Notes on Nervous Tissue and Function

Overview of the Nervous System
  • Organization:
    • CNS: Brain & spinal cord (100 billion neurons in the brain, 100 million in the spinal cord). Processes sensory info, thoughts, emotions, memories, stimulates muscles and glands.
    • PNS: Nerves, ganglia, enteric plexuses, sensory receptors. Receives information through sensory neurons and delivers responses through motor neurons.
  • Functions:
    • Sensory (Input): Detects internal/external stimuli.
    • Integrative (Processing): Analyzes sensory information to make decisions.
    • Motor (Output): Initiates responses by activating muscles and glands.
Histology of Nervous Tissue
  • Types of Cells:
    • Neurons: Functionally specialized, cannot undergo mitosis.
    • Neuroglia: Support and protect neurons, can divide.
  • Neurons Structure:
    • Dendrites: Receive signals,
    • Cell body (soma): Contains nucleus and organelles,
    • Axon: Conducts impulses away from the cell body, ends in axon terminals.
    • Myelin Sheath: Insulates axons, increases conduction speed.
Electrical Signals in Neurons
  • Types of Signals:
    • Graded Potentials: Local changes in membrane potential, vary in amplitude.
    • Action Potentials: All-or-nothing signals that travel along axons.
  • Phases of Action Potential:
    • Depolarizing Phase: Membrane becomes less negative.
    • Repolarizing Phase: Membrane potential returns to resting state.
    • After-Hyperpolarization: Brief hyperpolarization occurs after repolarization.
Signal Transmission at Synapses
  • Types of Synapses:
    • Electrical Synapses: Direct current flow through gap junctions, faster communication.
    • Chemical Synapses: Neurotransmitters released into synaptic cleft, binds to postsynaptic receptors, causing changes in potential.
Neurotransmitters
  • Types:
    • Small-molecule neurotransmitters: Acetylcholine (excitatory & inhibitory), amino acids, biogenic amines, ATP, nitric oxide, carbon monoxide.
    • Neuropeptides: Chains of amino acids that can have excitatory or inhibitory effects (e.g., enkephalins).
  • Clinical Connections: Excitotoxicity, depression, and effects of various substances on neurotransmitter functions.
Regeneration and Repair of Nervous Tissue
  • Limited capacity for regeneration in CNS, possible repair in PNS.
  • Common Disorders:
    • Multiple Sclerosis: Progressive destruction of myelin in CNS.
    • Epilepsy: Sudden recurrent seizures due to abnormal