The major glands in the endocrine system are shown in Figure 4. The pituitary secretes hormones that influence our responses to pain as well as hormones that signal the ovaries and testes to make sex hormones.
The pituitary gland also controls ovulation and the menstrual cycle in women. Other glands in the endocrine system include the pancreas , which secretes hormones designed to keep the body supplied with fuel to produce and maintain stores of energy ; the pineal gland , located in the middle of the brain, which secretes melatonin , a hormone that helps regulate the wake-sleep cycle; and the thyroid and parathyroid glands , which are responsible for determining how quickly the body uses energy and hormones, and controlling the amount of calcium in the blood and bones.
The body has two triangular adrenal glands , one atop each kidney. The adrenal glands produce hormones that regulate salt and water balance in the body, and they are involved in metabolism, the immune system, and sexual development and function. The most important function of the adrenal glands is to secrete the hormones epinephrine also known as adrenaline and norepinephrine also known as noradrenaline when we are excited, threatened, or stressed.
Epinephrine and norepinephrine stimulate the sympathetic division of the ANS, causing increased heart and lung activity, dilation of the pupils, and increases in blood sugar, which give the body a surge of energy to respond to a threat.
The activity and role of the adrenal glands in response to stress provide an excellent example of the close relationship and interdependency of the nervous and endocrine systems. A quick-acting nervous system is essential for immediate activation of the adrenal glands, while the endocrine system mobilizes the body for action. The male sex glands , known as the testes , secrete a number of hormones, the most important of which is testosterone , the male sex hormone.
Testosterone regulates body changes associated with sexual development, including enlargement of the penis, deepening of the voice, growth of facial and pubic hair, and the increase in muscle growth and strength.
The ovaries , the female sex glands , are located in the pelvis. They produce eggs and secrete the female hormones estrogen and progesterone. Estrogen is involved in the development of female sexual features, including breast growth, the accumulation of body fat around the hips and thighs, and the growth spurt that occurs during puberty.
Both estrogen and progesterone are also involved in pregnancy and the regulation of the menstrual cycle. Recent research has pinpointed some of the important roles of the sex hormones in social behaviour.
Dabbs, Hargrove, and Heusel measured the testosterone levels of men who were members of 12 fraternities at two universities. They also obtained descriptions of the fraternities from university officials, fraternity officers, yearbook and chapter house photographs, and researcher field notes.
The researchers correlated the testosterone levels and the descriptions of each fraternity. They found that the fraternities with the highest average testosterone levels were also more wild and unruly, and one of these fraternities was known across campus for the crudeness of its behaviour.
On the other hand, the fraternities with the lowest average testosterone levels were more well behaved, friendly and pleasant, academically successful, and socially responsible. Banks and Dabbs found that juvenile delinquents and prisoners who had high levels of testosterone also acted more violently, and Tremblay and colleagues found that testosterone was related to toughness and leadership behaviours in adolescent boys.
Although testosterone levels are higher in men than in women, the relationship between testosterone and aggression is not limited to males. Studies have also shown a positive relationship between testosterone and aggression and related behaviours such as competitiveness in women Cashdan, Keep in mind that the observed relationships between testosterone levels and aggressive behaviour that have been found in these studies do not prove that testosterone causes aggression — the relationships are only correlational.
Recent research has also begun to document the role that female sex hormones may play in reactions to others. The somatic nervous system is involved in the movement of our skeletal muscles. The autonomic nervous system — which as the name suggests is involved in a number of typically automatic, regulatory functions — is then further split up into the sympathetic nervous system SNS and the parasympathetic nervous system PNS.
These two systems are activated in times of arousal or recovery. To facilitate the rest and digest response, the PNS alters a number of functions in the body to help it recover. These functions are largely mirror opposites of SNS activation, and include: stimulation of the digestive and immune systems, decreases in pupil size and heart rate, and contraction of the lungs.
These processes optimize functions in the body at rest, and allow it to focus on maintenance. These functions appear in not only moments of life-or-death, but also with more common emotional responses. Imagine that you are going through a haunted house and a ghost jumps out at you.
Neurons feature many thin projecting fibers called axons, which penetrate deep into tissues. They are able to communicate with other cells by chemical or electrical means at synapses. Neuronal function is supported by neuroglia, specialized cells which provide nutrition, mechanical support, and protection. Major elements in neuron-to-neuron communication : Electrical impulses travel along the axon of a neuron.
When this signal reaches a synapse, it provokes release of neurotransmitter molecules, which bind to receptor molecules located in the the target cell. In most animals, including humans, the nervous system consists of two parts: central and peripheral. The central nervous system CNS is composed of the brain, spinal cord, and cerebellum.
The Human Nervous System : The major organs and nerves of the human nervous system. The CNS is comprised of the brain, cerebellum and spinal cord. Remaining neurons, and associated cells, distributed throughout the body form the PNS. The nervous system has three broad functions: sensory input, information processing, and motor output.
In the PNS, sensory receptor neurons respond to physical stimuli in our environment, like touch or temperature, and send signals that inform the CNS of the state of the body and the external environment. This sensory information is then processed by the CNS, predominantly by the brain. After information is processed, motor neurons return signals to the muscles and glands of the PNS, which responds with motor output.
Central neurons, which in humans greatly outnumber the sensory and motor neurons, make all of their input and output connections with other neurons. The connections of these neurons form neural circuits that are responsible for our perceptions of the world and determine our behavior. Along with neurons, the nervous system relies on the function of other specialized cells called glial cells, or glia, that provide structural and metabolic support to the nervous system.
The primary function of the nervous system is to coordinate and control the various body functions. The nervous system has three overlapping functions based on the sensory input, integration, and motor output.
The nervous system is a highly integrated system. Sensory input comes from the many sensory receptors that monitor changes occurring both inside and outside the body.
The total sum of the information gathered by these receptors is called sensory input. Long projection called axons from neurons carries nerve impulses directly to specific target cells. Schwann cells wrapped around the axon are called glial cells. They create a myelin sheath which allows the nerve impulse to travel very rapidly through the axons. A cell that receives nerve impulses from a neuron may be excited to perform a function, inhibited from carrying out an action, or otherwise controlled.
In this way, the information transmitted by the nervous system is specific to particular cells and is transmitted very rapidly. In fact, the fastest nerve impulses travel at speeds greater than meters per second!
Compare this to the chemical messages carried by the hormones that are secreted into the blood by endocrine glands. As you might predict, the human nervous system is very complex. The CNS includes the brain and spinal cord, and the PNS consists mainly of nerves, which are bundles of axons from neurons.
The PNS is divided into two major parts, called the autonomic and somatic nervous systems.
0コメント