Transcript File
The Nervous System Lesson objectives By the end of this lesson you should know: • The difference between the CNS and the PNS • The function of the nervous system • Distinguish between sensory, motor and interneurons in terms of structure and function Introduction In animals there are 2 systems of communication allowing the animal to respond to internal and external stimuli • Nervous system (Rapid responses) • Endocrine system (Slower responses) There are 2 parts to the nervous system: In order to make the correct response to a stimulus 4 processes are involved: • Reception • Transmission • Integration • Response NS ----- Co-ordination & Response Neurones • • • • Neurones are the basic units of nerve cells Are specialised to carry information as electrical impulses from 1 place to another Neurons not only vary in type but differ in size – in the brain they are tiny but the spine and feet can be up to 1m long There are 3 main types: Sensory neurons • Sensory (afferent) neurones – sends messages from sense organs to CNS Motor neurons • Motor (efferent) Neurones – send messages from CNS to muscles and glands Interneurons • Interneurons carry information between sensory and motor neurons – found only in CNS Structure of neurons Functions of the parts of neurons Relationship between nerve fibres and neurones • Many axons often combine to form nerve fibres (nerve) • Axons can be up to 1m in length What do you know? Can you.... • Distinguish between the CNS and the PNS? • Describe function of the nervous system? • Distinguish between sensory, motor and interneurons in terms of structure and function? Lesson objectives By the end of this lesson you should know: • How nerve impulses move along the axon • Activation and inactivation of the neurotransmitter at the synapse Transmission of nerve impulses • A neuron has to receive a stimulus of sufficient strength • The movement of the electrical impulse involves the movement of ions (charged particles) Features of nerve impulses Resting neuron • When a neuron is not carrying an impulse ions are pumped in and out of the axon – this results in the inside of the axon being negative and the outside positive Threshold • The threshold is the minimum stimulus needed to cause an impulse to be carried • A stimulus below the threshold has no effect but one that is at or above the threshold causes an electrical impulse to travel along the axon Features of nerve impulses The all or nothing law • The all or nothing law states that if the threshold is reached an impulse is carried but if the threshold is not reached no impulse is carried • Simply the impulse is either carried or not Transmission of nerve impulses Transmission of nerve impulses Refractory period • The refractory period is a short time span after a neuron has carried an impulse during which a stimulus fails to cause a response • While ions are moving in and out of each section of the neuron the region affected cannot carry another impulse • There has to be a slight delay of 5ms between any 2 impulses - the refractory period Transmission of nerve impulses • • • • Speed of impulse Depends on myelin sheath If myelin is absent speed is reduced to 2m/s In a myelinated neuron the changes can only move in and out of the gaps in the myelin - the impulse jumps from gap to gap and is transmitted more rapidly- 120m/s Also the larger the diameter of the axon the faster transmission Synapse • A synapse is a region where 2 neurons come into close contact – commonly found between the axon terminals of 1 neuron and the dendrites of another • A synaptic cleft is the tiny gap between the neurons at a synapse – 20nm Activation and inactivation of neurotransmitters Transmission Across a Synapse 1 Transmission Across a Synapse 2 Functions of synapses 1. They transmit impulses from 1 neurone to another or effector (muscle or glands) 2. They control the direction of the nerve impulse 3. They prevent over stimulation of effectors 4. The impulse can be blocked by certain chemicals (drugs) – important in controlling pain and certain psychiatric disorders What have you learned? Can you explain.... • How nerve impulses move along the axon? • Activation and inactivation of neurotransmitters at the synapse? Lesson objectives By the end of this lesson you should know: • The structure and function of the following parts of the brain: cerebrum, cerebellum, medulla oblongata, thalamus and hypothalamus • 1 nervous system disorder The central nervous system (CNS) Brain • The senses and individual sensory neurones act as receptors for incoming stimuli • Electrical impulses are passed along sensory neurons to the CNS particularly the brain • The brain acts as the interpreting centre to sort and process the incoming impulses and decide on a response Structure of the brain Functions of the cerebrum Functions of the cerebellum • Controls muscular co – ordination • Allows smooth refined muscular action • Controls balance • The responses of the cerebellum are involuntary once they have been learned Functions of the medulla oblongata • Connects the spinal cord with the rest of the brain • Controls involuntary actions like breathing, blood pressure, swallowing, coughing, salivation, sneezing and vomiting Functions of the Thalamus • Acts as a sorting centre for the brain and relays all incoming messages to the relevant part of the brain Functions of the Hypothalamus • It regulates the internal environment of the body (homeostasis) by monitoring blood temperature, appetite, thirst, osmoregulation and blood pressure • It is thought to be a link between the mind and the body Nervous system disorder – Parkinson’s disease • • • • Cause Symptoms include: Prevention Treatment What have you learned? Can you discuss... • The structure and function of the following parts of the brain: cerebrum, cerebellum, medulla oblongata, thalamus and hypothalamus? • 1 nervous system disorder? Lesson objectives By the end of this lesson you should know: • The structure and function of the parts of the spinal cord • The structure and function of the PNS • Discuss the simplest form of activity in the nervous system-the reflex action The Spinal Cord TS of spine The Peripheral Nervous System • Consists of nerve fibres outside the spinal cord • Made up of long dendrites or axons taking impulses to and from the CNS Reflex action/Reflex Arc • The simplest form of activity in the nervous system is a reflex action • It is an automatic, involuntary and unthinking response to a stimulus • The neurons forming the pathway taken by the nerve impulses in a reflex action make up a reflex arc Reflex response Reflex Arcs What have you learned? Can you discuss... • The structure and function of the parts of the spinal cord? • The structure and function of the PNS? • The simplest form of activity in the nervous system-the reflex action?