Download unit 5: the nervous and endocrine systems

UNIT 5: THE NERVOUS AND ENDOCRINE SYSTEMS.Introduction.To survive living things need nutrition, reproduction and relation (de second vital
function).
The objective of the function of relation is: adapt to change and coordinate different
parts of the body.
Remember the definition of relation: It is the capacity of the living things to detect
stimuli in the environment and to respond correctly to them.
Analyse this definition:
What is a stimulus? It is a change in the environment like temperature, light, a sound, a
taste, a smell, etc, that provoke a response in the organism.
What senses stimuli? Some special structures called receptors. There are different types
of receptors, the most important are:
- Mechanoreceptors: include the receptor of touch, the ear and the receptor of
balance.
- Thermoreceptors: detect changes in the temperature and are located in the skin.
- Chemoreceptors: catch information from chemical changes. These include taste
and smell receptors.
- Photoreceptors: detect light stimuli, and they are found in the eyes.
- The pain receptor
What analyses stimuli and do a responds? There are two systems:
- The nervous system
- The endocrine system
What responds? The effectors organs respond. There are two types:
- The muscles (the locomotory system), in this case the response is a movement.
- A gland and the response is a secretion of substances.
The nervous system.Function:
- Receive the information of the receptors, analyse this information and make a
correct response.
- Transmits instructions to the effectors.
- Coordinates the functions of our boy’s organs.
- Carries out intellectual and mental processes.
- Transmits emotions and feelings.
Components:
The nervous system is mainly made by special cells called neurons. They are a special
shape, star shape, and they have the following parts:
- A cell nucleus surrounded by cytoplasm.
- The neuronal body or soma.
- The dendrites, short and numerous branches.
- The axon: a long fibre with small branches at the end
- The myelin pod.
Neurons can’t divide like other cells. When neurons die they are not replaced by other
neurons.
Neurons aren’t joined together one by one, between one neuron and the next there is a
space.
Function of a neuron:
Neurons create and transmit nerve impulses from their dendrites to their axons (it is like
an electrical signal).
The information passes from one neuron to another without physical contact. This
happen by a special process called synapses.
At the end of the axon there are very small vesicles which contain neurotransmitters.
Impulses are transmitted across synapses by neurotransmitters.
Types of neurons:
- Sensory neurons: transmit the information from the receptors to the central
nervous system (CNS).
- Motor neurons: transmit the response from the central nervous system to the
effectors.
- Relay neurons: connect sensory neurons with motor neurons.
Parts of the nervous system:
- The central nervous system (CNS):
. The brain which includes the cerebrum, the cerebellum, the hypothalamus and
the brain stem.
. The spinal cord.
- The peripheral nervous system (PNS):
. The somatic nervous system.
. The autonomic nervous system, which includes the sympathetic system and the
parasympathetic system.
The central nervous system.It is a very important part in our nervous system, therefore it has a double mechanism of
protection:
1) A skeleton: the skull or the cranium that protect the brain, and the spinal column
that protects the spinal cord.
2) A system with three membranes called meninges that surround the brain and the
spinal cord. Between the meninges there is a fluid called the cerebrospinal fluid.
There are two types of material in the central nervous system:
- Grey matter: this is made of neuronal bodies and dendrites.
- White matter: this is made of axons covered in myelin.
The spinal cord: It is a cylinder of nerve tissues which runs down the central canal in the
spine.
Grey matter is found in the centre of the spinal cord, and it is shaped like the wings of a
butterfly. White matter is found on the outside of the grey matter.
In the spinal cord nerves begin which go of all the parts of the body except the head.
Functions of the spinal cord:
- It produces reflex actions: they are actions that happen automatically in response
to stimuli without the participation of the brain.
- It carries sensory impulses to the brain and motor signals from the brain to the
effectors organs.
The brain.It is found inside the skull or the cranium. It is made of four main areas: the cerebrum,
the cerebellum, the hypothalamus and the brain stem.
- The cerebrum: Its main characteristics are:
. It is the largest party of the brain and the most important organ in the nervous
system.
. It is made of grey matter on the outside and white matter on the inside.
. The outer layer of the cerebrum is the cerebral cortex and it is made of grey
matter.
. The cerebrum is responsible for all voluntary activity in the body.
. It has a lot of surface and expanse thanks to a lot of circumvolutions.
. The functions of the cerebrum are:
 To process information from sensory organs (except from the balance
organ).
 To work out responses from effectors organs.
 To regulate the functions of every part of the nervous system.
 To control higher nerve functions like memory, reasoning, intelligence,
conscience and will.
- The cerebellum: Its characteristics are:
. It is located in the back part of the brain.
. It is made of grey matter on the outside and white matter on the inside.
. Functions of the cerebellum are:
 Processing information from the ears related to balance.
 Coordinates the voluntary movements in our body like walking, writing,
playing an instrument or riding a bike.
- The hypothalamus: This is an area of the brain between the brain stem and the
cerebrum. It helps control sleep, body temperature, thirst, hunger, etc.
- The brain stem: This is where the spinal cord joins the brain. The ascendant
nerve tracts from the spinal cord and the descendant ones from the brain pass
through the brain stem. There they cross over so that the right hand side of the
side of the body and vice versa. The brain stem controls vital functions like
heartbeat, blood pressure, breathing, etc.
The peripheral nervous system (PNS).The peripheral nervous system is responsible for connecting all the sensory receptors
and effectors with the nerve centres. It is made for nerves and ganglia.
Types of nerves:
- According to location :
 Cranial nerves: they enter and leave the brain. There are 12 pairs.
 Spinal nerves: they emerge from the spinal cord. There are 31 pairs.
- According the information that they transmit:
 Sensory nerves which transmit information from the sensory organs.
 Motor nerves which send commands to the effectors.
 Mixed nerves: they contain both motor and sensory axons. A mixed
nerve can conduct impulses in both directions.
There are two parts to the peripheral nervous system:
1) The somatic nervous system: It controls the muscular system that realises
the voluntary movement.
It is responsible for:
 Receiving information from external stimuli.
 Receiving information from the position of our body.
 Transmitting signals for voluntary muscle contractions.
2) The autonomic nervous system: It is also called the involuntary nervous
system. It is responsible for regulating and controlling involuntary body
functions.
The autonomic nervous system has two parts:
 The sympathetic system
 The parasympathetic system
Both are antagonistic, the sympathetic nervous system controls the majority
of the organs in the body when they work under stress, and the
parasympathetic nervous system is responsible for maintaining the body’s
organs and systems when the body is at rest or working slowly.
Function of the nerve system: the nerve actions.The nerve system produces two types of actions:
1) Reflex actions: These are quick and automatic and the brain is not involved.
Sensory information only reaches the spinal cord, so a response is rapid and
automatic. They take place when a rapid response is required, for example,
pulling your hand away when you burn it. In reflex actions, the three types of
neurons are involved: sensory, relay and motor neurons.
2) Voluntary actions: These are than we do consciously. In a voluntary action,
sensory information reaches the brain, and the brain modifies the response.
THE ENDOCRINE SYSTEM.It is a collection of endocrine glands. They are called endocrine because they secrete
internally. The substances they produce (hormones) are secreted directly into the
bloodstream.
Hormones travel through the bloodstream to the cells. Although all hormones reach all
tissues, each one acts only on specific cells, called the target cells.
Hormones are secreted in very small quantities and if there is more or less than the
necessary characteristic illness appear.
Hormones produce long duration and slow responses.
The endocrine system controls functions like metabolism, growth or the reproduction.
The main endocrine glands are:
 The pituitary gland that releases a lot of very important hormones like:
oxytocin, growth hormones, antidiuretic hormone (ADH), etc.
 The thyroid that produces thyroxin.
 The Parathyroid that releases parathyroid hormone.
 The pancreas that produces insulin and glucagon.
 The adrenal glands that releases adrenaline, corticoids and aldosterone.
 The testicles that produce androgens.
 The ovaries that produce oestrogen and progesterone.