Human Nervous System: Structure, Function, and Components
The Nervous System: Structure and Function
Stimulus
Something that causes a response.The Nervous System
The nervous system is a complex, connected network of cells, tissues, and organs. Formed by neurons, it receives and processes information, coordinating responses throughout the body.
Divisions of the Nervous System
Central Nervous System (CNS)
Includes the brain and spinal cord. It interprets messages from other nerves and initiates responses.
Peripheral Nervous System (PNS)
A network of nerves that transmits messages to and from the CNS. It works quickly and controls immediate processes.
Neurons: The Building Blocks of the Nervous System
Neurons are specialized cells that store information and carry messages throughout the nervous system.
Parts of a Neuron
- Cell Body: Contains the nucleus and other organelles.
- Dendrites: Branch-like extensions of the cytoplasm and cell membrane that receive signals.
- Axon: A long extension that carries electrical messages away from the cell body.
Types of Neurons
- Sensory Neurons: Receive information from receptors.
- Motor Neurons: Transmit information to muscles or glands to initiate action.
- Association Neurons (Interneurons): Form connections and relay information between sensory and motor neurons.
Neural Communication: Signals and Connections
Resting Potential
The difference in electrical charge across the neuron’s membrane when it is not transmitting a signal. It occurs due to unequal concentrations of ions inside and outside the neuron.
Action Potential
A rapid, temporary change in the electrical potential across a neuron’s membrane, triggered by a stimulus. This moving electrical pulse requires ion channels in the membrane that open and close.
Sodium-Potassium Pump
A protein in the neuron’s membrane that uses energy to actively transport sodium ions (Na+) out of the cell and bring potassium ions (K+) into the cell, maintaining the resting potential.
Types of Ions in Neural Communication
- Sodium Ions (Na+): Primarily found outside the cell.
- Potassium Ions (K+): Primarily found inside the cell.
Synapse
The tiny gap between neurons where an action potential moves from one neuron to the next.
Axon Terminal
The end part of the axon from which the impulse leaves the neuron, typically releasing neurotransmitters into the synapse.
Neurotransmitters
Chemical signals of the nervous system that transmit impulses across synapses, connecting neurons.
The Brain: Command Center of the Body
The brain is protected by three layers of connective tissue called meninges.
Main Structures of the Brain
Cerebrum
The largest part of the brain, responsible for interpreting signals from your body, voluntary movements, and higher-level functions. It has distinct right and left halves.
- Cerebral Cortex: The outer layer of the cerebrum, responsible for complex thought, language, and sensory processing.
Cerebellum
Located at the back of the brain, it coordinates your movements, balance, and posture.
Brainstem
Connects the brain to the spinal cord and controls the most basic life-sustaining activities.
- Midbrain: Involved in motor control, vision, and hearing.
- Pons: Relays signals from the cerebrum to the cerebellum and controls sleep, respiration, and facial sensations.
- Medulla Oblongata: Regulates vital functions such as breathing, heart rate, and blood pressure.
The Spinal Cord and Reflexes
Spinal Column
Consists of vertebrae, cerebrospinal fluid, meninges, and encloses the spinal cord.
Spinal Cord
A rope-like bundle of neurons that connects the brain to the nerves throughout the body. If the spinal cord is damaged, messages cannot move between the brain and the rest of the body.
Reflexes
Involuntary movements that occur without conscious thought.
Reflex Arcs
Nerve pathways that require only two synapses (one sensory, one motor, often with an interneuron) before producing a rapid, automatic response.
Divisions of the Peripheral Nervous System (PNS)
Somatic Nervous System
A division of the PNS that regulates movements under voluntary control, such as skeletal muscle contractions.
Autonomic Nervous System
A division of the PNS that controls automatic, involuntary bodily functions, such as heart rate, digestion, and breathing.
Sympathetic Nervous System
A part of the autonomic nervous system that prepares the body for action and stress (the “fight or flight” response).
Parasympathetic Nervous System
A division of the autonomic nervous system that calms the body and helps conserve energy (the “rest and digest” response).
Spinal Nerves
Spinal nerves emerge from the spinal cord, organized by region:
- Cervical Nerves (C1-C8): Innervate the neck, shoulders, arms, and hands.
- Thoracic Nerves (T1-T12): Innervate the chest and upper abdomen.
- Lumbar Nerves (L1-L5): Innervate the lower back and legs.
- Sacral Nerves (S1-S5): Innervate the pelvis, buttocks, and legs.
- Coccygeal Nerve (Co): A single nerve innervating the coccyx region.