CONTROL AND COORDINATION THE HUMAN NERVOUS SYSTEM RESPONSE TO STIMULI STIMULI RECEPTORS BRAIN ELECTRICAL IMPULSES RESPONSE STIMULUS • An agent or a sudden change in the external or internal environment which causes a change in an organism or any of its body parts. • Example of external stimulus : sense of touch , sense of sight etc • Example of internal stimulus : hunger , thirst etc RECEPTORS • Nerve cells which initiate waves of impulses towards the central nervous system on receiving the stimulus. • • • • • Eyes : photoreceptors Ears : Auditory receptors Nose : olfactory receptors Tongue : taste receptors Skin : Thermoreceptors NEURON • A neuron is the structural and functional unit of nervous system. The three main parts of a neuron are : • Cell body : has a well defined nucleus and cytoplasm. • Dendrites : branched cytoplasmic projections of the cell body. • Axon : the end portions of axon have swollen bulb-like structures to store neurotransmitters NEURON • The synapse is the point of contact between the terminal branches of the axons. • Axon terminals of a neuron and the dendrites of another neuron are separated by a fine gap i.e a synaptic cleft • The nerve impulses are sent across the synaptic cleft with the help of neurotransmitters. REFLEX ACTION • Involuntary action response to the external or internal stimuli are termed as reflex actions. • The pathway of impulses during a reflex action is known as reflex arc. • Reflex arc can be represented as follows : STIMULUS > RECEPTOR > SENSE ORGAN > SENSORY NEURON > CNS (spinal cord) > MOTOR NEURON > MUSCLE > RESPONSE HUMAN NERVOUS SYSTEM NERVOUS SYSTEM CENTRAL NERVOUS SYSTEM BRAIN PERIPHERAL NERVOUS SYSTEM SPINAL CORD NERVES PROTECTION OF BRAIN • The brain is protected inside a bony case called the cranium or the skull. • It has a three layered membrane called the meninges and between them the cerebrospinal fluid is filled . • The cerebrospinal fluid is formed from the blood and reabsorbed into the blood . • The CSF provides oxygen and nutrition to the brain and protect it from mechanical shocks. PARTS OF HUMAN BRAIN • FOREBRAIN : It is composed of the cerebrum. • MIDBRAIN : It is composed of the hypothalamus. • HINDBRAIN : It is composed of the cerebellum , pons and the Medulla Oblongata . CEREBRUM • It is the largest part of the human brain . It is divided into two cerebral hemispheres. • The cerebrum controls the voluntary motor actions. • The cerebrum is the site of learning and memory HYPOTHALAMUS • The hypothalamus is at the base of cerebrum. • It controls the sleep and wake cycle (circadian rhythm) of the body. • It also controls the temptation for eating and drinking. CEREBELLUM • It lies below the cerebrum . It also coordinates the motor functions along with the cerebrum. • It controls the posture and balance of the body • It controls the precision of voluntary actions. MEDULLA • It lies at the base of the brain and is connected to the spinal cord . • It controls various involuntary actions like heart beat , respiration etc . • Eg : blood pressure , breathing rate etc. PONS • It relays impulses between the lower cerebellum and the spinal cord and higher parts of the brain like the cerebellum and the mid brain . • It regulates the process of respiration. PROTECTION OF SPINAL CORD • The spinal cord is protected within the vertebral column. • There is also the presence of cerebrospinal fluid which imparts nourishment to the spinal cord and protects it from external shocks . • The spinal cord is the main centre for the control of reflex actions. COORDINATION IN PLANTS • All living organisms react o their surroundings . • Chemicals produced by cells help plants respond to the stimuli as well. • Plant coordination is based on movements : one that is dependent on growth and the other which is not dependent on growth. MOVEMENT IN PLANTS • Movement which is dependent on the growth of plants are called tropic movements. • Movement which is not dependent on the growth of plants are called nastic movements. • Phototropism : growth towards light (positive phototropism) growth away from light (negative phototropism) • Geotropism : growth towards gravity (positive geotropism) growth away from gravity (negative geotropism) MOVEMENT IN PLANTS • Hydrotropism : growth towards the flow of water (positive hydrotropism) growth away from the flow of water (negative hydrotropism) • Thigmotropism : The movement of plants based on the sense of touch is known as thigmotropism. • Chemotropism : The movement or the growth of the organism in response to chemical substances . Eg : growth of pollen tube towards the ovule. PLANT HORMONES • The plant hormones are of mainly four types : • Auxin : helps in the growth of plants due to phototropism , more growt of cells towards the light. • Gibberellin : helps in the growth of stem. • Cytokinin : promotes cell division • Abscisic acid : inhibits growth and wilting of leaves (stress hormone) ENDOCRINE SYSTEM • The endocrine system is composed of several endocrine glands. • A ductless gland is called an endocrine gland. • Endocrine gland secretes its product directly into the blood stream . The hormones produced in the endocrine glands are mainly composed of proteins. • These hormones assist the nervous system in control and coordination. ENDOCRINE GLANDS • Adrenal glands : secretes adrenaline (emergency hormone) during emergency • • • • • situations Thyroid gland : secretes thyroxine . Regulates the metabolism of the body Pituitary gland : secretes growth hormone . Regulates the growth of body. Pancreas : secretes insulin . Regulates the blood sugar level. Testis : secretes testosterone . Regulates sperm production and development of secondary sexual characters Ovaries : secretes oestrogen . Regulates egg production and development of secondary sexual characters in females.
