chapter 12 Nervous system

Nervous System Overview

Major Anatomical Divisions of the Nervous System

• Central Nervous System (CNS): Comprises the brain and spinal cord.

• Peripheral Nervous System (PNS): Encompasses all nervous tissues outside the CNS, including nerves and ganglia.

Types of Nervous Tissue Cells

• Neurons:

• Functionally significant; responsible for signal transmission (action potentials).

• Composed of structures such as:

  • Cell Body: Contains the nucleus and organelles.

  • Dendrites: Receive signals from other neurons.

  • Axon: Conducts electrical signals away from the cell body.

• Glial Cells (Neuroglial Cells):

• Support and protect neurons.

• Types in CNS:

  • Oligodendrocytes: Myelinate axons in the CNS.

  • Astrocytes: Maintain chemical balance, respond to damage, part of the blood-brain barrier.

  • Microglial Cells: Act as immune defense in the CNS, engulfing pathogens.

  • Ependymal Cells: Produce cerebrospinal fluid (CSF).

• Types in PNS:

  • Schwann Cells: Myelinate axons in the PNS (wrap around one axon segment).

  • Satellite Cells: Support neuron cell bodies in ganglia.

Organization of Nervous Tissue

• Gray Matter: Regions with many neuron cell bodies.

• White Matter: Regions primarily with axons, myelinated by myelin (what makes it white)

• Nuclei: Collections of neuron cell bodies in the CNS.

• Ganglia: Collections of neuron cell bodies in the PNS.

• Nerve: Bundle of axons in the PNS; called a tract in the CNS.

Functional Divisions of the Nervous System

• Sensation: Receiving and interpreting stimuli from the environment (internal and external).

• Sensory structures like nerves detect stimuli.

• Integration: Process of interpreting signals, comparing with memories and past stimuli.

• Response: Generation of a reaction to stimuli, which can be voluntary (somatic nervous system) or involuntary (autonomic nervous system).

• Enteric Nervous System: Specializes in controlling digestive functions, operating independently of the CNS.

Neuron Signal Pathway

1. Sensation: Detect a stimulus (e.g., temperature).

2. Action Potential: Electrical signal travels along the axon of sensory neurons to the spinal cord.

3. Integration: Signal processed in the CNS; primarily involves the thalamus, except for olfactory information.

4. Response Generation: After processing, motor signals are sent from the CNS to muscles for a response.

5. Neuromuscular Junction: Where the motor neuron interacts with muscle cells to evoke contraction.

Summary of Functional Pathway (Example)

• Scenario: Checking the temperature of shower water.

• Sensory receptors in the skin detect the temperature.

• Signal travels via the sensory nervous system to the spinal cord and up to the thalamus.

• Thalamus processes the sensory input and forwards it to the cerebral cortex.

• Integration occurs, leading to a motor response signal sent down through the spinal cord to skeletal muscles.

• Response: Muscle contraction to pull away from unpleasant temperature, all happening in milliseconds.