The Nervous System

Functions of the Nervous System Respond to internal and external stimuli Transmit nerve impulses to and away from CNS Interpret nerve impulses at the cerebral cortex Assimilate experiences in memory and learning Initiate glandular secretions and muscle contraction Program instinctual behavior

Organs and Divisions of the Nervous System Central nervous system (CNS)— brain and spinal cord Peripheral nervous system (PNS)—all nerves Autonomic nervous system (ANS) – sympathetic and parasympathetic

Cells of the Nervous System Neurons Consist of three parts Cell body of neuron—main part Dendrites—branching projections that conduct impulses to cell body of neuron Axon—elongated projection that conducts impulses away from cell body of neuron

Cells of the Nervous System Neurons Neurons classified according to function or direction of impulse Sensory neurons: conduct impulses to the spinal cord and brain; also called afferent neurons Motor neurons: conduct impulses away from brain and spinal cord to muscles and glands; also called efferent neurons Interneurons: conduct impulses from sensory neurons to motor neurons; also called central or connecting neurons

Nerves Nerve—bundle of peripheral axons Tract—bundle of central axons White matter—brain or cord tissue composed primarily of myelinated axons (tracts) Gray matter—brain or cord tissue composed primarily of cell bodies and unmyelinated fibers

Nerves Nerve coverings—fibrous connective tissue Endoneurium—surrounds individual fibers within a nerve Perineurium—surrounds a group (fascicle) of nerve fibers Epineurium—surrounds the entire nerve

Reflex Arcs Nerve impulses are conducted from receptors to effectors over neuron pathways or reflex arcs Conduction by a reflex arc results in a reflex (i.e., contraction by a muscle or secretion by a gland) The simplest reflex arcs are two-neuron arcs— consisting of sensory neurons synapsing in the spinal cord with motor neurons; three-neuron arcs consist of sensory neurons synapsing in the spinal cord with interneurons that synapse with motor neurons

Reflex Arcs https://www.youtube.com/watch?v=wLrhYzdbbpE

Nerve Impulses Self-propagating wave of electrical disturbance that travels along the surface of a neuron membrane; sometimes called action potentials

Nerve Impulses Mechanism At rest, the neuron’s membrane is slightly positive on the outside—polarized—from a slight excess of Na+ on the outside A stimulus triggers the opening of Na+ channels in the plasma membrane of the neuron Inward movement of Na+ depolarizes the membrane by making the inside more positive than the outside at the stimulated point; this depolarization is a nerve impulse (action potential) The stimulated section of membrane immediately repolarizes, but by that time the depolarization has already triggered the next section of membrane to depolarize, thus propagating a wave of electrical disturbances (depolarizations) all the way down the membrane

The Synapse Place where impulses are transmitted from one neuron to another (the postsynaptic neuron) Synapse made of three structures—synaptic knob, synaptic cleft, and plasma membrane Neurotransmitters bind to specific receptor molecules in the membrane of a postsynaptic neuron, opening ion channels and thereby stimulating impulse conduction by the membrane https://youtu.be/Iws8w6NpsGg - easier video https://youtu.be/L41TYxYUqqs- Bozman science

Neurotransmitters Actions Disorder Involving It Acetylcholine Dopamine -Triggers muscle contraction and stimulates the excretion of certain hormones -In CNS: involved in wakefulness, attentiveness, anger, aggression, etc. Alzheimer’s disease (lack of acetylcholine in certain areas of the brain) Dopamine -Controls movement and posture, modulates mood, and plays a central role in positive reinforcement and dependency Parkinson’s disease (loss of dopamine in certain areas of the brain) GABA (gamma-aminobutyric acid) -Contributes to motor control, vision, and many other cortical functions; regulates anxiety Drugs that increase GABA in the brain are used to treat epilepsy and Huntington’s disease Glutamate -Learning and memory Thought to be associated with Alzheimer’s disease, whose first symptoms include memory malfunctions Norepinephrine -Attentiveness, emotions, sleeping, dreaming, and learning; also released as a hormone into the blood, where it causes blood vessels to contract and heart rate to increase Mood disorders like manic depression Serotonin -Regulating body temperature, sleep, mood, appetite, and pain Depression, impulsive behavior, and aggressiveness

Central Nervous System (CNS) Brain Divisions Brainstem Cerebellum Cerebrum Spinal Cord

Brain - Brainstem Consists of three parts, named in ascending order: medulla oblongata, pons, and midbrain Structure—white matter with bits of gray matter scattered through it Functions All three parts of brainstem are two-way conduction paths Sensory tracts in the brainstem conduct impulses to the higher parts of the brain Motor tracts conduct from the higher parts of the brain to the spinal cord Many important reflex centers lie in the brainstem

Brain - Brainstem Medulla oblongata Pons Midbrain Connects brain to spinal cord Regulates breathing, heart and blood vessel function, digestion, sneezing, and swallowing Pons Helps relay messages from the cortex and the cerebellum Midbrain Associated with vision, hearing, motor control, sleep/wake, arousal (alertness), and temperature regulation

Brain - Cerebellum Second largest part of the human brain Helps control muscle contractions to produce coordinated movements so that we can maintain balance, move smoothly, and sustain normal postures Recent evidence shows the coordinating effects of the cerebellum may be more extensive, also assisting the cerebrum and other regions of the brain

Brain - Cerebrum Largest part of the human brain Outer layer of gray matter is the cerebral cortex; made up of lobes; composed mainly of dendrites and cell bodies of neurons Interior of the cerebrum composed mainly of white matter (i.e., nerve fibers arranged in bundles called tracts) Functions of the cerebrum—mental processes of all types, including sensations, consciousness, memory, and voluntary control of movements

Brain – Lobes of the Cerebrum Frontal Lobe Personality, behavior, emotions Judgment, planning, problem solving Speech: speaking and writing (Broca’s area) Body movement (motor strip) Intelligence, concentration, self awareness Occipital Lobe Interprets vision (color, light, movement) Parietal Lobe Interprets language, words Sense of touch, pain, temperature (sensory strip) Interprets signals from vision, hearing, motor, sensory and memory Spatial and visual perception Temporal Lobe Understanding language (Wernicke’s area) Memory Hearing Sequencing and organization

Deep Structures of the Brain Hypothalamus gland: hunger, thirst, sleep, and sexual response, regulates body temperature, blood pressure, emotions, and secretion of hormones Pituitary gland: known as the “master gland,” it controls other endocrine glands in the body; produces many hormones Pineal gland: regulates the body’s internal clock and circadian rhythms by secreting melatonin Thalamus: serves as a relay station for almost all information that comes and goes to the cortex Limbic system (includes hypothalamus, amygdala, and hippocampus) Amygdala: emotional reactions Hippocampus: memory Corpus callosum: allows for communication between hemispheres

Brain Myths: Fact or Fiction? You only use 10% of your brain. A person can be either left-brained or right-brained. Each person’s brain has a set learning style. Some people are able to multitask very well.

Testing your memory I will recite a list of 10 words Do not record them in any way Try to remember as many of them as you can (in order if possible) You will then be able to write them down to see what you were able to remember

Sunflower ball Red money Chair rain Woman Globe Comb theater

Spinal Cord Columns of white matter, composed of bundles of myelinated nerve fibers, form the outer portion of the H-shaped core of the spinal cord; bundles of axons called tracts Interior composed of gray matter made up mainly of neuron dendrites and cell bodies Spinal cord tracts provide two-way conduction paths— ascending and descending Spinal cord functions as the primary center for all spinal cord reflexes; sensory tracts conduct impulses to the brain, and motor tracts conduct impulses from the brain

Coverings and fluid spaces of the brain and spinal cord Cranial bones (skull) and vertebrae Cerebral and spinal meninges Fluid spaces Subarachnoid spaces of meninges Central canal inside cord Ventricles in brain Fluid Cerebrospinal fluid – cushions and provides immune protection

Peripheral Nervous System (PNS) Cranial nerves 12 pairs—attached to undersurface of the brain Connect brain with the neck and structures in the thorax and abdomen Spinal nerves 31 pairs—contain dendrites of sensory neurons and axons of motor neurons Conduct impulses necessary for sensations and voluntary movements After exiting the vertebral column, they split, combine, and split again forming a plexus (there are 4) Cervical plexus Brachial plexus Lumbar plexus Sacral plexus

Autonomic Nervous System Responsible for controlling unconscious bodily functions (heartbeat, breathing, digestion) Composed of two divisions: the sympathetic system and the parasympathetic system

Autonomic Nervous System Sympathetic nervous system Serves as the emergency or stress system, controlling visceral effectors during strenuous exercise and when strong emotions (anger, fear, hate, or anxiety) are elicited Group of changes induced by sympathetic control is called the fight-or-flight response Parasympathetic nervous system Dominates control of many visceral effectors under normal, everyday conditions