Chapter 7 The Nervous System Functions of the Nervous System 1. Sensory input—gathering information Sensory receptors monitor changes, called stimuli, occurring inside and outside the body 2. Integration Nervous system processes and interprets sensory input and decides what action is needed 3. Motor output A response, or effect, activates muscles or glands Organization of the Nervous System Central nervous system (CNS) Brain and spinal cord Integration and command center which interprets incoming sensory information and issues outgoing commands Peripheral nervous system (PNS) Paired spinal and cranial nerves Carries messages to and from the spinal cord and brain Peripheral Nervous System: Two Functional Divisions Sensory (afferent; “carrying toward”) division Motor (efferent; “carrying away”) division Transmits impulses from the CNS to effector organs (muscles and glands) Motor Division: Two Main Parts Somatic nervous system Conscious control of skeletal muscles (voluntary nervous system) Autonomic nervous system (ANS) Regulates smooth muscle, cardiac muscle, and glands (involuntary nervous system) Divisions – the ANS is further divided down into the sympathetic and parasympathetic which work in opposition to each other Histology of Nerve Tissue Two main cell types of the nervous system: Neurons – excitable cells that transmit electrical signals Supporting cells (neuroglia) – cells that surround and wrap neurons Unable to conduct nerve impulses Never lose the ability to divide Support Insulate Protect neurons Neurons (Nerve Cells) Neurons send electrical signals in the body. Composed of a body, axon, and dendrites. Long-lived, generally amitotic (don’t divide) high metabolic rate (need a lot of glucose and oxygen) Dendrite Cell body Axon Nucleus One Schwann cell Axon terminal Schwann cells, forming the myelin sheath on axon Nerve Cell Components Nerve Cell Body: Contains the nucleus Dendrites: short, tapering, branches that receive input for the neuron and conduct impulses toward the cell body Neurons may have hundreds of dendrites Axons: Neurons have only one axon arising from the cell body They conduct impulses away from the cell body Nerve Cell Components Axonal terminal – the branched endings of the axon that contain vesicles with neurotransmitters Axonal terminals release neurotransmitters (signaling chemicals) Axon terminals are separated from the next neuron by a gap called the synaptic cleft Synapse— junction between two nerves where a nerve impulse is transmitted Myelin Sheath Whitish, fatty segmented material surrounding most long or thick axons Created by the Schwann cells (support cell) It functions to: Protect the axon Electrically insulate fibers from one another Increase the speed of nerve impulse transmission Found only with axons, never dendrites Nervous Tissue: Neurons Terminology Nuclei—clusters of cell bodies in the CNS Ganglia—collections of cell bodies outside the CNS in the PNS Tracts—bundles of nerve fibers in the CNS Nerves—bundles of nerve fibers in the PNS White matter—collections of myelinated fibers (tracts) Gray matter— unmyelinated fibers and cell bodies Neuron Classification: Functional Sensory (afferent) — transmit impulses toward the CNS Motor (efferent) — carry impulses away from the CNS Interneurons (association neurons) — lie between motor and sensory neurons in neural pathways and shuttle signals through CNS pathways where integration occurs. Over 99% of neurons in the body including those in the CNS are interneurons. Neurons classified by function Sensory neuron Spinal cord (central nervous system) Dendrites Afferent transmission Receptors Peripheral nervous system Efferent transmission Motor neuron To effectors (muscles and glands) Interneuron (association neuron) PNS Tracts Spinothalamic tract (anterior/lateral) Anterior: crude touch and pressure Lateral: pain and temperature Spinocerebellar tract (golgi tendon organs/muscle spindles) Proprioception Fine touch Neurophysiology Electrical conditions of a resting neuron’s membrane The plasma membrane at rest is inactive (polarized) A resting, polarized neuron’s plasma membrane is (+) on the outside and (-) inside of the membrane K+ is the major positive ion inside the cell Na+ is the major positive ion outside the cell As long as the inside of the membrane is more negative than the outside, the cell remains inactive Neurophysiology Certain stimuli can change the neuron’s permeability to sodium ions Sodium channels now open, and sodium (Na+) diffuses into the neuron The inward rush of sodium ions changes the polarity at that site and is called depolarization The depolarization initiates and generates an action potential (electrical nerve impulse). Neurophysiology Resting membrane is polarized. The external face of the membrane is slightly positive; its internal face is slightly negative. The chief extracellular ion is sodium (Na+), whereas the chief intracellular ion is potassium (K+). The membrane is relatively impermeable to both ions. 1 [Na+ ] [K+] Na+ Na+ Stimulus causes local depolarization. A stimulus changes the permeability of a local “patch” of the membrane, and sodium ions diffuse rapidly into the cell. This changes the polarity of the membrane (the inside becomes more positive; the outside becomes more negative) at that site. 2 Depolarization – the inside of the membrane becomes less negative Na+ enters the cell making the inside more positive (Depolarization) Repolarization – the membrane returns to its resting potential K+ exits the cell and internal negativity of the resting neuron is restored (Repolarization) Action Potential: Role of the Na+-K+ Pump Initial conditions of sodium and potassium ions are restored using ATP driven the sodiumpotassium pump. This restores the ionic original configuration. https://www.youtube.com/watch? v=_bPFKDdWlCg Synapses A synapse is a junction that mediates information transfer from one neuron to an effector cell. Effector cells are either: another neuron muscle gland Synapses: Neurotransmitters Transmission of the signal at synapses When the action potential reaches the axon terminal, the electrical charge causes the release of neurotransmitters into the synaptic cleft The neurotransmitter molecules diffuse across the synaptic cleft and bind to receptors on the membrane of the next neuron Eventually an action potential (nerve impulse) will occur in the neuron beyond the synapse Synaptic Cleft: Information Transfer BioFlix: How Synapses Work https://www.youtube.com/watch?v=Ibzfwtdtong © 2018 Pearson Education, Inc. Nervous Tissue: Reflexes Reflexes are rapid, predictable, and involuntary responses to stimuli Reflexes occur over neural pathways called reflex arcs Two types of reflexes: Somatic reflexes stimulate the skeletal muscles Autonomic reflexes regulate smooth muscles, the heart, and glands Central Nervous System (CNS) Brain regions 1. Paired (left and right) Cerebral hemispheres Lobes are named for the cranial bones that lie over them 2. Diencephalon 3. Brain stem 4. Cerebellum Regions of the Brain Functional Anatomy of the Brain Three main regions of cerebral hemisphere 1. 2. 3. Cortex is superficial gray matter White matter Basal nuclei are deep pockets of gray matter Left lateral view of the brain Frontal lobe Parietal lobe Occipital lobe Temporal lobe Cerebellum Cerebral cortex (gray matter) Medulla oblongata Spinal cord Cerebral white matter Functional Anatomy of the Brain: Cerebral Cortex (Gray Matter) Primary motor area (frontal lobe) Primary somatic sensory area (parietal lobe) Allows us to consciously move skeletal muscles Receives impulses from the body’s sensory receptors Cerebral areas involved in special senses Visual area (occipital lobe) Auditory area (temporal lobe) Olfactory area (temporal lobe) Primary motor area Primary somatic sensory area Gustatory area (taste) • Working memory and judgment • Problem solving • Language comprehension Broca’s area (motor speech) Olfactory area Visual area Auditory area Sensory and Motor Cortex Anatomy of the Brain: Diencephalon Made of three structures: 1. Thalamus 2. Hypothalamus 3. Epithalamus Sits on top of the brain stem Enclosed by the cerebral hemispheres Important autonomic nervous system center Regulates body temperature Regulates water balance Regulates metabolism Cerebral hemisphere Corpus callosum Occipital lobe Thalamus Pineal gland Hypothalamus Pituitary gland Medulla oblongata Spinal cord Cerebellum Anatomy of the Brain: Brain Stem Anatomy of the Brain: Cerebellum Controls balance Provides precise timing for skeletal muscle activity and coordination of body movements Spinal Cord Extends from the foramen magnum of the skull to the first or second lumbar vertebra Provides a two-way conduction pathway to and from the brain 31 pairs of spinal nerves arise from the spinal cord Cervical enlargement Cervical spinal nerves C8 Thoracic spinal nerves Lumbar enlargement T12 End of spinal cord Lumbar spinal nerves L5 S1 S5 Sacral spinal nerves Peripheral Nervous System (PNS) PNS consists of nerves and ganglia outside the CNS Nerves are bundles of neurons found outside the CNS Mixed nerves Sensory (afferent) nerves Contain both sensory and motor fibers Carry impulses toward the CNS Motor (efferent) nerves Carry impulses away from the CNS Axon Myelin sheath Endoneurium Perineurium Epineurium Fascicle Blood vessels Cranial Nerves 12 pairs of nerves that arise from the brain and serve mostly the head and neck Only the pair of vagus nerves (X) extends to thoracic and abdominal cavities I. Olfactory – smell II. Optic – vision VIII. Vestibulocochlear – Hearing and balance Testing Cranial Nerves https://www.youtube.com/watch?v=jdRJqbB0ZyA Spinal Nerves Spinal nerves 31 pairs Named for the region of the spinal cord from which they arise Plexus—networks of nerves serving motor and sensory needs of the limbs Four plexuses 1. 2. 3. 4. Cervical Brachial Lumbar Sacral Cervical nerves Thoracic nerves Lumbar nerves Sacral nerves C1 2 3 4 5 6 7 8* T1 2 3 4 5 6 7 8 9 10 11 12 L1 2 3 4 Cervical plexus (C1 – C5) Brachial plexus (C5 – C8; T1) No plexus formed (intercostal nerves) (T2 – T12) Lumbar plexus (L1 – L4) 5 S1 2 3 4 Sacral plexus (L4 – L5; S1 – S4) Axillary nerve Humerus Radial nerve Musculocutaneous nerve Ulna Radius Ulnar nerve Median nerve (a) Brachial plexus, anterior view Femoral nerve Femur (b) Lumbar plexus, anterior view Sciatic nerve Common fibular nerve Tibial nerve (c) Sacral plexus, posterior view Autonomic Nervous System Motor subdivision of the PNS Consists only of motor nerves Controls the body automatically (and is also known as the involuntary nervous system) Regulates cardiac and smooth muscles and glands Has two arms Sympathetic division Parasympathetic division Autonomic Functioning: Sympathetic Sympathetic—“fight or flight” division Response to unusual stimulus when emotionally or physically stressed or threatened Takes over to increase activities Remember as the “E” division Exercise Excitement Emergency Embarrassment Autonomic Functioning: Parasympathetic Parasympathetic—“housekeeping” activites “Rest-and-digest” system Conserves energy Maintains daily necessary body functions Remember as the “D” division Digestion Defecation Diuresis Parasympathetic vs. Sympathetic https://www.youtube.com/watch?v=7wFX9Wn70eM Kahoot Chapter Review https://create.kahoot.it/share/neuro/f67 8e984-78ff-4ef6-b2a4-4dd20b7472a9
