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Immagini e concetti della biologia Sylvia S. Mader Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

C2 - Nervous system Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

The response to stimuli The vertebrate nervous organization is characterized by cephalization, bilateral symmetry, spinal cord and an increased number of neurons. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

The response to stimuli A neural tube in the embryo is the precursor to the central nervous system (CNS). During the embryonic development, the neural tube differentiates into three regions: hindbrain, midbrain and forebrain. hindbrain midbrain forebrain Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

CNS PNS CNS and PNS Central nervous system Comprises the brain and spinal cord. Peripheral nervous system Consists of nerves and ganglia (neurons organized into clusters) outside the CNS. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Nervous system organization Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Neuroglia (or glial cells) node of Ranvier Schwann cells Neuroglia (or glial cells) Microglia destroy pathogens and remove dead cells. Astrocytes supply nutrients. Oligodendrocytes produce myelin and insulate axons in the CNS. Schwann cells insulate axons in the PNS with a myelin sheath. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Neurons are the functional units Sensory neurons (afferent) transport the input from receptors to the CNS. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Neurons are the functional units Motor neurons (efferent) carry commands to effectors (glands or muscles). Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Neurons are the functional units Interneurons in the CNS, store information and help with communication in the system and within motor and sensor neurons. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Inactive neurons have a resting potential In resting potential the axon is not conducting the impulse. Inside, the cell is negative at rest. The potential depends on the concentration of ions (Na+ and K+) in and out the membrane. [ Na+]out > [ Na+]in [ K+]in > [ K+]out Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Active neurons have an action potential An action potential is a rapid change in the membrane axon polarity as the impulse occurs. Voltage causes Na+ and K+ ions to move across cell membranes. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Active neurons have an action potential An action potential allows Na+ ions to flow in, thus inside the cell becomes more positive (depolarization). The action potential ends, K+ channels open and the equilibrium is reestablished (polarization). Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Propagation of action potential Ions channels are concentrated at the nodes of Ranvier, so action potential jumps from one node to the other and travels faster in a saltatory conduction. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Synapses Neurons communicate with other neurons at synapses, regions of close proximity between an axon terminal and a dendrite. Neurotransmitters are chemicals that transmit signals across a synapse. When a neurotransmitter is released into a synaptic cleft, transmission of a nerve impulse occurs. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Synapses Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Neurotransmitters Binding of neurotransmitters to a receptor can cause either stimulation or inhibition. Neurotransmitter Actions Notes Acetylcholine Neurotransmitter skeletal muscles and CNS Is involved in the Alzheimer’s disease. Norepinephrine in CNS and PNS, generally stimulates smooth muscles Involved in the response to stress and sugar consumption. Dopamine Neurotransmitter of the CNS Involved in emotions and schizophrenia (Parkinson’s disease). Serotonin Involved in pain control, sleep/wake control and mood. GABA Inhibitory neurotransmitter of the CNS Valium® amplifies the effects of the GABA. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Neurotransmitters Neurons integrate (sum) signals. 1. Inhibitory Signals: the threshold is not reached and the neuron is inactive 2. Excitatory signals: the neuron is activated 3. The Integrated signal is below the threshold and the impulse is not transmitted Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Some substances interfere with neurotransmitter dynamics Drugs (depressant or stimulant), alcohol (depressant), nicotine (stimulant) and marijuana (creates euphoria) affect the release of neurotransmitters and modify the transmission of the nerve impulse. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

CNS The CNS is composed by the brain and the spinal cord and is organized in neuronal nets. Brain and spinal cord function in strict connection and are protected by different structures: Skull, meninges, cerebrospinal fluid Brain Spinal cord Vertebral column Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

CNS: the spinal cord The spinal cord contains tracts that take the messages from and to the brain. The inner region of the spinal cord is the gray matter. The peripheral region is the white matter. vertebra spinal cord gray matter white matter Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

CNS: the ventricular system The brain contains a set of structures producing cerebrospinal fluid for mechanical protection. The system is composed of four ventricles: right and left lateral ventricles (in the cerebrum) third ventricle fourth ventricle Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

CNS: the cerebrum The cerebrum has two lateral cerebral hemispheres controlling the opposite side of the body connected by the corpus callosum. Each cerebral hemisphere has four lobes: frontal, parietal, occipital and temporal. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

CNS: the cerebrum A layer of neural tissue called the cerebral cortex overlays the cerebrum and is divided into two areas. The primary motor area sends voluntary motor commands to skeletal muscles. The primary somatosensory area receives sensory information from the skin and the skeletal muscles. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

CNS: other parts of the brain The diencephalon is composed by the hypothalamus, which controls homeostasis, and the thalamus which sends sensory inputs to the cerebrum. The cerebellum receives signals from eyes, ears and muscles and coordinates skeletal muscle contractions. The impulses to the motor and sensory systems pass through the brain stem, which contains the centers for regulating breathing, heartbeat and blood pressure. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

CNS: the limbic system The limbic system is involved in memory, emotions and learning. Hippocampus is involved in storing and retrieving memories, while the amygdala has a role in emotional reactions. The limbic system in purple Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

(containing the neuron body cell) PNS Is composed by: nerves (bundles of axons) ganglia (containing the neuron body cell) Cranial nerves: connect with the brain. Spinal nerves: connect with the spinal cord. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

PNS - the somatic system Brings sensory information from receptors (skin, joints, skeletal muscles) to the CNS Transports commands from CNS to skeletal muscles Responsible for voluntary control of body movements, with the exception of reflexes (automatic and involuntary). Reflex arch Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

PNS - the autonomic system Controls the involuntary visceral functions and movements (glands, cardiac muscle, smooth muscles). Parasympathetic - responses during relaxation/digestion Sympathetic - responses during times of stress Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018