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Reflex General Function of the Nervous System (NS)

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Reflex General Function of the Nervous System (NS) Physiology of the central nervous system Motor division of the CNS Reflex General function of the nervous system (NS) Nervous system -communication network of neurons that allows the organism to interact with the environment (external, internal) • main function: regulation of body functions • purpose: adaptation to changes - maintenance http://www.alz.org/braintour/images/neuron_forest.jpg of homeostasis and survival 1. Peripheral NS 2. Central nervous system Levels of the CNS • Spinal cord - conducts sensory information to the brain - conducts motor information to the effector organs - serves as a simple regulatory centre (reflexes) - damage of the spinal cord breaks down the connection between periphery and higher centres – serious consequences • Brain - subcortical level - control of involuntary and subconscious functions - brain cortex - control of voluntary functions - control of lower levels of CNS - site of cognitive (higher) functions: memory, learning, thinking Peripheral nervous system (PNS) - transmits information from periphery to the central nervous system and vice versa Includes - cranial nerves – originate in brain (I – XII) - spinal nerves - originate in spinal cord (C1, C2...Th,..L, S..) Components A. afferent (sensory) nervous system (incoming to CNS) B. efferent (motor) nervous system (outgoing from CNS) a. somatic nervous system (transmit impulses to skeletal muscle) b. autonomic nervous system (transmit impulses to smooth muscles, cardiac muscle and glands) I. sympathetic division (fight or flight) II. parasympathetic division (rest and repair) Motor functions and their regulation Spinal reflexes - simple movements – reflex movements Brainstem – posture control, hand and eye movements Cerebellum - making movements „smooth“ - precisely regulates the sequence and duration of the elementary movements of each of these segments Basal ganglia - regulation of well co-ordinated voluntary movements - cognitive control of voluntary movements (e.g. running away from a dangerous animal) Brain cortex – motor areas (primary, premotor, supple- mentary motor) decision about voluntary movements Knee jerk – the patellar reflex - tap on the tendon of m. quadriceps femoris - the leg makes a „kick“ (extension in knee joint occurs) Reflex • definition: predictable, quick, stereotyped and involuntary response to stimulus • action that results from passing a nerve impulse over a reflex arc • „lowest level“ of regulation of motor functions Reflex arc – the basic circuit that underlies a reflex: 1. sensory receptor – gathers stimuli 2. afferent nervous fibre – signal transduction into CNS 3. reflex (integration) centre – processes information 4. efferent nerve fibre – transduction of response 5. effector (muscle, gland)– performance, response to the stimulus Spinal reflex arc Classification of reflexes – with respect to: A/ Count of synapses: 1. Monosynaptic - 1 synapse in the reflex arc 2. Polysynaptic = 2 or more synapses in reflex arc https://s-media-cache-ak0.pinimg.com/originals/a6/41/3f/a6413f649558834e5541fb7e03124f54.jpg Classification of reflexes – with respect to: B/ Type of sensory receptor Exteroceptive – receptor in the reflex arc is an exteroceptor (gathers stimuli from external environment) Proprioceptive – receptor in the reflex arc is an proprioceptor (gathers stimuli about position of the body) Interoceptive – receptor in the reflex arc is an proprioceptor (gather stimuli from internal environment) C/ Integration (reflex) centre Cranial – centre in nuclei of the cranial nerves Spinal – centre in the spinal cord Extracentral – integration centre in autonomic ganglia D/ Effector Somatic – effector: skeletal muscle Autonomic (visceral) – effector: cardiac muscle, smooth muscle, gland E/ Origin Inborn – related to locomotion, defence, food intake, sexual behaviour Acquired – develop during life Spinal reflexes Spinal reflexes include - the muscle stretch reflex - the Golgi tendon reflex - the crossed extensor reflex - the withdrawal reflex Muscle stretch reflexes (myotatic) • monosynaptic • spinal reflexes – refelex centre in the spinal cord • example: knee jerk • involved in regulation of movement, muscle tone and posture – motor control • in part conscious • to major extent - subconscious reflex or automatic action – includes spinal reflexes • both receptor and effector are in the same muscle • types of sensory receptors involved in spinal reflexes: – a muscle spindle – Golgi tendon organs The muscle spindle •a stretch receptor in a muscle •a bundle of modified muscle fibres encased in a capsule Polar parts of the muscle spindle - composed of intrafusal fibres that are contractile (can respond to a stimulation by contraction) Central part of the muscle spindle - fibres non contractile – does not respond to stimulation by a contraction - can be passively stretched - a sensory nerve is wrapped around the fibres • adequate stimulus for the muscle spindle: muscle stretch - potential is transmitted via the sensory nerve stretch muscle to the reflex centre c • response – contraction of the extrafusal c muscle fibres of the same muscle Muscle stretch reflexes – reflex arc • tapping on the muscle tendon (of different muscles) passive prolongation of the muscle and also of the muscle spidle = stimulation(1) • action potential is transmitted by afferent fibre (2) • afferent fibre enters spinal cord through posterior roots c c • afferent fibre synapses with efferent fibre (a – motoneuron) • synapse = integration centre (3) (information is processed) • action potential is transmitted by efferent fibre (a – motoneuron) Tap the tendon, also the muscle and muscle into muscles (via the motor endplate) (4) spindle is prolonged • muscle contraction occurs (5-response) - this is seen as movement (muscle contraction) Golgi tendon organ • a proprioceptive sensory receptor • located at the insertion of skeletal muscle fibers into the tendons of skeletal muscle • made up of strands of collagen connected at one end to the muscle and at the other with the tendon • when the muscle contracts, the collagen fibrils are pulled tight, and this activates the Golgi tendon organ afferent • it detects tension of the muscle The Golgi tendon reflex (inverse myotatic reflex, polysynaptic) - receptor: Golgi tendon organ (can be stimulated by very strong contraction or stretching) - signal transmitted via afferent nerve fibre and by interneurons (inhibitory) in spinal cord to alpha motorneurons - efferent fibre: alpha motoneuron – it gets inhibited !!! - response: muscle relaxation (the same muscle where the receptor is located) - function: protection against rupture of the muscle https://acewebcontent.azureedge.net/blogs/blog-examprep-031615-2.png Withdrawal reflex (polysynaptic) -stimulus causes response in both flexors and extensors of the same side: 1. activation of alpha motoneurons of the ipsilateral flexor muscles, 2. at the same time inhibits alpha motoneurons that supply antagonistic extensor muscles - example: when touching a hot object – contraction of flexors and relaxation of extensors causes removing the hand Crossed extension reflex – polysynaptic - a stimulus causes response on both sides in bots extensors and flexors: 1.activation of alpha motoneurons of the ipsilateral flexor muscles 2.inhibits alpha motoneurons that supply antagonistic extensor muscles - the opposite pattern occurs on contralateral side 3.flexors are inhibited 4.extensors are stimulated - example: when a person steps on a nail, the leg that is stepping on the nail pulls away, while the other leg takes the weight of the whole body- reflex enhances postural support - example: locomotor pattern generator Spinal cord • segmental organization • segments (levels) of the spinal cord contain regulatory circuits involved in control of the movements of a particular region of the body • muscle stretch reflexes have their inegration centres in different segments of the spinal cord Muscles in axial parts of the body limbs (a motoneurons medial part) (a motoneurons -lateral part) = somatotopic organization Examination of reflexes in a human • basic examination in neurology • indicates the function of reflex arc (and all its components) • reflex - stereotypic reaction = predicted response • normoreflexia – normal reflex response on a stimulus • abnormal response indicates disorder in a part of reflex arc Types of abnormal results: • hyperreflexia (or clonus) – hyperactive reflex • hyporeflexia – diminished reflex • areflexia – absence of response • abnormal reflex – the response on the stimulation is abnormal Task: Examination of reflexes in a human Principle • sensory receptors are stimulated • the reflex response on stimulation is observed and evaluated Procedure • the patient is in sitting or lying position (depends on the reflex) • sensory receptors are stimulated by a reflex hammer, cotton, light, needle (depends on the reflex that we want to examine) • examine following reflexes (see next slides) Reflex examination video https://www.youtube.com/watch?v=eqOpNQH09pA Proprioceptive (deep tendon) reflexes - sensory receptor – in muscle, tendon • Masseter reflex (n V) S: tap on a spatula put on the lower jaw (mouth is moderately open) R: closing the mouth • Naso-palpebral reflex (n V,VII) S: tap on the nasal base R: closing of eyelids • Biceps reflex (C5) S: tap on lacerus fibrosus m. bic. brachii R: flexion of the forearm • Triceps reflex (C7) S: tap on olecranon ulnae R: extension of the forearm • Styloradial (brachioradial)reflex (C7) S: tap on proc. styloideus radii
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