Nervous System 2024 Student PDF

Unit 6 The Nervous System 1 THE NERVOUS SYSTEM FUNCTION Rapid response to environmental stimuli Voluntary action Involuntary action Two parts of the nervous system: 1. Central nervous system (CNS)- brain and spinal cord 2. Peripheral nervous system (PN...

Unit 6 The Nervous System 1 THE NERVOUS SYSTEM FUNCTION Rapid response to environmental stimuli Voluntary action Involuntary action Two parts of the nervous system: 1. Central nervous system (CNS)- brain and spinal cord 2. Peripheral nervous system (PNS)- nerves throughout the body that relay messages back to the CNS 2 THE NERVOUS SYSTEM: FUNCTION 4. Brain and spinal cord relays 3. Brain and spinal cord message; nervous system (CNS) receive message effectors carry message Peripheral nervous system (PNS) 2. Sensory nervous 5. Body reacts to system carries signal the stimulus 1. Sensory receptors detect stimulus (ex. Pain, temperature, etc) SUBDIVISIONS OF THE NERVOUS SYSTEM 4 CELLS OF THE NERVOUS SYSTEM 1. Neuron 2. Glia (aka neuroglia) 5 CELLS OF THE NERVOUS SYSTEM Neuron: a single cell that transmits impulses Parts of neuron 1. dendrite 2. cell body 3. axon 4. myelin sheath (Part of the axon) Fun fact: a single neuron can be over 3 feet long! (Sciatic Nerve) CELLS OF THE NERVOUS SYSTEM: A closer look at the axon Axon – long projection Myelin – fatty substance that wrap around the axons to provide protection PNS – produced by Schwann cells CNS – produced by oligodendrocytes Nodes of Ranvier – gaps between adjacent Schwann cells Neurilemma – most external portion of the Schwann cell plasma membrane; involved in neuron repair Note: Only neurons in the PNS have Schwann cells (and thus, neurilemma) – Oligodendrocytes produce myelin in the CNS Types of neurons 1. sensory neuron – carry impulses to CNS (aka afferent neurons) 2. motor neuron – carry impulses away from the CNS (aka efferent neurons) 3. Interneuron – conduct impulses from sensory neurons to motor neurons 7 CELLS OF THE NERVOUS SYSTEM 1. Neuron 2. Glia (aka neuroglia) 8 CELLS OF THE NERVOUS SYSTEM Schwann cells: Glial cells that produce myelin sheaths Only found in the PNS Wrap entirely around a single axon Outer plasma membrane = neurilemma StatPearls Publishing/NCBI 9 Schwann cells participate in PNS neuron repair 10 CELLS OF THE NERVOUS SYSTEM Oligodendrocytes Glial cells that produce myelin sheaths Only found in the CNS Wrap around multiple axons (as many as 50!) 11 CELLS OF THE NERVOUS SYSTEM Glia (neuroglia): specialized type of supportive cells; holds the neurons together for protection astrocytes – “star cells”; highly branched to attach to neurons and blood vessels Microglia – cells involved in phagocytosis; consume microbes during inflammation and cell debris Oligodendrocytes – hold nerve fibers together and produce myelin in CNS “Glia” = glue (Greek) Glia in CNS 12 PERIPHERAL NERVOUS SYSTEM PERIPHERAL NERVOUS SYSTEM - Nervous tissue that is not part of the brain or spinal cord - Consists of the Somatic Nervous System (voluntary) and Autonomic Nervous System (Involuntary) - Consists of nerves and ganglia - Ganglia = collection of cell bodies from different neurons - Nerves = a collection of axons from different neurons - Efferent = motor nerves; carries impulses from the CNS to the muscle (Somatic) - Afferent = Sensory nerves; carry impulses to the CNS (Somatic) - Sympathetic and Parasympathetic systems (Autonomic) NERVES Neuron Nerve Nerve: a collection of neuron axons bundled together Axons are wrapped by a fibrous connective tissue called endoneurium Axons are bundled together into fascicles Fasicles are wrapped by a thin, fibrous perineurium Nerves are wrapped by a tough, fibrous sheath called the epineurium SOMATIC NERVOUS SYSTEM (VOLUNTARY) Consists of afferent and efferent nerves to connect PNS to CNS Results in voluntary movement (i.e. muscle contraction) Afferent nerves – carry nerve impulse from sensory stimuli to CNS Efferent nerves – carry nerve impulse from CNS to motor neurons leading to movement 16 AUTONOMIC NERVOUS SYSTEM (INVOLUNTARY) Motor neurons that conduct impulses from the spinal cord or brainstem to: 1. Cardiac muscle tissue 2. Smooth muscle tissue 3. Glandular epithelial tissue Two subdivisions of the autonomic nervous system A. sympathetic nervous system: prepares body to react to stresses (threat, injury) muscles contract heart rate increases B. parasympathetic nervous system: maintains body systems at rest (homeostasis) muscles relax heart rate decreases 17 AUTONOMIC NERVOUS SYSTEM 18 AUTONOMIC NERVOUS SYSTEM: SYMPATHETIC Much of the sympathetic nervous system (SNS) is controlled by spinal nerves… Cues from the environment signal the SNS… Note how one spinal nerve branches into several secondary branches affecting different organs. This maximizes the efficiency of the SNS…it can activate one nerve, which results in several organs responding appropriately. 19 AUTONOMIC NERVOUS SYSTEM: PARASYMPATHETIC Much of the parasympathetic nervous system (PNS) is controlled by cranial nerves… …remember, the PNS is a part of the autonomic nervous system…you don’t have to think about regulating your breathing, HR, digestion, etc. In this case, the PNS is responsible for slowing things down 20 The Reflex Arc and Action Potential How do neurons transmit impulses? Nerves and synapses carry information between the Central Nervous System (CNS) and Peripheral Nervous System (PNS) 22 NERVE IMPULSES stimulus à dendrite à cell body à axon à synapse à dendrite à cell body à axon à synapse à muscle 1. Stimulus activates receptor (dendrite of sensory neuron) 2. Nerve impulse travels from dendrite à cell body (found in ganglion) à axon 3. Nerve impulse stops at the synapse 4. Chemical signals are sent across the synapse 5. New impulse travels along dendrite à cell body à axon of motor neuron Ganglion – group of nerve-cell bodies in the PNS 6. Motor neuron releases signal through synapse with effector Synapse – gap between nerve cells (muscle) Two-neuron reflex: sensory neuron + motor neuron 23 Three-neuron reflex: sensory neuron + motor neuron + interneuron NERVE INPULSES – action potential “Electrical” activity is propagation of a charge differential down the length of the axon…also known as an action potential. Myelin sheaths It takes advantage of the increase inherently negative charge the speed of inside the neuron and impulse travel replaces it with a positive charge (caused by an influx of Na+ ions). The process of going from a negative to a positive As one area of the neuron becomes charge is called depolarized, it triggers the next area to depolarization. depolarize, transmitting the signal along the 24 length of the neuron. NERVE INPULSES – action potential Inside cell Outside cell Membrane potential = difference in charge between inside the cell and outside of the cell When an action potential is initiated, more Na+ come into the cell turning the inside of the cell more + When Na+ stops entering the cell and K+ keeps leaving the cell, the inside of the cell becomes more - 25 NERVE INPULSES – action potential *Ion flow occurs at the Nodes of Ranvier 26 https://phet.colorado.edu/sims/html/neuron/latest/neuron_en.html Action Potential video 27 NERVE INPULSES How does the nerve impulse travel from one neuron to the next? Each “bulb” at the end of the dendrites and the end of the axons is a synapse, or a point at which “electrical” information is converted to “chemical” information 28 SYNAPSE How messages are transmitted from one neuron to the next neuron or cell 1. Presynaptic neuron 2. Postsynaptic neuron 3. Neurotransmitter 4. Synaptic vesicle 5. Synaptic cleft Where have we encountered a DENDRITE synapse before? 29 NEUROTRANSMITTERS Neurotransmitter- a chemical that is released from a presynaptic axon and passes along the synapse. Binds to specific receptors on the postsynaptic membrane binding to the receptor creates action potential of the receiving neuron and signal is passed to the next neuron Neurotransmitter activity is terminated by breakdown (via enzymes) or reuptake (engulfed by the presynaptic neuron) > 30 compounds have been identified as neurotransmitters that are all found in and released from different, specialized neurons 30 31 NEUROTRANSMITTER INBALANCES: ANTIDEPRESSANTS Serotonin- a neurotransmitter in the brain that determines mood. Depression is thought to occur due to a decrease of serotonin 32 CENTRAL NERVOUS SYSTEM Brain + Spinal Cord 33 PROTECTION OF THE CNS 1. Bone 1. Calvarium (skull) à Brain 2. Vertebral column à Spinal cord 2. Membranes (meninges) Dura mater, pia mater, arachnoid mater 3. Watery cushion (cerebrospinal fluid) Fills the meninges filtered out of the blood in the choroid plexus into the ventricles which is then returned to the blood (CSF circulation) 4. Blood-brain barrier 34 PROTECTION OF THE CNS: BONE Coronal Suture Frontal Bone Parietal Bone Key Points: -Bones named for the brain that underlies them Occipital Bone -Sutures are the points at which different bones “fuse” with age -At birth, sutures are NOT Temporal Bone closed Vertebral Body Spinous Process 35 PROTECTION OF THE CNS: MENINGES Meninges: Membrane layers that cover and protect the brain Home to arteries and veins Dura Arachnoid Pia 36 PROTECTION OF THE CNS: CEREBRAL SPINAL FLUID Cerebral Spinal Fluid (CSF) is a circulating fluid; supplies nutrients to CNS, collect waste products, and cushions the brain 37 PROTECTION OF THE CNS: BLOOD-BRAIN BARRIER (BBB) Some molecules can get past, other cannot. Astrocytes encapsulate capillaries and the “feet” serve as filters between the blood and the nervous tissue in the CNS. 38 CNS: The Brain Important Regions of the Brain: Cerebrum - Frontal lobe - Temporal lobe - Parietal lobe - Occipital Lobe - Insula Cerebellum Thalamus Diencephalon Hypothalamus Brainstem - Midbrain - Pons - Medulla Cerebrum - Responsible for integration of complex sensory information - Involved in planning and execution of voluntary movement - Comprised of cortex (gray matter – neuronal cell bodies), hippocampus (memory), basal ganglia (motor movement) Cerebrum Cortex is Made Up of Sulci and Gyri Sulci: “crevaces” between actual Brain Gyri: “convolutions” of brain matter Folding of the brain dramatically Increases the brain’s surface area! Cerebrum More folds/gyri are seen in higher order species: LOBES OF THE CEREBRUM Frontal Lobe: -Temperament, executive functions, planning of movement -Precentral gyrus = contains cell bodies of neurons that control movement of the OPPOSITE side of the body -Regions Involved in motor function of speech (Broca’s area, usually on left side) LOBES OF THE CEREBRUM Temporal Lobe: -Primary auditory cortex -Wernicke’s area: controls comprehension of speech (dominant side, usually left) -Contains hippocampus, important for memory and learning Cerebrum Clinical Correlate: Aphasias Aphasia: Inability to comprehend and/or produce speech Broca’s Aphasia: Patient’s can understand what others are telling them, but are not able to generate appropriate speech (dominant frontal lobe) Wernicke’s Aphasia: Patient’s are able to generate words/sentences well, but they are incoherent and not appropriate LOBES OF THE CEREBRUM Parietal Lobe: - Post-central gyrus à sensation of the OPPOSITE side of the body - Involved in perception and recognition of surrounding world LOBES OF THE CEREBRUM Clinical Correlate: Parietal Lobe Syndromes Dominant Parietal Lesion: Gerstman’s Syndrome à Agraphia (cannot write), acalculia (cannot perform simple arithmetic), left/right confusion (unable to differentiate between the left and right side), finger agnosia (not able to identify thumb, ring finger etc) Non-Dominant: “Neglect” à Patients do not acknowledge objects or things on the opposite side of the lesion LOBES OF THE CEREBRUM Occipital Lobe: Primary vision processing CNS: DIVISIONS OF THE BRAIN Cerebellum: important for coordination; posture; learning new motor skills Brainstem Connection between brain/spinal cord Medulla: - Origin or vagal nerve - Parasympathetic tone to heart/GI tract - Nerves that control swallowing Pons: - eye movements - equilibrium, hearing relay Midbrain: - eye movements 49 CNS: DIVISIONS OF THE BRAIN Diencephalon Hypothalamus: body temp. regulation; sleep/arousal cycle; sexual arousal; appetite (also part of the endocrine system) Thalamus: sensory relay station 50 DISORDERS OF THE NERVOUS SYSTEM Group 11 (October 29) Metopic craniosynostosis Intracerebral hemorrhages Hydrocephalus Parkinson’s Disease Aphasias (Broca’s and Wernicke’s) Parietal Lobe lesions Depression hemorrhage Hydrocephalus 51 HYDROCEPHALUS Cerebral spinal fluid = circulating fluid; flows into ventricles and is reabsorbed into the blood. It is important for cushioning the brain and transporting nutrients/siphoning waste Under normal conditions, the entire brain and spine is surrounded with spinal fluid When there is a buildup of this fluid, it leads to hydrocephalus This can be caused by tumors, trauma, infections, inflammation Too much CSF can lead to increased pressure within the brain and can lead to coma/death Treated by draining the excess fluid by creating a shunt  Unit 6 quiz now open: Complete by October 14 @ 11:59 pm QUESTIONS? 54