2_Nervous System.pdf

SENSITIVITY ◦ The ability to respond to a stimulus ‣ A change in the environment that causes a reaction in an organism is known as a stimulus ‣ The reaction is called a response ROLE OF NERVOUS SYSTEM ◦ the human nervous system regulates bodily function & activities...

SENSITIVITY ◦ The ability to respond to a stimulus ‣ A change in the environment that causes a reaction in an organism is known as a stimulus ‣ The reaction is called a response ROLE OF NERVOUS SYSTEM ◦ the human nervous system regulates bodily function & activities and how we react to the surroundings ◦ Voluntary actions are actives that are controlled consciously ◦ Involuntary actions are actinides that are not controlled consciously eg heartbeat, peristalsis, breathing movement Components of the Human Nervous System ◦ Central nervous system (CNS) consist the brain and spinal cord ‣ Spinal cord is involved mostly in automatic actions known as reflex actions ‣ Brain integrates touch, olfactory & sate information from our sensory organs ◦ The Peripheral nervous system (PNS) consists of the cranial nerves, spinal nerves and sense organs 1. When there is a stimulus, the receptors in our sense organs are stimulated to produced nerve impulses 2. They transmit these nerve impulses to the central nervous system by nerves (cranial and spinal) 3. The CNS then sends the nerve impulses to the effectors, which are muscles/glands Eg someone touches ur hand (simtuli) —> CNS send nerve impulses to muscles —> muscles will then effect an action (effectors) NEURONES the nervous system is made up of nervous tissue which consist of nerve cells called nuerones Each neurone consist of a cell body containing a nucleus and cytoplasm, and a number of nerve fibres (a nerve fibre is a strand of cytoplasm extending from the cell body) Relayneurone sensoryneurone motorneurone Sensory Neurone ◦ The sensory neurone transmits nerve impulses from the sense organs/receptors to the central nervous system ◦ Structure - Has a circular cell body - One long nerve fibre between the receptor & cell body, One short nerve fibre between the cell body & CNS Relay Neurone ◦ The relay neurone transmits nerve impulses from the sensory neurone to the motor neurone ◦ Contains many short nerve fibres ◦ Usually found in the CNS Motor Neurone ◦ The motor neurone transmits nerve impulses from the central nervous system to the effectors  ◦ Structure: Has a irregular-shaped cell body - one long nerve fibre between the cell body & effector SYNAPSE a synapse is the junction between 2 neurones Nerve impulses are transmitted across a synapse by chemicals released by the neurones ◦ Nerve impulses cannot directly cross from one neurone to the next using the tiny space between them ◦ If these tiny spaces were to be filled (eg painkillers) no nerve impulses will be transmitted and nothing will be felt DIFFERENT PATHWAYS OF NERVE IMPULSES IN THE SPINAL CORD Sensation (Blue Line) - sensory + relay neurone ◦ (When you hold a piece of ice, the temp receptors in your skin is stimulated) Nerve impulses produced by the receptors are transmitted to the spinal cord by the sensory neurone and then to the brain by the relay neurone  ◦ The brain interprets the nerve impulses, and you feel a sensation (there is no need for a motor neurone) Receptor in the skin —> sensory neurone —> relay neurone in the spinal cord —> brain Voluntary Action (Green Line ) - relay + motor neurone ◦ Eg you decide to raise your hand ‣ Nerve impulses are produced in the brain and are transmitted by the relay neurone from the brain to the spinal cord. Nerve impulses are then transmitted to the motor neurone, which transmits nerve impulses to the effector muscles in your arm. The muscles contract, and your hand is raised Brain —> relay neurone in the spinal cord —> motor neurone —> effector Reflex Action A reflex action is an immediate response to a specific stimulus without conscious control 2 types of reflex actions ◦ Cranial reflexes - controlled by the brain (eg blinking, pupil reflex and salivation) ◦ Spinal reflexes - controlled by the spinal cord (eg sudden withdrawal of hand on touching a hot object) Reflex Arc (red line) ◦ An reflex Arc is the shortest pathway by which nerve impulses travel from the receptor to effector in a reflex action ◦ Receptor —> sensory neurone —> relay neurone (CNS) —> motor neurone —> effector Eg Qn Describe the sudden withdrawal of the hand on touching a hot object based on reflex action. the heat from the object stimulates the receptors in your skin. Nerve impulses are produced. The sensory neurone transmits the nerve impulses to your spinal cord. i In your spinal cord, nerve impulses are transmitted first across a synapse to the relay neurone, then to the motor neurone The motor neurone transmits the nerve impulses from the spinal cord to the effector Your biceps muscle then contracts and causes your hand to withdraw suddenly ENDOCRINE CONTROL vs NERVOUS CONTROL  similarity ◦ In both systems, a stimulus causes the transmission of a message to a target organ (effector) which carries out a response differences ◦ Nervous control is usually localised while enedocrine control may affect more than one organ ‣ This is because endocrine control involves hormones as signals while the nervous control involves nerve impulses as signals,since hormones are usually transported around the body by blood, several target organs may be affected by the same hormone ◦ Nervous control usually have a quick response while endocrine control have slow responses ◦ Response from nervous control can be voluntary/involuntary/shortlived while response from endocrine control are involuntary/shortlived/longlived