Nervous System Overview
Major Components
- Central Nervous System (CNS)
- Comprises the brain and spinal cord.
- Functions as the main control center.
- Peripheral Nervous System (PNS)
- Connects the CNS to the rest of the body.
- Divided into sensory (afferent) and motor (efferent) divisions.
Information Flow
- Afferent Information: From body to CNS.
- Efferent Information: From CNS to body.
Sensory Division
- Processes external and internal sensations (e.g., touch, pain, temperature).
- Information sent to CNS for integration.
Motor Division
- Voluntary Response: Controlled by the somatic nervous system involving skeletal muscles.
- Involuntary Response: Controlled by the autonomic nervous system involving smooth muscles, cardiac muscles, and glands.
Autonomic Nervous System
- Sympathetic Nervous System
- Activates 'fight or flight' response.
- Increases heart rate, respiration, blood pressure.
- Parasympathetic Nervous System
- Activates 'rest and digest' response.
- Decreases heart rate, increases digestion.
Neurons vs. Nerves
- Neuron: A single cell designed to transmit information.
- Nerve: A bundle of neurons.
- Neurons can be sensory, motor, or mixed within a nerve.
Myelin and Insulation
- Myelin sheath acts as an insulator for neurons.
- Prevents electrical "short-circuiting."
- Neurons are bundled into fascicles within nerves.
Sensory Neurons and Receptors
- Mechanoreceptors: Detect physical changes like touch and balance.
- Chemoreceptors: Responsible for taste and smell.
- Osmoreceptors: Monitor blood pressure.
- Photoreceptors: Detect light in the eyes.
- Thermoreceptors: Sense temperature variations.
- Nociceptors: Detect pain, crucial for protection.
Neuroglial Cells
- Astrocytes
- Maintain blood-brain barrier.
- Form synapses and nourish neurons.
- Microglial Cells
- Act as phagocytes to clean up debris in CNS.
- Ependymal Cells
- Line brain ventricles, circulate cerebrospinal fluid.
- Oligodendrocytes (CNS)
- Produce myelin for CNS neurons.
- Schwann Cells (PNS)
- Produce myelin in the PNS.
Synapse Formation
- Plastic Synapses: Adaptable connections, important for learning.
- Cemented Synapses: Permanent connections, e.g., riding a bike.
Importance of Synapses
- Synapse plasticity is crucial for memory and learning capabilities.
- Cemented synapses retain essential learned functions.
Aging and Neuronal Flexibility
- Active brain use keeps synapses plastic and flexible.
- Sedentary lifestyle can lead to more cemented synapses, potential for dementia.
Summary
Understanding the nervous system, from its comprehensive structure to functional roles, is critical for comprehending how our bodies interpret and respond to the environment, maintain homeostasis, and support essential life functions.