Nervous System Anatomy & Physiology PDF

Nervous System Anatomy & Physiology Nervous System The nervous system’s function is rapid communication by electrical and chemical signals. It functions for coordination (integration) of many activities through the conduction of impulses from the receptors (sensory input – afferent)...

Nervous System Anatomy & Physiology Nervous System The nervous system’s function is rapid communication by electrical and chemical signals. It functions for coordination (integration) of many activities through the conduction of impulses from the receptors (sensory input – afferent) to the effectors (motor output – efferent). It helps maintain homeostasis and mental activity including consciousness, thinking, memory and emotions. Functions Lorem of the ipsum dolor Nervous sit amet, System: consectetuer 1. Receiving sensory input adipiscing elit. Maecenas porttitor congue 2. Integrating information 3. Controlling motor output 4. Establishing and maintaining mental activity 5. Maintaining homeostasis Nervous System Lorem ipsum dolor sit amet, consectetuer LOREM IPSUM DOLOR SIT AMET, adipiscing elit. Maecenas porttitor congue CONSECTETUER ADIPISCING ELIT2 Nervous System Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Maecenas porttitor congue Neuron Neurons or Nerve Cells are the functional units of the nervous system. It is a cell that communicates either with one another or with muscles and glands. A neuron sends messages by conveying a neural impulse. These signals result from the movement of charged ions across the cell membrane. Parts of the Neuron 1. Cell Body The cell body is the enlarged and rounded part that contains the nucleus, mitochondria that supply ATP, ribosomes that manufacture proteins, and other organelles. 2. Dendrites Dendrites are short, branched extensions that transmit information toward the cell body. The number of dendrites may range from one to thousands, and each can receive input from many other neurons. Parts of the Neuron 3. Axon The axon, also called the nerve fiber, conducts nerve impulses away from the cell body. It is a single long extension that is finely branched at its tip. Myelin Sheath The myelin sheath, composed of fatty material, coats sections of the axon speeding up nerve impulse conduction. Nodes of Ranvier These are gaps in the myelin sheath coating on the neural axon. Parts of the Neuron Neurons Based on Functions 1. Sensory / Afferent Neuron brings information to the central nervous system from the rest of the body. 2. Interneuron connects one neuron to another within the spinal cord and brain. 3. Motor / Efferent Neuron conducts its message from the central nervous system toward a muscle or gland cell. Neurons Based on Functions Neurons Based on Structure 1. Unipolar – single process from the cell body which is an axon. That single process splits into longer processes (a dendrite plus an axon). Unipolar neurons are most of the body’s sensory neurons. The dendrites are found at the receptor and the axon leads to the spinal cord or brain. 2. Bipolar – one dendrite and one axon attached to the cell body. Bipolar neurons are rare and found only in the eyes, nose, and ears 3. Multipolar – several dendrites and one axon. Multipolar neurons are found as motor and interneurons. Neurons Based on Structure Neuroglial Cells Neuroglia are the major supporting cells in the nervous system. These cells help hold the nervous tissues together. 1. Astrocytes – located at the brain and spinal cord, star-shaped cells containing microfilaments giving them considerable strength to support neurons. Processes of astrocytes wrapped around capillaries isolate the neurons from various potentially harmful substances in the blood maintaining selective permeability. 2. Microglia – located also at the brain and spinal cord, these cells function as phagocytes, removing microbes and damaged nervous tissues. Neuroglial Cells 3. Ependymal cells – cells that line the brain ventricles and central canal of the spinal cord (these are spaces filled with cerebrospinal fluid, which protects and nourishes the brain and spinal cord). Ependymal cells produce and assist in the circulation of CSF. 4. Oligodendrocytes – are responsible for forming and maintaining the myelin sheath around the neural axons of the brain and spinal cord. A single oligodendrocyte myelinates several axons. Neuroglial Cells 5. Schwann cells – these are cells that form the myelin sheath around the axons of nerves outside the brain and spinal cord. Several Schwann cells myelinate a single axon. 6. Satellite cells – flat cells that surround the cell bodies of neurons outside the brain and spinal cord providing structural support. These cells also regulate exchanges of materials between cell bodies and the interstitial fluid. Neuroglial Cells Neuroglial Cells Functions of Neurons 1. Irritability - the ability to respond to a stimulus and convert it to a nerve impulse. The transmission of a nerve impulse along a neuron from one end to the other occurs as a result of electrical changes across the membrane of the neuron. Action Potential – also known as a nerve impulse or nerve signal, a pulse-like wave of voltage that passes on through a neuron that influences other neurons. Irritability Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Maecenas porttitor congue Irritability Irritability Functions of Neurons 2. Conductivity - the ability to transmit the impulse to other neurons, muscles, or glands. When a nerve impulse reaches the end of an axon, the axon releases chemicals called neurotransmitters stored in its synaptic vesicles. Synapse A chemical synapse is a specialized junction at which a signal from one neuron’s axon flows with another neuron or an effector organ such as a muscle or gland. Conductivity Synapse Synaptic Cleft The space between 2 communicating nerve cells Presynaptic Terminal It consists of the end of an axon. The synaptic terminal contains many small sacs, or vesicles, that hold neurotransmitter molecules. Postsynaptic Membrane The receptor-containing membrane of the postsynaptic cell opposed to the presynaptic terminal. Postsynaptic cells are typically other neurons, muscles, or glands. Conductivity Conductivity Conductivity Neurotransmitters A neurotransmitter is a chemical signal that travels from a “sending” cell to a “receiving” cell. These substances may be excitatory or inhibitory. Neurotransmitters travel across the synapse between the axon and the dendrite of the next neuron. Neurotransmitters bind to the membrane of the dendrite. Conductivity Conductivity Removal of Neurotransmitters: Neurotransmitters have short-term effects on postsynaptic membranes because the neurotransmitter is rapidly destroyed or removed from the synaptic cleft. 1. Diffusion – the movement of molecules away from the synapse into the extracellular fluid 2. Enzymatic processes – breakdown of neurotransmitters by enzymes 3. Reuptake by cells – neurotransmitters are transported back into the presynaptic terminal where it is repackaged into the synaptic vesicles for reuse Nervous Tissue 1. Gray Matter The gray matter consists of neuron cell bodies and dendrites, along with the synapses by which they communicate with other cells. Information processing occurs in the gray matter. 2. White Matter The white matter consists of myelinated axons transmitting information throughout the nervous system. The white matter forms the nerve tracts or conduction pathways of the brain and spinal cord which propagate impulses. Outside the brain and spinal cord, the bundles of axons and their connective tissue sheaths are called nerves. Nervous Tissue Nervous System Divisions Central Nervous System The CNS consists of the brain and spinal cord, which act as the integrating and command centers of the nervous system. Brain - the largest and the most complex mass of nerve tissue in the body - functions to exert centralized control over the other organs of the body - acts on the rest of the body both by generating patterns of muscle activity and by driving the secretion of chemicals called hormones Brain Subdivisions Hindbrain 1. Cerebellum The cerebellum is the largest part of the hindbrain. The neurons of the cerebellum refine motor messages and coordinate muscle movements for posture and balance subconsciously. 2. Medulla Oblongata Pathway for ascending and descending nerve tracts. This region not only regulates blood vessel diameter, breathing, blood pressure, and heart rate, but it also contains reflex centers for vomiting, coughing, sneezing, defecating, swallowing, and hiccupping. 3. Pons The pons which means “bridge”, connects the forebrain with medulla and cerebellum enabling relaying of information. Hindbrain Hindbrain Midbrain 1. Brainstem The brainstem is made up of the midbrain and parts of the hindbrain (medulla oblongata and pons). It is a stalk-like lower portion of the brain that regulates essential survival functions such as breathing and heartbeat. It connects the spinal cord to the brain. 2. Reticular Formation It is nuclei scattered throughout the brainstem; controls many brainstem activities, including motor control, pain perception, rhythmic activities, and the sleep wake cycle (Circadian rhythm). Midbrain Forebrain 1. Cerebrum It controls the activities of the lower parts of the brain. The cerebrum contains the cortex enabling it to perform higher functions like interpreting touch, vision and hearing, as well as speech, reasoning, emotions, learning, and fine control of movement. The cerebrum controls the qualities of what we consider the “mind” that is personality, intelligence, learning, perception, and emotion. 2. Diencephalon It connects the brainstem to the cerebrum; has many relay and homeostatic functions. Forebrain Cerebrum The entire surface of the cerebrum exhibits elevated ridges called gyri (gyrus), separated by shallow grooves called sulci (sulcus). Both are considered anatomical landmarks and function to increase the brain’s surface area. It is divided into 2 hemispheres that gather and process information simultaneously. Left hemisphere: speech, language skills, mathematical ability and reasoning Right hemisphere: spatial, intuitive, musical, and artistic abilities Each hemisphere controls the opposite side of the body. Cerebrum Corpus Callosum The corpus callosum is a very large fiber tract that connects the cerebral hemispheres. The cerebral hemispheres work together, interconnected by a thick band of nerve fibers called the corpus callosum. Parts of the Cerebrum: 1. Cerebral Cortex 2. Limbic System 3. Basal Nuclei Cerebral Cortex The cerebral cortex is the outer layer of the cerebrum that consists of gray matter that processes information. Frontal Lobe – primary motor area that allows the conscious movement of the skeletal muscles. Parietal Lobe – somatic sensory area. The body’s sensory receptors are localized and interpreted in this area of the brain. Allows recognition of pain, coldness and light touch. Temporal Lobe – auditory and olfactory area. Occipital Lobe – visual area. Cerebral Cortex Cerebral Cortex Limbic System The Limbic System found also in the cerebrum is a loosely defined collection of brain structures that is sometimes called the emotional center of the brain. It plays a central role in basic survival functions such as memory, reproduction, and nutrition. Hippocampus – participates in long-term memory formation. Amygdala – center of emotions such as pleasure or fear. The amygdala sends signals to the hypothalamus which activates the autonomic nervous system and coordinates the physical sensations that accompany strong emotions. Basal Nuclei Basal Nuclei or Basal Ganglia It is located bilaterally in the inferior cerebrum, controls muscle activity and posture, largely inhibits unintentional movement when at rest. Nuclei – clusters of gray matter located deep within the brain. Diencephalon 1. Thalamus The thalamus is a mass of gray matter located between the midbrain and the cerebrum. This central relay station processes incoming sensory information and sends it to the appropriate part of the cerebrum. It also influences mood and movement. 2. Subthalamus Small area inferior to the thalamus. It contains nerve tracts and nuclei. The subthalamic nuclei are associated with the basal ganglia and are involved in controlling motor functions. Diencephalon 3. Epithalamus Small area superior and posterior to the thalamus. It contains nuclei responding to olfactory stimulation and contains the pineal gland for sleep wake cycle and other biorhythms. Pineal gland secretes melatonin. 4. Hypothalamus Neural and hormonal signals from the hypothalamus regulate body temperature, heartbeat, water balance, and blood pressure, along with hunger, thirst, sleep, and sexual arousal. It also functions for mood, motivation, and emotion. It also interacts with the reticular activating system coordinating the sleep wake cycle. Forebrain