The Nervous System
The Nervous System
The nervous system is comprised of two main parts, the Central Nervous System (CNS) and the Autonomic Nervous System (ANS). Volunary actions of the chicken are controlled by the CNS, while involuntary actions such as organs, digestion, breating, blood vessels and glands are controlled by the ANS. The primary function of the nervous system are to integrate the functions of the body. Sensory organs detect the various stimuli in the bird’s environment that it reacts to.
The brain is located in the head and is well protected by the bones of the cranium. The brain consists of a number of parts, which in turn consist of various special cells that have the ability to detect, recognise, remember and direct. Thus the brain is the control center for the many functions and activities of the many systems, organs and tissues that make up the bird’s body.
The parts and major regions that make up the avian brain are as follows:
There is a very small gland called the pituitary gland which is associated with the hypothalamus. This gland is an endocrine gland. It is often called the 'master' gland because it controls most of the endocrine system.
The spinal cord, as the name suggests, is a cord of nerve tissue that extends from the medulla oblongata of the brain along almost the full extremity of the vertebral column through the canal provided for that purpose. The spinal cord and the brain constitute the Central Nervous System (often referred to as the CNS). Like the brain, the spinal cord is well protected, firstly by its spinal fluid and the sheath that encloses it, all of which is fully enclosed within the bones of the vertebral column. The various nerves that provide for the control of the various systems, organs and tissues of the body leave the spinal cord through appropriate openings located in the joints between the different vertebrae.
If at any time the spinal cord is broken, the connection between the brain and what it controls will be broken and because of this effected parts will be lost. For example, a break of the spinal cord in the lower back will result in the loss of control (paralysis) of the legs and other functions that take place below the break.
The neuron (nerve cell) consists cell body with at least one elongated projection that extends from it. Contained in this cell body is a nucleus. The projections, called axons if they are long or singular, dendrites if they are short and branched, are part of the cell's cytoplasm. Nerve endings or receptors at one end carry the sensors that respond to the stimuli, while on the opposite side, the stimulus is transferred ultimately to the brain. The nerve endings are the means by which stimuli are perceived or control exercised. The remainder of the nerve cell acts as a message carrier to the brain in much the same way that telephone line carries a message between two telephones. These messages are in the form of very weak electrical currents.
The sensory organs receive the various stimuli from the bird’s environment. Depending on the mode of action of the stimuli, special endings on the nerves will perceive that stimulus. The sensory organs include:
Diagram 12 shows the structure of the chicken ear
The ears of the fowl are located on each side of the face behind the eye. While the ear is very similar to that of mammals, there are some differences. The fowl’s ear does not have a pinna, ear flap or lobe and the three bones of the mammalian middle ear have been replaced by a single structure of bone and cartilage.
The fowl ear consists of three main segments:
The middle ear is separated from the outer ear by the tympanic membrane which is stretched across the inner end of the ear canal in a similar way to that of a percussion drum top. A rod of cartilage replaces the three bones of the mammalian ear connecting the tympanic membrane to the inner ear and bone called the columella.
The inner ear consists of the cochlea in which special nerve endings are located that receive the sound waves for transmission to the area of the brain associated with hearing. Also located in the inner ear are the semicircular ducts that are associated with the maintenance of balance. A special duct connects the middle ear with the roof of the mouth with the ducts from each ear joining before entering the mouth. The function of this duct is to regulate the air pressure in the middle ear to that of the outer ear (the environment) to prevent air pressure injury to the tympanic membrane.
The fowl hears by sound waves that enter the outer ear canal and apply pressure in waves on the tympanic membrane. The wave-like nature of sound causes the tympanic membrane to vibrate. This vibration is transmitted by the columella to the cochlea where special nerve endings receive it and transmit it by the auditory nerve to the brain where it is recognized as sound.
The olfactory nerve of chickens is quite underdeveloped. This is the nerve associated with smell. It doesn't seem to affect a chicken's choice of food if removed.
A chicken's taste buds are located on the back of the tongue and floor of the mouth. They contain nerve endings from the glossopharyngeal nerve. Small quantities of the chemicals of taste are recognized by the taste buds and this information is transferred to the appropriate receptors of the brain. A chicken's sense of taste is weaker in the dry state than in the liquid state. Due to this, a chicken is more likely to reject something based on taste when it is in the water instead of when it is in the food.
The next section will discuss the excretory system.
The brain is located in the head and is well protected by the bones of the cranium. The brain consists of a number of parts, which in turn consist of various special cells that have the ability to detect, recognise, remember and direct. Thus the brain is the control center for the many functions and activities of the many systems, organs and tissues that make up the bird’s body.
The parts and major regions that make up the avian brain are as follows:
- The forebrain which consists mainly of the cerebral hemispheres and the olfactory lobes. The hypothalamus and pituitary gland are located on the lower side of the forebrain.
- The midbrain which mainly consists of the optic lobes.
- The hindbrain which consists mainly of the cerebellum and the medulla oblongata.
There is a very small gland called the pituitary gland which is associated with the hypothalamus. This gland is an endocrine gland. It is often called the 'master' gland because it controls most of the endocrine system.
The spinal cord, as the name suggests, is a cord of nerve tissue that extends from the medulla oblongata of the brain along almost the full extremity of the vertebral column through the canal provided for that purpose. The spinal cord and the brain constitute the Central Nervous System (often referred to as the CNS). Like the brain, the spinal cord is well protected, firstly by its spinal fluid and the sheath that encloses it, all of which is fully enclosed within the bones of the vertebral column. The various nerves that provide for the control of the various systems, organs and tissues of the body leave the spinal cord through appropriate openings located in the joints between the different vertebrae.
If at any time the spinal cord is broken, the connection between the brain and what it controls will be broken and because of this effected parts will be lost. For example, a break of the spinal cord in the lower back will result in the loss of control (paralysis) of the legs and other functions that take place below the break.
The neuron (nerve cell) consists cell body with at least one elongated projection that extends from it. Contained in this cell body is a nucleus. The projections, called axons if they are long or singular, dendrites if they are short and branched, are part of the cell's cytoplasm. Nerve endings or receptors at one end carry the sensors that respond to the stimuli, while on the opposite side, the stimulus is transferred ultimately to the brain. The nerve endings are the means by which stimuli are perceived or control exercised. The remainder of the nerve cell acts as a message carrier to the brain in much the same way that telephone line carries a message between two telephones. These messages are in the form of very weak electrical currents.
The sensory organs receive the various stimuli from the bird’s environment. Depending on the mode of action of the stimuli, special endings on the nerves will perceive that stimulus. The sensory organs include:
- Eye(s) – for sight
- Ear(s) – for hearing and balance
- Olfactory organ – for smell
- Taste buds – for taste
Diagram 12 shows the structure of the chicken ear
The ears of the fowl are located on each side of the face behind the eye. While the ear is very similar to that of mammals, there are some differences. The fowl’s ear does not have a pinna, ear flap or lobe and the three bones of the mammalian middle ear have been replaced by a single structure of bone and cartilage.
The fowl ear consists of three main segments:
- The outer ear
- The middle ear separated from the outer by the tympanic membrane (ear drum)
- The inner ear which consists of the cochlea and the three semicircular ducts
The middle ear is separated from the outer ear by the tympanic membrane which is stretched across the inner end of the ear canal in a similar way to that of a percussion drum top. A rod of cartilage replaces the three bones of the mammalian ear connecting the tympanic membrane to the inner ear and bone called the columella.
The inner ear consists of the cochlea in which special nerve endings are located that receive the sound waves for transmission to the area of the brain associated with hearing. Also located in the inner ear are the semicircular ducts that are associated with the maintenance of balance. A special duct connects the middle ear with the roof of the mouth with the ducts from each ear joining before entering the mouth. The function of this duct is to regulate the air pressure in the middle ear to that of the outer ear (the environment) to prevent air pressure injury to the tympanic membrane.
The fowl hears by sound waves that enter the outer ear canal and apply pressure in waves on the tympanic membrane. The wave-like nature of sound causes the tympanic membrane to vibrate. This vibration is transmitted by the columella to the cochlea where special nerve endings receive it and transmit it by the auditory nerve to the brain where it is recognized as sound.
The olfactory nerve of chickens is quite underdeveloped. This is the nerve associated with smell. It doesn't seem to affect a chicken's choice of food if removed.
A chicken's taste buds are located on the back of the tongue and floor of the mouth. They contain nerve endings from the glossopharyngeal nerve. Small quantities of the chemicals of taste are recognized by the taste buds and this information is transferred to the appropriate receptors of the brain. A chicken's sense of taste is weaker in the dry state than in the liquid state. Due to this, a chicken is more likely to reject something based on taste when it is in the water instead of when it is in the food.
The next section will discuss the excretory system.
- Next page: The Excretory System
- Previous page: The Circulatory System
