40 - 50 question test timed hour and 15 min
Reflexes 1 Reflexes Automatic responses to stimuli Visceral reflexes Activate visceral effectors → Smooth/cardiac muscle → Glands Somatic reflexes Activate skeletal muscle Reflexes Intrinsic Reflex Rapid, predictable motor response Unlearned and involuntary Built into our neural anatomy Reflexes Acquired Reflex Reflexes resulting from practice or repetition Reflex Arc Stimulus Skin Receptor Sensory neuron Integration center Motor neuron Effector 1 2 3 4 5 Interneuron Spinal cord (in cross scetion) Reflex Arc Receptor Site of stimulus Distal end of neuron (Dendrites) or other Sensory structure Responds to a specific stimulus by producing a Graded Potential Reflex Arc Sensory Neuron Transmits afferent impulses to CNS Action Potential travels along axon to Gray Matter of the spinal cord or brainstem 2 Reflex Arc Integration Center Point of connection between afferent and efferent pathways Monosynaptic → Simplest → Sensory neuron synapses with motor neuron Reflex Arc Integration Center Point of connection between afferent and efferent pathways Polysynaptic → Sensory neuron synapses with at least one interneuron Reflex Arc Motor Neuron Conducts efferent impulses from integration center to effector organ Reflex Arc Effector Responds to efferent impulse Muscle fibers contract Glands secrete Reflexes Cranial Reflex Integration center resides in the brain 3 Reflexes Spinal Reflexes Integration center resides in the spinal cord Spinal Reflexes Integration center resides in the spinal cord Effectors are skeletal muscle Important clinical assessment tools Spinal Reflexes To smoothly coordinate skeletal muscle nervous system must receive proprioceptor input Length of muscle →From muscle spindles Amount of tension in muscle →From tendon organs Muscle Spindles Proprioceptors Composed of 3– 10 modified skeletal muscle fibers wrapped in connective tissue capsule Sensory fiber Tendon Tendon organ Capsule (connective tissue) Muscle spindle Muscle Spindles Bundles of modified skeletal muscle fibers Throughout perimysium Sensory fiber Tendon Tendon organ Capsule (connective tissue) Muscle spindle Muscle Spindles Noncontractile in central regions lack myofilaments Stretch causes increased rate of impulses to spinal cord 4 Muscle Spindles Stimulus Stretch causes increased rate of impulses to spinal cord Response Contracting muscle reduces tension on muscle spindle How muscle stretch is detected Muscle spindle Intrafusal muscle fiber Sensory fiber Extrafusal muscle fiber Time Unstretched muscle. Action potentials (APs) are generated at a constant rate in the associated sensory fiber. Muscle Spindles Stimulus Stretch causes increased rate of impulses to spinal cord Response Contracting muscle reduces tension on muscle spindle How muscle stretch is detected Stretched muscle. Stretching activates the muscle spindle, increasing the rate of APs. Time Stretch Reflexes How stretch reflex works Stretch activates muscle spindle Sensory neurons synapse directly with motor neurons in spinal cord motor neurons cause stretched muscle to contract All stretch reflexes are monosynaptic Stretch Reflexes Positive reflex reactions indicate Sensory and motor connections between muscle and spinal cord intact Strength of response indicates degree of spinal cord excitability Hypoactive or absent if peripheral nerve damage or ventral horn injury Hyperactive if lesions of corticospinal tract Patellar ligament Patella Hamstrings (flexors) Muscle spindle Quadriceps (extensors) Spinal cord (L2–L4) Tapping the patellar ligament stretches the quadriceps and excites its muscle spindles. The patellar (knee-jerk) reflex—an example of a stretch reflex 1 1 + + – – Inhibitory synapse + Excitatory synapse Patellar ligament Patella Hamstrings (flexors) Muscle spindle Quadriceps (extensors) Spinal cord (L2–L4) Tapping the patellar ligament stretches the quadriceps and excites its muscle spindles. The patellar (knee-jerk) reflex—an example of a stretch reflex 1 2 1 + + – 2 – Inhibitory synapse + Excitatory synapse Afferent impulses travel to the spinal cord, where synapses occur with motor neurons and interneurons. 5 Patellar ligament Patella Hamstrings (flexors) Muscle spindle Quadriceps (extensors) Spinal cord (L2–L4) Tapping the patellar ligament stretches the quadriceps and excites its muscle spindles. Afferent impulses (blue) travel to the spinal cord, where synapses occur with motor neurons and interneurons. The motor neurons send activating impulses to the quadriceps causing it to contract, extending the knee. The patellar (knee-jerk) reflex—an example of a stretch reflex 1 2 3a 1 + + – 2 3a – Inhibitory synapse + Excitatory synapse Patellar ligament Patella Hamstrings (flexors) Muscle spindle Quadriceps (extensors) Spinal cord (L2–L4) Tapping the patellar ligament stretches the quadriceps and excites its muscle spindles. Afferent impulses (blue) travel to the spinal cord, where synapses occur with motor neurons and interneurons. The motor neurons (red) send activating impulses to the quadriceps causing it to contract, extending the knee. The interneurons make inhibitory synapses with ventral horn neurons that prevent the antagonist muscles (hamstrings) from resisting the contraction of the quadriceps. The patellar (knee-jerk) reflex—an example of a stretch reflex 1 2 3a 3b 3b 1 + + – 2 3a 3b – Inhibitory synapse + Excitatory synapse Tendon Organs Proprioceptor Located in tendons, close to skeletal muscle Small bundles of collagen fibers Sensory terminals coil between and around collagen Tendon Organs Muscle contraction stretches the tendon fibers Nerve fiber is compressed Reflex reaction is triggered → Muscle relaxes Quadriceps strongly contracts. Tendon organs are activated. Interneurons Spinal cord Quadriceps (extensors) Tendon organ Hamstrings (flexors) + + +– + Excitatory synapse – Inhibitory synapse 1 Quadriceps strongly contracts. Tendon organs are activated. Afferent fibers synapse with interneurons in the spinal cord. Interneurons Spinal cord Quadriceps (extensors) Tendon organ Hamstrings (flexors) + + +– + Excitatory synapse – Inhibitory synapse 21 6 Quadriceps strongly contracts. Tendon organs are activated. Afferent fibers synapse with interneurons in the spinal cord. Interneurons Spinal cord Quadriceps (extensors) Tendon organ Hamstrings (flexors) Efferent impulses to muscle with stretched tendon are damped. Muscle relaxes, reducing tension. + + +– + Excitatory synapse – Inhibitory synapse 3a 21 Quadriceps strongly contracts. Tendon organs are activated. Afferent fibers synapse with interneurons in the spinal cord. Interneurons Spinal cord Quadriceps (extensors) Tendon organ Hamstrings (flexors) Efferent impulses to muscle with stretched tendon are damped. Muscle relaxes, reducing tension. Efferent impulses to antagonist muscle cause it to contract. 3b + + +– + Excitatory synapse – Inhibitory synapse 3a 21 Flexor & Crossed-Extensor Reflexes Flexor reflex Initiated by painful stimulus Causes automatic withdrawal of threatened body part Protective & important Brain can override Flexor & Crossed-Extensor Reflexes Crossed-Extensor reflex Occurs with flexor reflexes in weight- bearing limbs maintains balance + Excitatory synapse – Inhibitory synapse Afferent fiber Efferent fibers Arm movements Extensor inhibited Flexor stimulated Interneurons Efferent fibers Flexor inhibited Extensor stimulated Site of reciprocal activation: At the same time, the extensor muscles on the opposite side are activated. Site of stimulus: A noxious stimulus causes a flexor reflex on the same side, withdrawing that limb. + + + – – + Autonomic Nervous System Involuntary nervous system General visceral motor system Make adjustments to ensure optimal support for body activities Operate via subconscious control 7 Autonomic Nervous System Involuntary nervous system General visceral motor system Consists of motor neurons that innervate smooth and cardiac muscle, and glands Central nervous system (CNS) Peripheral nervous system (PNS) Sensory (afferent) division Motor (efferent) division Somatic nervous system Autonomic nervous system (ANS) Sympathetic division Parasympathetic division Somatic versus Autonomic Both have motor fibers Differ in Effectors Efferent pathways and ganglia Target organ responses to neurotransmitters Somatic Nervous System Effector Skeletal muscle Cell body in CNS thick, myelinated fiber extends in spinal or cranial nerve to skeletal muscle Somatic Nervous System Somatic nervous system All somatic motor neurons release acetylcholine (ACh) Effects always stimulatory Cell bodies in central nervous system Peripheral nervous system Neurotransmitter at effector Effector organs Effect S O M A T IC N E R V O U S S Y S T E M Single neuron from CNS to effector organs ACh Skeletal muscle Stimulatory + Heavily myelinated axon Autonomic Nervous System ANS pathway uses two-neuron chain 1. Preganglionic neuron (in CNS) has a thin, lightly myelinated preganglionic axon. 2. Postganglionic (ganglionic) neuron in autonomic ganglion outside CNS has nonmyelinated postganglionic axon that extends to effector organ 8 Autonomic Nervous System Two-neuron chain from CNS to effector organs Ganglion Nonmyelinated postganglionic axon Epinephrine and norepinephrine Adrenal medulla Blood vessel Ganglion Nonmyelinated postganglionic axon ACh Smooth muscle (e.g., in gut), glands, cardiac muscle Stimulatory or inhibitory, depending on neuro- transmitter and receptors on effector organs NE + – S Y M P A T H E T I C P A R A S Y M P A T H E T I C Divisions of the ANS 1. Sympathetic division 2. Parasympathetic division Dual innervation ~ All visceral organs served by both divisions, but cause opposite effects Dynamic antagonism between two divisions maintains homeostasis Parasympathetic Division Rest & Digest Blood pressure, heart rate, and respiratory rates are low Gastrointestinal tract activity high Pupils constricted; lenses accommodated for close vision Sympathetic Division Fight or Flight Exercise, excitement, emergency, embarrassment Increased heart rate; dry mouth; cold, sweaty skin; dilated pupils Sympathetic Division Fight or Flight During vigorous physical activity Shunts blood to skeletal muscles and heart Dilates bronchioles Causes liver to release glucose 9 Parasympathetic Sympathetic Eye Eye Salivary glands Brain stem Cranial Sympathetic ganglia Salivary glands Heart Cervical Lungs T1 Lungs Heart Stomach Thoracic PancreasStomach Pancreas Liver and gall- bladderL1 Liver and gall- bladder Lumbar Adrenal gland Bladder Bladder Genitals Sacral Genitals Skin* Cranial part of Parasympathetic Cell bodies in brain stem Preganglionic fibers in oculomotor, facial, glossopharyngeal, and vagus nerves CN III CN VII CN IX CN X CN III Ciliary ganglion Eye Lacrimal glandPterygo- palatine ganglion Nasal mucosa Submandibular ganglion Submandibular and sublingual glandsOtic ganglion Parotid gland Heart Cardiac and pulmonary plexuses Lung CN VII CN IX CN X Preganglionic Postganglionic CN Cranial nerve S Sacral nerve Cranial part of Parasympathetic Ciliary Ganglia Preganglionic axons Within CN III CN III CN VII CN IX CN X CN III Ciliary ganglion Eye Lacrimal glandPterygo- palatine ganglion Nasal mucosa Submandibular ganglion Submandibular and sublingual glandsOtic ganglion Parotid gland Heart Cardiac and pulmonary plexuses Lung CN VII CN IX CN X Preganglionic Postganglionic CN Cranial nerve S Sacral nerve Cranial part of Parasympathetic Ciliary Ganglia