Human Anatomy & Physiology NERVOUS SYSTEM Biology – Chapter 35 1

Nervous System Functions  Control & coordinate functions throughout the body  Respond to internal & external stimuli  Provides fast communication between body systems and parts 2

Nervous system cells dendrites cell body axon synaptic terminal  Neuron  a nerve cell  Structure fits function  many entry points for signal  one path out  transmits signal signal direction signal direction dendrite  cell body  axon synapse myelin sheath 3

Neuron Basic Structure Messages sent by the nervous system are electro- chemical signals (impulses) carried by neurons (nervous system cells) Impulses always travel from dendrites, through the cell body to the axon terminal 4

Neuron Anatomy Dendrites – short, branched extensions that receive impulses from the environment or other neurons toward the cell body Cell Body – the largest part of a neuron, containing most of the cytoplasm and the nucleus Axon – the long extension that carries an impulse away from the cell body Myelin (myelin sheath) – insulating membrane surrounding most axons (roduced by Schwann cells) separated by small gaps (Nodes of Ranvier = “nodes”) Axon terminals – branches at the end of an axon Neurons may have many dendrites and axon terminals, but only one axon Nerve – bundle of axons and dendrites from many neurons 5

Fun facts about neurons Most specialized cell in animals Longest cell – blue whale neuron meters – giraffe axon 5 meters – human neuron 1-2 meters Nervous system allows for 1 millisecond response time 6

Neuron Types Sensory Neuron – carries impulse from sense organs to brain & spinal cord Motor Neuron – carries impulse from brain to muscles & glands Interneuron – connects sensory and motor neurons 7

Nerve Impulse HOW does a signal travel along an neuron? 8 (Click)

Transmission of a signal Think dominoes! – Start the signal knock down line of dominoes by tipping 1 st one  trigger the signal – Propagate the signal do dominoes move down the line?  no, just a wave through them! – Re-set the system before you can do it again, have to set up dominoes again  reset the axon 9

Transmission of a nerve signal Neuron has similar system – protein channels are set up – once first one is opened, the rest open in succession All or nothing response – a “wave” action travels along neuron – have to re-set channels so neuron can react again 10

Resting Neuron When a neuron is resting (NOT transmitting an impulse), the outside of the cell has a net positive ion charge, while the inside has a net negative charge. Na + ions are pumped out of the cell while K + ions are pumped into the cell, using active transport 11

Na + K + pumps (active transport) and leakage channels This creates a difference in charge between the inside and the outside of a neuron = Resting Potential 12

Measuring cell voltage Unstimulated neuron = Resting Potential of -70mV 13 (Click)

Moving Impulse The neuron remains in a “resting state” until it receives a stimulus large enough to start an impulse (“All or nothing response”) from the environment or another neuron. The electrical imbalance between the inside and the outside of the neuron is reversed as the impulse travels along the axon toward the axon terminals = ACTION POTENTIAL (nerve impulse) 14

Synapse Impulse has to jump the synapse! – junction between neurons – has to jump quickly from one cell to next What happens at the end of the axon? How does the wave jump the gap? 15

The Synapse The action potential travels along the axon (“jumping” from node to node) until it reaches an axon terminal and the gap (synapse) between it and another cell Chemicals (neurotransmitters) travel between the axon terminal and the next cell through the synaptic cleft (synapse) 16

Divisions of the Nervous System  Central Nervous System (CNS) – brain and spinal cord  “Coordination/communication center”  Receives most impulses and determines “next steps”  Sends communication along spinal cord  Peripheral Nervous System (PNS) – all the nerve cells not part of the CNS  Receives internal and external sensory input  Receives and sends impulses to muscles or glands  Reflex arcs  Autonomic Nervous System – regulates activities that are involuntary 17

CNS and PNS 18

The Brain Cross-section of brain anatomy Cerebrum – largest part of brain Outer layer = cortex (gray matter) Inner layer = white matter Processes info from sense organs & directs signals to brain stem Cerebellum – back of skull, coordination & balance Brain stem – connects brain & spinal cord; regulates information flow & controls very basic body functions 19

Spinal Cord Carries signals between the brain and the rest of the body 20

Reflex Arc Impulse pathway travels directly from sensory neuron to spinal cord, interneuron and back to muscle or gland 21

Autonomic Nervous System Regulates activities that are involuntary 22

Summary – Brain Basics & Neuroscience 23