Coordination
NERVOUS COORDINATION IN
HUMANS
CONCEPTS:
1. Neurons
- The structure of Motor sensory and Relay neurons
- The roles Motor Sensory and Relay neurons
2. The Central Nervous System
- Meaning of the Central Nervous System
- Components of the Central Nervous System and their functions
- Describe the structure of spinal cord and brain
3. Peripheral Nervous System
- The meaning of Peripheral Nervous System
- Components of the Peripheral Nervous System and their functions
4. Reflex Action
- Understand the meaning of Reflex Action
- Describe the Neuronic pathway of the reflex action
- Distinguish simple reflex from conditioned reflex
CONCEPT OF NERVOUS SYSTEM
Nervous system consists of tissue, which conducts messages called Nerve impulses at high speed to and from all parts of the body.
The Nervous System is divided into the Central Nervous System (brain and spinal cord) and the Peripheral Nervous System. The Peripheral Nervous System can be divided into the voluntary nervous system, which is under voluntary control from the brain and automatic nervous system, which operates automatically (involuntarily). The system is divided into Sympathetic Nervous System (SNS) and Parasympathetic Nervous System (PNS). These act antagonistically from each other (oppositely)
I. THE CENTRAL NERVOUS SYSTEM
The Central Nervous System consists of the Brain and the spinal cord. Brain and spinal cord consists very delicate cells which are supported and protected as follows:
- Brain is enclosed with a tough bone called SKULL or CRANIUM next to the nervous tissues. Between the two is the ARACHNOID MEMBRANE. This includes a space and sub-arachnoid space, strands of connective tissues, blood vessels and Cerebral Spinal fluid. Most of these fluids forward to expand and occupy carities within the brain called the VENTRICLES. The blood vessels lie within it for the supply of Nutrients and Oxygen to the Nervous tissue. Also contain Lymphocytes to protect against infections.
THE SPINAL CORD
The spinal cord is the cylinder of nervous tissues running from the base of the brain down the back. The vertebra of the backbone protects it (Vertebral Column) and the meringues. It has a central core called H-zone. This region is filled with grey matter, which makes the region appear grey in color. The outer surface of grey matter composed of nerve cell bodies; dendrites and synapses surrounding a central canal contain cerebral spinal fluid. Around the grey matter is another layer of white matter containing nerve fibres whose fatty myelin sheaths give it its characteristic color.
a. Meninges, which consists Pia,matter membrane found beneath the cranium. Meninges consist of Pia matter and the space between Chira matter and Pia matter is called Arachnoid space, which is filled with fluid, called Arachnoid fluid.
Fig. Meninges of the brain (Dura matter, Arachnoid and Pia Matter)
b. Cerebral Spinal fluid surrounds the brain and therefore reduces friction of the brain and membranes.
THE MENINGES AND CEREBRAL SPINAL FLUID
Three layers of membrane called meninges surround the Central Nervous System and it is completely enclosed within the protective bones of the skull and vertebral column. The outer membrane forms the tough DURA MATTER which is attached to the skull and vertebrae and the inner membrane forms the thin PIA MATTER which lies….
Diagram of a spinal cord
THE FUNCTION OF THE SPINAL CORD
- It controls the reflex action
- It communicates the information from Peripheral Nervous System to the brain where the interpretation takes place
THE BRAIN
The human brain weighs about 1.5kgs and contains thousands of millions of neurons. It contains millions of nerve cells. It consists of nerve cell fibres.
The brain consists of the following parts:
- Medulla Oblongata
- Cerebellum
- Cerebrum
- Hypothalamus
- Pituitary gland
MEDULLA OBLONGATA
This region is concerned with many unconscious processes including:
- Regulation of blood pressure
- Body temperature
- Rate of heart beat
- Sneezing
- Breathing rate
CEREBELLUM (HIND BRAIN)
This is located at the back of the brain under cerebral hemisphere. It is very folded and has an outer region the cortex, which contains many nerve fibres and cell bodies. The Cerebellum is calledGyroscope of the body because it is concerned with balance and posture. Also it coordinates muscles during activities like walking, running, dancing and riding a bicycle. It receives these information from the organs of balance in the ears and thus concerned with control and precision of all movements involving voluntary muscles. Also cerebellum controls the autonomic nervours system like heart beat, pressure, digestion, ventilation and so on.
CEREBRUM
This is the largest part of the human brain. It is a dome-shaped mass of nervous tissue made up of two halves called the Cerebral hemispheres. The cerebrum consists of an outer layer called cerebral cortex. It is a region where the main functions of cerebrum are carried out. The cortex is concerned with all forms of Conscious activities. It is here that sensation of touch, taste, hearing, vision and smell are generated. Cerebrum is used to direct the muscled so that movements have definite purposes.
MID-BRAIN/MIDDLE BRAIN
- It controls the movements of the head, sound and visual reflex
- It communicates messages between fore brain and hind brain
- Maintains body posture and balance
FORE BRAIN
Fore brain consists of the following:
Cerebral Cortex
- It is sensory centre, it receives nerve impulses from various receptors
- It acts as association centre
- It acts as a motor centre
Hypothalamus
- It controls the functions of the pituitary gland, sleeping, hunger, thirst and sexual desire
- Maintain the constant internal environmental temperature
Pituitary gland
- Secretes number of hormones and controls other glands. It influences the growth and thus called “master gland”.
THE GENERAL FUNCTIONS OF THE BRAIN
- The brain controls the involuntary actions such as regulation of blood, sneezing, coughing, salivation, heart beat and breathing
- It helps to balance the body
- It controls voluntary actions such as touch, vision, taste and hearing
- Coordinates muscle activities
- Controls the movement of the head, sound and visual reflex
- Coordinates and interprets various information
Diagram of the Human Brain
NEURONES
- Also called nerve cell. It is the basic unit and function of nervous system, which conducts the information from one part of the body to another.
FUNCTIONS OF NEURONES
- They receive stimulus from the environment
- They convert stimulus into electrical form called electrical impulse by process called TRANSDUCTION
- They transfer the converted information from the receptor to the effectors
ADAPTATION OF THE NEURONES
- They have long nerve fibres which increase large surface area for chemical reactions to occur
- Have many Golgi bodies for production of neuro- transmitters
- They respond easily to the stimulus hence are called Excitatory cells while other cells are called Non-excitatory cells
- Are able to transmit electrical impulses while other cells are not able to
- They are packed with a lot of mitochondria for supply of energy for impulse transmission
TYPES OF NEURONES
There are three types of neurons as follows:
i. Sensory/Afferent neurons
These are neurons, which conducts impulses from receptors to the central nervous system. Carry impulses towards the central nervous system, which is the brain and spinal cord.
ii. Motor/Efferent neurons
These are neurons, which transmit impulses from the central nervous system to the effector i.e. muscles and glands
Diagram of Motor neuron
iii. Relay neurons
These are neurons, which carry the information to both coordinator and receptor away. They are non-myelinated neurons, they take the information from cell body and central nervous system.
Diagram of Relay neuron
THE STRUCTURE OF THE NEURONS
Neurons are made up of swollen body called cell body, from which arises the arm like structure calledDendron. Dendron is divided into five-finger like structures called Dendrites. Within the cell body there is cytoplasm, which is called Neucleoplasm. At hthe centre of Neucleoplasm there is a Nucleaus and Nissil’s granules. The major Dendron or protoplasm is called Axoplasm.
Within axoplasm, there are mitochondria and other organelles. An insulator material called Myelin sheath covers the axon of most neurons. Another membrane, which is very thin called Neulilema, is composed of Shum cells.
REFLEX ACTION
These are sudden and automatic uncontrolled responses, which are controlled by spinal cord only. E.g. salivation, sneezing. It is the simplest form of responses in the nervous system.
REFLEX ARC
- This is a pathway taken by nerve impulses during reflex action.
- Depending on the number of neurons involving forming reflex arc we have:
i. DINEURONIC ARC
Are reflex arcs which consists of two neurons example Knee jerk
ii. TRINEURONIC ARC
Are reflex arcs consisting of three neurons e.g. withdrawal responses
There are two types of reflex action, which are simple reflex and conditioned reflex. Simple reflex actions are unlearnt or involuntary activities like salivation and sneezing, while conditioned reflexes are modified by the past experience. They are learnt responses hence conditional reflex actions are controlled by both, spinal cord and the brain. Pav Lov did the first demonstration of conditional reflex; he observed that a dog could learn a reflex by ringing a bell every time he gave them food. Eventually they would start to produce saliva when he rang the bell even if no food was presented.
IMPORTANCES OF REFLEX ACTION
- It enables the body to respond quickly to change hence rescues the body
- It enables the brain to deal with complex action since doesn’t involve the brain
- It helps to control the internal environment such as breathing rate and blood pressure
THE PERIPHERAL NERVOUS SYSTEM
These are central nervous system, which radiates away from the nervous system. All the nerves of the body make up the peripheral nervous system. They all enter or leave the central nervous system either the spinal cord in the case of spinal nerves or the brain in the case of cranial nerves.
There are two types of cranial peripheral nervous system. There are somatic and autonomic nervous systems.
Somatic nervous system
- These are nervous systems, which control voluntary activities
- These are made up of two types of nerves:
- Spinal nerves. These are nerves, which arise from the spinal cord. The number of spinal cord depends on the length of spinal cord/vertebral column. These are two roots in which the spinal cord nerves enter the spinal cord is ventral and Dorsal roots. Spinal nerves are mixed nerves.
- Carnial nerves: These are nerves, which arise from the brain. In vertebrates there are 10 pairs but in human beings there are 12 pairs. They transmit impulses found in the brain. There are three types of Cranial nerves: sensory nerves, mixed nerves and motor nerves.
There are 31 pairs of spinal nerves. These are:
- 8 cervical nerves
- 5 lumbar nerves
- 12 thoracic nerves
- 5 saecal nerves
- 1 caudal nerve
THE AUTONOMIC NERVOUS SYSTEM
The autonomic nervous system is that pair of the peripheral nervous system which controls activities inside the body that are normally involuntary such as heart rate, peristalsis and sweating.
Autonomic nervous system us divided into two parts, which are:
- Sympathetic nervous system
- Parasympathetic nervous system
i. SYMPATHETIC NERVOUS SYSTEM
This is a system, which sympathizes in stress conditions. It prepares a body to respond in emergency situations.
This type of response is known as flight and synapse of the fright is near the spinal cord.
ii. PARASYMPATHETIC NERVOUS SYSTEM
This is a nervous system, which is systematic and also does not prepare the body to respond in emergency situations.
DIFFERENCES BETWEEN SYMPATHETIC AND PARASYMPATHETIC NERVOUS SYSTEM
SYMPATHETIC NERVOUS SYSTEM
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PARASYMPATHETIC NERVOUS SYSTEM
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