Biology B10 (The Nervous System)

B10.1

The internal environment is the conditions inside the body. Homeostasis is the act of balancing and keeping processes inside the body as constant as possible, to provide optimum conditions so that enzymes can function. Internal conditions like blood glucose concentration, water content, and body temperature are controlled. Examples of homeostasis includes exercising  warming the muscles, blood glucose rising after a meal, and when hot, losing salt and water through sweating.

Receptors are special cells detecting changes in the environment (stimuli). Coordination centres are areas receiving and processing information from the receptors, sending out signals, and coordinatr a response of the body. Effectors are muscles or glands bringing about the response: muscles respond by contracting and glands by secreting a substance.

B10.2

The nervous system helps find food, find mates, and avoid danger.

Once a sensory receptor detects a stimulus, it is sent as an electrical impulse passing along neurons found in nerves. The impulse travels along the neuron, until it reaches the CNS (the brain and spinal cord). Cells carrying information from the sense organs to the CNS are sensory neurons. Motor neurons carry information from the CNS to the rest of the body and the effectors respond.

stimulus - receptor - coordinator (CNS) - effector

The ears' receptors are sensitive to sound and change in position for balance, the eyes' receptors are sensitive to light, the skin's receptors are sensitive to pressure, pain, temperature change, and touch; and the nose and tongue's receptors are sensitive to chemicals for food and taste.

Required practical: Investigate how quickly nerve impulses travel in the body. Use the ruler drop test/digital sensors to measure how quickly you respond to a visual stimulus. Listening to music, drinking cola, or talking on the phone affect reaction time. Don't drink or eat in the laboratory.

B10.3

Reflexes are automatic responses. They help avoid danger and take care of bodily functions.

A reflex arc is the path of an electrical impulse from the receptor along the sensory neuron to the CNS, then along a relay neuron, along the motor neuron, and then the effector.

There are junctions between neurons, called synapses, where impulses travel across. Diffusion of the chemical is slower than the electrical impulse in the neurons. The impulse arrives in the neuron, chemicals are released into the gap between neurons (chemicals that are released cross the synapse and arrive at the receptor sites on the next neuron), and they attach to the surface of the next neuron, setting up a new electrical impulse. 

stimulus - receptor - sensory - relay - motor - effector - response

For example, when touching a hot object: a receptor in the skin is stimulated and the impulse from it passes along a sensory neuron in the CNS. When the impulse from the sensory neuron arrives at the synapse with a relay neuron, a chemical is released ad the chemical diffuses across the synapse to the relay neuron where it sets off a new impulse…