12.3 The Function of Nervous Tissue

Nervous tissue communication is a complex dance of electrical and chemical signals. Neurons generate action potentials, which travel along axons, while neurotransmitters facilitate communication between cells. This intricate system allows for rapid and precise information transfer throughout the nervous system.

The nervous system processes sensory input and generates motor output through a coordinated sequence. Sensory receptors detect stimuli, the central nervous system processes the information, and motor neurons transmit commands to effector organs. This pathway enables our bodies to respond to environmental changes efficiently.

Nervous Tissue Communication and Function

Communication in nervous tissue

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• Electrical signals
  • Neurons generate electrical signals called action potentials
    • Brief, rapid changes in the membrane potential of a neuron
    • Generated when the neuron's membrane potential reaches a threshold value
  • Action potentials propagate along the axon of the neuron
    • Voltage-gated sodium and potassium channels open and close in a coordinated manner
    • Allows the action potential to travel from the cell body to the axon terminal (synaptic terminal)
  • Resting membrane potential is the baseline electrical state of a neuron when not actively transmitting signals
• Chemical signals
  • Neurons communicate with each other and with target cells through chemical signals called neurotransmitters
    • Released from the axon terminal of the presynaptic neuron
    • Bind to specific receptors on the postsynaptic cell (target cell)
  • Binding of neurotransmitters can cause excitatory or inhibitory effects on the postsynaptic cell
    • Excitatory neurotransmitters increase the likelihood of the postsynaptic cell generating an action potential (glutamate, acetylcholine)
    • Inhibitory neurotransmitters decrease the likelihood of the postsynaptic cell generating an action potential (GABA, glycine)
  • Neuromodulators are chemicals that can modify the effects of neurotransmitters on target cells

Sensory input to motor output sequence

1. Sensory input
   • Sensory receptors detect stimuli from the internal or external environment
     • Specialized cells or structures that respond to specific types of stimuli (light, sound, touch, temperature)
   • Sensory receptors transduce the stimulus energy into electrical signals (receptor potentials)
   • Sensory neurons transmit the electrical signals to the central nervous system CNS (brain and spinal cord)
2. Processing in the CNS
   • Sensory information is processed and integrated in the CNS, particularly in the cerebral cortex
     • Outermost layer of the brain, responsible for higher-order processing and decision-making
   • Neural circuits in the CNS analyze and interpret the sensory information
   • The CNS generates an appropriate response based on the processed sensory information
3. Motor output
   • The CNS sends motor commands to the appropriate effector organs via motor neurons
     • Effector organs include muscles and glands
   • Motor neurons transmit electrical signals (action potentials) to the effector organs
   • The effector organs respond to the motor commands, resulting in a specific action or response
     • Muscle contraction, gland secretion
   • The neuromuscular junction is the specialized synapse where motor neurons communicate with skeletal muscle fibers

Key structures of nervous system

• Sensory receptors
  • Detect stimuli from the internal or external environment
  • Transduce the stimulus energy into electrical signals (receptor potentials)
  • Initiate the process of sensory transduction and transmission of sensory information to the CNS
• Neurons
  • Basic functional units of the nervous system
  • Generate and transmit electrical signals (action potentials) along their axons
  • Communicate with other neurons and target cells through chemical signals (neurotransmitters)
  • Types of neurons:
    1. Sensory neurons: Transmit sensory information from receptors to the CNS
    2. Interneurons: Process and integrate information within the CNS
    3. Motor neurons: Transmit motor commands from the CNS to effector organs
• Synapses
  • Functional connections between neurons or between neurons and target cells
  • Allow for the transmission of information from one neuron to another or from a neuron to a target cell
  • Consist of a presynaptic neuron, a synaptic cleft, and a postsynaptic cell
  • Neurotransmitters are released from the presynaptic neuron, cross the synaptic cleft, and bind to receptors on the postsynaptic cell
• Cerebral cortex
  • Outermost layer of the brain, responsible for higher-order processing and decision-making
  • Divided into four main lobes: frontal, parietal, temporal, and occipital
  • Each lobe is associated with specific functions:
    1. Frontal lobe: Executive functions, planning, decision-making, and motor control
    2. Parietal lobe: Somatosensory processing, spatial awareness, and attention
    3. Temporal lobe: Auditory processing, language comprehension, and memory
    4. Occipital lobe: Visual processing and perception
  • Plays a crucial role in processing and integrating sensory information, generating appropriate responses, and coordinating complex behaviors and cognitive functions

Supporting cells and plasticity

• Neuroglia (glial cells) provide support and protection for neurons in the nervous system
• Neuroplasticity refers to the brain's ability to change and adapt in response to experience and learning
• Graded potentials are small changes in membrane potential that can summate and lead to the generation of action potentials