Lecture 4 Nervous System.pdf

Nervous System Overview

  • Schuetere Quifere: Presentation header or reference

  • John Sullivan, M.D., Ph.D.: Presenter from Touro College in Madrid.

Central Nervous System (CNS) vs Peripheral Nervous System (PNS)

  • CNS includes: Brain and spinal cord.

  • PNS includes: All neural pathways outside the CNS; divided into sensory and autonomic.

Components of the Central Nervous System

  • Cerebrum: Main part of the brain responsible for higher mental functions.

  • Brain Stem: Comprises midbrain, pons, and medulla oblongata; responsible for basic life functions.

  • Cerebellum: Responsible for motor control and coordination.

  • Diencephalon includes thalamus and hypothalamus; regulates sensory information and functions.

  • Sagittal Section: Depicts medial view of these structures.

Developmental Neurology

  • Lissencephaly: A condition characterized by smooth brain due to lack of gyri; can impact cognitive function.

Spinal Cord Anatomy

  • Enlargements: Cervical and lumbar enlargements; regions of increased neuronal cell bodies for limb innervation.

  • Spinal Nerves: Formed from dorsal (sensory) and ventral (motor) roots fuse; exits the CNS to the PNS.

  • Reflex Arcs: Pathway that mediates reflexes rapidly; integrates changes in the environment via CNS.

  • Dural Sheath: Protective covering surrounding the spinal cord.

  • Subarachnoid Space: Contains cerebrospinal fluid (CSF).

Gray and White Matter

  • Gray Matter: Contains neuronal cell bodies, dendrites, and unmyelinated axons.

  • White Matter: Composed predominantly of myelinated axons, facilitating communication between different brain regions.

Functional Classification of Neurons

  • Sensory (Afferent) Neurons: Carry signals toward the CNS; typically unipolar.

  • Motor (Efferent) Neurons: Transmit signals away from CNS; usually multipolar, innervating muscles and glands.

  • Interneurons: Located within CNS; process and integrate information for reflexes.

Reflex Arcs

  • General Components: Ipsilateral response; automatic, fast, and predictable.

  • Integration in Gray Matter: Main site for reflex processing within spinal cord.

  • Types of Reflexes:

    • Monosynaptic Reflex: Direct sensory-motor neuron communication.

    • Polysynaptic Reflex: Involves interneurons for sensory-motor communication.

Dermatome Mapping

  • Dermatomes: Skin segments innervated by specific spinal nerves; important for assessing sensory function.

Neuron Structure

  • Neurons consist of dendrites, soma (cell body), and axon; specialized for signal transmission.

  • Types include Multipolar, Bipolar, and Pseudo-unipolar Neurons based on structure.

Neuroglia of the CNS

  • Include astrocytes, oligodendrocytes, microglia; support and protect neurons, contribute to homeostasis in the CNS.

  • Astrocytes: Help maintain the blood-brain barrier and provide nutrient support.

  • Oligodendrocytes: Myelinate axons in the CNS.

Synapses and Signal Transmission

  • Synapse Types: Gap junctions in electrical synapses for quick signaling; chemical synapses involve neurotransmitter release.

  • Presynaptic and Postsynaptic Neurons: Signal transfer at synapses involves neurotransmitter release and receptor binding.

Chemical Synapses

  • Excitatory Postsynaptic Potentials (EPSP): Depolarizing signals that increase the likelihood of action potentials.

  • Inhibitory Postsynaptic Potentials (IPSP): Hyperpolarizing signals that decrease the likelihood of firing action potentials.

Neurotransmitter Dynamics

  • Signal Removal: By diffusion, reuptake, or enzymatic degradation (e.g., acetylcholinesterase).

  • Drugs Affecting Synaptic Activity: Include local anesthetics, botulinum toxin, and antidepressants.

Neurogenesis and Repair in CNS

  • Limited repair capabilities due to

    • Inhibitory signals from neuroglia.

    • Absence of growth-promoting cues.

    • Rapid formation of scar tissue following injury.