- Slides: 27
The Nervous System Peripheral Nervous System
Human Nervous System Central Nervous System Brain + Spinal Cord Peripheral Nervous System Nerves (extensions from the CNS) Provides Basis For Conscious Experience
Peripheral Nervous System Skeletal - controls voluntary movements of skeletal muscles Afferent Efferent Autonomic - self-regulating, controls glands & muscles of internal organs (e. g. , heart) Sympathetic (arousing) Parasympathetic (calming)
Central Nervous System (billions of neurons & trillions of connections) Spinal Cord • Conduit between peripheral nervous system and the brain • Organize certain behaviors without the brain Conduit Function - Ascending tract carries sensory info to brain - Descending tract carries info from brain to muscles Organization Function - Governs reflexive actions of muscles
Organization of the Nervous System Central Nervous System Brain Spinal Cord Peripheral Nervous System Somatic Autonomic
Skeletal/Somatic Nervous System Nerves that connect to voluntary skeletal muscles and to sensory receptors Afferent Nerve Fibers Axons that carry info away from the periphery to the CNS Efferent Nerve Fibers Axons that carry info from the CNS outward to the periphery
Autonomic Nervous System Nerves that connect to the heart, blood vessels, smooth muscles and glands Sympathetic Division Mobilizes the body’s resources for emergencies (e. g. , stim adrenal gland) Fight Parasympathetic Division or Generally conserves bodily resources Flight (e. g. , slows heart rate) Response Cannon (1932)
The Nervous System Peripheral Nervous System (PNS) Made up of axons and dendrites. Central Nervous System (CNS) – brain and spinal cord directs mental and basic life processes. It send messages to and from the CNS. Somatic Nervous System (SNS) (Voluntary) sends sensory info to the CNS and motor messages to the muscles. Autonomic Nervous System (ANS) Involuntary serves our basic life functions. Sympathetic Nervous System Parasympathetic Nervous System Readies the body for a threat Calms the body down and maintains energy
What is a neuron? • Neurons are the individual cells that transfer information throughout the body. One trillion in our bodies. • The Dendrites receive the input from other neurons and sensory receptors. • Cell Body (Soma) receives the information and sends it down the axon. • The Myelin Sheath covers the axon and helps speed up the message. • Glial cells provide structural and nutritional support to the neuron.
Different Types of Neurons • Sensory Neurons send info. from the body tissues to the brain. • Motor Neurons take info from the brain and send it to the tissues. • Inter-neurons are our internal highway.
Neural Communication Sensory Neurons (few million) Interneurons (100 billion) Motor Neurons (few million)
Neural Transmission • • Action Potential – neural impulses or messages Ions – chemicals inside and outside the tube. Resting (polarized) – fluid outside has more + charged ions. Action potential creates depolarization of the membrane. - charge inside becomes + • Refractory Periods occur after each action potential +++---+++ ----++++---
Nerve Impulses more (+) less (+)
Nerve Impulses Action Potential 1. Depolarization - Na+ channel open, Na+ rushes in . . . a brief electrical charge traveling down the axon, like a line of dominos
Properties of Nerve Impulses • Once an AP is initiated, it travels down the length of the axon without stopping or changing size. • All or None Response • Stimulus Intensity: 8 SIZE of nerve firing é RATE of nerve impulse
Some Additional Properties Speed of AP determined by: 8 Axon Diameter ( diameter = ¯ resistance) 8 Myelin Sheath ( myelin = speed) Approx 200 mph!
The Synapse Now I can afford that hair piece! Santiago Ramón y Cajal • Synapse is the space between Dendrite and next neuron. • Chemical process bridges gap between neurons
Neural Transmission • The Synapse – the gap between the neurons – Terminal buttons & synaptic gap Terminal buttons release neurotransmitters that attach to the membrane of adjacent neuron Neurotransmitters can be excitatory or inhibitory. Terminal Button Synapse ØPresynaptic neuron – sends message ØPostsynaptic neuron – receives message
The Synapse 1. Nerve Impulse reaches Synaptic Vesicles in Terminal Button 2. Synaptic Vesicles release Neurotransmitters 3. Neurotransmitters are Excitatory or Inhibitory
Effects of Neurotransmitters Approx 15, 000 Synapses per Neuron • If sum of Inhibitory & Excitatory transmitters is greater than threshold èIMPULSE!
Neurotransmitters & Behavior 75 substances are clearly neurotransmitters Other chemicals may serve similar function Specific neurotransmitters work at specific kinds of synapses Agonists – excite or mimic neuro. Antagonist – inhibit by blocking neuro. Lock & Key
Acetycholine (ACh) ACh contributes to: Attention Arousal & Memory Processes Curare and the Black Widow Motor Neurons ACh Voluntary Muscles
Endorphins (aka Endogenous Morphines) Endorphins Entire family of internally produced chemicals that resemble opiates in structure and effects Cross Blood-Brain Barrier and bind to specialized receptors in the brain Neuromodulators Chemicals that modulate activity of specific NTs (e. g. , Decrease NT that delivers pain signals)
Endocrine System • Exocrine (outside body/glands) – salivary, tear, sweat • Endocrine (ducts) – release of hormones in the blood • Hormones move more slowly than neurotransmitters, but last longer. • Effect growth, reproduction, metabolism, mood Adrenal Gland Release hormone (epinephrine) Increase heart rate, blood pressure Increased energy
Endocrine System • • • Hypothalamus – control center Anterior pituitary – growth hormone Posterior pituitary – raises blood pressure Thyroid (thyroxin) – increases metabolic rate, growth Parathyroid – increases blood calcium, decreases potassium • Pancreas (insulin, glucagon) – regulates level of sugar • Ovary (estrogen) – promotes ovulation and sex characteristics • Testes (androgen)– promote sperm production and male sex characteristics