Nervous System - PDF

# The Nervous System The Nervous System is the organ system that is made up of the brain, the spinal cord, and the peripheral nerves. ## Structural Features The nervous system is divided into two main systems: - **The Central Nervous System (CNS)** - Consists of the brain and the spinal cord...

# The Nervous System The Nervous System is the organ system that is made up of the brain, the spinal cord, and the peripheral nerves. ## Structural Features The nervous system is divided into two main systems: - **The Central Nervous System (CNS)** - Consists of the brain and the spinal cord. - **The Peripheral Nervous System (PNS)** - Consists of the nerves that connect the body to the central nervous system. - Relays information about the internal and external environment to the brain. - Relays instructions from the brain to body parts. ## Peripheral Nervous System The PNS can be further divided into three groups of nerves: 1. Nerves that control voluntary muscles. 2. Nerves that carry information from sensory organs to the brain. 3. Nerves that regulate involuntary functions (ex.: breathing, heartbeat, digestion). ## Nerve Tissue - Made up of special cells called neurons. - Neurons are found in the brain, spinal cord, and nerves. - Estimated 100 billion neurons in the brain. - Neurons are communication specialists: they can send information around your body by conducting electrical signals (nerve impulses) from one area of the body to another. - The axons on some neurons are covered by a fatty material called myelin sheath. - This sheath acts like the insulation on an electrical wire, preventing electrical impulses from passing to the wrong neuron. - **Structure of a Typical Neuron:** Nerve tissue consists of bundles of neurons that are surrounded by connective tissue. - Injured neurons in the CNS do not easily regenerate. - Some neurons in the PNS can regrow to repair a small gap between the ends of severed nerves. ## Sensory Receptors - Special cells or tissues that receive input from our external environment and sends signals along the PNS to our CNS (ex. Eyes have receptors that are sensitive to light). - All the sensory receptors around the body send information to the brain. ## Communication, Coordination, & Perception - Overall function of the CNS is to transmit signals in both directions between your brain and the rest of your body. - This allows your body to respond both to the outside world and to the internal environment. - Another function of the brain is perception: interpreting or making sense of all the information we receive from our environment. - The spinal cord has another important function as well, it acts as a short cut for reflexes. - Reflexes are actions that do not require the involvement of the brain. ## Bionic Arm - Artificial arm that is controlled by nerve impulses. - Nerves that once served the amputated arm are rerouted and connected to healthy muscle in the chest and other surrounding muscles. - The rerouted nerves grow into these muscles and direct impulses, originally intended for the amputated arm, to the robotic arm. - This allows for movement of the arm by just simply thinking about it. ## How the arm works 1. Doctors redirected the nerves to the patient's chest muscles. 2. When the patient thinks about a specific movement of the arm or hand, the nerve impulse travels from the brain to the corresponding location on the muscle. 3. Electrodes attached to the harness worn on the shoulder detect electrical impulses emitted from the nerves and forward them to the arm. 4. A computer processes the electrical impulses and makes the arm perform certain movements, such as flexing the elbow, opening and closing the hand, and extending the elbow and wrist. 5. Sensation nerves to the hand are rerouted to a patch of skin on the chest, giving the user a sense of touch. ## Diseases and Disorders of the Nervous System - Brain can be permanently damaged by viruses or bacteria. - **Multiple sclerosis** is caused by a malfunction of the immune system (this disease destroys the myelin sheaths of neurons). Symptoms include muscle weakness, slurred speech, and difficulty walking. - **Physical trauma**, such as a fall or a blow can create severe damage to the spinal cord often resulting in paralysis.