The various organs of the body must work in coordination if an organism is to survive effectively in the environment. To achieve this, the body has a series of receptors which pass information about the environment to a coordinating center called the central nervous system or CNS. The CNS is made up of the brain and the spinal cord. After receiving the information, the CNS directs a response in the appropriate effectors.
The nervous system of mammal consists of brain, spinal cord and the nerves. Together, they coordinate and regulate body functions.
The structure of central nervous system
- CEREBELLUM: the cerebellum is the guru of skilled, coordinated movement and is involved in some learning pathways.
- CEREBRUM: control most of our body functions, including the mysterious state of consciousness, the senses, the body’s motor skills, reasoning and language.
- HYPOTHALAMUS: It monitors numerous bodily functions such as blood pressure and body temperature, as well as controlling body weight and appetite.
- Medulla: The medulla or medulla oblongata is an essential portion of the brain stem which maintains vital body functions such as the heart rate and breathing.
- Thalamus: It helps to control the attention span, sensing pain and monitors input that moves in and out of the brain to keep track of the sensations the body is feeling
- Midbrain: help regulate body movement, vision and hearing.
- Pons: It interprets information that is used in sensory analysis or motor control. It also creates the level of consciousness necessary for sleep.
- Pituitary gland: secretes a number of hormones directly on to the blood which controls and regulates the activities of other endocrine glands
- Spinal cord
The spinal cord is a long, fragile tube like structure that begins at the end of the brain stem and continues down almost to the bottom of the spine.
The spinal cord consists of nerves that carry both incoming and outgoing messages between the brain and the rest of the body.
The spinal cord consists of grey and white matter. The grey matter contains dendrites and cell bodies. The front or ventral root contains motor nerves, which transmit information from the brain or spinal cord to muscles, stimulating movement. The back or dorsal root contain sensory nerves, which transmit sensory information from other parts of the body through the spinal cord to the brain. The surrounding white matter contains columns of axons that carry sensory information to the brain from the rest of the body .and columns that carry impulses from the brain to the muscles.
- Nerves and neurons
The nervous system is connected to all parts of the body by nerves.Nerves Nerves are made from hundreds of microscopic units called neurons. Neurons bundle together to form nerve.Neurons A single nerve cell is called neuron. A nerve fiber is a long protoplasmic extension of the cell body of neurons. It serves to transmit impulses. A nerve is a collection of nerve fibers. Neuron consists of three main parts:
- Cell body: each neuron has a cell body consisting of nucleus surrounded by a little cytoplasm and has cell membrane.
- Axon: has single fiber that extends from the cell body and long and un branched. They are surrounded by fatty structure called myelin sheath.
- Dendrites: from the cell body arise fibers which are branched to small, fine fibers called dendrites. They make contact with other nurons.
Types of neurons
- Sensory neurons:
- A receptor neurons,
- Transmits impulses from the sense organ (receptor) to the CNS.
- Motor neurons:
- Effectors neurons.
- Transmits impulses from the CNS to the effectors.
- Relay neurons:
- Connects sensory neurons to motor neurons.
The components and of the coordinate behavior
There are five main components:
- Stimulus: stimulus is n event in the surrounding or in the internal part of which triggers response.
- Receptors: sense organ which detects stimulus. With receptors it passes the information about the changes to the coordinator.
- Coordinator: central nervous system receives the message and directs to the appropriate effectors.
- Effectors: it is a tissue or an organ which respond to the stimuli.
- Response: it is the behavior provoked by the originl stimulus.
Reflex actions involve messages being transmitted from the sensory neuron to the motor neuron without involving the conscious part of the brain.A reflex arc is the shortest pathway by which impulses travel from the receptor to the effectors in a reflex action.
Types of reflex action
- Spinal reflex –The inborn reflexes mediated by control centers in the spinal cord; although the central pathway involves only spinal cord segment control.
- Cranial reflexes – The inborn reflexes by control centers in the brain; the pathway usually involve cranial and cervical spinal nerves.
The sequences of events in a reflex action( touching hot object)
- When the hand accidentally touches hot object, pain receptors in the skin will sense the stimulus and produce a nerve impulse.
- The nerve impulse is transmitted via the sensory neuron and then across a synapse to interneuron in the grey matter of spinal cord.
- From the interneuron, the impulse crosses a synapse gain to the motor neuron.
- The motor neuron sends the impulse to the effector organ, which is the biceps.
- The biceps contract and the hand withdraw from the hot object.
The human eye
Eye is the one of the most important organ (receptor) sensitive to light. It provides us information on dimension, colors and distance of the objects in the environment.
The structure of eye
Cornea: It is white, hard and transparent because it does not contain any blood vessels. As it is situated in front of the eye, it can be seen and touched from outside. It is curved and convex in shape. It is the part through which light rays enter the eye.
Aqueous humor: The space between the cornea and the pupil is called the anterior chamber, and is filled with a transparent substance called aqueous humor.
Iris: It is a circular muscle tissue of dark brown color. The iris is opaque. It controls the amount of light that enters the eye, by either constricting the pupil, or expanding the pupil.
Pupil: It is through the pupil, light rays enter the eye. The size of the pupil is controlled by the constriction and relaxation of the iris.
Lens: It is a rubbery, bean-shaped, transparent and crystalline lens, which bends the light rays onto the retina. It is surrounded by a circular mass of smooth muscles called the ciliary muscles.
Vitreous humor: The space between the lens and the retina is called the oosterior chamber and is filled with a transparent substance called vitreous humor.
Retina (Innermost layer): The basic function of the eye is to convert the light waves into neural signals that the brain can process. This function is carried out in the retina.
Optic nerve: This carries message to the brain. As the optic nerve exits the eye, it leaves a small area of the retina without the receptor cells. This area is called the blind spot.
Accommodation of the eye
- Viewing distance image- ciliary muscles relax, the suspensory ligaments become taut pulling the lens outwards. As the result the lens becomes thinner. This will in turn, increased the focal length hence enable you to view distance object.
- Viewing near object- ciliary muscles contract, the suspensory ligaments become slacken. Hence there is no pulling force to pull the lens outward. As the result the lens becomes thicker and this will in turn, decreases the focal length hence enables you to view near object.
The pupil reflex in response to bright and dim light
The way the iris in our eye adjusts the size of the pupil in response to bright or dim light is also a reflex action.
In bright light:
- Radial muscles of the iris relax.
- Circular muscles of the iris contract.
- Less light enters the eye through the contracted pupil.
In dim light:
- Radial muscles of the iris contract.
- Circular muscles of the iris relax.
- More light enters the eye through the dilated pupil.
- A hormone is a chemical substance produced by endocrine gland and directly release to the blood streams which carries it to one or more specific target organ in the body where they alter the activity of the organ.
- A hormone may reach all parts of the body, but only specific target cells respond to specific hormones.
- A given hormone traveling in the bloodstream elicits specific responses from its target cells, while other cell types ignore that particular hormone.
Different endocrine glands in human body
- The Pituitary Gland
- A sort of master gland. It is a cherry-sized endocrine gland
- The hormones it secretes affect the growth and secretion of other endocrine glands.
- It produces number of hormones.
a. Growth hormone – controls the rate of the bone growth.
b. Thyroid- Stimulating Hormone (TSH) – stimulates the thyroid gland to secrete thyroxin.
c. Gonads- Stimulating Hormone (GSH) – stimulates the gonads to secrete sex hormones.
- Anti- Diuretic Hormone(ADH) – promotes the absorption of water in kidneys and reduce the volume of urin.
- Thyroid gland
- It is present in front of the larynx in the throat
· It secrets a hormone Thyroxin- Target organs – primarily skeletal, muscle tissue stimulates metabolic rate for growth increases oxygen consumption and cell metabolism
- It is present below the stomach
- It secrets hormone
– stimulates growth and development in utero and child- decreases blood glucose (metabolic pathway)
- Glucagon: – secreted by the Alpha Cells- promotes higher blood glucose
Diabetes mellitus – signs and symptoms
- High blood glucose.
- Frequent urination
- Excessive thirst
- Unexplained weight loss
- Extreme hunger
- Sudden vision changes
- Tingling or numbness in the hands or feet
Treatment: diet control and take regular doses of insulin via injection.
Adrenal Glands (on top of kidneys)
hormones in the fight/fright responsea) Glucocorticoids – raises glucose levels in the blood, stimulates glucose production by cellsb) Epinephrine – complement supply from the sympathetic system function is to give the body an energetic boost, increase metabolic rate, dilates bronchioles in the lungs, increases heart rate, etc. Target – most systems of the body· The overall effect is to prepare the body for FIGHT, FLIGHT and FRIGHT.
- Male gonads – testes (pelvic region on men)
- Testosterone, maintain secondary sexual characteristics, stimulate sperm production
- Female gonads – ovaries (pelvic region of women)
- a) Estrogen and progesterone, maintain secondary sexual characteristics, regulate reproductive cycle