Nervous System - Chapter 35

• Chapter 35 focuses on the nervous system

Organization of the Nervous System

• Neurogenesis is referenced
• The nervous system has two major parts: the CNS and PNS

CNS (Central Nervous System)

• Consists of the brain and spinal cord
• The brain and spinal cord are covered by three membranes:
  • Outer layer is the dura mater
  • Middle layer is the arachnoid mater
  • Innermost layer is the pia mater

PNS (Peripheral Nervous System)

• Is divided into the autonomic nervous system and the sensory-somatic nervous system
• The autonomic nervous system includes:
  • Sympathetic components
  • Parasympathetic components
• The sensory-somatic nervous system includes sensory and motor neurons
  • Consists of 12 cranial nerves
  • Consists of 31 spinal nerves

Cranial Nerves

• Are part of the PNS

Central Nervous System Components

• Skin
• Periosteum
• Bone
• Dura mater
• Arachnoid mater
• Pia mater
• Brain

Cerebrospinal Fluid (CSF)

• Includes the choroid plexus and ventricles (4)

Ventricles

• Four ventricles are present
• Contain choroid plexus
• Consist of cerebrospinal fluid
• Volume of CSF is ~25-30 tsp or 1 ½ - 2/3 cup
• Hydrocephalus is referenced

Spinal Cord

• Covered by three layers:
  • Outer layer (dura mater)
  • Middle layer (arachnoid mater)
  • Innermost layer (pia mater)

Brain Anatomy

• The brain has a central sulcus and a longitudinal fissure

Brain - Somatosensory and Motor Cortex

• Includes a lateral view, motor cortex, somatosensory cortex and a central sulcus

Deep Brain Structures

• Frontal Lobe
• Temporal Lobe
• Parietal Lobe
• Occipital Lobe
• Cerebellum
• Brain Stem
• Spinal Cord
• Precentral Gyrus
• Central Sulcus
• Postcentral Gyrus

Brain Lobes

• Frontal Lobe: involved in problem-solving, emotional traits, reasoning, speaking, and voluntary motor activity.
• Temporal Lobe: involved in understanding language, behavior, memory, and hearing.
• Parietal Lobe: involved in knowing right from left, sensation, reading, and body orientation.
• Occipital Lobe: involved in vision and color perception.
• Cerebellum: involved in balance, coordination, and control of voluntary movement and fine motor control.
• Brain Stem: involved in breathing, body temperature, digestion, alertness/sleep and swallowing.

Somatosensory and Motor Cortex

• Output: motor cortex, which controls the body's right side using the left hemisphere section.
• Input: sensory cortex, which receives input from the body's right side using the left hemisphere section.

Neuron Structure

• Includes dendrites, a nucleus, an axon, myelin sheath (insulation), nodes of Ranvier, Schwann cells, axon terminals, and a cell body
• Conveys chemical signals from one neuron to another neuron, muscle cell, or gland.

Neurotransmission

• A process involving neurotransmitters reaching the postsynaptic neuron and can be reviewed in a video
• The video is ~2 minutes long

Nerve Impulses

• Pre-synaptic neuron
• Axon
• Synapse
• Neurotransmitter
• Dendrite
• Cell body with nucleus
• Axon to axon terminal
• Synapse
• Dendrites
• Post-synaptic neuron

Nerve Impulse Transmission

• Can be learnt by watching the linked video of ~8 minutes long
• Resting membrane potential, threshold potential, and action potential are discussed, along with the role of sodium (Na+) and potassium (K+) ions (sodium-potassium pump).
• Resting membrane potential and threshold potential are subject to all-or-none law

Saltatory Conduction

• One node to the next
• Skips myelinated sections of axon
• Speeds up electrical impulse

Neurotransmitters

• Neurotransmitters are either excitatory or inhibitory
• Excitatory neurotransmitters include glutamate, norepinephrine, and dopamine.
• Inhibitory neurotransmitters include GABA and serotonin
• Low levels of GABA are associated with schizophrenia, autism, anxiety, and depression.

Serotonin vs Dopamine

• Serotonin regulates mood and inhibits impulsive behavior
• Dopamine regulates motivation and establishes reward pathways

Synapses

• Chemical synapses have a slight delay, require a neurotransmitter, are unidirectional, and can be blocked.
• Electrical synapses are almost instantaneous and always excitatory and require a gap junction channel
• Electrical Synapses
• Some are bi-directional
• Often used for communications in neuroglia
• More reliable but less flexible

Nerve Impulses and Reaction Time

Reaction time varies

• From individual to individual
• Depending on factors such as sex, physical condition, fatigue, distraction, etc
• From one kind of stimulus to another
  • On average, it takes:
    • 0.25 seconds to react to a visual stimulus
    • 0.17 seconds to react to an audio stimulus
    • 0.15 seconds to react to a touch stimulus

Disorders of the Nervous System

• Neurodegenerative disorders involve neuronal death and include:
  • Alzheimer’s disease (amyloid plaques, tangled brain fibers, and overall shrinking of the brain).
  • Parkinson’s disease (loss of neurons that produce dopamine in basal ganglia).
  • Multiple sclerosis (autoimmune).
  • Amyotrophic lateral sclerosis (genetic), also known as Lou Gehrig’s disease.
• Neurodevelopmental disorders involve disturbance of the nervous system development and include:
  • Autism
  • Attention Deficit Hyperactive Disorder (ADHD).
• Mental illnesses (e.g., schizophrenia, bipolar disorder, depression, phobia, OCD, PTSD).