1

2 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Sylvia S. Mader Immagini e concetti della biologia

3 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 C2 - Nervous system

4 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 The response to stimuli The vertebrate nervous organization is characterized by cephalization, bilateral symmetry, spinal cord and an increased number of neurons.

5 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 The response to stimuli hindbrainmidbrainforebrain 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.

6 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 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. CNS PNS

7 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Nervous system organization

8 node of Ranvier Schwann cells Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 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.

9 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Neurons are the functional units Sensory neurons (afferent) transport the input from receptors to the CNS.

10 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Neurons are the functional units Motor neurons (efferent) carry commands to effectors (glands or muscles).

11 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Neurons are the functional units Interneurons in the CNS, store information and help with communication in the system and within motor and sensor neurons.

12 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 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

13 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 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.

14 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 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).

15 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 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.

16 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 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.

17 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Synapses

18 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Neurotransmitters Binding of neurotransmitters to a receptor can cause either stimulation or inhibition. Neurotransmitter ActionsNotes 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 CNSInvolved in emotions and schizophrenia (Parkinson’s disease). Serotonin Neurotransmitter of the CNSInvolved in pain control, sleep/wake control and mood. GABA Inhibitory neurotransmitter of the CNS Valium® amplifies the effects of the GABA.

19 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Neurotransmitters 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 Neurons integrate (sum) signals.

20 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 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.

21 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 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: Brain Spinal cord Skull, meninges, cerebrospinal fluid Vertebral column

22 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 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

23 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 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

24 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 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.

25 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 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.

26 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 The diencephalon is composed by the hypothalamus, which controls homeostasis, and the thalamus which sends sensory inputs to the cerebrum. CNS: other parts of the brain 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.

27 The limbic system in purple Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 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. CNS: the limbic system

28 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Is composed by PNS GANGLIA Containing the neuron body cell NERVES Bundles of axons Cranial nerves: connect with the brain. Spinal nerves: connect with the spinal cord.

29 Sylvia S. Mader Concepts of Biology © Zanichelli editore, Brings sensory information from receptors (skin, joints, skeletal muscles) to the CNS 2.Transports commands from CNS to skeletal muscles Responsible for voluntary control of body movements, with the exception of reflexes (automatic and involuntary). PNS - the somatic system Reflex arch

30 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Controls the involuntary visceral functions and movements (glands, cardiac muscle, smooth muscles). PNS - the autonomic system Parasympathetic responses during relaxation and digestion ("rest and digest") Sympathetic responses during times of stress ("fight or flight")