Human Growth and Development

Neurons are nerve cells that send and receive signals throughout the body. They use dendrites to receive information, which triggers an electrical signal called an action potential in the cell body. If the signal is strong enough, sodium channels in the axon open, sending the signal down to the next neuron. The myelin sheath, made by Schwann cells , insulates the axon, speeding up signal transmission. Within the synapse , there is a small space known as the synaptic gap that enables neurotransmitters to transmit signals between neurons. Neurotransmitters include: ●​ Dopamine: Controls attention, learning, voluntary movement, motivation, and pleasure. ●​ Serotonin: Regulates sleep, hunger, and mood. ●​ Glutamate: Important for learning and memory. ●​ GABA: Inhibits brain activity; linked to anxiety, motor control, and Huntington’s disease. ●​ Endorphins: Reduce pain and promote well-being. Learning and memory depend on neural connections. As we gain new experiences, neurons repeatedly send signals, strengthening pathways in the brain. Neural Communication

Neurons vary in size, shape, and function. Some are specialized for sensory input, others for motor output, while interneurons connect sensory and motor neurons. An action potential is an electrical impulse that travels down an axon, enabling fast communication for actions like muscle movement and sensory perception. A neuron at rest maintains a resting membrane potential , a slightly negative charge inside the cell. When stimulated, the membrane depolarizes, triggering an action potential and sending a signal. Peripheral Nervous System (PNS)

The Peripheral Nervous System (PNS) consists of spinal and cranial nerves that link the brain and spinal cord to the rest of the body. It transmits sensory signals to the brain and motor signals to the muscles. It is divided into the Autonomic Nervous System (ANS) and the Somatic Nervous System (SNS). The autonomic nervous system (ANS) regulates involuntary functions and has two main divisions:

Parasympathetic Nervous System

Sympathetic Nervous System

This system is responsible for the "rest and digest" activities that occur when the body is at rest. It conserves energy by slowing the heart rate, increasing intestinal and gland activity, and relaxing sphincter muscles.

This system prepares the body for the "fight or flight" response during stressful situations. Key functions include increasing heart rate, dilating airways, and releasing stored energy. It mobilizes the body's resources to respond to a threat.

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