Nervous System Transmission of signals for communication and for coordination of body systems

Organization of Body Systems Organ System Central Nervous System Organ Brain Tissue Nerve Cell Neuron

Structure of a Neuron Dendrites (receive signals) Cell Body (maintains cell metabolism) Myelin Sheath (insulator) Axon terminal Axon (conducts signals) Dendrite of another neuron Axon of another neuron

Transmission of Nerve Impulse Along a Neuron Involves a change in charge across the neuron’s membrane, caused by the movement of ions Action Potential = rapid depolarization and repolarization of membrane

Electrical Events During An Action Potential 80 40 -40 -80 Recorded Potential (millivolts) Action Potential Extracellular Fluid (uncharged) 2 depolarization Threshold Resting Potential repolarization 3 1 EPSP polarized IPSP Time (milliseconds)

Resting Potential Depends on Ionic Gradients Net negative charge inside neuron Inside: Potassium ions are pumped into cell Na+ Na+ Cl- Large organic molecules cannot pass through membrane Cl- Na+ Org- K+ Org- K+ Org- K+ Org- Org- Org- Na+ K+ K+ Outside: Cl- Cl- K+ Org- Org- Sodium ions are pumped out Na+ Na+ Cl- Org- Chloride ions found in extra-cellular fluid Cl- K+

An Unstimulated Neuron at Resting Potential (Extracellular Fluid) Na+ Cl- Na+ K+ Na+ Cl- Cl- Cl- Na+ Sodium Channel (closed) Potassium Channel (Neuronal Membrane) K+ Org- Org- Org- K+ K+ Org- Org- K+ (Neuronal Cytoplasm, negatively charged)

Action Potential (Extracellular Fluid) Depolarization due to influx of sodium Repolarization due to efflux of potassium (Extracellular Fluid) Org- Na+ K+ Cl- Cl- Na+ K+ K+ K+ Na+ Na+ Na+ Org- Na+ K+ (Neuronal Cytoplasm, positively charged) (negatively charged)

Propagation of an Action Potential

Propagation of an Action Potential

Intensity of Nerve Signals 1 2 1 Fires slowly Gentle Touch 2 Silent 1 2 1 Fires more rapidly Moderate Pressure 2 Silent 1 2 1 Fires even faster Strong Pressure 2 Fires slowly

Transmission of Nerve Impulses Between Neurons Signal is carried by neurotransmitters that diffuse across the space between neurons Synapse: junction between neurons Synaptic cleft: space between neurons Neurotransmitters bind to receptors on next neuron, opening ion channels synapse

Structure and Operation of the Synapse 1 An action potential is initiated Structure and Operation of the Synapse 2 Action potential reaches synaptic terminal 3 Synaptic vesicles release neurotransmitter 5 Action Potential can be triggered in post-synaptic cell 4 Receptor binds neurotransmitter & opens ion channel

Transmission of Nerve Impulses Between Neurons Neurotransmitters can be Stimulatory: initiate action potential eg. Acetylcholine Inhibitory: prevent action potential eg. Dopamine

Neurotransmitters carry signals to muscle cells to stimulate contraction.

Applying Your Knowledge Potassium Ions (K+) Neurotransmitters Sodium Ions (Na+) Which one is responsible for Transmission of a nerve impulse across a synapse? Depolarization of a neuron’s membrane? Transmission of a nerve impulse along an axon? Repolarization of a neuron’s membrane?

Types of Neurons Receives information from environment Carries signal between sensory and motor neurons Generates a response

Pain-Withdrawal Reflex 2. Signal transmitted by sensory neuron 1. Pain receptor stimulated 3. Signal transmitted within spinal cord 4. Motor neuron stimulates muscle 5. Effector causes withdrawal

Nervous System Organization Central Nervous System (CNS) brain spinal cord Peripheral Nervous System (PNS) Sensory nerves carry sensory information into brain and spinal cord Motor nerves carry motor information from CNS to effectors somatic sensory nerves: signals from skin, muscles, joints, special senses Somatic motor nerves: signals to skeletal muscles, voluntary Autonomic motor nerves: signals to smooth muscle, cardiac muscle, glands, involuntary visceral sensory nerves: signals from body organs Sympathetic division “fight or flight” Parasympathetic division “rest and digest”

Autonomic Nervous System dilates pupils constricts pupils dilates air passages constricts bronchioles speeds heart slows heart decreases stomach and intestinal activity increases stomach and intestinal activity

Cortex: thinking, learning, memory, speech movement, senses Parts of the Brain sends sensory input to cerebrum homeostasis breathing, heart rate, blood pressure muscle coordination

Sensory Areas on Cerebral Cortex

Limbic System and Thalamus emotions, drives, behaviors Thalamus Cerebral Cortex relay center Hippocampus Hypothalamus Amygdala

Maintaining Homeostasis Negative Feedback: A change that initiates a series of events to counteract the change and restore the original state

Applying Your Knowledge Central Nervous System Somatic Nervous System Autonomic Nervous System Which one Is responsible for increasing breathing rate when you start running? Includes the spinal cord? Controls muscle movement?