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Biology - Nervous Coordination

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    Study Guide Biology – Nervous Coordination 1. Animal Nerve Cells Living organisms need to react quickly to what is happening around them and inside their bodies. In animals, this fast response is made possible by nervous coordination , which is the job of the nervous system . Nervous coordination usually begins when a stimulus (such as light, sound, heat, or pain) is detected by receptors in the sense organs, often found at the body surface. The response to this stimulus usually involves a muscle or a gland . To make this happen, signals travel along a pathway made of special cells called nerve cells . 1.1 What Are Neurons? Animal nerve cells are called neurons . They are highly specialized cells designed to carry messages quickly. In humans, there are about 12 billion neurons , most of which are located in the brain and spinal cord . Each neuron has three main parts: • Cell body – the main part of the cell that contains the nucleus • Dendrites – short, branched extensions that receive incoming signals • Axon – a long extension that carries signals away from the cell body The axon is usually covered by a fatty layer called the myelin sheath , which helps the signal travel faster. A group of axons bundled together forms a nerve . 1.2 Types of Neurons Neurons work together in teams, and they can be grouped into three types based on their function: • Sensory neurons These neurons detect stimuli from the environment (such as touch, temperature, or light) and carry signals toward the brain or spinal cord.

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    Study Guide • Interneurons (association neurons) These neurons connect sensory neurons to motor neurons. They are found in the brain and spinal cord and help process and interpret information. • Motor neurons These neurons carry signals from the brain or spinal cord to muscles or glands , causing a response. Neurons are supported and protected by special helper cells called glial cells . Together with surrounding tissue, these cells form the neuroglia , which nourishes and insulates neurons. 1.3 The Nerve Impulse A nerve impulse is the signal that travels along a neuron. It is an electrochemical event , meaning it involves both electrical charges and chemical movement. 1.3.1 Resting Potential When a neuron is not sending a signal, it is in a resting state. At this time: • The inside of the neuron is negatively charged compared to the outside. • This charge difference is maintained by actively pumping sodium ions out of the cell. A neuron in this state is said to have a resting potential and is polarized . 1.3.2 Action Potential A nerve impulse begins when a stimulus reaches the tip of a dendrite. This causes: • The cell membrane to become more permeable to sodium ions. • Sodium ions rush into the neuron. • The difference in electrical charge disappears. This sudden change creates a nerve impulse called an action potential , and the neuron becomes depolarized . The sodium ions then trigger nearby areas of the membrane to do the same. In this way, a wave of depolarization moves along the neuron. This wave is the nerve impulse.

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    Study Guide After the impulse passes, the neuron restores its original charge by: • Pumping potassium ions out , and • Pumping sodium ions back in This prepares the neuron to fire again. 1.4 The Synapse The nerve impulse travels along the dendrite, through the cell body, and down the axon. However, neurons do not touch each other directly. At the end of the axon, there is a tiny fluid - filled gap called a synapse . When a synapse occurs between a neuron and a muscle fiber, it is called a neuromuscular junction . When the impulse reaches the end of the axon: 1. Chemicals called neurotransmitters (such as acetylcholine) are released. 2. These chemicals cross the synapse. 3. They increase the permeability of the next cell’s membrane. 4. Sodium ions enter the next cell. 5. A new nerve impulse is generated. Once the impulse has passed on, the neurotransmitters are quickly broken down to prevent continuous stimulation. 1.5 The Reflex Arc A reflex arc is the simplest and fastest type of nervous response. It allows the body to react quickly, often without conscious thought. A reflex arc works in this order: 1. A stimulus is detected by sensory receptors. 2. The impulse travels along a sensory neuron to the spinal cord. 3. The impulse passes through one or more interneurons .

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    Study Guide 4. A response signal is sent along a motor neuron . 5. A muscle or gland responds. This rapid pathway helps protect the body from harm, such as pulling your hand away from a hot object. Reflexes and the Brain In some reflexes, the brain is also involved. Interneurons send signals up the spinal cord to the conscious areas of the brain, where the stimulus is interpreted. However, the response often happens before you are fully aware of it. 2. Quiz Animal Nerve Cells 1. Question What type of neuron is responsible for carrying stimuli in the brain and spinal cord? Answer Choices • interneurons • motor neurons • sensory neurons Correct Answer interneurons Why This Is Correct Interneurons are found within the brain and spinal cord. Their main role is to carry nerve impulses between sensory neurons and motor neurons and to help process information inside the central nervous system. For example: When you touch something hot, interneurons in the spinal cord help relay and interpret the signal before a response is sent to your muscles.

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    Study Guide 2. Question What is the first step in nerve impulse generation? Answer Choices • increased permeability of the cell membrane to sodium ions • increased permeability to calcium ions • potassium ions pumped out of the cytoplasm Correct Answer increased permeability of the cell membrane to sodium ions Why This Is Correct A nerve impulse begins when the neuron’s cell membrane becomes more permeable to sodium ions. Sodium ions rush into the cell, causing depolarization of the membrane. This change in electrical charge triggers the nerve impulse to start. For example: When a stimulus reaches a neuron, sodium channels open first, allowing sodium ions to enter and initiate the nerve signal. 3. Question What type of cell protects, nourishes, and supports neurons? Answer Choices • dendrite • glial • interneuron Correct Answer glial

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    Study Guide Why This Is Correct Glial cells (also called neuroglia) do not transmit nerve impulses. Instead, they protect neurons, supply them with nutrients, maintain the surrounding environment, and help support and insulate nerve cells. For example: Glial cells form myelin sheaths around neurons and help keep nerve cells healthy and functioning properly. Here is a clear, student - friendly rewrite of the chapter. The language is simpler, ideas are broken into short sections, and the flow is smoother — while keeping all scientific facts accurate . 3. Human Central Nervous System The human nervous system is usually divided into two main parts: • Central nervous system (CNS) – made up of the brain and spinal cord • Peripheral nervous system (PNS) – made up of all the nerves that branch out from the CNS to the rest of the body The central nervous system acts as the body’s control center . It receives information, processes it, and decides how the body should respond. 3.1 The Spinal Cord The spinal cord is a long, white cord of nervous tissue that runs through a protective bony tunnel formed by the vertebrae . It starts at the base of the brain and extends down to the lower end of the backbone. 3.1.1 Protection and Structure • The spinal cord is protected by three membranes called meninges . • The outer region of the spinal cord is made of white matter . • The inner region is made of gray matter .

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    Study Guide This arrangement helps nerve impulses travel efficiently. 3.1.2 Nerve Roots and Fluid • Thirty - one pairs of nerve roots extend from each side of the spinal cord. • These nerve roots contain axons from sensory neurons and motor neurons . • A central canal runs through the spinal cord and carries cerebrospinal fluid . Cerebrospinal fluid supplies nutrients and oxygen to spinal cord tissues and helps remove waste. 3.1.3 Functions of the Spinal Cord The spinal cord has two main roles: 1. It acts as a coordinating center for reflex actions . 2. It serves as a communication link between the brain and the peripheral nervous system. 3.2 The Brain The brain is the main control and processing center of the central nervous system. It is responsible for consciousness, sensation, memory, intelligence, and decision - making . The brain: • Receives impulses from the spinal cord • Receives information from 12 pairs of cranial nerves • Can also initiate actions on its own , without any external stimulus 3.2.1 General Structure of the Brain The brain is divided into two hemispheres : • Left hemisphere • Right hemisphere The outer layer of the brain is gray matter , while the inner layer is white matter .

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