Nervous Tissue Lecture Notes

Overview

• Nervous tissue consists of two types of cells:
  • Neurons: Form complex networks in the brain and spinal cord, connecting body regions to the brain and spinal cord.
  • Neuroglia: Support and protect neurons.

Neurons

• Neurons provide the unique functions of the nervous system:
  • Sensing
  • Thinking
  • Remembering
  • Controlling muscular activities
  • Regulating glandular secretions

Characteristics of Neurons

• Electrically excitable: Responds to stimuli and converts it into an action potential.
  • Action Potential: Electrical impulse used for communication within the nervous system.
  • Stimulus: Environmental change strong enough to initiate an action potential.

Propagation of Action Potential

• Travels along the neuron's membrane due to ion movement (e.g., sodium, potassium).
• Neurons vary in size:
  • Short-distance propagation (less than 1 mm).
  • Long-distance (e.g., neurons from lumbar spinal cord to feet).

Structure of a Neuron

• Cell Body (Soma):

  • Contains nucleus and cytoplasm.
  • Includes organelles: lysosomes, mitochondria, Golgi complex.
  • Contains Nissl bodies (rough endoplasmic reticulum clusters).

• Dendrites:

  • Receiving/input parts of the neuron.
  • Short, tapered, highly branched.
  • Plasma membrane with receptor sites for chemical messengers.

• Axon:

  • Propagates action potentials towards neurons, muscles, or glands.
  • Ends in axon terminals.
  • Contains synaptic end bulbs or varicosities with synaptic vesicles.

Synapse

• Site of communication between neurons or neuron and effector cell (muscle/gland).
• Neurotransmitters: Chemicals released from synaptic vesicles, affecting the next cell.

Classification of Neurons

• Structural Classification: Based on number of processes from the cell body.
  • Multipolar Neurons: Several dendrites, one axon.
    • Most neurons in brain/spinal cord, all motor neurons.
  • Bipolar Neurons: One dendrite, one axon.
    • Found in retina, inner ear, olfactory area.
  • Unipolar Neurons: Dendrites and one axon fused into one process.
    • Function as sensory receptors for stimuli such as touch, pressure, pain, thermal.

Functional Classification

• Based on the role in the nervous system and types of neurotransmitters used.