Nervous System PDF

 Brain Spinal cord The nervous system consists of: The central nervous system (including the brain and spinal cord) The peripheral nervous system (including nerve cells that carry information to and from...

 Brain Spinal cord The nervous system consists of: The central nervous system (including the brain and spinal cord) The peripheral nervous system (including nerve cells that carry information to and from the central nervous system)  Central Nervous System (CNS) ✓ the main processing center for the entire nervous system ✓ main components are the brain and the spinal cord Parts of the Brain: CEREBRUM – controls activity and thought Spinal Cord CEREBELLUM – controls controls simple posture, balance and musculoskeletal coordination reflexes without BRAIN STEM – controls input from automatic functions such the brain as breathing, heart rate, digestion, and blood pressure So Peripheral Nervous System (PNS) ✓ connects the CNS to the organs and limbs responsible for conscious responsible for the involuntary perception and voluntary control of the body, usually for the motor responses (ex. sake of homeostasis contraction of skeletal regulates the organ systems of the muscle) body Somatic has 2 parts: The Spinal has 2 subdivisions: Sympathetic & Autonomic Nervous Nerves (carry motor and Nervous Parasympathetic Sympathetic – activated when sensory signals between System the spinal cord and the System body is in dynamic role/stress (example: increased heart rate and body) and the Cranial breathing, dilation of pupil, Nerves (carry the sweating) information into and out Parasympathetic – maintains body of the brainstem functions and restores the body to normal or relaxed mode. 1. SENSATION – receiving information about the environment. Sensory functions register the presence of a stimulus. 2. RESPONSE – produced by the nervous system based on the stimuli perceived by the sensory structures (ex: movement of muscles such as withdrawing of hand from a hot stove, production and secretion of sweat by the sweat glands in the skin to lower body temperature). 3. INTEGRATION –Stimuli are compared with or integrated with other stimuli, memories of the previous stimuli, or the state of person at a particular time. This leads to the specific response that will be generated.  also referred to as neurons the basic units of the nervous system adapted to transport electrical impulses around the body. highly specialized cells that act as information processing and transmitting units of the brain a group of neurons forms a nerve Parts of a Neuron  SENSORY NEURONS-are nerve cells that 1. are located within the nervous system and which are responsible for converting external stimuli from the environment of the organism into electrical impulses 2. MOTOR NEURONS- neurons with a cell body that is located in the brainstem, motor cortex, or the spinal cord of the body ; control effector organs (glands and muscles) 3. INTERNEURONS- provide communication between the sensory and motor neurons so that some action can result  Nerve Impulse ❖ a combination of an electrical charge and a chemical reaction ❖ not a flow of electricity, but an electrochemical signal moving along a neuron. ❖ cannot jump from one neuron to another. When a nerve impulse comes to the end of an axon, it produces the chemical, called neurotransmitter, to be released. The chemical crosses the space between neurons called synapse and stimulates the nerve impulse to start in the next dendrite  Blinking: When something flies toward your eyes, you blink to protect them Coughing or sneezing: These actions clear your airways of irritants Withdrawing your hand: If you prick your hand with a pin, you'll suddenly jerk your hand away Pupil constriction: When you're exposed to bright light, your pupils constrict to reduce the amount of light entering your eyes Shivering: When you're cold, you shiver to generate heat Raising your arm: If someone throws a ball your way, you raise your arm to catch it Jerking your knees: If someone stamps your leg or you're hit, your knees will jerk Homeostasis is the state reached when each part of the body functions in equilibrium with other parts. This is attained through the regulation of the bodily functions by the endocrine and nervous systems. Body systems maintain homeostasis by using FEEDBACK MECHANISMS, Example of Negative Feedback Mechanism Regulation of body temperature First, nerves in the body and brain detect if a person is getting too hot or too cold. These signals are sent to the hypothalamus, which then coordinates a physiological response: If body temperature is too high, the person begins to sweat and blood vessels dilate (widen), increasing blood flow to the skin. This increases the amount of heat lost to the surroundings. If body temperature is too low, the person begins to shiver so that their muscles will generate more heat through cellular respiration. In addition, blood vessels constrict (narrow), decreasing blood flow to the skin which limits heat loss. Example of Negative Feedback Mechanism Regulation of water balance Water levels in the body can drop if a person doesn’t drink enough water, or loses too much water through sweating. When blood water levels drop, the concentration of substances dissolved in the blood increases. The hypothalamus detects this change in the blood and signals the posterior pituitary gland to release antidiuretic hormone (ADH) into the blood. ADH travels to the kidneys, where it prompts them to reduce the amount of water entering the urine (which in turn keeps more water inside the body). The hypothalamus also initiates the feeling of thirst so that the person will drink more water. If the body has too much water, the production of ADH is suppressed and the kidneys allow more water to enter the urine. As a result, urine with a higher water content leaves the body, helping to restore water balance. Example of Negative Feedback Mechanism Regulation of blood sugar Increased blood glucose levels trigger the pancreas to secrete the hormone insulin into the bloodstream. Insulin promotes the uptake of glucose into the body's cells, where it is used for energy. Insulin also stimulates the liver and muscle cells to store excess glucose, further reducing glucose levels in the blood. As blood glucose levels begin to fall between meals, the pancreas secretes a different hormone called glucagon. Glucagon promotes the release of glucose into the bloodstream from the liver, which increases blood glucose concentrations. This allows cells to have steady access to glucose over time. Examples of Positive Feedback Mechanism Blood clotting When a blood vessel is injured, platelets release chemicals that attract more platelets, which release more chemicals, and so on. This process continues until the clot is large enough to stop the bleeding. Labor (Childbirth) During labor, the posterior pituitary gland releases oxytocin, which stimulates muscle contractions that push the baby through the birth canal Fruit Ripening Fruit ripening in a tree by the release of ethylene gas which stimulates ripening in the other fruits nearby as well