Irritability in Humans THE HUMAN NERVOUS SYSTEM Coordination by The Nervous System • The job of the nervous system is to coordinate the activities of all parts of the body. • It gathers information from receptor via sensory neurons. • It then processes this information and sends messages out to the effectors via motor neurons so that most appropriate action can be taken. • Messages are passed between the brain and the spinal cord by relay neurons. DEFINITIONS STIMULUS: a change in the internal or external environment of an organism that initiates a response. RESPONSE: a change in an organism or part of an organism which is brought about by a stimulus. RECEPTOR: the part of the organism that detects the stimulus. ( In animals, the SENSE ORGANS contain the receptor e.g the eyes, ears, nose, tongue and skin contain specialized receptor cells that detect stimuli. In plants the very tips of roots an shoots act as receptors EFFECTORS: the part of an organism that responds to a stimulus. ( In animals, muscles and glands are effectors. In plants, the regions just behind the tips of roots and shoots and the petioles of leaves are the effectors. . DEFINITIONS • STIMULUS: a change in the internal or external environment of an organism that initiates a response. • RESPONSE: a change in an organism or part of an organism which is brought about by a stimulus. • RECEPTOR: the part of the organism that detects the stimulus. ( In animals, the SENSE ORGANS contain the receptor e.g the eyes, ears, nose, tongue and skin contain specialized receptor cells that detect stimuli. In plants the very tips of roots an shoots act as receptors. • EFFECTORS: the part of an organism that responds to a stimulus. ( In animals, muscles and glands are effectors. In plants, the regions just behind the tips of roots and shoots and the petioles of leaves are the effectors. Neurones or nerve cells make up both the CNS and PNS. Neurones They transmit messages called nerve impulses. Sensory neurons send nerve messages known as impulses from receptors in the body to the CNS. TYPES OF NEURONES Motor neurons carry impulses from the CNS to effectors in the body. Intermediate neurons (also called interneurons or relay neurons) are neurons that connect sensory neurons to motor neurons. The Structure of a Motor Neurone The Structure of A Sensory Neurone Synapses • Please note that adjacent neurons don't actually touch, but are actually separated by spaces called synapses. • Chemicals are released into the synapses by synaptic knobs, which cause impulses to form in adjacent neurons. • This ensure that impulses only travel in one direction. What happens in a Synapse? What happens at a synapse? Voluntary and Involuntary Actions A voluntary action is an action that is consciously controlled by the brain. An involuntary action is an action that occurs without conscious thought. Types of Involuntary Actions Actions controlled by the autonomic nervous system Reflex actions What are Reflexes? Reflexes are automatic, quick, involuntary responses to stimuli by a muscle or gland. What is Reflex Arc? • When a receptor detects a stimulus, nerve cells known as neurons carry the signal from the stimulated receptor to the central nervous system to the correct effector. • A sensory neuron carries the message from the receptor to the central nervous system (the spinal cord and brain). • A motor neuron carries the message from the central nervous system to the effector. • This is known as a reflex arc. • The reflex arc is a neural pathway that controls a reflex. Simple Reflex Actions • Simple reflex actions occur without conscious thought. They are not learned, but rather are necessary for survival. • Simple reflex actions can either be cranial or spinal based on which part of the central nervous system the impulse passes through. • The impulses of cranial reflexes pass through the brain, for example, the pupil reflex, sneezing, coughing and saliva production • The impulses of spinal reflexes pass through the spinal cord, like the knee jerk reflex and the withdrawal reflex. SPINAL REFLEXES In Spinal reflexes , impulses pass through the spinal cord, e.g the knee jerk reflex and the withdrawal reflex The Knee Jerk Reflex The Withdrawal Reflex Spinal Reflexes • You may be wondering how exactly the correct connection is made between a sensory and motor neuron. • This is the work of the intermediate neurons of the central nervous system, and it is called integration. • Integration is like what happens when you call a friend. The request goes to a central office at your service provider (like the impulse goes through a sensory neuron to the central nervous system). The central office directs your request to your friend (integration). Cranial Reflexes In cranial reflexes, impulses pass through the BRAIN,i.e there are coordinated by the brain e.g the pupil reflex, blinking, sneezimg coughing and saliva production The Pupil Reflex The Pupil Reflex
