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UNIT 7: Systems involved in relationship: nervous and endocrine system
1- Coordination systems
The relationship function is the ability to perceive what is going on in both the environment
and the inside of the organism itself, and the ability to produce responses.
There are two coordination systems which regulate all the human body funtions:
A – The nervous system
B – The endocrine system
Differences between the nervous system and the endocrine system:
The nervous system
The endocrine system
Picks up information and produces answers
Controls important functions as growth
Its answer is rapid and does not last long
Its answer is slow and lasts long
It consists of neurons which transmit It consists og endocrine glands which release
information through electrical and chemical hormons
signals.
A -Nervous system:
It follows the following pathway:
Stimulus→Repectors→Effectors→Answer
There are two types of stimuli:
External stimuli: Chemical sustunces (that can be tasted or smelled), pressure,
temperature, light.
Internal stimuli: Thirst, need to urinate, headache,...
Sentitive receptors: They are neurons which detect external stimuli. Sensitive receptors
are grouped in the sense organs ans their main characteristics are:
- Are very specific for every type of stimulus.
- They are stimulated as long as the stimulus exceeds a threshold of excitation.
-They can suffer adaptation if the stimulus is persistent (do not respond).
- A very intense stimulus can cause pain or destruction of receptors.
There are different types of sentive receptor, according to the stimulus:
-Mechanoreceptors: Stimuli involved: pressure, touch (by receptors locatated in the skin),
vibrations and balance (by receptor located in the ear).
Hearing is the process by which humans use their ears to perceive sounds. The hearing process
occurs as follows: sound waves enter the pinna, travel through the ear canal and impacts on the
eardrum, and causes it to vibrate. Then, the three ossicles bones vibrate and transmit this sound to
the endolymph within the cochlea. The movement of the endolymph provokes the vibration of the
receptors (covered with cilia) which transmit the information to the brain through the auditory
nerve .
The balance occurs as follows: The three canals are at right angles to each other. The fluid in these
canals rotates according to the position of the head, provoking that receptors located in these
canals vibrate. The information is transmited to the brain through a nerve .
- Thermoreceptors: They are located in the skin (dermis). Stimulus involved: temperature
- Chemorecptors: They are in nose and tongue. Stimuli involved: chemical susbtances in air or
dissolved in water.
Nose:
Tongue:
-Photoreceptors: These receptors are called cones (detect colors) and rod cells (detect shapes).
They ar located in the eyes (retina). Stimulus involved: the light.
Altough our eyes collect visual information, actually we “see” with our brains. The lens
allows the image to be focused onto the retina that contains photoreceptor cells (cones and
od cells) that convert light into electrical signals. This signals travel to the brain through the
optic nerves.
The blind spot is a phenomenom due to lack of receptors (rods or cones) just where the
optic nerve leave the eye..
Nervous system composition:
 Neurons: transmit electrical signals (nervous impulse). There are three types of neurons:
-Sensory neurons: They are in the sense organs. They are receptors that
recieve information from outside.
-Interneuron: They are in the spinal cord. They take the nervous impulse
from the sensory neuron to the motor neuron.
-Motor neurons: They take the information to the effectors (muscles and
glands) to produce an answer.
 Glial cells: Astrocytes (feed the neurons), Schwann cells (insulate the neurons through a
compound called myelin) and microglial cells (defend the neurons against pathogen agents).
 Nerves: Group of axons from different neurons
effector: a bodily organ (as a gland or muscle) that becomes active in response to
stimulation
In vertebrates, the mechanism of comunication between two neurons is called synapses. The
electrical signal goes through the neuron membrane, from the cell body to the axon terminals,
jumping from one node of Ranvier to another. There is not a phisical contact between two neurons,
so once the signalhas reached the axon terminal, it releases subtances calles neurotransmitters to
the synaptic gap. Teses subtances will get to the following neuron dendrites provoking a new
electrical signal which will travel on its surface.
The nervous impulse meets three characteristics:
-
It is necesary that the stimulus exceeds a threshold of excitation for the nervous
impulse to starts.
Follows the “all or none law”: It means that neurons either respond to a stimulus
completely or not at all.
They propagate by “saltatory conduction” along axons from one node of
Ranvier to the next node, increasing the velocity of conduction.
Nervous system structrures in human beings:
Voluntary actions:
Example: You see a ball and kick it. Scheme of the pathway for this voluntary action:
Stimulus (Light) →Photoreceptors (on retin) in eyes (sense organ) →Craneal nerve →Brain (The
information is processed and the answer is decided) → Spinal cord → spinal nerves → effector
(muscles) → answer (kick the ball).
Involuntary actions (reflex actions):
Example: The doctors hits a patient’s knee with a small object and the patient extends his knee
involuntarily. Scheme of the pathway for this involuntary action:
Stimulus (pressure) →Mecanoreceptors in skin (sense organ) → spinal nerves → Spinal cord →
Spinal nerves → effector (muscles) → answer (to extend the knee).
B-Endocrine system
Is the cordination system formed by glands which release to the blood substances called hormones.
The hormones act on different cells of the body called target cells.
Gland
Hypothalamus
Pituitary gland
Hormone produced
Hypothalamic hormone
Pituitary gland
Thyroid
Parathyroid
Thyroxine
Parathyroid hormone
Pancreas
Insulin and glucagon
Adrenal glands
Adrenaline
Ovary
progesterone
Testis
Testosterone
Effect on the body
Control the pituitary gland
Regulate manu other endocrine
glands
Regulates the metabolism
Regulates the level of calcium
in blood
Regulates the level of sugar in
blood
Help the body deal with a
danger
Responsible for the secundary
sex characteristics in females
Responsible for the secundary
sex characteristics in males
2- Locomotor system
Locomotor system, which involved in relationship function, allows the body to move.
It consists of the muscular system and the skeletal system.
A)-Skeletal system: It’s formed by bones and joints.
Functions:
-Provides support to the body.
-Protects internal organs (such as brain, heart, spinal cord...).
-Produces blood cells.
Joints: are connections between the bones. There are three types of joints:
-Inmovable joints: i.e. Skull bones
-Semi-mobile joints: i.e. Between the vertebrae (Intervertebral discs)
-Movile joints: i.e. elbow, shoulder,...(Thery are connected each other through
ligaments (Ligaments are fibers that bind bones
together)).
Bone structure:
B)- Muscular system: is formed by muscles and tendons.
Body muscles
Tendons: are collagen strings that attach muscles to bones (when the muscle contracts, pulls the
bone).