Spinal Cord Reflex Arc Worksheet

Refer to the following diagram, which shows a cross-section of the spinal cord of a mammal: Sensory neurons transmit impulses from the receptor, and motor neurons transmit impulses to the effector. Normally when receptor X is stimulated, muscles Y and Z contract. Which one of the following circumstances will cause only muscle Z to contract when receptor X is stimulated?

• One interneuron is not functioning.

• Neither motor neuron is functioning.

• No reflex response is occurring.

• One motor neuron is not functioning.

Which one of the following combinations correctly compares a feature of the nervous system with a feature of the endocrine system?

• J. produces longer-lived messages | produces shorter-lived messages

• K. produces a slower response to a stimulus | produces a faster response to a stimulus

• L. transmits electrochemical messages | transmits chemical messages

• M. uses chemicals to detect a stimulus | uses hormones to detect a stimulus

The gills of a marine snail close when its skin is touched. Which one of the following combinations correctly identifies the receptor, the direction of transmission, and the effector in this reflex response?

• J. Skin cells, Sensory nerve to motor nerve, Gill muscles

• K. Gill cells, Sensory nerve to motor nerve, Skin tissue

• L. Skin cells, Motor nerve to sensory nerve, Gill muscles

• M. Gill cells, Motor nerve to sensory nerve, Skin tissue

When faced with a sudden and unexpected threat, the human body will often react by releasing adrenaline into the blood. Adrenaline is a

• neurotransmitter that increases the speed of nerve impulses.

• catalyst that increases the breakdown of glucose.

• hormone that increases blood pressure and breathing rate.

• protein that is a source of instant energy for muscle cells.

In 1877 the American biologist Joel Allen observed that the length of arms, legs, and other appendages of warm-blooded animals affected the rate at which they lost heat to the environment. Allen observed a consistent difference in the limb length of individuals in populations of the same species living in warm climates near the equator, in comparison with those living in cold climates further from the equator.

• J. In cold climates, animals need to conserve as much heat as possible and therefore have longer limbs.

• K. In warm climates, the larger the surface area of the limbs, the faster the animals lose heat to the environment.

• L. In warm climates, animals have longer limbs that increase their surface area and minimise heat loss.

• M. In cold climates, animals have shorter limbs and a larger surface area-to-volume ratio.

When a person eats a sugary meal, the pancreas detects an increase in blood glucose. The pancreas secretes the hormone insulin which causes muscle cells to take in glucose from the blood. Which one of the following statements is true? Mark only one oval.

• This is an example of a feedback mechanism because the insulin is transported around the body in the blood.

• This is not an example of a feedback mechanism because in people with diabetes, blood sugar is not controlled.

• This is an example of negative feedback because the muscle cells will reduce the blood glucose level.

• This is not an example of negative feedback because the message is hormonal and does not rely on nervous transmission.

Scientists at Washington University have recently discovered that odour receptors are found not only in the nose, but also in the lungs. When odour receptors in the nose detect chemicals such as cigarette smoke, they send a nerve impulse to the brain and the smell of the cigarette smoke is then sensed. Odour receptors in the lungs are called pulmonary neuroendocrine cells (PNECs). When PNECs detect chemicals such as cigarette smoke, they release hormones that cause the airways to constrict. In some people constriction of the airways results in an asthma attack. It is thought that people with asthma may have hypersensitive PNECs. Which one of the following statements is not consistent with this information? Mark only one oval.

• J. The airways of people with asthma would be constricted before they sense the smell of cigarette smoke.

• K. Hormones released by PNECs would travel through the bloodstream.

• L. Drugs that block hormone receptors in the airways could be used to treat asthma.

• M. The constricted airways will not return to normal until the smell can no longer be sensed.

A person detects the smell of hot food in the air as he passes a restaurant. Shortly afterwards he notices that the amount of saliva in his mouth has increased considerably. Which one of the following statements is correct?

• The smell of hot food is the sensor and the brain is the effector.

• The smell of hot food is the receptor and the nasal mucous membranes are the effectors.

• The smell of hot food is the reflex and the central nervous system is the effector.

• The smell of hot food is the stimulus and the salivary glands are the effectors.

Thyroxine is a hormone that is involved in the regulation of body temperature in human beings. Which one of the following responses will result from an increase in body temperature?

• An increased release of thyroxine, resulting in a decreased cell metabolism.

• A decreased release of thyroxine, resulting in a decreased cell metabolism.

• A decreased release of thyroxine, resulting in an increased cell metabolism.

• An increased release of thyroxine, resulting in an increased cell metabolism.

The graph below shows changes in the body temperature of an endotherm with time. Which one of the following accurately describes the regulatory mechanism shown in the graph?

• Negative feedback

• Positive feedback

• Thermoregulation

• Both J and L.