Hydrogen nuclei in water create a magnetic signal that indicates more active regions

What are some examples of brain injuries?

• Split brain syndrome: Corpus callosum is severed

  • Deficits in tasks and learning that require coordination of both sides of the body

• Parietal lobe injury: Problem with somatic sensory perception and coordination due to damage to primary somatic sensory cortex and sensory association area

• Temporal lobe injury: Auditory and language issues

• Occipital lobe injury:

  • Visual issues; blindness, blind spots, visual distortion, visual inattention, spatial analysis

What did Phineas Gage do?

Rod entered his skull by accident → dramatic change in personality afterwards → learned that frontal lobe controls personality

What are the three functional areas of the cerebral cortex?

• 3 functional specializations

  • Sensory areas: Receive sensory input and translate into perception (awareness)

  • Motor areas: Direct skeletal muscle movement

  • Association areas:

    • Integrate info from sensory and motor areas

    • Can direct voluntary behaviors

• Cerebral lateralization:

  • Some functions are more concentrated on one side

    • Left brain → logical, analytical, and verbal processing (language, math, facts)

    • Right brain → intuitive, creative, and holistic thinking (arts, emotions, visualization)

  • This doesn’t mean we are “left-brained” or “right-brained”

How are sensory information perceived by the brain?

• Each sense has a devoted region:

  • Visual cortex, auditory cortex, olfactory cortex, gustatory cortex, proprioception (the "sixth sense" of body awareness, enabling the brain to understand the position, movement, and effort of limbs and trunk without visual input)

• Primary somatic sensory cortex:

  • Skin, musculoskeletal system, and viscera

  • Somatosensory pathway (touch, temp, pain, itch)

• Neural pathways extend from sensory areas to association areas, which integrate stimuli into perception

• Integration of spinal reflexes

What are the three major types of CNS output?

• Skeletal muscle movement: Somatic motor division

• Neuroendocrine signals: Hypothalamus and adrenal medulla

• Visceral responses: Autonomic division

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• Voluntary movement:

  • Primary motor cortex

  • Motor association areas

• Neuroendocrine and visceral responses are coordinated in the hypothalamus and medulla

What is the behavioral state system?

• Behavioral state neurons: Reticular formation of brain stem, hypothalamus, and limbic system

• Modulator of sensory and cognitive processes, sleep/wake cycles, attention, arousal, modulation of muscle tone, and the ability to focus

• Reticular activating system

• 14 brain nuclei

What are the four diffuse modulatory systems?

• Originate in reticular formation in brain stem

• Project axons to large areas of the brain

  • Noradrenergic (norepinephrine)

  • Serotonergic

  • Dopaminergic

  • Cholinergic

What are the components of the noradrenergic/norepinephrine diffuse modulatory system?

• Functions: Attention, arousal, sleep-wake cycles, learning, memory, anxiety, pain, and mood

• Neurons Originate: Locus coeruleus of the pons

• Neurons Terminate: Cerebral cortex, thalamus, hypothalamus, olfactory bulb, cerebellum, midbrain, spinal cord

What are the components of the serotonergic/serotonin diffuse modulatory system?

• Functions:

  • Lower nuclei: Pain, locomotion

  • Upper nuclei: Sleep-wake cycle, mood, and emotional behaviors, such as aggression and depression

• Neurons Originate: Raphe nuclei along brain step midline

• Neurons Terminate:

  • Lower nuclei project to spinal cord

  • Upper nuclei project to most of brain

What are the components of the dopaminergic/dopamine diffuse modulatory system?

What are the components of the cholinergic/acetylcholine diffuse modulatory system?

What are the components of sleep?

What is circadian rhythm?

Where are emotions regulated?

What is motivation?

What is mood?