Neurophysiology 2023-1.ppsx

Neurophysiology Chapter 9 Objectives         Describe structures & functions of neurons & other cells in the nervous system (NS) Discuss the organization of the NS Discuss autonomic vs somatic NS Discuss sympathetic vs parasympathetic NS Describe depolarization & repolarization & discus...

Neurophysiology Chapter 9 Objectives         Describe structures & functions of neurons & other cells in the nervous system (NS) Discuss the organization of the NS Discuss autonomic vs somatic NS Discuss sympathetic vs parasympathetic NS Describe depolarization & repolarization & discuss the role of the Na+-K+ pump Describe conduction of nerve impulses & the role of excitory/inhibitory neurotransmitters Discuss the function of the synapse Discuss the functions of afferent and Objectives      List the three neurotransmitters and their functions List the divisions of the brain and their functions Know the structure & function of the meninges, CSF & BBB List & explain reflex arcs Know how evaluating reflexes can aid the veterinarian in diagnosing spinal cord injuries Basic Functions of the Nervous System  Sensory  Integration  Motor  Cells of the Nervous System Glial cells (Neuroglia)  Provide structural & functional support & protection for the NS (outnumber neurons ~ 10 to 1)  Neurons  Function - Responsible for transmission of information (impulses) through the NS  Structure • Central cell body (soma or perikaryon) • Two different types of extensions  Dendrites – receive impulses from other neurons & convey to soma or serve as sensory receptors  Axon – conducts impulses away from Organization of the Nervous System  Anatomical Location (CNS vs PNS)  Direction of Impulses (Afferent vs Efferent)  Function (Autonomic vs Somatic) Organization of the Nervous System Anatomical Location  Central Nervous System (CNS) Brain and spinal cord  Peripheral nervous system (PNS) Sensory neurons in the periphery sending info. to CNS Components of the nervous system extending away from the central axis toward the periphery of the body • Cranial nerves • Spinal nerves Organization of the Nervous System Direction of Impulses Two Functional Types of Nerves  Afferent nerves Conduct impulses towards the CNS Sensory nerves  Efferent Nerves Conduct impulses away from the CNS Motor nerves  Cranial & spinal nerves in PNS and nerve tracts in CNS may carry nerve fibers that are sensory, motor or both Organization of the Nervous System Function Autonomic vs Somatic  Somatic nervous system  Voluntary (Conscious)  Efferent motor impulses from brain to skeletal muscle -> cause body movement = Somatic motor function  Afferent sensory impulses from sensory receptors in muscle, skin, eye, ear to brain = Somatic sensory function Functional Organization of the Nervous System  Autonomic nervous sytem Involuntary (Subconscious) Sends efferent motor impulses from brain to smooth & cardiac muscle and endocrine glands -> regulate autonomic body functions = Autonomic motor function Afferent sensory impulses from sensory receptors to brain -> automatically regulate these body functions = Autonomic sensory function Autonomic Nervous System     Divided into Parasympathetic & Sympathetic Nervous Systems Generally have opposite effects on organs & tissues (See Table 9.3, pg 252) Whichever system dominates at any given time determines the state of the organ systems Drugs and/or diseases may stimulate, imitate, or inhibit either system and produce the signs that mimic either the sympathetic or parasympathetic nervous system Sympathetic NS “Fight or Flight”  It has a excitatory effect (catecholamines)  Increases breathing (dilates bronchioles) – (beta2-adrenergic)  Increases heart rate & contractility (beta1arenergic)  Decreases GI secretions  Dilates pupil  Dilates blood vessels in skeletal muscle, constricts (alpha1-adrenergic) those in GI tract, skin, kidney  Sympathetic nerves emerge from the thoracic and lumbar spinal cord Parasympathetic NS “Rest and restore”  Antagonizes excitatory effects of SNS (acetylcholine)  Helps the body replace body stores during fight or flight mode Increases GI motility Decreases heart rate Restore respiratory rate to normal Constricts pupils  Parasympathetic nerves emerge from the brain and spinal cord Neuron Function     When neuron is not being stimulated = Resting state Actively mintained by Na+/K+ pump Distribution of + and - charges on either side of the cell membrane creates a difference in electrical charge across the cell membrane (more – on inside of cell) -> this electrical difference in charges across the cell membrane = resting membrane potential Cell is polarized (2 distinct “poles” of ions - + on outside & - on inside) Sodium-Potassium Pump  Specialized cells on the neuron’s cell membrane Na+ ions pumped out of the neuron K+ ions pumped into  Action of the pump helps keep a higher concentration of Na+ outside the cell  And a higher concentration of K+ inside the Depolarization What’s happening in the neuron when a nerve “fires” (sends an impulse)?  Sodium channels open in the plasma membrane  Na+ ions passively diffuse along the concentration gradient (more Na+ outside) into the cell through these channels  Negatively charged environment within the cell membrane attracts the positive charged ions, also  Influx of positively charged sodium ions causes depolarization because the “poles” of oppositely charged ions on either side of the membrane are lost & the cell goes from being negatively Repolarization  Within a fraction of a second after depolarization starts, the cell begins to repolarize (change of cell back to the negative resting membrane potential)  Na+ channels close stopping influx of Na+  Potassium channels open in cell membrane  K+ ions passively diffuse out of the cell  Also like charge ions repel each other  The re-polarization follows closely behind the "wave" of de-polarization as it moves across the neuron  Cell is repolarized – sodium & potassium ions are again on opposite sides (poles) of the cell membrane  Na+/K+ pump restores the ions to their original sides of the cell membrane Nerve Impulse    When stimulus is strong enough to cause complete depolarization -> threshold reached & cell “fires” (depolarizes) Sodium channels open & influx of sodium causes adjacent sodium channels to open = wave of depolarization = conduction of the action potential = nerve impulse All-or-None Principle = when threshold reached -> action potential is conducted along the entire neuron w/ uniform strength Refractory Period  During depolarization (sodium influx) & early repolarization (potassium outflow), neurons are refractory (insensitive) to new stimuli – they cannot depolarize again until the cycle is completed (absolute refractory period)  At end of repolarization, the cell may depolarize again if stimulus is large enough (relative refractory period) – cell is still refractory to stimuli of normal intensity but may respond to “relatively” larger stimuli Saltatory Conduction    Myelin sheath prevents sodium ion influx so in myelinated axons depolarization can only occur at Nodes of Ranvier (gaps in myelin sheath) Impulse skips from node to node accelerating the rate of wave of depolarization from soma to other end of axon This makes vision & fine motor control possible Synapses  Once the depolarization wave has been conducted to end of the axon, it must be transmitted to the next neuron or to target organ or tissue  Occurs via synaptic transmission  Adjacent neurons do not physically touch so depolarization wave cannot be continued (Review text on synapses – pg 242243) Synaptic Transmission       Presynaptic neuron releases a chemical that stimulates another neuron or target tissue The synapse is the junction between two neurons or a neuron and a target cell The space between the two cells is called the synaptic cleft Chemical released is a neurotransmitter The receptor of the neurotransmitter is called the postsynaptic neuron Vesicles within the cell contain the Synaptic Transmission    When the wave of depolarization reaches the synapse, calcium channels > influx of calcium Causes vesicles w/ neurotransmitter to fuse w/ cell membrane & release neurotransmitter chemical into the synaptic space The neurotransmitter binds w/ specific specialized protein receptors on postsynaptic membrane triggering a change in the postsynaptic cell Types of Neurotransmitters Two Categories    Excitatory neurotransmitters  Catecholamines  Norepinephrine, dopamine, epinephrine Inhibitory neurotransmitters  Gamma-aminobutyric Acid (GABA) and glycine Either  Acetylcholine Review text pg 243-244 Brain     Cerebrum Cerebellum Diencephalon Brain stem Cerebrum    Largest part of mammalian brain “Higher order” behaviors Receives and interprets sensory information, initiates conscious nerve impulses to skeletal muscles and integrates neuron activity that is associated with communication, expression of emotion, learning, memory & recall and other behaviors Cerebellum  Allows the body to have coordinated movement, balance, posture and complex reflexes  Controls the accuracy of (finetunes) movements Diencephalon   Passageway between the brain stem and cerebrum Major structures associated with the diencephalon include: Thalamus - relay station for regulating sensory impulses to the cerebrum Hypothalamus - interface between the nervous and endocrine systems; role in regulation of temperature, hunger, thirst and rage & anger responses Pituitary gland - endocrine “master Brain Stem     Connection between brain and spinal cord Involved in autonomic control functions related to the heart, respiration, blood vessel diameter, swallowing and vomiting Composed of: Medulla Pons Midbrain Many of the cranial nerves originate Meninges    Connective tissue that surrounds the brain and spinal cord Responsible for providing blood vessels (nutrients & oxygen) and cushioning Three layers Dura mater Arachnoid Pia mater Cerebrospinal Fluid (CSF)    Fluid circulates between the meninges and cavities of the brain and spinal cord Cushions brain from hard surface of skull It has some properties that are involved in regulation of certain autonomic functions Blood Brain Barrier (BBB)     Functional barrier separating the capillaries in the brain from the nervous tissue The brain does not have the capillary fenestrations that normally are found in vessels in other parts of the body This prevents certain molecules, drugs, and proteins from passing from the blood to the brain Acts as a protectant Reflexes      Automatic responses designed to protect the body May be autonomic or somatic All have the same basic structure called the reflex arc Originates at the sensory receptor Impulse is sent out from spinal cord or brain stem by the motor neuron which ends at the target organ Somatic Reflex Arcs Evaluated by Veterinarians  Used to aid in the diagnosis of spinal cord trauma, peripheral nerve damage or muscle disease Stretch (Patellar) reflex Withdrawal (Flexor) reflex Cross Extensor reflex (Review text bottom pg 255-256) Stretch (Patella) Reflex Withdrawal Reflex Crossed Extensor Reflex Spinal Reflexes     An animal with severe spinal cord damage (L1, L2) can still have reflexes in hind limb Reflex arcs in the lumbar spine (L3-L5) caudal to the trauma can still function even though the sensory pathway leading to the brain is blocked or conscious motor impulses from brain to hind limbs are interrupted The animal is not aware that the legs are moving Hyperreflexive Review         Describe structures & functions of neurons & other cells in the nervous system (NS) Discuss the organization of the NS Discuss autonomic vs somatic NS Discuss sympathetic vs parasympathetic NS Describe depolarization & repolarization & discuss the role of the Na+-K+ pump Describe conduction of nerve impulses & the role of excitory/inhibitory neurotransmitters Discuss the function of the synapse Discuss the functions of afferent and Review      List three neurotransmitters and their functions List the divisions of the brain and their functions Know the structure & function of the meninges, CSF & BBB List & explain reflex arcs Know how evaluating reflexes can aid the veterinarian in diagnosing spinal cord injuries