SBI 4U: Metablic Processes THE NERVOUS SYSTEM Section 1.3

Try These! Brain teasers worksheet Stroop test Reflex test with a yardstick Short-term memory test at https://www.psychologistworld.com/memory/test2.php

Vertebrate Nervous Systems Autonomic (involuntary) system Brain Central Nervous System Motor pathways Parasympathetic Peripheral Nervous System Sensory pathways Somatic (voluntary) system Spinal cord Sympathetic

Vertebrate Nervous Systems

Our Communication System SBI 4U: Metablic Processes Our Communication System Nervous system senses and responds to stimuli Works in coordination with the endocrine system, among others, to maintain homeostasis There are 100 billion nerve cells in the brain alone! Section 1.3

Central Nervous System (CNS) SBI 4U: Metablic Processes Central Nervous System (CNS) Composed of the brain, spinal cord, and nerves Coordinating centre Processes information sent by nerves Section 1.3

Peripheral Nervous System (PNS) SBI 4U: Metablic Processes Peripheral Nervous System (PNS) Network of nerves Carry sensory messages to the CNS Send info from the CNS to muscles, glands, and organs Composed of somatic & autonomic systems Section 1.3

Somatic vs. Autonomic 1. Somatic Nerves Controls skeletal muscle, bones and skin Relay info about the environment to the CNS and respond accordingly 2. Autonomic Nerves Special motor nerves that control internal organs Control involuntary processes like heartbeat and peristalsis

Autonomic System: 2 types Divided into 2 systems that work in opposition to each other 1. Sympathetic  “fight or flight” Initiates arousal and energy production 2. Parasympathetic  “rest & relax” Calming Returns systems back to homeostasis

Cells in the Nervous System SBI 4U: Metablic Processes Cells in the Nervous System Nervous system is composed of 2 main types of cells: 1. Neurons  basic functional unit Conduct nerve impulses Specialized to respond to stimuli, conduct signals, and release chemicals that regulate body processes 2. Glial cells  from Greek word ‘glue’ Structural support of nerve cells Nourishes neurons, removes their waste, defends against infection Do not conduct electrical impulses like neurons Section 1.3

SBI 4U: Metablic Processes So What’s a Nerve Then? A bundle of neurons Nerves are tissue composed of clusters of neurons (cells combine to form tissues, which combine to form organs, ...) Section 1.3

Neuron Anatomy

SBI 4U: Metablic Processes Anatomy of a Neuron Dendrites  finger-like projections Receive nerve impulses from other neurons or sensory receptors Numerous and highly branched Increases surface area available to receive information Cell body  aka the soma Contains nucleus and majority of cytoplasm The cell’s metabolic reactions happen here Processes input from dendrites Section 1.3

SBI 4U: Metablic Processes Anatomy of a Neuron Axon  long, thin tube Carries nerve impulses away from the cell body Range in length from 1 mm to 1 m depending on its location in the body axon diameter also affects speed smaller diameter = faster impulse transmission Terminal releases chemical signals into the space between it and the dendrites of neighbouring cells to communicate (with surrounding neurons, glands, or muscles) Section 1.3

SBI 4U: Metablic Processes Anatomy of a Neuron Myelin Sheath  insulates the axon Insulating layer made of fatty protein Made by Schwann cells Covers some neurons but not all Called “myelinated” neurons Speeds up nerve impulse transmission Schwann cells  type of glial cell Specialized cells that produce myelin Section 1.3

SBI 4U: Metablic Processes Anatomy of a Neuron Nodes of Ranvier  gaps between myelin on an axon regularly occurring nerve impulses jump from one node to another increases speed of the impulse Section 1.3

SBI 4U: Metablic Processes Anatomy of a Neuron Neurilemma  thin membrane that surrounds the axon Found on all nerve fibres in the PNS Promotes regeneration of damaged axons Not all nerve cells contain neurilemma Ex: Grey matter in the CNS do not regenerate after injury ( paralysis) Section 1.3

Neuron Anatomy

myelinated, contains neurilemma unmyelinated, does not contain neurilemma The PNS has greater ability to regenerate than the CNS (ex: spinal cord injuries) Scientists have found a growth inhibitor in the CNS, which prevents neurilemma & myelin production Scientists are looking for ways around this with therapeutic cloning (stem cell research) Possibility of nerve regeneration, reversal of paralysis, etc.

Types of Neurons

Sensory Neurons Aka afferent neurons Carry impulses from sensory receptors to the CNS for processing Ex of sensory receptors = photoreceptors in eyes (light), chemoreceptors in nose and skin (chemicals), thermoreceptors in skin, hypothalamus (heat/cold) Ganglia  clusters of sensory neurons Located outside of the CNS Singular = ganglion

Motor Neurons Aka efferent neurons Carry impulses from the CNS to effectors (muscles, organs, glands, etc.) These are the neurons that actually produce a response Ex: muscle contraction/ relaxation, secretion of hormones, etc.

Interneurons Link sensory & motor neurons within the body Found mostly in the CNS Integrate and interpret sensory information and connect neurons to outgoing motor neurons Aka association neurons

The Reflex Arc Look online or use p. 416 of your textbook to make your own note on a reflex arc Record background info Use an example to summarize a typical reflex arc Draw a picture or find an image that illustrates a reflex arc

SBI 4U: Metablic Processes The Reflex Arc Neural circuit through the spinal cord that provides a framework for a reflex action Simplest nerve pathway Involuntary, unconscious Section 1.3

Example: Accidentally touching a hot stove SBI 4U: Metablic Processes Example: Accidentally touching a hot stove Heat is detected by thermoreceptors in skin Sensory neuron carries the nerve impulse to the spinal cord Interneuron in spinal cord passes the impulse to a motor neuron Motor neuron carries impulse to muscles in arm/ hand Muscles contract and hand pulls away Section 1.3

SBI 4U: Metablic Processes The Reflex Arc Happens in less than a second Information has not even travelled to the brain When it does, the sensation of pain will become noticeable and you may scream! If you had to wait to feel the pain first, the burn would be a lot worse Section 1.3