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Nervous System

Nervous System. Complex network of nerves and cells that carry messages to and from the brain and spinal cord to various parts of the body. Nervous System. Neurons. Specialized nerve cells Functional unit of nervous system 3 parts Cell body Dendrites axon. Neuron. Cell Body

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Nervous System

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  1. Nervous System • Complex network of nerves and cells that carry messages to and from the brain and spinal cord to various parts of the body

  2. Nervous System

  3. Neurons • Specialized nerve cells • Functional unit of nervous system • 3 parts • Cell body • Dendrites • axon

  4. Neuron • Cell Body • contains nucleus and most organelles in cell • Synthesizes proteins, carbohydrates, lipids • Dendrites • Tree like branches that send signals towards the cell body • Axons • Single long, thin extension from cell body • Carry signals away from cell body • Contains axon terminals at tip of axon that enable signals to be transmitted from one neuron to another

  5. Neurons • 3 classes • Afferent neurons (sensory) – transmit stimuli collected by sensory receptors • Interneurons – integrate information, formulate a response • Efferent neurons (motor) – carry response signal to effectors (muscle, glands)

  6. Neural Signalling • Communication by neurons • Response to stimuli • 4 components • Reception – detection of stimulus (eyes, skin) • Transmission – movement of message along a neuron • Integration – interpretation of message • Response – output or action

  7. Neuronal Circuit/Reflex Arc • Connections between axon terminals of one neuron and the dendrites or cell body of a second neuron • Receptor → afferent neuron → one or more interneurons → efferent neuron → effector

  8. Reflex Arc • Simplest of neural circuits which does not require coordination of brain

  9. Neuron Support System • Speed rate at which electrical impulses move along axons • Glial cells • Provide nutrition and support to neurons • E.g. Schwann cells – form tightly wrapped layers of plasma membrane around axons – myelin sheaths • Myelin sheaths – electrical insulators (high lipid content) • Nodes of Ranvier • Gaps between Schwann cells • Expose axon membrane directly to extracellular fluid

  10. Nerve Signals • Use internal cellular energy to generate current (ATP) • Communicate across a synapse • Site where neuron makes a connection with another neuron or an effector • Two sides to a synapse • Pre-synaptic cleft – axon terminal • Post-synaptic cleft – dendrite or cell body • Communication occurs in 2 ways • Chemically • Electrically

  11. Chemical Synapse • Pre-synaptic cleft and post-synaptic cleft are separated by a gap (25nm) – synaptic cleft • Uses neurotransmitters to communicate between neurons

  12. Electrical Synapse • Pre-synaptic cleft and post-synaptic cleft are in direct contact • Current flows directly through nerurons • Gap junctions allow ions to flow • Provides rapid/synchronous transmission between neurons

  13. Conduction of Electrical Signals by Neurons • Membrane potential – difference in charge across the plasma membrane (K⁺ Na⁺) • Resting membrane potential/action potential • Sudden flow of ions across the plasma membrane via ion channels (Na⁺/K⁺ active transport pump) causes nerve impulses

  14. Na⁺/K⁺ Pump • Pumping of 3 Na⁺ ions out of the cell for every 2 K⁺ pumped into the cell • Net positive charge outside of cell

  15. Resting Membrane Potential • Neuron is not conducting a nerve impulse • Steady negative membrane potential (-70mV) • Cell is polarized

  16. Action Potential • Neuron conducts an electrical impulse • Temporary change in membrane potential • Positive charges flow inside the cell • 6 phases • Action potential is produced only if the stimulus is strong enough to cause depolarization to reach threshold – all or nothing principle

  17. Refractory Period • Threshold elevated to ensure a one way direction in neuron and gives channels time to reset themselves (resting period)

  18. Action Potential • Magnitude remains the same as it travels along the axis • The greater the stimulus, the faster the action potential is • Rate of conduction increases with diameter of axon

  19. Myelinated Axons • Saltatory conduction • Hopping of action potentials over myelin onto nodes of Ranvier • Na⁺ and K⁺ channels are crowded into nodes allowing for action potentials to develop • Speeds of up to 130 m/s compared to 1 m/s in unmyelinated • Allows for smaller sized and more tightly packed axons

  20. Conduction Across Chemical Synapses • Action potentials cannot jump across synapses • Use of neurotransmitters • Transmission becomes delayed allowing neurons to receive hundreds to thousands of axon terminals at the same time

  21. Conduction Across Chemical Synapses • Neurotransmitters are stored in synaptic vesicles in the cytosol of an axon terminal • Action potential stimulates the release of Ca²⁺ into the cytosol • Triggers a protein which allows vesicle to fuse with the plasma membrane releasing neurotransmitters into the synaptic cleft by exocytosis

  22. Role of Neurotransmitters • Diffuse across the synaptic cleft and bind to receptors located on the post synaptic cell • Binding opens gated ion channels (Na⁺, K⁺, Cl⁻) • Causes stimulatory/inhibitory effects

  23. Neurotransmitters

  24. Central Nervous System • Comprised of the • Brain, spinal cord • Manages body activities by integrating incoming sensory information from the PNS into effective responses • Control centre of the body

  25. Protective Connective Tissue • Meninges • 3 layers of connective tissue that surround and protect the brain and spinal cord • Cerebrospinal Fluid • Cushions the brain and spinal cord, nourishes and protects from toxic substances

  26. Spinal Cord • Carries impulses between brain and PNS • Contains interneuron circuits that control motor reflexes • Structures • Grey matter – consists of nerve cell bodies and dendrites • White matter – consists of myelinated axons • Dorsal root – incoming afferent neurons • Ventral root – outgoing efferent neurons • 31 pairs of spinal nerves • Caudaequina – collection of spinal nerves that leave inferior end of spinal cord

  27. Anatomy of Spinal Cord

  28. Cross Section

  29. Brain • Receives, integrates, stores, retrieves information • Interneurons generate responses that provide the basis for • Voluntary movements, consciousness, behaviour, emotions, learning, reasoning, language, and memory • Contains • Grey matter, white matter, meninges, cerebrospinal fluid • Broken into • Forebrain, midbrain, hindbrain

  30. Structures of Brain • Medulla oblongata • Involuntary behaviours – breathing, digestion, heart rate, blood pressure • Cerebellum • Voluntary behaviours – muscle contraction, balance, fine motor control • Pons – mass of fibres that connects cerebellum to higher centres of brain • Brain stem – pons and medulla • Connects forebrain to spinal cord

  31. Cerebrum • Controls most of the sensory and motor activities • Makes up most of the brain • Cerebral Cortex • Surface layer of cerebrum • Thin layer of grey matter – unmyelinated neurons • Carries out higher brain functions • Divided into left and right hemispheres – capability of functioning separately • Divided into parietal, frontal, temporal, occipital lobes

  32. Left and Right Hemispheres • Corpus Callosum • Thick axon bundles • Connect two hemispheres together and coordinates function • Recognizing faces, sense of time, recognizing emotions

  33. Sensory Regions of Cerebral Cortex • Frontal Lobe • Reasoning, motor skills, higher level cognition, expressive language • Parietal Lobe • Processing somatosensory area - touch, pain, temperature, pressure • Temporal Lobe • Primary auditory cortex, interpreting sounds and language • Hippocampus – memory • Occipital Lobe • Interpreting visual stimuli and information

  34. Somatosensory/Motor Cortex • Regions of the cerebral cortex that are involved with different functions • Form bands across the top of the brain

  35. Thalamus, Hypothalamus, Basal Nuceli • Thalamus • Receives sensory information and relays to appropriate regions of cerebral cortex • Waking and inducing drowsiness or sleep • Hypothalamus • Regulate homeostatic functions of body • Basal Nuclei/ganglia • Grey-matter centres that surround thalamus • Moderate voluntary movements directed by motor centres in cerebrum • Parkinsons disease

  36. Blood Brain Barrier • Tight junctions (impermeable membrane between two cells) that prevent most substances dissolved in blood from entering cerebrospinal fluid • Astrocytes protect from viruses, bacteria, toxic substances

  37. Peripheral Nervous System • Regulates both movement and internal environment of the body

  38. Efferent System • Made up of axons of neurons • Carries signals to muscle glands which act as effectors • Divided into • Somatic system – communicates with skeletal muscles • Autonomic system – communicates with smooth muscles and glands

  39. Somatic System • Conscious and voluntary • Controls body movements • Carries signals from CNS to skeletal muscles • 31 pairs of spinal nerves • 8 cervical, 12 thoracic, 5 lumbar, 5 sacral,1 coccygeal • Somatic nerves consist only of axons • Some Involuntary contractions • Reflexes, shivering, balance posture

  40. Autonomic System • Works with endocrine system to regulate the body in response to change • Uses motor nerves • Controls involuntary processes • Digestion, secretion, circulation, reproduction, excretory, contraction of smooth muscle, breathing • Broken into • Sympathetic – associated with nerves of chest and abdomen • Parasympathetic – associated with brain

  41. Sympathetic/Parasympathetic • Always active • Have opposing effects on organs they affect (precise control) one stimulates, the other inhibits • Uses two neurons • Dendrites and cell body in CNS • Ganglion outside CNS – enlargement of nerve where cell bodies of neurons are located • Sympathetic predominates during situations of stress, excitement, strenuous physical activity • Parasympathetic predominates during situations that are quiet, low stress

  42. Sympathetic/Parasympathetic

  43. Pain/Painkiller • Interpretation by the brain of sensory input received by specialized cells called substantiagelatinosa (SG) • Forms a band in the dorsal horn of grey matter in spinal cord • These cells are unmyelinated • SG cells are stimulated by an afferent nerve of PNS (stub your toe) • SG sends signal to brain to release endorphins and enkephalins (opioids) • Attach to receptors of SG and prevent communication

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