[BIO] Chapter 11 - Nervous System

© Hee Xin Wei (Copyrighted) Topic 11: Nervous System

Chapter Analysis FOCUS EXAM WEIGHTAGE •Constitute to 0% in Paper 2 in the past 5 years •commonly tested in MCQ •haven't been tested in structured in the past 5 years (MAYBE this year it will be) •one of the three chapters under umbrella topic of Co-ordination and Response in Humans •together with eyes and hormones

brain, spinal cord and nerves neurones reflex action Key Concept

human nervous system Human Nervous System consists of i.Central Nervous System (CNS) consists of the brain and the spinal cord ii.Peripheral nervous system (PNS) consists of the nerves connecting the central nervous system and the rest of the body The role of nervous system: -Help the body to adjust rapidly to any changes in the environment -Enable the various parts of the body to coordinate with one another quickly -Control involuntary actions, actions that cannot be consciously controlled, such as heartbeat, peristalsis, vasoconstriction and reflex actions -Control voluntary actions, actions that are consciously controlled, such as picking up the cookie on the table

human nervous system Stimulus is a change in environment which is detected by receptors CNS then transmits nerve impulses to effector to react to the changes in surroundings) Receptor will produce electrical messages called nerve impulses to send to the central nervous system by neurones Effectorresponse CNS Receptor Stimulus

Nerves •Nerve is a bundle of neurones or nerve cells that transmit nerve impulses •All neurones have (a)A large cell body containing the nucleus and organelles. (b)Dendrons are nerve fibre that conduct nerve impulse towards the cell body of the neurone (c)Axons are nerve fibre that conduct nerve impulses away from the cell body. (d)At the terminal ends of axons and dendrons, the nerve fibre branches. These branches are known as dendrites. Where the axon is connected to muscles, these branches are also known as motor end plates. Three types of neurones 1.Sensory neurones - Transmits nerve impulses from receptors / sense organs to CNS 2.Relay neurones - Transmit nerve impulses from the sensory neurones to the motor neurones; found within the CNS 3.Motor neurones - Transmit nerve impulses from the CNS to the effector muscle cells or gland cells dendrites dendron cell body axon axon terminal

structure of neurones Sensory Neurones Motor Neurones Cell body smooth and roundedRelatively large and irregular shape Dendron Long Short Axon Short Long Axon terminalsTransmit nerve impulses to relay neurones Transmit nerve impulses to the effector Direc&on of signal Sense organs (receptors) Axon terminal Direc&on of signal Effector eg muscles cells Sensory Neurones Motor Neurones

brain and spinal cord Grey matter consists mainly of the cell bodies of neurons. •It forms the outer layers of the brain and the central parts of the spinal cord. White matter consists mainly of nerve fibres (dendrons and axons). •It forms the central parts of the brain, and the outer layers of the spinal cord.

transmission of nerve impulses Along axons of neurones, •Myelin sheath is made up of schwann cells which are fats. It provides insulation to the nerve impulses which are electrical signal •Nodes of ranvier are regions where myelin sheath is absent. •Nerve impulses which are electrical signals cannot be transmitted through the myelin sheath, so they “jump” from one node to the next, speeding up transmission of impulses Across neurones, •A synapse is a junction between two neurones or between a neurone and an effector. •impulses from the axon of one neurone are transmitted to the dendrites of another neurone or to effector cells. •Nerve impulses are transmitted across the tiny space of a synapse by chemicals called neurotransmitters.

reflex arc •Reflex actions are involuntary responses to a specific stimulus •Reflex arc is the pathway which nerve impulses travel during reflex actions synapse synapse Receptor —> Sensory neurone —> Intermediate neurone / relay neurone —> Motor neurone —> Effector 1.Receptors in the skin detect the stimulus such as pricked by a needle or touching a hot object 2.Nerve impulses are produced which are transmitted by the sensory neurone to the spinal cord. 3.In the spinal cord, the nerve impulses are transmitted across a synapse to a relay neurone and then across another synapse to the motor neurone. * 4.Nerve impulses travel along the motor neurone to the motor end plate, then the effector 5.The effector muscles contract causing the hand to withdraw *When nerve impulses arrive at the spinal cord from sensory neurone, nerve impulses are also sent to the brain. The brain will interprets the impulses, and the cold sensation or pain will be felt