NERVOUS SYSTEM C H A P T E R 2 8

Transcription

1 NERVOUS SYSTEM C H A P T E R 2 8

2 CAN AN INJURED SPINAL CORD BE FIXED? Injuries to the spinal cord disrupt communication between the central nervous system (brain and spinal cord) and the rest of the body There are millions of nerve fibres make up the spinal cord, it is well protected by vertebrae from being severed but they can be crushed resulting in scar tissue that impedes the signals from passing There are different locations where these injuries can occur from resulting in debilitating injury

3 CHRISTOPHER REEVE The late actor Christopher Reeve Suffered a spinal cord injury during an equestrian competition Two vertebrae were in his neck were fractured, crushing the spinal cord at the base of his skull and causing quadriplegia Was an influential advocate for spinal cord research

4 UNIT M & N STANDARDS Core I can create a graphic organizer for the divisions of the nervous system. I can relate parts of the brain to various body functions. I can describe how the nervous and endocrine systems work together and provide a relevant example. I can compare and contrast sympathetic to parasympathetic nervous responses. I can explain overall function of a reflex arc. Advanced I can compare and contrast structures and functions of 3 kinds of neurons. I can provide an overview of the nervous impulse. I can provide an overview of the synaptic gap process. Crash Course Intro to the Nervous System

5 NERVOUS SYSTEM STRUCTURE AND FUNCTION Nervous systems receive sensory input, interpret it, and send out appropriate commands Nervous systems, are the most intricately organized data-processing systems on Earth A neuron consists of a cell body with A nucleus and organelles Long thin extensions called neuron fibres that convey signals

6 TWO MAIN DIVISIONS Two main divisions are: The central nervous system (CNS) Consists of brain and spinal cord The peripheral nervous system (PNS) Is mostly made up of communication lines called nerves that carry signals into and out of the CNS The PNS also has ganglia, which are clusters of neuron cell bodies

7 ORGANIZATION OF A NERVOUS SYSTEM The nervous system obtains and processes sensory information And sends commands to effector cells, such as muscles, that carry out appropriate responses It is organized as Sensory input: conduction from sensory receptors Integration: interpretation of the sensory signals Motor output: is the conduction of signals from the integration centres to the; Effector cells, such as a muscle or gland

8 AUTOMATIC RESPONSES Our body has automatic responses called reflexes

9 THREE FUNCTIONAL TYPES OF NEURONS Sensory Neurons: convey signals (information) from sensory receptors into the CNS Interneurons: Located entirely in CNS; integrate data and relay appropriate signals to other interneurons or motor neurons Motor Neurons: convey signals from the CNS to effector cells

10 THREE FUNCTIONAL TYPES OF NEURONS

11 NEURONS ARE THE FUNCTIONAL UNITS OF NERVOUS SYSTEMS Neurons are cells specialized for carrying signals and consist of A cell body Two types of extensions (fibers) that conduct signals, Numerous dendrites and axons

12 DENDRITES AND AXONS Dendrites are highly branched extensions that receive signals from other neurons and convey this information toward the cell body Axons are typically longer extensions that that transmit signals to other cells which may be other neurons or effector cells Axons from your spinal cord to muscle cells in your feet (1m long!)

13 SUPPORTING CELLS Supporting cells, known as glial cells are essential for the structural integrity and normal functioning Schwann Cells (PNS) or Oligodendrocytes (CNS) Covered in a myelin sheath (insulation) Nodes of Ranvier: are the only point on axons where signals can be transmitted

14 NERVE SIGNALS AND THEIR TRANSMISSION A neuron maintains a membrane potential across its membrane At rest, a neuron s plasma membrane has an electrical voltage called the resting potential

15 THE RESTING POTENTIAL The resting potential Exists because of differences in ionic composition of the fluids inside and outside of the cell K+ freely flows out, leaving an excess of negative charge Is caused by the membrane s ability to maintain a positive charge on its outer surface opposing a negative charge on its inner surface

16 A NERVE SIGNAL BEGINS AS A CHANGE IN THE MEMBRANE POTENTIAL A stimulus alters the permeability of a portion of the membrane allowing ions to pass through and changing the membrane s voltage A nerve signal, called an action potential Is a change in the membrane voltage from the resting potential to a maximum level and back to the resting potential

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18 THE ACTION POTENTIAL PROPAGATES ITSELF ALONG THE NEURON Action potentials Are self-propagated in a one-way chain reaction along a neuron Are all-or-none events The frequency of action potentials change but not their strength Will only change in frequency with strength in stimulus Crash Course Action Potentials

19 PROPAGATION OF THE ACTION POTENTIAL ALONG AN AXON 1 1. When this region of the axon (blue) has its Na+ channels open, NA+ rushes inward (blue arrows), and an action potential is generated 2. Soon, the K+ channels in that same region open allows K+ to diffuse out of the axon (green arrows), Na+ channels are closed and inactivated. Downswing of AP 3. Short time later, no signs of an AP because axon has returned to its resting potential 2 3

20 28.6 NEURONS COMMUNICATE AT SYNAPSE When an action potential reaches then end of an axon, it generally stops there. Action potentials are not transmitted from cell to cell rather information is transmitted at a synapse Synapses come in two varieties 1. Electrical 2. Chemical

21 ELECTRICAL SYNAPSE Electrical synapses pass electrical current directly from one neuron to the next The receiving neuron is stimulated quickly and the same frequency of action potentials as the sending neurons Electrical synapses are found in the heart and digestive tract, where nerve signals maintain steady, rhythmic muscle contractions

22 CHEMICAL SYNAPSES Chemical synapses have a narrow gap called the synaptic cleft which separates the sending neuron from the receiving neuron The electrical signal of the action potential is converted to a chemical signal The chemical signal consists of molecules called neurotransmitters that are stored in synaptic vesicles which are secreted out into the synaptic cleft The neurotransmitter crosses the synaptic cleft and binds to a receptor on the surface of the receiving cell

23 NEURON COMMUNICATION

24 CHEMICAL SYNAPSES MAKE COMPLEX INFORMATION PROCESSING POSSIBLE A neuron may receive information from hundreds of other neurons via thousands of synaptic terminals Neurons can have excitatory neurotransmitters (green) and inhibitory (red) which can create more action potentials or decrease action potentials respectively. The summation of excitation and inhibition determines whether or not a neuron will transmit a nerve signal

25 A VARIETY OF SMALL MOLECULES FUNCTION AS NEUROTRANSMITTERS Many small, nitrogen-containing molecules serve as neurotransmitters Acetylcholine is important in the brain and synapses between motor neurons and muscle cells They can act as both excitatory and inhibitory Biogenic amines are derived from amino acids These biogenic neurotransmitters are important in the CNS Epinephrine, norepinephrine, serotonin, dopamine

26 NEUROTRANSMITTERS Serotonin and dopamine affect sleep, mood, attention and learning Imbalances lead to various disorders Lack of dopamine Parkinson s Diseases Excess of dopamine Schizophrenia Reduced norepinephrine and serotonin types of depression LSD Acid produces hallucinogenic effects by binding to serotonin and dopamine receptors in the brain

27 NEUROTRANSMITTERS CONT D Four amino acid based neurotransmitters in CNS Aspartate and glutamate excitatory Glycine and GABA (gamma aminobutyric acid) are inhibitory Peptides can make neurotransmitters Substance P mediates our perception of pain Endorphins are both neurotransmitters and hormones decrease pain during physical and emotional stress Dissolved gases Nitric Oxide (NO) for E.D. Crash Course Synapses and Neurotransmitters

28 28.9 MANY DRUGS ACT AT CHEMICAL SYNAPSES Many psychoactive drugs act at synapses and affect neurotransmitter action

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30 A N I M A L N E R V O U S S Y S T E M P T 2

31 VERTEBRATE NERVOUS SYSTEMS ARE HIGHLY CENTRALIZED AND CEPHALIZED Skip The spinal cord runs lengthwise inside the vertebral column and conveys the information from the brain and integrates simple responses to certain kinds of stimuli like the knee-jerk reflex The brain includes the homeostatic centers that keep the body functioning smoothly The brain capillaries are the most selective to allow nutrients and oxygen in and keep other chemicals out using the blood brain barrier

32 COMPONENTS OF THE CNS Both the brain and the spinal cord have fluid-filled spaces Ventricles in the brain are continuous with the narrow canal of the spinal cord These cavities are filled with cerebrospinal fluid, which is the formed in the brain by filtering the blood. Also protecting the brain are the meninges, layers of connective tissue

33 GRAY AND WHITE MATTER White matter is mostly composed of axons with their myelin sheaths Gray matter consists mainly of nerve bodies and dendrites Cranial nerves originate in the brain and terminate in structures in the head and upper body Spinal nerves originate in the spinal cord and extend to everything else!

34 28.12 THE PERIPHERAL NERVOUS SYSTEM OF VERTEBRATES IS A FUNCTIONAL HIERARCHY The PNS can be divided into two functional components The somatic nervous system and the autonomic nervous system The somatic nervous system Carries signals to and from skeletal muscles, mainly in response to external stimuli The autonomic nervous system Regulates the internal environment by controlling smooth and cardiac muscles and the organs of various body systems Crash Course PNS

35 28.13 OPPOSING ACTIONS OF SYMPATHETIC AND PARASYMPATHETIC NEURONS REGULATE THE INTERNAL ENVIRONMENT The autonomic nervous system The parasympathetic division of the autonomic nervous system Primes the body for activities that gain and conserve energy for the body The sympathetic division of the autonomic nervous system Prepares the body for intense, energyconsuming activities Crash Course Autonomic Nervous System

36 28.14 THE VERTEBRATE BRAIN DEVELOPS FROM THREE ANTERIOR BULGES OF THE NEURAL TUBE The vertebrate brain develops from the forebrain, midbrain, and hindbrain The size and complexity of the cerebrum in birds and mammals correlates with their sophisticated behavior

37 28.15 THE STRUCTURE OF A LIVING SUPERCOMPUTER: THE HUMAN BRAIN The human brain is more powerful than the most sophisticated computer The human brain is composed of three main parts The forebrain, the midbrain, and the hindbrain

38 MAJOR STRUCTURES OF THE HUMAN BRAIN

39 THE BRAIN The midbrain and subdivisions of the hindbrain, together with the thalamus and hypothalamus Function mainly in conducting information to and from higher brain centers Regulate homeostatic functions, keep track of body position, and sort sensory information The forebrain s cerebrum Is the largest and most complex part of the brain

40 THE BRAIN CONT D Most of the cerebrum s integrative power resides in the cerebral cortex of the two cerebral hemispheres

41 28.16 THE CEREBRAL CORTEX IS A MOSAIC OF SPECIALIZED, INTERACTIVE REGIONS Specialized integrative regions of the cerebral cortex include The somatosensory cortex and centers for vision, hearing, taste, and smell The motor cortex Directs responses Association areas Concerned with higher mental activities such as reasoning and language, make up most of the cerebrum The right and left cerebral hemispheres Tend to specialize in different mental tasks

42 28.19 THE LIMBIC SYSTEM IS INVOLVED IN EMOTIONS, MEMORY, AND LEARNING The limbic system Is a functional group of integrating centers in the cerebral cortex, thalamus, and hypothalamus Is involved in emotions, memory, and learning